The development of a technical costmodel for composites

Adapted to the automotive industry

MATHILDA KARLSSON

Degree project inMechanical engineering

Second cycleStockholm, Sweden 2013

The development of a technical cost model forcomposites - adapted to the automotive industry

18th June 2013

Degree project in lightweight structures, second cycleMathilda Karlsson, (mathk@kth.se)

Supervised by Malin ÅkermoTRITA: AVE 2013:29, ISSN:1651-7660

Aeronautical and vehicle engineering, Lightweight structures, SE-100 44 STOCKHOLM

Sammanfattning

Kompositer har en låg vikt samtidigt som deras skräddarsydda mekaniska egen-skaper konkurrerar, och ibland överträffar, traditionella material som stål. En stornackdel är dock tillverkningskostnaden. Om användningen av kompositer ska ökainom mer kostnadskänsliga industrier måste denna tillverkningskostnad sjunka. Ettsätt att angripa problemet är att tillverka större volymer vilket därmed betyder enlägre kostnad per färdig produkt. Givetvis måste produktionen göras så resurssmartsom möjligt för att minimera kostnaden. En resurssmart tillverkning tilltalar inte baraplånboken utan även miljön, vilket är nödvändigt i ett hållbart samhälle.

Det övergripande målet för det här examensarbetet är att undersöka och värderahur tillverkningskostnaden beror av tillverkningsvolymen och andra variabler såsomkomponentstorlek. Studien genomförs genom utveckling och tillämpning av en tekniskkostnadsmodell för kompositer. Tre tillverkningsmetoder ligger i fokus: High-PressureResin Transfer Moulding (HP-RTM) , Compression Moulding of Thermoplastic (CM-TP) och Advanced Sheet Moulding Compound (A-SMC). Materialsystemen somtillämpar dessa metoder är högautomatiserade för att möjliggöra tillverkningen avstora årliga volymer.

Den utvecklade kostnadsmodellen utgår från ett nedifrån och upp perspektiv därvarje underprocess analyseras fristående från resten av processen. Ledtid och kostna-der defineras och anges för varje underprocess, därefter summeras alla underprocesserför att ge en helhetskostnad.

Tillverkningskostnaden är relaterad till olika delar inom tillverkningsprocessen ochinkluderar investeringar, arbete, material samt elektricitet och lokaler. Hydrauliskapressar är en större del av den totala investeringskostnaden för alla tre tillverknings-metoder. HP-RTM har den högsta investeringskostnaden medan CM-TP har denlägsta, kopplat till det faktum att CM-TP kräver lägre presskapacitet än HP-RTM.Däremot har CM-TP den högsta materialkostnaden medan HP-RTM har den lägsta.Arbetskostnaden är också ett av de större bidragen till den totala tillverkningskost-naden. Minskas denna minskas också den totala tillverkningskostnaden.

Kostnaden per färdig del avtar med ökande årlig tillverkningsvolym. Vid lägretillverkningsvolymer är kostnaden starkt knuten till investeringskostnaden, den fastakostnaden. Vid högre tillverkningsvolymer dominerar materialkostnaden för samtligatre tillverkningsmetoder. En metod som kräver ett dyrare råmaterial har därmed enklar nackdel vid dessa högre tillverkningsvolymer. Kostnaden per färdig del som funk-tion av tillverkningsvolymen kan representeras av en finit summa. Vid tillräckligt högatillverkningsvolymer nås en lägst möjlig komponentkostnad där ytterligare ökning itillverkningsvolym inte påverkar kostnaden nämnvärt.

Att dela en större komponent i flera mindre delar, för att fogas samman vid ettsenare stadie, kan spara tillverkningskostnad vid lägre tillverkningsvolymer. Hur stordel av kostnaden som sparas varierar med tillverkningsmetod. Tillverkningsmetod medhög investeringskostnad sparar en större del av kostnaden jämtemot en process medlägre investeringskostnad.

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Abstract

Composites are light, durable and can be designed to have mechanical propertiesrivaling those of steel. In order to use composites in more cost-sensitive fields theirmanufacturing-cost must decrease. One way of decreasing this cost is to manufac-ture larger volumes. Large manufacturing volumes means high investment costs butlow cost per manufactured part. Cost-efficient thinking also brings about less envi-ronmental impact as the goal is to manufacture as many parts as possible, for thesmallest amount of resources - a necessary part of a sustainable society.

The overarching goal of this master thesis is to investigate and evaluate the invest-ment costs at different manufacturing volumes, as a function of component size andother influencing variables. The investigation is carried out through the developmentand utilization of a basic technical cost model. The investigation involves three man-ufacturing methods commonly used for structural composites: High-Pressure ResinTransfer Moulding (HP-RTM), Compression moulding of thermoplastics (CM-TP)and Advanced Sheet Moulding Compound (A-SMC). A fully automated material sys-tem is chosen and simulated for each method in order to manufacture large annualmanufacturing volumes.

The developed technical cost volume is designed using a bottom-up perspectivewhere the steps of each manufacturing method is analysed separately from each other.For each sub-step its corresponding lead-time and containing costs is deduced andpassed on to the final sum of all sub-steps.

The manufacturing cost consists of the investment cost, operator cost, the ma-terial cost as well as further fixed costs such as electricity and plant costs. Hydraulicpresses are one of the highest cost-contributes to the total investment cost, for allthree studied manufacturing methods. HP-RTM has the highest investment costwhile CM-TP has the lowest, correlating with the fact that a higher pressure is nec-essary in the former. CM-TP has the highest material cost whilst HP-RTM has thelowest. The operator cost is also a large contribution to the total manufacturing cost.Decreasing this will decrease the final cost per part.

The cost per part decrease with increasing annual manufacturing volume. At lowermanufacturing volumes the cost is closely related to the size of the investment cost aswell as other fixed costs. At higher manufacturing volumes material cost dominates forall three studied processes. A process using a more expensive raw material thereforehas a clear disadvantage at these higher annual production volumes. The cost perpart decrease could be described as a finite sum. At a large enough annual productionthe lowest cost part is reached and further increase in volume will not affect the costnoticeably.

Dividing a large component into several smaller pieces for later merging is cost-saving at lower manufacturing volumes. How cost-saving depends on the manufac-turing method. Manufacturing methods with a high investment cost has a highercost-save by dividing the component into several smaller parts.

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ContentsSammanfattning i

Abstract ii

I Scope of work 1

1 Background 1

2 Objective and means of realization 1

3 Delimitations 13.1 Production rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23.2 Component properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23.3 Manufacturing methods . . . . . . . . . . . . . . . . . . . . . . . . . . . 23.4 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

II Frame of reference 3

1 Technical cost modelling 31.1 Composite cost models . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2 Materials 52.1 Dry reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.2 Prepregs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3 Manufacturing methods 63.1 Preforming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3.1.1 Preform waste . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73.2 Post-processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.3 Main processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.3.1 High pressure resin transfer moulding (HP-RTM) . . . . . . . . . . 93.3.2 Compression moulding (CM) of fibre-reinforced thermoplastic . . . 113.3.3 Advanced sheet moulding compound (A-SMC) . . . . . . . . . . . 123.3.4 Combination of techniques . . . . . . . . . . . . . . . . . . . . . . 13

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4 Moulding theory 144.1 Liquid resin flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144.2 Resin viscosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154.3 Permeability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164.4 Consolidation theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174.5 Curing of thermosets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

5 Example composites and cycle times for each manufacturing method 185.1 Carbon-reinforced Epikote . . . . . . . . . . . . . . . . . . . . . . . . . . 185.2 Carbon-reinforced Polyamide 12 . . . . . . . . . . . . . . . . . . . . . . . 185.3 HEXCEL HexMC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

III Analysis 19

1 Developed cost model 191.1 Cost model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

1.1.1 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211.1.2 Installation and adaptation-fees . . . . . . . . . . . . . . . . . . . 211.1.3 Operator cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211.1.4 Machine and tooling lifetime . . . . . . . . . . . . . . . . . . . . 21

1.2 Manufacturing method . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221.3 Machines and tooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

1.3.1 Binder dispersal robot . . . . . . . . . . . . . . . . . . . . . . . . 231.3.2 CNC-cutter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241.3.3 260 Degree capacity conveyor oven . . . . . . . . . . . . . . . . . 251.3.4 HP-RTM-injection equipment . . . . . . . . . . . . . . . . . . . . 251.3.5 Hydraulic draping press . . . . . . . . . . . . . . . . . . . . . . . 251.3.6 Hydraulic press . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261.3.7 Material handling robot . . . . . . . . . . . . . . . . . . . . . . . 271.3.8 Milling machine . . . . . . . . . . . . . . . . . . . . . . . . . . . 271.3.9 Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281.3.10 Freezer storage . . . . . . . . . . . . . . . . . . . . . . . . . . . 281.3.11 Draping mould . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281.3.12 Hydraulic press mould . . . . . . . . . . . . . . . . . . . . . . . . 281.3.13 Implementing new functions . . . . . . . . . . . . . . . . . . . . . 29

1.4 Material cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

2 Adaption 30

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3 HP-RTM 313.1 Preforming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323.2 RTM station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333.3 Post-processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353.4 Material cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

4 CM-TP 364.1 Preforming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374.2 CM-TP station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384.3 Post-processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394.4 Material cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

5 A-SMC 405.1 Preforming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405.2 A-SMC station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415.3 Post-processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415.4 Material cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

IV Results and discussions 42

1 Benchmark cases - general analysis 421.1 Traditional outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421.2 Comparative analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

2 Sensitivity analysis 502.1 HP-RTM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

2.1.1 Hydraulic press cycle times . . . . . . . . . . . . . . . . . . . . . 502.1.2 Material cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

2.2 CM-TP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552.2.1 Hydraulic press cycle times . . . . . . . . . . . . . . . . . . . . . 552.2.2 Material cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

2.3 A-SMC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592.3.1 Hydraulic press cycle times . . . . . . . . . . . . . . . . . . . . . 592.3.2 Material cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

3 Non-value adding operations 623.1 HP-RTM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

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4 Cost-benefits with splitting a component into parts for later merging 664.1 HP-RTM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 664.2 CM-TP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 694.3 A-SMC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

5 Evaluation of developed cost model 75

6 Conclusions 76

7 Future work 77

8 Acknowledgement 78

A Machine data 85

B Hydraulic press invest cost 86

C Closed moulds 87

D Benchmark cases: part cost contribution 88

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Part I

Scope of work1 BackgroundComposites are light, durable and can be designed to have mechanical properties rivalingthose of steel. In order to use composites in more cost-sensitive fields their manufacturing-cost must decrease. One way of decreasing this cost is to manufacture larger volumes. Largemanufacturing volumes means high investment costs but low cost per manufactured part.Cost-efficient thinking also leads to a more sustainable society as the goal is to manufactureas many parts as possible, for the smallest amount of resources.When aiming for a low part cost it becomes increasingly important to determine a goodapproximative manufacturing cost before starting the production. To determine the manu-facturing cost beforehand is a tricky problem. A manufacturing method that is cost-efficientat a low manufacturing volume is not necessarily so at a higher production rate. This meansthat apart from considering the current manufacturing need it is also necessary to predictthe future production rate in order to choose a proper manufacturing method. It is thereforenecessary to investigate the manufacturing cost as a function of the manufacturing volume.Apart from being dependent on the manufacturing volume the cost also is a function of othervariables as size and complexity of the manufacturing component. This thesis addresses theproblem of determining the manufacturing cost of a composite through the development ofa technical cost model.

2 Objective and means of realizationThe main goal with this master thesis is to investigate, describe, analyse and evaluate themanufacturing cost of composites, as a function of manufacturing volume and size. Thisis done through the development, utilization and validation of a technical cost model. Thecost model is structured in such a way as to allow further expansion and introduction ofother involved variables in future work.

3 DelimitationsThe cost model developed in this thesis is aimed to be used in an early conceptual design-stage when limited data is known. The cost model is not in any way complete but shouldrather be considered as a developed methodology which can extended to incorporate manydifferent composite manufacturing methods apart from the treated current material systems.The focus of this thesis with it’s limitations is introduced in the following subsections.

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3.1 Production rate

The production rate of interest is the manufacture of large annual manfacturing volumes.Large annual volumes means lower cost per manufactured part, a necessity to incorporateexpensive composites into more cost-sensitive industries. In order to manufacture largerannual volumes the treated material systems are highly automated. Main focus of thisthesis is the automotive industry, a classic example of a cost-sensitive industry manufacturinghundred-thousands of cars a year.

3.2 Component properties

The targeted components are structural and load-bearing. This means the composite manu-facturing must produce high-quality components with high mechanical properties.The man-ufacturing quality must be consistent throughout the long series, placing a demand ofrepeatability on the manufacturing method of choice. The model produced in this thesisonly estimates the cost of each treated manufacturing method. The mechanical propertieswhich is a direct result of the manufacturing method, must be determined elsewhere andconsidered in parallel to the investment cost produced by this model.

3.3 Manufacturing methods

The main manufacturing methods treated are High-Pressure Resin Transfer Moulding (HP-RTM), Advanced Sheet Moulding Compound (A-SMC) and Compression Moulding of Ther-moplastics (CM-TP). These methods are the focus of this study due to their repeatablityand possible large-scale production-rate.

3.4 Materials

A set of different materials are considered depending on manufacturing method. Dry rein-forcements, mainly non-crimp fabric (NCF) and 2D-plies, coupled with liquid resin are usedin HP-RTM. Compression moulding of A-SMC and TP use appropriate moulding compoundand reinforced PA12 prepreg respectively. The reinforcement material in all three materialsystems are high strength (HS) carbon fibres.

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Part II

Frame of reference1 Technical cost modellingThere are a vast number of cost model algorithm in existance. Previous research [1, 2]indicates the possibility to divide all cost modelling methods into two main branches; quan-titative and qualitative cost modeling. The qualitative cost modeling method is a methodthat can only determine if a design can be considered better or worse [2], thus an unsuitablemethod in this project. The quantitative cost modelling can according to some authors [1, 2]be further branched into three subgroups: statistical, analogous, generative and analytical.Other more recent research [3] also includes feature based cost modeling as a sub-group tothe quantitative cost modeling branch. Figure 1 illustrates a tree-structure describing thestructure of all cost modeling methods according to reference [3].

