Reasons of tool wear in metal cutting machining
Tool wear can be divided into two categories: normal wear and abnormal wear. In normal cutting conditions, the basic form of tool wear is shown as edge wear, front face wear, rear face wear and tip wear. Abnormal wear forms, manifested as tool breakage, plastic deformation and so on.
The main reasons of tool wear are as follows.
1, hard point wear Because the material contains some carbide, nitride, chip tumor residue and other quality point impurities.
2, bonding wear machining process, chip and tool contact surface at a certain temperature and pressure, plastic deformation and cold welding phenomenon, the tool surface bonding point is chip away and the wear occurs.
3, diffusion wear Due to the high temperature effect when cutting, the tool and the work-piece material in the alloy elements of mutual diffusion, and cause tool wear.
4, oxidation wear carbide tool cutting temperature of 700-800 ℃, some carbon in the tool, cobalt, titanium carbide, such as air oxidation, the formation of a layer of lower hardness in the tool surface oxide film, when the oxide film wear off in the tool surface caused by wear.
5, phase change wear in the cutting of high temperature, the tool metallurgical organization changes, thus causing a reduction in hardness caused by wear.
Tool in the intermittent cutting conditions, due to strong mechanical and thermal shock, more than the tool material strength, will cause tool breakage. Under the effect of alternating mechanical loads, the fatigue strength of the tool material is reduced, easily causing mechanical cracks and breakage.
There are many factors affecting tool life, which are mainly summarised in 5 aspects: work-piece material, tool material and its geometrical parameters, cutting dosage, tool sharpening quality, lubrication and cooling conditions.
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