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The design of an effective assembly system
Master Thesis
Technology Management
Gemco E-trucks
Adress: Science park 5053
5692 EB
Son
Company supervisor: Ing. M. van Rijen
Rijksuniversiteit Groningen
Faculty: Economie en Bedrijfskunde
Adress: Landleven 5
9747 AD Groningen First Supervisor: Drs. R. van der Velde Second supervisor: Drs. Ing. H.L. Faber
Author
Name: Jens van Kemenade
Adress: Paaihurken 6
5671 BD, Nuenen Studentnumber 1602810
Email: j.vankemenade@gmail.com
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Acknowledgements
This report is been written for my graduation project, part of the Msc Technology management, at the University of Groningen. An assignment was done at Gemco E-trucks in Son and gave rise to this research written in this report. For giving me the opportunity to perform the assignment at Gemco E-trucks, I would like to thank Gemco E-trucks for that opportunity.
Valuable and crucial information came from throughout the whole company and was essential for completing this research. My gratitude goes throughout the whole company that provided me with support, information and insights.
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Summary
Gemco E-trucks is a developer and producer of electric driven trucks in the medium duty vehicles segment. The truck that Gemco E-trucks develops is called the “Bandit” and distinguishes itself not only by that it is electrically driven, but also that it can lower the entire cargo part of the truck to the ground. This research is involved in only a part of the “Bandit” namely in the component that is responsible for the transfer of electric power into a rotating movement, breaking system, the rear wheel suspension and the
lifting/lowering of the cargo floor. This component is called the E-corner.
The E-corner is almost ending its development phase and will enter the product launch phase which means industrialization of the product. All standard parts of the E-corner will be bought in by Gemco E-trucks and the production of special custom made parts will be outsourced to specialist suppliers. Gemco E-trucks will only execute the final assembly of the E-corner. Gemco E-trucks initiated this research to prepare for an expected demand in the form of a design of an assembly system.
The main research question of this research is; “How can Gemco E-Trucks effectively industrialize the E-corner to meet increasing market demand?”
The scope of this research concerns the organizational issues of the assembly system and specific chosen engineering considerations. Engineering considerations that fall outside of the scope are CAD designs for the assembly system. Personnel and labour related issues are also left outside of the scope of this research too. Decision area’s that fall within the scope of this research are: Lay-out, Quality control, Planning and control, Capacity and the selection of types of machinery.
In the Diagnose phase of this research the specifications of E-corner are investigated and set out in a clear overview of parts and their interrelations. This was done by interviews, desktop research and observations and resulted in a clear product model and product hierarchy. With this information of the product the actual assembly sequence is determined by two methods for enforcing reasons. These models are the Simplified Method of bourjault by De Fazio and Whitney (1987) and the Component ordering method by Lee and Ko (1987). In order to secure the outcome for the assembly sequence not one but two methods were used. This outcome is a sequence of 18 steps and indicate where a possibility exists for a subassembly. After the determination of the sequence the process plan and times are created by a time motion system called MOST. This system is a basic measurement technique that covers all motions and addresses the time to these motions. The time study showed that the assembly sequence has a total duration of 41 minutes.
5 expand the output volume of the production system to overcome possible increasing demand. To assure the quality of the E-corner in the assembly system a proposition of pokayoke is done. This is a Japanese term for error proofing or mistake proofing. In the design phase of this research possible layouts are described and the possible layouts for the E-corner are mentioned. These possibilities are further examined into concrete concept layouts for the E-corner and resulted in a fixed positioned layout and two assembly lines one with 6 and one with 8 workstations.
The final decision for the assembly system of the E-corner is based on three types of criteria namely, Overall decision criteria, Capacity and Costs. The overall decision criteria was quantified by an Analytical Hierarchy Process done within Gemco E-trucks, Capacity decision was done by evaluating the output of the assembly system and the Cost decision was evaluated by a cost calculation.
Based on these outcomes the most effective assembly system that should be used for the E-corner is a Fixed position layout. The use of a fixed position layout answers to the required output for the E-corner and the possibility to increase capacity by adding another assembly cell see Figure 1.
Lifting gear: Costs: €25.000 (Leenstra Friesland) workpiece H eigh t se nsorDrive shaft
Cooling tubes Brake tubes W iring harnass C ooling fluid Oil Brake fluid Test run Assembled product Cooling devi ce Mou ntin g p late Swing arm Pow er electronics Elect ric motor Electri c cables R eductio n box Shoc k absorber Air-suspension Air -over-h yd. M12 (2x) M8 (6x) M6 (1x) M16x50(16x) M16x50 (12 x) Tools: - Air impac t wrench Costs: €165 (Atlas Copco) Tools: - Air ratched wrench Costs: €82 (Atlas Copco) Tools: Automatic oil dispensor C osts: €1210 (eurolube ) Automatic colling fluid dispensor C osts: €412 (Viton) Pneumatic oil pump C osts: €640 (eurolube ) M18x70(2x) Tridec (2x) M24x100(2x) M12 (2x) Hose clamps M12 (4x) M12 (4x) 1 2 3 4 5 6 Mounting pl ate Air-su sp ensi on Air-ov er-h ydr. Sw ing arm Shoc k abs orber Powerelectroni csElectric m otor Height s ens or Reduc tion bo x Drive s haft Coolin g dev ice Coolin g tube s
Brake tubesWiring
harnas s Co oling fluid OilBrake f luid
Station load7.4 min Station load7.0 min Station load9.5 min Station load7.1 min Station load7.1 min Station load4.8 min M12 (6x) M18x70(2x) Tridec (2x) M24x100 (2x)M16x50 (12x) M8 (6x) M6 (1x)