Figure 1 – Division of cost models according to some authors.

Statistical cost modeling is a method that involves finding causal links between cost andproduct characteristics through statistical models and criteria using large quantities of his-torical data. Parametric cost modeling, used in the commercial cost modeling softwareSEER-MFG by Galorath [4], is a statistical cost model. A disadvantage with statistical costmodeling is that it is necessary to accumulate a large amount of qualitative data to findand test suggested relations [3]. Parametric cost models are mostly developed at largercompanies who have access to large amount of data [5]. A pure parametric cost modelapproach is rejected for this project as there is limited data available within some aspectsof composite manufacture and its automation.Analogous cost modeling reuses and adapts previously found material. It can for instancebe data from a previously manufactured product or cost model of an earlier product [1, 5].As the resulting cost model of this project should be as general as possible, analogous costmodeling is not an option.Feature-based cost modeling is a technique in which features of the component governs itscost. This means that the cost is predicted through knowing that a certain complexity, such

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as a rib or a cut-out, of a product correspond to a certain cost [3]. That means that thefinal cost is only a multiple times the cost for one feature. If this method could be appliedin a general way allowing any component of any complexity to be described it would be apowerful tool interesting to this thesis.Generative and analytical cost modeling is a method using a bottom-up perspective inwhich the cost is calculated for each sub-process and eventually summarized over the entireprocess. Clearly more in-depth knowledge about the field is necessary when such a detailedmethod is used. Analytical cost modeling can also implement parts of the other four majorsub-groups such as parametric models found from statistical cost models [1, 6]. The costmodel then usually use the bottom-up-approach as the “skeleton” of the model whilst othermodels are used in particular instances. Generative and analytical cost modeling has beenused extensively in the literature [7–9]. Models such as activity-based-costing (ABC), usedfrequently both within the automobile industry [10] and the aerospace industry [6, 11] shouldaccording to the presented classification be sorted as an analytical cost model.An ABC-costing approach is chosen for the cost-model developed in this project mainly dueto the possibility to build a very general model but also since it allows for implementation ofmany variables. Other advantages are the possibility to revise the model as new data occursas well as the intuitiveness of the model. In some sub-steps, parametric cost modeling ismade use of in order to make the model more general.

1.1 Composite cost models

Analytical cost models connected to composite manufacturing is demanding due to diffi-culties in procuring necessary data, in particular connected to high-volume manufacturing.Other issues arise when it comes to comparing the mechanical properties of compositesmanufactured from different manufacturing methods. To solve this the cost module is com-monly combined with other seperate modules that evaluate the component geometry andmechanical properties separately [11, 12].Previous work [13] presents a cost estimation of a specific component to be manufacturedwith resin transfer moulding (RTM) of different degree of automation. This cost model isof interest due to the fact that it incorporates lean thinking and instability through discreteevent simulation. The model also stands out as it has some focus on automation solutions.Results clearly show the advantages of increased automation with a cost per part at halfthat of the cost of comparable manual process.Other work [12], again focused on a specific component, presents a comparitative cost esti-mation of a number of different composites manufacturing methods. The work introducesflexural stiffness as a performance index that adjusts the dimension of the considered com-ponent, allowing the model to take into consideration that different manufacturing methodsproduce different mechanical properties. Results from this model show that the material costis the main contributant to the cost per finished product while the second most importantcontributants are the plant cost and the labour cost. Downside with the cost model is thatthe presented plant-cost is treated as a bulk sum with contributions both from equipmentand the plant itself, thus becoming a somewhat blunt tool of measure. Also worth men-

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tioning is the low manufacturing volume studied in this case, with an annual manufacturingvolume of 750 parts per year for HP-RTM parts and 8000 parts per year for SMC. Thisdecreases the model’s comparability to that of this thesis.ABC-methods treating composites [7, 11] are of interest to this project. The first model [7]predicts component cost as a function of component size, complexity and annual productionvolume, closely related to the problem at hand. The cost model implements steel stampingas well as compression moulding of thermosets and thermoplastics, with a focus on sandwich-components. Results from using the model show that composite moulding can indeed becost competitive to that of steel if the component is of a simple, small geometry whenmanufacturing higher annual volumes. The model also repeat the conclusion made byprevious author [12] at determining that the material cost is the primary contributant of thefinal cost per part. The second cost-model [11] is a module of a larger developed system,this type of system of modules is beyond the scope of this thesis but it is of interest to thefuture. The resulting cost-model in this thesis should eventually be integrated into such asystem.The developed cost model in this thesis should implement automation [13], a few differ-ent manufacturing methods [12], component size, complexity and manufacturing-volumedependence [7] together with a throughout module-thinking [11]. Module-thinking does inthis case refer to dividing the problem into smaller, more easily understood, pieces whichare connected to make up the entire solution. For visual reference, think of a jigsaw-puzzlewhere sub problems are separate pieces.

2 MaterialsMaterials used in the three considered material-systems are further discussed in this section.

2.1 Dry reinforcement

There are four basic methods of manufacturing 2D-plies of dry fibre reinforcement andthese are weaving, knitting, braiding and stitching. Weaving, knitting and braiding are forcost-reasons mostly used to create 2D-plies of dry fibers even though it is possible to create3D-solids through for instance 3D weaving. There is a multitude of litterature availabledescribing reinforcement textile manufacturing [14–16] and their difficulties [17–19] .Non-crimp fabric (NCF) is a reinforcement that consists of several layers of weaves withdifferent fibre-orientation joined together through cross-thickness-stitches. The NCF is su-perior in comparison to other textiles in that there is no crimp. Crimp is the extra lengthnecessary to connect the fibres, for instance when weaving fibres extra yardage is necessaryin the interweave-points in between fibres that does not add to the actual surface area. Ifthe fabric is non-crimp it means the total length of the fibres contributes to the surfacearea, both increasing the weight- and cost-efficiency [16].For the dry reinforcements used in HP-RTM mainly non-crimp fabrics (NCF) are consideredbut to generalize 2D-plies merged by the use of binders are also included in the developed

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cost-model.

2.2 Prepregs

A prepreg is a pre-reinforced sheet of polymer resin. The polymer resin can be either athermoset or thermoplastic polymer. Prepregs are raw materials and are not manufacturedin-house. The cost for a prepreg material is higher as it is semi-finished when purchased.When the prepreg resin is a thermoset polymer the resin can be classified as a A-,B orC-staged and is a measurement of its degree of crosslinking. An A-staged resin is notcrosslinked while a C-staged is fully crosslinked. An A- or B-staged prepreg must be storedin a freezer during its shelf-life to avoid further crosslinking [16]. A thermoplastic prepregcan also be of different types such as powder-impregnated, co-mingled, co-weaved or filmstacked prepreg [16, 21, 22] when considering a continous fibre reinforcement. Not manythermoplastic prepregs are available in the market today. The most common type would bethe co-mingled thermplastic prepreg.

3 Manufacturing methodsIt is possible to dissect the considered composite manufacturing methods into three parts,as illustrated in Figure 2. Most manufacturing methods contains preforming and post-processing of some kind but to different extent, depending on the main process.

Figure 2 – Three sections making up a manufacturing process.

3.1 Preforming

Preforming is one of the most important parts of the manufacturing process. The processof preforming can vary from simple, with the cut of a fabric, to advanced, with the formingof a complex 3D-solid. The impact of the preforming on the overall manufacturing costthus differs in magnitude depending on the complexity of the process.When parts are to be manufactured through injection-moulding, such as RTM or HP-RTM,it is desirable to manufacture a dry preform of the same shape and quality to that of the finalcomponent. A high quality preform greatly simplifies the injection process but it naturallyalso means a higher cost will be spent on its manufacture.A quality dry 3D-preform can be manufactured using 2D-plies of dry reinforcements. The2D-plies of dry fibers is cut in appropriate size and stacked on top of each other in suitableorder. The plies are often connected either through the use of an external applicated

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binder or through stitching as a physical mean [14, 23]. Neither stitching nor binder as amerging tool is commonly used in the automobile industry as these steps add unnecessarycost [10, 20]. In these cases the preform keeps its shape thanks to additives in the rawmaterial that melt and hardens in the heated draping mould. For simple preforms, eventhis is sometimes not necessary as long as the preform is moved carefully to avoid anylarger displacements before final use. If stitching is necessary to keep the layers togetherfor a certain component an industry manufacturing large annual volumes usually buy NCF,tailored to their particular need. This means the industry avoid needing to stitch layers of2D-plies in-house. The 2D-preform is commonly draped to a mould of correct shape toachieve the final preform geometry.Manufacturing methods such as A-SMC does not need more preforming other than a cutof the prepreg to the correct outer geometry followed by a stacking. The tackiness ofprepreg makes the use of binder unnecessary, again simplifying the preforming process.Manufacturing methods using thermoplastic prepreg, such as CMTP, is similar to that ofthe A-SMC thermoset prepreg with the difference that the stacks of thermoplastic blanksare consolidated through heating.Figure 3 illustrates a schematic view over basic preforming-steps involved depending onmaterial.

Figure 3 – Schematics showing common preforming steps.

3.1.1 Preform waste

Previous research show that material waste in different RTM-connected preforming processescan be high, 20% reported by Mills [24] and 27% reported by Verrey [10]. The amountof material waste or scrap depends on the used fabric. If NCF are used a scrap level of20 % is not unusual as a form of seam-allowance. When a prepreg consisting of choppedfibers is used the scrap level is virtually zero but as the cost of prepreg is quite high it isnot certain that this advantage cancels the high price. Compression moulding as a whole

7

is a method with low scrap rates compared to that of RTM. Main scrap of this process isnot within the preforming stage but rather in it’s main process, presenting itself as flashoccuring in the prepreg pressing[25]. If the fibre reinforcement in the prepreg consists ofcontinous fibres however, such as the case for the thermoplastic prepreg used in CM-TP,the waste percentage will be similar to that of RTM.One way to reduce the preforming-cost is to focus on decreasing the material waste. Ex-amples of methods doing this worth to be mentioned would be the F3P process developedby Ford Motor Company [26] who reports scrap level as low as 1% as well as Tailored FiberPlacement (TFP) used by for instance LayStitch Technologies [27] who claims zero scrapis a possibility[28] .

3.2 Post-processing

Similarly to the preforming, the post-processing is highly dependent on the capability ofthe main process as well as the complexity of the manufactured component. Virtuallythe same post-processing steps that are usually seen in metal manufacture are present incomposite manufacture. Post-processing can thus be everything from actual machining ofmaterial such as drilling holes or cut-outs to surface painting. The differences betweenthe machinability of metals and composites are however large. Machining of a metal is theremoval of small pieces of uniform material. The crystallographic structure of a metal allowsfor a predictable dislocation movement. The deformation and fracture of a composite ismuch less predictable due to its many governing variables such as the heat-sensitivity of thepolymer matrix, matrix- and fibre- hardness and composite construction such as sandwich orsolid laminate. The anisotropy of composites with its fibre and matrix composition meansit is difficult to achieve as exact machined edges as within an isotropic material such assteel. Improper machining could even cause delamination, fracture in the fibre- matrix-interface. The conclusion from this is that all the listed classic metal-machining-processesmust be adapted to the need of a composite [16], [29]. Figure 4 summarizes a few possiblepost-processing actions for composite manufacturing.Machining composites can be done in two ways: rotary- (such as milling) and waterjet-machining. For heat-sensitive composites waterjet-cutting is preferable. Waterjet-machiningemploys a concentrated high-pressure beam of powder grinding material such as granularsilicate mixed with water released through a narrow nozzle. The beam works as a “liquid”cutting tool. The water-mix means the material is cut and cooled at the same time,thus avoiding heating-defects and fault that can arise in a heat-sensitive material [29],[30]. Carbon-reinforced composites are not as sensitive to heat-degradation as the carbon-fibres has a high heat conductivity, effectively distributing the heat to avoid local heatspots[16]. Whichever machining-type is chosen both techniques are possible to use inadvanced trimming as 5- and 6-axis solutions are available. The simplest form of machiningpost-processing is the trim of flash. RTM and compression moulding need this type ofpost-processing.Surface-treatments such as grinding is generally not done to a composite due to theirpoor machinability as mentioned previously. Some polishing can be done with fine sand-

8

paper. A proper surface need to be the result of a good mould and the use of gelcoat.A gelcoat is applied to give an extra surface layer to hide the component reinforcementstructure. Release agents are used to avoid fractures and cracks when demoulding. RTMand compression moulding use double-sided moulds which means the surface finish of thecomposite can only be as good as the mould and gelcoat [16]. Extra painting is often done.A painting-station involves high temperatures and can somtimes also function as an extracuring station [20]. For a double-mould-process it is also possible to carry out the paintingwhile the component is still curing within its mould, this is called in-mould painting. Thepaint then functions as a gelcoat, being sprayed in the mould and left to dry before themoulding process begins [31]. Again this approach calls for a highly qualitative mould.

Figure 4 – Schematics over composite post-processing.

3.3 Main processes

The manufacturing methods of focus to this thesis are outlined in this sub-section.

3.3.1 High pressure resin transfer moulding (HP-RTM)

Resin Transfer Moulding (RTM) is one of the most commonly used liquid moulding tech-niques today. RTM is favoured as it produces components with good mechanical propertiesand surfaces. Volume fibre fraction content of up to 60 % is possible. The method isflexible in that it allows manufacture of complex components with inserts as well as variableseries length. Its uses are numerous especially within the field of transportation such ascars, busses and airplanes [16]. Products in cars being manufactured using RTM includebody panels and internal furnishings such as panels and seatings as well as structural partsand housings [32].

9

If RTM is to be used for larger annual manufacturing volumes, the process cycle time needto be short. High speed RTM, referred to as HP-RTM in this thesis, has a higher resin-injection pressure in order to speed up the filling process. Regular RTM usually does notinvolve pressures higher than 1 MPa [16] while HP-RTM may involve pressures up to tentimes that amount [33]. The major advantage with HP-RTM is that it can be used whenmanufacturing larger, and thus more cost-efficient, quantities in comparison to regular RTM.A higher degree of automation further improves the process’ profitability [34]. Drawbackswith the process is the high involved pressures which means expensive hydraulic presses,tooling and injection machines.The counter-part to HP-RTM is RTM Light. The resin-injection in RTM-Light is donethrough a vacuum pump, this means the pressures of the process never outgrows the pressureof vacuum. Advantage with the process is that no external presses or clamps are necessaryand the tooling cost is much lower. The major drawback with RTM Light is the longercycle times which minimizes the possibility to produce larger manufacturing volumes. Highercomponent tolerances and quality surfaces are also sometimes a bit more difficult to achievewith the method [35].

