In the process of NC lathe cutting, tool wear to a certain extent, cutting edge collapse or damage, cutting edge roll edge (plastic deformation) , the tool will lose its cutting ability or can not guarantee the quality of processing, called tool failure. The main forms, causes and countermeasures of tool breakage are as follows:

       1. CNC lathe, flank wear, flank wear is caused by mechanical stress in the flank of the friction and wear. Because the tool material is too soft, the back angle of the tool is small, the cutting speed is too high, the feed is too small, causing excessive wear on the back surface, which reduces the precision of the machined surface and increases the friction, the tool material with high wear resistance should be selected, cutting speed should be reduced, feed rate should be increased, and tool back angle should be increased so as to avoid reducing flank wear.

      2. Tool turret turning and milling compound center, Edge wear, Edge wear on the main cutting edge is common in the contact surface with the workpiece. The main reason is the friction caused by surface hardening and serrated cutting, which affects the flow direction of cutting and leads to edge collapse. Only by reducing the cutting speed and feed speed, at the same time select wear-resistant tool materials and increase the rake angle, can make the cutting edge more sharp.

       3. CNC lathe, rake face wear, friction and diffusion in the rake face caused by wear than rake face wear. The rake face wear is mainly caused by the contact between cutting and workpiece material and the diffusion to heating area. In addition, the tool material is too soft, the cutting speed is too high, the feed is too large, but also rake surface wear. Rake face wear can cause tool deformation, interfere with chip removal, reduce cutting edge strength. Reducing the cutting speed and feed speed, while selecting coated cemented carbide materials, can reduce rake face wear.

       Four. The plastic deformation of NC lathe tool is the deformation of cutting edge under the action of high temperature or high stress. The main causes of plastic deformation are high cutting speed, high feed speed, the role of hard point in workpiece material, too soft cutting tool material and high cutting edge temperature. It will affect the quality of chip formation, and sometimes there can be broken edge. To reduce plastic deformation, cutting speed and feed speed should be reduced, and tool materials with high wear resistance and thermal conductivity should be selected.

        5. Chipping tumor, chipping tumor is the workpiece material on the tool adhesion. Chip accumulation tumor will reduce the quality of the machined surface and change the shape of the cutting edge, and finally lead to the collapse of the cutting edge. The countermeasures adopted are to increase the cutting speed, select coated cemented carbide or cermets and other materials with low affinity tool materials, and the use of cutting fluid.

        6. NC lathe, Edge spalling, cutting edge leisure some small gaps and uneven wear, that is, edge spalling, mainly by intermittent cutting, chip removal is not smooth. Cutting Edge spalling can be avoided by reducing feed rate at the beginning of machining, selecting tough materials and cutting edge strength blades.

        7. NC lathe tool edge, Edge collapse will damage the tool and workpiece. The main reason is the transition wear and higher stress of the cutting edge, it may also be due to the tool material too hard, cutting edge strength is not enough and feed too much. We should choose the alloy material with good toughness, reduce the feed and cutting depth when machining, and choose the high-strength or the blade with big corner.

       8. The hot crack of NC lathe tool is caused by the temperature change during intermittent cutting, which is perpendicular to the cutting edge. Hot cracks can reduce the surface quality of the workpiece and lead to edge spalling. Alloy materials with good toughness should be selected, while reducing feed and cutting depth, and dry cooling or in wet cutting when there is sufficient cutting fluid.

       In this paper, the cutting tool material, geometric angle, coating, edge strengthening and machining conditions of NC Lathe are summarized, complement each other. A good tool, should have a smooth chip groove, long service life, can save processing costs.