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Kovar – Machinability Information

Information about the machinability of Kovar

The information provided below is freely available in the public domain, and while we endeavour to keep the information up to date and correct, we make no representations or warranties of any kind.
In no event will we be liable for any loss or damage including without limitation, indirect or consequential loss or damage, or any loss or damage whatsoever.

Kovar
Density g/cm ³ 8.26
Tensile Strength: 75 Ksi (518 MPa)
Yield Strength: 40 ksi (276 MPa)
Elongation % 50.8 / 30
Typical Hardness in the annealed condition: Rockwell HRB 80
Curie temperature 435°C
Melting Range 1449°C
Thermal Conductivity at 20°C
Electrical Resistivity 49 mm ² /m
Modules of Elasticity at 20°C Mpa 207

Please be aware that the following information is for guidance only.

Workability

The principal precaution to observe in forging is to heat quickly and avoid soaking in the furnace. Long soaking may Result in a checked surface due to absorption of sulfur from the furnace atmosphere and/or oxide penetration. A forging temperature of 1094/1177°C is preferred.

Coolant

It is important to control heat buildup, the major cause of warpage. Almost any cutting fluid, or none, can be used in machining nickel alloys. In many applications, nickel alloys respond well to ordinary sulfurized mineral oil; sulfur imparts improved lubricity and antiweld properties. If the temperature of the oil and work piece becomes high enough during machining to cause brown sulfur staining of the work, the stain can be readily removed with a cleaning solution of the sodium cyanide or chromic-sulfuric acid type. This should be done before any thermal treatment, including welding, because during further exposure to high temperature the staining may cause intergranular surface attack. To avoid intergranular corrosion, the parts should be immersed in cleaning solution only long enough to remove the stain. High-speed machining operations that create high temperatures might preclude the use of a sulfurized oil because of sulfur embrittlement of carbide tools. (Many sintered carbides have a nickel or cobalt matrix that is sensitive to sulfur attack at high temperature.) However, flooding the cutting area with cutting fluid generally cools the tool enough to avoid breakdown of the carbide bond.

Tool Material / Tooling

Carbide tools permit the highest cutting rates and are recommended for most turning operations involving uninterrupted cuts. Cast alloy tools are recommended for turning materials with Nickel content in excess of 95% as with carbide tools; interrupted cutting is not included in this recommendation. High speed steel tools should be used for uninterrupted cuts such as occur in the roughing of an uneven surface. They are also used for finishing to close tolerances, finishing to the smoothest surfaces, and cutting with the least work hardening.

If steel cutting tools are used, try a feed of approximately 0.254mm to 0.305mm per revolution and a speed as high as 35/FPM could probably be attained. Some of the angles on the cutting tools would be as follows:

End cutting edge angle – Approximately 7°
Nose radius – Approximately 0.127mm
Side cutting edge angle – Approximately 15°
Back rake – Approximately 8°
Side rake – Approximately 8°

When cutting off high speed tools are better than carbide tools, and a feed of approximately 0.0254mm per revolution should be used. The cutting tools should have a front clearance of about 7° and a fairly big tip–larger than 25° would be helpful.

Drilling

When drilling a 4.76mm diameter hole, a speed of about 40/FPM could possibly be used, and the feed should be about 0.0508mm to 0.0635mm per revolution, for a 12.7mm hole, approximately the same speed could be used with a feed of about 0.1016mm to 0.127mm per revolution. The drills should be as short as possible, and it is desirable to make a thin web at the point by conventional methods. By conventional methods, we mean do not notch or make a crank shaft grinding. It is suggested that heavy web type drills with nitrided or electrolyzed surfaces be used. The hole, of course, should be cleaned frequently in order to remove the chips, which will gall, and also for cooling. The drill should be ground to an included point angle of 118° to 120°.

Reaming

Reaming speeds should be half the drill speed, but the feed should be about three times the drill speed. It is suggested that the margin on the land should be about 0.127mm to 0.254mm, and that the chamfer should be 0.127mm to 0.254mm and the chamfer angle about 30 Degrees. The tools should be as short as possible, and have a slight face rake of about 5° to 8°.

Tapping

In tapping, a tap drill slightly larger than the standard drill recommended for conventional threads should be used, because the metal will probably flow into the cut. It is suggested that on automatic machines, a two or three fluted tapping tool should be used. For taps below 4.76mm, the two fluted would be best. Grind the face hook angle to 8° to 10°, and the tap should have a 0.0762mm to 0.127mm chamfered edge. If possible, if binding occurs in the hole in tapping, the width of the land may be too great, and it is suggested that the width of the heel be ground down. Again, it is suggested that nitrided or electrolyzed tools be used. Speed should be about 20/FPM.

The information provided above is freely available in the public domain, and while we endeavour to keep the information up to date and correct, we make no representations or warranties of any kind.
In no event will we be liable for any loss or damage including without limitation, indirect or consequential loss or damage, or any loss or damage whatsoever.

Should you choose to use any of the information below it is strictly at your own risk.