Process description Dry fibre reinforcement is placed into a matching mould as illustratedin Figure 5. Preheated resin is injected into the mould while it is subjected to a constantpressure and heated to proper temperature, see Figure 6. The set temperature initiatesthe curing process. Curing continues when the resin injection of the mould is complete.The component can then either finish curing within the mould or be removed when thegel point has been reached. If the second option is chosen the component must be furthercured within a seperate oven. The component is finally removed for post-processing [16].The post-processing step is in general not very extensive and is in most cases limited toedge-trimming of flash.

Figure 5 – A schematic RTM-mould.

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Figure 6 – Resin is injected through one or several gates while mould is pressed shut, impregnatingthe dry fibres.

3.3.2 Compression moulding (CM) of fibre-reinforced thermoplastic

Compression moulding of reinforced thermoplastic is a manufacturing process suitable forlong series of components with lower demands on mechanical properties and surfaces. Adap-tions are numerous including components for automobiles, containers and housing and hel-mets [16]. Possible volume fibre fraction content is determined by the matrix and goes upto 55 % [20].Necessary pressures depends on component size, complexity and type of preform. If the pre-form is created through melt impregnation the necessary pressure is lower than for preformsmade from for instance co-mingling, co-weaving and film stacking. Necessary pressure forthese three impregnation-material-processes could be between 1-8 MPa while for stackedmelt-impregnated prepregs 1 MPa suffices. Typical compression cycle time is between 20-60seconds. [16]

Process description Thermoplastic blanks are cut to the outer geometry of the compo-nent and stacked in proper order, to build thickness. The stack is pre-heated in an oven toconsolidate the stack. Finally the stack is placed in a press, see Figure 7. As the chargeis pressed the melted thermoplastic is forced into the details of the mould, see Figure 8 .Solidification occurs as the thermoplastic is in contact with the cool press mould [16].

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Figure 7 – A schematic compression mould with a fully covering charge.

Figure 8 – The compression step forces the charge to conform to the mould.

3.3.3 Advanced sheet moulding compound (A-SMC)

Compression moulding of SMC, or SMC for short, is a cheap manufacturing process suitablefor long series. A component manufactured using SMC has lower mechanical properties thanthose manufactured using RTM, depending on material and fibre reinforcement percentageused. Surfaces are of lower quality with further polishing or coating necessary in moredemanding cases. SMC is used in a multitude of different adaptions and its similarities tosheet metal stamping make it especially interesting for industries adapt in this technique.Examples of products manufactured through SMCare: car body panels, electrical wall switchplates and protective helmets. The difference between A-SMC and regular SMC is thepossible volume fractions of reinforcement fibers. A-SMC allows for volume fractions ofabout 60% while regular SMC can achieve fractions of 30% as most.Applied pressures for SMC varies depending on the component complexity and size. Differentauthors report different values, 3-20 MPa [16], 14-41 MPa [36] and in the region of 20 MPa[7]. The applied pressure for A-SMC is higher than for SMC by necessity to mould charges

12

with higher volume fractions. The compression cycle time is governed by the curing timewhich usually ranges between 1- 3 minutes [16]. Hexcel, a manufacturer of prepreg and othercomposite moulding materials, states that the applied pressure when compression mouldingtheir HexMC can range from 5 to 15 MPa depending of component size, thickness andcomplexity [37].

Process description The process in itself is fairly simple. Appropriate pieces of a SMCis cut and stacked in one part of a matching mould. Due to the limited flow of the resinwhen compression moulding SMC the placing of the stacks is important. Thanks to thetackiness of SMC-prepreg no binder is necessary to keep the stacks in position during it’splacing within the mould. When the charge is properly mounted the mould is closed throughapplying pressure. The stack of SMC conforms to the mould. To induce crosslinking themould is heated and the press is kept shut until crosslinking is complete [16], [25]. Theschematic Figures 7 and 8 can be refered to for A-SMC as well with one difference: theSMC-charge covers less of the mould, typical coverage is less than 80 %.

3.3.4 Combination of techniques

Apart from the three techniques previously listed there are of course a multitude of otherpossible candidates for manufacturingen composites. One option of particular interest isdifferent combination of RTM, A-SMC and CM of thermoplastics.A major disadvantage with HP-RTM is the pressure-levels. Pressures of 6-10 MPa whenmanufacturing a large component inevitably brings a large investment cost through necessaryclamp force and thick steel tooling. There are a few ways of attacking this problem.One possibility is to lower the necessary injection pressure. A lower injection pressure meansa smaller press and neater moulds are possible. A possible technique put forth is to allowthe reinforcement to be placed in a larger volume during the injection phase [38]. Thiswould greatly increase the permeability, and thus increase the filling speed, at a muchlower pressure. An adaption of this theory has recently been presented [39] in which thefibre reinforcement is hold in place using a plastic film. The plastic film is locked usingonly vacuum during the injection. When the resin is successfully injected the compositeis pressed to proper geometry, thus implementing the technique of compression moulding.Results from the study shows that the filling and compression parts of this process could befinished in a shorter time compared to RTM. These results are reasonable if considering theinfluence of increased permeability on the flow, see Darcy’s formula, equation (3). Furtherstudy of this RTM-compression moulding combination method is necessary to determine ifit would work in an industrial scale.Another possibility to achieves a larger injection volume is through injecting with a semi-closed mould. Researchers at Fraunhofer refer to their version of the method as CompressionRTM (CRTM). Focus of this techniques is to shorten the cycle time rather than to decreasethe pressure levels. The pressure levels are as high as for HP-RTM but with an increasedthroughput the cost per finished part will be lower. Another stated advantage is thatthere will be less resin waste compared to regular RTM. There are difficulties connected

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to necessary injection tools and clamp pressures that need to further investigated. Apartfrom this it is necessary to do further studies with higher volume fibre percent (>30%) Thismethod is yet to be fully adaptable in an industrial scale but it has been under researchsince 2006 [40].

4 Moulding theoryThe physics that govern the treated composite manufacturing processes is further explainedin this section. The theory mentioned are important in order to understand the cost drivingparameters of the different manufacturing volumes. Cost-driving parameters are for instancethose that influence the cycle time. Higher cycle time means a higher cost per finishedproduct, this means parameters that influence the cycle cost also influence the final cost.

4.1 Liquid resin flow

The mould fill time, tfill , depends on the resin flow rate, and the component volume as

tfill = V

Q(1)

where V is the component volume and Q is the volumetric flow rate. When filling the mouldthe resin must travel through the porosity of the fibre reinforcement. The flow through sucha reinforcement can be found through Darcy’s law. Darcy’s law in it’s three-dimensionalform for a Newtonian fluid can be written as

Q = KA

µ∆P (2)

where K is the permeability tensor, A is the cross-sectional area, ∆P is the pressure-gradientand µ is the resin viscosity [41].Darcy’s law can be used to describe the filling process of a RTM-mould. The dry preformto be used has a certain permeability. The resin to be injected has a given viscosity. Thepressure in the process is the difference between the injection pressure and the pre-existingpressure within the mould. There is some deformations of the dry preform as the resin isinjected which affects the permeability. When assuming that these are small Darcy’s lawis sufficient to describe the filling behavior. In the case of compression moulding however,consolidation models must be used as the deformation of the preform is large.From equation (2) it is understood that the flow fluctuates as the cross-sectional area differsfrom position to position. This also means that the fill time in (1) must be calculated foreach position and finally summarized to find the total mould fill time. This method isused by some researchers [41] in combination with control volume finite element method(CVFEM). Controlling the mesh of CVFEM limits the number of calculations.

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Figure 9 – The filling of a RTM-mould can be described using Darcy’s law.

In some cases the 3-dimensional Darcy’s law (2) can be simplified to its one-dimensional-form, see Figure 9 for such a scenario. The volume flow of a thin laminate-composite is lowin the thickness-direction and can thus be neglected [41]. If the component is of a fairlyuniform cross-sectional area and is filled through one inlet port the flow dominates in thelength-direction after initial turbulence, as is familiar from basic flow mechanics. This leadsto an unidirectional flow that can be described as

Q = −(AKx

µ)∆PL

(3)

whereKx is the permeability in the longitudal direction and L is the length of the flow channel[41–43]. The pressure gradient is in the simplified one-dimensional case the differencebetween the injection pressure pinj and the ambient atmospheric pressure pair as

∆P = pinj − pairL

. (4)

Darcy’s law, equation (2), is dependent on the permeability and the resin viscosity, both arevariables that change throughout the process. This makes Darcy’s law a difficult equationto use for some instances.

4.2 Resin viscosity

The resin viscosity varies throughout the filling process [44] The viscosity can be expressedas

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µ = µ∞e(U/RT+κα) (5)

where µ∞ and κ are constants, U is the resin’s viscosity activation energy and α is thedegree of cure. The absolute temperature T and the universal gas constant R are also partof the dependency. Knowing formulation (5) it is clear that several more experiments andresin data is necessary to fully model the resin viscosity. In most cases this modeling is doneby the resin-manufacturing company and readily supplied to the composite-manufacturer.

4.3 Permeability

The permeability is the measure of flow through a porous medium. A low permeabilitymeans a low flow throughput. A sought-after high permeability means a short mould filltime as the flow through the medium is high.The permeability is governed by the geometry and arrangement of the reinforcement as wellas the fibre fraction. To predict the permeablity analytically is not simple, a number ofdifferent models exists. One often used is the Kozeny Carman model [42, 43, 45] whichexpresses the reinforcement permeability as

K =r2f (1− Vf )3

4kV 2f

(6)

in which rf is the fibre radius, Vf if the volume fraction and k is the Kozeny constant. Thevalue of the Kozeny constant varies with specific fibre arrangement and determing this is anissue in itself, mostly done experimentally. An improved model is the Gebart’s model [46],which states the permeability along, K‖, and perpendicular, K⊥, to the fibre length as

K‖ =2d2

f

53(1− αy)3

αy(7)

andK⊥ = 4

9π√

6

(√π

2√3αy− 1

)5/2

d2f (8)

where αy is the fibre volume fraction and df is the fibre diameter. It must be noted thatthe geometry used to deduct both the Kozeny Carman and Gebart model are too perfect tobe completely comparable to that of an actual material, which means deviations will occur[47].The permeability can also be determined experimentally through flow tests, either 1D or 2D,in which a Newtonian fluid is injected into a transparent mould while the injection-front andpressures are recorded. The permeability is then found through inputing the recorded datainto Darcy’s law (2) [41]. Deformation of the reinforcement fibres during the preformingstage affects the permeability [48], this decreases the accuracy of permeability-experimentsdone on original fabrics [49]. Another difficulty with calculating the permeability is that thevolume fraction change during the resin injection process [44].

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4.4 Consolidation theory

A thermoset consolidates through the process of curing and the creating of cross-links.A thermoplastic solidifies through cooling and can be reused through melting. The twoconsolidation-processes are influenced by their differences and similarities.When a heated prepreg is compressed, as during compression moulding, air is vacated andthe laminate’s shape is deformed. The resin of the composite is forced to flow to fill,and conform to, the mould and the deforming reinforcement. The deformation of thereinforcement affects the permeability and volume fraction at every time-step. Influencingfactors throughout the process is temperature, pressure, mass- and momentum- transfertogether with the continous curing of the resin . Clearly this is a difficult scenario to modeland understand. There are several models available that is adaptable in different cases.Simple cases can sometimes be solved analytically, but mostly the solution is numerical.Early models of interest have been developed by Springer [50], Gutowski [51] and Kardos[52] respectively [44]. The Springer model is adaptable if the resin content is high, as itassumes no fibre-fibre-contact. The models presented by Gutowski and Kardos are similar,and take fibre-fibre contact into consideration thus making the models applicable in caseswith higher fibre volume fraction content.Subtracting the influence of the resin curing the consolidation of a pre-heated thermoplasticblank is governed by the same factors as that of the thermoset. If the consolidation ofa thermoplastic blanks were to be performed without preheating however, the behaviourwould be different depending on the matrix/fibre distribution in the blank. The blank wouldbe compressed while the matrix is still solid, giving an initial compression of solid matrixand fibre yarns. First when the matrix yarn is melted the compression would be similar tothat of a compressed prepreg[53].

4.5 Curing of thermosets

When a thermoset resin is curing it is converted from liquid state to solid state, passingthrough a semi-solid, gelatinous stage. The solidification occurs through cross-linking. Ma-terial system properties, temperature and crosslinking-degree governs the necessary time ofa curing process. Apart from these basic parameters extra curing agents can be used toaffect the resin’s reactivity. If all necessary curing parameters together with possible advan-tages from curing agent is considered it is possible to limit the necessary curing time to afew minutes.The curing time tcure is the time the composite needs to cure before desiredcuring degree is reached. The curing time can be described as

tcure = tgel + tpost cure (9)

where tgel is the necessary time for the component to reach spatial stability (semi-solidstate) and tpost cure is the following post-cure time that is necessary to reach determinedcuring degree[43]. There are a number of different formulations to model the curing of athermoset. In most cases the curing cycle is however determined using data supplied by theresin-manufacturer.

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5 Example composites and cycle times for each manu-facturing method

There are several possible material-choices available for each manufacturing method. Dif-ferent materials mean different cycle times. In this section reasonable cycle times for eachsample material are discussed.

5.1 Carbon-reinforced Epikote

For RTM to be truly competetive with fast processes such as A-SMC and compressionmoulding of thermoplastic the resin system need to have a low melt viscosity and a fastcuring-behaviour. Epikote, an epoxy-resin trademarked by the material moulding companyMomentive, is used as an example system. Advantages with this resin are the low meltviscosity (10 cP at 25 degrees Celsius) and the multitude of available curing additives[54]. Epikote is available in a vast range of different resin-curing system with differentcombinations of possible fill-time and final cure time. It is assumed that there exist acombination of Epikote and curing additives which has a combined fill- and curing- time of5 minutes, where the available fill time is 2 minutes [20, 38, 55]. More complex componentsneed a higher fill time while less complex components could make do with a shorter fill time.

