The commonly used PCD cutting tool grinding process includes diamond grinding wheel mechanical grinding, electric discharge grinding, electrolytic grinding, etc., in which the diamond grinding wheel mechanical grinding is the most mature technology, and is also the most widely used at present. Although this method has low grinding efficiency and high machining cost, it can obtain good cutting edge quality and complete and clean front and rear cutting face.
The material removal mechanism of PCD cutting tool with diamond grinding wheel is relatively complex. Scholars at home and abroad have conducted a lot of research on it. At present, there are mainly the following viewpoints:
(1) German scholar M. According to Kenter, scratching and sliding occur in the process of grinding PCD tool with diamond wheel, and the main removal methods of materials are bonding, scratching, tribochemical reaction and surface fracture. He believes that in most cases, the removal of PCD materials is mainly by tribochemical reaction and surface fracture. Due to the high brittleness of PCD materials, it is easy to induce cracks under the extrusion of diamond abrasive particles. The cracks expand under the action of mechanical and thermal stress, and eventually lead to the spalling of PCD materials. At the same time, the friction heat will make PCD graphitization and other tribochemical reactions.
(2)GE's K. J. Dunn et al. observed the surface morphology of the grinding PCD composite sheet with scanning electron microscope, and concluded that the failure mechanism of PCD material was mainly micro-brittle crushing and fatigue damage.
(3) Chinese academician Ai Xing et al. believed that the removal method of PCD material is as follows: when the grinding wheel contacts with PCD at the moment, the grinding force increases suddenly, and severe mechanical impact causes PCD surface to crack or even break. During the stable grinding period, the grinding wheel particles are squeezed and rubbed on the PCD surface. When the pressure reaches a certain degree, the PCD surface cracks will form. When the friction temperature reaches a certain level, the PCD will undergo graphitization and other chemical reactions.
Conditions of grinding machine tools
The characteristics of PCD materials determine the requirements of PCD cutting tool grinding machine: not equal to ordinary tool grinding machine, that is, must meet the following conditions:
The grinding wheel spindle and the machine tool as a whole are required to have high rigidity and stability to maintain the constant pressure of grinding wheel on PCD material.
The grinding wheel can swing laterally to ensure uniform wear of the grinding wheel end face. The swing frequency and amplitude of the grinding wheel can be adjusted.
Equipped with optical projection device and high precision rotary table.
Adopt special diamond grinding wheel.
Selection of grinding wheel
The mechanical grinding of PCD tool mainly depends on the tribochemical reaction and surface fracture with diamond grinding wheel to remove the excess material. The particle size, concentration and binder of diamond grinding wheel have a great influence on the quality and efficiency of PCD tool grinding. Therefore, the correct selection of grinding wheel is very important. After comparison, we choose the European TY-R0LIT grinding wheel. The diamond grains of this grinding wheel are implanted into the grinding wheel one by one and arranged in an orderly manner. The grinding rate per minute is 20 ~ 30 times that of the ordinary diamond grinding wheel. The experience shows that the grinding wheel with larger particle size should be selected as far as possible under the premise of satisfying the machining quality requirements. The diamond grinding particle size we selected is: coarse grinding particle size 22um; Semi-fine grinding particle size 15um; The fine grinding particle size is 9um.
Treatment of blades before and after grinding
Before grinding PCD cutting tools, observe whether there are aluminum chips on the front and rear cutting surfaces. If there are, erase them with diamond whetstone. After grinding the edge, the front end is ground with diamond paste. After rough grinding, semi - fine grinding, fine grinding, grinding treatment of PCD tools can really meet the requirements of use.
After grinding, the dimensional accuracy and straightness of the PCD cutting tool can be detected directly on the projector of the machine tool, and no obvious defects such as uneven or jagged shape are allowed. The flatness of the cutting edge can also be examined under a microscope of more than 100 times.