The form of tool wear and its causes
Four - column cutting machine in the cutting of metal, the tool on the one hand cutting chips, on the other hand the tool itself will also be damaged. There are two types of tool damage: wear and tear. The former is continuous wear and tear; The latter includes brittle damage (such as breakage, breakage, spalling, crack damage, etc.) and plastic damage. After the tool wear, the workpiece processing accuracy decreases, the surface roughness increases, and lead to increased cutting force, cutting temperature, and even vibration, can not continue to normal cutting. Therefore, tool wear directly affects processing efficiency, quality and cost. There are several forms of tool wear:
The front cutting surface is worn
Back face worn
From the degree of dependence on temperature, the cause of normal tool wear is mainly mechanical wear and thermal, chemical wear. The mechanical wear of four-column cutting is caused by the marking action of hard points in the workpiece material, while the thermal and chemical wear is caused by bonding (the bonding phenomenon when the tool and the workpiece material touch the atomic distance) and diffusion (the chemical elements of the two friction surfaces of the tool and the workpiece to each other, corrosion, etc.).
Tool wear process, dulling standard and tool life
Tool wear increases with the lengthening of cutting time. According to the cutting experiment, the typical wear curve of the normal wear process of the tool can be obtained. In this figure, the cutting time and the wear amount VB(or the wear depth KT) of the front cutting surface are taken as the abscissa and ordinate respectively. The tool wear process can be divided into three stages:
Initial wear stage
Normal wear phase
Sharp wear stage
Tool wear to a certain limit can not continue to use. This wear limit is called the dulling standard. The actual cutting time of a new knife (or a resharpened tool) from the beginning of use until it reaches the dulling standard is called tool life.