[Wsiel]

The parts are required to be HT. before machining to Hrc 46 13-8ph ss. then broach is .25 by .26 deep . Both slater tool and somma tool tell me trying to broach material this hard won't work but, some one some how has been making these parts for the customer I just can't find out how!

Any suggestions would be greatly appreciated.

[keebler303]

broaching before HT?

EDM?

[Wsiel]

Customer wants it done after HT. I don't think EDM is an option because I have to make 600+ parts.

[keebler303]

Customer doesn't always know what is best. Maybe that is why the old guy isn't making them anymore?

What shape is it and what is the purpose of the hole?

[Wsiel]

It is a stud bolt with a ground diameter for a bearing with a blind hole .375 max. depth. .
Part is aerospace not commercial.

[txdrillmillturn]

I broached some hardened 410sst and titanium 6al4v used slater tool rotary broach on Haas SL-10.
HSS broaches worked the best. cobalt too brittle and chipped. I drilled hole on high side of recommendation and turned a .031 undercut to allow the chip to roll over easily.
I put an M0 in program to blow out hole prior to broaching and applied a dab of Blaser Swisslube tap honey on broach. Run around 10SFM F.002

[Wsiel]

Is that .031 wide undercut or .031 deep?


Thanks for the info , how many parts per broach were you getting?

[florida]

Broaching stainless is challenging and not always successful. Since your parts are heat treated, this makes it even more difficult. However, like you said, someone else is doing it, so I believe with a little patience you'll get it. You may need to try and make some concessions though:
1. Chamfer.
Is your chamfer all the way out to the sharp corner? This is critical to getting the chips to curl properly.
2. Oversize pilot hole.
For hexagons, we recommend 3% oversize. Our 1/4" hex broach is .2525" across the flats. 3% oversize is .260". But any increase will help reduce chip size and increase tool life. The G drill is .261", or a 17/64 is .2656" if you can get away with it (or more!).
3. Room for chips.
Make sure the chips aren't binding up and clogging the hole, and that the bottom is deep enough to allow them to curl and not bottom out.
4. Broach material.
We have the best success with PM M-4 broach material in stainless. If available, you can also get one with a coating. We usually stock both. PM T-15 may also work, it is harder and has high tungsten. But I agree, a high cobalt steel like M-42 is too brittle.
5. Feed rate.
It is critical to reduce the feed for stainless. We recommend reducing the feed to .001 IPR from our standard .002-.003.
6. Speed
Slow the speed to 50-100 RPM until the broach is engaged about .005-.010" deep. This will eliminate skidding on the chamfer surface, allow the broach to dig in and start curling the chip, and improve tool life.
7. Alignment.
If you're using and old screw machine holder, try to adjust the center as close as possible. (Not as applicable with a newer adjustment free model)

I wouldn't expect good tool life, but I hope that helps. Let us know how it goes.
[disclaimer - Product Engineer at Rotary Broach Manufacturer Polygon Solutions]

[txdrillmillturn]

.031 wide x .031 deep

[txdrillmillturn]

The hardened 410sst was a small order of around 20 parts used 1 broach. the 6al4v job was a bigger order of 100pc used 2 broaches.
Like Florida said make sure you have a good 45 degree chamfer to help the broach engage better.
I never used any PM broaches but have used PM drills in inconel,drilled lots of holes at 20sfm they worked great.

[Wsiel]

Would TiALN coating on the broaches improve tool life?

[florida]

TiAlN does offer some advantages. Our most popular rotary broach coating is TiN, followed by TiAlN and TiCN. You can see the options on a 1/4" hex broach online. The problem with choosing a broach coating is that these highly technical coating were designed for high heat applications, like drilling. There is a minimal amount of heat generated during wobble broaching. However, the coating can help strengthen the tip of the broach, and improve lubricity over HSS. TiAlN is amazing, it will actually reform itself on the tool in some applications. I would test one with, and one without to see if its worth the cost. Delivery is usually an extra week for coating.

[Wsiel]

I've not only been able to get the job running but, so far I've broached one hundred plus with the same tool!

Thanks for all your replies , it was a big help!

[florida]

Great news!

[Machineit]

May sound crazy, but sometimes machining a hardened steel is better than soft. I have done quite a bit with 4140 prehard and some other steels after hardening. I generally find that they machine very sweet and consistent. I think is because they are molecularly consistent because of the heat treating. You treat it with respect and it treats you fairly.

Glad it worked for you and keep it going.

Mike

[txdrillmillturn]

Awesome, glad it worked out for you.
Bet it gives you lots of confidence now in taking those jobs no one else wants in their shops.