Tapping in hardened Material

[machinist77]

Can anyone help me? I need ti drill and tap a M12x1.75 into a steel block hardened to appox 60 rc. What I would like to know is what sfm to use to figure my speeds and feeds right. Any help I would be most grateful for.
Thanks
machinist77

[DareBee]

I use my EDM tapping machine - takes about 1/2 hour.
I've never seen a tap that will cut 60Rc.

[kalmah]

Tapping hardened tool steel is very expensive and problematic but it's possible. The tool life duration is very low (2-10 holes). If you want immediatly a solution, OSG produce taps for hardened tool steel.
http://www.osgtool.com/product_detail.asp?id=1105101208

Warning !!! The tool life is very low and the tapping torque is enormous !!! Most of spindle aren't able to "give" the asked torque. I esteem the torque more than 30Nm

Use whirling tool !!! The time for one hole is approximatly 1minute, but the tool life duration is 70holes.

I have an application, the parameters are

- M6 hole, depth 7mm
- Material: Hardened tool steel DIN X155CrVMo12-1 at 60 HRC !!!
If you are intersted, send me a private message. I work for a swiss cutting tool company, which produces whirling tool, but the distribution for USA isn't very good.

And a rules: The more the material is difficult to cut, the more the solution of whirling tool is adapted. WIth whirling tool it's possible to thread HSS

[NC Cams]

We tried to tap some case hardened 8620 that was at 60-62.

Result: two broken Emuge hard tapping taps and a huge waste of time and effort.

Want a solution that works? Simply find someone with an EDM and have them do it.

Even at $25/hole, you're going to get of cheaper than what it will cost to find and break "hard tapping" taps.

Don't waste your time and money trying to put a tap thru it!!!!!!!!!!!!!!!!!!!

[kalmah]

Sorry it's on french, but here is an application of whirling tool.
http://www.dixipolytool.ch/fileadmin..._f_02%2007.pdf

It's quicker than EDM and if the tool breaks, there is no waste, except the cutting tool.

[RICHARD ZASTROW]

Unfortunately, that example is 32Rc, machinist77 is blessed with 60Rc. I still vote for EDM. If thread milling is what is required, try www.hornusa.com

[kalmah]

Originally Posted by RICHARD ZASTROW Unfortunately, that example is 32Rc, machinist77 is blessed with 60Rc. I still vote for EDM. If thread milling is what is required, try www.hornusa.com

The translation:

For this application on french with 32 HRC material.

Tool life with tap: 7 holes
Tool life with whirling tool: >>70 holes without coating !!!

I've done 70holes with 60HRC material.

FOr the tool path

1) YOu aproach in the center of hole (X0, Y0), but the Z is Z + your thread pitch
2) You go down several 3D circular interpolation (Circle X,Y,Z)from the up to the down, where the radius is the hole diameter and height is the thread pitch. Of course you need to be in G42 mode.
3) You retract the tool

It's like a thread mill tool path, but it's from the up to the down and it's several 3D circular interpolation.
The advantage compared to a thread mill is the cutting force.
FOr thread mill, you have 10 profiles which machine and it produce high tool deflection. FOr whirling tool, there is only two profiles which machine and there is low deflection, low cutting forces => Long tool life.

Thread mill isn't possible in hardened tool steel because there is too much deflection and cutting force. With whirling tool the tool deflection and cutting force are very low.

I hope that I can take pictures of my parts

[RICHARD ZASTROW]

kalmah, It's just a different description of what is referred to in the phhorn site as a "thread mill". To me "thread whirling" is performed by a machine that has cutters on the ID of a circular cutter body. The circular tool/body is rotating rapidly (referred to as "whirling") and moved along on a carriage similar to an engine lathe. The carriage has a feed rate that is the thread lead of the threaded part being machined. These machines are often used to machine feed screws for plastic injection molding machines, feed augers etc.
I will try to find a machine on the net and add the site later.

www.schrillo.com/whatiswhirling.asp shows what I was speaking of. While searching this site, I found others that also refer to intenal threading as whirling. So in this case both can be called whirling I suppose.

[kalmah]

Most of whirling tool are used like your links describe.

But you can use a whirling tool like a thread mill. The tool path is several 3D circular interpolation from the up to the down of hole.

I know that the use of whirling tool like a thread isn't common, but it works whatever the material.

[DareBee]

Like NC said (about tapping)
"Result: two broken Emuge hard tapping taps and a huge waste of time and effort"
Like I said
"I've never seen a tap that will cut 60Rc."
My key word is "seen". I've been told they will, I've read the will, I've bought them and broke them all without getting a single finished hole.

I can easily see that thread "whirling" will do the job.

I will still be EDM tapping mine.

[davereagan]

Hello,
Are you dealing with pre existing parts that are hard and cannot be practically annealed? Can you possibly tap the hole before hardening? I know the answers are probably no, it cannot be pre-tapped or annealed, but I have to ask because it would be exponentially easier, even at Rc40.

Dave



quote=machinist77;288125]Can anyone help me? I need ti drill and tap a M12x1.75 into a steel block hardened to appox 60 rc. What I would like to know is what sfm to use to figure my speeds and feeds right. Any help I would be most grateful for.
Thanks
machinist77[/quote]

[stustev]

I would have to agree with DareBee. I have never seen it successfully done. I think the speeds and feeds and coolant or no coolant will make no difference. When you are done and the tap is broken in the hole EDM will be the answer to remove the broken tap. When the EDM is finished removing the tap you can have them tap the hole for you. They will have a little, but not much, difficulty matching the threads to the scratches you have in the hole. To make it easier for them why don't you just send them the parts without the broken taps in them.