Hard turning with wiper inserts 22:45

The most common tool life criterion in finish hard turning is surface roughness. Traditionally the R_a-value is used, and a typical R_a value for gearbox components such as gears and shafts is 0.8 mm.

Surface roughness in a turning operation depends on a variety of factors. Feed rate and the size of the corner radius are considered to be the most influential of these. When the feed rate is increased the surface roughness increases rapidly. Selecting a larger nose radius will decrease surface roughness.

In finish hard turning it is vital to reach the required surface roughness tolerances, since it is the final operation before assembly. A feed rate of 0.1 mm/rev is common in hard turning operations where wiper inserts are not used. According to the diagram below, it is possible to run at 2 to 3 times higher feed rates with wiper inserts, and still maintain the required surface roughness.

Why focusing on feed rates? Well, the only way to improve productivity is to increase cutting data, and there are three possibilities:

• Increase cutting speed
• Increase feed rate
• Increase depth of cut

In finish hard turning it is usually not possible to increase depth of cut, only 1 cut is needed. Increasing cutting speed will improve productivity (increasing the cutting speed from 160 to 180 m/min would give a 12% increase in productivity), but increasing the cutting speed will usually also decrease tool life.

Therefore, the most common way to increase productivity and improve surface quality in finish hard turning is to use wiper inserts. The productivity can be increased significantly (increasing the feed rate from 0.1 to 0.2 mm/rev will give a 100% increase in productivity). This increase in feed rate will not affect tool life significantly, and the result is that more components can be machined in a shorter time while maintaining a good tool life.

Wiper geometries are available in different formats, in the first example below, a tipped wiper insert was used, and in the second example, a solid PCBN insert with wiper was used.

For more information, please contact your local Seco representative, or our Advanced material (PCBN/PCD/CERAMIC) team.

Author: Henrik Sandqvist Product Specialist SECOMAX PCBN/PCD/CERAMIC SECO TOOLS Shanghai CO., Ltd. Level 2, Building 8, 456 HongCao Rd., Shanghai 200233, China Office: +86 21 5426 5849 Mobile: +86 186 167 90063 e-mail: henrik.sandqvist@secotools.com