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TECHNICAL PAPERS

Investigating Machining Impact on Fatigue Variance: A Machining Quality Perspective

[+] Author and Article Information
Xiaoping Yang

 Cummins Inc., 1900 McKinley Avenue, Mail Code 50224, Columbus, IN 47201

C. Richard Liu

School of Industrial Engineering, Purdue University, 1287 Grissom Hall, West Lafayette, IN 47907-1287

J. Manuf. Sci. Eng 127(3), 492-502 (Dec 21, 2004) (11 pages) doi:10.1115/1.1947206 History: Received March 12, 2003; Revised December 21, 2004

Fatigue life of nominally identical structures under nominally identical loading conditions can scatter widely. This study has investigated the impact of machining processes on such scatters. After Ti 6Al-4V samples were surface ground and face turned, they were subject to constant amplitude four-point bending fatigue tests under room temperature. The best-case scenario of process capability ratios of fatigue for these samples were evaluated with assumed tolerances of fatigue life. Based on these ratios, the numbers of nonconforming parts were estimated. Under the machining conditions from the Machining Data Handbook (Machining Data Center, Cincinnati, 1980), up to 39% of samples due to one process are expected to be nonconforming, whereas only up to 0.6% of samples due to the other process are expected to be nonconforming. The ramifications in terms of cost for machining quality control due to the different capability ratios have been discussed. The current findings indicate an urgent need to further the study of this issue in a scientific manner.

Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Example of the partition of fatigue life variance (after (6))

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Figure 2

Second set sample dimensions for fatigue test (not drawn to scale)

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Figure 3

I and MR chart for fatigue life of samples face turned by CNGG inserts after transformation

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Figure 4

Process capability analysis for fatigue life of the first set of face-turned samples

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Figure 5

Process capability analysis for fatigue life of the first set of ground samples

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Figure 6

Process capability analysis for fatigue life of the second set of samples face turned by PCBN inserts

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Figure 7

Process capability analysis for fatigue life of the second set of ground samples

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Figure 8

Process capability analysis for fatigue life of the second set of ground samples with residual stress relief

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Figure 9

Machining processes versus expected nonconforming parts per million with zero process average shift

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Figure 10

Process capability study for fatigue life of the first set of face-turned samples (*Sixpack refers to the six graphs in this figure)

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Figure 11

Process capability study for fatigue life of the first set of ground samples

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Figure 12

Process capability study for fatigue life of the second set of samples face turned by PCBN inserts

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Figure 13

Process capability study for fatigue life of the second set of ground samples

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Figure 14

Process capability study for fatigue life of second set of ground samples with residual stress relief

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Figure 15

Machining processes versus expected nonconforming parts per million of the transformed fatigue data with zero process average shift

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