5.2 Carbon-reinforced Polyamide 12

Compression moulding of thermoplastic use thermoplastic blanks. The thermoplastic blankis to be preheated to melt temperature and then pressed in a room-temperature-mould. Athermoplastic matrix of lower melt temperature such as Polyamide 12, with a melt tempera-ture of 180 Deg Celsius, is therefore an advantage. Possible thermoplastic blanks to considercould be xecarb 21-C50-AE by xenia [56]. This thermoplastic blank consist of polyamide 12matrix HS carbon fibres. It is assumed that this type of material solidifies in a compressedmould in about 1 minute.

5.3 HEXCEL HexMC

Compression moulding of high fibre volume-content SMC, A-SMC, use prepregs as feedstock.As an example the prepreg material HexMC from Hexcel could be used. Typical curingtemperature is 150 degrees C and typical curing time is 3 minutes. However the thicker thecomponent, the longer curing time is necessary. Another prepreg suitable could be offeredfrom Quantum Composites, used both in cars and aircrafts [57].

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Part III

Analysis1 Developed cost modelThe cost model is made up of a number of functions. The information flow through themodel is illustrated in Figure 10 below. The master function, cost model, collects plant infoand material info from its two subfunctions according to input values. The collected datais summarized and returned. The subfunctions are in turn supplied with data concerningindividual machines, tooling or material data from their respective subfunctions.

Figure 10 – Information flow through the developed Cost Model.

The cost model is validated through comparison to previous existing work as well as toparallell work in the automotive industry [20].

1.1 Cost model

The cost model is governed by certain input-data, see Table 1. Input data supportingvector inputs are the manufacturing volume, n, and the number of pieces making up onecomponent, split. Sometimes it is of interest to investigate if there would be any cost-reductions by manufacturing a larger component in several smaller parts to then merge,rather than to manufacture the component as a one-piece. For these cases altering thevalue of the variable split is possible. Altering the default split value affects the projectedarea, but not the perimeter of the component. The complexity factor, C, is an importantfactor. A component of higher complexity means a higher cost and component cycle time.The current cost model is prepared for implementation of such a complexity factor, howeverthe actual contribution of it within each function will need to be developed in future work.

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Input variable Extra Notes

M Manufacturing methodManufacturing method,

function name

n Manufacturing volume per year Input is usually a vector

nr_workdays Workdays/year

Machine and toolingmaintenance cost isconsidered throughdecreasing the total

amount of workdays peryear.

nr_workhours Workhours/day

d Dedication degree [%]

Percentage of totalprocessing timeattended to by

(manual) operators. Ahighly automated

process might have adedication degree of 0.2

margin Installation and adaptation-fee

Extra percentage tocover for machine andtooling installation- andadaption-fees. Default

value is 0.2

salary Manual work cost [€] per hour

kvm_cost Cost [€] per square metreRent and maintenance

cost

el_var_cost Electricity cost/kWh

fill_time Mould filling time [min]

press_cure_timeComponent time in mould, apart from fill_time

[min]

Gel time if post-curingis used, else total cure

time.

post_cure_time Cure outside mould/tool [min]

Area Component projected area [m2]

Perimeter Component perimeter [m]

weight Component weight [kg]

C Component complexity factor

r Volume reinforcement percentage [%]

m Material system

nr_plies Number reinforcement layers

split Number of Component pieces

Table 1 – Necessary Cost Model Input Data.

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The cost model plots lead-time per station, total undepreciated investment cost as a functionof n and cost per part as a function of n. Important to note is that the investment costcalculated for each part is that of the depreciated value. Apart from the graphical outputthere is also a structural output allowing the user to further plot output data accordingto their specifications. The structural output contains lead time per station, cost per partas well as data concerning the necessary machine park. The data ouput containing thenecessary machine park has several outputs where it is possible to find necessary machinesand how many as well as machine cost for one instance and total depreciated machine cost.

1.1.1 Maintenance

Necessary maintenance of machines and tooling is an indirect input, through input of yearlyworkdays or workhours per day. This means the user can choose to either decrease theamount of workhours per day or the yearly available days to account for extra maintenance.A three-shift day, 24 hours per day and 200 days per year of production, accounts foradequate maintenance in many cases [20].

1.1.2 Installation and adaptation-fees

Installation and adaption-fees are regular extras when investing in a new machine or tool.These fees are accounted for through an extra added percentage margin to the total finalcost.

1.1.3 Operator cost

Fully automated production means it is possible to have a lower degree of manual labour.There will however always be a need of some degree of manual labour to supervise theproduction of expensive materials both in view of cost and safety. The investment labourcost is calculated as

Investlabour = dttotCl

where d is the dedication degree, ttot is the total production time in hours and Cl is thehourly labour cost. The dedication degree is a percentage of the degree of manual labour.For a fully automated process a 20 % dedication degree could be assumed [7]. The hourlylabour cost is found through tables [58].

1.1.4 Machine and tooling lifetime

The lifetime of a machine or a tool is set separately in each function rather than to begoverned by the user directly. This is to decrease necessary input data while still keepingthe flexibility to decide different lifetimes for each particular machine or tool. In this modelthe deprecitation considers a zero scrap value.

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1.2 Manufacturing method

This function controls the machine park. The user adds machines and tooling accordingto their preferences for any given method. The three manufacturing methods of interestare premade and can be used as a reference when another manufacturing method is to becreated within the program.

1.3 Machines and tooling

Machines possible to add are: binder dispersal robot, CNC-cutter, conveyor oven (260deg capacity), HP-RTM-injection equipment, hydraulic draping press, hydraulic press andmaterial handling robot. Tooling possible to add are drape mould (2 MPa pressure capacity)and press mould (20 MPa pressure capacity). Apart from machines and tooling it is alsopossible to add a room-temperature storage and a freezer storage.Each function contains five calculation-categories: lead-time, investment, electricity, tool-ing and floor space. These categories are what is returned to the calling function, themanufacturing-method, see Figure 11. If the function is a machine the tooling vectorT = [TCost, TCost,tot] is zero while the investment vector, I = [ICost, ICost,tot] is nonzero.Vice versa is true when the function is a tool. If the function is a storage, both the in-vestment vector and the tooling vector are zero. The calculation of the electrical vector,El = [ElCost,F ix,tot, ElCost,V ar,tot], and the floor cost, FloorCost,tot is repeated in each func-tion, in the same fashion. The fixed electrical cost is determined using the annual cost of70kEuro for a 1200 Ampere fuse [7], given as

ElCost,F ix,tot = Fuse× nmachines1200 70000

where Fuse is the necessery electrical input in Ampere and nmachines is the number ofthe particular machine. The variable electrical consumption is determined in each functionthrough data concerning the machine’s power-consumption. The variable electrical cost iscalculated as

ElCost,V ar,tot = kWh× €/kWh

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Figure 11 – Detailed return information flow, added machine to manufacturing method.

Machine-specific data is found within its function, allowing the advanced user to alter certainvalues if it is desirable. Input-data will vary depending on machine. Machines implementedin the current version are further explained in the following subsections, machine data isfound in Appendix A. The floor space cost is calculated using a cost per square meter thatincludes rental [59]and maintenance cost [20].

1.3.1 Binder dispersal robot

Dispersal of binder in the preforming-phase is done by a painting-robot. Reference data istaken from IRB 5400 from ABB [60], see Appendix A. Necessary equipment attached to itis an atomizer, such as RB1000.The painting speed of a IRB 5400 is approximately 1.5 m/s and the size of the circularpaint pattern diameter varies from 80 - 600 mm depending on used bell cup [61, 62]. Forthis case the pattern diameter is assumed to be 300 mm. The time necessary to paint onecircular patter is

tp = dpvp

= 0.31.5 = 0.2s (10)

where dp is the painting diameter and vp is the painting velocity. Using a painting speed of1.5 m/s gives a time to paint one “dot” to be 0.2 seconds. Total paint time is then

tpaint tot = A

Apatterntp (11)

where A is the component area and Apattern is the circular pattern area. With a componentarea of 1 m2and a painting speed of 1.5 m/s the binder dispersal time is approximately 3seconds. This time is the shortest theoretical time. The binder dispersal may to be done inseveral layers which means the time calculated in equation (11) is multiplied until necessarybinder-thickness is reached, according to indata.

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1.3.2 CNC-cutter

Cutting of raw material is carried out through the usage of a CNC-cutter. Reference datais taken from Zünd, [63, 64], see Appendix A.The raw material is first loaded into the CNC-machine. The fabric is cut according tocomponent geometry with optimum nesting. The cutting machine has a maximum cuttingspeed of 1m/s in single x- or y-direction [63]. The actual cutting speed depends on thecomplexity of the profile as well as the thickness and stiffness of the fabric. A conservativeestimate is a cutting speed, vcut, of 0.25 m/s [13]. This means the cutting time for onecomponent is

tcut = split( Pvcut

)nplies (12)

where P is the perimeter of the component and nplies is the number of reinforcing layers.This also means that the necessary cutting time for the entire manufacturing volume is∑

tcut = ntcut.

Apart from the actual cutting time it is also necessary to account for the necessary rawmaterial refill time. Changing one roll is estimated to take 5 minutes of manual labour,tswitch. Since a number of components can be cut from the same roll, the time-contributionon each component will be found as a its share of the total

troll refill = tswitchnrollsn

where nrolls is the number of fabric rolls necessary to manufacture the entire manufacturingvolume n. The number of fibre rolls for the entire manufacturing volume is calculated as

nrolls = nAcompAroll

= n(Anplies)Aroll

where Acomp is the fabric area necessary for manufacturing one component and Aroll is thefabric area contained on one purchased roll. The total fabric refill time is thus the productof the number of fabric rolls and the time it takes to change one roll. This means theCNC-cutter usage time is the sum of the cutting time and the refill time as

tCNC = ntcut + ntroll refill.

The necessary number of CNC-cutters can now be found as

nCNC = tCNCtavailable

where tavailable is the available factory run time. A material handling robot must then identifyand grab a finished cut from the cutter-area and pass the leftover scrap into a scrap box.Thus the CNC-cutter should be followed by a robot. Worth to note is that the CNC-cuttercan at most cut through 5 cm thick material, depending on material stiffness.

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1.3.3 260 Degree capacity conveyor oven

Pre-heating and post-curing is in a highly automated process carried out in an industrialconveyor oven. This means it is possible to both transport and heat the material at thesame time. Reference data is taken from Despatch Industries [65], see Appendix A.The conveyor oven allows for pre-heating and post-curing up to 260 degrees C. Its size isdetermined by the component size. From data concerning the specific oven the lead timecan be calculated as

toven = 1.1AAovenvbelt

split

where Aoven is the heated belt area and vbelt is the conveyor belt velocity. The scale factor,1.1, is added to allow some extra component size variations. Necessary number of ovens isthen calculated as

novens = ntoventavailable

.

The conveyor oven is a sort of oven storage, and opens up to extra load and unloading spaceto allow for proper material-loading both into and out of the oven.

1.3.4 HP-RTM-injection equipment

Injection of resin under high pressure is done by high-pressure injection equipment. Referencedata used is taken from KraussMaffei [66], see Appendix A.The injection machine is considered to have a zero lead-time, it’s corresponding lead timeis instead attributed to the hydraulic press on which it is mounted. The number of injectingmachines necessary is thus determined by the number of hydraulic presses present in the line.To calculate the electricity consumption the necessary fill time, which is an user parameter,for n components is used.

1.3.5 Hydraulic draping press

Draping of textile reinforcement is done by a hydraulic press. Omera presses are used forreference values [67], see Appendix A and B for further information.The function describing the hydraulic draping press first choose the proper press accordingto reinforcement size, then proceed to calculate the five main cost categories.Draping of carbon fibres and other reinforcement does not require particularly high pressures.As a result of this the dimensioning factor for drape of carbon-fibre-mats is in this caseconsidered to be the size of the reinforcement. This means the press chosen is the machinecorresponding to the lowest press-force available for the proper reinforcement size.The hydraulic draping press cycle time is made up of several stages as

tdrape = tload + tclose press + tpress + topen press + tunload.

25

The press is preferably served by a robot, and its cycle time is supplied from previousknowledge or calculations through, tload and tunload. The actual press time tpress is set to15 seconds and the press time per component is then

tpress,1comp = split× tpress.

The closing-, and opening- time of the press is calculated through the possible press ramvelocity as

tclose press = topen press = splitdaylight opening

vpress

where vpress and daylight opening is specific to chosen press. Finally the necessary numberof hydraulic draping presses can be determined as

ndrape press = ntdrapetavailable

.

1.3.6 Hydraulic press

A hydraulic press can both be used to press raw material into a shape, and to keep mouldhalves shut while resin is injected. Omera presses are used for reference values [67], seeAppendix A and B for further information.The function describing the hydraulic press first choose the proper press according to nec-essary moulding pressure, then proceed to calculate the five main cost categories.The necessary moulding pressure for a certain manufacturing method requires a certainclamping pressure in order to keep the mould shut throughout the process. For hydraulicpresses, the required clamping pressure, or tonnage, is one of the governing cost factors.The clamping force needed to mould a certain component cannot be calculated exactly butit can be estimated. This can be done through knowing the component’s projected areaand its injection- or compression pressure. An elementary estimation of necessary clampingforce can easily be found as

Fclamp = ApP (13)

where Ap is the projected area and P is the injection- or compression pressure. The necessarypressure, P , must be supplied (in Pa) by the user when designing their manufacturingmethod within the cost model. The calculated clamping pressure is then converted toamerican ton-force, the unit most commonly used for sizing an hydraulic press, and someextra force is added through a safety factor, 1.25 [25] , to produce the necessary clampingforce. The used estimation is not entirerly true if the component contains narrow cavitiesthat are more than 4 cm deep [68]. If this is the case the clamping force must be higherin order to properly force the material into the deep regions. It is possible to calculate theclamping force according to

26

Fclamp = Ap(P + ρde) (14)

where ρ is an experimentally determined pressure factor and de is the extra depth of thecavity such that

de = da − 4cm (15)

where da is the depth of the cavity. However it is difficult to adapt equation (14) in thecost model as it involves the experimental pressure factor ρ as well as further knowledgeof the projected area and depth. These factors are often unknown to the user at an earlystage. Apart from this, it is also unclear exactly what size a “narrow” cavity has. Underthe assumption that the component do not contain any of these especially difficult cavities,equation 13 is used with AP = A for all cases.The hydraulic press cycle time is calculated much the same way as for the hydraulic drapingpress with the exception that the press time tpress is set by the user as an input. Electricityconsumption due to heating of the press surfaces is neglected.

