How to get better cutting die from D2 3

[petecul]

We do high speed punching, each run our dies has punched 250 000 times, but for reason that we couldn't found out yet, some die, make only 20 000 parts and others do 500 000 parts before taking them off for grinding.

We evaluate if or not the die need to be replaced by the quality of the cut on parts.

I suspect that our problems come from grinding. Each time we remove up to 0.010" by step of 0.002" and we do final step at 0.0002".

We use coolant, grinding wheel is sharpened each time we grind the die. It takes 20 minutes to get the die like new. Material is D2 at 62HRC.

We take care of not burning the surface of the die when we grind to keep the hardness high. Often, the first 2 or 3 grinding cycles, we do not have good results but further in the the life of the die, we obtain better results and for the 2 or 3 lasts grindings, we start again having the same problem.

I'll welcome any recommandations that can help us to get more parts between each grinding.
Is there any way, we can get D2 harder than 62HRC. Maybe an other matherial should be use instead of D2??

Thanks
petecul

 

[Pressed]

There are many factors that can lead to low tool life. Material is only one. Have you kept track of each individual tool through say four regrinds?

The die bores and the punch diameters are made within a tolerance and by natural selection a small bore and a big punch will be mated; likewise a big bore and small punch. As you can imagine the forces, friction and clearance will be different. In a critical operation, pairing might help.

If your application causes enough friction for a tool to get hot enough and temper back in hardness, the tool life will go down. D2 has a low tempering temperature. I am not sure if a micro-hardness tester would detect softening of a cutting edge, but if you have one, you might try it.

Without knowing your exact application I can only suggest that I have replaced D2 with M2 on pierce tooling resulting in better tool life.

D2 can be coated with TiN or Nitrided and regrinds need to remove enough material to clean up the striations. The only way to determine if this will help you is to test it.

If you have multiple piercings occurring on the same press stroke, differing placement on the press bed and different cutting heights will result in various localized forces in some cutting edges. Also the guiding of each tool pair and the perpendicularity of the punch to die face are factors.

Another factor effecting your quality of cut and tool life is the velocity at the moment of piercing. An eccentric press has a fast changing ram velocity towards TDC. If your pierce die cutting edge height changes (from re-grinds) on this type of press, it is possible to cut too fast or too slow resulting in poorer cutting. You can test re-registering the die height with shims after re-grinds.

The type of press and its gibbing and the total load can contribute as well. There are other things but this is good for now. If you can measure a group of tools and see if there is a correlation to quality and tool life, you will be on your way.

Oh, if your die grinding was the problem you should be able to measure a hardness change on the ground face. 20 minutes is slow enough, depending on how big the surface area is.

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[petecul]

Thanks Pressed!! Really appreciate, It gave me a better idea of the problem but stil, so many factors involved! I'll start some testing and give you some feed back.
thanks
petecul

 

[tripleZ]

How big is the die? For sandwich shim-cutting jobs that I used to make for customers, we had a D2 upper guide plate that was precision doweled to a D2 lower cut plate. The cut place used a carbide insert in lieu of a steel insert. This dramatically increased the life of the die and decreased the frequency of re-grinds.

This may or may not be applicable to the type of stamping that you're doing.

 

[saberblue]

very often when we see this kind of problem it is associated with the cleanleness of the grinding fluid -- if you recirculate any swarf it can cause real wheel loading problems. This will result in less effecient gridning and more heat which could cause your hardness problem. I would recomend getting all the hard particles out of the fluid. as a general rule of thumb you are looking at removing all particles that at 10% more of the tightest tolerance band that you are dealing with.

Also make sure that the fluid is actually getting to the point of cut.plan an 1 to 1.5 GPM per HP used at the point of cut.

This link should get you to some more comprehensive inforation on this and other fluid related subjects

http://www.masterchemical.com/na_en/technical_information/tech_bulletins.php

The cutting fluid is not all of this probem but I will bet it is part of it.

 

[petecul]

Hi

The die is square foot big, we already thinked for carbide insert but the thing is maybe we gonna have more tool life but will have the get this more life to more more life, always more! Right know, it's faster, cheaper and easier for us to find out all details that affect tool life with D2, When we gonna be more in control, we will try to use some insert.

For coolant, I'll have a look, didn't thought that wcould affect our dies' hardness. I'll do some testing on that.

Thanks
petecul

 

[tripleZ]

I'll warn you that some of the development work that you do with steel may change with a carbide insert. As the carbide chips much easier, you have to be much more careful with tool alignments and edges that may witness impact.