Binderless diamond: Turning Performance

Molds for making plastic lenses can be effectively machined with conventional polycrystalline and single-crystal diamond tools because the molds are made of relatively soft materials, such as electroless nickel. However, molds for making high-performance glass lenses, such as for digital cameras and sensors, are often made of hard cemented carbide.

In those applications, natural and synthetic single-crystal diamonds tend to split, or cleave, in one direction because of the nature of the crystalline structure. While sintered, PCD tools don’t cleave, they have problems consistently achieving the required accuracy and suffer from short tool life, in part because their metallic binder makes them not as hard as single-crystal diamond tools.

Those cutting tool drawbacks mean moldmakers require diamond grinding wheels to produce hard molds. This also creates challenges because the need to true wheels makes it difficult to achieve submicron-level form accuracy and nanometer-level surface roughness. Also, grinding small concave molds with small-diameter wheels means only a small number of abrasive particles inefficiently remove material.

Courtesy of A.L.M.T.

A comparison of the cutting edges of a monocrystalline diamond tool (left) and a nano-polycrystalline diamond tool after machining tungsten carbide on a CNC lathe using elliptical vibration cutting.