Mar 04, 2020
The picture shows a roller part.The material is 1Cr17Ni2. The strength, section shrinkage and impact resistance of this material are better than ordinary 40 steel. When turning this material, it shows the following characteristics: The phenomenon is serious, the cutting resistance is high, the cutting heat is high, and it is easy to stick with chips, which has a great impact on the processing quality of the part.
1.The turning characteristics of stainless steel
The cutting performance of stainless steel materials is poor.In the actual cutting process, there are some problems as follows:
First, work hardening is more serious.There are three reasons for work hardening:
(1) Due to the large plastic deformation of stainless steel materials, the lattice strengthening coefficient is large during deformation;
(2) During cutting, under the action of cutting stress, the austenite has poor stability and will transform into a martensite with greater hardness;
(3) Excessive cutting heat during cutting can cause hardened layers. The work hardening phenomenon seriously affects the progress of subsequent processes. Secondly, the cutting force of stainless steel is relatively large. Due to the large plastic deformation of the stainless steel material during the cutting process and the work hardening during the cutting process, the cutting force is greatly increased, and a reasonable choice should be made for the cutting tool. The third cutting temperature is high. Because of the large plastic deformation of stainless steel, the friction between the workpiece and the tool will increase, and the cutting heat will increase. At the same time, the work hardening phenomenon will occur when the temperature is too high. The fourth chip is easy to stick. Due to the toughness of stainless steel, the chip is not easy to cut after turning, and the chip will squeeze the processed surface between the workpiece and the tool, which affects the quality of the cutting surface. If the adhesion is serious, it will form a chip. Knobs not only increase the wear of the tool, but also cause a lot of wear on the machined surface.
2.Reasonable choice of tool materials
According to the cutting characteristics of stainless steel materials, tool materials are required to have good heat resistance, high wear resistance, and low affinity with stainless steel materials. Commonly used tool materials include high-speed steel and hard alloy steel.
Cemented carbide tools include YG and YT cemented carbide materials. It is better to use YG alloy materials for rough turning and intermittent turning, because YG materials have better toughness, faster cutting speed, and the tool and Chips do not stick. At the same time, the thermal conductivity of YG materials is also good. YT-type alloy materials can be semi-finished and finished.
3.The choice of tool geometric parameters
The geometric parameters of the tool have a great impact on the cutting force, wear resistance and surface quality of the workpiece.
Tool rake angle: The tool rake angle directly affects the strength and durability of the tool. Properly increasing the rake angle can reduce the cutting heat, the cutting temperature will not be too high, and the durability of the tool will be improved. Usually, the rake angle is 12o-20o.
Cutter angle: If the rake angle is too small, the friction between the tool and the workpiece surface will increase, which will seriously affect the surface quality of the workpiece, and increase the wear of the tool, which will affect the service life of the tool. Reduced cutting edge strength and increased tool wear. Under normal circumstances, 5o-8o is more suitable for the rear angle, and the maximum does not exceed 10o.
Tool's main declination angle: Using a smaller main declination angle can increase the working length of the cutting edge, which is conducive to the dissipation of cutting heat. At the same time, it will increase the radial force during the cutting process and easily cause vibration.
turning edge inclination of the tool: In order to increase the strength of the cutting edge and increase the deformation of the chip, it is usually guaranteed that the cutting angle is between 0o and 5o. In actual production, a double-edged tilting turning tool is usually used to break the chip more easily and prevent chip sticking.
Tool structure: Y-shaped arc rolling chipbreakers are often used for external turning tools. The chip radius is large near the tool tip and the chip radius is small at the far tool tip. At the same time, the chip is turned to the surface to be processed. Will damage the machined surface.
4. The choice of turning amount
For different types of stainless steels, due to the different chromium and nickel content, there are obvious differences in mechanical properties, and the cutting amount selected also changes accordingly. The amount of cutting has a great influence on the work hardening and cutting force of stainless steel, especially the tool's durability. To choose the cutting amount from the following aspects:
First of all, cutting speed, stainless steel materials are more difficult to process than ordinary steel materials, and their cutting speeds are also lower. Cutting speeds will increase tool wear. For different stainless steel materials, there is an optimal cutting speed. Life, processing efficiency and surface quality of parts have a great impact. Select a speed of 40mm / min-60 mm / min for this part.
Secondly, excessive feed will reduce the durability of the tool, and the same feed will affect the chip discharge and the quality of the workpiece surface. The size of the feed depends on the size of the workpiece and the speed of the spindle. Slightly bigger.
Third, when turning depth, rough machining, you can choose a larger turning depth, reduce the number of passes, reduce tool wear, but too large turning depth will increase the cutting force, which will cause vibration. Generally rough turning depth is 2-5mm. The turning depth should be reduced during finishing, and work hardening should be prevented when exiting. The cutting depth should be 0.2-0.5mm.
The processing of stainless steel materials is more difficult than that of ordinary material steels. Not only must we consider some processing characteristics that stainless steel materials tend to appear during processing, but we must also choose the corresponding processing technology according to the performance of different types of stainless steel materials to ensure processing. Quality and processing efficiency.