During the milling process, the milling cutter itself will be worn and blunt while cutting chips. After the milling cutter is blunt to a certain extent, if it continues to be used, it will lead to a significant increase in milling force and cutting temperature, and the wear of the milling cutter will also increase rapidly, which will affect the machining accuracy, machining surface quality and the utilization rate of the milling cutter.
The position of tool wear mainly occurs in the front and back of the blade and its vicinity. The wear of milling cutter is mainly the wear of the back and the edge of the blade.
1、 Causes of milling cutter wear
The main causes of milling cutter wear are mechanical wear and thermal wear.
1. Mechanical wear: mechanical wear is also known as abrasive wear. Because there are tiny hard spots on the friction surface of chips or workpieces, such as carbides, oxides, nitrides and debris, grooves of different depths are carved on the tool, causing mechanical wear. The harder the workpiece material is, the stronger the ability of hard particles to scratch the tool surface. This kind of wear has obvious effect on high-speed tool steel tools. Improving the grinding quality of milling cutter and reducing the surface roughness value of front, back and blade can slow down the mechanical wear speed of milling cutter.
2. Thermal wear: during milling, the temperature rises due to the generation of cutting heat. The hardness of the tool material decreases due to the phase change caused by the increase of temperature, and the tool material is adhered to the chip and the workpiece, resulting in adhesive wear; Under the action of high temperature, the alloy elements of the tool material and the workpiece material diffuse and replace each other, which reduces the mechanical properties of the tool and produces diffusion wear under the action of friction. These wear caused by cutting heat and temperature rise are collectively referred to as thermal wear.
2、 Wear process of milling cutter
Like other cutting tools, the wear of milling cutters gradually develops with the increase of cutting time, and its wear process can be divided into three stages:
1. Initial wear stage: in this stage, the wear is fast, mainly because after the milling cutter is grinded, the convex peak generated by the grinding mark of the surface grinding wheel and the burr at the blade are quickly ground down in a short time. If the convex peak is large and the burr is serious, the wear is large. Improving the grinding quality of milling cutter, polishing the front and back of the blade with grinding or oilstone can effectively reduce the wear amount in the initial wear stage.
2. Normal wear stage: in this stage, the wear is relatively slow, and the wear amount increases uniformly and stably with the increase of cutting time.
3. Sharp wear stage: after a long time of cutting and use, the cutting edge of the milling cutter becomes blunt, which increases the milling force, the cutting temperature, the milling conditions become worse, the milling cutter wear speed rises sharply, the wear rate increases sharply, and the cutter quickly loses its cutting ability. When using the milling cutter, it should be avoided to make the milling cutter wear into this stage.
3、 Blunt standard of milling cutter
In actual work, if one of the following conditions occurs to the milling cutter, it indicates that the milling cutter has been blunt: the surface roughness value of the machined surface is significantly higher than the original, and there are bright spots and scales on the surface; The cutting temperature increases obviously, and the chip color changes; The cutting force increases, and even vibration occurs; The back near the cutting edge is obviously worn, and even abnormal sound appears. At this time, the milling cutter must be removed for grinding, and milling cannot be continued, so as to avoid serious wear and even damage to the milling cutter.