Modeling Machining Geometric Variation in a N-2-1 Fixturing Scheme

[+] Author and Article Information
Weiping Zhong1

Department of Mechanical Engineering, The University of Michigan, Ann Arbor, MI 48109-2125

S. Jack Hu

Department of Mechanical Engineering, The University of Michigan, Ann Arbor, MI 48109-2125


Now with Bayer HealthCare, Elkhart, IN 46515.

J. Manuf. Sci. Eng 128(1), 213-219 (Apr 08, 2005) (7 pages) doi:10.1115/1.2114927 History: Received October 16, 2003; Revised April 08, 2005

Fixtures are used to locate and constrain workpieces in machining. Fixture properties, such as accuracy and locator layout schemes, directly affect the resultant geometric variation on the machined workpiece surfaces. N-2-1 fixturing schemes (N>3) are often used for large or compliant workpieces in machining. However, the impact of N-2-1 fixturing on product geometric variation is not well understood because of the uncertainty of contact under the overconstraint condition. This paper presents a modeling methodology to study the machining geometric variation in a 4-2-1 fixturing scheme. The model integrates the fixture-workpiece interactions resulted from the rigid-body variation in fixtures, workpieces, and machine tools, and the static deformation under external forces. The uncertainty of the fixture-workpiece contact condition due to the 4-2-1 constraint condition is modeled using the minimum potential energy theory. A numerical example of face milling is presented to demonstrate the methodology.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

A 3-2-1 fixturing scheme

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Figure 2

Typical 4-2-1 fixturing system

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Figure 3

Contact modes in a 4-2-1 fixturing scheme

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Figure 4

Representation of the workpiece

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Figure 5

Representation of the machining operation

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Figure 6

Representation of the fixturing error

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Figure 7

Determination of the locator-workpiece contact pair

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Figure 8

Sample workpiece

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Figure 9

Results of the 4-2-1 fixturing



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