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Accepted Manuscript The engineering aspects of automated prepreg layup: History, present and future D.H.-J.A. Lukaszewicz, C. Ward, K.D. Potter PII: S1359-8368(11)00545-2 DOI: 10.1016/j.compositesb.2011.12.003 Reference: JCOMB 1624 To appear in: Composites: Part B Received Date: 8 July 2011 Revised Date: 30 November 2011 Accepted Date: 10 December 2011 Please cite this article as: Lukaszewicz, D.H.-J.A., Ward, C., Potter, K.D., The engineering aspects of automated prepreg layup: History, present and future, Composites: Part B (2011), doi: 10.1016/j.compositesb.2011.12.003 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Page 1: Articolo ATL

Accepted Manuscript

The engineering aspects of automated prepreg layup: History, present and future

D.H.-J.A. Lukaszewicz, C. Ward, K.D. Potter

PII: S1359-8368(11)00545-2

DOI: 10.1016/j.compositesb.2011.12.003

Reference: JCOMB 1624

To appear in: Composites: Part B

Received Date: 8 July 2011

Revised Date: 30 November 2011

Accepted Date: 10 December 2011

Please cite this article as: Lukaszewicz, D.H.-J.A., Ward, C., Potter, K.D., The engineering aspects of automated

prepreg layup: History, present and future, Composites: Part B (2011), doi: 10.1016/j.compositesb.2011.12.003

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers

we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and

review of the resulting proof before it is published in its final form. Please note that during the production process

errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Page 2: Articolo ATL

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The engineering aspects of automated

prepreg layup: History, present and future

D.H.-J.A. Lukaszewicz (1)

, C. Ward (2)

, K.D. Potter (3,*)

(1) Research Assistant, ACCIS, University of Bristol, Queen’s Building, University

Walk, BS8 1TR, UK; Email: [email protected] Phone: +44 (0)

117 33 15331; Fax: +44 (0) 117 927 2771

(2) Research Assistant, ACCIS, University of Bristol, Queen’s Building, University

Walk, BS8 1TR, UK; Email: [email protected] Phone: +44 (0) 117 33

15503; Fax: +44 (0) 117 927 2771

(3) Professor in Composites Manufacture, ACCIS, University of Bristol, Queen’s

Building, University Walk, BS8 1TR, UK; Email: [email protected]

Phone: +44 (0) 117 33 15277; Fax: +44 (0) 117 927 2771

(*): Corresponding author

Abstract

Highly consistent quality and cost-effective manufacture of advanced composites

can be achieved through automation. It may therefore open up new markets and

applications for composite products in aerospace, automotive, renewable energy, and

consumer goods. Automated Tape Laying (ATL) and Automated Fibre Placement

(AFP) are the two main technologies used to automate the layup of prepreg. The

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historical development and past research of both technologies is reviewed; with an

emphasis on past issues in application and capability as well as their solution, including

both thermoset and thermoplastic material layup. It is shown that past developments

have moved away from simply emulating manual layup into the now unique layup

procedures for ATL, and into the current AFP technology base. The state of the art for

both technologies is discussed and current gaps in the understanding of both processes

highlighted. From this, future research needs and developments are derived and

discussed.

Keywords: E. Lay-up; E. Automation; A. Laminates; A. Prepreg

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1 Introduction

Future aircraft programs, such as the Boeing 787 and Airbus A350XWB, contain

more than 50% by weight of advanced composite components. Consequently the rate

and economy of composite manufacture needs to improve to meet the requirements of

these and future build programs. Additional areas where advanced composites are of

increasing interest are renewable energy and automotive, where advanced composites

need to be cost effective in manufacture when compared to their metallic counter-parts.

To achieve this automation is one way forward.

Automated Tape Laying (ATL) and Automated Fibre Placement (AFP) are the

two main technologies that are employed today to manufacture advanced composite

laminates from unidirectional prepregs. ATL is employed to deliver wide prepreg tape

onto a surface whilst automatically removing the ply backing. Layup speed, tape

temperature, speed and tape tension can be controlled during layup. AFP is similar to

ATL but utilises a band of narrow prepreg slices, which are collimated on the head and

then delivered together.

A review of ATL layup was published by Grimshaw [1], however this source

covers only a single industrially relevant equipment supplier. Similarly, Evans [2]

published a review of AFP systems only pertaining to a single industrial system. Short

introductions to different aspects ATL and AFP are also given by Åstrøm [3], Campbell

[4] and Gutowski [5]. Recently, Sloan [6] has published an industrially focused

overview of ATL and AFP.

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Despite this, the authors are not aware of any other independent review of this

important area of composite manufacture; indeed even the above reviews were never

peer-reviewed publications. Further, while most components are manufactured from

thermoset prepreg, most research in the field was directed at thermoplastic layup.

Currently, an increasing amount of research is being conducted to improve existing

thermoset layup processes, see Figure 1. It shows the result of a literature search on

Google Scholar for the number of archivable publications for AFP and ATL. The results

were summed over a five-year period to provide meaningful trends. Filament winding

with respect to composite manufacture (excluding process relevant to electrical

components) is shown in an insert graph as a reference to illustrate the relative

shortcomings in terms of scientific publications, and consequently understanding, for

ATL and AFP.

With this in mind, this paper will review the historic development of ATL and

AFP to highlight the development, and also present the current State-of-the-Art (SOA)

for both processes. Lastly, current and future research opportunities are discussed. This

work will mostly aim to identify the engineering aspects of thermoset prepreg layup, but

thermoplastic prepreg is also discussed, where analogies are appropriate. Special

emphasis is placed on the impact of current trends in areas such as structural tailoring

and out-of-autoclave curing with respect to automated layup.

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2 Automated Tape Laying (ATL)

2.1 Historical developments of ATL

2.1.1 Early developments

Carbon fibres became commercially available from 1966 [7] onwards, and very

early on it was realised that prepreg layup could be automated to improve the

productivity and consistency of manual layup. ATL systems were conceived from the

end of the 1960’s onwards [8] and by the middle of the 1970’s research systems were

developed and in application use. The earliest known reference to an ATL is a patent

assigned to Chitwood and Howeth [9] in 1971, describing a method of laminating

composite tape onto a rotatable base-plate using Computer Numeric Control (CNC). In

1974 Goldsworthy et al. [10], see Figure 2, described an automated system delivering

76mm wide tape over a curved surface where the head was able to rotate and withhold

material to improve the part complexity that could be manufactured using ATL layup.

Huber [11] noted that aerospace manufacturers and research institutions built most ATL

systems as early as 1975 in-house, and as a result they were normally part of a

component centred production system for a given aircraft program, see Figure 3. Layup

speeds were given to be 10-20 m/min, however it was argued that this did not affect

overall productivity.

More importantly, ATL could reduce layup errors and material wastage, which

resulted in improved material utilisation. For example, Grimshaw [1] in 2001 calculated

the material wastage generation of an ATL layup as a function of part size to be up to

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30% for small parts and decreasing exponentially to 2-4% for larger parts; with similar

results having been reported elsewhere [12]. Productivity of manual forming at the

beginning of 1980 was stated as ~1kg/h [13,14] and materials wastage rates were 50-

100 %, due to both the lack of automated ply cutters and optimised consumables and

prepregs. Postier [15] reported a comparison between manual and ATL layup, with

ATL capable of achieving a 65% reduction in layup time and an additional reduction in

material wastage rates for certain components.

2.1.2 ATL development from the 1980’s

To enable ATL to become more widespread the technology was converted into a

more generic process. The early 1980’s were as such a time of rapid development with

multiple competing concepts. To address the issue of higher layup speeds, Eaton [16]

and Saveriano [17] introduced a layup system with a lightweight head that dispensed

tape over a rotatable surface, similar to the first patent of Chitwood and Howeth [9], at

up to 60m/min. At that time most ATL systems were Flat Tape Laminating Machines

(FTLM), which could only deliver tape onto a flat tool. Coad, Werner and Dharan [18]

by contrast discussed a robotic pick-and-place system to overcome ATL’s limitations

regarding geometric complexity.