Lift ing gear: - 110 kg Station 4 - 30 kg St ation 5 Co sts: €25.000 (Leenstra Friesland) Electric cabl es M16x50(16x) Test run Hose clamps Tools: - Air impact wrench Co sts: €165 (Atlas Copco) Tools: - Air ratched wrench Co sts: € 82 (Atlas Copco) Tools: - Air impact wrench Costs: 165 (Atlas Copco) Tools: - Air impact wrench Costs: €165 ( Atlas C opco) Tools: Automatic oil dispensor Costs: €1210 (eurolube ) Automatic colling f luid dispensor Costs: €412 (Viton) Pneumatic oil pump Costs: €640 (eurolube ) Lifting gear: - 60 kg Station 1 - 81 kg Station 1 - 65 kg Station 2 - 225kg Station 2 C osts: €25 .000 (Leenstra Friesland) Co veyor system Co sts: € 9450 (Railtechniek van Herwijnen) Co mpresso r Co sts: €699 Tu bi ng wirin g Co sts: €634 Workpi ece carri er Co sts: €2300 (De bruyn metaal) Fl oo r stock racks Co sts: €445 (Vink lisse) Tools: - Air ratched wrench Co sts: €82 (Atlas Copco) 1 2 3 4 5 6 Mountin g pl ate Air-su spensio n Air-ov er-hyd. Sw ing arm Shoc k abs orbe r Po wer elec tronics Electri c motor He ight sens or Redu ction box Driv e shaft Cool ing de vice Cool ing t ubes Brak e tube s Wiring ha rnass Cooling f lu id OilBrak e flui d Station load 3. 8 min Station load 3. 6 min Station load 6. 0 min Station load 6.1 min Station load 45 min Station load 5.2 min 7 Station load 4.7 min 8 Station load 2.5 min M12 (2x) M18x70(2x) Tridec (2x) M24x100(2x) M8 (6x) M6 (1x) M16x50(16x) 4 Elec tric cables M16x50 (12x) Lifting gear: - 110 kg Station 5 - 30 kg Station 6 Costs: €25.000 (Leenstra Friesland) Lifting gear: - 65 kg Station 1 - 81 kg Station 2 Costs: €25 .000 (Leenstra Friesland) Tools: - Air impact wrench Costs: €165 (Atlas C opco) Tools: - Air impact wrench C osts: €165 (Atlas C opco) Tools: - Air impact wrench Costs: €165 (Atlas C opco) Tools: - Air ratched wrench C osts: €164 (Atlas C opco) Tools: - Air ratched wrench Costs: €82 (Atlas Copco) Te st run Lifting gear: - 65kg Station 3 - 225 kg Station 3 C osts: €25.000 (Leenstra Friesland) C oveyor system C osts: € 9945 (railtechniek van herw ijnen) C ompressor C osts: €699 Tubing wiring C osts: €634 Workpiece carrier C osts:€3500 (De Bruyn metaal) Floor stock racks C osts: €623 (Vink lisse) Tools: Automatic oil dispensor Costs: € 1210 (eurolube ) Automatic colling fluid dispensor Costs: € 412 (Viton) Pneumatic oil pump Costs: € 640 (eurolube ) 1 Cell Line 6 stations Line 8 stations
=
=
=
+1 +1 +1 +1 +11 Cell 6 stationsLine 8 stationsLine
Capa city Costs +1 +1 +1 +1 +1 Output 1 Cell Line 6 stations Line 8 stations
Figure 1 Assembly systems described by the decision criteria
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Index
Acknowledgements... 3 Summary ... 4 1 Introduction... 8 1.1 The Organization ... 8 1.2 The E-corner ... 9 1.3 Assembly system ... 10 2 Research outline... 11 2.1 Research motive... 11 2.2 A new company ... 122.3 The current situation ... 13
2.4 Future situation ... 14
2.5 The need for an assembly system plan ... 15
2.6 Problem Statement ... 16
2.6.1 Research goal ... 16
2.6.2 Research question ... 16
2.7 Decision area’s and Scope ... 17
2.8 Conceptual model ... 22
2.8.1 Operationalisation of the conceptual model ... 22
2.8.2 Model Validation ... 24
2.8.3 Assumptions... 26
2.8.4 Demand ... 26
2.9 Scope overview... 28
2.10 Research model... 29
2.10.1 Structure of the report ... 30
3 Methodology ... 31
3.1 Diagnose ... 32
3.1.1 Data Gathering methods ... 32
3.1.2 Data Analyze methods ... 33
3.2 Design ... 34
3.3 Change ... 34
3.4 Validation and reliability ... 35
4 Project specification... 36
4.1 Product model of the E-corner... 36
4.2 Product hierarchy ... 38
5 Process specification... 39
5.1 Sequence models... 39
5.2 Simplified method of bourjault... 40
5.2.1 Result of simplified method of bourjault... 43
5.3 Component ordering method ... 44
5.4 Assembly sequence conclusion... 48
5.5 Proces plan and times... 49
5.6 System requirements... 52
5.6.1 Capacity ... 52
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5.6.3 Flexibility... 56
6 The concept design for an assembly system of the E-corner... 58
6.1 Decision criteria ... 59
6.2 Theoretical approach... 62
6.2.1 Assembly systems... 62
6.2.2 Layouts... 64
6.2.3 Case studies... 65
6.3 Reviews on capacity and costs... 69
6.3.1 Capacity review ... 69
6.3.2 Cost review ... 70
6.4 Final decision ... 78
7 Production planning and control... 79
7.1 Push... 81
7.2 Pull ... 82
7.3 Push vs Pull... 83
7.3.1 Variability ... 83
7.4 Production planning and control and the assembly cell... 85
7.4.1 Production scheduling... 85
7.4.2 Material order generation... 86
8 System configuration ... 89
9 Final assembly process and system... 92
9.1 Conclusion ... 92
9.2 Discussion ... 95
9.3 Validity and Reliability... 96
9.4 Further research ... 99
9.5 Reflection... 99
Appendix I: Liaison answers ... 104
Appendix II: Mating conditions... 107
Appendix III Clarification pictures on assembly operations ... 109
Appendix IV: Assembly sequence breakdown ... 110
Appendix V: Classification of assembly systems... 113
Appendix VI Classification of assembly layouts... 117
Appendix VII: E-corner in respect to the assembly parameters ... 124
Appendix VIII Elaboration of the boujault sequence method ... 125
Appendix IX Workstation load with different cycle time ... 127
Appendix X : Subsystems and components of assembly system evaluation scheme... 128
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1 Introduction
Gemco Mobile Systems B.V. (GMS), situated in Son (Science Park ‘Eindhoven’) is a company that is specialized in the development and production of special trucks and container systems. GMS developed a concept for an electric driven truck and produced one prototype and a batch of four definite models under the name “Bandit”. The bandit is a distribution truck that apart from being electric driven also possesses over a cargo floor that can lower to the ground. Market research proved that there is a demand for this product which leads to a new company that only focuses on the production of this hybrid driven truck. This company will operate under the name ‘Gemco-E-trucks B.V’, further called ‘GET’, also situated on the Science park ‘Eindhoven’ at Son.
Mr. van Rijen is the program manager at GET and is responsible for the development of the new company. Within this new business development of electric driven trucks, he presented me with an assignment. Mr. van Rijen will be my supervisor at the company. This report describes the research that has been done within GET on the production function, in particular the production of a module (The E-corner) that is part of the complete electric truck concept ‘Bandit’ which will be further developed by GET. The establishment of a plan for an assembly system for this module is the main issue of this research.
1.1 The Organization
GET, founded in 2009, is a full ‘sister company’ of GMS. Both are SME (small medium enterprises) companies in the Netherlands, see Figure 2.
