Research And Application On Grinding Heat And Its Monitor-ing Methods In High-speed Cylindrical Precision Grinding

The extreme manufacturing technology was listed as one of the key frontier technologies with prior support in "The National Medium-and Long-Term Program for Science and Technolo-gy Development (China,2006-2020)". As one of the important extreme manufacturing technolo-gies, super precision manufacturing requires more studies on higher grinding quality and higher grinding efficiency. As Dr. Konrad Guhring, a German grinding specialist, said that, high perfor-mance grinding is meeting the new challenges in the whole grinding process and grinding system, including grinding grinder, grinding wheel, the cooling and the safety device, the original shape of workpiece and the extreme cutting conditions. Knowledge in multi-disciplinary of thermal, chem-ical and metallurgical are required to be fully understood in the process of the instantaneous con-tact between the wheel and the workpiece during the grinding. Most of the power produced by the grinding speed and grinding force is converted into grinding heat, which will significantly affect the surface quality and performance of workpiece surface. In this dissertation, monitoring and controlling methods for grinding heat was studied by simulation and experiments of high-speed cylindrical grinding and several achievements and innovations were made.(1) The simulation of single grain grinding process was researched in this dissertation. The results show the real contact length in the grinding area was twice of the traditional geometric length, and the number of chip formation was increased as the grinding wheel speeds up. The highest temperature of the grinding area occurred on the chips and the shear surface with a short acting time less than1μs. The value of the highest temperature on the workpiece surface was only50-80%of the highest temperature in the grinding area. These conclusions were valuable for the related simulation and experiment researches in the field of high speed grinding or high speed machining.(2) A method of multi-point temperature monitoring on the grinding contact area in high-speed cylindrical grinding was presented in this dissertation. A device and a testing system of real-time multi-point temperatures measurement were designed in this dissertation. The real-time tem-perature distribution over location and time on the surface of the workpiece in grinding zone could be obtained with this device. The time when the grinding wheel enters and leaves the grinding area could be calculated by using the sparks of thermal among the temperature curves of the workpiece, and a calculation method of the real contact length in the grinding area could be obtained. Based on the experimental data of TC4with different grinding parameters, the real contact length calcu-lated by temperature curves was about1.5-2times of the traditional geometric contact length. The results showed that the plastic deformation and thermal deformation in the grinding process have important influence on the real contact length. A reliable prediction, using the heat flux distribu-tion model, of the temperature distribution on workpiece surface can be supported by this real contact length.(3) Based on the surface temperature acquired by grinding experiments with different grinding parameters, the heat flux distribution along the contact length was derived which is asymmetric and is similar shape as Rayleigh distribution. By comparing with the quadratic heat flux distribution model, the maximum heat flux of Rayleigh distribution was found closer to the entrance of grinding area, in the position of40%contact length, which provided an effective basis for the design of the cooling location in high-speed cylindrical grinding. An empirical formula of energy partition ratio into the workpiece was then derived by using the energy partition model based on the workpiece surface temperature, the tangential grinding force and the average chip temperature from the grinding process simulation of single grain. Thus, the temperature distribu-tion monitoring of the grinding contact area could be realized based on the regression equation of energy partition ratio, Rayleigh distributional heat flux and the tangential grinding force monitor-ing.(4) The influence of grinding parameters on the surface temperature, forces and the workpiece quality was analyzed based on the simulation and experiments. The relevant character-istics of the materials which are difficult to machine under high speed grinding were obtained. 1) In case of TC4, a plastic material, the material strain rate and grinding temperature im-proved while the strain and the grinding force decreased as the wheel speed increased. The de-crease of strain and increase of the strain rate was one of the main factors leading to ductile brittle transition and the surface roughness improvement. The chip formation and material removal rate was increased at the same time.2) In case of SiC, a brittle material, the strain rate increased while the grinding force de-creased as the wheel speed increased. The grinding temperature had an inflection point at80m/s, indicating the workpiece surface temperature decreased when the grinding wheel speed was higher than that80m/s. The higher temperature on the workpiece surface was one of the main factors that leads to the brittle ductile changes on the workpiece surface, namely, the surface temperature of high speed grinding was conducive to reduce the micro crack damage layer and improved the surface roughness of brittle materials.3) The workpiece surface temperature was reduced by improving simultaneously the grind-ing wheel speed and the workpiece speed. It was also conducive to control the ratio of generated residual tensile stress, the grinding burn due to the grinding heat, and improve the surface quality.