Machining Nickel Alloys

Nickel base corrosion and temperature resistant alloys are classified as moderate to difficult when machining, however these alloys can be machined using conventional production methods at satisfactory rates. During the machining processes these alloys work harden rapidly, generate high heat during cutting, weld to the cutting tool surface and offer high resistance to metal removal because of their high shear strengths. Following are key points that should be considered during machining operations. The actual operating parameters are to serve only as a guide and are not to be taken as absolute values.

Capacity – All nickel alloys can be face-turned and bored on practically any machine. Factors such as speed, feed, depth-of-cut and tooling will be the determining factors that allow you to utilize machinery available for the job. Drilling large holes and tapping require sturdy machinery with plenty of power.

Tooling – Due to the nature of the alloys being worked, tools will tend to dull fairly quick and the need to change tooling or re-sharpen tools will be frequent. Although expensive, C grade inserts should be used whenever possible.

Lubrication/Coolants – Lubricants/coolants are desirable. Good results can be obtained using water-miscible vegetable oil based fluids in CNC equipment and engine lathes. However, tapping and heavy drilling (large diameter or deep-hole drilling) requires a heavy duty, light viscosity petroleum cutting oil. Other facilities may use different lubricants based on trial and error. What works for one shop may not work for another.

Drilling – When using insert drills in CNC machines use the same speeds (SFM) for facing, turning and boring for the specific alloy. Feed rates should be .002” per revolution. When twist drill bits are used, cobalt drills are preferred but high speed steel (HSS) drills will also work as long as you keep the speed slow and steady. Solid carbide drills work well in some applications.