In the machining process of CNC milling machine, the choice of tool is an important link to ensure the machining quality and improve productivity. It is necessary to comprehensively consider the degree of automation of the machine tool, the processing content in the process, the cutting performance of the parts material and other factors.

1. Requirements for CNC tools

In the machining process of CNC milling machine, the cutting performance of the tool depends on the material of the cutting part of the tool, which directly affects the tool life, tool consumption, processing accuracy, the quality of the machined surface and processing efficiency. Tool material refers to the material of the cutting part of the tool.

(1) High hardness. The hardness of the tool material needs to be higher than the hardness of the workpiece material to be processed, otherwise under high temperature and pressure, it can not maintain the sharp geometry of the tool, which is the basic performance of the tool material. The hardness of high speed steel HBC: 63 ~ 70. The hardness of cemented carbide HRA is 89-93.

(2) Sufficient strength and toughness. The material of the cutting part of the tool must withstand great cutting force and impact force when cutting. For example, when turning No. 45 steel, when the back cut quantity a. , 4ram. When the feed rate is, =o 5mm/r, the blade should withstand a cutting force of about 4000N. Therefore, the tool material has sufficient strength and toughness. General bending strength of tool materials. (Unit Pa=N/m2) indicates its strength, with impact toughness a. (unit: J/m2) indicates the size of its toughness, which reflects the ability of the tool material to resist brittle fracture and crack.

(3) High wear resistance and heat resistance. The wear resistance of tool materials refers to the ability to resist wear. In general, the higher the hardness of the tool material, the better the wear resistance. The wear resistance of the tool material is also related to the metallographic structure, the more carbides in the metallographic structure, the finer the particles, the more uniform the distribution, the higher the wear resistance.

The wear resistance and heat resistance of the tool material are also closely related. Heat resistance is usually measured by its ability to maintain high hardness at high temperatures, that is, high temperature hardness, or "red hardness". The higher the high temperature hardness, the better the heat resistance, and the stronger the tool material's ability to resist plastic change and wear resistance at high temperatures. Tool materials with poor heat resistance will soon wear and even plastic deformation due to the significant decrease in hardness at high temperatures. Lose its cutting ability.

(4) Good thermal conductivity. The thermal conductivity of the tool material is expressed by the thermal conductivity [w/(m?k)]. Large thermal conductivity means good thermal conductivity, and the heat generated during cutting is easily transmitted out, thereby reducing the cutting temperature and reducing tool wear.

(5) Good manufacturability. In order to facilitate manufacturing, the tool material is required to have good machinability, including forging, welding, cutting, heat treatment and grindability.