Hi Carbide Bob:
I'm really curious why you are endorsing bead blasting carbide that's been wire EDM cut.
How do you believe it would improve the performance of carbide punches and die sections?
After all they're cutting tools just like end mills, so the edge geometry matters and I've had the same experience that JTB3 has had about the bad effects of abrasive blasting on the sharpness of the punch edges.
Wire cut parts are already inferior to ground ones due to cobalt depletion at the edges; bead blasting them only makes this worse and forces a face grind to restore the sharpness of the punch and die edges after the blasting.
If you believe that face grind is a necessary part of creating excellent punches and dies, I'd be prepared to do it in order to make the best possible tools, but I can't yet see what the benefit is.
I'm arguing it cannot be to remove the recast; the wire finishing passes do that.
One of the things about wirecutting carbide that's not all that widely known except by carbide WEDM specialists is that the wirecutting strategy is supremely important in a way that's simply not true for wirecutting steel.
The underlying reason is that sintered carbide is so full of stress that a poor die design or poor cutting strategy carries a big risk of cracking the carbide, and we're not talking just microcracks in the recast layer.
JTB3 alludes to this when he talks about 5 to 8 wire passes; the first cuts are typically strategic stress relief cuts, the intermediate cuts block out the form and the final ones create precision and finish and remove the microcracks and macro cracks created from the roughing.
The corollary benefit of all these passes is that the recast layer is minimized, because the finish passes have so little spark energy that virtually no new recast is formed and all the roughing recast is cut away during semifinishing.
So blasting the carbide doesn't remove undesirable recast but only degrades the punch and die corners, and if done with enough enthusiasm, will dig out tungsten grains from the surface and ruin the punch surface geometry as JTB3 has pointed out.
I can't see any upside to bead blasting; but you have huge experience with carbide and I'd love to know your reasoning.
So what am I missing??
Cheers
Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com
EDIT: Looks like you type faster than I do.
OK your comments are well reasoned and fair, but a point that sticks out to me is that you are referring to as sintered or ground surfaces when you make the observation that a bead blast at 40 PSI will not change the surface of the carbide.
The corollary to this as you also correctly comment is that the carbide left on the surface of a wire EDM cut punch is not "good carbide" and you are right; however we have to accept that reality whenever we choose to wire cut a punch with a water dielectric.
Best possible punches have ground geometry...no argument there, and the next best thing is probably oil dielectric in the wire machine, but the geometry even of a typical wire cut punch is still very important and my experience is that it doesn't do well when bead blasted.
So which way to compromise??
Cheers
MC