Research Papers: Materials and Fabrication

Machining of Aircraft Titanium With Abrasive-Waterjets for Fatigue Critical Applications

[+] Author and Article Information
H.-T. Liu, Y. Hovanski, M. E. Dahl

Senior Scientist,  OMAX Corporation, Kent, Washington 98006Research Engineer Senior Technician, Pacific Northwest National Laboratory, Richland, Washington 99354

1Tilt-A-Jet is a registered trademark of OMAX Corporation (http://www.omax. com/accessories-tilt-a-jet.php).

Lasers are being used to cut thin titanium sheets. However, the effects of the induced heat-affected zone on the fatigue performance are not yet fully understood.

Attempt to measure residual compressive stress on the AWJ-cut titanium dogbone specimens using the x-ray diffraction facility at NIST Center for Neutron Research has yet to produce useful results.

J. Pressure Vessel Technol 134(1), 011405 (Dec 22, 2011) (10 pages) doi:10.1115/1.4004834 History: Received February 23, 2011; Revised May 17, 2011; Published December 22, 2011; Online December 22, 2011

Laboratory tests were conducted to determine the fatigue performance of abrasive-waterjet- (AWJ-) machined aircraft titanium. Dog-bone specimens machined with AWJs were prepared and tested with and without sanding and dry-grit blasting with Al2 O3 as the secondary processes. The secondary processes were applied to remove the visual appearance of AWJ-generated striations and to clean up the garnet embedment. The fatigue performance of AWJ-machined specimens was compared with baseline specimens machined with Computer Numerical Control (CNC) milling. Fatigue test results of the titanium specimens not only confirmed our previous findings in aluminum dog-bone specimens but also further enhanced the fatigue performance of the titanium. In addition, titanium is known to be difficult to cut, particularly for thick parts, however, AWJs cut the material 34% faster than stainless steel. AWJ cutting and dry-grit blasting are shown to be a preferred combination for processing aircraft titanium that is fatigue critical.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 11

Comparison of AWJ machinability of titanium and stainless steel

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Figure 1

Typical AWJ-cut dog-bone specimen

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Figure 2

AWJ system and three nozzle assemblies

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Figure 3

Hydraulic grip of dog-bone specimen

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Figure 4

(a) Striation patterns on faces of titanium dog-bone specimens: AQ180, AQ380, and AQ580 (Refer to Table 2 for the description of the code names of specimens). (b) Striation patterns on faces of titanium dog-bone specimens: AQ1220, AQ3220, and AQ5220. (c) Striation patterns on faces of titanium dog-bone specimens: AQ5320, AS63, MS63, and AQ5220G.

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Figure 5

Failure of specimens cut at Q1 and Q3 quality levels

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Figure 6

Failure of specimens cut at Q5 quality level

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Figure 7

Failure of AWJ-cut specimens after grit blasting

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Figure 8

Grit-blasted specimens that did not break at gage and at all after 2 M-cycles, respectively.

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Figure 9

Fatigue life versus Ra

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Figure 10

Fatigue life of AWJ-cut titanium specimens with 80-mesh garnet at Q1, Q3, and Q5 quality levels



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