First, the shape of the tool wear and its causes
When cutting a metal, the four-column cutting machine cuts the chips on the one hand and the tool itself on the other. The forms of tool damage are mainly wear and tear. The former is continuous progressive wear; the latter includes brittle fractures (such as chipping, chipping, spalling, crack damage, etc.) and plastic damage. After the tool wears, 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 is generated, and normal cutting cannot be continued. Therefore, tool wear directly affects machining efficiency, quality and cost. There are several forms of tool wear:
From the perspective of temperature dependence, the main causes of tool wear are mechanical wear and thermal and chemical wear. The mechanical wear of the four-column cutting is caused by the scribing action of the hard spots in the workpiece material. The thermal and chemical wear is caused by the bonding (the bonding phenomenon when the tool and the workpiece material contact the distance between the atoms) and the diffusion (tool and workpiece). The chemical elements of the two friction surfaces are caused by each other, corrosion, etc.).
Second, the tool wear process, blunt standard and tool life
Tool wear increases as the cutting time increases. According to the cutting experiment, the typical wear curve of the normal wear process of the illustrated tool can be obtained. The figure takes the cutting time and the flank wear amount VB (or the rake face crater wear depth KT) as the abscissa and the ordinate, respectively. The tool wear process can be divided into three phases:
Initial wear stage
Normal wear stage
Rapid wear stage
If the tool wears to a certain limit, it cannot be used any more. This wear limit is called the blunt standard. The actual cutting time experienced by a new knife (or re-sharpened tool) from the start of use until the blunt standard is reached is called tool life.