Over the last few blogs, we have been discussing machining techniques for a variety of metals and alloys. This time around, we will touch on machining nickel iron. The nickel-iron alloy family includes some recognizable names, including Invar, Kovar®, Alloys 42, 46, 48, and 52, Alloy 42-6, and the magnetic shielding alloys, such as MuMetal.
So, what does it take to properly machine nickel iron alloys? Let’s take a closer look at both the makeup of these alloys and what you can do to make the process more successful, as outlined in our General Guide to Machining Nickel-Iron Alloys.
In general, nickel iron alloys are hardenable only through cold working and not by heat treatment. As far as hardness, when it is in annealed conditions, they can become soft and gummy, which makes machining more difficult. Instead of proper cutting, you can find yourself in a position where tools plow through the metal. All of this can be made less of an issue if you descale nickel iron alloys.
As with any machining process, coolants play a big role in machining nickel iron. In this case, they help limit warpage by controlling heat buildup. At Ed Fagan, we suggest Keycool 2000 or Prime Cut. Whatever you choose, make sure to avoid coolants that contain sulphur.
When it comes to tooling, there are a few suggestions. First it is critical that all feathered or wire edges are removed from your tools. It also helps to do repeated inspections to maintain their condition. We suggest tools made of T-15 alloy as well as carbide tools (K-6, K2S).
Turning and Drilling
If steel cutting tools are used, we think you should following these approximate parameters:
- 0.10” to 0.12” per revolution feed with a speed as high as 35/FPM
- 7° end cutting edge angle
- .005” nose radius
- 15° side cutting edge angle
- 8° back and side rake
For drilling, a good example would be when drilling a 3/16” diameter hole, a speed of about 40/FPM could possibly be used with a feed of about .002”-.0025” per revolution. In most cases, the drill should be ground to an included point angle of 118° to 120°.
Reaming and Tapping
We suggest reaming speeds that are half the drill speed, with a feed that is three times the drill speed. As far as tapping, you should use a tap drill slightly larger than the standard drill recommended for conventional threads. This is needed in order to prevent metal from flowing into the cut.
These are just a few general suggestions about properly machining your nickel iron. Above all else, it’s important to have the highest quality alloys and know how to work with them!