GMS is a manufacturer of custom made medium and heavy duty vehicles for niche applications, such as fire fighting systems, maintenance and repair, decontamination - and rest-units, personnel care -, rescue & medical - and communication systems. The last seven years GMS adapts between 40 and 50 vehicles yearly for such niche applications and operates worldwide. She has developed extensive experience with driver expectations and experience for delivery trucks.
9 In 2005, GMS developed a distribution truck, called “Bandit”, to answer to customer needs, this vehicle can lower the cargo floor on to the road surface and uses electrical motors for driving. This vehicle is equipped with a module that is, among others, an essential part for enabling the unit to lower the floor and drive electrical, this module is further called ‘E-corner’.
Within GET this knowledge of GMS is reused in a dedicated business for development of electric driven trucks. Their first design is also called the “Bandit”, see Figure 3
Figure 3 Sketch of the new design of the "Bandit"
1.2 The E-corner
This module that GET will implement in the “Bandits”, is responsible for the translation of electric power into a rotating movement, breaking system, the rear wheel suspension and finally the lifting of the cargo floor. Figure 4 shows where the E-corner is situated and what it looks like in detail.
Figure 4 The E-corner situated and in detail (Source: Gemco E-trucks)
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1.3 Assembly system
As mentioned previously the E-corner is going to be assembled within GET and will be produced in larger quantities than GMS did before. An assembly system will help to increase production en cut back on assembly costs.
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2 Research outline
In this chapter an explanation of the research is given, the motivation and purpose behind it and her boundaries. The current situation is mentioned and what the future situation is going to look like. The way the research problem is looked at is visualized with a conceptual model and is presented after the research question. For this research assumptions are necessary and will be treated and explained as well.
2.1 Research motive
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2.2 A new company
The project ‘Bandit’ under the flag of GMS was managed and handled on the GMS way of doing things, which handling can be described as determined by the quantity of output and size of an existing process or operation, (Nicholas,1989) The way products are made by GMS can be characterized as a production, job-shop like.(Tomi, K., 1989, Heizer, J. and Render, B., 2004) see figure 3:
Figure 5 Production strategies (taken from Heizer, J. and Render, B., 2004).
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2.3 The current situation
As mentioned above, GET is in an early stage of business, which means that the end product that will be produced in the future, is not ready yet. In respect to the time frame of this research and to minimize the amount of assumptions to be made, the focus of this research has been laid on the production of the E-Corner module of the electric driven truck.
In the current situation the design of the E-corner can still change in small ways, but for this research the E-corner’s design is frozen. The amount of components, parts, sub-assemblies and the way of fastening are known for this research, a detailed product description is written in chapter 4.
If the E-corner module is placed in the life cycle of a concept (Crawford and Di Bennedetto, 2006) within the product process of GET, one can see in what situation it appears right now and where this research is situated. Figure 6 shows the life cycle of this concept and it distinguishes five phases. The E-corner is situated in the fourth phase called the development phase, see Figure 6. Until now GMS has made 4 prototypes of the ‘Bandit’ and the E-corner, so the work of GMS can be indicated as belonging to phase 1 until 3, see Figure 6. GET revised the concepts in some ways so that the E-corner is coming closer to a final design. Within this development phase one specifies the development process and grow to the point of slowly scaling up the production so that the product can be launched.
14 Crafword and Benedetto give three aspects that come into play in developing the production process, namely: Resource preparation, Body of effort and Comprehensive Business Analysis. Resource preparation falls in the scope of this research, because it concerns the industrialization1 of the E-Corner. Resource preparation is making sure that all the interfaces between business resources (such as labour, skills, production capacity, finance etc.) and the production process are well defined in order to be fully prepared for production (Crawford and Di Bennedetto, 2006, Lohse et al. 2004). Body of effort and Comprehensive Business Analysis fall outside of the scope since Body of effort means the realization of a marketing plan and Comprehensive Business Analysis means the business plan of the actual product. These are two aspects that are not given by GET as aspects that need to be examined in this research.
2.4 Future situation
In consultation with GET a future situation is described in the following paragraph and certain demands and deliverables of this research are given.
The future situation looks like a situation where a well operating assembly system exists, where quality, reliability and flexibility are of great importance. These criteria came out of an analytical hierarchy process AHP (see chapter 10) taken from GET where several criteria were weighted (Saaty, 1980). The overview of which weight was given to which criteria is shown in Table 6 in paragraph 6.1
Quality is important within the assembly system not because the E-corner design will be improved, but the assembly system should prevent failures in the product because of wrong assembled products. So these criteria by GET are an
opportunity for provable quality control
Reliability is set as a criterion because the assembly system should have minimal machine breakdown, low absenteeism of operators and reliability in delivering non-defect products.
Flexibility should be seen as the ease of the assembly system handling with adjustments to the E-corner and increasing demand.
Another issue is that handling of the material should be easy for operators. This could be done with help of transport assistance and trestles (workpiece carrier). This issue is mentioned because experience of the past prototypes showed that assembly was hard due to heavy components.
1 Industrialization is the process of applying mechanical, chemical, and/or electrical
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2.5 The need for an assembly system plan
Karl Marx’ thoughts about industrialization was that he expected that advanced firms would mass produce standard wares and simplify tasks expected of workers to reduce the input of labor per product manufactured (Biernacki, 2004). Henry Ford’s assembly line in 1920 in the car industry answers to that same thought of Marx and is a good practical example of filling the gap between supply and demand by mass production (Biernacki, 2004, Alizon, F. et al., 2009). Although the thoughts of Marx and Ford were of a different order of magnitude, GET is dealing nonetheless with industrializing the E-corner module and is preparing for an increase in demand based on market research. Taking these thoughts of Marx and Ford and the problem of GET into consideration, designing an advanced production function is a logical step.
The creation of an assembly system fulfils the purpose in responding to demand, to prepare for this a plan is needed.
A plan can be seen as a human activity system of future activities with the corresponding task setting. A plan is also a system of activities and serves as coordination instrument next to other instruments.(de Leeuw, A.C.J., 2002). Such a plan will be made for the assembly system.
A survey of 355 companies in France showed that one of the most important obstacles to assembly automation is that product designs are generally not assembly-oriented(Hird, G. et al, 1988) So although the design of the E-corner is frozen and adjustments to the design are outside of the scope of this research it is an important issue to mention. Because this research on the assembly system will help to provide engineers information on the product design in favor of assembly in the future.
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2.6 Problem Statement
GET wishes to be able to industrialize the E-corner module and this raises several
questions and problems. Therefore a problem statement is formulated which consists of a research goal and research questions. The conceptual model and research model is presented later in paragraph 2.8.
2.6.1 Research goal
The aim of this research is to present a plan of a new market assembly system to be realized within the coming five years which is able to respond to increasing market demand. As mentioned in paragraph 2.5 an increase in demand is expected in the future, thus a different strategy for GET in comparison to GMS has to be introduced with regards to the assembly production activities.