To finally address this limitation, Stone [19] introduced a commercial ATL

system in 1984 from Cincinnati Milacron (now MagCincinnati) who had acquired a

license for a UD-tape layup head from Vought Corp, Dallas, TX. The system was

capable of delivering tape over geometries with curvature up to 15° using an ultrasonic

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tracking system, to follow the contour of the mould, making it the first example of a

Contour Tape Laminating Machine (CTLM). However, several technical issues still

remained, including layup speeds, accurate layup onto complex moulds, and improved

reliability and quality. Albus [20] pointed out the limitations that robotic arms had

during the middle of the 1980’s, which were limited to speeds < 60m/min for layup

applications, and that accuracy was key to enabling off-line programming. To alleviate

this issue most ATL systems became high-rail gantries resulting in heavy and stiff

structures that were associated with very poor machine dynamics [21]. Furthermore,

layup systems were still not capable of delivering tape with defined compaction

pressure and regular debulking cycles were still necessary. Reliability was likely to be

low, for example due to breakage of the ply backing. While layup dexterity had been

increased by modifications and additions to the layup head, layup speeds remained

fairly low.

In 1986, Meier [22] introduced a system that has formed the basis for all modern

commercial single-phase ATL systems. Direct layup force control and head normality

over curved surfaces was enabled by replacing the previous ultrasonic tracking system

with force-controlled Z- and A-axes [23]. However, no mention of tape heating

facilities was made and remaining issues were mostly related to layup reliability as a

function of out-time of the prepreg and initiation of the first ply, which usually had to

adhere to a coated mould or release cloth.

Grone, Schnell and Vearil [24] then patented a method to finalise the end of a tape

course cut under an oblique angle using a second flexible layup element. This method

has since been modified by Torres [25] not only to finalise a tape course, but also to

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start a ply, and in particular to overcome the technical difficulties of first-ply

attachment. However, prepreg layup was still limited to fairly simple components and

reliabilty was still affected by tack levels and their degradation with out-life due to

limited heating. To address the first, Lewis and Romero [26] introduced a layup system

combined with significant software capability, to enable layup over a curved surfaces

along a natural (the path a tape will take over a surface without friction) or geodesic

path.

As layup capability had increased to more and more complex geometries at the

end of the 1980s, ply alignment increasingly became an issue. The soft rollers employed

for layup over complex geometries lead to uneven layup pressure and tape tension on

the head. Both of which could result in compressive forces acting on the tape between

the layup roller and the tape supply and allowed transverse movement of the ply prior to

delivery. To prevent such movement tape was delivered with controlled tension and

combined with tightly controlled layup pressure to enable correct alignment of a ply.

One such system is shown by Torres [27] which combined means for ply tensioning

with layup pressure control. Grimshaw [28] further demonstrated an ATL system

having a segmented layup shoe connected to a pressure chamber, enabling accurate

layup pressure and improved ply alignment over contoured surfaces. In 1995 this

approach was extended to multiple layup elements operating independently from the

layup head [29]. The other aim in using layup pressure control was to reduce debulking

operations, as it detrimentally affected productivity, but it is unclear whether ATL layup

systems at the time were sufficiently capable to achieve this. For example, Olsen and

Craig [30] argued that the effective pressure transferred from the head onto the laminate

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was a function of layup speed, and had to be much higher than during vacuum

debulking, due to the fact that it is applied over a much shorter time frame. The pressure

on the laminate depends on the machine capability, the roller geometry, roller material,

and the shape of the mould the material is applied onto.

All of the works explored so far were aimed at increasing the manufacturing

capability of ATL equipment but the issue of material outlife and changing tack levels

remained unresolved. Further, whilst layup systems enabled accurate pressure control

during layup it was unclear what the desirable pressure level was, or what it depended

on. Disappointingly, actual layup speeds were generally unchanged from the 10-20

m/min previously achieved.

A particular issue that remained in this period was the cost of an ATL system,

which was given by Goel [31] as ~ US$3.5 M for most basic systems. This meant that

ATL had to be highly productive to offset the initial capital expenditure, making its

adoption into the commercial aircraft industry a slow process. Krolewski and Gutowski

[13,14] and Foley [32] published economic assessments of various manufacturing

methods available at the end of the 1980’s in terms of productivity and part cost. They

showed that automated layup offered no appreciable increase in productivity over

manual forming. Considering the additional capital investment for layup systems, the

recurring part cost increased for automated layup, however the authors concluded that

automation was still desirable due to effects that were not accounted for in their study,

including improved reliability, consistency, and reduction of material wastage.

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2.1.3 Development in the 1990s until today

Tape heating was introduced in the 1990’s to overcome issues during layup of

complex laminates, and also enable tack control for layup of large parts. It is unclear

from the literature when heating was first used for thermoset layup, but irradiation

heating for thermoplastic layup was in use by 1991 [33]. Benda and Stump [34]

discussed the joint development of a component and layup system, where a hot-air

heating system was added to an ATL to enable tape attachment onto complex contours.

Further changes included the layup roller diameter, which was reduced from 150mm to

50mm to improve dexterity when delivering tape onto contours with > 30° curvature.

To enable layup onto such complex geometries some tape tension was required to keep

the plies aligned. Lastly, it was mentioned that the effective layup rate was 13m/min,

again unchanged from the earliest discussion dating back to 1981.

Sarrazin and Springer [35] addressed the question of optimal processing

conditions for thermoset tape, in the context of a cure-on-the fly system, to effectively

reduce post-curing. Their work proposed a layup system where thermoset tape was

heated to 150°C and used at speeds ~0.06m/min. It was observed that the thermoset

material only reached a limited degree of cure and that post-curing was still a necessity;

that layup pressure was independent of the number of plies, and scaled weakly with the

roller diameter and ply orientation. Finally the authors concluded that a high layup

pressure could result in delamination during layup, as the material is pushed and pulled

apart in front of and behind the layup roller compressing the material onto the tool,

however their study did not include tack, which could prevent such separation.

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Grove [36] (in 1988) proposed a model for the laser assisted heating of

thermoplastic tape to enable direct layup and consolidation of thermoplastic materials,

however, the focus of thermoplastic layup shifted quickly to AFP. Since the middle of

the 1990’s to the present day, further developments to ATL have thus been rather

limited and were starting to be dominated by productivity requirements.

Torres [37] introduced a system that combined at least two rolls of either 75, 150

or 300mm wide material on one ATL head to potentially improve both productivity and

layup dexterity, though this can also be considered an AFP layup system. Forest-Liné

[38,39] developed a nesting technology for ATL layup, to improve productivity for

large parts with small features. Ply patches are pre-cut in a separate operation, stored on

a ply-backing, and wound back onto a roll. Forest-Liné’s system employ two separate

head sides to deliver either the continuous ply course or small pre-cut prepreg patches,

often referred to a twin (or dual) -phase layup, with conventional layup being single-

phase layup.

Today, ATL layup has further diversified by returning to the earliest ATL systems

using a part centred layup approach, and machines are currently being developed that

can address specific layup issues while also yielding very high productivity rates.

ATL can be considered a highly productive process for prepreg layup, which is in

widespread use in the aerospace and renewable energy industries in particular.

Advantages are high layup rates, high mechanical properties due to the use of prepreg,

capability to manufacture large parts, capability to handle high areal weight materials,

and simplified offline machine programming. Disadvantages are high initial capital

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expenditure, limited geometric complexity capability, and higher material wastage rates

than AFP (see 3.1). Despite the potential complexity limitations of ATL manufacture, it

has recently received renewed interest due to the high productivity achievable for flat

laminates [40]. After layup, flat laminates can be formed into the desired shape by hot

drape forming [41], offering a cost competitive manufacturing route for large composite

components and material with high prepreg areal weight, however forming may

detrimentally affect the mechanical performance of the structure, e.g. due to fibre

wrinkling.

ATL systems are used for manufacture of a variety of parts, such as tail planes,

wing skins [42,43] and the centre wing box of the A380 [43,44]. The main

manufacturers of aerospace ATL equipment are MAGCincinnati (USA), MTorres

(Spain), and Forest Liné (France), although the latter was recently acquired by

MAGCincinnati. GFM (Germany), Mikrosam (Macedonia), Entec (USA) and ATK

(USA) supply ATL systems, but do not have a comparable number of installed systems.

Ingersoll (USA) currently only supplies AFP systems, but has delivered ATL systems in

the past.

2.2 ATL Process description

ATL (and AFP) can be interpreted as a form of additive manufacturing or inverse

machining, since the part is built up by adding material, as opposed to material removal

during machining [5]. The ATL head handles the prepreg tape, which is typically 75,

150, or 300mm wide and supplied on a cardboard core [12] similar to the prepreg used

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for manual layup. However, the prepreg can be modified for automated layup by

changing the backing paper or degree of impregnation. Most commercially available

systems store the prepreg material directly in the layup head, and a schematic according

to Ästrøm [3] is shown in Figure 4, and a picture of ATL head is shown in Figure 5.

