Tool Materials and Coatings

The choice of tool material has a direct and measurable effect on broach life, especially as workpiece hardness increases or as manufacturers push for higher cutting speeds.

Conventional high-speed steel (HSS), such as SKH55 (equivalent to AISI M35), has long been the standard broach material. It offers a good balance of toughness and wear resistance for general-purpose applications on carbon and alloy steels within the typical broaching hardness range.

Powder metallurgy (PM) high-speed steels represent a significant step up. PM grades offer finer, more uniform carbide distribution, which translates to better wear resistance and edge retention. Within PM grades, there is a range of options: some are optimized for general high-wear applications, while others are formulated specifically for difficult-to-machine materials like nickel-based superalloys found in aerospace turbine components.

On the coatings side, the industry has moved well beyond basic nitriding. Physical vapor deposition (PVD) coatings, particularly aluminum-based nano-structured formulations, can dramatically extend tool life. Advanced PVD coatings can double the number of parts produced between resharpenings compared to conventional titanium nitride (TiN) coatings, while also improving the surface finish of the broached workpiece by reducing tooth surface roughness to extremely low levels (on the order of Ra 0.03 µm). This smoother tooth surface also reduces flaking on the finished part—a meaningful quality improvement for gear and spline applications.