HRSA and titanium milling


Heat resistant super alloys (HRSA) fall into three material groups; nickel-based, iron-based and cobalt-based alloys.
Titanium can be pure or alloyed. The machinability of both HRSA and titanium is poor, especially in the aged condition, which imposes particular demands on the cutting tools. ​

 

General recommendations - valid both for HRSA and titanium alloys

Use round insert cutters to minimize notch wear
Stay in cut
ae 30% of Dc​

Main issues

  • Milling HRSA and titanium often requires machines with high rigidity, and high power and torque at low rpm.
  • Notch wear and edge chipping are the most common wear types.
  • High heat generation limits the cutting speed.

Suitable cutter concepts and inserts

  • Use round insert cutters (CoroMill 300, CoroMill 200) whenever possible to increase the chip thinning effect.
  • The CoroMill 690 long edge cutter is optimized for titanium machining. For cutting depths below .197 inch (5 mm), the lead angle should be large than 45°. In practice, a round, positive-rake insert is recommended.
  • 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.
  • The cutting edge geometry should always be positive 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 should be as high as possible. This will provide good productivity if there is stability. Use extraclose pitch cutters.​

 

Changes have varying impacts on tool life; the cutting speed, vc, has the greatest impact, followed by ae, etc.​

​Cutting fluid

Unlike milling in most other materials, coolant is always recommended to assist in chip removal, to control heat at the cutting edge, and to prevent the re-cutting of chips. High pressure coolant (1015 PSI) applied through the spindle/tools is always to be preferred instead of an external supply and low pressure.

Exception: Cutting fluid should not be applied when milling with ceramic inserts due to the thermal shock.

 

​CoroMill 690
Cutting fluid supplied through the cutters is advantageous when using carbide inserts

Insert/tool wear

The two most common causes of tool failure and poor surface finishing are:

  • Excessive flank wear and edge line frittering.
  • Notch wear.
  • The best practice is to index the cutting edges at frequent intervals, to ensure a reliable process.
  • Flank wear around the cutting edge should not exceed .0079 inch (0.2 mm) for a cutter with a 0 degree lead angle, like the CoroMill 490, or a maximum of .012 inch (0.3 mm) for round inserts.

Grade and geometry recommendations

  • GC2040 for roughing and difficult conditions
  • GC1030 for semi-roughing and finishing
  • Use positive geometries, like -ML and -PL
  • GC1620 is the basic choice for CoroMill Plura solid carbide end mills.​

 

Typical insert wear
 

Ceramic inserts cutter for roughing HRSA

  • Ceramic milling typically runs at 20 to 30 times the speed of carbide, although at lower feed rates (~.0039 inch/tooth (~0.1 mm/tooth)), which results in high productivity gains. Due to intermittent cutting, it is a much cooler operation than turning. For this reason, speeds of 2297-3280 ft/min when milling are adapted, compared with 656-984 ft/min for turning.
  • Ceramics have a high tendency for notching, which is why round inserts are primarily used to ensure a high lead angle.
  • Never use coolant.
  • Ceramics have a negative effect on the surface integrity and topography, and are therefore not used when machining close to the finished component shape.
  • The primary application for grade CC6060 (sialon) is milling Inconel 718 engine castings and oil drilling equipment, in both cases due to the high metal removal rates.
  • Maximum flank wear when using ceramic inserts in HRSA is .024 inch (0.6 mm).
  • Cutter assortment – please contact your local Sandvik Coromant representative for ordering.

 

Ceramic insert cutter for HRSA.

Note:

  • Ceramic inserts are NOT recommended in titanium
  • Cutting fluid should NOT be used with ceramic inserts.​