Machining Void in Blind hole
Machining Void in Blind hole
(OP)
Hi Guys,
I have a product which is a honeycomb shape with lots of round blind holes. The quality issue that I am facing right now is that I am seeing void (some can be as big as 5mm long and 2mm wide) on the vertical side wall of a random blind hole.
I did a search and found that to reduce such defect, it is recommended to
1) Apply cutting fluids by drip, mist or through the tool to minimize the machine fluids present. Avoid flood application. Use air or vacuum to remove chips.
2) Use low viscosity, low surface tension fluids that will drain easily.
Questions:
1) Is this defect (void in blind hole) inherent in the blind hole process?
2) Should I drill a pilot hole first before the blind hole process in order to eliminate these void?
Thanks.
I have a product which is a honeycomb shape with lots of round blind holes. The quality issue that I am facing right now is that I am seeing void (some can be as big as 5mm long and 2mm wide) on the vertical side wall of a random blind hole.
I did a search and found that to reduce such defect, it is recommended to
1) Apply cutting fluids by drip, mist or through the tool to minimize the machine fluids present. Avoid flood application. Use air or vacuum to remove chips.
2) Use low viscosity, low surface tension fluids that will drain easily.
Questions:
1) Is this defect (void in blind hole) inherent in the blind hole process?
2) Should I drill a pilot hole first before the blind hole process in order to eliminate these void?
Thanks.





RE: Machining Void in Blind hole
What is the L/D.
What is the material?
Number of holes?
RE: Machining Void in Blind hole
RE: Machining Void in Blind hole
RE: Machining Void in Blind hole
Thanks for the quick reply. Here are more details:
1) What are some sizes? The random void size can varies from 5mmL x 2~3mm W and it is usually shape like a snake. This appears on the vertical wall of the blind hole. It looks like a casting porosity but it is not.
2) What is the L/D. Blind hole Dia 4.5mm, depth 7.89mm
3) What is the material? Aluminum 6061-T651
4) Number of holes? 96 holes.
5) Is it a casting? No, it is a full machining from a standard block say 120mm x 75mm x 10mm.
6) How did the void appear originally. Like bobm3 mentioned is it a casting? Else difficult to get a void in a rolled plate. According to my supplier, the chip got spot welded onto the cutter and caused the void. Is this true?
Need your expertise. Thanks.
Cheers.
RE: Machining Void in Blind hole
I have to ask; how did this become your problem?
If you're buying the machined part from a supplier, why is it not the supplier's problem?
Mike Halloran
Pembroke Pines, FL, USA
RE: Machining Void in Blind hole
Questions:
1)Other than the r.p.m. of cutter and the coolant, does the feed rate of the cutter play an important part?
2) Do you think a pilot blind hole (slightly smaller than the actual spec called out) prior to the actual hole size will give considerable leverage in reducing the void in the blind hole.
Regards
RE: Machining Void in Blind hole
RE: Machining Void in Blind hole
Another approach might be no more than changing you cutting fluid for the current setup to something specific like the Tap Magic product for Al or any other fluid specific for Al.
htt
http://www.tapmagic.com/TMaluminum.htm
RE: Machining Void in Blind hole
RE: Machining Void in Blind hole
Try running it on a machine that can apply high pressure coolant through the middle of the (special) drill. Or try a secondary reaming operation or secondary cleanup with an end mill.
RE: Machining Void in Blind hole
A.R. "Andy" Nelson
Engineering Consultant
anelson@arnengineering.com
RE: Machining Void in Blind hole
The galling is the reason that some operations use highly evaporative coolants, such as alcohol. We used Trichloroethylene + oil for years until we found out that we could have an explosion.
As stated in my previous post there are different approaches for getting the chips out by using drill bit geometry in drilling Al. A lot of manufacturers use a shallower point with high helix flutes while people like Guhring uses parabolic flutes with sharper point. There are three and four flute drills. Most Al drill bits don't really bit into the metal as they tend to shave if off as on a lathe. Speeds and feeds are all over the map but one should go with the manufacturers recommendation.
Another point often missed when drilling Al is the setup must be rigided.
RE: Machining Void in Blind hole