2.6.2 Research question
In this paragraph the main question will be presented. The main research question is followed by subquestions to attempt specific problem areas belonging to the main research problem.
How can GET effectively industrialize the E-corner to meet increasing demand expectations?
Literature that will be discussed in paragraph 2.7 and chapter 3 show problem areas that are involved and divide the main problem. To attempt these problems several Sub-questions are formulated that need to be answered in order to solve the overall research question, these are:
1. What are the E-corner specifications?
2. What are the assembly process specifications?
3. What are the existing expectations on demand characteristics of the E-corner? 4. Which type of assembly system suits the E-corner best?
5. Which layout for the assembly of the E-corner is most effective? 6. What are the criteria by GET for the choice of the assembly system?
7. How should the production and inventory be organized in terms of planning and control?
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2.7 Decision area’s and Scope
Several decisions need to be made on managerial issues, that are involved in the design of an assembly system, in order to accomplish the goal mentioned in 2.6.1. Decision area’s are a clustering of decisions, that are involved in the same managerial issue, but need to mesh with other decision area’s in order to reach the goal (Wheelwright, 1978).
To choose the right decision area’s and to form the scope, several articles on this issue by frequently quoted authors were thoroughly examined. The reason for this literature was acknowledgement, clear defined and stated decision area’s which made it easy to compare. An overlap exists between the models of these authors, but they can also replenish each other, see Figure 7.
Facilities Facilities Facilities
capacity Capacity
Quality management Quality
Vertical integration Organization Organization structure vertical integration Sourcing Vendor relations
process technologies Technology Assembly
employment
Human resources Labour and staffing
Workforce Human resources
process technologies Technology
Scope/new products Process technology Manufacturing structure Plant and equipment Organization and managemen Process technology Hayes and Wheelwright, 1984 Production planning and control Nof, S.Y. 1997 Fine and Hax, 1985 Skinner,
1969 Miltenburg, 2005 Organizational rationalisation mechanization /automation of production Production planning/material control O rgan is a tio nal an d pe rs onn el c o ns ider at ions Engin . Co ns . Production planning and control product design for assembly Labour related rationalisation Assembly automation product design and engineering
18 The columns of Figure 7 correspond to the terminology of the belonging author and the rows correspond to the different decision areas. When cells are blank this means that this author did not cover this area or fitted in another area. This is the case with:
Quality: Fine and Hax (1985) and Hayes and Wheelwright (1984) cover this issue, but the other authors did not see this as a separate decision area. This could be seen as a replenishment in the total area of strategic decisions.
Vendor relations: Fine and Hax (1985) see this as a decision area that stands alone because it belongs to the sales department which they divided in three areas. The other authors do treat the same decision area but incorporate this in the
organization decision area because they see the sales department as a whole. Automation: turning manual handlings into automated handlings and thus
minimizes manual labour. Nof (1997) divides automation in two decision areas, namely automated assembly and mechanization/automation. They both concern the automation area, but assembly automation covers the economic decisions on technology and the engineering considerations cover the technical aspects. Skinner (1969) and Fine and Hax (1985) do not cover an economical perspective on automated processes and non-automated processes where the other authors do consider the economics.
Product design and production design: Hayes and wheelwright (1984) and Miltenburg (2005) are the only two authors that do not cover the interrelationship between product design and production design.
The model of decision area’s of Nof, S.Y., et al.(1997) is taken as the guide through this part because it has its focus on an assembly system whereas the other authors have their focus on a general manufacturing system.
Nof, S.Y., et al.(1997) begin their model with a distinction of two directions where decisions need to take place for an assembly system, namely :
Engineering considerations
organizational and personnel considerations.
These two directions separate the business design aspect from the technological design aspect.
Apart from the fact that Nof, S.Y., et al.(1997) is written especially for an assembly system it also begins to define its decision area’s on an abstracter level and works his way down to a detailed level. Although this detailed level is clear for the engineering
considerations, the organizational rationalization can be empowered by the other authors to specify this decision area in detail. This can be seen later on in this chapter.
Not all aspects of the Engineering-, Organizational- and Personnel considerations are treated in this research, see Figure 8. Within the engineering considerations the
19 Figure 8 Managerial issues concerning the rationalization of the assembly system
So if we zoom in further into the organizational and personnel issues of the model of Nof replenished by the other authors, then four issues appear which are further explained below, see Figure 9. Two of these issues belong to the organizational part, namely organisational rationalization and Assembly automation. The other two issues are related to the human factor of an assembly system, namely assembly employment and labour related rationalization. The personnel problems call for a “soft” approach in comparison to the organizational problems which call for a “hard” approach (De Leeuw, 2002). De Leeuw characterizes “soft” with a pluralistic way of dealing with things and “Hard” is characterized by a unitary way of viewing things. Seen the time restriction and different kind of literature needed for the “soft” type of problems, this is left out of this research.
Design for assembly Labour related rationalisation Assembly employment Organizational rationalization Inside
scope Outside scope
Organizational and personnel issues Engineering Considerations Mechanisation/ automation Assembly automation
20 The two issues outside the scope are:
Assembly employment
Determination of what kind of personnel needs be employed for the type of assembly system. General characteristics of assembly personnel could be: in automotive repetitive industries, unskilled/semi-skilled/skilled personnel, younger personnel.(Nof, S.Y. et al. 1997; Skinner, 1969) mentions apart of the amount of specialization needed also about the amount of supervision needed, which also determines the type of person needed.
Labour related rationalization
This issue deals with the job design within the assembly system. It is long recognized that a preferred working environment by employees creates motivation which leads to
achievement of production volume and quality goals. (Hill and Perkins, 1985;
Shackleton, 1981; Nof, S.Y. et al. 1997) Fine and Hax (1985) mention for the quality of work; participation of the employees in decision making and a compensation system. Hayes and Wheelwright (1984) can add to this that there should be an existence of a certain degree of employment security.
Also outside of scope: The next issues belonging to the organizational rationalisation Organization and management (Skinner, 1969)
This area involves determining the type of organization, the underlying culture, measurement of system performance, degree of risk assumed and executive style.
Vendor relations (Fine and Hax, 1985)
21 The two issues inside the scope are:
Automated assembly & Mechanization/automation
These issues deal with how much manual operation can and should be replaced by
automated mechanical operations. Automated assembly area deals with the organizational decision in terms of costs and Mechanization/automation deals with the technological issues.