1.3.7 Material handling robot

Material handling is taken care of by a robot. Reference data is taken from IRB 2400 fromABB [13, 69], see Appendix A for further information.In the different processes the industrial robot need to handle a diverse set of task. Simplematerial handling actions such as picking up a single ply from a cutting machine and placingit in the next station could be calculated through a simplified motion. Difficult actions suchas picking up several plies or unloading a finished cured component from a mould mayneed to be physically tested. In order to account for this difference in cycle time the robotmovement time is to be supplied as input data. This means the lead time per componentis known and the total lead time is simply that value times the manufacturing volume. Thenumber of robots is also set as input data since a robot mostly serves another machinewhich is the larger bottleneck of the two.

1.3.8 Milling machine

The milling machine can trim flash and do similar secondary machining operations. Refer-ence data is supplied by industry [20].As necessary machining is different between components, the machining-time is an input-variable. The necessary number of milling machines can thus be calculated as

nmilling machine = ntmachiningtavailable

where tmachining is the necessary machining time for one part.

27

1.3.9 Storage

Intermediate waiting step between stations necessary for the total cycle flow is representedby a storage. Reference data is supplied by the industry[20], see Appendix A. The storagecontains no particular climate-control, but is simply kept to that of the standard factory.The electricity consumption of the storage is therefore considered to be part of the floorcost.The storage time of course depends on several factors such as the process throughput andefficient inventory sizes, coupled with lean-thinking. To allow for flexibility, the storage timeis an user input. The storage space is set to 100 square metres, to allow for plenty of storagespace as well as material-handling-space. The storage space can of course be changed fromwithin its function. The storage output cost is added to the factory floor cost. The storagecost per square meter is found as a sum of the maintenance cost [20] and the facility rentalcost[59].

1.3.10 Freezer storage

A freezer controlled storage is sometimes necessary, such as when storing prepregs. Datais extrapolated from a freezer room from Bureca [70] and then sized up to the size of anindustrial freezer room. See Appendix A for further data.Similar to a regular storage, the freezer storage time is set by the user. The size of thefreezer storage is set to 100 square metres. The storage output cost is added to the factoryfloor cost.

1.3.11 Draping mould

The draping mould is an aluminium mould with 2 MPa-pressure capacity, and can thereforebe used in low-pressure processes such as that of draping of carbon fibre reinforcement.Reference data used is updated data from Åkermo [7]. See Appendix A for further informa-tion.The proper mould is chosen according to the component size. The mould as such is notconsidered to have any lead-time, instead the component time in mould is attributed to thepress in which it is mounted.

1.3.12 Hydraulic press mould

The drape mould is a steel mould with 20 MPa-pressure capacity, and can therefore be usedin high-pressure processes such as A-SMC, CM-TP and HP-RTM. Reference data used isupdated data from Åkermo [7]. See Appendix A for further information.The proper mould is chosen according to the component size. The mould as such is notconsidered to have any lead-time, instead the component time in mould is attributed to thepress in which it is mounted.

28

1.3.13 Implementing new functions

New functions describing other machines and tooling can be added if desired. Importantwhen creating new functions for these subfunctions is that the output-data corresponds tothe created norm, such that

output = [name, nr machines, time, invest, tooling, electrical cost, f loor cost];

where name is a describing text string, nr machines is a scalar, time is the vector [t, ttot],invest is the vector [ICost, ICost,tot], tooling is the vector [TCost, TCost,tot], electrical costis the vector [ElCost,F ix,tot, ElCost,V ar,tot] and floor cost is a scalar. It is important todifferentiate between ICost and ICost,tot. The former ICost is the cost of one machine or toolwhile ICost,tot is the depreciated cost of the particular machines such that

ICost,tot = ICostnmachineslifetime

where lifetime is the decided lifetime when the machine has a zero scrap value.

1.4 Material cost

Material system specific data is defined in the Material data function and used for calcu-lations in the Material cost function, see the information flow between the material costfunctions in Figure 12.

Figure 12 – Detailed information flow between the material cost functions.

The ideal material cost is calculated as

MtrlCost = (rfibre,weightρfibreCostkg,fibre) + ((1− rfibre,weight)ρresinCostkg,resin).

However extra scrap-material is necessary such that

MtrlCost,scrap = MtrlCostscrap

where scrap is a percentage, depending on used material system and manufacturing method.Material systems involving resin and fibres as seperate raw materials has two scrap values,

29

one representing the amount of waste fibres,scrapfibre and one representing the amountof waste resin, scrapresin. In those cases, the fibre scrap is much higher than that of theresin scrap. Material systems where the resin and fibres are intermixed as raw-material,such as prepreg, have one scrap value, since its preforming-step does not only remove fibresbut also resin. In the model waste is considered as a loss, however in actual productionthe scrap material can usually be sold or used in other components, regaining some of itslost value. The calculation of final cost for a prepreg raw material is also adjusted using aprepreg-factor, which essentially is a scalar such as

MtrlCos,prepreg = MtrlCostscrap× pp

where pp is the prepreg-factor. The prepreg-factor accounts for the extra manufacturingcost that is added on the price compared to simple raw materials such as resin and dryreinforcement.

2 AdaptionThe cost model is used to evaluate the three manufacturing methods of interest to thisthesis: HP-RTM, CM-TP and A-SMC. General data for all three adaptions are defined inTable 2 below.

Input variable Valuen see Figures

nr_workdays 200nr_workhours 24

d 1margin 0.2salary 30

kvm_cost 137el_var_cost 0.081

Area 0.2 (0.633×0.316, rectangular plate)Perimeter 1.9 (1:2 relationship)weight 1

C 1r 0.55m 1

nr_plies 1split See Figures

Table 2 – Input Variables for HP-RTM.

30

3 HP-RTMThe flow chart in Figure 13 features the considered high-degree automated industry layoutand process cycle of the HP-RTM manufacturing process [10, 16, 20, 38, 71]. Whiteboxes are sub-processes that are un-active unless otherwise specified. The left part of theFigure has some different shapes: A triangular shape corresponds to a storage, square boxescorrespond to a machine and elliptical shapes correspond to a material-handling robot. Theright part the Figure explains the process steps with all elliptical shapes, corresponding toprocess actions.

31

Figure 13 – Industry layout (left) and process cycle (right) of the HP-RTM process.

3.1 Preforming

The RTM-preforming cell can either be expanded or compressed. The expanded preformingcell contains a CNC-cutter machine (1), material-handling robots (2), a binder dispersalrobot with process table (3) and a draping press with mould (4). Inventories are shatteredthroughout the cell to allow for variations in production rate, recognized as yellow trianglesin Figure14 as well as in following processing line figures. A schematic drawing of the

32

preforming-cell is illustrated in Figure 14 below. The compressed preforming cell contains aCNC-cutter machine, material-handling robots and a draping press and mould . A schematicdrawing of the compressed preforming-cell is illustrated in Figure 15 below. For the HP-RTM-benchmark case, the compressed preforming-cell is used.

Figure 14 – The fully expanded HP-RTM preforming station.

The CNC-cutter machine and draping press is served with one material-handling robot each.As is visible in Figure 14, each expanded preforming-line containing one CNC-cutter includesone binder dispersal robot. Material robots working in the preforming cell is considered tohave a single-ply-movement of 10 seconds.

3.2 RTM station

The basic RTM-station cell contains a mould mounted in a hydraulic press (5), resin injectionequipment (6) and material robots (2). A schematic drawing of the RTM-cell is illustrated

33

Figure 15 – The compressed HP-RTM preforming station.

in Figure 16 below. A material robot positions a preform in the mould within the hydraulicpress. The mould is then pressed shut as the resin is injected by the injection equipment.When form filling is complete the mould is kept shut throughout the curing process. As thecuring is completed the mould is opened and a material robot moves the cured componentinto storage.The hydraulic press is served by two material robots but at a 50 % dedication. This meansthe material robot can serve two hydraulic presses. The dedication of 50 % is chosen on anumber of premises. The curing-time of the Epikote resin mix is assumed to be 5 minuteswhich means the material-handling robot will be idle during that time. With the assumedmaterial loading and un-loading time of 18 seconds [69] it is evident that the robot wouldbe able to serve several presses during its “wait”. How many presses the robot can serve isin this case determined through its working range rather than its possible utilization degree.Hydraulic presses are large and the industrial robot’s range is limited. One possibility couldbe to physically move the robot to the next press when not used, for instance through usinga system of rails. Such a system would however introduce variances and disturbances thatwould influence the production in an unwanted way. To avoid this the industrial robot iskept stationary, serving two hydraulic presses.

34

Figure 16 – The basic HP-RTM cell.

When the number of hydraulic presses is increased the RTM-station grows as schematicallydrawn in Figure 17. Thus another parallel line is added to the layout.

Figure 17 – Schematics over how the RTM-cell is expanded as the number of presses grows.

The number of hydraulic presses is determined by the press time, tpress, which is made upof the injection-time and the cure time ,tfill, is set to 2 minutes and the cure time is set to3 minutes. The necessary pressure is set to 10 MPa. Material robots serving the hydraulicpress is considered to have a loading and unloading time of 18 seconds.

3.3 Post-processing

The post-processing-station is simple, only containing a milling-machine (7) to trim flashand mtrl robots serving it, see Figure 18. Two material robots are necessary for the largemilling machine. A trimmed component is finally stored in a storage. Machining time percomponent is set to one minute while its robot serving time is set to 10 seconds.

35

Figure 18 – The HP-RTM Postprocessing cell.

3.4 Material cost

Material data is supplied by the industry [20], see Table 3 below.

Assumed Material Data, HP-RTM

Volume fibre fraction 55 [%]Resin Density 1.2 [kg/m3]Fibre Density 1.8 [kg/m3]Resin Cost/kg 5 [€/kg]Fibre Cost/kg 20 [€/kg]Fibre Scrap 20 [%]Resin Scrap 2 [%]

Table 3 – Material Data HP-RTM.

4 CM-TPThe flow chart in Figure 19 features the considered high-degree automated industry layoutand process cycle of the thermoplastic compression moulding manufacturing process [16,20, 21, 38, 72].

36

Figure 19 – Industry layout (left) and process cycle (right) of the compression moulding of thermo-plastic process.

4.1 Preforming

The CMTP-preforming cell contains a CNC-cutter (1), material robots (2), a conveyor oven(8) as well as storages distributed throughout the line, see Figure 20. The CNC-cutterand conveyor oven is served by one material robot each. Material robots working in thepreforming cell is considered to have a single-ply-movement of 10 seconds [69].

37

Figure 20 – CMTP Preforming station

4.2 CM-TP station

The CMTP-station contains a hydraulic press (5), material robots (2) and storages, seeFigure 21. Analogous to the industrial layout of the HP-RTM process, each hydraulic pressis served by two material robots. The material robot serving time per part is set to 18seconds. The press time, tpress, is set to one minute. The necessary pressure is set to 6MPa.

38

Figure 21 – CMTP station layout.

4.3 Post-processing

The CMTP post-processing is identical to that of the HP-RTM process as simple trimmingof flash is considered adequate.

4.4 Material cost

Material data is supplied by the industry [20], see Table 4 below.

Assumed Material Data, CM-TP

Volume fibre fraction 55 [%]Resin Density 1.2 [kg/m3]Fibre Density 1.8 [kg/m3]Resin Cost/kg 10 [€/kg]Fibre Cost/kg 20 [€/kg]

Scrap 20 [%]Prepreg-factor 2 [-]

Table 4 – Material Data CM-TP.

39

5 A-SMCThe flow chart in Figure 22 features the considered high-degree automated industry layoutand process cycle of the A-SMC manufacturing process[16, 20, 37, 38].

Figure 22 – Industry layout (left) and process cycle (right) of the A-SMC process.

5.1 Preforming

The A-SMC-preforming cell contains a CNC-cutter (1) and material robots (2) , see Figure23. There is also a freezer storage (9) to properly store the prepreg-raw material as well asa regular storage finishing of the preform line. The material robot working in the preformingcell is considered to have a single-ply-movement of 10 seconds.

40

Figure 23 – The A-SMC Preforming cell.

5.2 A-SMC station

The A-SMC station is identical to that of the CM-TP-station, refer to Figure 21, sincethe heating effect of the ram surfaces is neglected. The material robot serving time perpart is set to 18 seconds. The press time, tpress, is set to three minutes. Hexcel statesthat the applied pressure when compression moulding HexMC can range from 5 to 15 MPadepending of component size, thickness and complexity [37] The necessary pressure is setto a value in between, 10 MPa.

5.3 Post-processing

The CMTP post-processing is identical to that of the HP-RTM process as simple trimmingof flash is the considered scenario.

5.4 Material cost

Material data is supplied by the industry [20], see data in Table 5 below.

Assumed Material Data, A-SMC

Volume fibre fraction 55 [%]Prepreg Cost/kg 36.5 [€/kg]

Scrap 2 [%]

Table 5 – Material Data A-SMC.

41

Part IV

Results and discussionsDifferent mechanical properties arises from different manufacturing methods meaning thatsome manufacturing methods will result in significantly heavier components and some willnot in order to achieve the same mechanical properties. The results in this section do nottake this into account, instead all results are given per kg material.

1 Benchmark cases - general analysisThe three material-systems presented for the three manufacturing methods is considered tobe benchmark cases. The results for the benchmark cases is presented in this section. Firstthe traditional output produced by the developed cost model, at each run, is presented anddiscussed. Secondly the cost model is used to study a larger manufacturing volume spanand the results is compared between the benchmark-cases.

