CBN is synthesized under high temperature and high pressure, and its hardness is second only to diamond. Besides, its thermal stability is much higher than diamond, with good chemical stability and no chemical reaction with ferrous metal elements at 1200 ~ 1300℃. Therefore, CBN tools are mainly used in ferrous metal materials, such as cast iron/steel, which are hard to process with high hardness.
During the machining process, CBN tools can be divided into continuous cutting and intermittent cutting according to the working conditions. According to different working conditions, the replacement factors of CBN tools are different. For example, the replacement form of continuous cutting tools is worn, and common intermittent cutting Tool replacement forms include hemming, cracks, etc. The following Demina focuses on the replacement form of CBN tool intermittent cutting.
1. Crushing blade
This is a common form of damage when CBN tools cut steel and cast iron intermittently. It is a small cut in the cutting edge, in which several small cuts or pieces break off. The general notch size is equal to or slightly larger than the feed. If the cutting tool of the micro-chipping edge can continue cutting within the allowable wear limit, the out-of-tolerance needs to be replaced.
In the end milling process of steel and cast iron, shell-like spalling is most common on the surface of the rake. When the CBN tool end mills hardened steel (HRC58-65), a large area of shell-like peeling will appear on the surface of the rake, and this kind of wear will occur. The cutting speed can be increased, the feed can be reduced, negative chamfering can be used, and the edge of the blade has been dull.
CBN cutting tools for cutting high hardness materials or intermittent cutting workpiece frequent breakage form. This is due to the excessive impact load when the intermittent cutting high hardness of the workpiece. And short time cutting after the occurrence of early damage, although the cutting condition. The appropriates cutting after a long time, but no tool change in time, because of the cutting tool material fatigue occurs a large fracture.
After a long period of intermittent cutting, the CBN tool produces fatigue cracks parallel to the cutting edge due to mechanical shock, and cracks perpendicular or inclined to the cutting edge due to thermal shock. As these cracks spread and coalesce, they cause the blade to crack or break.