# Contour Method: Making the Cut Using Wire EDM

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Residual Stress
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 Make Cut

The ideal method for making the cut would satisfy the following:
• Make a very straight cut
• Not remove any further material from already cut surfaces
• Not put in any stresses

 So we use wire EDM (Electric Discharge Machining) Uses an electrically charged wire A spark jumps from the wire to the workpiece Material is locally vaporized The wire never contacts the part! Puts in virtually no stress if cut in "skim cut" mode drawing: Charmilles

For a discussion of the assumption about the cut, see M. B. Prime and A. L. Kastengren, "The Contour Method Cutting Assumption: Error Minimization and Correction" Proceedings of the SEM Annual Conference & Exposition on Experimental and Applied Mechanics Indianapolis, Indiana USA, Society for Experimental Mechanics Inc., June 7 - 9, 2010, paper # 507 (LA-UR-10-1605).

For more on cutting errors and how to select an EDM machine, see P John Bouchard et al., "Making the Cut for the Contour Method,"Proc. of the 15th Int'l Conf on Experimental Mechanics, Paper 2960, Porto, Portugal, 22-27 July 2012

For some good information on making a good cut, see Hosseinzadeh, F., Ledgard, P., and Bouchard, P., 2012, "Controlling the Cut in Contour Residual Stress Measurements of Electron Beam Welded Ti-6Al-4V Alloy Plates," Experimental Mechanics.

## Self-restraint, also called embedded cut

Recent work has shown great promise for self-restraint to be a better way to hold the part during a cut.

 Figure taken from a good discussion of self-restraint.: Hosseinzadeh, Foroogh; Kowal, Jan; Bouchard, Peter John: 'Towards good practice guidelines for the contour method of residual stress measurement', The Journal of Engineering, 2014, 2014, (8), p. 453-468. Open Access!. Originally proposed in: Traore, Yeli, Bouchard, P. John, Francis, John, and Hosseinzadeh, Foroogh. "A Novel Cutting Strategy for Reducing Plasticity Induced Errors in Residual Stress Measurements Made With the Contour Method." Proceedings of the ASME 2011 Pressure Vessels and Piping Conference. Volume 6: Materials and Fabrication, Parts A and B. Baltimore, Maryland, USA. July 17–21, 2011. pp. 1201-1212. ASME. https://doi.org/10.1115/PVP2011-57509

## Pictures of EDM cutting for contour measurements:

See this paper for a robust technqiue for clamping: Hacini, L., Van Lê, N., and Bocher, P., 2009, "Evaluation of Residual Stresses Induced by Robotized Hammer Peening by the Contour Method," Experimental Mechanics, 49(6), 775-783.

It is important to carefully fixture the part during cutting to keep the cut plane from moving as stresses relax. So here are some samples of clamping the part:

A newly designed fixture that does a very nice job of holding the part. The part shown here is a Ti-6Al-4V friction stir weld (FSW).

 This is the clamping and cut for a large aluminum forging, see forging results page. This is the clamping for the weld plate (results page). This plate has already been cut, you can see the cut running horizontally in the picture. This is the clamping for a friction stir weld between 7050 and 2024 aluminum (see results page). This is the clamping for a piece of British rail. The cut went from front to back in this picture. The shiny regions is where rust was cleaned away to improve the cutting. See rail page.

 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA contact: Mike Prime at prime@lanl.gov | Copyright & Disclaimer U.S. patent 6,470,756 | Last Modified: January 24, 2020