Development of superhard materials
With the rapid development of modern science and technology, the types of knives made of superhard materials such as polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (PCBN) are becoming more and more abundant, and their performance has also been continuously developed and improved. The particle size of blade abrasives ranges from tens of microns, several microns to nanometers; the content of diamond and cubic boron nitride is divided into low content, medium content and high content; binders include metal, non-metal and mixed materials; PCD layer thickness from From the millimeter level to the micron level; the combination of the PCD layer and the cemented carbide substrate has a flat surface and a corrugated surface; the PCD layer has different characteristics such as high wear resistance, high toughness, and high heat resistance.
Application of PCD/PCBN tools
At present, the application scope of PCD and PCBN cutting tools has been expanded to automobile, aerospace, precision machinery, home appliances, wood, electronic and electrical industries, etc., for making turning tools, boring tools, milling cutters and drills, reamers, countersinks, saws, Routing tools, razors, etc.
Key Points of PCD Tool Grinding Process
(1) The precision of the spindle of the grinding machine is better, and the runout of the end face of the general grinding wheel should be ≤0.02mm. The runout of the end face of the grinding wheel is too large, the grinding wheel impacts the cutting edge intermittently during grinding, it is easy to cause chipping of the cutting edge, and it is difficult to obtain a high-precision cutting edge;
(2) The grinding wheel should have a good dynamic balance. The unbalance of the grinding wheel will cause the vibration of the machine tool, which will affect the cutting edge quality and machining accuracy of the processed tool;
(3) Vitrified bonded diamond grinding wheels should be preferred for sharpening pcd tools. Because the ceramic bond is prone to microcracks during the grinding process, the abrasive grains are renewed and sharpened, the grinding process is stable, and it is beneficial to improve the precision and efficiency of the processed surface; secondly, the resin bond with high heat resistance can be selected diamond grinding wheel;
(4) Pay attention to the sharpening of the grinding wheel at the right time, and the grain size of the sharpening oilstone should be appropriate. When processing PCD tools with diamond grinding wheels, the grinding wheel will be clogged, passivated, high temperature and rapid wear, resulting in reduced processing speed and vibration, noise, and burns. Usually, the soft silicon carbide oilstone that is 1-2 finer than the used grinding wheel is selected as the sharpening oilstone;
(5) Because diamond is easy to chemically diffuse with iron-based alloys, which accelerates the wear of the grinding wheel, it should be avoided as much as possible to grind metal blades and PCD blades at the same time;
(6) The rotation direction of the grinding wheel must be rotated from the rake face of the tool to the flank face. From the force on the cutting edge of the PCD tool during grinding, it can be known that when the grinding wheel rotates from the rake face to the flank face, the grinding force (the sum of tangential and normal forces) acts on the cutting edge inward, that is, the tool is subjected to Compressive stress, it is not easy to chip; on the contrary, it is tensile stress, and the cutting edge is easy to chip. If it is necessary to reverse the sharpening due to the structure of the tool, the resin bonded grinding wheel is better than the metal and vitrified bonded grinding wheel;
(7) In order to ensure the quality of the cutting edge and improve the sharpening efficiency, the back angle of the tool can be divided into a large back angle and a small back angle. Use coarse-grained grinding wheel to grind the large relief angle first, because of the large contact surface and large grinding force, the sharpening efficiency is high; then use fine-grained grinding wheel to sharpen the small relief angle, and control the margin width of the small relief angle at about 0.1-0.3mm , small contact surface and good sharpening quality;
(8) Complete the machining of the cutting edge of the tool in one clamping as much as possible;
(9) PCD sharpening coolant should be preferably water-based grinding fluid. Due to the high hardness and poor heat resistance of PCD materials, the cooling effect of water-based grinding fluid is better than that of oil-based grinding fluid, which can improve processing efficiency and edge quality. In addition, the cooling should be sufficient during the grinding process, and the flow should not be interrupted, so as to avoid the large consumption (oxidation, graphitization) of diamond (grinding wheel, tool) and the damage of the cutting edge of the tool due to the small amount of grinding fluid or intermittent supply.