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Creating an assembly system of tomorrow, today: A case study of how to reach flexibility and productivity in a mixed model assembly system
KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Industrial Management.
KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Industrial Management.
2012 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]


The purpose of this master thesis is to investigate how the choice of assembly system design relates to lean production and in what way the system design affects the system flexibility when changes are made to the product mix or takt. The production system under study is the bus chassis assembly at Scania CV AB in Södertälje and the specific unit of analysis is the preassembly of cooling packages. This assembly has proven to be interesting for this master thesis – partly since the product variety is high but also because the production is in a break point since older product families are about to be taken out of production at the same time as new models are on the way in. Furthermore, Scania has a well stated objective for its assembly operations which is to achieve a significantly higher productivity with the existing structures which makes the flexibility for future production increases important to have in mind. Worth pointing out is also that lean production has been a starting point in this master thesis since it is a universal language in many assembly industries. Different assembly systems have for this reason been classified based on the definitions of waste as described in the lean philosophies.

Design/methodology/approach A number of methods have been used to in the best way be able to  implement  a  comprehensive  and  valid  study.  These  methods  include  both  quantitative  data collection  through  observations  –  which  include  video  recordings,  time  studies  and  ergonomic studies – but also qualitative studies through numerous interviews and conversations with people who  have  knowledge  of  different  areas  that  have  proven  to  be  interesting  in  this  context.  As complement, benchmarking of different areas within Scania has also been made – of both similar preassemblies and of different outstanding projects within the Chassis operations.

Findings, Wastes will always exist within mixed assembly systems even if these can be largely reduced through a suitable selection of assembly system. If variations in time and assembly are not too large between different products, a single one-piece flow is always to prefer. The reason for this is that serial flows bring structure and synchronization possibilities at the same time as the division of the  assembly  process  becomes  visual  and  simplifies  reduction  of  waste.  In  order  to  manage variations in the product range it is also possible, in different ways, to use additional aspects of system configuration to level the flow and separate non-value adding activities. Moreover, a serial flow  is  beneficial  in  aspects  of  flexibility  since  it  is  relatively  easy  to  expand  the  flow  with  an additional position without large costs. 

Research limitations/implications, The delimitations of this master thesis have been made so that only methods which can be interesting for the specific unit of analysis has been considered and evaluated. This means that nothing but aspects which are related to manual assembly systems have been considered. Since a single preassembly has been studied it means that the results can be seen as a form of sub optimization since logistical concerns and aspects regarding to the overall assembly process have not been taken into consideration.

Practical implications, As for the preassembly of bus coolers, a serial flow has partly proven to be possible. The assembly system must be adapted to three different product families and for the families which are at issue in the future a serial flow is the best alternative. However, the third product family which includes models which are going to be taken out of production differs so much in terms of time usage and assembly sequence that it needs to be handled separately from the other two families. Despite of this it has been proven that the number of assembly positions can be reduced from three to two when comparing the proposed serial flow with the currently used bench assembly.

Originality/value, Mass customization is currently an up to date phenomenon which can be seen in both  organizations  and  in  scientific  journals.  This  occurrence  has  lead  to  new  demands  on organizations when it comes to managing rapid adjustment in the production operations to deal with changed customer requirements and increased demand. This master thesis aims to consider both product variations and possibilities to create flexible assembly solutions and to connect these with the  prerequisites  of  lean  production.  This  is  a  trinity  which  has  not  been  clarified  in  existing literature.

Place, publisher, year, edition, pages
2012. , 162 p.
Keyword [en]
Assembly system, Flexible assembly systems, Flexibility, Lean production, Material handling, Mixed model assembly lines, Preassembly, Product variety, Serial flow, System configurations models, System balancing, Takt, Waste
National Category
Economics and Business
URN: urn:nbn:se:kth:diva-143185OAI: diva2:705717
Available from: 2014-04-17 Created: 2014-03-17 Last updated: 2014-04-17Bibliographically approved

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