Key Points for Turning with CBN Benefits of using CBN inserts
Can replace grinding operations, which reduces machining costs.
Dimensional stability, which is especially important in mass production. Minimizes the amount of scrapped parts.
“Green” approach, due to minimized usage of coolant.
There are a few guidelines to follow in order to achieve best results and high productivity when machining hard materials:
CBN is characterized by hardness of 4500 HV. The high hardness of CBN enables it to machine hard materials at high speeds and feeds.
Successful HPT (Hard Part Turning) demands not only suitable cutting tools, but also the right conditions, preparation and environment.
HPT begins with a correct “soft” state machining design that will create the best possible conditions for HPT.
The “soft” state is the state in which the workpiece material is yet to be hardened to its final hardness (around 20-40 HRc).
Important points when planning the “soft” machining process:
- Avoid burrs
- Keep close dimensional tolerances
- Do not enter or exit cut suddenly
- Enter and exit by planning radius movements
- Use wiper inserts to achieve superior surface finish
- Do not leave sharp corners (round or chamfer)
Machine stability, rigidity and thermal stability are vital conditions for producing a high quality finished part.
The better the stability of the overall machine concept, the closer the tolerances will be achieved.
Clamping the workpiece with sufficient force will prevent its movement and improve surface finish. Make sure that you employ wide clamping jaws which offers better grip on the workpiece, compared to ordinary three point jaws.
Using tailstock in long parts will add even more stability & rigidity to the machining process.
Rigid clamping of the workpiece and toolholder
"Soft state" preparation
Large cross section tools further add to the system rigidity.
Coolant - Generally, do not use coolant when machining hard materials. CBN inserts tolerate high cutting temperatures, so therefore have no need for coolant. Avoiding coolant is more economical, environmentally friendly and better because as the material heats up during the turning process, it becomes slightly softer and easier to machine. However, there may be some applications that require using coolant: in cases of continuous turning when high surface finish is required.
