The cutting part of the tool will be gradually worn under the action of high temperature and high pressure. The causes of tool wear are very complex. It involves mechanical, physical, chemical and gold functions, including abrasive wear, bonding wear, diffusion wear, phase change wear and oxidation wear. Tool wear will affect the surface quality, production efficiency and processing cost. Now let's introduce the main forms of tool wear and the process of tool wear.
Form of tool wear
The main forms of tool wear are rake face wear, flank wear and simultaneous front and rear face wear.
1. Wear of rake face
When cutting plastic metal, the cutting speed is high and the cutting thickness is large, and the crescent groove is ground on the rake face. When the tool wear continues to expand, it will lead to edge collapse and tool damage.
2. The flank is worn
When cutting brittle metals with high hardness, such as low cutting speed and feed rate, flank wear usually occurs. This form of wear occurs on the flank connected with the cutting edge, and the flank with a back angle equal to or less than zero is ground.
3. The front and rear knife surfaces are worn at the same time
In the process of cutting plastic metal, this kind of wear often occurs when using medium cutting speed and medium feed rate.
Tool wear process
1. Initial wear stage: tool wear is fast in this stage. This is caused by the rough surface of the tool or the surface structure defects.
2. Normal wear stage: in this stage, the contact area increases, the pressure decreases, the wear speed has slowed down, the wear increases evenly with the increase of time, and the cutting is stable.
3. Sharp wear stage: after the normal wear of the tool reaches a certain limit, if you continue to cut, the temperature will increase sharply, the cutting force will increase, the wear will accelerate, and even cause the edge to collapse and damage the tool. In use, it should be strictly stipulated that the tool should be changed before entering the sharp wear stage.
Cutting tool dulling standard
The tool should not be used again when it is worn to a certain limit, which is called the blunt standard. Generally, the width of the wear band measured on the tool surface later is specified as the blunt standard of the tool.
In actual production, it is often judged whether the tool has been blunt according to some phenomena occurring in cutting. During rough machining, you can observe whether there are bright bands on the machined surface, whether the color and shape of chips are different, whether there are abnormal sounds, etc. During finish machining, observe whether the roughness of the machined surface changes and measure the size and shape accuracy of the parts.
In mass production, due to the stable cutting conditions, the tool dulling standard can be determined through process tests, and the dulling standard can be transformed into the easily controlled number of machined parts or cutting time, so as to forcibly change the tool edge grinding to ensure that the tool does not enter the stage of sharp wear.
Due to different processing conditions, the blunt standards are also different. The standard value of finish machining is less than that of rough machining. Different materials and types of cutting tools have different blunt standards.