With the development of modern science and technology, various high-hardness engineering materials are increasingly used, and traditional turning technology is difficult or impossible to process certain high-hardness materials. Coated cemented carbide, ceramics, PCBN and other super-hard tool materials have high high-temperature hardness, wear resistance and thermochemical stability, which provide the most basic prerequisites for the cutting of high-hardness materials. Obvious benefits have been achieved in production.
The material used by superhard tools and their tool structure and geometric parameters are the basic elements for hard turning. Therefore, how to choose superhard tool materials and design reasonable tool structures and geometric parameters is very important to stably realize hard turning.
Blade structure and geometric parameters of superhard tools
Reasonable determination of insert shape and geometric parameters is essential to give full play to the cutting performance of the tool. In terms of tool strength, the tip strength of various blade shapes from high to low are: round, 100° diamond, square, 80° diamond, triangle, 55° diamond, 35° diamond. After the blade material is selected, the blade shape with the highest strength should be selected. Hard turning inserts should also choose the largest possible nose arc radius, and rough machining with round and large nose arc radius inserts. The nose arc radius during finishing is about 0.8μm.
Hardened steel chips are red and soft ribbon-like, brittle, easy to break, non-sticky, hardened steel cutting surface quality is high, generally does not produce built-up edge, but the cutting force is large, especially the radial cutting force It is larger than the main cutting force, so the tool should adopt a negative rake angle (go≥-5°) and a larger relief angle (ao=10°~15°). The entering angle depends on the rigidity of the machine tool, generally 45°~60° to reduce the chatter of the workpiece and the tool.
Superhard tool cutting parameters and requirements for process system
1. Selection of cutting parameters
The higher the hardness of the workpiece material, the lower the cutting speed should be. The suitable cutting speed range for hard turning and finishing using superhard tools is 80~200m/min, and the commonly used range is 10~150m/min; when large cutting depth or strong intermittent cutting of high hardness materials is adopted, the cutting speed should be kept at 80~100m /min. Under normal circumstances, the cutting depth is between 0.1 and 0.3 mm.
For workpieces with low surface roughness, a small depth of cut can be selected, but it should not be too small and should be suitable. The feed rate can usually be selected from 0.05 to 0.25mm/r, and the specific value depends on the surface roughness value and productivity requirements. When the surface roughness Ra=0.3~0.4μm, hard turning with superhard tools is much more economical than grinding.
2. Requirements for the process system
In addition to choosing a reasonable tool, the use of superhard tools for hard turning has no special requirements on the lathe or turning center. If the lathe or turning center is rigid enough, and the required accuracy and surface roughness can be obtained when processing soft workpieces, that is Can be used for hard cutting. In order to ensure the smoothness and continuity of the turning operation, the commonly used method is to use a rigid clamping device and a medium rake angle tool. If the positioning, support, and rotation of the workpiece can be kept fairly stable under the action of cutting force, the existing equipment can use superhard tools for hard turning.
After years of research and exploration, my country has made great progress in superhard tools. However, the application of superhard tools in production is not extensive. The main reasons are as follows: manufacturers and operators do not know enough about the effect of hard turning with superhard tools. It is generally believed that hard materials can only be ground; the cost of tools is too high. The initial tool cost of hard turning is higher than that of ordinary cemented carbide tools (for example, PCBN is more than ten times more expensive than ordinary cemented carbide), but the cost allocated to each part is lower than that of grinding, and the benefits brought are more than ordinary Cemented carbide is much better; the research on the machining mechanism of superhard tools is not enough; the specifications of superhard tool machining are not enough to guide production practice.
Therefore, in addition to in-depth research on the machining mechanism of superhard tools, it is also necessary to strengthen the training of superhard tool processing knowledge, successful experience demonstrations and strict operating specifications, so that this efficient and clean processing method can be used more in actual production.
