tungsten carbide 3

[alfa247]

Hi everybody,

I work with tungsten carbide tools (fin blades for metal forming) and couple of them are chipped. Is there a possibility to patch them and after that to polish that area?

Thank you,
Alfa

 

[Aubryann]

If this tool is running in a press I would not patch it. Most of the time we have to have our carbide tools sent out for repair ,but I guess it depends on the application of course.

 

[alfa247]

it is pressure there but not so big... i'm thinking if is smth. like epooxy or...

Thx,

 

[EdStainless]

Prob won't work. The strength and stiffness will be too different.

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[NickE]

Not a chance.

Carbide cannot be welded, nor can it be effectively brazed as a repair.

I have seen it silver soldered to change its size for a different press fit, however that was not on the working areas of the tool.

Also due to the brittleness of carbide the cracks may extend to a much deeper level than the chip is at.

The company I work for makes most of our stamping tools from micrograin carbide. I've seen a chip ~.005x~.004 (inches) with a crack extending through the whole detail.

If you have to use carbide for tooling there is likely no other material that can provide the combination of compressive strength, hardness, modulus, wear resistance that modern micrograin carbide tooling materials provide.


Nick
I love materials science!

 

[jck26]

As a big carbide user I'd say you're done. If the chips are restricted truely to the edge maybe you can regrind the tool, if that is allowed. If edge chipping is a constant issue then you need to look at another grade of carbide.

The changes in carbide materials and the coatings for carbide over the last 5 years is amazing. If you have not talked with your supplier about what is availalble you need to do so. I try new metal cutting grades of carbide tooling every year. Also for metal cutting the use of other tool materials (ceramic, diamond and CBN) make the job of selecting tooling very interesting.

 

[tomwalz]

Boy is jck26 right. If you haven’t changed carbide grades in five year you are way behind. Here's an article I just wrote about it. The focus is cutting tools for wood but it will give an idea as to what is available in advanced grades.

You can braze the chip back in successfully with proper surface preparation of the carbide. If it is a great big chunk it might work.

Also go to:

http://www.cs4u.org/newsletters/2006/20068August.pdf

and scroll down until you find the article on crack initiation and propagation. This will give some pictures to explain NickE’s comments.

Tom

New Carbide Grades Cut Faster and Last Longer

There are a couple new grades of carbide that are doing extremely well in custom tool shops.

Most production tools are made using standard carbide grade such as C-3 and C-4. These are grade designations from World War II and they are proven, reliable performers. Today’s “C” grade carbide is much better made than the 1940’s version but still essentially the same tungsten carbide grains in a cobalt matrix.

The new grades are being used in applications where fast feeding, clean cuts and long tool life are paramount. Since a 10” x 60 tooth or 10” x 80 tooth can run between $80 and $90 there needs to be a compelling reason to use them.

One of the big advantages is a dramatic reduction in the size of the carbide grains. Advanced carbide grains are now well below, one millionth of an inch in size. This means that they pack much tighter and more evenly than the much larger grains of the older grades. Because the particles are much smaller you can get a much sharper edge and keep it longer. What has been a surprise with these nano-grain carbides is that they are both tougher and longer wearing than conventional carbides.

The chemistry of advanced grades is considerably different. The standard was tungsten carbide grains cemented with a cobalt binder. This was the first one used because it was the first one that worked. Advanced grades vary somewhere from the traditional formula all the way up to titanium Carbonitride with a Nickel / Chrome binder. The advanced materials provide sensational wear properties especially in areas of chemical attack such as green lumber and MDF as well as other man made materials.

Advanced grades also use special chemistries.

Straight tungsten carbide grades have the highest resistance to abrasion (flank wear) of any carbide grades and have the greatest strength. Titanium Carbide gives "lubricity" to the carbide so that the chip slides across the face of the cutter with less heat and friction. Titanium carbide, Tantalum Carbide and Tantalum Niobium Carbide (TaNbC) additives are frequently used to maintain structure edge strength at cutting temperatures. In addition, Tantalum carbide and Vanadium carbide are used as additives to make finer carbide crystals and improve the property of the material.

This advanced technology is being used primarily in two ways. First is an extremely tough carbide. Since a great deal of carbide wear is actually micro-chipping it also gives much, longer life. This would be used for saw mills, pallet operations, old flooring and similar. The second use is in a fast cutting, long life grade such as Cermet II where the primary use is man made materials, such as MDF mills, and general cutting, such as cabinet shops.

How long the advanced grades last depends on the use but they are lasting about fifty percent longer in fiberglass up to eleven times as long in green wood in a sawmill. As a rule of thumb they are lasting about 5 to seven times as long in man made materials.

Because the cutting edges grind smoother and sharper, they also cut faster. This testing was done in a free fall test. Think of a chop type saw allowed to cut its way through the material with no additional weight on it. In a test of four major saw blades and an advanced, Cermet II grade the cermet II cut though in an average of 2.4 seconds. The others ranged from 2.7 seconds to 8.3 seconds. (This was the average of ten of each brand of blades.)

What is even more important is what happened after cutting a mile of MDF. The cermet II cut in an average of 3.4 seconds while the others ranged from 7.3 to 48.4 seconds.

The Cermet II blade took about 40% longer to cut while the standard blades took up to five times as long to cut.



Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

 

[swall]

Great article, Tom!

 

[tomwalz]

jck26,

Anybody have anything new worth trying?

Thanks,
Tom

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

 

[jck26]

tomwalz,

For custom tooling I've been using Maximet and Micro 100 as the basis for a lot of tooling where I need toughness and wear resistance. I feel that the improvements in the production of micro-grain carbides have pushed the curve so you can have both hardness (for wear resistance) and toughness to over come the abuse that tooling encounters.

And for off the shelf applications I've been machining tons, and I mean tons, of 7075-T6 aluminum with Kennametal grade KC5410 with very positive geometry and have gotten killer (500+ pcs per edge) tool life. This is a TiB2 chemistry coating which is different from the nitride based tool coating that I've typically used. We almost doubled our tool like over the typical TiN style coatings.

Additionally, we also use PCD tooling dry for one of our high volume milling operations with great results. Most company accountants seem to have a problem with $45 per inserts but we do some heavy face milling and found them to be the most cost effective solution for a narrow set of machining conditions.

Tom, since you're a carbide guy tell us what the hot setup is currently for aluminum as well as other machining.


jck26