Surface Finish

Cutting Edge Geometry and Surface Finish Surface Roughness Rt and Feed Rates

There is no difficulty in working out the theoretical value of the surface roughness Rt- also known as R max and Rz. (In practice it usually runs up to four times the Ra value). The theoretical value, however, is based on a perfect cutting edge geometry with a wide minor cutting edge angle. Using our ultrahard cutting materials of Mono- and Polycrystalline Diamond when machining nonferrous metals and nonmetallics or Polycrystalline Cubic Boron Nitride for grey cast iron there is hardly any flank wear or deformation of the cutting edge due to the excellent flank wear resistance of our tools. It is therefore possible to compute the precise data for the required surface roughness, provided the cutting environment in itself will not hamper the machining as such.

In practice, the values of roughness will always fall short to the theoretical ones when hard-cutting with PCBN. This is due to a simple reason: the cutting process itself is influenced by self-induced hot-cutting mode which can cause an extremely high passive cutting pressure.

01 Surface Finish

Practise, however, shows that the theoretically computed value can hardly be achieved, since the environmental conditions are lacking perfection. Instable conditions of machine and/or workpiece, incorrect chucking, faulty or wrong tool system, wrong cutting speed and depth of cut etc. will impair the results. On the other hand, perfect working conditions can result in a much better surface finish due to improved and optimized cutting edge geometries. Especially the general reduction of the minor cutting edge angle as well as the cutting edge micro-geometries with PCBN (for more cutting pressure) are to be mentioned. In order to obtain the various stages of very good surface finish while hardcutting the T-land styles are of great influence. For a mirrow-finish surface of nonferrous metals and nonmetallics we are able to supply even MDC-inserts with T-land, if necessary.

As to high-performance cutting of all kinds we developed various inserts with WIPER geometry for internal, external and milling processes. The WIPER edge in that case replaces the above-mentioned minor cutting edge, reducing its angle to a minimum, it automatically reduces the theoretically computed surface roughness by 2 to 4 times.

In practise this is the alternative for high-performance and high-tech cutting:

02 Surface Finish

Optimized cutting edge geometries in connection with our extremly flank wear resistant ultrahard cutting materials will help you to a considerable degree not only of productivity but of product quality as well.