1. The form and cause of tool wear
When the four-post cutting machine cuts metal, the tool cuts off the chips on the one hand, and on the other hand, the tool itself is also damaged. The main forms of tool damage are wear and breakage. The former is continuous gradual wear; the latter includes brittle damage (such as chipping, chipping, spalling, crack damage, etc.) and plastic damage. After the tool is worn, the machining accuracy of the workpiece is reduced, the surface roughness is increased, and the cutting force is increased, the cutting temperature is increased, and even vibration occurs, and normal cutting cannot be continued. Therefore, tool wear directly affects processing efficiency, quality and cost. There are several forms of tool wear:
Rake face wear
Judging from the degree of dependence on temperature, the main causes of normal tool wear are mechanical wear and thermal and chemical wear. Four-post cutting mechanical wear is caused by the scribing effect of hard points in the workpiece material, and thermal and chemical wear are caused by adhesion (the bonding phenomenon produced when the tool and the workpiece material contact the distance between atoms), diffusion (the tool and the workpiece The chemical elements on the two friction surfaces face each other, corrosion, etc.).
2. Tool wear process, blunt standard and tool life
As the cutting time increases, tool wear increases. The tool wear process can be divided into three stages:
Initial wear stage
Normal wear stage
Rapid wear stage
If the tool is worn to a certain degree, it cannot be used. This degree of wear is called the blunt standard. The actual cutting time for a new knife (or a re-sharpened tool) from the beginning of use until it reaches the blunt standard is called the tool life.