Cubic boron nitride (CBN) is a pure synthetic material and is another new superhard material after synthetic diamond. When the cubic boron nitride tool is cut intermittently, the main form of damage is damage. There are two types of early and late: CBN car blade early breakage is the damage that occurs immediately after cutting or short cutting. At this time, the front and back flank surfaces have not produced significant wear. This type of breakage occurs most often when cutting high-hard materials or interrupted cutting. Late damage is damage caused by fatigue of the tool material after a certain period of processing. The forms of brittle fracture are as follows:
 
       1, chipping
       This is the most common type of early damage in the case of cubic boron nitride tools for continuous or intermittent cutting of steel and cast iron. It is a small gap created in the cutting edge, with a few small gaps in the blade or a small piece that has collapsed. Generally, the gap size is equal to or slightly larger than the feed rate. The micro-cracking tool continues to cut within the allowable wear limits.
       2, peeling off
       When end-milling steel and cast iron, shell-like spalling occurs most often on the rake face. When the cubic boron nitride tool is end milled hardened steel (HRC58-65), a large area of ​​shell-like spalling on the rake face, such wear occurs, which can improve the cutting speed, reduce the feed rate, and use negative Chamfered, blade with a passivated edge.
       3, broken
       Small pieces or large pieces of fracture occur on the cutting edge, and normal cutting cannot be continued. Cubic boron nitride cutters often break through high-hard materials or interrupted cutting. When turning hardened steel, due to the high cutting speed, small cracks occur at the tip of the tool, and usually can be reground and repaired. . When the cubic boron nitride tool is intermittently turned (40MnNi3CrMo), the low alloy steel has a large fracture at the tip of the tool. In this case, the tool cannot be reground. This is due to the excessive impact load during intermittent cutting and the early damage that occurs after short-time cutting. Although the cutting conditions are appropriate, after cutting for a long time, there is no timely tool change, which occurs due to tool material fatigue. The break.
       4, crack
       After a long time of intermittent cutting, the cubic boron nitride tool has mechanical fatigue cracks parallel to the cutting edge caused by mechanical impact, and cracks perpendicular to or inclined to the cutting edge due to thermal shock. When these cracks are continuously expanded and merged, the blade is broken or broken.
In actual production, the workpiece is far from regular and uniform, regardless of its geometry or the physical and mechanical properties of the material. For example, irregular blank geometry, uneven machining allowance, uneven surface hardness, and grooves, grooves, holes, etc. on the surface of the workpiece, all of which make the cutting process more or less always with intermittent cutting properties. Some other processing methods, such as end milling, are interrupted cutting. Under intermittent cutting conditions, it must be accompanied by strong mechanical shock and thermal shock. In addition, the cubic boron nitride tool has high hardness and brittleness, and belongs to the powder sintered material. Its microstructure is uneven, and there are many defects and Void. Therefore, it is easy to cause damage to the tool, especially early damage is more common. The main causes of damage are impact, mechanical fatigue and thermal fatigue. Early damage is the damage caused when the flank surface has not produced significant wear. At this time, the cutting edge is subjected to a small number of cutting cycles. Mechanical fatigue and thermal fatigue are not the main contradictions. The stress caused by mechanical impact exceeds the permission of the tool material. The strength causes a brittle fracture to occur.