CBN is synthesized under high temperature and high pressure, its hardness is second only to diamond, and the thermal stability is much higher than diamond, chemical stability is good, and iron metal elements in 1200 ~ 1300℃ also does not occur chemical reaction, so CBN tools are mainly used in ferrous metal materials, such as cast iron/steel high hardness difficult to process materials field.
CBN tool in the process of processing, according to the processing conditions can be divided into continuous cutting and intermittent cutting, according to the different working conditions, the CBN tool change factors are different. Such as continuous cutting is the common form of tool change wear, and intermittent cutting common form of tool break, crack and so on. The following emphasis on the CBN tool intermittent cutting tool change form.
The CBN tool intermittent cutting tool change form
(1) Breaking edge
This is a common form of breakage in the intermittent cutting of steel and cast iron by CBN tools. It is a small cut in the cutting edge, several small cuts in the blade or a small piece are broken. Generally, the size of the gap is equal to or slightly larger than the feed. If the micro - edge of the tool can continue to cut within the allowable wear limits, out - of - tolerance needs to be replaced.
(2) Peeling
When end milling steel and cast iron, shell-like spalling occurs most often on the front cutting surface. CBN tool ends milling hardened steel (hrc58-65), a large area of shell spalling on the front knife surface, such wear, can be increased by cutting speed, reduce feed, use negative chamfering, blade after passivation treatment.
(3) Broken
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 appropriate cutting after a long time, but no tool change in time, because of the cutting tool material fatigue occurs a large fracture.
(4) Crack
After a long time of intermittent cutting, there are mechanical fatigue cracks parallel to the cutting edge caused by mechanical impact, and also cracks perpendicular to or inclined to the cutting edge caused by thermal impact. When these cracks expand and merge, they can cause the blade to break or break.