Due to the mass of both the head and material, as well as the size of the parts typically

manufactured, ATL systems are normally mounted on horizontal gantries, Figure 6

[45], or a vertical column system, Figure 7.

For most aerospace structures, courses consist of ramps and valleys as well as ply

terminations, resulting in complex surface topologies. ATL’s are CNC systems that

follow predefined paths accurately and reproducibly, allowing the elimination of layup

errors that could occur in manual layup. During the layup of each ply, a tape course is

placed next to one other with a gap of 0.5-1mm, which is required to accommodate

variations in placement due to layup control and tape tolerances. Material tolerances are

normally sufficiently small to minimise the impact of gaps on mechanical performance.

At the start of a layup sequence, the ATL system attaches a pre-determined length

of tape onto the tool using a soft silicone roller. Once the course has been applied, the

system accelerates to the layup speed and delivers the remaining material [23-25,28,29].

During layup the material is attached to the tooling using controlled additional force that

is transferred through the end-effector. This can be a flexible silicone roller, but more

sophisticated methods have also been developed to control the pressure distribution over

complex surfaces, such as segmented laying shoes [24,29]. Most ATL systems achieve

a maximum linear layup speed of 0.83-1ms-1

and accelerate at 0.5ms-2

and typically

deliver a compaction of F = 445N (for 75mm wide thermoset tape [46]) - 1000N (for

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300mm wide thermoset tape), which would translate to a pressure of ~0.1 MPa. By

contrast, for thermoplastic material layup, Colton [47] quoted a necessary pressure of

1.4 MPa for APC-2 at 316°C, whilst layup pressures up to < 3.6 MPa have been

reported elsewhere [48]. The head controls the input tension on the plies and ply

backing between the material supply and the layup point during layup. Tension is

imparted to avoid tearing of the backing paper, improving the alignment of the plies,

and enabling layup into curved geometries. To control the temperature during layup the

material can be heated either in front of the layup head or on the layup system in

delivery.

At the end of the ply course the head decelerates just prior to finishing and cuts

the tape automatically, using rotating or pinching blades. The distance between the

blade position and the roller contact point is termed the “minimal course length”, and it

is used as a lower bound on the part sizes that can be manufactured - around 100mm for

most systems. After severing the tape, the remaining or minimal course length, is

delivered to finish the ply course. This entire process is repeated course by course until

the ply is finished, the system is stopped by the program, user intervention, or if an

automated fault detection system has identified a layup error.

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3 Automated Fibre Placement (AFP)

3.1 Historical developments of AFP

3.1.1 Early developments

Quite possibly the first published AFP system has already been introduced in

Figure 2. The 1974 Goldsworthy [10] patent described an ATL system but also

highlighted the challenge of conforming a tape to a curved surface. To address this the

layup head had the ability to slit down the wide tape into 3.2mm slices and then deliver

those at individual speeds by keeping the additional material on the head, Figure 8. In

reality this would have resulted in technical limitations during material layup and it is

unclear whether these issues were resolved, but further developments in this process

could not be identified.

3.1.2 Development from the 1990

AFP systems were commercially introduced towards the end of the 1980’s, and

were described as a logical combination of ATL and Filament winding (FW) [49]; by

combining the differential payout capability of FW and the compaction and cut-restart

capability of ATL. Several of the lessons learnt during the development of ATL, such as

roller design and material guiding were incorporated into these AFP systems and as

such they were immediately available from commercial suppliers.

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Evans [50] initially overcame the limitations of Goldsworthy’s approach by

keeping slit tape on separate bobbins, which were also individually driven. Bullock,

Kowalski, and Young [51] demonstrated another type of AFP machine together with an

offline programming system, and argued that offline programming was essential to AFP

productivity as it directly affected machine production time. The AFP system controlled

layup speed, pressure, temperature, and tape tension. They also showed that a layup

speed of 7m/min would result in a productivity of 5kg/h, which was given to be

comparable to ATL. Barth [52] showed an AFP system that made use of cooled creel

houses to reduce prepreg tack, thus enabling reliable despooling and improved layup

reliability. Additionally, the compression-after impact strength of laminates

manufactured by AFP and manual forming was evaluated, showing that mechanical

properties of both were comparable.

Technical issues that remained unresolved in this period were the tension in the

tows, reliability, productivity, and layup accuracy. The tows were typically delivered in

a very complex path to the head prior to collimating, which could increase tension in the

material and affect layup reliability. Layup accuracy is highly important for AFP

because the narrow tape will result in gaps between the material, which are a function of

the placement accuracy, and may affect mechanical performance. This had not however

been studied in any detail, though later studies showed a significant impact on

mechanical performance [53,54].

To enhance productivity, Enders [55] for example introduced an AFP system that

could deliver up to 24 tows in a sequence. The system was uniquely tightly integrated

into the Computer-Aided-Design (CAD) system to address the earlier note [51]

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regarding AFP productivity. In use on a demonstrator component, a layup rate of up to

30m/min was reported - yielding a productivity of 1.9kg/h – and this was compared to a

manual layup productivity of 0.7kg/h for the same component. Rather differently, Evans

[56] improved productivity by focussing on reliability, such as material changes, tape

tolerances and intermittent debulking. More reliable layup over complex geometries

was achieved by delivering the tows along a curvilinear path; this is often referred to as

steering. Quickly, it was realised that the ability to deliver material in curved fibre

orientations added additional design freedom and enabled potential improvements in

mechanical performance. Due to the smaller individual tape widths that were used for

AFP, smaller steering radii could be achieved than for ATL.

Some very interesting results for an industrial application were shown by Measom

[57], who reported on the development process of a part with a complex layup. The

component had initially been manufactured by FW and manual layup but manufacture

with AFP reduced material wastage rates from 62% to 6% and productivity improved

by 450% for layup of a single 12.7mm wide tape. However, to improve material

delivery the areal weight was doubled, resulting in reduced downtime and further

improved productivity. This result was supported by Pasanen [58] who reported a 43%

cost reduction for AFP over manual layup.

A schematic of an AFP layup head for layup of multiple tows was given by Evans

[2], see Figure 9. Whilst the benefits of AFP for complex layups had been successfully

demonstrated, the process was still not productive enough to quickly offset the initial

capital expenditure with systems costing up to US$6 M [31]. The limitations were now

affordability, process reliability, and productivity. Furthermore, the development of

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AFP in this period coincided with the advent of thermoplastic composites for aerospace

structural applications, and significant research effort was devoted at developing AFP

for thermoplastic layup. As Gruber [59] noted, this was driven by the need to

manufacture large spacecraft and submarine structures, that exceeded most autoclaves

diameters and required in-situ processing and reduced thermal residual stresses.

The earliest approaches for developing thermoplastic layup were reported by

Grove [36], Mantell and Springer [60,61], and Sarrazin and Springer [35]. These works

identified a trade-off between layup pressure, temperature, and speed. Layup quality,

mainly measured by interfacial healing and voidage, was detrimentally affected by

layup speed; and as discussed by Bourban [62] the main limiting factor for

thermoplastic layup was the amount of time required to heat the material above its

melting point. Thus, the maximum layup speed was limited, with works reporting

speeds of 3.6mmin-1

[63] to 5mmin-1

[64], resulting in considerably lower layup

productivity than thermoset materials. This was further explored by Ranganathan [65],

Pitchumani [66,67], and Tierney [68] to predict the optimal processing conditions for

reduced void growth, as well as maximising speed and interfacial bonding. Most works

used hot gas torches for material heating, but a laser heating was also successfully

developed by Funck and Neitzel [69], Rosselli [70], and Pistor [71]. Goodman [72], and

Burgess [73], similarly reported a method for curing photoactivated thermoset prepregs

on the fly using an electron beam or ultra-violet-light(UV) as a radiation source for

faster processing and reduction of residual thermal stresses. Overall however, both

thermoplastic and thermoset in-situ processing approaches achieved limited layup

speeds, whilst also exhibiting reduced mechanical properties.

