Appearance of CNC tool breakage

1) Cutting edge micro collapse

When the material structure, hardness, and margin of the workpiece are uneven, and the front angle is too large, resulting in low cutting edge strength, insufficient rigidity of the process system causing vibration, or intermittent cutting, and poor grinding quality, the cutting edge is prone to micro collapse, namely small collapse, notch, or peeling in the edge area. After this situation occurs, the tool will lose some of its cutting ability but can still continue to work. During further cutting, the damaged part of the cutting edge area may rapidly expand, leading to greater damage.

2) Chipping of cutting edge or tip

This type of damage often occurs under more severe cutting conditions than causing micro chipping of the cutting edge, or further development of micro chipping. The size and range of fragmentation are larger than those of micro fragmentation, causing the tool to completely lose its cutting ability and have to terminate its work. The situation where the blade tip breaks is often referred to as falling off the tip.

3) Blade or tool breakage

When the cutting conditions are extremely harsh, the cutting amount is too large, there is impact load, there are micro cracks in the blade or tool material, and residual stress exists in the blade due to welding, grinding, and careless operation, it may cause the blade or tool to break. After this form of damage occurs, the tool cannot continue to be used, resulting in scrapping.

4) Blade surface peeling

For materials with high brittleness, such as hard alloys with high TiC content, ceramics, PCBN, etc., due to defects or potential cracks in the surface structure, or residual stress in the surface due to welding and grinding, surface spalling is prone to occur when the cutting process is not stable enough or the tool surface is subjected to alternating contact stress. Peeling may occur on the front blade surface, while the blade may occur on the back blade surface. The peeling material is in the form of flakes and has a large peeling area. The possibility of peeling off of coated tools is high. After slight peeling of the blade, it can still continue to work, but after severe peeling, it will lose cutting ability.

5) Plastic deformation of cutting area

Due to their low strength and hardness, tool steel and high-speed steel may undergo plastic deformation in their cutting areas. When hard alloys work directly under high temperature and triaxial compressive stress, surface plastic flow can also occur, even causing plastic deformation of the cutting edge or blade tip, resulting in collapse. Collapse generally occurs when the cutting amount is large and hard materials are processed. The elastic modulus of TiC based cemented carbide is smaller than that of WC based cemented carbide, so the former has an accelerated resistance to plastic deformation or rapid failure. PCD and PCBN basically do not undergo plastic deformation.

6) Hot cracking of blades

When the tool bears the alternating mechanical load and thermal load, the cutting surface will inevitably produce alternating thermal stress due to repeated thermal expansion, which will make the tool fatigue and crack. For example, when a hard alloy milling cutter is used for high-speed milling, the cutter teeth are constantly subjected to periodic impacts and alternating thermal stresses, resulting in comb like cracks on the rake face. Some cutting tools may not have obvious alternating loads and stresses, but due to inconsistent temperatures on the surface and inner layers, thermal stress will also occur. In addition, there are inevitably defects in the tool material, so the blade may also produce cracks. After the formation of cracks, the tool can sometimes continue to work for a period of time, and sometimes the cracks rapidly expand, causing the blade to break or the tool surface to severely peel off.