1.1 Traditional outputs

Resulting output graphs for the three cases, HP-RTM, CM-TP and A-SMC are shown inFigure 24, 25 and 26 respectively. The graphs contains three subplots. The first presentsthe cycle times for each station of the process. The second presents the undepreciatedinvestment cost per machine-type for every set manufacturing volume. The third presentsthe resulting cost per part .From the Figures presenting the undepreciated investment cost it is visible that the hydraulicpress is one of the dominating contributions to the investment cost for the three methods.In the HP-RTM and CM-TP-case a large contribution is also from the injection equipmentand the pre-heating ovens respective.The complete part cycle time is the longest for HP-RTM at approximately 14 minutes.CM-TP and A-SMC has a similar complete cycle time at a little less than 10 minutes.From the Figures presenting the part cost it can be seen that at higher annual manufacturingvolumes, the investment cost is not a large contribution to the final cost per part. Instead theraw material cost is the dominating post. The operator cost is also a large contributant, butit should be noted that full manning is simulated for the three cases. For highly automatedprocessing such as these, it is probable that the degree of manpower will be less.It can be seen from the figures that the necessary investment cost is highest for HP-RTMand lowest for CM-TP . Vice versa is true for the material and waste cost per part as its costis lowest for HP-RTM at approximately 30 Euros and highest for CM-TP at approximately66 Euros.

42

Figu

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-RTM

.

43

Figu

re25

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-TP.

44

Figu

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45

1.2 Comparative analysis

The investment-cost increase in a step-by-step manner, see Figure 27 with increasing man-ufacturing volume. The sharp steps correspond to reinvestment points where the machine-park must be upgraded to meet the annual production rate. A reinvestment point could forinstance mean another hydraulic press with surrounding machinery.Comparing the three methods to each other, it can be seen that the reinvestment pointsare many and steeper in a falling order HP-RTM, A-SMC and CM-TP. The differencein steepness between the methods is attributed to the fact that the cost of the necessaryreinvestment-equipment is different between the three. For instance, if the HP-RTM-processmust reinvest in another hydraulic press with surrounding material robots it is also necessaryto purchase another HP-RTM injection equipment set. The amount of reinvestment pointsis connected to the necessary component cycle time for each machine, thus the investment-cost for CM-TP only has three reinvestment points in the manufacturing-volume-span. Thereinvestment points for the three considered manufacturing methods mostly correspond tothe reinvestment in another hydraulic press, meaning the expansion of the main processingstep.

Figure 27 – Investment cost for the three benchmark-cases.

The part cost manufacturing-volume-dependence, see Figure 28, exhibit the same behaviourbetween the three cases. The part cost decrease with increased manufacturing volumes. Thedecrease is first logarithmic until it reaches an almost stable cost per part value, thus thelowest possible cost per part. Again it is possible to identify the reinvestment points as thereoccuring peaks in the curves.

46

Figure 28 – Cost per part as a function of manufacturing volume, from 10000 ppy to 350000 ppy.

The stable lowest cost can be defined as a linear interpolation of a set of stable points.see the dashed lines for each process method in Figure 29. The linear interpolation pointsare found through identifying and comparing reinvestment points. If the difference betweentwo consecutive reinvestment points are low ( max±1BC) and the distance between thereinvestment point and its immediatly preceeding point is less ( max±0.5 BC ), the pointis saved and used for the interpolation. The larger span of manufacturing volume and themore calculation points used when finding the interpolation points, the better. For thegraphs produced in this part, the annual production volume is set to fall between 10 000and 500 000, with a intermediate step of 2500.As can be expected from the appearance of the curve, the slope of the stable region ispractically zero with a marginal difference between the three cases. The curve could becompared to that of a convergent series such that

Cost per part = Direct cost+ Indirect costs

n+

k∑i=1

Reinvestment cost

n

where k is the number of reinvestment points. Indirect costs are the fixed costs that areconstant for each part such as the electricity and operator cost. The direct cost is thematerial and scrap cost for each component. Every process reaches a lowest possible costwhere the dominating contributions comes from fixed costs and material and scrap costwith the latter being the dominating contributor.

47

Figure 29 – The stable cost is determined through linear interpolation, dashed curves interpolation ofsame-coloured curve.

The lowest stable cost is herein defined to be reached when the falling curve is within 5 %margin from that of the linear interpolation, see Figure 30. The curve can thus be dividedinto two sections with one highly volume-dependent region (left of dashed vertical line),region 1, and one stable region (right of dashed vertical line), region 2. It needs to be notedthat the determination of the transition point between the two sections is very sensitive, asit depends on the discontinuity of the process curve. This means that a process curve withmore and sharper reinvestment points often reach its stability region before an oppositecase, examplified by the fact that the HP-RTM and A-SMC base case reach their stabilityregion before the CM-TP base case. Apart from this the transition point is also affected bythe chosen manufacturing interval and by which “mesh”, thus number of calculation points,that are used.The reinvestment points have a larger impact on the part cost in the the highly volume-dependent region. This means it is necessary to map the boundaries of a manufacturingvolume falling within region 1 to avoid a reinvest-point with a sudden, high, increase in partcost. However in the stable region an upcoming reinvest-point does not influence the partcost to the same degree which means greater leniency can be allowed when mapping theinvestment’s boundaries.Comparing the three base-cases to each other it is visible that although the investmentcost for CM-TP is the lowest with fewest reinvestment-points, its fixed costs are the mostexpensive. Not only is the thermoplastic prepreg expensive but there is also a large amountof scrap, clearly a disadvantage. Advantages of CM-TP to the other two methods is its few,and late, reinvestment points as well as its early stabilization. The curves of HP-RTM andA-SMC are close to each other, with A-SMC as the slightly more expensive method. This

48

is due to the similarity in material and scrap cost between the two methods. Important tonote however is that the scrap cost of HP-RTM is much larger than that of A-SMC. SeeAppendix D for Figures showing the part cost contribution for all three methods. Fromthese Figures, it is clear that an alteration in fixed cost and material cost will influence thepart cost.

Figure 30 – The curve consists of two regions: to the left the volume-dominated region and to theright the stable region.

Summarized results The results of each benchmark case are summarized and presentedin Table 6.

49

HP-RTM BC CM-TP BC A-SMC BC

First breaking-point [ppy] 52 500 147 500 80 000Transition point [ppy] 146 300 158 800 151 300

Stable cost [BC] 45 74 47Percentage stable cost consisting of

- material cost [%] 54 72 77- waste cost [%] 12 18 2

- investment cost [%] 7 1 3- operator cost [%] 16 7 10

- variable electricity cost [%] 8 1 5- fixed electricity cost [%] 2 <1 <1

- floor cost [%] 1 <1 1- tooling cost [%] <1 <1 <1

Table 6 – Results for the defined benchmark cases.

2 Sensitivity analysisThe press-times can be altered in order to produce a min-max-curve. This can be a referencein order to see what effect an improvement would give and also, to determine the worst casescenario. It is also of interest to investigate what influence a lower material cost would haveon the final part cost. In this section first two or three different press-times per process arestudied. Secondly a material decrease of 50 % is added to the same process-time-alteredcases.

2.1 HP-RTM

2.1.1 Hydraulic press cycle times

The cycle time of the RTM-process is governed by fill time and cure time. The fill time isdetermined by the viscosity of the resin, which decrease with increasing temperature. Thusthere is a time gap early in the process in which the resin filling must take place in orderto avoid slow filling and even damage to the fibre preform and its placement. Differentresin systems offering different time-gaps is applicable depending on the complexity of thecomponent. A complex component need a larger filling time gap, in order to properly fillall the nooks and cavities of the mould while a simple component can make do with a resinsystem offering a smaller time gap.A resin system suitable for a very simple component can be RTM resin System B, Epikoteresin 05475 and Epikure curing agent 05500, from momentive [55] that has a possible filltime of 1 minute and a full cure time (tfill+tcure) of 2 minutes. A more complex componentcan use resin System A, Epikote resin 05475 and Epikure curing agent 05443, which allowsfor a fill time of approximately 110 seconds and a full cure time of 5 minutes. For this

50

analysis, a fill time coinciding with that of the HP-RTM benchmark, 2 minutes, is used.Thicker components will need extra time for curing.Investment Cost as a function of manufacturing volume for different press cycle times ispresented in Figure 31, below. Apart from the evident conclusion that higher investmentcost is necessary with longer press cycle times, the figure show the investment-breakingpoints for the different cases. For instance all three cases use one line containing onehydraulic press at the volume 10 000 ppy. Case 3 must reinvest in a parellel hydraulic presswith connected machinery already at 45 000 ppy while case 2 minute and case 1 mustreinvest at 52 500 and 107 500 ppy respectively.

Figure 31 – Invest Cost for different manufacturing volumes depending on component time in press.

Cost per part is presented in Figure 32, below. Again the slope of the linear interpolationis practically zero.The three transition points are very similar in value and with all discrepencies considered,the process transition point could be considered to be the mean value of the three, at anapproximate annual production of 161 250 units.Case 3 has a stable cost per part of approximately 47 Euro, case 2 approximately 45 Euro andcase 1 approximately 40 Euro. Quantifying this in comparison to the HP-RTM-benchmark,(case 2), case 1 corresponds to a 60 % press time reduction and case 3 to a 20 % press timeincrease. The 60 % press time reduction only brings a part cost reduction of approximately9 %. Likewise, the 20 % press time increase brings a 4 % part cost increase. Thus theconclusion is that the press-time influence, in the span of 2-6 minutes, is not large whenat high manufacturing volumes. The highly volume dependent region, region 1, howevershow a high difference between the three cases at certain manufacturing values. A clear

51

advantage with case 1 is its few reinvestment-points, meaning the same investment canmanufacture a larger span of annual manufacturing volumes. This allows for a process tofirst be tried out in a lower-scale, and still be used without re-investment if a higher demandarises.

Figure 32 – Cost per part for different manufacturing volumes depending on component time in press.

Summarized results The results of HP-RTM case 1-3 are summarized and presented inTable 7.

52

HP-RTM 1(-0.6)

HP-RTM 2(0)

HP-RTM 3(+0.2)

First breaking-point [ppy] 107 500 52 500 45 000Transition point [ppy] 176 300 146 300 161 300

Stable cost [BC]/ Cost change [%] 41 /-9 45/0 47/+4Percentage stable cost consisting of

- material cost [%] 60 54 52- waste cost [%] 14 12 12

- investment cost [%] 5 7 8- operator cost [%] 14 16 16

- variable electricity cost [%] 5 8 9- fixed electricity cost [%] <1 <1 <1

- floor cost [%] 1 1 1- tooling cost [%] <1 <1 <1

Table 7 – Results for a decreased and increased press cycle time.The stated cost change is in comparisonto the HP-RTM benchmark case.

2.1.2 Material cost

A 50 % material and scrap cost decrease result in a decrease in the lowest stable cost, seeFigure 33. The lowest stable cost is then approximately 26 Euro, 30 Euro and 32 Euro forcase 4 - 6. This corresponds to an approximate part cost decrease of 34 % in comparisonto case 1-3. Thus for these three cases it is of more value to decrease the material costrather than to decrease the component time in press if a lower cost per part is sought.

53

Figure 33 – Cost per part for different manufacturing volumes with a 50 % reduced material cost.

Summarized results The results of HP-RTM case 4-6 are summarized and presented inTable 8.

HP-RTM 4(-0.6/-0.5)

HP-RTM 5(0/-0.5)

HP-RTM 6(+0.2/-0.5)

First breaking-point [ppy] 107 500 52 500 45 000Transition point [ppy] 176 300 146 300 161 300

Stable cost [BC]/ Cost change [%] 26/-37 30/-33 32/-32Percentage stable cost consisting of

- material cost [%] 48 40 38- waste cost [%] 11 9 9

- investment cost [%] 8 11 12- operator cost [%] 22 24 24

- variable electricity cost [%] 8 12 13- fixed electricity cost [%] <1 <1 <1

- floor cost [%] 2 2 2- tooling cost [%] <1 <1 <1

Table 8 – Results for an increased and a decreased press cycle time together with a decreased materialcost.The stated cost change is in comparison to HP-RTM case 1-3 respectively.

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2.2 CM-TP

2.2.1 Hydraulic press cycle times

The compression time used in the presented CMTP-model is one minute, a fair averagetime. Since the compression moulding time of a thermoplastic is limited by its coolingtime in a room-temperature press the press cycle time should not be much longer than oneminute. For certain thermoplastic geometries a short compression time of 20 seconds hasbeen achieved [73], however a compression time of 30 seconds might be more reasonable.The investment cost at the two cases for different manufacturing volumes is presented inFigure 34, below. At an annual production of 10 000 units both cases make do with asingle line. The first reinvestment-step coincide for the two cases, at an annual productionof 150 000 units and correspond to the reinvestment in another parallel pre-heating ovenin the preforming-step. The next reinvestment-point for case 2, at an annual productionrate of 200 000 units corresponds to a reinvestment in another parallel hydraulic press withsurrounding equipment. The second reinvestment point for case 1 coincides with the thirdreinvestment point for case 2 at an annual production rate of 292 500 units. It correspondsto the reinvestment in another milling-machine and surrounding equipment for the post-processing section.

Figure 34 – Investment cost for different manufacturing volumes depending on component time inpress.

Cost per part is presented in Figure 35. Both cases result in very similar lowest part cost atapproximately 73 and 74 Euro for case 1 and 2 respectively. This difference is very low ifconsidering the fact that case 1 has a 50% decrease press cycle time. The stability region

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start is also similar for the two cases. The mean value of the two could be considered as thetrue transition point at an annual production of approximately 163 750 units. As previouslynoted, the CM-TP manufacturing method has the highest material and waste cost togetherwith the lowest investment cost in comparision to HP-RTM and A-SMC. This echoes inthese results, the contribution of the investment cost is not a major influence on the costper part.

Figure 35 – Part cost for different manufacturing volumes depending on component time in press.

Summarized results The results of CM-TP case 1-2 are summarized and presented inTable 9.

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CM-TP1

(-0.5)

CM-TP2(0)

First breaking-point [ppy] 147 500 147 500Transition point [ppy] 171 300 158 800

Stable cost [BC]/ Cost change [%] 73/-<1 74/0Percentage stable cost consisting of

- material cost [%] 72 72- waste cost [%] 18 18

- investment cost [%] 1 1- operator cost [%] 6 7

- variable electricity cost [%] <1 1- fixed electricity cost [%] <1 <1

- floor cost [%] <1 <1- tooling cost [%] <1 <1

Table 9 – Results for an increased and a decreased press cycle time.The stated cost change is incomparison to the CM-TP benchmark case.

