Need Tougher Carbide Insert 10

[swall]

We have a cut-off tool on a spring coiler using a Kennametal grade KC 850 square insert to make the cut. It is basically a shearing operation on spring temper 1095 strip approx 1/4" wide and .060" thick. Strip is coiled into a ring, then cut off. Although this is obviously a misapplication of a milling insert, I would like to know what grade of insert I could use that would be tougher and give longer life.

 

[Maui]

High speed steel might be worth considering in place of carbide in this application. Compared to carbide, it has relatively high toughness, and a grade with the appropriate balance of toughness and wear resistance could be identified by sharing your application requirements with one of your tooling suppliers.

Maui

 

[TVP]

Does it have to be in the form of a milling insert? If so, then maybe KC720:

http://www.kennametal.com/images/pdf/cat_help/Mill_Ins_CutMatGradeSel.pdf

Kennametal does supply cemented carbide grades that would be more specifically suited for this application. K3520 would be one example:

http://www.kennametal.com/images/pdf/US/victoriacatalogold.pdf

 

[swall]

Wow, TVP. 20% cobalt binder content. Didn't know they went that high. At this point, I think the shop wants to stay with a standard square insert. As this job has run for years, I am thinking any grade with higher cobalt content than what the KC 850 would be an improvement. I haven't been able to determine Co content of 850 from the Kennametal literature.
Maui--I was thinking along the same lines, perhaps M2. Not sure at this point how much leeway the shop has to reconfigure the cutter.

 

[swall]

Well, I called Kennemetal and the tech rep suggested a KC725M, which is a supposedly higher shock resistance of the KC720 suggested by TVP. (And higher cobalt content than the KC850 we were using). So, we will give those a try. In the meantime, out on the shop floor, the elves were cobbling up an M4 version of the insert. It just so happens that the form tool also used on this job is made (in house) from M4 and only differs from the 3/8" square insert by virtue of a rounded edge and no hole. So, they drilled a hole and turned rounded edge away from the cutting edge. But, that is the expensive option,as it gets EDM'd from square stock, ground,drilled and then sent out for hardening. Probably considerably more than a $10 off the shelf insert.

 

[saberblue]

If you decide to go the M4 route there are tool makers who make them from powdered metal etc. and you may be able to get them in a cost effective manner

 

[Maui]

Swall, this should prove to be an interesting comparison. Once you have the opportunity to test both the M4 inserts that you are making and the inserts from Kennemetal, let us know how their performance compares. The up front costs may be higher for the M4 insert if you make them in-house, but if it has 4 times the life at 3 times the tooling cost, then it represents a more cost effective solution. And Saberblue is correct - some tooling manufacturers may be able to provide you with a PM M4 insert that is produced cost-effectively.

Maui

 

[Frederick]

Cryo treat the carbide insert to improve toughness

 

[BenWhite]

I was just looking at Cryo treating carbide to gain additional toughness, Could somebody (Fredrick?) please explain the mechanism at work here? I understand how Cryo treatment of steel works, but I am rather baffled by carbide. So if I just carefully dunk a piece of tungsten carbide in liquid nitrogen for 10-24 hours it will come out noticeably tougher? If so why is this process not utilized more?

 

[Frederick]

I cannot yet explain the mechanism. Air Liquide US Industrial LP and my company are working on some research to find out. We have sponsored some research at Wayne State University, and Air Liquide is also doing research in their labs in France. We have a theory that cryo is making the crystal structure of metals more uniform. In carbides we think it works on the cobalt based binder.

"Dunking" is not a valid cryo process because of the extreme temperature gradients it creates. A slow cool down to cryogenic temperatures is required, then the part needs to be held there for a period of time.

By the way, cryo treatment of the above mentioned HSS inserts would be very advantageous also.

Why is cryo not used more? It is not unusual for companies that make products that are benefited by cryo to tell us they do not want to sell fewer products. They end up selling a lot fewer when their competition starts using it. Others give the excuse that they have to understand why it works even after they see it work. I would have loved to see that in the early process of heat treating metal. Imagine the knight Sir Dumbalot claiming he would not use a harder and stronger sword blade because he didn't understand why heat treating made it harder and stronger. He would have been a candidate for a posthumous Darwin award. We get a lot of silly excuses, so many that we started a list of them on our web site.

 

[BenWhite]

So I just ordered a custom carbide piece, where toughness is the main issue; and I am wondering if I should send it out for cyro treatment after I am done grinding it, or is this process too risky, as I cant afford a failure.

 

[tomwalz]

1. Your KC 850 is a coated insert. The only information given on the underlying carbide is “special”. If you identify the failure mode it will go a long way toward solving your problem. The failure mode can be in the coatings or in the carbide.

When I do carbide failure analysis I generally look at the part 17 different ways. See the information in the following link to see the different considerations.

http://www.carbideprocessors.com/pages/How-Carbide-Wears.html

2. The KC 850 is an old grade and there've been tremendous advances in carbide since Kennametal introduced it. However, since Kennametal never identified the underlying grade, it could be anything. Kennametal has a history of changing the compositions of their grades while still using the same identifiers.

3. There are some extremely tough new grades. Some of the old grades been greatly enhanced with modern technology. An example would be a 20% cobalt with some micron or nano grain technology. This ends up producing an extremely tough and extremely long wearing carbide part.

4. I have been following cryo technology for decades and would love to use it but so far it is neither predictable nor reliable. Anecdotal evidence indicates that when it works it can work extremely well however it may or may not work and there doesn't seem to be any way to predict that without actually using it.

If you like the idea of Cryo, then go ahead and try it. It doesn't seem to make things any worse.

Conclusion: We have quit using Kennametal for two reasons. 1. Their tech support is horrible. It is extremely difficult finding anyone who really knows anything. As mentioned above we have had projects going along swimmingly and then Kennametal change the composition of the grade without telling us causing the project to fail disastrously.

I would not place a lot of faith in cryogenics unless they could predict performance and guarantee consistent improvement. Every time we've asked about the reliability of the process, we have been told that they won't charge us if it doesn't work.


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[WESHardmetal]

If you are looking for custom carbide parts, I suggest you click this link.

 

[BenWhite]

Hey I found a paper on Cryogenic processing of tungsten carbide inserts. And the best part, its not published by a cryo treatment company!
here

 

[tomwalz]

It is more than just the grade. It is how well it is made. Here is a picture of a C2 saw tip that suffered excessive, chipping (flaking, spalling, etc.)cutting clear, new Hemlock. The tips is .220" wide and you can see aboput.160" of its face here.

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[tomwalz]

Here's the link.

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[swall]

Update--we tried to order the 720 inserts and Kennemetal was unable to fill the order. In the meantime, the shop found that they were getting over 100,000 cut-offs using the in house fabricated pieces made from M4. End of excercise.