Robotics and Computer Integrated Manufacturing 19 (2003) 107–111

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Just-in-sequence material supply—a simulation based solution inelectronics production

Sebastian Wernera,*, Marc Kellnerb, Eberhard Schenkb, Gerald Weigerta

aElectronics Technology Laboratory (ETL), Dresden University of Technology, Dresden, 01062, Germanyb IT and Organization, Diehl AKO, Nuremberg, 90451, Germany

Received 29 August 2002

Abstract

Just-in-time and just-in-sequence (JIS) concepts have been presented by the automotive industries in the past years. Today, where

customer-oriented manufacturing is more and more demanded, electronics production is in a similar situation. The integral

organizational means at Diehl AKO Nuremberg have been realized to achieve JIS material supply in the electronics sector. The right

cooperation of software solutions from SAP (ERP), LES (logistics) to BOFOS (manufacturing planning) results in a set of

improvements in material flow, scheduling, and document flow. The following paper shows the concepts, realizations, and

achievements of the partners Diehl AKO and ETL. The main interest lies on the general approach, not on a particular detail.

r 2003 Elsevier Science Ltd. All rights reserved.

1. Introduction

In electronics, production flexibility and customer-oriented manufacturing are keys for success in today’smarket situation. New forms of organization andcontrol are required. Software tools alone cannot solvethese problems; entire organization strategies, in combi-nation with those tools, will help to reach improvementsin this sense. The automotive sector belongs to theavant-garde, where just-in-time (JIT) and just-in-sequence (JIS) realizations have been presented in thepast years. Concepts of supply of parts and componentsat the right time and at the right place have been used inthis highly customer related manufacturing area, whereproduct variety has increased. JIS supply tops JITby adding the right sequence for supplied parts andcomponents. JIT and JIS require high discipline of both,supplier and manufacturer [1,2].

Electronics production and the automotive industryhave something in common. Especially in printed circuit

board (PCB) technology where assembly uses manyparts in different technological steps. JIS supply ofelectronic parts is one of the goals we reached byintroducing organizational concepts and software toolsin manufacturing control. Manufacturing executionsystem (MES) is the name that has been used for thecoupling of different tools to a whole instrument formanufacturing control.

2. Electronics production structures

In contrast to automotive industries, assembly hier-archies are flat. Most of the assembled parts are boughtfrom suppliers and assembled in the first technologicalsteps, where the number of technological steps is notnegligible and different from product to product.Because of the customer-oriented structure, whichinvolves high product and technological variety, man-ufacturing often is more job shop like than a serialproduction.

This implies that organizational means do effect theproduction value, rather than in a serial productionwhere manufacturing cells should be optimized inadvance. Important objectives of organization are duedate keeping and reduction of cycle time for lower

*Corresponding author. Tel.: +49-351-463-35051; fax: +49-351-

463-37069.

E-mail addresses: werner@iet.et.tu-dresden.de (S. Werner), marc.

kellner@diehlako.de (M. Kellner).

URLs: http://www.iet.et.tu-dresden.de/rosi, http://www.diehlako.

com.

0736-5845/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved.

PII: S 0 7 3 6 - 5 8 4 5 ( 0 2 ) 0 0 0 6 7 - 4

capital commitment. Those goals can only be reached inconsideration of the material supply during the techno-logical process.

Fig. 1 shows a typical technological sequence found inelectronics production. The PCB assembly consists ofseveral technological steps, where components areplaced on the board (SMT—surface mount technology,THT—through hole technology). Once the PCB isfinished, a final assembly process follows. Hundreds orthousands of components are placed in a product, butonly a few steps are entry points for material aspresented in the example in Fig. 1. Material is notmanufactured in-house, but purchased from externalsuppliers and then stored in stocks. Standard compo-nents are delivered in large lots, e.g. SMT resistors intapes of 10,000 pieces.

Machine group definition is a very rare phenomenonin electronics industry. In most cases the resources andthe related standard time for a product are predefined incharts. In other cases processing time can be calculatedfrom technological parameters.

These are exactly the conditions we met in our plantof Diehl AKO in Nuremberg, where control systems forelectronic goods in automotive and domestic appliancesin more than 3000 varieties are being produced; each ofthem contains various types of PCBs. The pursuedconception has been extended to approximately 20 unitsof the plant. Material posting, stock control, manufac-turing planning and simulation form a total approachfor the benefit of all. The following sections focus on therealization at Diehl AKO in Nuremberg.

