Counter sinking in tooling

[ajack1]

Hi, I am not sure if this is the right forum for my question but I hope so. I have a new project that involves changing some old tooling and second operations into a progression tool. It is fairly low volume (in automotive terms) and cost is the main consideration.

One of the problems is the part is 6mm thick had has a full counter sunk hole in it, I have never tried counter sinking anything this thick in tooling and it will obviously displace a fair amount of metal. I have heard, sort of third hand that this can be done by pre piercing a “star” * and then simply forming it with a punch with a pilot on the front.

Has anyone come across this idea? Is it simply a question of piercing out 50% of the metal that will get displaced? Do you get flashing (burr) from the pilot? I could of course knock up some development tooling and experiment with different piercing, but would like to know the idea is sound before doing this as we may not win the work anyway, but if we do this operation will have to be done in the tool, a bit chicken and egg really.

Thanks in advance.

 

[JDana]

Although I can't really help, what material are you working with?

 

[ajack1]

Not really sure and I am holiday at the moment so I cannot find out, but I think it is CR4, putting the indent in is not an issue, if that is what you are thinking. What are the problems as I see them is keeping the surface flat within 0.2 mm the hole tolerance +0.2/ -0.0 (minor diameter) and the fact that they do not want any major burrs, although what a major burr is open to debate I guess.

Hopefully when I return from holiday some kind person will have put me on the right track.