best drill material for drilling hardened high strength steel?? 2

[dtwo]

We are using a manual drilling process for reworking items.The material being drilled is a hardened high strength steel. The bit sizes are 4.1mm and 6.7mm and made of carbide. We are using an air drill with no lubrication.

Currently we can drill only 1 or at the most 2 holes before the bit is dull. Any suggestions on drill materials and or coatings??

 

[unclesyd]

Carbide drills drilling hardened steel and hand drills isn't a good match.
My first step would be to introduce a drill press into the process.
Second I would get with one of the larger carbide drill manufacturers and present your problems, like materials, hardness, etc.

 

[dtwo]

Thanks for the response however a drill press just isn't feasible in this application due to lack of space and the multiple orientations needed.

 

[eromlignod]

How about a portable magnetic drill?

Don
Kansas City

 

[dtwo]

No just don't have the space and flat surface for a magnetic drill.

 

[bill1898]

You are in a lose/lose situation. The torque requirements for such an operation are way beyond manually operated air drills. You require a constant feed rate and rotational rpm. The drills are getting dull because when you drill manually you cannot maintain a constant feed rate, plus air is compressible which affects the speed of rotation. If you cannot provide the amount of constant power required to perform this operation you need to consider another process such as EDM.

 

[tomwalz]

Tungsten carbide gets dull because it wears down or because it micro-fractures. In a hand held operation the drill bit is wobbling and you are getting the severe micro-fracturing.

Tungsten carbide is actually tungsten carbide grains cemented in a binder. The binder is usually cobalt.

Use the finest grain, highest cobalt % drill you can find. If you can find drills with a little Vanadium and chrome in the binder as well that could help.

Otherwise I’d find a really good tool shop and get the drills reground regularly.

You might also check the drill design.

Tom


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

 

[unclesyd]

Exactly what are you trying to accomplish?

How did you make the holes during the first pass?

Can you give some hardness numbers?

 

[dtwo]

Hardness is between Rockwell 58 to 60 on C-scale. It's a rework process where the original self pierce rivet is drill out and a "pop" rivet is put in its place.

 

[BillPSU]

The answer to your original question is there is no better way to drill out a hardened piece.

Here is a suggestion, use a small hole saw / trepan tool slightly larger than the rivet. Cut the whole rivet out and replace the pop rivet with another fastener.

 

[adrianviorel]

Did you try a local heat treatment, for softening the material?

 

[unclesyd]

Here is speciality drill bit for hardened steel, but again it needs to be in a rigid drill press.

http://www.bamanufacturing.com/sp_series.html

 

[carbidedrills]

Hello,

A critical component is the edge prep of the drills you are using. In hardened materials you can apply a Conicity EMG edge prep and actually push the drill harder than before. Although a hand held air drill is not the ideal operating condition you can still do better in the tool life department. You must make sure that your feedrate exceeds the size of the edge prep, otherwise it will rub and basically work harden your material and dull the drill.

 

[MikeHalloran]

Try "hardsteel" drills.

Search for "black drill" on this page:

http://www.astralloy.com/print/rolman.asp

Mike Halloran
Pembroke Pines, FL, USA

 

[griffengm]

dtwo,
Have you considered driving the old rivet out?
I would first punch it with a cheap center punch and then a pin punch. Cheap center punch because the point will likely not be hard enough to damage the base metal but would get the rivet body moving. It should also form a bit of a cup to guide the pin punch. Similar set up used for splitting roller chain and chain saw chain. Cheap enough to try.

Griffy

 

[metman]

if space allows, make a simple drill jig to eliminate the wobble mentioned earlier and clamp the jig to your work. This will reduce the tendency to chip the edges of the bit(s).

 

[Edgeprep]

I work for Conicity Technologies and we put the edge prep on tools the way they are being used. On your drill we would put .003-.004 in the center and maybe .0015 to the corner leaving it sharp so there is no rubbinb. Both flutes will be exactly the same and it cuts around it's own center line making it cut straighter. We improve tool life and hole quality. Where the SFM is low we have small edge prep, where it is high SFM we put on larger edge prep. Were making the edge cut along the chip load. Visit

http://www.conicity.com

We can help,
Steve Roberts