3. Material classification

The material flow follows certain schemes. Thereforematerial has been classified into two types:

* Order related material.* Pass related material.

Order related material has to be supplied at thebeginning of the manufacturing process. Before startingan order, the material needs to be in the production unitat the required place (e.g. raw PCBs) and goes throughthe whole manufacturing process. Pass related materialis being assembled in subsequent processing steps andneeds to be supplied at a later point of time (e.g. SMTcomponents, see Fig. 2).

As components, especially electronic components, arebeing delivered in large lots, the right amounts ofcomponents per order are hard to handle. Differentmaterial containers are in use before the assembly. In thePCB assembly unit, material is delivered from stock viacarts to the production places. Then it is loaded to themanufacturing resources, where two types of loads haveto be distinguished: fixed loads on machines andinterchangeable feeder tables, the so-called modularchangeover tables, which can be allocated to differentassembly lines. Once the components are placed on theresources, they can be considered as another type ofstock within the manufacturing area. Fig. 3 illustratesthe supply and stock in the PCB assembly unit. Theunderlined resources represent material stocks.

As tapes often contain much more components thanrequired for a single order, there will be remaining partson the manufacturing resources, which have to bereturned to stock if directly allocated to the manufac-turing order. The control over material stocks onmanufacturing resources and the use of remainingcomponents for subsequent orders is one of the goalsthat has been reached in organization in considerationof stock on manufacturing resources in form of binlocations.

4. Material posting—SAP R/3

Stocks and bin locations are controlled by SAP/R3.The definition of manufacturing resources as new bin

Fig. 1. Typical technological sequence in electronics production.

Fig. 2. Material—order related and pass related.

S. Werner et al. / Robotics and Computer Integrated Manufacturing 19 (2003) 107–111108

locations allows us to control material amounts on theresources. When material is supplied to the manufactur-ing units, in SAP, a material transfer posting fromcomponent stock to the relevant bin location in themanufacturing area is executed.

Before starting a particular manufacturing order theamount of relevant components on the resources ischecked. Only the required difference is to be supplied.If sufficient material is still in the manufacturing unit, nomaterial needs to be delivered for the order. At the sametime a retrograde material posting process does thereservation of the required material amount for theorder. Remaining parts are not returned to stock, butstay on the resources for the next orders.

For example there are two different orders, eachof them requires 3000 SMT 4.7 K 0603 resistors. Bysupplying a tape of 10,000 resistors for the first order tothe modular changeover table G1, a remainder of 7000resistors is left. The second order is manufactured withG1 as well. No resistors are to be supplied for this order.

5. Material availability—LES

The logistics execution system (LES), determines thedynamic material availability for a sequence of manu-facturing orders. It is a supplementary software exten-sion in SAP that gives information about current statesof materials, in traffic light appearance—red–yellow–green—for orders, and components of them, inconsideration of all reservations and revisions. Beforestarting the supply process, the availability is checked. Ifany material is missing the process is skipped. Onlymanufacturing orders with all materials available can beproduced (Fig. 4).

LES knows the manufacturing resources of an order,and therefore the material on hand of the relevant binlocations. The system supports material posting toresources, and reservation of material on resourcesin SAP.

6. Production control and simulation—BOFOS

For manufacturing planning we installed a systemcalled BOFOS, which has been developed by thepartners Diehl and ETL. A decentralized solution wasapplied to more than 20 units of the plant. Each unit hasaccess to all manufacturing related information for itselfvia BOFOS. It interacts with SAP to get main ERP dataas presented in [4]. Manufacturing resources, materialstates, and material carrying resources are known tothe system. The planner can adjust the manufacturingschedule to his or her requirements by controlling theinput parameters. A discrete event simulation, thatmodels the current production structure and considersthe material conditions met for each order and proces-sing pass, determines a schedule.

BOFOS stores all input information from SAP, LESand others in a SQL Server database. The simulationmodel built from this information does not startprocessing passes before a possible availability ofmaterial for the pass, in consideration of the capacitiesof the supply units, is determined. The optimizedschedule gives start dates for each processing pass whichare translated to required supply dates for material. Theonline coupling to terminals in the production areadisplays manufacturing instructions directly to the workcenters. For material supply, a second connection to

Fig. 3. Component supply and stock in PCB assembly.

