טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentMoran Elnekave
SubjectComputerized Assembly Cell Design
Comprising Manual Processes
DepartmentDepartment of Industrial Engineering and Management
Supervisor Professor Gilad Issachar
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

The thesis describes an original design model, which answers pragmatic needs for assembly cell design.  The model is based on translating time and ergonomics into cost, enabling quantitative design decision making.  A procedure for computerized assembly cell design, driven by time and ergonomic metrics does not exist in literature or in practice.  The proposed model is constructed of three main stages: (1) Definitions and requirements - where initial parameter inputs of the product assembly (parts and required assembly operations) and the manufacturing environment (e.g. man-hour costs, floor costs, energy costs, required assembly quantity, alternative interest rate and payback period) are introduced; (2) Design assembly cell - where economic operation sequence is reached, tools and fixtures aiding to perform assembly operations with reduced cost are selected and assembly cell layout is dimensioned; and (3) Design improvements - where local improvements to the work-method are proposed and quantitatively analyzed.  A cost function, summing operator costs, machine costs and environmental costs, calculates assembled unit costs in the designed cell.  The cost function, based on parameter inputs and cell performance, serves for comparison of design alternatives and for final assembly cost output.  The model was verified through implementation in design of assembly cells for two products: a personal computer and a bed linen box.  Results were validated by comparing the proposed model’s outputs to actual performance of industrial assembly cells, which function for the assembly of the investigated products.  While similar motion patterns reinforce the ability of the proposed model to reflect reality, conducted comparisons show 37% and 16% improvement in cost and 45% and 15% improvement in time when comparing existing and designed assembly cells for personal computer and bed linen box in accordance.  The research concludes that in reality, operation sequences are not necessarily carried out economically nor best tools are used to support the human operator.  As well, neither fixtures nor ergonomic work-heights are considered in existing designs.  These yield in higher risks of occupational injury and also higher assembly costs due to extending allowed time for rest and recovery.  Using the proposed model leads to success in design of assembly cells, foreseeing poor work-postures, lengthy operation times and tools that contribute to cost reduction.