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3.1.3 Development from the 2000 until today

Grant [8,74,75] described the change in focus for AFP layup from novel processes

to addressing issues regarding affordability, process reliability, and productivity, and

showed that AFP had mainly been employed in military and space programs until 2000,

Table 1. Process reliability was detrimentally affected by splicing (welding of the tape

ends) errors at the end of a bobbin, dropped tows, and material changes, which would

result in unscheduled downtime and decrease productivity. Torres [76] introduced an

automated system for splicing the tows together, and this could improve productivity by

reducing down-time for material refilling. Oldani [77] also introduced an automated

system to detect layup errors, improving productivity by reducing the time for quality

inspection after ply layup. To increase tack levels and further minimise layup errors

infrared heating of thermoset tape was introduced by Calawa and Nancarrow [78] to

allow faster heating and higher layup temperatures. Furthermore, Hamlyn [79]

introduced a system for rapidly exchanging layup heads and tools by keeping a second

layup head ready for immediate layup, and this led reduced system downtime. Material

delivery was also improved by using systems that either reduced the feed length, or by

minimising the amount of redirects and twists in the tow using appropriate guide

systems [80].

Despite improvements in raw productivity and reliability, several technical issues

remained. Foremost, capital expenditure was still high compared to other manufacturing

methods, and offline programming was still un-optimised although layup of curved

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tapes onto a mould and AFP layup control are currently an area of ongoing research

[81,82]. The capability to automatically manufacture unsymmetrical laminates that can

have locally changing fibre orientations makes AFP a lead technology for future

developments in the areas of smart and tailored structures, and their application.

The main manufacturers of AFP systems are Automated Dynamics (USA),

Accudyne (USA), MAGCincinatti (USA), Coriolis (France), Electroimpact (USA),

Foster Miller/ATK (USA), Ingersoll (USA), Mikrosam (Macedonia) and MTorres

(Spain). Automated Dynamics, Accudyne, Coriolis and Electroimpact supply their

systems on industrial robots and gantries. Cincinnati, Foster Miller, Ingersoll, Mikrosam

and MTorres use either column type or horizontal gantries. Robotic layup systems tend

to have a lower initial capital expenditure and can be better tailored for specific

applications. Gantry layup systems offer improved general productivity and reliability

by handling more tows in the head.

3.2 AFP Process description

AFP systems differ from ATL in the width of the material that is laid down with

typical material widths of 3.2mm, 6.4mm, and 12.7mm, however AFP will normally

deliver several [83] tows in a single sequence, termed bands. A band then forms a

course, while a sequence of courses is termed ply. Presently, AFP can deliver up to 32

tows in parallel at linear speeds of up to 1ms-1

[83]. The systems also tend to have

higher acceleration in the linear axes with typical values around 2ms-2

. Rotational

speeds and accelerations are more varied by company and therefore not quoted.

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However, it is important to note that rotational speed and acceleration can have great

impact on layup productivity for complex components, and are therefore more relevant

to AFP than ATL. The width and number of tows delivered depends strongly on the

complexity and local geometry of the part that the course is to be laid over, thus

material width and tow count will affect productivity.

Each tow is normally driven individually and can be clamped, cut, and restarted,

during manufacture [83,84]. This makes it possible to deliver each tow at individual

speeds, enabling layup over complex geometries and some tow steering, as Figure 10

shows, and is beneficial for example in structures such as fuselage sections with

window cut-outs, or wing skins with numerous pad-ups and valleys. Whilst steering was

initially conceived to improve layup over surfaces with double-curvature [10], the

individual tow payout may improve productivity and reduced materials wastage rates

[13]. An important consideration is the amount of gap between the tows, which is much

larger than for ATL and typically scales with the amount steering. This may affect

mechanical performance detrimentally and is often countered by transversely offsetting

subsequent plies by half a tow-widths.

The quality of the “on-the-fly” cut normally decreases with increasing speed

during cutting and secondary operations are therefore still necessary to remove

crenulations around a geometric feature. For this reason AFP systems tend to have a

lower “minimal course length’” than ATL, typically around 50mm.

AFP productivity is typically lower than ATL because it is generally employed

for more complex parts. For example, productivity for layup of a complex fuselage

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section is ~8.6kg/h [85], which is about half of current ATL rates. During AFP layup

tow tension on the head is negligible or controlled to be very low to enable layup into

the convex geometries and features. The composite material for AFP layup can either be

impregnated tows or slit prepreg tape. Slit tape is more expensive than impregnated

tows but potentially offers advantages with respect to productivity, reliability, and

product quality [12]. The slit tape or impregnated tows are normally wound onto

cardboard bobbins and supplied with an interleaf film to reduce tack and friction in the

material supply. The small diameter of the bobbin can additionally enable accurate

tension control during unwinding.

Despite the differences in material form and material supply to the layup head, the

layup operation during AFP is similar to that of ATL. The prepreg tape or tows are

either delivered to the head from a creel cabinet, or stored directly on the head [86]. The

first allows the use of simple industrial robots due to the reduced head weight; the latter

requires column or gantry type systems, see Figure 11. The material is delivered from

the spools to a compaction roller, where additional heat and force are again applied to

compact the material in an attempt to eliminate vacuum void removal. AFP systems

tend to use flexible rollers to compress the material and reduce voidage, but as

previously mentioned for ATL the short contact times may be ineffective to achieve

sufficient compaction. To heat the tapes hot torches, Laser, and infrared irradiation

techniques are used. Robotic systems improve the affordability of AFP since industrial

robots are significantly cheaper than gantry units, and as a result robotic AFP systems

are presently cheaper than comparable gantry AFP or ATL systems.

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4 Research Opportunities

4.1 Productivity

Currently, increases in productivity are the overriding goal for both ATL and

AFP. Consequently, all potential improvements that are discussed in the following are

governed by, or linked to potential productivity increases. Potential improvements are

possible through improved software, machine layouts, materials and enhanced layup.

The first two are discussed in this section, while the latter two are discussed in

following sections.

Examples of software improvements can be found in Debout, Chanal and Duc

[87], where AFP layup paths were optimised to reduce unnecessary acceleration with

reported possible reductions in layup time of 33%. Theoretical productivity drivers have

been studied using simple models based on the machine capability. Lukaszewicz,

Weaver and Potter [88] and Lukaszewicz [89] have published productivity estimates for

a simple flat component for both technologies based on the raw productivity values of

the layup systems, see Figure 12 and Figure 13. It is interesting to note that AFP was

found to be more productive for all part sizes studied but particularly for small parts. To

translate this model into real productivity estimated it needed to be considered that a

typical ply course of a primary structural aerospace laminate is 2m long [90]. For

typical machine data productivity was thus expected to be around 29.2kg/h for ATL and

41.3kg/h for AFP [89]. This correlated well with laydown-rate estimates for APF from

Boeing given to be 45.4kg/h [85], however, actual productivity quoted was given to be

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8.6kg/h, a knockdown of 80%. This shows that theoretical productivity can be well

estimated, but the translation into real productivity is still unresolved. More recently,

Ward, Lukaszewicz and Potter [91] have studied the AFP layup of a small complex

component with symmetric layup on a flat bottom side and contoured topside. By

comparing the relative layup time between the two sides the productivity reduction due

to part complexity was estimated to be 29% to 51% for this component due to

acceleration and deceleration during layup.

This large productivity reduction can further be explained by the fact that layup

machines only spend a fraction of the time on actual layup. For the speed and

acceleration data given in Section 2.2 for ATL, and 3.2 for AFP, the layup time for an

8m long course is 4s and 2.5s respectively including time for acceleration and

deceleration. However, time for starting a new ply, including ply cutting, turning and

repositioning is ~9s for ATL and ~7s for AFP due to the lack of cutting operations [89].

This shows that that even during layup of simple components the ratio between

productive time and secondary operations is unfavourable. In addition, quality

inspection and layup errors will result in further productivity reductions.

This downtime of layup machines, due to material refilling, error correction or

cleaning is significant, up to 50% for AFP [77]. Further increases in layup speed are

thus unlikely to yield any further productivity increases [88,89] since current

productivity is already largely constrained by part design, secondary operations and

down-time. Addressing any of these productivity constraints should easily yield

increases in productivity. To enhance the predictive capability of existing software

approaches, a better understanding of the part complexity is required. It is likely that

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small geometric features heavily impact layup time. This can only be resolved during

the design phase to achieve higher productivity.

Lastly, AFP is currently limited to low areal weight prepregs, which restricts its

use to aerospace applications. Since prepregs in renewable energy industries and others

tend to have higher areal weights, up to 1600gsm and more, future AFP systems need to

be able to deliver these materials. To address this novel cutting methods are required,

possibly laser cutting.

