1) What are the ramifications of selecting between a 90° and a lead-angle cutter for facing?

Lead-angle cutters such as 45°, 60°, and 75°, have always been a first choice for facing operations. Axial chip thinning enables increased feed rates vs. 90° lead-angle cutters. Smooth cutting forces are also associated with 90° lead-angle cutters, but they have no axial chip thinning advantages, limiting feed rates and increasing radial cutting forces on the workpiece and setup.

2) Why should users select a 90° approach angle cutter for facing?

Designs with 45°, 60°, and 75° lead angles tend to interfere with component features and/or fixturing. Because 90° lead angle cutters avoid that, they allow greater machining flexibility for facing and shoulder milling.

3) What are the pros and cons of common cutter designs?

Radially clamped, single-sided inserts are typically freer cutting due to insert positioning in the cutter body pocket in a positive axial and radial inclination. A single-sided insert also has more flank clearance vs. its double-sided counterpart, reducing cutting forces on the workpiece. Designs usually offer two, three, or four cutting edges per insert.

Radially clamped double-sided inserts are more affordable per edge than single-sided ones, though not as free cutting because they are typically positioned in the cutter body pocket in a negative axial and radial inclination for flank clearance. A molded rake face with positive inclination to the workpiece reduces cutting forces, shearing instead of plowing workpiece material. Designs usually offer four, six, and eight cutting edges per insert.

Tangentially mounted technologies put more cutting pressure on the workpiece than radially clamped double-sided cutters and allow more inserts around the periphery of the cutter body, boosting productivity. The chip gullet is not as deep as a radially mounted double-sided cutter, so full radial engagement at max depth of cut is limited for facing. The core diameter is much more robust, allowing for a stronger tool. Most inserts offer four-to-eight cutting edges, improving price per edge.

4) How does insert price per edge impact total cost per part?

On average, 3% of cost-per-part comes from cutting tools. Tier 1 and Tier 2 suppliers want to use as many corners of an insert as possible to reduce the cost per unit (CPU) on any automotive component.

5) Which coating option is best?

Chemical vapor deposition (CVD) and physical vapor deposition (PVD) coatings can have a huge impact on performance and cost.

CVD coatings:

  • Thick Al2O3 coating withstands heat
  • More wear resistant
  • Thick, brittle coating can handle more feed pressure than PVD
  • Require higher surface speeds to perform on an atomic/molecular level
  • Excel in long in-cut times with large radial engagements
  • Heavily interrupted cuts can cause temperature fluctuations on the coating surface, reducing tool life
  • Typically incorporated with TiC or TaC to improve crater resistance
  • Perform better with dry machining in ferrous materials

PVD coatings:

  • Thin, smooth, hard coating layers
  • Less wear resistant than CVD
  • Cutting edges typically sharper, tougher
  • Excel in short in-cut times, inconsistent and/or low radial engagements
  • Better suited for heavily interrupted cutting
  • Thin, multi-layer TiN, TiAlN, or TiAlSiN coatings
  • Perform better with wet machining

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