Types of Cutter Coatings

I'm confused, so many different types and I can't find an explanation of what to use when ?

Any pointers please

HSS

Titanium Coated

Tin Tipped

Carbide Tipped

Cobalt

Hi Chris,

Sorry about this it will be an essay but I hope it makes sense and helps.

HSS = High speed steel. A special tough, high carbon tool steel usually alloyed with cobalt (a metallic element, hence cobalt steels) which gives it high wear resistance. It is used for many tools including drills, milling cutters,lathe tools etc. It needs special high temperatures for hardening and tempering and will retain its cutting edge even when running red hot. It was the general; purpose tool steel until the advent of carbide tooling. It is also available as round or square sections to grind your own lathe tools etc but can be bought in preshaped sets for use on lathes etc.

TiN = Titanium Nitride a very hard ceramic used to coat tools, especially HSS tools to add extra hard wearing propertiess to the tooling, it is that gold colour you often see on milling cutters and twist drills these days. It is the same as titanium coating. because of its gold colour it is often used a coating in jewellery. Sometimes only the high wear areas such as the tips of drills are coated

Carbides are carbon based compounds which are very hard but brittle. They are mixed with metals, pressed into shapes and heated until the metal melts and cements the carbide particles together to form a very hard but less brittle matrix. hence its correst name is cemented carbide. The metal gives toughness to the matrix i.e. it is less brittle. Tungsten is often used hence 'Tungsten Carbide'. This is still quite brittle so small tips are brazed onto steel shafts which absorb the shock loads somewhat to produce carbide tipped tooling. Shaped tips which have several cutting edges are often used in lathe and milling tools and when blunted can be turned, or indexed and the next cutting edge used, they are held on a steel shank with special screws. Hence replaceable, indexible carbide tipped tooling.

Many folks use carbide tipped tooling these days but it was really intended for high speed, fast metal removal, production work, the fast removal shortening production times It is quite expensive (at least for me) but in production work the cost of tooling is negligible compared with production time and labour costs. It is not usually worth trying to sharpen carbide tooling,

I prefer HSS tooling for my lathe and mill as it is relatively inexpensive, easy to keep sharp and gives excellent finish on smaller lathes etc. It is easy to touch up and keep sharp once you have learned how to grind the angles, but as only a few basic shapes are required for the vast majority of the work we do this is not difficult.

Best regards

Terry

Hi Chris,

Sorry about all of the postings, I think I might have caught a virus - PC gone a bit haywire

Best regards

Terry

Edited By Terryd on 11/11/2012 00:24:29

Another rogue post

Best regards

Terry

Edited By Terryd on 11/11/2012 00:25:09

There's also TiALN - Titanium Aluminium Nitride. This is harder than TiN, but requires high temperatures to function correctly. The theory is that as the temperature rises the aluminium forms aluminium oxide more easily, which is very hard, and which then also prevents further oxidation. High temperature means running the cutter dull red, so no coolant! The coating is intended primarily for cutting harder materials with no coolant, just an air blast to remove chips. I use TiAlN coated end mills for cutting stainless steel and gauge plate.

Thinks: Might be worth trying a TiAlN cutter on HSS to see if it's any better than plain uncoated carbide.

Regards,

Andrew

Hi Chris,

Glad to be of some help in clearing the fog, but sorry about the multiplicity of posts. As I said my PC was acting rather strangely last night, perhaps it was tired. In fact I had to restart it on several occasions.

There is an error though in my main posting in that I inadvertantly wrote that the metal used for the matrix is Tungsten, The usual material for 'cementing' tungsten carbide for 'sintered' tooling is cobalt. Sorry about that but my only excuse is that i was also tired at the time. Also, TiN coatings are used on Carbide tooling at times, especially on 'inserts' hence the gold colour you often see. Other coatings are also used - often based on titanium, which explains the other colours that you see, but the basic material, tungsten carbide,is the same.

The problem is that users often shorten names, hence machinists (and catalogues) will properly talk of Tungsten Carbide while others call it just carbide, it is the same with Titanium Nitride (TiN - not Tin), which is often just referred to as titanium coated. Despite the howls of indignation to some of my recent posts, I still think that such confusion as yours could be avoided by proper use of terms snd good spelling.

