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Research Papers: Design for Manufacturing

Product and Process Tolerance Allocation in Multistation Compliant Assembly Using Analytical Target Cascading

[+] Author and Article Information
Zhijun Li

Department of Mechanical Engineering, University of Michigan, 2350 Hayward Street, Ann Arbor, MI 48109-2125zhijunli@umich.edu

Michael Kokkolaras1

Department of Mechanical Engineering, University of Michigan, 2350 Hayward Street, Ann Arbor, MI 48109-2125mk@umich.edu

Panos Papalambros

Department of Mechanical Engineering, University of Michigan, 2350 Hayward Street, Ann Arbor, MI 48109-2125pyp@umich.edu

S. Jack Hu

Department of Mechanical Engineering, University of Michigan, 2350 Hayward Street, Ann Arbor, MI 48109-2125jackhu@umich.edu

1

Corresponding author.

J. Mech. Des 130(9), 091701 (Aug 08, 2008) (9 pages) doi:10.1115/1.2943296 History: Received August 17, 2006; Revised April 16, 2008; Published August 08, 2008

Tolerance allocation is the process of determining allowable dimensional variations in products (parts and subassemblies) and processes (fixtures and tools) in order to meet final assembly quality and cost targets. Traditionally, tolerance allocation is conducted by solving a single optimization problem. This “all-in-one” (AIO) approach may not be desirable or applicable for various reasons: the assembler of the final product may not have access to models and∕or data to compute appropriate tolerance values for all subassemblies and parts in the case of outsourcing; optimization algorithms may face numerical difficulties when solving very large-scale, simulation-based nonlinear problems; interactions are often obscured in AIO models and trade-offs may not be quantifiable readily. This paper models multistation compliant assembly as a hierarchical multilevel process and proposes the application of analytical target cascading for formulating and solving the tolerance allocation problem. Final product quality and cost targets are translated into tolerance specifications for incoming parts, subassemblies, and station fixtures. The proposed methodology is demonstrated using a vehicle side frame assembly example. Both quality- and cost-driven tolerance allocation problems are formulated. A parametric study with respect to budget is conducted to quantify the cost-quality trade-off. We believe that the proposed multilevel optimization methodology constitutes a valuable new paradigm for tolerance design in multistation assembly involving a large number of parts and stations, and creates research opportunities in this area.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Variation models as an ATC process

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Figure 2

Fixture layout in the multistation compliant assembly system

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Figure 3

Reduction in final product variation as a result of increased budget for both scenarios

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Figure 4

Reduction in part product variation as a result of increased budget for both scenarios

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Figure 5

Comparison of allocated tolerance values for KPCs of parts, subassemblies, and final assembly, with and without process tolerance allocation

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