1. The form of tool wear and its causes
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. There are mainly two types of tool damage: wear and damage. 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 reasons for 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 generated 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. According to the cutting experiment, the typical wear curve of the normal wear process of the tool can be obtained. The graph uses cutting time and flank wear amount VB (or rake face crescent crater wear depth KT) as the abscissa and ordinate respectively. The tool wear process can be divided into three stages:
Initial wear stage
Normal wear stage
Rapid wear stage
If the tool wears to a certain limit, it cannot be used. This wear limit 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.