Key Engineering Materials Vols. 359-360

Abstract: Grinding wheel passivation is an inevitable phenomenon during grinding process. It has important guiding significance for the formulation of grinding technique to unveil the passivation rule and generation mechanism. Taking grinding efficiency as evaluation indicator, the passivation curve of grinding wheel during full passivation period under the constant-force grinding condition is established through experiments in this dissertation, which is divided into three stages according to passivation speeds and passivation patters, i.e. early passivation stage, stable passivation stage and sharp passivation stage. Of which, the passivation speed is the slowest but with the highest grinding efficiency in early passivation stage. The change of passivation curve with the time is a process from concave to convex, which is totally different from the wearing process of grinding wheel in this stage. With combination of experiment conditions and wearing characteristics of grinding wheel, the passivation rule and its generation reasons are discussed deeply. Furthermore the exponential function y = abx is adopted to make fitting for passivation curve based on the scatter plot of stable passivation stage and regression equation is derived through the fitting result of origin thus to testify the correctness of the inference.

Abstract: Based on grind-hardening experiments, the two side-direction burrs were studied. Three main stages (burr generation, augmentation and formation) in the burr yielding process were clarified and the varying laws of burr morphologies and dimensions were systematically revealed. In turn raises, some new technologies, processes and methods of actively controlling burrs were put forward.

Abstract: Quick-point grinding is used to machine the round surface with super abrasive wheel at high grinding speed. Because it is point contact between the grinding wheel and the workpiece due to the point grinding angles in the process, the grinding model is different from the conventional cylindrical grinding in theory. Especially, the edge contact width between the wheel and the workpiece is not always equal to the thickness of the wheel, but rests with the depth of cut and the grinding angles greatly. The depth of cut has the effects on the micro-geometric properties especially the ground surface roughness by means of the variations of the edge contact width, the grinding force and heat in the process. Based on the theoretical studies on the surface roughness, the quick-point grinding experiments and the measures for the surface roughness were performed at different depth of cut. The effective mechanism of the depth of cut on the ground surface roughness was analyzed deeply. Some conclusions to influence surface roughness were also gained.

Abstract: This paper deals with the development of a high-efficiency and precision grinding technology for producing HIPSN ceramic bearing races. A new high-speed CNC grinding machine has been developed, which is equipped with a high-speed ceramic spindle with a built-in motor. Extensive experiments have been performed with this new machine to investigate the influence of various process parameters such as wheel speed, work speed, depth of cut, and wheel grit size on material removal rate, surface finish, grinding forces, and so on. The results of these investigations are presented in this paper. With the application of this technology, a low cost production of ceramic bearings race was realized with the most optimized process parameter.

Abstract: The KDP (Potassium Dihydrogen Phosphate) crystal, used as an important photoelectron part in the laser nuclear fusion system, is a typical kind of hard-to-machine material because of its soft, brittle, anisotropic property and nano-scale requirement for the shape and plane precision. Based on the experiments of the KDP crystal’s grindability, certain process parameters, such as the wheel granularity, the grinding depth and the workpiece’s feeding speed etc., and their influences on the grinding force and the surface roughness of KDP workpiece are analyzed. Furthermore, some KDP crystal’s typical surface damages in grinding are analyzed and some technical approaches to increasing the ultraprecision machining surface quality of KDP crystal are suggested as well.

Abstract: The present study was undertaken to compare the consumed power in surface grinding of three different materials with a vitrified CBN wheel. High speed steel, stainless steel, and natural granite were used as the workpiece materials in the experiments. Two different depth of cut and workpiece velocity were combined to give different material removal rates. The spindle power was in-process monitored in each pass of grinding. The radius wear of the grinding wheel was also measured and the morphologies of CBN grains were observed during the grinding of high speed steel and granite. The power for the grinding of high speed steel was found to be the lowest under any operating parameters. For other two materials, the results became complex. At shallower depth of cut, the power for the grinding of stainless steel was higher in most cases. However, the power for the grinding of granite was higher under larger depth of cut. It was found that the grinding wheel failed much earlier in the grinding of granite as compared with the grinding of high speed steel.

Abstract: Some key parts used in such area as the national defence are made of high performance hard and brittle materials, and they should meet not only the requirement of geometry accuracy but also that of specified physical performance in manufacturing. The Radome is one of such key parts in the active homing guidance weapon, with a typical complicated surface. In order to meet the electric thickness requirement, a controlled removal grinding point-by-point is needed for the radome during its precision machining. A special 3-coordinates equipment with spherical diamond grinding wheel is adopted; the grinding paths are generated in the planes normal to the cutter axis with a Z-level profile machining method; the feed step is determined by step screening method; and the stepping between layers is carried out according to the remaining scallop crest height. Process conditions including the grinding depth and the workpiece speed are determined through experiments, and the process errors under different processing conditions are analyzed to put forward an optimized processing tactics. As a result, a basis for precision removal process of any other part of high performance hard and brittle materials with complex surface is established, and a technology support for precision machining of key parts in the national major projects is provided.

Abstract: In order to understand the grinding mechanism and analyze the grinding operation, it is necessary to study the contact phenomena between wheel and workpiece during grinding operation. The contact length, the grinding temperature distribution within the contact zone, and the grinding forces are measured in-process by using Critical Contact State mode, thermocouple method, and 3-axis piezoelectric dynamometer, respectively. It is found that the grinding conditions and the properties of work material have effects on the contact length, moreover, the mechanism of which is discussed in this paper. The results show that the contact length significantly interacts with grinding force and grinding temperature in the grinding zone.

Abstract: In the present study, zirconia ceramic was ground with a resin-bonded diamond wheel on a precision surface grinding machine. Grinding temperatures generated at the wheel-workpiece contact zone were measured using a sandwiched foil thermocouple, and the net consumed grinding powers were also measured. The energy partition to the diamond abrasives was estimated using measured grinding temperatures and powers. Based on the energy partition values obtained from the analyzed results, the diamond tip temperature was calculated and found to be over 1000°C if the circular grain contact of radius was less than a critical value for ductile field grinding of zirconia ceramic.

Abstract: This paper introduces the new technology of ultrasonic vibration honing, and analyzes the cutting principle of ultrasonic honing in terms of cutting motion, grain performance and cutting quantity. Then, the applied effect used in the cast-iron cylinder of DY90 is introduced. The principle and the structure of this device are discussed. This new technology can further be used in micro-car’s cylinder, can provides a high-productivity, high-quality for cast-iron cylinder.