Advanced Materials Research Vol. 1136

Abstract: Electroplated profiled superabrasive grinding wheels which integrate both advantages of grinding and profile milling have been widely used in the machining process the wide chord hollow fan blade rabbets made of Ti-6Al-4V alloy. However, the employment of these tools has been impeded by drastic forces and thermal damage. In order to investigate the variation regularities of grinding forces and temperature with different machining parameters, experiments were carried out with single layer electroplated CBN grinding wheels. Grinding forces and temperature were measured and analyzed. Meanwhile, tool life and metallography of workpiece were studied. The results showed that higher spindle speed leads to lower forces and higher temperature. With the increase of feed rate and radial cutting depth, forces and temperature increase. Strong adherence of chips makes abrasives grits blunt which results in the increase of grinding forces after a great deal of tests. Metallographic structure of the machined workpiece is almost identical with the original sample.

Abstract: An investigation was undertaken to explore the grinding characteristics in grinding of yttrium vanadata (YVO4) crystal by using a resin diamond wheel. The grinding forces and surface roughness were measured and the morphological features of ground workpiece surfaces were examined. The results indicate that the depth of cut is the leading factor in affecting grinding forces whereas the surface roughness is mainly governed by the grinding speed. The material removal mechanism was found to be dominated by brittle fracture mode at conventional grinding speeds, and gradually transfer to ductile flow mode under higher grinding speeds, which is greatly related to the maximum undeformed chip thickness.

Abstract: The loading of the grinding wheel and adhesion of the workpiece material to the cutting edges of the grinding tool are among the main reasons which limit the process efficiency when grinding ductile materials. The micro topography of the grinding tool changes drastically as a result of loading. Higher grinding forces and temperatures, poorer surface quality and process accuracy are the consequences of the adhesion of the workpiece material to the grinding tool surface. A novel and promising technique to reduce the possibility of loading and adhesion in the grinding process is the infiltrating of the grinding tool. This study describes the results of infiltration of vitrified bonded conventional grinding wheels with graphite in the surface grinding process. The effects of infiltration have been studied for the first time on various grinding wheels with different grain materials, grit sizes, porosity and hardness. Two different types of steel which are very popular in the automobile industry, 100Cr6 and 16MnCr5, were chosen as the workpiece material by the surface grinding experiments. The selected cutting parameters cover a wide range of the practical surface grinding processes which are utilized generally in the industry. It has been experimentally shown that the type of infiltration plays an important role in reducing the loading of the wheel. Better surface quality and longer dressing intervals are the main results of the infiltration of the grinding tools.

Abstract: While grinding with CNC cylindrical grinding machines, there are many factors that determine the precision and accuracy of the finished product. These may include dimensional accuracy, surface roughness, circularity (roundness), cylindricity, etc. But all these factors pertain to the work. The condition of the tool, in this case, the cutting edges of the grinding wheel, also greatly influence the profile and precision of the work. So, in order to maintain the precision of the work, there is a need to repeatedly and regularly maintain the cutting edges in a good cutting condition, by the process of dressing. In other words, when the swarf gets adhered to the grinding wheel, the abrasive particles can no longer perform machining with the same efficiency, due to increase in contact surface area between the abrasive particles and the work. This dissertation describes a technique that can be adopted to continuously monitor the grinding forces generated during the grinding operation, by using an in-process 2-dimensional piezoelectric force sensor, which can simultaneously measure the force and break it down into its two force components. The force sensor not only calculates the force generated, but also quantifies the force variation. By analyzing the variation in the radial and tangential force components individually, and by conducting Fourier analysis on the observed data, it is found that deterioration of the grinding wheel and the dress pattern can be continuously monitored and controlled.

Abstract: The new processing technique of vacuum evaporative pattern casting (V-EPC) process was explored to fabricate the cast-iron bonded cBN grinding wheels in this paper. The influences of pouring temperature, degree of vacuum, percentage and size of the cBN grits on the microstructures, distribution and thermal damage of cBN grits in the grinding layer, as well as the surface quality of the grinding layer were investigated. The experimental results revealed that thermal damage of the cBN grits and severe damage of nodulizer occurred when the pouring temperature was around 1480°C. The optimized pouring temperature for fabricate the austenite-bainite ductile cast-iron bonded cBN grinding wheels was about 1400°C. The appropriate degree of vacuum was 0.06Mpa. Too high or too low level of degree of vacuum would result in low surface quality of the grinding layer. The uniformity of the distribution of cBN grits in the metal matrix improved with the increase of the percentage and size of the cBN grits.

