Research Papers

A Method for Integrating Form Errors Into Geometric Tolerance Analysis

[+] Author and Article Information
Robert Scott Pierce

Department of Physics and Engineering, Sweet Briar College, Sweet Briar, VA 24595

David Rosen

Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0405

J. Mech. Des 130(1), 011002 (Dec 07, 2007) (11 pages) doi:10.1115/1.2803252 History: Received January 31, 2006; Revised April 17, 2007; Published December 07, 2007

In this research, we describe a computer-aided approach to geometric tolerance analysis for assemblies and mechanisms. A series of as-manufactured component models are generated within a NURBS-based solid modeling environment. These models reflect errors in component geometry that are characteristic of the manufacturing processes used to produce the components. The effects of different manufacturing process errors on product function are tested by simulating the assembly of imperfect-form component models and by measuring geometric attributes of the assembly that correspond to product functionality. A tolerance analysis model is constructed by generating and testing component variants that represent different manufacturing precision levels. The application of this approach to tolerance analysis is demonstrated using a case study that is based on a high-speed stapling mechanism.

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 1

Application of geometric tolerances of form and orientation to a rectangular parallelepiped. (a) Nominal part with geometric tolerances. (b) The actual part surfaces must fall within tolerance zones formed by planar surfaces.

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Figure 2

A high-speed stapling mechanism

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Figure 3

Generation of a model of a typical manufacturing variant of the slider in a prismatic joint. (a) The nominal joint design. (b) Slider with point measurements that define an as-manufactured surface. (c) Nominally planar bottom surface replaced with the as-manufactured surface. (d) All three mating surfaces (bottom and two sides) of the slider replaced with as-manufactured surfaces.

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Figure 4

Testing the effect of one set of manufacturing errors on product functionality. (a) Mating between as-manufactured component models is simulated. (b) Attributes of functionality (angular misalignment between components) are measured. (c) and (d) For a mechanism, the process is repeated at a series of positions through the range of travel.

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Figure 5

The slider/guide problem with cutter deflection errors. The error magnitude has been increased by a factor of 10 for illustrative purposes. (a) The mating surfaces and grid points. (b) The closest-point mating distance.

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Figure 6

Details of the stapling process

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Figure 7

Dimensioned views of the stapling head components. Geometric form tolerances have been assigned; tolerance magnitudes are to be determined. All dimensions are in millimeters. (a) Driver. (b) Bender. (c) Bonnet.

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Figure 8

Grouping of the mating surfaces of the stapling head into four manufacturing process groups

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Figure 9

Interaction between bonnet and outer bender surfaces. The error magnitude has been increased by a factor of 10 for illustrative purposes. (a) Bonnet and outer bender both at the higher-precision values. The bottom groove surface of the bonnet has a ridge running down the center due to cutter deflection from either side face. (b) The bonnet is at the lower-precision value, while the outer bender is at the higher-precision value. (c) The bonnet is at higher precision, while the outer bender is at lower precision.



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