Mechanisms or technologies, as mentioned by the other authors, for automation can differ in terms of the degree of automation (semi-automated and fully automated), in terms of complexity (automatic station, assembly cell, assembly line), and the degree of flexibility (dedicated line, flexible assembly system, assembly system with industrial robots). (Nof, S.Y. et al. 1997, Miltenburg 2005, Hayes and Wheelwright,1984) Detailed explanation about these terms will be further discussed in paragraph 6.2
Organizational rationalization
This research is mostly involved in the organizational rationalization which is described by Nof et al (1997) by this one covering term. The other authors describe the same area but accomplish that in subdividing this area. Adding the specified named sub area’s of the other authors will clarify organizational rationalization in further detail. The most suitable and clear terms out of Figure 7 are chosen to strengthen the broad term of organizational rationalization, these are:
Facilities (Hayes and Wheelwright, 1984; Fine and Hax, 1985; Miltenburg 2005)
This decision area deals with the focus on the process, such as size, specialization of the process and types and times of changes. An assembly layout is a good tool to help to visualize the interrelationships between resources and deals with the best location for facilities and resources in the available plant area. (Manzini et al., 2004) Detailed explanation about these terms will be further discussed in paragraph 6.2
Capacity (Hayes and Wheelwright, 1984; Fine and Hax, 1985)
Aspects that are involved in this area are amount of personnel, amount of machines, overtime, third shifts.
Quality management (Hayes and Wheelwright, 1984; Fine and Hax, 1985)
The authors describe this area as dealing with prevention of defects, monitoring and intervention
Production planning and Control (Skinner, 1969; Hayes and Wheelwright, 1984; Fine and Hax, 1985; Miltenburg 2005
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2.8 Conceptual model
The way the problem situation is seen is presented in Figure 10 and shows the variables that are of influence in achieving the goal of this research.
Figure 10 Conceptual model
2.8.1 Operationalisation of the conceptual model
The variables that can be manipulated, mentioned in the conceptual model, are already discussed in paragraph 2.7 and will be explained further into detail.
2.8.1.1 Product and process specification
Information about the to be assembled product and the desired process will lead to information for the actual design of the assembly system. This information will be in the form of a bill of material of the E-corner, relations between components and parts and the system requirements.
2.8.1.2 Lay-out
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2.8.1.3 Planning and control
Volmann T.E. and Berry L.W. (1997) mention ten management activities supported by a manufacturing planning and control system. The activities that will be treated in this research and covered in this report in chapter 8, are;
Plan capacity requirements and availability to meet marketplace needs Plan for materials to arrive on time and in the right quantities
Ensure utilization of capital equipment and other facilities is appropriate
Maintain appropriate inventories of raw materials, work in progress and finished goods- in the correct locations
This means that six of the ten management activities are not treated, because of the nature of the chosen assembly system, the position of the E-corner in the product life cycle and the scope of this research. So management activities not included are:
Schedule production activities so people and equipment are working on the correct things.
Meet customer requirements in a dynamic environment that may be difficult to anticipate.
Track material, people customer’s orders equipment and other resources in the factory
Communicate with customers and suppliers on specific issues and long-term relationships.
Respond when things go wrong and unexpected problem arise
Provide information to other functions on the physical and financial implications of the manufacturing activities.
2.8.1.4 Demand characteristics
The demand characteristics of the E-corner have great influence on the variables in this problem situation, which can be seen in the conceptual model. Demand determines several decisions in this research, but it is based on expectations and assumptions by GET and their partner which is an Official Equipment Manufacturer (OEM). Because it is not certain what demand will be, GET gave the assignment to deal with 200 E-corners a year. Still a possible rise of demand in 5 years from the moment of introduction should be taken into account.
2.8.1.5 Machine selection
With machinery are meant the tools and any kind of special attachments needing to move parts from one place to another. Also lifting tools and additional instruments that
24
2.8.2 Model Validation
According to Barlas (1996) the validity of a causal descriptive model is justified by the internal structure of the model. Thus models that are statements as to how real systems actually operate in some aspects, must not only reproduce/predict its behaviour, but also explain how the behaviour is generated and possibly suggest ways of changing the existing behaviour.
In order to achieve this, the following steps were taken: 1. Model construction
This is the actual forming of a model that not only reproduces/predict the future behaviour, but also how the behaviour is generated and possibly suggest ways of changing the existing behaviour.
In the case of this research it started off with coming up with aspects that could be involved in the problem situation and which could influence the problem just by plain knowledge known at the beginning of the research, by experience and previously read literature, see figure 10.
Figure 11 First sketched conceptual model not validated
Off course the model changed after taken actions described next, there was a constant feedback to the model.
25 2. Theoretical structure
Theoretical structure involves comparing the models’ structure with generalized knowledge about the system that exists in the literature.
In the case of the empirical model for the assembly system of the E-corner, several articles existed that indicate the problem area’s as mentioned in paragraph 2.7. These problem area’s where further examined to obtain the parameters that are described in the literature to test the model created on plain knowledge. Several parameters matched the literature parameters, such as machinery and the production politic. But literature used different terminology and/or filled the parameters in differently. Layout and
project/process specification replenished the old model in Figure 11. Another action was taken to seek for relations with the real world situation
3. Empirical direct structure
Empirical structure involve comparing the model structure with information (quantitative or qualitative) obtained directly from the real system being modeled. In the case of the E-corner assembly system this was done by comparing the structure of the model structure with the way the prototype corner was assembled and how the concepts for the new E-corner looks like. This test resulted in which parameters were taken into account and which other parameters were left out of the scope. For example labour and supplier selection process were left out because it did not resemble the behaviour for this system of the problem situation. Planning and control was used in the conceptual model rather than production politic, because it covers inventory as well as planning production. The outcome of the design of the assembly system in the first model was supposed to be minimal costs, reliability and quality. Although these aspects are important, it appeared that the outcome of the design of the assembly system in the model should be different. Interviews revealed a different outcome for the design of the assembly system, namely, capacity, flexibility and quality. Reliability and costs should be maintained by the effectiveness of the design of the assembly system, which means that they are still taken into account.
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2.8.3 Assumptions
The selection of the most effective assembly system and designing of the product to suit assembly early in the product development process can have a major impact on
production costs and ultimately the final product cost (Swift, K. G. et al, 2004).
As mentioned in the previous part GET is still in an early stage of the product life cycle and is not considering making variations on the E-corner yet. The assumption is made for this research that the assembly line will be faced with just one variation of this module. One variation still means that there is a left and a right version of the E-corner. This does not mean that a totally different assembly process is needed and only one component has a left and a right version. A left and a right version will have impact on the workpiece carrier, this will have a left and a right version.
Cost efficiency and producing a higher amount of modules than in times when the “bandit” was developed by GMS are the main goals for GET right now.
As mentioned before in the current situation the assumption is made on the status of the design of the E-corner. The design of the current E-corner is frozen. In reality the design can change in time, although the rough design will not change considerable nor will the amount of components. This is confirmed by the program manager. The only changes that could be made are adjustments in the electro motor for example, or adjustments to mechanical parts for loosing weight, but all this will not influence the assembly process.
