When milling super alloys, there are certain process requirements which must be observed.

• Milling of high-temperature alloys often requires more rigid and powerful equipment than the milling of carbon steels.
• Cutter accuracy in both radial and axial directions is essential to maintain a constant tooth load and a smooth operation, and to prevent premature failure of individual cutter teeth.
• Cutting edges must be sharp with an optimized edge-rounding, to prevent chip adherence at the point where the edge exits the cut.
• The number of cutting teeth actually in cut during the milling cycle must be as high as possible. This will give good productivity provided that the stability is good enough.
• Cutting speeds for super alloys are generally low. Common practice is to employ a fairly low cutting speed in combination with a moderately high feed per tooth, to produce a chip thickness not less than .004 inch which prevents work-hardening of the material.
• Coolant should be applied in generous quantities around the cutting edge when the cutting speeds are low, in order to reduce chip adhesion. Coolant supplied through the machine tool spindle is recommended for HRSA materials. High pressure coolant (HPC) will give better tool life. (no coolant for ceramic milling)
• The cutting edge geometry should always be positive.
• For cutting depths below .200 inch, the entering angle should be less than 45 degrees. In practice, a round, positive-rake insert is recommended.
• If special design cutters are being considered for an application, it is essential to allow sufficient space between each tooth for effective chip evacuation around the cutting edge.
• Flank wear around the cutting edge should not exceed .008 inch for R390, .012 inch for round inserts in carbide, and .024 inch in ceramics, otherwise the chance of catastrophic failure increases rapidly. Normal best practice is to index the cutting edges at frequent intervals, to ensure a reliable process.
• Down milling (climb milling) should be used, to obtain the smallest chip thickness where the edge exits cut and reduce any chip adherence.
• Iron-based super alloys, and solution treated, nickel-based alloys (Inconel 625), are usually easier to machine than nickel-based and cobalt-based super alloys.

Learn more about Milling solutions at Sandvik Coromant.