4.2 Steering and Control

Shirinzadeh and co-workers [81,82,91-93] give an excellent overview of the

relevant work relevant to path planning for AFP and ATL. To match the material to a

mould a point-cloud is typically generated that the control system will aim to follow.

The placement accuracy depends on the density of this cloud with a higher density

leading to more accurate layup. However, as discussed by Debout, Chanal and Duc [87]

this will also lead to unnecessary acceleration and deceleration as the control system

follows the defined layup path. Optimising the layup program or identifying suitable

starting points can alleviate this problem.

The available degree of steering in AFP and ATL layup is often reported to be the

smallest possible radius fibres can be laid into without significant defect development,

such as detachment from the tool and ply wrinkling. There are, in principle three main

tow steering defects, tow buckling, tow pull-up and tow misalignment, see Figure 14.

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Twisted tows can also occur but are less common. Tow buckling occurs on the inside

radius of a tow if compressive forces are too high, similarly tow pull-up occurs on the

outside of a tow due to excessive tensile forces. Lastly, tow misalignment is the result of

variability in the layup system, layup control or prepreg material.

Wiehn and Hale [94] reported the successful layup of AFP tows into radii as small

as 50.8cm compared to 610cm for ATL layup of 150 mm wide tape. Moon, Johnson,

and Hale [95] reported that the number of defects is a function of the smallest steering

radius. Recently, a model for the defect development during layup of a curved tape was

reported by Beakou et. al. [96], however their model was not directly validated by the

experimental results. A possible explanation could be the effect of viscoelastic material

behaviour, which was not included in the model. This, and the importance of material

tack are discussed in section 4.4. The interaction between material properties and

processing conditions needs to be studied further to gain a more detailed understanding

of limitations of steering during layup. A combination of experimental and modelling

approaches is required to explain the changes in the tow or tape during steering. Further,

current steering approaches aim to incrementally form a radius by forcing the tape to

follow the head rotation whilst being attached to the substrate and different steering

approaches, such as shearing of the tape [97] need to be explored.

Other steering defects include tow gaps, steering overlaps, and gaps, see Figure

15, but the impact of these defects on the mechanical performance of laminates has not

been extensively studied. Wang and Gutowksi [21] presented a theoretical approach to

reduce laps and gaps during thermoplastic layup by allowing the plies to flow

transversely during layup, to simplify layup accuracy requirements for thermoplastic

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layup. There is continued interest in this topic due to the higher number of gaps during

AFP layup and the relative difficulty of placing tows with the required tolerances. Blom

et. al. [53] explored the mechanical performance of AFP laminates using numerical

modelling, and results showed significant strength reductions, up to 32%, and stiffness

reductions arising from tow drop areas, see Figure 16 and Figure 17. By contrast, Croft

et. al. [54] conducted a number of mechanical tests on AFP laminates containing all the

aforementioned defects and found significantly lower (3-15%) strength reductions than

previously predicted, see Table 2. This may be explained with defect reduction and fibre

rearrangement during autoclave curing and is as such not a demonstration of the

robustness of AFP but rather autoclave curing. The impact of AFP layup on mechanical

performance as well as its reduction thus warrants further research. In particular,

approaches are required that aim to capture the translation of initial layup defects, laps

and gaps into the final cured component.

4.3 Processing conditions during layup

The exact conditions during layup may have a significant impact on the

mechanical performance of the final laminate. To this end Lukaszewicz, Weaver and

Potter [98], and Lukaszewicz et.al. [99], conducted layup trials on industrial equipment

to correlate the voidage in an uncured laminate to the processing conditions, such as

layup speed, temperature or pressure. In an additional study Lukaszewicz and Potter

[100] showed that the variability in the prepreg material was too high to allow simple

development of strong analytical models. It has been shown that this was aggravated by

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the additional variability in the layup control [89], which had an additional impact on

analytical layup quality models. Mechanical testing on laminates manufactured using a

wide range of layup conditions and subsequent oven cure showed a change in

mechanical performance of up 50% for the ILSS and compressive strength due to layup

conditions alone [101], see Figure 18 and Figure 19. Further work in this area will be

required to establish the impact of different layup conditions on the microstructural

features of laminates, such as the fibre volume fraction and the void content. To

overcome the limitations due to inaccurate layup control, Lukaszewicz and Potter [88]

have introduced a small research layup system, that can be used to manufacture small

test coupons using automated layup. Experimental results from such a system could

then be used to evaluate models that link the deformation of plies during layup to

microstructural features, such as voidage.

4.4 Material research

Prepreg materials have historically been developed with mechanical performance

in mind and were then simply adapted for automated layup by developing specific ply

backing films, or slitting prepreg tape for AFP layup. Despite this, research on the use

of thermoplastic tape has illustrated the importance of tape uniformity, porosity and

interface properties on the quality of the final product in in-situ layup [102,103] and this

can be applied to thermoset layup. An improved understanding of the translation of the

initial prepreg microstructure into the final part is thus required. Material variability

needs to be reduced to achieve uniform properties at the slit-tape level, which is

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typically only 3.2 or 6.4mm wide. In most cases the dimensional and physical

tolerances between manual and automated layup are the same and only the backing and

tack specification are changed [24,50,56], which consequently leads to unreliable layup.

For example, Figure 20 shows an image of slit tape for AFP layup with fuzzy edges.

This would lead to unscheduled downtime for AFP layup and could result in excessive

voidage in the dry fuzzy areas. To avoid this, slit tape needs to be prepared in the future

with high degrees of impregnation. Figure 21 shows a defect in a roll of ATL tape. This

area would need to be removed and laid outside of the part. Removing materials

wastage during layup is very time consuming and naturally has an excessively

detrimental effect on productivity. The most promising method of improving the

uniformity of the final prepreg is an improvement of the uniformity of the resin film that

is used during hot-melt processing. Further, computerised optical fault detection is

required to ensure that prepregging defects are detected during manufacture.

Another aspect of the prepreg layup process is the material tack. Ahn et.al [104]

used a compression-tension test on a stack of prepregs to measure the energy of

separation, which was linked to tack. They observed that prepreg tack was a bulk

property as well as surface-sensitive with viscoelastic behaviour that depended on

material as well as operating conditions. Later, this approach was extended to material

aging as well. It was observed that prepreg tack correlated with the glass transition

temperature and instantaneous temperature which was linked to both the increase in

wetting area as well as the change in resin viscosity [105]. More recently, this topic has

found new attention due to the impact tack can have on productivity, process reliability

and tow steering. Dubois, Le Cam and Béakou [106] used a probe tack test to measure

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various parameters influencing on a modern, high toughness prepreg. They observed an

increase in tack force with increasing hold-time, contact force, deformation rate and

humidity, while tack decreased with increasing temperature and outlife.

However, all the works previously explored use low deformation rates during

testing, which differ by one or two orders of magnitude from the deformation rates

found during high-speed layup. Crossley, Schubel and Warrior [107] thus introduced a

novel tack test which enabled testing at higher deformation rates. Their work

demonstrated a non-linear behaviour of prepreg tack as a function of layup temperature

and speed of deformation which should help to understand the development of defects

during layup further.

4.5 Layup modelling and simulation

This section will not address existing Computer Aided Manufacturing (CAM)

software, but rather discuss a more fundamental understanding of the effects of layup on

thermoset prepreg. This is important as currently, models for the layup of thermoset

prepreg that enable modelling of defects and their development do not exist.

Depending on the pressure, temperature, and contact time of the roller, some flow

can occur between the plies during layup, which may reduce interply-voidage and

improve laminate quality prior to cure [102]. Currently this interaction is not well

understood and further improvements in this area should be made. Lukaszewicz and

Potter [108] recently proposed a model for the compaction of thermoset prepreg during

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layup, which can be used to describe this interaction and to enable direct layup at high

quality, effectively reducing debulking instances [34]. Again, it has been demonstrated,

that an understanding of this interaction can improve ILSS and compressive strength by

50% [101].