2.8.4 Demand
According to the partner of GET, a big Original Equipment Manufacturer (OEM) in the automotive industry, possible demand will worth
preparing for. This is based on the OEM’s market research done in November 2009, called “Bandit concept market potential.” According to this market research the Bandit can in the best case scenario replace almost every existing tail-lift (see Figure 12) truck in the segments between 12 ton and 18 ton. The tail-lift is the device that makes it possible to load and unload goods in a regular truck.
GET has made their own market research, but is cautious, because only in theory all the tail-lift trucks in these segments can be replaced.
For this reason the assumption on demand is made on 50-200 products per year, based on prior experiences on willingness to buy and based on the market research by the OEM and internally by GET.
The assumption of 50-200 products per year can have an impact on which assembly system suits best; if demand increases than this could call for a different assembly system. This is shown in this report in chapter 6 and will cover different scenarios with different demand states and the best suitable assembly system. In order to confirm these
27 findings, several case studies used as benchmarks were examined and covered in
paragraph 6.2.3.
The reliability of these figures can not be said by a 100 procent certainty, however GET has made a planning for the coming 10 years were the production of 200 E-corners is reached easily. Reason for that is because right after launching the “Bandit”, the partner of GET will order several trucks for own use. When the partner of GET starts to take the “Bandit” in their own scala of products after 3 to 5 years, demand for the E-corner will increase. The estimations of the OEM reaches a demand far above the 200 E-corners a year, this estimation after 5 years is what makes the 200 E-corners a year a certain estimation. If, as can be seen in Table 1, demand will reach to the extend showed from the year 2017 on, the assembly system should be able to cope with a higher demand.
E-corner demand expectations
40 100 170 250 550 1150 1150 1150 1150 0 200 400 600 800 1000 1200 1400 2012 2013 2014 2015 2016 2017 2018 2019 2020 Year P ro duc ti on v o lu m e E -co rn er s
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2.9 Scope overview
Several issues are discussed that need to be considered with the design of an assembly system. Some are part of this research and some not. Figure 13 gives an overview of the managerial issues mentioned in paragraph 2.7, that fall within or outside the scope of this research.
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2.10 Research model
The next model is a clarification of how this report is build up in regards to the
methodology, the research questions and the aspects that will be treated in this research, see Figure 14. The model shows the specific variables out of the conceptual model with their matching chapters. On the left side of the figure the steps from the methodology of de Leeuw (2002) are shown to indicate what the purpose is of the mentioned chapters. The topic methodology will be further explained in the next chapter.
Ch an ge Dia gn ose De si gn Process specification Concept Design Methodology
Introduction Research outline
Project specification
System configuration
Final assembly process and system Ch. 1 Ch. 2 Ch. 3 Ch. 4 Ch. 5 Ch. 6 Ch. 8 Ch. 9 Production planning and control Ch. 7 - Company profile - E-corner
- Reason for this research - Problem statement - Scope
- The role of demand
- How the research is setup
- The product E-corner clarified
- Assembly process of the E-corner clarified - Generation of assembly sequence
- Process plan and times - System requirements
- Criteria of GET
- Theoretical approach on assembly systems and layouts
- Decision based on costs and capacity - Machinery selection - Production politic - Coordination of materials - Final design - Wrap up Sub question 1
Sub question 2 and 3
Sub question:4, 5, 6, 7 and 8
Sub question 9 Sub question 10
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2.10.1 Structure of the report
Chapter 1: The introduction gives an insight in the company and which elements give the incentive to this investigation. Chapter 2: The research outline gives the reason for this research, the problem statement with the belonging research question and what is
involved and what is left out of this research. Also the role of demand is explained in the chapter and how it relates to this research. Chapter 3: The methodology clarifies the path and steps about how the problem is addressed.
Chapter 4: The specification of the project will give insight in what the product to be assembled looks like and what it is made of. Chapter 5: The process specification deals with how the characteristics of the assembly process should be in order to answer to demand and the product specifications.
Chapter 6: Concept design will treat the issue of the design of the assembly system and the assembly layout. This means the positioning and formation of machines, material and it indicates material flows. This chapters starts with the criteria that GET has on the assembly system, than it will cover the theoretical background on the topic assembly system, layout. Chapter 6 will also show three case studies to form a benchmark with ather companies that certain similar challenges on assembly systems. Eventually decisions are made on costs and capacity.
Chapter 7: The production planning and control issue deals with timing in the assembly process so that the process runs properly and is able to respond to demand and that the costs are minimized.
Chapter 8: The selection of the machinery will give an indication of which machines are needed for the assembly process.
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3 Methodology
In this chapter the methodology of this research will be discussed together with the research model. This model shows how this report is structured and indicates when which part of the methodology is used.
The methodology of this research will be based on the D.O.V. method of De Leeuw (2002) together with the assembly system design methodology developed by Lohse N. et al. (2004). D.O.V. stands for Diagnose, Ontwerp and Verandering, these are the three different phases within the research. D.O.V. translated means for Diagnose (diagnose) phase, Ontwerp (design) Phase and the Verandering (change) phase. This research will mainly concern the first two phases and this is exactly what the methodology of Lohse does. The extra addition to the methodology of De Leeuw is a methodology specific for the design of an assembly system. These two methodologies have the same structure but Lohse has extra elements in comparison to the methodology of De Leeuw, namely the business resources element and the performance evaluation, see Figure 15. This extra element shows the importance of the interfaces between business resources and the assembly system in terms of needed knowledge to create an assembly system.
Project
specification Process specification
Concept design System
configuration Performance evaluation Final assembly process and system Resources Diagnose Verandering (change) Ontwerp (Design) Methodology of
De Leeuw (2002) Lohse et al. (2004)Methodology of
Figure 15 Two methodologies compared
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3.1 Diagnose
This phase is described by the Leeuw (2002) as the phase where it is necessary to model purposefully and judge the functioning of a problem situation which is seen as a system. According to De leeuw (2002) the whole system begins with an incentive or “signal” that triggers to begin the diagnose. This is in this case the need for an assembly plan. Lohse describes this phase in the form of specifying the project and process. The specification of the project at GET is defining the E-corner, with a detailed product model including the hierarchical structure of its parts, part characteristics and part liaisons. Specifying the process is done by determining the assembly sequencing steps and functions of these steps according to the hierarchy between parts and part characteristics. This specification is the connection between requirements of the engineering process and design process. It begins with the determination of alternative assembly sequences. The validity of
sequences is based on the assemblability of the components in the resulting tasks. Each base task – a task that represents the assembly of only two components – is further broken down into operations and actions to define how the assembly of the components occurs. These sequences tasks and operations need to be refined by negotiating with other disciplines (Lohse N. et al. 2004).
