Machining Nickel Alloys
It’s reckoned that nickel-based temperature and corrosion resisting alloys can be quite difficult to machine. It’s true that they do work harden rapidly and can weld to cutting tool surfaces. They also generate high heat levels when being cut, and thanks to their high shear strengths, offer a higher resistance to metal removal.
However, these alloys offer many unique benefits in the processes where they are used, and can be machined satisfactorily using conventional methods. So here are some general tips to guide you through these processes.
Tooling options when machining nickel alloys
Thanks to the unique properties of the various nickel alloys, you will find that your tools may dull quite quickly. So it will be necessary to either re-sharpen tools, or change tooling, at regular intervals. It is recommended that you use more expensive C grade inserts if these are available to you.
With CNC machines, if you are using insert drills, it’s best to select the same speeds (SFM) when facing, boring or turning any specific alloy. It’s also recommended that feed rates should be .002″ per revolution.
Cobalt drills should be your preferred option when using twist drill bits. Alternatively, high speed (HSS) drills should also work but usually at slower and steadier speeds. A final option, in certain applications, would be solid carbide drills.
If you are using steel cutting tools, it’s likely that a speed as high as 35/FPM could be attained, with a feed of roughly .010″ to 0.12″ per revolution. When cutting off, you are likely to find that high speed tools are more effective than carbide ones. Your tools should have a front clearance of around 7 degrees and a tip larger than 25 degrees is suggested.
Here speeds should be half, and the feed around three times, your drill speed. Short tools are recommended with a marginal face rake of between 5 and 8 degrees.
It’s recommended that you choose a tap drill slightly larger than the standard drill recommendation for conventional threads. This is because the metal is likely to flow into the cut.
The use of coolants and lubricants
Heat build up is a major cause of warpage. Simply aim to find what works best in your specific situation – often through a careful trial process. Here are a couple of suggestions to help. Firstly, in tapping and heavy drilling situations (involving large diameters or deep holes), a good choice is usually a light viscosity but heavy duty petroleum cutting oil. For CNC equipment and engine lathes you may find excellent results with water-miscible vegetable oil based fluids.
A wide range of nickel alloys can be both bored and face-turned on almost any appropriate machine. You’ll consider specific factors such as cut-depth, speed, tooling and feed when making your individual choice. Both larger holes and tapping will require a high degree of machine power and strength.
The simplest way to obtain specific expert advice
The above is a general guide to the machining processes. Specific professional advice can easily be obtained from our experts. Contact us and tap in to our thirty plus years of experience in supplying high performance nickel alloy solutions.