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TECHNICAL PAPERS

Experimental Investigation of Thread Formation in Form Tapping

[+] Author and Article Information
Curtis Warrington, Shiv Kapoor, Richard DeVor

Department of Mechanical and Industrial Engineering,  University of Illinois at Urbana-Champaign, Urbana, IL 61801-2906

J. Manuf. Sci. Eng 127(4), 829-836 (Jan 12, 2005) (8 pages) doi:10.1115/1.1951784 History: Received January 16, 2004; Revised January 12, 2005

In form tapping, the generation of unfinished thread forms results in the appearance of split crests. An experimental technique is developed to study the nature of split crest formation. Custom tools are modeled after tap tooth geometry to perform the forming process in a vertical milling machine. Single-tooth experiments replicate the initial deformation stages and determine the tap geometry and tapping process parameters that significantly affect ridge size and shape. This method is then expanded to consider two axially consecutive tap teeth and the interaction of consecutive ridges to create the final thread form. It is found that certain tap geometrical characteristics are important to the final thread form and, therefore, determine the size and shape of the resulting split crest.

Copyright © 2005 by American Society of Mechanical Engineers
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References

Figures

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Figure 5

Custom tool made from tap blank

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Figure 6

Experimental setup

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Figure 7

Four traces showing variation along scratch (Y) direction

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Figure 8

Progression of ridge formation

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Figure 9

Comparison of two ridge shapes

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Figure 10

Illustration of elastic recovery

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Figure 11

Two-factor interaction graph between α1 and W

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Figure 12

Ridge shapes comparisons when varying a single variable

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Figure 13

The effect of W on the direction of elastic recovery

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Figure 14

Tool with axially consecutive teeth

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Figure 15

Progression of ridge and split crest formation, 7–13 scratches (up to 65% thread)

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Figure 16

Split crest formation from commercially available form tap (from Fromentin (1))

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Figure 17

Finished thread form at 65% thread height

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Figure 18

Full thread form showing void

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Figure 1

Thread profiles showing the formation of split crests

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Figure 2

Cross-section of a row of tap teeth showing split crest formation (adapted from Chowdhary (6))

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Figure 3

Example of varying tap tooth perimeter geometry

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Figure 4

Parameterized geometry model

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