By the way, 'sintering' (sorry to introduce another term) is simply the act of heating powdered materials to high temperatures under pressure, this bonds the matrix together. It is also described as 'cementing'. With Tungsten Carbide tooling, TC powder is mixed with say cobalt powder and heated to very high temperatures at high pressure in moulds to form the tips that you see in catalogues.

I hope that explains a bit more of this technology and is not too confusing. But my advice is to stick to HSS tools and learn to grind them, it is quite simple - see here for a useful guide.

Best regards

Terry

Edited By Terryd on 11/11/2012 11:59:19

Terry,

In your Avatar I presume you are the one on the right ?

If so then I have noticed that as you have got older your Avatar has got younger ?

Is there some Freudian connection to this ?

Perhaps you should go the whole way and use this ?

Cheers John,

But I've already used too many of those .

I must admit, despite trying to stave off ageing (tried to give it up with smoking but no deal ) I am the one on the left, the other is my first grandchild, now 3 1/4 ,

Best regards

Terry

Edited By Terryd on 11/11/2012 12:33:34

You're the one on the left? I hadn't realised that ,

I'm asking this in ignorance, and not trying to be argumentative. Does the TiN coating not wear off cutting edges fairly quickly? And, on the same theme, is it used more on "throwaway" tools, rather than those which are likely to be resharpened?

Andy

Hi Andy,

Properly applied TiN coatings are long lasting and do not wear off. TiN is in fact a very hard wearing ceramic, not a metal. It is the poorly applied coating on cheap tools which wears off, probably by not reaching the very high temperatures needed for proper deposition. Perversely the thinner the coating the better, as the thicker coatings can flake. It is calculated that TiN coatings can help the tool keep its edge for more than three times longer than normal and it has a plus that it prevents metal deposition during machining causing the phenomenon known as a 'built up tip' which can be a real problem in turning steels and other tenacious materials.

Of course on re sharpening the coating is removed but that merely means that the HSS core is exposed as in uncoated tooling so nothing is lost. 'Throw away' tooling is essentially a term used for industrial (HSS and carbide) tools where re sharpening is not cost efficient, most HSS types can be sharpened by an amater using a tool and cutter grinder, hence the second hand market in these.

I have good quality milling cutters and drills which have seen quite a lot of 'action' without any noticeable reduction in the TiN layer.

Best regards

Terry

All my metric drills (Dormer) are TiN coated; the coating doesn't seem to wear off even after hundreds of holes. I don't know whether this would be true for lower cost cutters.

The question of re-sharpening coated cutters doesn't really apply. For small cutters it simply isn't worth resharpening. I was talking to the salesman at the industrial tool shop I use on Friday. He was saying customers always ask for a discount on cutting tools. His point was that since the cost of the cutting tools is about 3% of production cost why bother with a 10% discount. A lot of commercial machining is done with CNC machines so if you use a resharpened cutter not only do you have to pay for the resharpening you also need to especially set the machine for that particular cutter diameter and length. Cutters are made for industry, the ME fraternity has to use what is available.

And before anyone jumps in about industry versus ME, I do have a fairly well equipped Clarkson T&C, but it simply isn't worth me sharpening small cutters. I've got better things to do with my time.

Regards,

Andrew

Edit: D**n, Terry beat me to it!

Edited By Andrew Johnston on 11/11/2012 14:46:24

Edited By Andrew Johnston on 11/11/2012 14:47:16

Edited By chris j on 11/11/2012 14:52:29

No won't cut better, just stay sharper longer

Assuming that was in reply to my post John, would that not make it a better cutter ?

Not all PVD (Physical Vapour Deposition) coatings are TiN. Much of the current research into tool coatings is aimed at eliminating, or at least reducing, machining fluids by providing a low friction surface to the tool. Tool suppliers sell milling cutters with a variety of different coatings; whether these coatings are relevant to the sorts of feeds and speeds used by model engineers is a moot point. However, for those of us who don't have coolant on our milling machines, keeping an eye on these developments could be beneficial, particularly for milling aluminium alloys where build up of swarf on the tool is an issue.

cheers,

Rod