2.2.2 Material cost

A 50 % material and scrap cost decrease result in a decrease in the lowest stable cost, seeFigure 36. The lowest stable cost is then approximately 40 and 41 Euro for case 3 and 4respectively. This correspond to approximately 45 % lower part cost for both cases. Thehigh material cost influence is tied back to the fact that CM-TP has the highest materialand waste cost and the lowest investment cost.

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Figure 36 – Cost per part for different manufacturing volumes with a 50 % reduced material cost.

Summarized results The results of CM-TP case 3-4 are summarized and presented inTable 10.

CM-TP 3(-0.5/-0.5)

CM-TP 4(0/-0.5)

First breaking-point [ppy] 147 500 147 500Transition point [ppy] 171 300 158 800

Stable cost [BC]/ Cost change [%] 40/-45 41/-45Percentage stable cost consisting of

- material cost [%] 66 65- waste cost [%] 16 16

- investment cost [%] 3 3- operator cost [%] 11 12

- variable electricity cost [%] 2 2- fixed electricity cost [%] <1 <1

- floor cost [%] <1 <1- tooling cost [%] <1 <1

Table 10 – Results for an increased and a decreased press cycle time together with a decreased materialcost.The stated cost change is in comparison to CM-TP case 1-2 respectively.

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2.3 A-SMC2.3.1 Hydraulic press cycle times

The compression time for an A-SMC-component is determined by the necessary curing time.For a component made from HexMC-material the cure time of a 4 mm thick plate variesbetween 3 to 8 minutes depending on curing temperature (120oC -150oC)[37]. Investmentcost as a function of manufacturing volume for these two different press cycle cases ispresented in Figure 37 below. Case 2 has many reinvestment points and the investmentcost increase steeply compared to case 1. At an annual production of 10 000 units bothcases make do with one line containing one hydraulic press. The first reinvestment-pointoccur at 35 000 and 80 000 for case 1 and case 2 respectively with a parallel hydraulic pressline being the reinvestment.

Figure 37 – Investment cost for different manufacturing volumes depending on component time inpress.

Cost per part for the two cases is presented in Figure 38 below. Case 1 correspond tothe A-SMC-benchmark case. The slope of the curves is practically zero. It can be seenthat the curve with more reinvestment points, case 2, reach its stability region before case1. Similarly to the HP-RTM-case, the stability starting points are within close proximityto each other. If taking the error marginal into consideration, the transition point can beconsidered to be the mean of these two points, at an approximate annual production of 152500 units. The stable lowest cost is approximately 54 Euro for case 2 and 47 Euro for case1. Case 2 is a 167 % press time increase in comparison to the A-SMC-benchmark (case1) and has an approximate part cost increase of 15 %. Thus, the part cost increase is notlarge in comparison to its press time increase.

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Figure 38 – Cost per part for different manufacturing volumes depending on component time in press

Summarized results The results of A-SMC case 1-2 are summarized and presented inTable 11.

A-SMC1(0)

A-SMC2

(1.67)First breaking-point [ppy] 80 000 35 000Transition point [ppy] 151 300 153 800

Stable cost [BC]/ Cost change [%] 47/0 54/+13Percentage stable cost consisting of

- material cost [%] 77 67- waste cost [%] 2 1

- investment cost [%] 3 6- operator cost [%] 10 14

- variable electricity cost [%] 5 9- fixed electricity cost [%] <1 <1

- floor cost [%] 1 1- tooling cost [%] <1 <1

Table 11 – Results for an increased and a decreased press cycle time.The stated cost change is incomparison to the A-SMC benchmark case.

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2.3.2 Material cost

A 50 % material and scrap cost decrease result in a decrease in the lowest stable cost, seeFigure 39. The lowest stable cost is then approximately 29 Euro and 36 Euro for case 3and 4 respectively. This correspond to approximately 40 % lower part cost for case 3 incomparison to case 1 and approximately 35 % lower part cost for case 4 in comparisonto case 2. Thus reducing the material cost is clearly a larger influence than altering thepress-cycle-times for large enough manufacturing volumes.

Figure 39 – Cost per part for different manufacturing volumes with a 50 % reduced material cost.

Summarized results The results of A-SMC case 3-4 are summarized and presented inTable 12.

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A-SMC 3(0/-0.5)

A-SMC 4(1.67/-0.5)

First breaking-point [ppy] 80 000 35 000Transition point [ppy] 151 300 153 800

Stable cost [BC]/ Cost change [%] 29/-39 36/-32Percentage stable cost consisting of

- material cost [%] 64 51- waste cost [%] 1 1

- investment cost [%] 5 8- operator cost [%] 17 21

- variable electricity cost [%] 8 14- fixed electricity cost [%] <1 <1

- floor cost [%] 3 2- tooling cost [%] <1 <1

Table 12 – Results for an increased and a decreased press cycle time together with decreased materialcost.The stated cost change is in comparison to A-SMC case 1-2 respectively.

3 Non-value adding operationsBy reducing non-value adding operations, or as lean puts it: “eliminating waste”, the totalcost can be reduced. An attempt to integrate some processes and remove unnecessaryintermediate steps is analysed for the HP-RTM benchmark-case. It is important to note thata more integrated process is more sensitive to disturbances and deviations. The processesof CM-TP and A-SMC is already as compressed as can be expected. It could be possibleto remove some inventories, but this will affect the controllability of the system too muchto be of interest.

3.1 HP-RTMThe HP-RTM has the most potential when it comes to integration of sub-steps. For one,it is possible to perform both the draping and the resin transfer within the same press. It isimportant to note that this is not always possible. If the manufactured component is largeand intricate thus demanding a high-capacity hydraulic press it might not be possible todrape of the reinforcement in the same press. Many high-capacity hydraulic presses do notperform well at lower pressures. Assuming this is no problem for this case, the HP-RTM-process is abbreviated as defined in Figure 40. The process consists of a CNC-cutter (1),material robots (2), a hydraulic press with attached injection equipment (4) and (6) as wellas a post-milling machine (7). Inventories are scattered throughout the process line. Forthe abbreviated HP-RTM-process the preforming is considered to include the CNC-cutterand its material robot, the main forming is considered to include the hydraulic press withinjection equipment and its two material robots and finally the post-processing is consideredto include the post-milling machine and its two material robots.

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Figure 40 – Abbreviated HP-RTM-process.

The same input data as for the HP-RTM benchmark case is used for the machines present.This means the cycle time in press correspond to 5 minutes and resin transfer is carried out

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for the 2 first minutes. The hydraulic press time is increased with the necessary draping time,15 seconds, together with necessary time to open and close the press one more time. Theresulting investment cost is presented in Figure 41. The investment cost for the abbreviatedHP-RTM is slighlty lower for each manufacturing volume, but the reinvestment points alsooccur earlier.

Figure 41 – Investment cost for different manufacturing volumes, comparison abbreviated HP-RTMand benchmark HP-RTM.

The resulting part cost is presented in Figure 42. At an annual production rate of 10 000units the abbreviated HP-RTM part cost is about 73 Euro while HP-RTM is about 77 Euro,not a large difference. The lowest part cost is for both methods approximately 45 Euro. Thefirst breaking point for the abbreviated line is early, at an annual production of 45 000 unitscompared the the benchmark case that occur at 55 000 units per year. It is questionableif the abbreviated HP-RTM line is interesting since its effect on the part and invest cost islow, while shifting the first breaking point more to the left.

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Figure 42 – Part cost for different manufacturing volumes, comparison between abbreviated HP-RTMand benchmark HP-RTM.

Summarized results The results of abbreviated HP-RTM are summarized and presentedin Table 13. Data for the HP-RTM benchmark case, plotted in Figure 42, can be found inTable 6.

Abbreviated HP-RTMCost at 10 000 ppy/Cost change [%] 73/-5

First breaking-point [ppy] 45 000Transition point [ppy] 123 800

Stable cost [BC]/ Cost change [%] 46/-<1Percentage stable cost consisting of

- material cost [%] 53- waste cost [%] 12

- investment cost [%] 8- operator cost [%] 14

- variable electricity cost [%] 9- fixed electricity cost [%] <1

- floor cost [%] 1- tooling cost [%] <1

Table 13 – Results for an increased and a decreased press cycle time.The stated cost change is incomparison to the HP-RTM benchmark case.

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4 Cost-benefits with splitting a component into partsfor later merging

A large component means a large hydraulic press for all three manufacturing methods. If thecomponent can be divided into several parts and then merged, a smaller hydraulic press maybe used. The question is if this proceedure is cost efficient or not. Several pieces makingup one component means there will be more repeating tasks, such as moving materialor opening and closing the hydraulic press, in order to create one component. It is alsoimportant to note that the curing time does not decrease as the component is split intoseveral parts since the curing time depends on the thickness of the component rather thanits width. It must also be pointed out that there is an extra cost associated to the assemblyof the splitted component. The size of this cost is unknown in this study but it’s clear thatthe cost-benefit of splitting the component must be larger than the cost of merging it.Interesting behaviour in this section occur early in region 1, the highly volume-dependentregion, far from the lowest part cost. In order to focus on region 1 in the curve, thecalculated points is increased by a multiple of 5 for this set of tests. The manufacturingvolume interval is also expanded to starting at an annual production of 500 units instead ofas previously, 10 000 units. Note that the graphs in this section are drawn using y-valuesbetween 0 and 1400 and x-values between 0 and 20 000. For this reason the transition pointit is not visible in the presented Figures.Two component sizes are tested. First the same area and perimeter as in the presentedbenchmark-cases. Secondly an area of A = 1 m2 with a perimeter of P = 4 m, at thesame component weight as in the first case. Each component size consider the split of thecomponent into 1,2 and 4 pieces. Thus for a component of size 0.2 m2there are three casesfor each manufacturing method: S1-S3. For a component size of 1 m2 the cases for eachmanufacturing method are: S4-S6.

4.1 HP-RTM

The part cost for the HP-RTM-benchmark-case for dividing the component into 1, 2 and 4parts is presented in Figure 43below. Thus, Case S1 is the HP-RTM benchmark case with more calculation points thanpreviously presented. For these cases it is considered that reducing the component size doesnot alter the fill time. There is a cost gain by splitting the component, but only at lowermanufacturing volumes. At an annual production of 500 units the cost per part is about765 Euro, 710 Euro and 689 Euro for case S1-S3 respectively. Splitting the component into4, S3, parts become non-cost-efficient already at an annual production of 4000 units andsplitting the component into 2 parts, S2, becomes even in cost to S1 at an annual productionof 9000 units. As the manufacturing volume increase the influence of the investment costdecrease, thus the cost gain from splitting a component decreases.

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Figure 43 – Part cost at different values of split, HP-RTM, when A=0.2 m2.

When increasing the component area to 1 m2 and the perimeter to 4 in respect to the HP-RTM-benchmark-case there is a larger cost-decrease, see Figure 44 below. At an annualproduction of 500 units the cost per part is about 1316 Euro, 998 Euro and 822 Euro forcase S4-S6 respectively. Thus the larger the component, the greater gain with dividingit into several pieces. The breakpoint between cost-efficient and not occur at an annualproduction of 21 000 for S5 (not shown in Figure 44) and at 12 500 for S6.

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Figure 44 – Part cost at different values of split, HP-RTM, when A=1 m2.

Summarized results The results of splitting two different component sizes are summa-rized and presented in Table 14. Data for the HP-RTM benchmark case, corresponds tothat of case S1 however for this test, more calculation points are used. This slightly affectsthe position of the first breaking point and transition point.

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HP-RTM, A = 0.2m2 HP-RTM, A = 1m2

S1(split=1)

S2(split=2)

S3(split=4)

S4(split=1)

S5(split=2)

S6(split=4)

Cost at 500 ppy/Costchange [%] 765/0 710/-7 689/-10 1316/0 998/-24 822/-38

Cost Efficiency breakpoint [ppy] - 9 000 4 000 - 21 000 12 500

First breaking-point[ppy] 51 000 27 000 13 000 46 500 25 000 12 500

Transition point [ppy] 144 300 127 800 114 300 83 750 73 750 108 800Stable cost [BC]/ Cost

change [%] 45/0 50/+11 63/+29 61/0 68/+11 85/+40Percentage stable cost

consisting of- material cost [%] 54 49 39 40 36 29- waste cost [%] 12 11 9 9 8 7

- investment cost [%] 7 9 13 17 16 16-operator cost [%] 16 22 33 17 22 30

-variable electricity cost[%] 8 6 4 13 15 16

-fixed electricity cost[%] <1 <1 <1 <1 <1 <1

-floor cost [%] 1 2 2 2 2 2-tooling cost [%] <1 <1 <1 1 <1 <1

Table 14 – Results for splitting and merging a component.The stated cost change is in comparison tocase S1 for case S2-S3 and in comparison to case S4 for case S5-S6.

4.2 CM-TP

The part cost for the CM-TP-benchmark-case for dividing the component into 1, 2 and 4parts is presented in Figure 45 below. At an annual production of 500 units the cost perpart is about 586 Euro, 551 Euro and 534 Euro for case S1-S3 respectively. Splitting thecomponent into 4 parts, S3, is cost-efficient up to an annual production of 5 500 unitsand splitting the component into 2 parts, S2, becomes even in cost to S1 at an annualproduction of 12 000 units.

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Figure 45 – Part cost at different values of split, CM-TP, when A=0.2 m2.

When increasing the component area to 1 m2 and the perimeter to 4 in respect to theCM-TP-benchmark-case there is a larger cost-decrease, see Figure 46 below. At an annualproduction of 500 units the cost per part is about 946 Euro, 714 Euro and 617 Euro for caseS4-S6 respectively. The cost when splitting the component into four parts, S6, becomeseven to S4 at an annual production of 19 500 units. At an annual production of about28 500 units (not shown in Figure 46) the part cost for S5 also coincide with that of S4.For CM-TP too, the larger the component, the greater gain is given from dividing thecomponent into several parts.

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Figure 46 – Part cost at different values of split, CM-TP, when A=1 m2.

Summarized results The results of splitting two different component sizes are summa-rized and presented in Table 15. Data for the CM-TP benchmark case, corresponds to thatof case S1 however for this test, more calculation points are used.