3.1.1 Data Gathering methods
The following methods were used to map out the situation around the problem in this research.
3.1.1.1 Literature research
Literature research in academic-orientated thesis and reports, but also graduation reports of students mainly from the Rijksuniversiteit Groningen was done to support this
research. In this report is chosen to apply the literature when needed in the specific chapter or paragraph and not in one dedicated theory chapter.
3.1.1.2 Desktop research
Desktop research is done to read-in on the “Bandit”, the company and the E-corner in specific. Especially on parts and technical data, but also on market research and internal regulations there are many documents present within GET. These documents were:
Purchasing reports on the prototype “Bandits”: For information on suppliers and costs of the parts in the “Bandit”. These are full reports, categorized.
Drawings of the prototype bandits (mostly 2D): Gain information of old parts, such as weight and size.
Drawings of the new concept designs (3D digital models): Helping to create inventory of parts
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3.1.1.3 Interviews
Interviews are done with the people that worked on the “Bandits” and who were
responsible for the assembly of the old versions of the bandit and with the people who are responsible for the future design.
Informational interviews: done with the mechanics of the old “Bandits” and formed the evaluation of certain assembly actions done on the old “Bandit”. Other informational interviews were done with the former mechanical engineers, present mechanical engineers and electrical engineer. This led to a understanding of the assembly processes Formal interviews: with project leader of the new bandits to gain the
criteria on the new assembly system.
3.1.1.4 Observation and practical involvement
Observations of the old design and working along on the work floor on the old design was helpful in finding out what the E-corner will look like and what it means to assemble an E-corner in practice.
3.1.2 Data Analyze methods
The following methods are used to interpretate the gathered information to mold it for the use of this research.
3.1.2.1 Assembly Sequence models
Two methods were used to determine the order of the assembly steps of the E-corner, also known as the assembly sequence. The two methods used are:
Simplified Method of bourjault (for complete description, see paragraph 5.1) Identifies the relations between parts and visualizes this in a liaison diagram. Then according to a review of all relations the hierarchy of the parts is determined.out of the product hierarchy and practical criteria the assembly sequence can be made.
Component ordering method (for complete description, see paragraph 5.1) Interference checking is the basic criteria between parts and makes sure the parts do not collide during assembly. According to preferences and practical criteria the assembly sequence is made.
3.1.2.2 MOST method
This is a tool for describing and evaluating existing and concept designs of assembly systems and it determines the relative operation times, (Crowsen, 2006
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3.1.2.3 AHP
An Analytical Hierarchy Process (AHP) is used in the formal interview with the project manager to report the criteria of GET on the assembly systems, for a detailed explanation of AHP see chapter 6. The AHP was able to convert the total problem preferences about an assembly system in to understandable elements. Another advantage of the AHP was that the non measurable preference of the project manager were converted into
measurable preferences by weighted elements.
3.2 Design
The design phase consists of the development of a concrete solution for the diagnosed problem. The target here is not to develop a control decision, but a controlling functional unit. This enables to make a good decision in ever situation in respect to the problem. Designing is choosing a model of a future desired system in an environment that realizes goals, Leeuw (2002).
According to Lohse N. et al. (2004) this is an intermediate step between process specification and assembly system configuration. This phase consists of several steps namely;
1. Grouping the tasks of the overall assembly process. The grouping of tasks to form the system and its cells is based on the parallel tasks in the process plan and hence on the product hierarchy described in the diagnose phase.
2. Assign tasks to workstation, in case of multiple workstations. 3. Form a process plan, which is the flow of parts.
4. Generate process times that are given to operations are determined according to demand. After this several conceptual design alternatives are made (Lohse et al. 2004).Once the concept structure has been defined, the maximum process times for each concept entity can be derived from the structure and the maximum system cycle time required for the project.
5. System configuration consists of the selection of suitable equipment modules and configures them to build assembly system
6. Design Inventory and Production planning and control, the design of material order generation plan, planning of production and inventory control.
3.3 Change
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3.4 Validation and reliability
To make sure that this research upholds its validity and reliability certain measures need to be taken. The measures are categorized according to the 4 types of validity by De leeuw (2003), he recognizes 4 types of validity:
1. Content validity
This covers the area of whether all the aspects of the concept are expressed right and provide adequate coverage of the investigative questions guiding the study.
To maintain the content validity the following measures will be made:
Use frequently and reliable quoted resources out of acknowledged literature.
Avoid overreliance on accessible and elite respondents, “elite bias” Using different sources for the same subject, “method triangulation”,
theory as well as interviews and company documents. “source triangulation” which is the use of different sources.
Gain information in different areas of the company in all layers of the company.
2. Conceptual validity
Criticises the concept on whether it is representative for the characteristics that hold for the real situation
Mapping out the problem situation and making sure the concerned party agrees upon the correspondence with the concept.
Let history not influence the situation to be modelled. (awareness of different settings that set the prototype of the E-corner)
3. Predictive validity
This type of validity is the degree in which the operational notion really leads to the desired outcome.
Making sure the criteria of Gemco E-trucks is clear in order to respond to the criteria.
4. Competitive validity
This deals with whether the operational notion corresponds to another which is declared reliable.
Use case studies
Use former designs on prototype E-corners 5. Reliaibility
Interviewing representative respondents
Making the group interviewed as big as possible Communicate reasons for research and interview.
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4 Project
specification
Interviews, desktop research and observations were held and gave great insight in the problem situation and resulted in the needed knowledge about the E-corner.
The interview with the mechanical engineer gave a total picture of which parts and components are included in the E-corner, but also how these components are positioned. But since this research aims especially at the assembly process, it needed more than just this interview and more interviews were taken with the mechanics that worked on the previous “bandit” projects. This gave a lot of information on how the parts should be mounted and what is needed to finish the final assembly.
Observations of the previous bandit rear wheel driving unit and the drawings of the future design of the E-corner gave a realistic and physical impression of what the product is like.
Also practical experience was gained by helping the mechanic with installing several components of the E-corner in an existing “Bandit” that had some revisions done to it.
4.1 Product model of the E-corner
The interviews about the E-corner module resulted in a bill of material which consists of 18 components or subassemblies supplied by various suppliers. The parts differ in weight between a range of 10 grams by bolts and nuts and 204 kilograms of a mechanic rotating component. This gives an important indication which parts need to be accompanied by lifting gear and which not and thus the difficulty of mating the different components. Figure 16 shows an assembled and exploded view of the components and how they are positioned.
37 The following components are part of the E-corner module:
Mounting plate
This is the backbone of the E-corner because it helps connecting the components
belonging to the E-corner to the frame of the truck where the E-corner is inserted. It helps giving support, it serves as a positioning device and conducts forces to the frame of a vehicle.