Other aspects of the layup process that could be captured by modelling are the

development of wrinkles and bridging at geometric features, however it is likely that

these issues are not only related to the material and the processing conditions, but also

to the choice of system. As an example, flexible rollers are commonly used to conform

difficult ramps, but by using flexible rollers some chatter during layup inevitably occurs

which may then lead to wrinkling or bridging. Potential solutions to this would either

use a layup roller with tailored stiffnesses or uncouple the necessary flexibility of the

layup system from the layup element. Further, bridging over concave features or

crowning over convex features is often observed. Both may lead to wrinkling in the

final part, which can severely affect mechanical properties. If machine control is

inaccurate both types of defects can be linked to the amount of material that is available

on the head. However, even if it is assumed that material delivery is accurately

controlled these defects can occur due to the interpolation of geometric features in the

CNC program. Approaches are therefore necessary to ensure that the interpolation and

axis control result in the correct amount of material being available at any point during

layup.

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4.6 Functional integration

Returning to Figure 1, it is important to note that automated layup derives its

possible increases in productivity not only from automation of the manual operations,

but also from combining several serial tasks into a single or parallel operation. Future

layup systems will thus likely target automation and integration of more functions onto

the head, as well as higher productivity by controlling more tows, having less

downtime, or allowing the layup of high prepreg areal weight materials.

Additional functions feasible for integration on the manufacturing process are

tooling preparation and online inspection systems [109]. Systems that allow inline

quality control by optical means are already in use or in development, for example by

Ingersoll. Multiple robot interaction and synchronisation, improved layup kinematics,

and optimised CNC post-processing can deliver further gains in productivity for both

ATL and AFP. Synchronisation of multiple robots can greatly improve the layup of

large parts as several robots can work on different part areas and different stages of a

ply sequence. Adding more and more features to a single layup system will inevitably

result in reduced per task performance. The most promising approach is therefore the

combination of multiple robots into a single work-cell, where the robots either

cooperate to achieve tasks quicker, for example through reducing unproductive travel of

the individual units, or by equipping each robot for a specific task which can be carried

out more efficiently.

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5 Summary

ATL and AFP are finding more wide-spread adoption in a number of industries

due to potential reliability and economic improvements. ATL has been developed since

the 1970’s as an automated version of manual tape laying and offers high productivity

and reliability for simple or low complexity components. It is in particular highly

productive for large simple flat components, and able to handle high areal weight

materials with few modifications. Future developments in renewable energy, for

example rotor blade manufacture, will likely rely on ATL layup of low-cost, high-areal-

weight prepreg. Overall, potential productivity gains for ATL are limited, due to the

robust nature and long history of the technique.

AFP improves on ATL layup by allowing direct layup of more complex

components. In addition, material wastage rates are reduced and productivity for

aerospace components may be higher due to the unique cut, clamp, and restart

capability per tow. Since the 1980’s AFP has become a relatively mature process, which

also has greater potential for future improvements. Productivity improvements can be

expected from improved programming, reduction of secondary operations, reduction of

down-time and multiple robot interaction. Currently, AFP seems more suitable for

typical aerospace components and materials and modifications are necessary to enable

layup of wider and higher areal weight materials.

The automated layup systems we see today were developed by industrial machine

companies with either none or limited background in the composite industry. Currently

these companies are developing their composite expertise and tend to look for material

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solutions to address constraints in the manufacturing system. Material suppliers have

historically worked with composite users employing manual layup and have limited or

no expertise in the industrial machine industry and tend to look for machine

modifications to address current constraints. The design approaches and software

packages used by end-users to design components are often derived from manual layup

and/or are insufficiently integrated with the layup machines. This results in unnecessary

constraints on the machine and its capability.

By addressing the topics and future targets outlined within this paper, the

academic community will have an important role in the future of composites and

automated composite layup.

Acknowledgements

Studentship funding for D.H.-J.A. Lukaszewicz from Airbus Operations Ltd. is

gratefully acknowledged. The authors would like to thank Dr. K. Hazra, Dr. J. Etches

(University of Bristol) and M. Buckley (Airbus Operations Ltd.) for helpful discussions.

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References

[1] Grimshaw MN. Automated Tape Laying. Cincinnati: Cincinnati Machine, 2001.

[2] Evans DO. Fiber placement. Cincinnati: Cininnati Machine, 1997.

[3] Åström. Manufacturing of Polymer Composites. London, UK: Chapman& Hall;

1997.

[4] Campbell FC. Manufacturing processes for advanced composites. Oxford, UK:

Elsevier Advanced Technology; 2004.

[5] Gutowski TG (ed). Advanced composites manufacturing. New York: John

Wiley & Sons, Inc.; 1997.

[6] Sloan J. ATL and AFP: Defining the megatrends in composite aerostructures.

High Performance Composites: Gardner Publications, 2008.

[7] Dorey. Carbon fibres and their applications. J Phys D: Appl Phys. 1987;20:245-

56.

[8] Grant C. Automated processes for composite aircraft structure. Ind Robot.

2006;33(2):117-21.

[9] Chitwood; Composite tape laying machine with pivoting presser member, Patent

4627886, 6th April 1971.

[10] Goldsworthy WB; Geodesic path length compensator for composite-tape

placement method, Patent US 3,810,805, 14th May 1974.

[11] Huber J. Automated lamination of production advanced composite aircraft

structures. SAE International Congress and Exposition. Detroit, Michigan, USA,

1981.

[12] Anon. MIL-HDBK-17-3F-Composite materials handbook.In: Volume 3F:

Departement of Defense; 2002.

[13] Krolweski S, Gutowski T. Effect of the automation of advanced composite

fabrication processes on part cost. Sampe J. 1987;23(3):21-6.

[14] Krolewski S, Gutowsi T. Economic comparison of advanced composite

fabrication technologies. 34th International SAMPE Symposium. Volume 34.

Covina, California, USA: SAMPE, 1989:329-40.

[15] Postier RA. Factory automation for composite structures manufacturing. Sampe

Quart. 1985;April:45-8.

[16] Eaton HL. Cost effective tape laying. 29th National SAMPE Symposium. Reno,

Nevada, USA, 1984.

Page 37: Articolo ATL

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

[17] Saveriano JW. Automated contour tape laying of composite materials. 16th

National SAMPE Technical Conference. Albuquerque, New Mexico, USA,

1984.

[18] Coad CL, Werner SM, Dharan CKH. Design of a composite four-axis robot for

prepreg layup. 29th National SAMPE Symposium. Reno, Nevada, USA, 1984.

[19] Stone KL. Automation in composite processing. 29th National SAMPE

Symposium. Reno, Nevada, USA, 1984.

[20] Albus JS. Research issues in robotics. 16th National SAMPE Technical

Conference. Albuquerque, New Mexico, USA, 1984.

[21] Wang EL, Gutowsi T. Laps and gaps in thermoplastic composites processing.

Compos Manuf. 1991;2(2):69-78.

[22] Meier RA. An advanced control system for composite material placement. 31st

International SAMPE Symposium. Covina, California, USA, 1986.

[23] Grone RJ, Grimshaw MN; Composite tape laying machine with pivoting presser

member, Patent US 4627886, 30 May 1985.

[24] Grone RJ, Schnell LR, Vearil L; Composite tape laying machine and method,

Patent US 4557783, 5 December 1983.

[25] Torres Martinez M; Torres Martinez, M., Tete enrubanneuse pour l'application

de bande en materiau composite, Patent EP 1097 799 A1, 9 May 2001.

[26] Lewis HW, Romero JE; Composite tape placement apparatus with natural path

generaton means, Patent US 4,696,707, 29.9.1987.

[27] Torres Martinez M; Tete pour l'application de bande de composite, Patent FR

2713213-A1, 30 November 1994.

[28] Grimshaw MN; Machine for applying composite and presser assembly therefor,

Patent EP 0371289-A1, 8 November 1989.

[29] Grimshaw MN, Hecht JR; Method and apparatus for laying composite material,

Patent EP 0644040-A1, 8 November 1994.

[30] Olsen HB, Craig JJ. Automated composite tape layup using robotic devices. In:

IEEE International Conference on robotics and automation. Atlanta, Georgia,

USA: 1993.

[31] Goel A. Economics of composite material manufacturing equipment [BSc

Thesis]. Cambridge, MA: Massachusetts Institute of Technology, 2000.

[32] Foley MF. Techno-economic analysis of automated composite manufacturing

techniques. 22nd International Sampe Technical Conference. Boston,

Massachusetts, USA, 1990.

Page 38: Articolo ATL

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

[33] Zaffiro JA; Cincinnati Milacron Inc., Control of radiation heating system for

thermoplastic composite tape, Patent 5177340, 5 January.

[34] Benda BJ, Stump KH. A case study of contoured tape laying. American

Helicopter Society 52nd Annual Forum. Washington D.C., USA, 1996.

