I have drilled holes using EDM with rotary electrodes and then took cross section of these holes. I want to investigate the heat affected zone (HAZ) in EDM process.
I am measuring the microhardness values along the edge of in Lateral direction. I observed that microharness value increased as we move away from the edge of the workpiece. Is this observation is correct? what would be the reasons behind the decrease of microhardess value near to hole edge and increase ways from the edge of the holes?
please give your valuable suggestions?
It depends the type of material that you cut. For example, if the material is an steel with medium or high percentaje of carbon, the steel would be temper, because the dielectric is water and make as temper liquid.
The first thing to consider is whether a "white layer" has formed, because this layer is characterized by a high hardness. In addition, there may be a number of cavities between the white layer and the HAZ, so that the white layer breaks quickly when stressed. To prevent the white layer from being destroyed or lost during preparation of the sample, the surface should be fixed with a thin layer of silver or nickel.
The hard maximum is very rarely directly on the surface, which depends on which workpiece material was used and which dielectric was used.
Hi
I agree with Dr. Schulze. Please repeat your tests for the hardness in another places. Check the method you used to prepare the surface for the hardness test. Good Luck
Hi,
I am also agree with with Dr. Schulze, in EDM, decrease in hardness is basically depends upon the material combination of electrode and workpiece material and also depend upon the formation of white layer whether it is existing or not, the presence of whitelayer leads to an increase hardness of the machined surface.
Hello!
You may already be aware, but the hardness decrease may just be due to the strain field being relieved by the presence of an open surface. Make sure you're 3 diameters of the indent away from the edge and from other indents; this distance can be reduced by using smaller loads.
Dr. Schulze is right about white layer, but this relates to steels primarily; different materials may not reveal damage the same way. Many cuts including rough cuts I've done with a Mitzubishi FA20S have not shown apparent microstructural damage right up to the very edge.
I agree with Dr. Schulze. Please repeat your tests for the hardness in another places. Check the method you used to prepare the surface for the hardness test.
Kindly go through the following paper. It may be helpful to you
Effect of tool electrode resolidification on surface hardness in electrical discharge machining
T Muthuramalingam, B Mohan, A Jothilingam
Materials and Manufacturing Processes 29 (11-12), 1374-138
Muthuramalingam
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