Swingarm
This is the part that holds the electric motor and is attached to the mounting plate via a hinge. This hinge is also the center of a rotating point what makes it possible to bear with unevenness of the road surface, but it is also the rotating point for the bandit to lower the cargo floor. Mounted on to the swingarm are the air suspension and shock absorber, these are also two components that provide the suspension and damping and need to be
assembled by the assembly system.
Electro motor
This is the essential part for making a rotating movement out of electrical energy. The electrical motor has its own load-bearing frame and is mounted to the swingarm. The reduction box will be attached to the electro motor.
Reduction box
The reduction box takes care of a transmission from the drive shaft that is connected to the electrical motor which on his turn is connected to the tire. The main function is to reduce the speed and increase torque. It also holds the disc brake system.
Air-over-hydraulic converter
This part is there for converting an air brake system into a hydraulic brake system. So this device is air actuated and converts pneumatic pressure into hydraulic pressure to make the truck brake.
Cooling device
For cooling the electric motor. This is done by a closed circuit of cooling canals and tubes where fluid runs through from the electrical motor to the radiator/heat exchanger where the warmth is transmitted to the air.
Power electronics
This component consists of a rectifier inverter that changes AC to DC power and also DC to AC power. This change of AC to DC and DC to AC is because of easier transport of the electricity and because of the battery pack in the truck itself.
Cables
38
Wiring Harness
There are also cables which connect several sensors, namely the height sensor, the motor position sensor and the ABS sensor.
Brake Tubes
There is a brake tube from the air-over-hydraulic converter to a splitter and then two tubes to the brake cylinder.
Cooling tubes
These tubes connect the electrical motor with the cooling device and form a closed cooling circuit.
Fluids
There are three different liquids in the E-corner, brake fluid, lubricant oil for the reduction box and cooling liquid.
Axle
The axle is positioned between the reduction box and the electrical motor and provides the transfer of rotation.
4.2 Product hierarchy
The relationship of the parts has great impact on the way the product will be assembled and even how the assembly sequences will be planned.
Mechanical products can be assembled in different order or sequences, but resulting in the same product (Ben-Arieh, D, 1994). Every different sequence has a different degree of difficulty for the various assembly operations, because of different mechanical
constraints. Selection of the right assembly operation at the right time has great impact on maximizing the production profitability and has great impact on the assembly line
balancing, machine utilization and feasibility of subassembly realization (Ben-Arieh, D, 1994).
39
5 Process
specification
This part of the report analysis and describes the assembly process of the E-corner, also described as the process decomposition. According to the product specification in the previous chapter the parts and components involved in the E-corner are clear. Choosing the correct assembly sequence will affect the assembly shop layout, repair and test options (whitney, 1988 as reffered to in Ben-arieh, 1994). The sequence determines which connection between parts is done when and where. Since every connection calls for tasks to be performed by an operator in order to establish a connection, the assembly sequence determines which tasks are performed when. Because of the relevance of the determination of the assembly sequence, two methods are used in this chapter for the process decomposition. Using two methods instead of one increases the reliability on this topic.
5.1 Sequence models
As already mentioned before the generation of possible sequences is essential for
optimizing the assembly process (Ben-arieh, 1994) and therefore several methods exist to come to the right sequence of an assembly. In this research three methods which are frequently reffered to in the literature and are considered to use to determine the assembly sequence, namely:
Simplified Method of bourjault (De Fazio and Whitney, 1987) De Fazio and Whitney (1987) start with identifying the relations between parts and visualized in a liaison diagram see Figure 17, where lines and bullets resemble connections (liaisons) and parts respectively. The liaisons or connections are then carefully examined by answering questions. Stated answers represent the precedence relations among liaisons (connections). These precedence relations are then used to generate all the assembly sequences leading from one selected base part to the final assembly. No computer program is used in this method.
Component ordering method (Lee and Ko,1987), this method generates a rather simple sequence. Interference checking is the basic criteria and makes sure the parts do not collide during assembly. This method uses an algorithm for the generation of
assembly sequences that runs through the parts according to the hierarchy to check viable mating conditions. This method is initially designed to describe the assembly to a
40 Three layer strategy (Lin and Chang, 1991, as referred to in Ben-arieh, 1994), this method uses a special tree structure to represent the assembly and to generate one feasible sequence. The goal of this method is to minimize the human activity in the planning of sequences but they still want to involve actual assembly practice. In the research of Lin and Chang a software system was used for the automated mechanical assembly planning on a powerful computer to cope with these calculations. Gemco E-trucks is not in the possession of such a powerful computer which makes it not possible tot apply this method.
Two of the three methods can be used in this research namely the simplified method of bourjault and the component ordering method. Both methods are applied to the E-corner so that the outcome of the first method can be be supported by the other method.. The following paragraphs describe the two methods.
5.2 Simplified method of bourjault
As mentioned before the simplified method of bourjault by De Fazio and Whitney (1987) starts with a liaison diagram, the visualization of the liaisons (connections).
The liaison diagram for the E-corner is presented in Figure 17 where the nodes represent the parts and the lines represent the relations between the parts.
Figure 17 Liaison diagram of the E-corner
An assembly step in the definite assembly system will be characterized by the establishment of one or more of the liaisons of the diagram in Figure 17.
The next step is to ask two questions on every relation between the parts (De Fazio and Whitney 1987), these are;
Q1: What liaison must be done prior to doing liaison i? (i represents the concerning liaison)
41 These questions will give close knowledge of the design details of the assembly. It gives information about precedence relationships between liaisons or between logical
combinations of liaisons. A note to this is that the question addresses to what needs to be done, is not necessary what is convenient to do. Practical information is needed to verify the possibility of the liaison. This was done in this research by evaluating the assembly steps with the program manager and the constructive engineer.
There are 26 liaison in the E-corner which mean 56 questions to answer in order to gain all the necessary information, see Appendix I: Liaison answers
Out of these questions the following constraints and hierarchy came forward: (11 and 10) → 12
4→13 4 → 18 4 → 19
(8 and 25) → 20
The numbers resemble the liaisons showed in Figure 17 and the numbers in front of the arrow are the ones that need to precede before the liaison number after the arrow can be done. These constraints are based on the characteristics of the parts, dimensions and dependency.
De Fazio and Whitney (1987) do not describe the type of mating conditions specifically, s, therefore the paper of Ben-Arieh (1994) is used to describe the significant mating properties.
Two types of significant properties are involved when considering an assembly operation (how tasks are assembled), properties related to the geometry and the ones related to the type of contact between the components. (Ben-Arieh, D, 1994) The following parameters are geometry based
Shape: Operations with irregular or asymmetrical shape have a high degree of difficulty in assembly
Force required: The amount of force required to complete the operation
Mating direction: The way parts come together. Example: axial, radial etc. See Appendix III Clarification pictures on assembly operations