[35] Sarazin H, Springer GS. Thermochemical and mechanical aspects of composite

tape laying. J Compos Mater. 1995;29:1908-43.

[36] Grove SM. Thermal modelling of tape laying with continous carbon fibre-

reinforced thermoplastic. Composites. 1988;19(5):367-75.

[37] Torres Martinez M; Head for application of carbon-fibre strips and application

method, Patent WO 2008/020094 A1, 21 February 2008.

[38] Tillement PAH, Charra SRE; Device for separating and discharging trimmings

cut in a pre-impregnated strip, Patent Wo 2008/135645 A1, 13 November 2008.

[39] Tillement PAH, Charra SRE; Composite lay-up head with a retractable device

for separating a prepreg from its support tape, Patent WO 2008/142273 A2, 27

November 2008.

[40] Larberg YR, Åkermo M. On the interply friction of different generations of

carbon/ epoxy prepreg systems. Compos Part A-Appl S. 2011;42(9):1067-74.

[41] Gutowski TG, Dillon G, Chey S, Li H. Laminate wrinkling scaling laws for

ideal composites. Composite Manufacturing. 1995;6(3-4):123-34.

[42] Kau. Automated fabrication of grpahite-epoxy composites. 32nd International

SAMPE Symposium. Anaheim, California, USA, 1987.

[43] Thomas J. The A380 Programme - The big task for Europe's aerospace industry.

Air & Space Europe. 2001;3(3/4):35-9.

[44] Hinrichsen J, Bautista C. The challenge of reducing both airframe weight and

manufacturing cost. Air & Space Europe. 2001;3(3/4):119-21.

[45] . Torreslayup - Tape Layer Machine. Volume

2010, http://www.mtorres.es/pdf/torreslayup.pdf, 2010.

[46] Land IB. Design and manufacture of advanced composite aircraft structures

using automated tow placement [Master Thesis]. Cambridge, MA, USA:

Massachusetts Institute of Technology, 1996. 91 p.

[47] Colton JS, Baxter J, Behlendorf J, et al. The automation of the lay-up and

consolidation of PEEK/Graphite fiber composites. 32nd International SAMPE

Symposium. Anaheim, California, USA, 1987.

Page 39: Articolo ATL

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

[48] Lamontia MA, Gruber MB, Waibel BJ. Conformable Compaction System used

in Automated Fiber Placement of Large Composite Aerospace Structures.

Proceedings of the 23rd Sampe Conference. Paris, France, 2002.

[49] Knight BW. The technique of filament winding. Composites. 1970;June:228-33.

[50] Evans DO, Vaniglia MM, Hopkins PC. Fiber placement process study. 34th

International SAMPE Symposium. Covina, California, USA, 1989:1822-33.

[51] Bullock DE. Automated prepreg tow placement for composite structures. 35th

International SAMPE Symposium. Anaheim, California, USA, 1990.

[52] Barth JR. Fabrication of complex composite structures using advanced fiber

placement technology. 35th International SAMPE Symposium. Anaheim,

California, USA, 1990:710-20.

[53] Blom AW, Lopes CS, Kromwijk PJ, Gurdal Z, Camanho PP. A Theoretical

Model to Study the Influence of Tow-drop Areas on the Stiffness and Strength

of Variable-stiffness Laminates. J Compos Mater. 2009;43:403-25.

[54] Croft K, Lessard L, Pasini D, Hojjati M, Chen J, Yousefpour A. Experimental

study of the effect of automated fiber placement induced defects on performance

of composite laminates. Compos Part A-Appl S. 2011;42:484-91.

[55] Enders ML, Hopkins PC. Developments in the fiber placement process. 36th

International SAMPE Symposium. San Diego, California, USA, 1991:778-90.

[56] Evans DO. Design considerations for fiber placement. 38th International

SAMPE Symposium. Anaheim, California, USA, 1993:170-81.

[57] Measom R, Sewell K. Fiber placement low-cost production for complex

composite structures. American Helicopter Society 52nd Annual Forum.

Washington D.C., USA, 1996.

[58] Pasanen MJ, Martin JP, Langone RJ, Mondo JA. Advanced composite fiber

placement: process to application. Schenectady, NY: Automated Dynamics

Corporation, 1997.

[59] Gruber MB, Lamontia MA. Automated fabrication processes for large

composite aerospace structures: a trade study. 46th International SAMPE

Symposium. Volume 46. Long Beach, California, USA, 2001:1986-97.

[60] Mantell SC, Wang QL, Springer GS. Processing thermoplastic composites in a

press and by tape laying - experimental results. J Compos Mater.

1992;26(16):2378-401.

[61] Mantell SC, Springer GS. Manufacturing process models for thermoplastic

composites. J Compos Mater. 1992;26(16):2348-77.

Page 40: Articolo ATL

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

[62] Bourban P, Bernet N, Zanetto J, Manson J. Material phenomena controlling

rapid processing of thermoplastic composites. Compos Part A - Appl S.

2001;32(8):1045-57.

[63] Hulcher AB. Processing and testing of thermoplastic composite cylindrical

shells fabricated by automated fiber placement. 47th International SAMPE

Symposium. Long Beach, California, USA, 2002.

[64] Lamontia MA, Gruber MB. Limitations on mechanical properties in

thermoplastic laminates fabricated by two processes: Automated Thermoplastic

Tape Placement And Filament Winding. 26th SAMPE Europe Conference.

Paris, 2005.

[65] Ranganathan S, Advani SG, Lamontia MA. A nonisothermal process model for

consolidation and void reduction during in-situ tow placement of thermoplastic

composites. J Compos Mater. 1995;29(8):1040-62.

[66] Pitchumani R, Ranganathan S, Don R, Gillespie J, Lamontia M. Analysis of

transport phenomena governing interfacial bonding and void dynamics during

thermoplastic tow-placement. Int J Heat Mass Tran. 1996;39(9):1883-97.

[67] Pitchumani R, Gillespie J, Lamontia M. Design and optimization of a

thermoplastic tow-placement process with in-situ consolidation. J Compos

Mater. 1997;31(3):244-75.

[68] Tierney J, Gillespie J. Modeling of heat transfer and void dynamics for the

thermoplastic composite tow-placement process. J Compos Mater.

2003;37(19):1745-68.

[69] Funck R, Neitzel M. Improved thermoplastic tape winding using laser od direct-

flame heating. Composite Manufacturing. 1995;6(3-4):189-92.

[70] Rosselli F, Santare M, Guceri S. Effects of processing on laser assisted

thermoplastic tape consolidation. Compos Part A - Appl S. 1997;28(12):1023-

33.

[71] Pistor C, Yardimci M, Guceri S. On-line consolidation of thermoplastic

composites using laser scanning. Compos Part A - Appl S. 1999;30(10):1149-

57.

[72] Goodmann DL, Weidman DJ, Bryne CA, et al. Automated tape placement with

in-situ electron beam cure: a viable process. 46th International SAMPE

Symposium. Long Beach, California, USA, 2001:2127-39.

[73] Burgess JW, Wilenski MS, Belvin HL, Cano RJ, Johnston NJ. Development of a

cure-on-the-fly automated tape placement machine for electron curable prepregs.

46th International SAMPE Symposium. Long Beach, California, USA,

2001:2024-36.

Page 41: Articolo ATL

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

[74] Grant C, Martin J. Automated processing technology for composites: Current

status and vision for the future. 48th International SAMPE Symposium. Long

Beach, California, USA, 2003.

[75] Grant CG. Fiber placement process utilization within the worldwide aerospace

industry. 45th International SAMPE Symposium. Long Beach, California, USA,

2000:709-20.

[76] Torres Martinez M; Faserstreifenverbinder fuer Bandwickler, Patent DE 10

2008 010 424 A1, 2nd October 2008.

[77] Oldani T. Increasing Productivity in Fiber Placement Processes. SAE

Aerospace Manufacturing and Automated Fastening Conference & Exhibition.

North Charleston, South Carolina, USA, 2008.

[78] Calawa R, Nancarrow J. Medium wave infrared heater for high-speed fiber

placement. SAE Aerofast. Los Angeles, California, USA, 2007.

[79] Hamlyn A, Hardy Y; Fibre application machine with tool changing system,

Patent WO 2008/149004 A1, 11th December 2008.

[80] Hamlyn A, Hardy Y; Fibre application machine with fibre supply flexible tubes,

Patent WO 2008/122709-A1, 28 February 2007.

