Research Papers

A Framework for Explicating Formal Geometrical and Dimensional Tolerances Schema From Manufacturing Process Plans for Three-Dimensional Conformance Analysis

[+] Author and Article Information
Payam Haghighi, Prashant Mohan, 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 November 26, 2014; final manuscript received December 9, 2014; published online April 8, 2015. Editor: Bahram Ravani.

J. Comput. Inf. Sci. Eng 15(2), 021003 (Jun 01, 2015) (13 pages) Paper No: JCISE-14-1434; doi: 10.1115/1.4029555 History: Received November 26, 2014; Revised December 09, 2014; Online April 08, 2015

A process plan is an instruction set for the manufacture of parts generated from detailed design drawings or computer-aided design (CAD) models. While these plans are highly detailed about machines, tools, fixtures, and operation parameters, tolerances typically show up in less formal manner, if at all. It is not uncommon to see only dimensional plus/minus values on rough sketches accompanying the instructions. On the other hand, design drawings use standard geometrical and dimensional tolerances (GD&T) symbols with datums and datum reference frames (DRFs) clearly specified. This is not to say that process planners do not consider tolerances; they are implied by way of choices of fixtures, tools, machines, and operations. Process planners do tolerance charting in converting design tolerances to the manufacturing datum flow based on operation sequence, but the resulting plans cannot be audited for conformance to design specification. In this paper, we present a framework for explicating the GD&T schema implied by machining process plans. The first step is to derive DRFs from the fixturing method in each setup. Then, basic dimensions for features machined in the setup are determined with respect to the extracted DRF. Using shop data for the machines and operations involved, the range of possible geometric variations are estimated for each type (form, size, orientation, and position). The sequence of operations determines the datum flow chain. Once we have a formal manufacturing GD&T schema, we can analyze and compare it to design specification using the T-map math model.

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Fig. 1

A Design drawing of a part with formal GD&T specifications

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Fig. 2

First step in the process plan of machining the connecting rod. (a) Process plan sample sheet and (b) process plan sample sketch.

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Fig. 3

Overview of computational procedure

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Fig. 4

Part design and process plan: (a) design GDT spec of a part and (b) partial plan

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Fig. 5

Illustration of 3-2-1 principle

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Fig. 6

First two stages of machining a connecting rod: (a) first setup and (b) second setup

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Fig. 7

Different fixturing methods for machining the same part (a) first fixturing method, (b) DRF extracted for the first fixturing method, (c) second fixturing method, and (d) DRF extracted for the second fixturing method

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Fig. 8

Different machines and the DRF derived with respect to their coordinate systems (a) turning machine and (b) milling machine

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Fig. 9

Annotated figures accompanying the first stage of connecting rod process plan

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Fig. 10

Process data for extracting errors in machining the connecting rod

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Fig. 11

Process plan intent

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Fig. 12

Process plan steps

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Fig. 13

Example PCTF graph for part in Fig. 14

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Fig. 14

Cylinder cap assembly, where rotational constraint is important

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Fig. 15

Design GD&T for Cap

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Fig. 16

Manufacturing steps of machining the cap-cylinder assembly

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Fig. 19

Example of a T-map: (a) T-map, (b) M-map, and (c) T-map versus M-map

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Fig. 20

Cross-sections of the T-map and M-maps for comparison (a) cutting planes and cross sectioning and (b) 2D cross sections of the maps for comparison




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