Abstract: Laser-dressing has been shown to be a promising method for overcoming some shortcomings of the conventional methods such as high wear of the dressing tool and its environmental concerns, high induced damage to the grinding wheel, low form flexibility and low speed. In this study, a resin bonded cBN grinding wheel has been dressed with a picosecond Yb:YAG laser. The efficiency of the laser-dressed grinding wheels has been compared with the conventionally dressed and sharpened grinding wheels through execution of cylindrical grinding tests on a steel workpiece (100Cr6). The conventional dressing and sharpening processes have been performed by using a vitrified SiC wheel and vitrified alumina blocks, respectively. By recording the spindle power values along with the surface topography measurements of the ground workpieces and the extraction of two roughness parameters (the average roughness R_a and the average roughness depth R_z), it is possible to provide an assessment of the cylindrical grinding process with different dressing conditions i.e. laser-dressing and conventional dressing. Accordingly, a strategy will be proposed to optimize the cylindrical grinding process with laser-dressed wheels regarding the forces and roughness values.

Abstract: High-efficiency and precision machining of complicated components can be realized by using metal-bonded CBN grinding wheel. However, the difficulty in dressing those superabrasive grinding wheels is one of the main obstructions to popularize its application in industry. Different from the traditional methods, the aim of the paper is to investigate the electro-discharge dressing of bronze-bonded CBN formed grinding wheel. Based on the analysis of electrical discharge parameters and grinding performance, the results show that electro-discharge dressing of CBN formed grinding wheel is feasible. With the increase of pulse duration, pulse voltage and pulse current, the dressing efficiency is increasing, more abrasive grains are protruding, but surface topography of grinding wheel is worsen. Therefore, grinding tests show that, in order to get the dressing quality better and keep the dressing efficiency higher, the bigger electrical discharge parameters are chosen for rough dressing process and the smaller ones are chosen for finishing process.

Abstract: The concern for environmental problems has been increasing rapidly in recent years. Water-soluble coolants are widely used in machining processes. To reduce management costs and the environmental load of water-soluble coolants, the authors studied a recycling system for water-soluble coolants. With this recycling system, water is extracted from a waste coolant by chemical or biochemical treatment; the recovered water is re-utilized as a diluent for a new coolant. Coolant recyclability depends on the coolant type. Most water-soluble coolants contain alkanolamines for corrosion inhibition and maintenance of putrefaction prevention. However, alkanolamines are difficult to eliminate from water-soluble coolants by chemical and physical waste treatment processes. Some amine-free, water-soluble coolants have been developed and are commercially available. The reduction of environmental load in the treatment of waste coolants is anticipated for amine-free coolants. We applied the recycling process to a commercially available amine-free, water-soluble coolant. The amine-free coolant showed good recyclability and lubricating performance. However, the corrosion inhibition performance of the coolant was inadequate for use in general machining. Recently, our cooperative company developed a prototype amine-free, water-soluble coolant with improved corrosion inhibition. In this study, we experimentally examined the recyclability and performance stability of this newly developed coolant. The experimental results showed that the new amine-free coolant has good corrosion inhibition equivalent to conventional amine-containing coolants. In addition, the recyclability, stability, and cooling and lubricating performance of the coolant are equal to conventional amine-free coolants. The amine-free, water-soluble coolant with improved corrosion inhibition has the advantage that it can be used in the recycling system for water-soluble coolants.

Abstract: An experimental investigation of the hole machining performance for woven carbon-fiber reinforced PEEK (polyetheretherketone) sheets by an abrasive waterjet (AWJ) is presented. It is shown that AWJ machining can produce good quality holes if the cutting parameters are properly selected. Plausible trends of the hole quality with respect to the process parameters are discussed. Nozzle traverse speed and intended or programmed hole size are found to have a significant effect on the diameter error of the machined holes, hole roundness, and hole wall inclination angle, while water pressure and abrasive mass flow rate exhibit an insignificant effect. An increase in the traverse speed decreases the overall hole quality, while an increase in the programmed hole diameter decreases the hole diameter error and roundness error, but increases the hole wall inclination. There is not any clear trend of the hole wall surface roughness with respect to the process parameters. Moreover, high water pressures may result in hole defects, such as entrance surface chipping, delamination, internal cracking and fiber pull-out. It is found that the optimum process parameters are about 200 MPa water pressure, 2 mm/s nozzle traverse speed and 7.0 g/s abrasive mass flow rate. Recommendations are made for compensating for the hole size deviation and empirical models are fianlly developed for these hole characteristics.

Abstract: Composite materials, such as CFRP, are hard-to-cut materials but useful for their specific strength. Usually creating small holes in them is done using drill tools, but tool abrasion occurs early, reducing quality, raising processing costs. Comparing drilling with other processing methods, it was revealed in a previous report that it was possible to effectively create large quantities of small holes using blasting [1]. However, such blast processing involves unknown mechanisms. In the present report, we investigated the material-removing mechanisms of blasting from the viewpoint of erosion abrasion, and looked into the most suitable method by changing hole sizes and processing conditions. The results revealed, relationships between abrasive particle size and hole accuracy or hole processing efficiency as well as the optimum abrasive combinations according to hole diameter.