Broach Tool Life

[NHATLEY6]

Hello,

We are creating a spline with a pull through broach and a tolerence of .001 in spinodal bronze. The broach will do the job for around 20 to 30 parts then it out of range. My main question is should we be completely submerging the part and tool or is cutting oil flow over the top of the part and tool acceptable? We have went to a 2 broach approach so a rough pass and finish pass it it still wears the tools out. We tried a TIN coat and tool life was reduced further strangely.We varied the amount taken out by each tooth and it didnt seem to help. From our experience spinodal bronze is very abrasive and machines better when larger cuts are taken. Any advice is greatly apprieciated.


Nate

 

[MikeHalloran]

A gun barrel was rifled by a series of 32 pull broaches.
The tooling engineers couldn't figure out why the last one in the set wore out twice as fast as any other one, even though they calculated and balanced the chip loads very carefully.

The engineers didn't actually watch the process long enough to discover what everyone else knew; in order to give themselves a little extra slack time, the machinists were using the broach sets in halves, i.e. making one barrel with just the odd numbered broaches, then the next with just the even numbered broaches. ... but of course they had to pull the last broach through every barrel. The doubled chip thickness didn't seriously affect the other broaches, but the doubled chip volume did affect that last broach.

Sorry, that was kind of a tangent, but it serves to illustrate that broaches are consumables, not true tools.

Still, 30 passes seems a relatively small number of passes to go out of size.

It's probably time to do a single stroke, and capture and measure and photograph all the chips produced, and correlate the measurements of each chip to the measurements of the tooth that produced it. In that way, you should be able to figure out which teeth are working about right, and which teeth could stand a little adjustment. Your broach supplier might wish to participate in this process a few times, so he can make some detail refinements to his process.

I'm not convinced that total submergence is absolutely necessary, but broaches seem to like having a lot of lubricant/coolant around. It might be enough to just be sure the coolant gets to where the heat is generated without fail.







Mike Halloran
Pembroke Pines, FL, USA

 

[racookpe1978]

Is the part, or the broach, the sp. bronze? Seems like a bronze part would have very soft chips .... unless they were "too soft" (too big a chip?) and were plugging up the relief areas between teeth.

How long is the material (through what thickness are you pulling the broach)?

 

[MikeHalloran]

Nickel Tin Bronze is not the nice soft stuff you find in plain bearings and such.

But it is a good idea to check that the gullets are big enough and smooth enough.

I sure hope that the broach supplier knows exactly what the broach is cutting, and is working with you on the problem.





Mike Halloran
Pembroke Pines, FL, USA

 

[NHATLEY6]

Thank you guys for your reply,

The broach is made from PM4 about a 64-66 Rockwell C. The part is made form spinodal bronze AMS 4596 with a min 30 Rockwell c. Its fairly hard and its very abrasive. The spline we are pulling the broach through is about an inch in length. There is not much "meat" around the spline and we think it could be "breathing" or in other words expanding. We are discovering the material likes bigger cuts then smaller but its just wearing the broach slap out. The presedint of the broach company was in here trying to figure it out so they are trying.

 

[racookpe1978]

Odd.

So the part is somewhat flexible (not much meat around the hole, as you put it.)
You pull the broach, it pushes out the metal around the hole, that metal moves and the "hole" artificially gets bigger (rather than being cut), and then the "hole" would flex back in when the broach cutter passes. I can see this happening - but only if the part were thin, or the distance between teeth a substantial portion of the part thickness.

But at 1 inch thick, the next tooth of the broach would certainly engage the walls of the hole before the first moves so far that the part moves back... How much is the broach cutting between each row of teeth?

 

[BillPSU]

I checked some of the data on this material and your broaching speed may be too fast for this material. You are cutting a hardened tough material with a hardened steel tool. Drilling this material is hard on HSS twist drills. You are probably using a carbide drill to make the hole in this part and had to slow the tool down.

I found no machinablility data on this material but I did see that making this material correctly requires special manufacturing process. Hopefully your supplier of the material is has good uniformity and microstructure of this material. Your company needs to have good control good control of the heat treatment process.

Bill

 

[TVP]

Some thoughts:

[li]These spindoally hardened copper alloys are very strong and ductile, so they will tend to adhere to the tool. Adhesive wear is a different wear mechanism than abrasive wear, so you need to especially understand (a) lubrication and (b) tool coating.[/li]

[li]The slow cutting speed during broaching further exacerbates adhesive wear.[/li]

[li]What lubricant are you using? Is it specifically formualted for copper based alloys?[/li]

[li]TiN is not the optimal tool coating for non-ferrous metals that tend to adhere, e.g. Cu and Al. Oerlikon Balzers recommends either their Balinit Hard Carbon, which is a monolayer coating based on tetrahesral amorphous carbon (ta-C), or Balinit Triton which is a diamond like coating, DLC (a-C:H) Richter Precision calls these Titankote C10 and C11 respectively.[/li]

http://coating-guide.balzers.com/we...Zn&auswahlStahl=mg&verglnorm=WerkNr&p1=1&p2=1

http://www.richterprecision.com/dlc-coatings.html

 

[NHATLEY6]

I do not know the specifics of the broach, the person who was working here before did and the broach company will not release a drawing as of right now. We did try to take less material out per tooth and it didnt help. We have found taking bigger cuts when reaming this material prevents tool breakage.

Thank you,
We are currently using a MobilMet 404 and its just flowing over the area at hand not part submersion. I would say its not specifically formulated for copper alloys, but the Mobil cutting oil page says

"It also can be used for the general machining of nickel-tin-bronze alloys and the free-machining of steels, as well as for severe cutting operations of difficult-to-machine non-ferrous alloys, including silicon-copper, silicon-bronze, and copper-nickel"

Thank you