The Appearance of tool breakage
The Appearance of tool breakage
1) micro collapse of cutting edge
When the structure, hardness and allowance of the workpiece are not uniform, the strength of the cutting edge is too low due to the large rake angle, the rigidity of the process system is not enough to produce vibration, or the quality of the cutting edge is not good due to intermittent cutting, the cutting edge is easy to have micro-collapse, a small break, notch, or spalling in the blade area. In this case, the tool will lose some of its cutting ability, but will continue to work. During further cutting, the damaged portion of the cutting edge may expand rapidly, resulting in greater breakage.
2) crumbling of cutting edge or tip
This type of breakage often occurs under cutting conditions worse than or further development of micro-chipping. The size and extent of the breakage are larger than the minor breakage, resulting in the complete loss of cutting ability of the tool and its termination. The condition in which the tip of a knife breaks off is often called falling off.
3) broken blade or knife
When the cutting conditions are extremely bad, the amount of cutting is too large, there is impact load, there are micro-cracks in the blade or tool material, and there is residual stress in the blade due to welding and grinding, plus careless operation and other factors, may cause the blade or cutting tool to break. After this form of breakage occurs, the tool can not continue to be used, resulting in obsolescence.
4) surface flaking of blade
For the materials with high Brittleness, such as hard alloy, ceramics, PCBN and so on with high content of TiC, there is residual stress in the surface layer because of defect or potential crack in the surface structure, or because of welding and grinding, when the cutting process is not stable or the tool surface bears the alternating contact stress, it is easy to produce the surface flaking. Spalling may occur on the front face of the knife, and the knife may occur on the back face of the knife. The spalling is flaky and the spalling area is large. There is a high possibility of spalling of coated tools. The blade can continue to work after slight peeling off, and will lose cutting ability after serious peeling off.
5) plastic deformation of cutting position
Due to their low strength and hardness, tool steels and high speed steels may undergo plastic deformation at their cutting positions. When cemented carbides work under high temperature and three-dimensional compressive stress, the surface plastic flow will occur, and even the plastic deformation surface of cutting edge or tip will collapse. Collapse generally occurs in the case of large cutting and processing of hard materials. The elastic modulus of TiC-based cemented carbide is less than that of WC-based cemented carbide. PCD, PCBN do not occur plastic deformation phenomenon.
6) hot cracking of the blade
When the tool is subjected to alternating mechanical load and thermal load, the surface of the cutting part will inevitably generate alternating thermal stress because of repeated thermal expansion and cold contraction. For example, when the carbide cutter is milling at high speed, the cutter teeth are subjected to periodic impact and alternating thermal stress, and comb-like cracks are produced on the rake face. Although some cutting tools do not have obvious alternating load and alternating stress, but because the surface layer and the inner layer temperature are not consistent, also will produce the thermal stress, in addition to the tool material interior inevitably has the flaw, therefore the blade may also produce the crack. Sometimes the tool can continue to work for a period of time after the crack is formed, and sometimes the crack spreads rapidly and causes the blade to break or the knife face to peel off seriously.
