clearing small blind holes of silicon metal

[M. Roberts]

Good morning everyone! I have some smallish, cylindrical parts...1" long x 0.9" diameter. They have a series of blind holes, 2.5mm and 3.0mm diameter (not overly critical) x 0.850" deep. The base material is a diamond reinforced ceramic composite....ridiculously hard and tough stuff. In some parts, there is residual silicon metal in the holes; I am looking for a fast economical way to remove the silicon. My thoughts thus far: hole pop EDM...due to the lack of conductivity of the base material, not the best option. Second; use a drill press and a PCD tool....because the silicon isn't flat or even, it wants to grab and break the tool. Third, I thought of a small diamond grinding nib...it works, but it is slow. Lastly, I thought of something like an air gun with a needle tip, and somehow introduce an abrasive media...just like a waterjet machine, but hand held...or something like a coolant inducer for the old style core drills....does anyone have any ideas?
Thanks,
Mark

 

[Milland]

If the remnant silicon is from a preform that the diamond composite was cast into prior to firing, then perhaps use a different core material? I'd look into carbon for something friable, or tungsten or molybdenum for something that can be pulled out (if given a slight taper) after firing.

Presumably the firing was done in a vacuum or inert atmosphere to avoid oxidation of the diamond?

If the substition idea can't work (gotta use what you have), then my standby is small stainless tubes used as drill bits, with a diamond slurry brushed in for the cutting action. I've drilled angled holes in sapphire this way. Still tedious, but it works...

Sounds like an interesting project, anything you can tell us about?

 

[memphisjed]

Acid?

 

[Milland]

Acid?

No thanks, had a bad trip once...

That could work, but you'd need to get some good PPE and check into legal/safe disposal. Not sure just buffering it to death would be enough.

 

[M. Roberts]

Milland, for all of the off the wall things that I have inquired about, you generally have a good understanding as to what I'm dealing with. The holes are cast in the preform, and then the part goes thru the firing process...to keep it simple. I do not know the rhyme or reason why/why not they fill holes in some parts. I did see online that HCL acid will eat silicon metal; but the hazards would most likely prohibit that...

 

[jim rozen]

I believe you would have to use HF as the etch for this material. Proably best to avoid.

 

[Bill D]

Pure silicon is not a metal. What are you actually dealing with/. A metaloid of some sort or pure silicon?

 

[jim rozen]

"...not a metal..."

Depends on how heavily its doped.

 

[Milland]

Milland, for all of the off the wall things that I have inquired about, you generally have a good understanding as to what I'm dealing with. The holes are cast in the preform, and then the part goes thru the firing process...to keep it simple. I do not know the rhyme or reason why/why not they fill holes in some parts. I did see online that HCL acid will eat silicon metal; but the hazards would most likely prohibit that...

Hah! I blame the education I got from years of working at universities and R&D companies. It gave me a pretty broad understanding of lots of processes, so I've been useful in aerospace to medical to wafer fab. Still not rich, maybe I should have gone into finance instead...

 

[M. Roberts]

Interesting...so, I was given some parts to attempt to EDM hole pop out the residual silicon metal from the blind holes (2.5mm x 19.5mm D). Mounted the part in a vise, and if I bring the electrode down and touch the part, the machine beeps to indicate that it is grounded, but yet when I go to actually burn the hole, there is no progress. I am running 2mm copper, multi channel pipe, Di water....any thoughts?

 

[jim rozen]

Possible the resistivity of the silicon is low enough to satisfy the sensor on the EDM machine, but too high to allow enough current to flow to actually cut.