First of all, a reasonable hard turning system can reduce or even eliminate grinding and the high tool costs and long processing time associated with it. A reasonable hard turning process can achieve 0.0028mm surface finish, 0.0002mm roundness, and ± 0.005mm diameter tolerances. The goal of hard turning is to remove at least 80% of the heat with the chips. Such accuracy can also be achieved on the same machine with "soft turning" of the workpiece before hardening, thereby maximizing equipment utilization. However, some factories choose the insert incorrectly or it is unclear whether the machine tool used is sufficiently rigid to withstand twice the pressure of ordinary turning, so that the hard turning process has not fully exerted its high effect.

1. Coolant

The biggest problem is whether to use coolant or not. For interrupted cutting parts such as gears, it is best to use "dry turning", otherwise the thermal shock when entering and retracting is likely to cause the blade to break. As for continuous cutting, the high temperature generated by the cutter head during dry turning is sufficient to toughen (soften) the pre-cut area, thereby reducing the hardness of the material and making it easier to cut. This phenomenon illustrates the benefit of increasing speed during dry cutting. At the same time, the coolant-free cutting method has obvious cost advantages.

In continuous cutting, coolant may help extend tool life and improve surface finish. The key to the problem is to make the coolant reach the cutter head. High-pressure coolant is the best way to solve this problem because it is not easy to evaporate at high temperatures. In addition, high pressure reduces chip buildup, which reduces the effect of chip blockage on coolant flow to the cutter head. Another method is to release the coolant to the top and bottom of the blade at the same time to ensure that the coolant reaches the cutter head continuously. If coolant is used, it must be water-based. Chips formed during a perfectly matched hard turning process can take away 80% to 90% of the heat (the maximum temperature in the cutting area can reach 1700 ° F). Once such hot chips come into contact with low-ignition-point cooling oil, the entire process may be completely destroyed. If hard turning is performed on open machine tools, appropriate protective devices must be added to prevent the operator from being burned by chips.