S. Werner et al. / Robotics and Computer Integrated Manufacturing 19 (2003) 107–111 109

component stock is generated by BOFOS that instructsworkers about:

* what type of material is to be supplied,* for which order,* at what time,* and place,* and in which sequence.

This instruction is best described as a materialrequest. Each request is checked against the materialon hand, on the related manufacturing resource in LES,and only required differences are supplied to themanufacturing unit, in the right quantity: JIS.

The finished supply procedure is reported to BOFOS(PDA). In simulation the passes for which material hasbeen provided are started without delay, and prioritizedto others so that supplied material is quickly leaving themanufacturing.

In BOFOS production workers perform data acquisi-tion, and thus the current production state is transpar-ent. Information exchange in the production area isdone on terminals as shown in Fig. 5. At the end of atechnological sequence for an order (finished order), atransfer order is generated online to bring producedgoods to the right bin location. The carried out andconfirmed transfer action is reported to SAP, where amaterial posting follows. Fig. 5 demonstrates theinformation flow for material.

The material flow within the plant follows the sameprinciples. Components produced in-house are trans-ferred to subsequent units via bin locations. The

availability of the required material is controlled bythe described techniques, and used for productionplanning. Each unit is communicating to its suppliers,and its customers, and therefore considering its bound-aries.

Discrete event simulation is a powerful method totake into account the complex conditions for thosestrategies. The models are flexible and the dynamicprocess itself can execute resource allocation and haveregard to special rules, as required in the material supplyproblem. The used simulator ROSI, is a general discrete

Fig. 5. BOFOS—production planning and material control.

Fig. 4. LES—material availability for manufacturing order and its components.

S. Werner et al. / Robotics and Computer Integrated Manufacturing 19 (2003) 107–111110

event simulator with focus on manufacturing systems. Ithas been designed at ETL and applies to many differenttasks in manufacturing applications. In this case it istotally embedded in BOFOS in the form of an ‘‘engine’’that calculates schedules in the background. The plannerdoes not interact with the simulation model that hasbeen implemented by an expert, and completely reflectsthe pursued strategies [3–5].

7. Results

The organizational network supported by the soft-ware means is a realization that results in effectiveimprovements for the manufacturing. It affects manyareas, the most important of them are: material flow,production schedule, and document flow.

JIT or, better, JIS supply of material in manufactur-ing units, guarantees that the right material is at theright place, at the right time, in the right quantity, andin the right sequence. The circulating capital coulddrastically be reduced. Material return processes couldbe prevented, and material supply in lots is reducedto the necessary minimum. The JIT delivery reducesunnecessary material in the manufacturing floors, whichleads to clearness in the plant.

Manufacturing schedules are determined and opti-mized in consideration of the material situation andmany more constraints, by adequate simulation models.Automated calculation of schedules enables shortplanning cycles and fast interaction in case of changes.Due date keeping and cycle time for orders could beenhanced. Operation instructions to workers are clearlypresented on terminals, where everyone knows whatto do.

The transparency within the corporation is higher bymaking more information online-available. BOFOS isa framework for information exchange in this sense. Apositive side effect of it is the reduction of documents forthe manufacturing flow, because state changes arereported to the IT system where it is not only readablefor the owner of the document, but for everybody. Alarge number of documents for manufacturing ordershave been abolished.

All contributors in the project run had to beinstructed to be able to act within the rules of theconception. In most cases it was easy to meet the right

motivation, because benefits for users were clear at thebeginning. The introduction was not pushed but anincreasing demand from planners and workers helpedto realize the goals.

8. Conclusion

JIS material supply in an electronics production planthas been realized by a set of organizational means. Thecooperation of software solutions to an integral systemhelped to improve the manufacturing in different areas.ERP, logistics, and simulation based manufacturingplanning interact in the right mode to achieve thepursued goals.

The decentralized approach for each manufacturingunit offers advantages for many purposes. An overview,from the organizational point of view presented in thispaper, does not include details about technical realiza-tions, and neglects some other aspects. The main focusstill lies on the manufacturing planning and thesimulation where many improvements have to be madein the near future.

The presentation to other companies has aroused highinterest. All points in the organization have beenrealized in a very general way, which is applicable toother circumstances, too. Manufacturing planning inthis consequent manner, as implemented at Diehl AKO,could be carried to other partners as well; our tools andexperiences are available.

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