Meeting the challenge of processing PcBN

The VGrind 360S machine

The ultra-hard cutting material PcBN (polycrystalline cubic boron nitride) achieves the highest degree of hardness and is extremely temperature-resistant, but this makes it a challenge to process. To enable cutting tool manufacturers to grind PcBN cutting edges with the highest level of precision, Germany-based sharpening specialist Vollmer has retrofitted a VGrind 360S grinding machine with an optional dressing unit for the grinding wheel with automatic wheel probing. Working in two work steps for both roughing and finishing, Vollmer says this innovation is a game-changer for tool manufacturers.

Considered the hardest cutting material in the world after PCD (polycrystalline diamond), the ultra-hard cutting material PcBN can achieve an operating life of up to 25-times longer than solid carbide tools. With characteristics such as exceptional chemical resistance even at high temperatures, PcBN retains almost all of its original hardness even at 1,200°C. This makes PcBN the perfect material for cutting tools that are used for machining ferrous metals such as grey cast iron and hardened steel.

The VGrind 360S grinding machine is ideal for the precise machining of PcBN tools with its stable wall concept with a rigid and compact design. Furthermore, the two grinding spindles with the grinding wheel set positioned at the C-axis pivot point enable efficient multi-layer machining. The high system rigidity in combination with the drive of the X, Y and Z axes via linear induction motors, allows tool manufacturers to machine a PcBN cutting edge with the grinding wheel oscillating across its contact surface for a chip-free high-quality surface.

Thermal stability
Meanwhile, thermal stability is ensured by a plate heat exchanger that effectively cools the spindles and motors. In addition, the integrated spindle indexing of the VGrind 360S stops a spindle at the same position during grinding wheel replacement, thereby reducing planing and run-out errors in grinding wheel packages.

To support the processing of this ultra-hard material, the optional dressing unit for the grinding wheel on the VGrind 360S means that after roughing the PcBN cutting edge, the dressing unit re-profiles the grinding wheel to regain its precise concentricity and correct geometric shape.

Subsequent finishing operations give the PcBN tool the desired surface finish and geometric accuracy. Customers can also retrofit the optional dressing unit with software updates to existing VGrind 360S machines. Tool manufacturers can carry out the installation independently or with the support of the Vollmer service team in just a few simple steps.

Eric Scheffold, product manager at Vollmer, concluded: “We have seen a positive development in the market for PcBN tools worldwide for several years, which is why we have now further developed our VGrind 360S for PcBN machining.”