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Research Papers

Toward Automatic Tolerancing of Mechanical Assemblies: First-Order GD&T Schema Development and Tolerance Allocation

[+] Author and Article Information
Payam Haghighi, Prashant Mohan, Nathan Kalish, Prabath Vemulapalli, Jami J. Shah, Joseph K. Davidson

Design Automation Laboratory,
Arizona State University,
Tempe, AZ 85287

Contributed by the Computers and Information Division of ASME for publication in the JOURNAL OF COMPUTING AND INFORMATION SCIENCE IN ENGINEERING. Manuscript received March 4, 2015; final manuscript received May 31, 2015; published online August 6, 2015. Assoc. Editor: Bahram Ravani.

J. Comput. Inf. Sci. Eng 15(4), 041003 (Aug 06, 2015) (9 pages) Paper No: JCISE-15-1083; doi: 10.1115/1.4030939 History: Received March 04, 2015

Geometric and dimensional tolerances must be determined not only to ensure proper achievement of design function but also for manufacturability and assemblability of mechanical assemblies. We are investigating the degree to which it is possible to automate tolerance assignment on mechanical assemblies received only as STEP AP 203 (nominal) geometry files. In a previous paper, we reported on the preprocessing steps required: assembly feature recognition, pattern recognition, and extraction of both constraints and directions of control (DoC) for assembly. In this paper, we discuss first-order tolerance schema development, based purely on assemblability conditions. This includes selecting features to be toleranced, tolerance types, datums, and datum reference frames (DRFs), and tolerance value allocation. The approach described here is a combination of geometric analysis and heuristics. The assumption is that this initial geometric dimensioning and tolerancing (GD&T) specification will be sent to a stack analysis module and iterated upon until satisfactory results, such as desired acceptance rates, are reached. The paper also touches upon issues related to second-order schema development, one that takes intended design function into account.

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Figures

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Fig. 1

High-level architecture

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Fig. 2

Assembly preprocessing modules and data flow

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Fig. 3

First-order GD&T schema development procedure

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Fig. 4

Cylinder-cap assembly and preprocessing results (partial)

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Fig. 5

Tolerance loops for cover plate

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Fig. 6

Progressive steps in autotolerancing of cover plate. (a) Master datum selection, (b) Sizes, Dimensions and Patterns, (c) Size and Position tolerances, and (d) Form, orientation and other tolerances.

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Fig. 7

Autotolerancing results

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Fig. 8

Master datum reference frame for military vehicle hull

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