Removal of a case hardened layer 01:24

In most cases, case hardened steel components for the automotive industry (gears, shafts, sleeves etc.) are soft machined, case hardened and then a final cut is used to reach the required surface and dimensional tolerances.

In some cases though, there is a need to remove the case hardened layer. It can be that the component needs to be welded together with another component, and this cannot be done if the surface is hardened to 62 HRC.

This is a very challenging operation, where tool life is usually very low. PCBN is the best insert material for machining hardened surfaces, and when removing only 0.1-0.2 mm, tool life is very long. But if you need to remove 1 mm, how do you do that? 1 mm down into the component, the hardness is only 40-45 HRC and tool life will decrease significantly due to chemical wear.

 Well, there are a few alternatives:

• Multiple cuts with PCBN 
• This will work, but the deeper you go, the more affected the insert will be by chemical wear. Time in cut will also be longer due to multiple cuts.
• One PCBN cut and one or more cuts with carbide 
• You could remove the hard surface with PCBN, and then change to carbide for the subsequent cuts. The problem with this is that the ends of the component will still be 62 HRC, even when you have removed the hard skin, and this will influence tool life. Also here, time in cut will be longer due to multiple cuts, and one tool change from PCBN to carbide.
• One “roughing” cut with PCBN 
• Tool life will be affected by the lower hardness, but time in cut per component is low. 

The data below shows one successful example of removing the case hardened layer on a gearbox component using one “roughing” cut.

Each application when you remove the case hardened layer is unique, and very often involves extensive testing to find out which method is best. In this case, using Seco Tools’ solid CBN300 insert, and taking a roughing cut proved to be the optimal.

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: +86 185 1520 6942 e-mail: henrik.sandqvist@secotools.com