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Machining (turning) the products from cermet TiC-(Ni-alloy)

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Rustam1

Rustam1

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Apr 16, 2016
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Hi everybody!

Wе have developed the technology of fabrication of complex shapes items from cermet TiC-(Ni-alloy) for use at temperatures up to 1000 C.
We must select the incisors for turning.
Experiments have shown that the incisors of cubic boron nitride, of diamond composites (content diamond 70%) quickly crumble and wear - photo attached.
Cermet TiC-(Ni-alloy) have heterogeneous structure and consists of grains of solid titanium carbide, located in a soft metallic matrix - photo attached.
Is possible rapid grinding with diamond wheels. The grain should be at least 0,35-0,50 mm.
However, for complex shapes, such as balls and seats ball valves (have spherical surface) need special grinding machines and tools.
Therefore, for turning workpieces on conventional lathes and machining centers need wear-resistant inserts (incisors).
Thank you in advance for your advice, suggestions and information.
 
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If your 'soft metallic matrix' is a nickel alloy, you and I have different definitions of 'soft'.

However, from your description of the composite material's morphology, I'd guess that machining techniques as used for Macor(r) and similar 'machinable' ceramics might be worth investigating.

To review, to machine Macor, you use an impact resistant cutting tool, e.g. HSS, with a feed per tooth and depth of cut somewhere near the grain size of the stock material, basically knocking off grains instead of cutting them, and capture the swarf with a vacuum cleaner so the dust/powder waste won't foul your lathe.

The tooling needs to be very stiff wrt to that used for cutting ordinary metals.
Cutting edge life will be shorter than you would expect for ordinary metals.

Diamond will be useful only for grinding and lapping to improve the surface finish.



Mike Halloran
Pembroke Pines, FL, USA
 
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Hi everybody,

Thank you very much for your answers.
Was no feedback, so i was unable to respond in time.
I attached the explanatory files:

SANDVIK did experiments on the processing of our billet cermet in different modes and with different incisors in a very tough machines, but to no avail.
Here, apparently, need some special cutters (incisors).
On your proposal we will to appeal to Macor. Perhaps they will offer something.

Thank you in advance for your comments,

Rustam

 
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This may get expensive.

My mentors at F in 1966-67 reported that they had tried electrolytic grinding some time before that. It amounts to EDM, using the grinding wheel as an electrode.

The metal removal rate was huge.
The deal killer for them was that the workpiece was left with nearly zero fatigue life.
That may not matter so much to you.

Your St.Gobain rep should be able to dig up some useful info, given a little incentive.



Mike Halloran
Pembroke Pines, FL, USA
 
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For electrolytic grinding spherical surfaces also need special equipment and tooling.
Cermet contains 30-50% metal, therefor possible processing electrochemically. Electrode speed - 0.1 mm / min.
This is a good speed. But for every item needs its own electrode.
Probably, incisive processing - it is a dead end road, due to lack of wear-resistant cutting tools.
If the processing with incisors to combined to the electrolytic grinding?
Instead perform electrolytic grinding to do electrolytic cutting with incisor.
Can do that?
 
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The difference between grinding and single-point cutting is that a grinding wheel has many thousands of cutting points available, where an incisor, as you say, has but one.

In grinding,
you don't know exactly where each point is,
but dressing establishes a limiting locus where a number of points will pass by,
and new points are automatically presented as the active points are fractured and fall away.

So, grinding is sort of like having an array of tiny incisors with an automatic mechanism for introducing them to the workpiece in succession as each incisor wears away and becomes ineffective.


EDM works by applying a voltage between a consumable electrode and the workpiece, and flowing a dielectric fluid through the gap to carry away burned detritus of electrode and workpiece. There is no contact between electrode and workpiece.

Electrolytic grinding, as it was outlined to me (decades ago) allows contact as in regular grinding, and applies a voltage too, which I think requires a conductive coolant to carry the current through the grinding wheel.

I heard that EG works great, on hardened steel, which is a relatively homogeneous material.

On your composite material. ... well, I don't know. It should be relatively easy to remove the nickel matrix, basically by reverse electroplating, which should weaken the support for the TiC grains, allowing them to knocked out by the abrasive grains.

It will be a lot of fun, balancing the etching current against the grinding wheel composition, speed, feed, etchant/coolant flow and who knows what else to get a decent MRR and a decent surface finish.








Mike Halloran
Pembroke Pines, FL, USA
 
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Hello, Mike,
Many thanks for a clear and comprehensive response.
Our task - to minimize machining allowances.
On ball from cermet TiC-(Ni-alloy) diameter of 100 mm we can do machining allowance of 0.3-1.0 mm.
After our experiences and taking into account your valuable advice one conclusion - processing with incisors is problematic.
We metallurgists and machining is not our profile. Conduct research on electrolytic grinding with no guarantee of success, probably we will not.
At the moment we have two methods that have used:
1. Grinding with diamond wheels, first large grain (350-500 microns), then fine grain (40-150 microns).
Lathe turret CNC with drive heads, for example, Haas or Fryer. In the disk drive head set diamond grinding wheel. All movable parts are protected from abrasive.
2. Electrochemical machining. Electrodes from brass or stainless steel.
Machines are available.

Best regards,
Rustam
 
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