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CM-TP, A = 0.2m2 CM-TP, A = 1m2

S1(split=1)

S2(split=2)

S3(split=4)

S4(split=1)

S5(split=2)

S6(split=4)

Cost at 500 ppy/Costchange [%] 586/0 551/-6 534/-9 946/0 714/-25 617/-35

Cost Efficiency breakpoint [ppy] - 12 000 5 500 - 28 500 19 500

First breaking-point[ppy] 147 500 91 500 45 000 40 000 50 000 29 500

Transition point [ppy] 158 300 143 800 125 800 107 300 140 300 128 800Stable cost [BC]/ Cost

change [%] 74/0 75/+2 80/+9 81/0 82/+2 87/+8Percentage stable cost

consisting of- material cost [%] 72 70 66 65 64 61- waste cost [%] 18 18 17 16 16 15

- investment cost [%] 2 2 2 4 3 3-operator cost [%] 7 9 14 9 11 17

-variable electricity cost[%] 1 <1 <1 3 4 3

-fixed electricity cost[%] <1 <1 <1 <1 <1 <1

-floor cost [%] <1 <1 <1 1 <1 <1-tooling cost [%] <1 <1 <1 <1 <1 <1

Table 15 – Results for splitting and merging a component.The stated cost change is in comparison tocase S1 for case S2-S3 and in comparison to case S4 for case S5-S6.

4.3 A-SMC

The part cost for the A-SMC-benchmark-case for dividing the component into 1, 2 and 4parts is presented in Figure 47 below. At an annual production of 500 units the cost perpart is about 717 Euro, 661 Euro and 639 Euro for cases S1-S3 respectively. At an annualproduction of 6000 units a component split into four pieces, S3, turns more costly than nosplitting, S1. Splitting the component into two pieces, S2, loses its cost-effeciency againstS1 at an annual production of 14 000 units.

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Figure 47 – Part cost at different values of split, A-SMC, when A=0.2 m2.

When increasing the component area to 1 m2 and the perimeter to 4 in respect to the A-SMC-benchmark-case there is a larger cost-decrease, see Figure 48 below. For this particularcase the manufacturing interval is increased to 600 000 parts per year to be able to identifyenough interpolation points in order to find the lowest stable cost with set standard. Atan annual production of 500 units the cost per part is about 1201 Euro, 901 Euro and 764Euro for cases S4-S6 respectively. At an annual production of 16 500 units case S6 losesits cost-effeciency against S1. The equivalent case for S5 occur at an annual production of33 000 units (not show in Figure 48).

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Figure 48 – Part cost at different values of split, A-SMC, when A=1 m2

Summarized results The results of splitting two different component sizes are summa-rized and presented in Table 16. Data for the CM-TP benchmark case, corresponds to thatof case S1 however, for this test, more calculation points are used.

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A-SMC, A = 0.2m2 A-SMC, A = 1m2

S1(split=1)

S2(split=2)

S3(split=4)

S4(split=1)

S5(split=2)

S6(split=4)

Cost at 500 ppy/Costchange [%] 717/0 661/-8 639/-11 1201/0 901/-25 764/-36

Cost Efficiency breakpoint [ppy] - 14 000 6000 - 33 000 16 500

First breaking-point[ppy] 78 000 43 500 20 500 68 000 38 000 19 000

Transition point [ppy] 149 300 157 800 118 800 286 800 179 800 129 800Stable cost [BC]/ Cost

change [%] 47/0 49/+4 57/+20 55/0 58/+5 69/+24Percentage stable cost

consisting of- material cost [%] 77 74 64 66 63 53- waste cost [%] 2 2 1 1 1 1

- investment cost [%] 4 4 5 10 8 8-operator cost [%] 11 15 24 10 14 23

-variable electricity cost[%] 5 3 2 9 10 12

-fixed electricity cost[%] <1 <1 <1 <1 <1 <1

-floor cost [%] 2 2 2 2 2 1-tooling cost [%] <1 <1 <1 <1 <1 <1

Table 16 – Results for splitting and merging a component.The stated cost change is in comparison tocase S1 for case S2-S3 and in comparison to case S4 for case S5-S6.

5 Evaluation of developed cost modelThere is room for improvement of the developed cost model.The next major step to improve the cost model is to implement the component complexityin order to accurately size the cost. Investigating and determining the influence of thecomponent complexity on the component cost is an extensive project.Another improvement would be to incorporate a scrap-sell-profit, instead of as now treatwaste as a pure loss. The sell-profit could be given either through simply selling the scrapmaterial to someone else, or more interestingly, by handing over the material to anotherproject within the same company. Can the scrap material be merged into new components?Of course a higher amount of merging influences the mechanical properties of a component,all of this needs to be further examined. In any case, simply throwing away the scrap materialis rarely an option, neither for cost-reasons nor for environmental reasons.

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There are also details within some implemented tooling and equipment that should beexpanded and improved. For one tooling-costs can be investigated further. The cost modelcould also benefit from some extra data concerning pre-heating ovens and the heatingof a hydraulic press ram with mounted material. Apart from this it could be of interestto investigate material cost as a function of manufacturing volume. The material costconsidered in this thesis is that of a high-volume-order, for lower orders the material cost ishigher.

6 ConclusionsThe methodology of the developed cost model is exhaustive enough to allow for improve-ments through adding processes and input of more detailed data. The thesis has helped toidentify further knowledge needed in order to improve the current developed cost model.More importantly however the process of dissecting the different manufacturing methodsand finding necessary materials, equipment and tooling for each has helped to get a furtherinsight into the cost-dominating factors of the manufacturing process. For one, it is clearthat the material cost is of major importance. A low investment cost that necessitates ahigh material and scrap cost is not the best choice at higher manufacturing volumes. Majorconclusions are:

• The component cost decrease with increasing manufacturing volume can be dividedinto two regions

– Region 1, highly manufacturing volume dependent cost. Reinvestment-pointsclearly affect the component cost. Investment cost has a high influence on thepart cost.

– Region 2, the component cost is governed by direct and indirect costs. Reinvestment-points are relatively unimportant. Material and scrap costs are the dominatingcost. Investment cost has a low influence on the part cost.

• The cost-contribution from each category varies with the manufacturing process

– HP-RTM has the highest investment cost, CM-TP has the lowest.– HP-RTM has the lowest material and scrap cost, CM-TP has the highest.– The hydraulic press cost is one of the larger parts of the total necessary invest-

ment cost.

• Lower cycle time decreases the total number of reinvestment points.

– Fewer reinvestment points means a larger possible manufacturing span for a setmachine park

• Dividing a component into several pieces is cost-efficient in region 1.

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– The cost decrease increases with increasing component size.

• Reducing non-value adding operations does not influence the cost that much whileshifting the first breaking point to the left.

7 Future workFurther research can, and should, be focused on the cost-dominating factors identified inthis project.The dominating cost-factors such as material and operator costs are difficult to address.Naturally a cheaper material can be used to decrease the cost but for such a decision theperformance of the component at hand need to be further specified. This cannot be doneby using the cost model developed in this thesis. Material waste can be addressed by usingmore optimized pattern nesting techniques when cutting the raw material. There is also theoption of swapping a material reinforced with continuous fibres to discontinuous fibres inorder to decrease the necessary seam-allowance. Again this affects the mechanical propertieswhich cannot be studied here.Operator costs can be reduced by increasing the automation of the process but this alsoincrease the investment cost. The studied processes in this thesis are highly automated, thusthe operator cost presented can probably be decreased. By how much is however unknownat this point.Another cost factor is the investment cost and its dominating cost-contributors. For HP-RTM and A-SMC hydraulic presses are large cost-contributors. High-pressure techniquesalso become increasingly expensive with increasing component-size due to the necessityof higher-capacity presses and tooling. With the current trend of integrating compositecomponents into larger, one-piece structures, the necessary investment cost can becometoo high at lower manufacturing volumes.An alternative to high-pressure techniques could be clever use of vacuum-technology. Themajor downside with traditional vacuum-technologies such as vacuum-infusion and vacuumassisted RTM is the long filling time which would not be acceptable if higher productionrates are necessary. However as the investment cost is of a minor concern at large enoughmanufacturing volumes, vacuum technology can be a good solution for region 1 components.A promising method to use vacuum in the RTM-process while maintaining the filling time ofa HP-RTM could be to inject the resin into an undeformed preform. An undraped preformhas a higher permeability which allows for a higher flow and thus a shorter filling time ata lower, perhaps even vacuum, pressure. The injected preform is pressed to correct shapewhen the filling is complete. A laboratory method has been developed using this thought of“loose” preforms followed by press to geometry, referred to by researchers as VACRTM [39].The incorporating of such a technique could mean the expansion of the usability of a highlyautomated process. If a highly automated process was cost-efficient at lower manufacturingvolumes the producer could gain all the advantages (such as consistensy in quality) to muchless of a disadvantageous cost.

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There are also other ways to modify the different manufacturing methods which could be offuture study interest. High-volume-production could for instance be carried out by mouldingseveral components in the same press, this will decrease the cycle time per part and decreasethe necessary investment cost. Another solution can be to use an overlapping press-step.For instance, the same mould-top is shared between two presses and while one press isworking (thus using the top mould part) the other press is open being loaded or unloaded.This means only one top half mould is necessary per two presses. In the case of HP-RTM,the injection nozzle can also be mounted and dismounted between the two presses, againsaving considerable investment costs!Combining the results in this thesis with that of concurrent research [20] could result in amulti-functional model, which would be very useful to a composite-designer.

8 AcknowledgementI would like to thank those who have supported me throughout this thesis work.Professor Dan Zenkert and Assistant Professor Malin Åkermo are gratefully acknowledgedfor accepting me as master thesis student and for the friendly atmosphere in the group. Iwould like to thank my supervisor Malin Åkermo for valuable advice and support throughoutthe project. I would also like to thank Ph.D. student Per Mårtensson at Volvo PV for bringingideas and input from the industry. Finally I want to thank Kjell Wikenfors at Din maskinAB for supplying data regarding hydraulic presses referred to in this thesis.

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A Machine dataEquipment, tooling and storage data is presented in Table 17, 19 and 18 below. Datamarked with a star is extrapolated, assumed or calculated from other data. In several casesthe fuse is calculated from known electricity consumption and necessary supply voltage.

Machine Cost [k€] Fuse [A]ElectricityConsumption

[kW ]

Floor Space[m×m]

Binder DispersalRobot:

IRB 5400 [60]60* 3 1.5 (0.3 in stand-by

mode) 0.66×0.75

CNC-Cutter:Zünd G3 [63]

150 51 18.6 1.8×2.5

Conveyor Oven:PCBC1-40-3E [65]

45 32* 12 1.22×2.41

Conveyor Oven:PCC1-88 [65]

55 42* 16 1.01×4.32

Conveyor Oven:PCC2-15-1E [65]

100* 84* 32 1.52×4.32

HP-RTM-Equipment:[66]

300 57* 65 3.536×2.200

Hydraulic Press[67]

See appendix B

Hydraulic DrapingPress[67]

See appendix B

Material-handlingrobot:

IRB 2400 [69]60 1.34 0.67 0.723×0.6

Post-millingmachine:

[20]300 100* 50 2.5×2.5

Table 17 – Cost Model Machine data

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Tooling Cost [k€] Fuse [A]ElectricityConsumption

[kW ]

Floor Space[m×m]

Drape Mould [7] See Appendix CHydraulic press

Mould[7]

See Appendix C

Table 18 – Cost Model Tooling data

StorageFloorCost

[k€/m2]Fuse [A]

ElectricityConsumption

[kW ]

Floor Space[m×m]

Storage:[20]

137 0 0 100

Freezer Storage:Freezer room F3550

[70]800 66 22 100

Table 19 – Cost Model Storage data.

B Hydraulic press invest costThe cost of a hydraulic press depends, among other things, on the required tonnage. Theinvestment cost could be approximated as

PressCost = 1.25× 1000× tonnage (16)

where tonnage is the necessary press force capacity in ton-force (1 ton ≈ 10kN) [67],see Figure 49. This calculated cost does not include installation, shipping or any customfeatures. Equation (16) is used together with chosen data for 14 different Omera presses,see Table (20). Data for C-frame presses are used for lower press capacities (<160 ton).At higher press capacities data for pillar-presses are used. Necessary fuse for the hydraulicpress is extrapolated from knowing that a 630 ton press need 400 volt and approximately a120 Ampere fuse.

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Figure 49 – The cost of a hydraulic press can in some cases be determined from its tonnage capacity.

PressCapacity[ton-force]

Max RamSize [mxm]

DaylightOpening

[m]

Open/close

speed [m/s]

ElectricityConsumption

[kW]

50 0.75×0.6 0.8 0.045 7.580 1.2×1.1 1 0.06 15125 1.2×1.1 1 0.105 2×22160 1.2×1.1 1 0.078 55200 1.4×1.2 1 0.063 55250 1.4×1.2 1 0.065 110315 1.6×1.2 1.3 0.052 110400 2.5×1.5 1.3 0.083 2×75500 2.5×1.5 1.3 0.066 2×75630 2.5×1.5 1.3 0.054 2×75800 2.5×1.5 1.3 0.043 2×751250 1.5×4.5 1.3 0.044 2×1101600 1.5×4.5 2 0.033 2×1102000 5×2.5 2 0.035 4×74

Table 20 – Hydraulic press data.

C Closed mouldsAluminium and steel moulds are possible to use in the developed cost model. A steel mouldcan withstand higher pressures than an aluminium mould. An aluminium mould also needsdifferent and more maintenance in comparison to that of a steel mould. An aluminium

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mould is however less expensive than a steel mould. Reference mould data used originatesfrom previous work [7]. The cost is increased for all moulds according to [74], see Table(21) below.

Mould Type Mould Area [m×m] Cost [k€]

Aluminium 0.25×0.25 110.5×0.5 190.65×0.85 481×1.2 116

Steel 0.25×0.25 310.5×0.5 550.65×0.85 661×1.2 158

Table 21 – Closed mould data.

D Benchmark cases: part cost contributionThe size of each contribution to the part cost for the three benchmark-cases is presentedin Figure 50 to 52 below. The material and waste cost is the largest contributer as themanufacturing volume grows large, for all three methods.

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Figure 50 – Part cost contributions as a function of manufacturing volume, HP-RTM.

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Figure 51 – Part cost contributions as a function of manufacturing volume, CM-TP.

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Figure 52 – Part cost contributions as a function of manufacturing volume, A-SMC.

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1651-7660AVE 2013:29

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