[81] Shirinzadeh B, Alici G, Foong CW, Cassidy G. Fabrication process of open

surfaces by robotic fibre placement. Robot Com-Int Manuf. 2004;20(1):17-28.

[82] Shirinzadeh B, Cassidy G, Oetomo D, Alici G, Ang MH. Trajectory generation

for open-contoured structures in robotic fibre placement. Robot Com-Int Manuf.

2007;23(4):380-94.

[83] Izco L, Isturiz J, Motilva M. High speed tow placement system for complex

surfaces with cut / clamp / & restart capabilites at 85m/min (3350IPM). SAE

Aerospace manufacturing and automated fastening conference and exhibition.

Toulouse, France, 2006.

[84] DeVlieg R, Jeffries K, Vogeli P. High-speed fiber placement on large complex

structures. SAE Aerofast. Los Angeles, California, USA, 2007.

[85] Airbus SAS. Boeing 787 - Lessons learnt.

http://www.slideshare.net/aergenium/b787-lessons-learnt-presentation, 2008.

[86] Kisch RA, Vogeli P, Jeffries K, DeVlieg R; End effector and methods for

contructing composite membranes, Patent US 2008/0295954 A1, 4th December

2008.

[87] Debout P, Chanal H, Duc E. Tool path smoothing of a redundant machine:

Application to Automated Fiber Placement. Computer-Aided Design.

2011;43(2):122-32.

Page 42: Articolo ATL

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

[88] Lukaszewicz DH-JA, Weaver PM, Potter K. An automated ply collation system

for material and process development. SAMPE Seico. Paris, France, 2010.

[89] Lukaszewicz DH-JA. Optimisation of high-speed automated layup of thermoset

carbon-fibre preimpregnates [Ph.D. Thesis]. Bristol: University of Bristol, 2011.

[90] Morey B. Automating composites fabrication. Manufacturing Engineering.

2008;140(4): http://www.sme.org/cgi-bin/find-

articles.pl?&ME08ART28&ME&20080415&&SME&.

[91] Alici G, Shirinzadeh B. Enhanced stiffness modeling, identification and

characterization for robot manipulators. IEEE Transactions on Robotics.

2005;21:554-64.

[92] Shirinzadeh B. Robotic fibre placement process planning and control. Assembly

Automation. 2000;20:313-20.

[93] Alici G, Shirinzadeh B, McConville A, Foong CW, Ang M. A mathematical

model for a pneumatically actuated robotic fibre placement system. Robotica.

2002;20:545-51.

[94] Wiehn MP, Hale RD. Low cost robotic fabrication methods for tow placement.

47th International SAMPE Symposium. Long Beach, California, USA, 2002.

[95] Moon RS, Johnson CC, Hale RD. Nondestrcutive evaluation and mechancial

testing of steered fiber composites. 47th International SAMPE Symposium.

Long Beach, California, USA, 2002.

[96] Beakou A, Cano M, Le Cam J-B, Verney V. Modelling slit tape buckling during

automated prepreg manufacturing: a local approach. Compos Struct.

2011;93(10):2628-35.

[97] Potter K. In-plane and out-of-plane deformation properties of unidirectional

preimpregnated reinforcement. Compos Pt A - Appl Sci Manuf.

2002;33(11):1469-77.

[98] Lukaszewicz DH-JA, Weaver PM, Potter K. The impact of processing

conditions on the final part quality in automated tape deposition technologies.

Sampe Seico. Paris, France, 2009.

[99] Lukaszewicz DH-JA, Weaver PM, Potter K. An empirical model for the

automated deposition of thermoset composite. ACS - 24th Technical Conference

Newark, Delaware, USA, 2009.

[100] Lukaszewicz DH-JA, Potter KD. The internal structure and conformation of

prepreg with respect to reliable automated processing. Compos Part A-Appl S.

2011;42:283-92.

[101] Eales J, personal communication. 2011.

Page 43: Articolo ATL

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

[102] Lamontia MA, Gruber MB, Tierney JJ, Gillespie Jr. JW, Jensen BJ, Cano RJ. In

situ thermoplastic ATP needs flat tapes and tows with few voids. 30th

International SAMPE Europe Conference. Paris, France, 2009.

[103] Khan MA, Mitschang P, Schledjewski R. Identification of Some Optimal

Parameters to Achieve Higher Laminate Quality through Tape Placement

Process. Adv Polym Tech. 2010;29(2):98-111.

[104] Ahn KJ, Seferis JC, Pelton T, Wilhelm M. Analysis and characterization of

prepreg tack. Polym Comp. 1992;13(3):197-206.

[105] Ahn KJ, Peterson L, Seferis JC, Nowacki D, Zachmann HG. Prepreg aging in

relation to tack. J Appl Polym Sci. 1992;45(3):399-406.

[106] Dubois O, Le Cam JB, Béakou A. Experimental analysis of prepreg tack. Exp

Mech. 2009.

[107] Crossley RJ, Schubel PJ, Warrior NA. The experimental characterisation and

investigation of prepreg tack. Proceedings of ICCM-18. Edinburgh, 2009.

[108] Lukaszewicz DH-JA, Potter KD. Through-thickness compression response of

uncured prepreg during manufacture by automated layup. Proc IMechE, Part B:

J Engineering Manufacture. 2011; DOI: 10.1177/0954405411411817.

[109] Bannister M. Challenges for composites into the next millennium - a

reinforcement perspective. Compos Part A - Appl S. 2001;32(7):901-10.

[110] Lukaszewicz DH-JA, Potter K. Modelling of automated layup processes for

improved efficiency and sustainability. In: Sampe Setec. Leiden, Netherlands:

2011.

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Figure 1: Overview of annual publications on ATL and AFP, with Filament winding

added in an insert graph as reference.

Figure 2: Drawing of an ATL delivering slit tape over a curved surface [10].

Figure 3: Drawing of an early composite components manufacturing system from [11].

The material is moved from left to right and material is applied to a mould using a

bespoke tape layup head.

Figure 4: Schematic of an ATL layup head, according to Ästrøm [3].

Figure 5: Picture of an ATL layup head with relevant functional groups labelled. The

prepreg material supply is not shown.

Figure 6: Example of a gantry type ATL laying onto a female tool [45].

Figure 7: Column Type ATL laying 300mm wide tape onto a vertical tool.

Figure 8: Integrated slitting unit with individual tow pay-out from [10]. This can be

interpreted as the first AFP concept.

Figure 9: Schematic of an AFP head [2].

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Figure 10: AFP layup of steered tows on a flat mould [53].

Figure 11: Ingersoll gantry-type AFP laying into a female mould [77].

Figure 12: Theoretical productivity comparison for ATL and AFP layup of a flat

laminate as a function of part size, from [89].

Figure 13: Theoretical productivity comparison for ATL and AFP layup of a flat

laminate as a function of maximum layup speed, from [89].

Figure 14: Overview of the most common tow steering defect.

Figure 15: Illustration of Laps and Gaps during AFP layup.

Figure 16: Effect of tow drop angle T0 and to drop area on the stiffness reduction of a

panel with steered tows, from [53].

Figure 17: Effect of tow drop angle T0 and to drop area on the strength reduction of a

panel with steered tows, from [53].

Figure 18: ILSS for a laminate manufactured at different layup temperatures and

subsequently oven-cured [110].

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Figure 19: Void content, measured by light microscopy, for the ILSS samples from

Figure 18, from [110].

Figure 20: Example of fuzzy edges at the edge of a roll of slit tape.

Figure 21: Example of a common defect in ATL grade prepreg.

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Table 1: Overview of AFP applications in 2000, from [75]. AFP was mostly used for

military applications.

Table 2: Overview of the effect of various layup defects on the tensile, compressive, in-

plane shear, open-hole tension (OHT) and open-hole compression (OHC) strength of

AFP laminates, according to [54].

Page 48: Articolo ATL

Aircraft program Components made by AFP

F-18 E/F Inlet Duct, Aft Center Side Skins, Stabilator Skins

C-17 Globemaster Fan Cowl Doors, Landing Gear Pods

Bell Agusta 609 Fuselage Panels

V-22 Osprey Aft fuselage, Side Skins, Drag Angle, Sponsons, Grips

Premier I Fuselage Sections

Hawker Horizon Fuselage Sections

F22 Raptor Stabilator Pivot Shaft

Sea Launch Payload Fairing