Key Engineering Materials Vols. 389-390

Abstract: The purpose of this study is to make clear the machining effect of the precision abrasive machining using the cavitation in reversing suction flow, which can easily finish to a fine surface by a simple apparatus. The machining fluid including loose micro abrasive grains is sucked by a pump, and the cavitation occurs ahead of the nozzle fixed in the suction chamber because of the rapid decrease of pressure of machining fluid. We use the cavitation impact to make the abrasive grains to interfere with the workpiece surface. In this report, the possibility of application of the new abrasive machining to the precision manufacturing is investigated by analyzing the behavior of machining fluid, the stock removal and the surface finish in machining of glass. The cavitation impact is strongest under the nozzle clearance of 20mm and restriction nozzle diameter of 4mm. Glass surface is finished up to several nanometers in Ry with slight stock removal by the proposed abrasive machining.

Abstract: Due to the high grinding speed and the less contact length, there is the super high material strain rate in the contact layer during quick-point grinding process. Based on the principle of micro-damages mechanics, it is the impact process between the workpiece and the grits on the wheel in the process. The weakening effects of the super high strain rate caused by the mechanical impact micro-damages and the adiabatic shearing damage can lower the dynamic strength of the material in contact layer and the micro-plastic pile-up deformation on the ground surface in the process. Therefore, it is possible to improve the surface integrity of the workpiece since the materials removal mechanism is changed in quick-point grinding process. In this paper, the impact performances and the model of quick point grinding process were studied. Based on the above, the model of the ground surface roughness related to the plastic pile-up deformation was established. The effects of the strain rate on the ground surface roughness and the materials removal ratio were analyzed. In addition, the grinding experiment was performed to testify such investigations. It is indicated that quick-point grinding is an impact process assuredly during the removing material process.

Abstract: Quick-point grinding is more advanced and more efficiency as a method of high and super-high speed grinding. Its main grinding properties are low grinding forces and temperature. Its basic characteristic is the axis of wheel and workpiece are not parallel and not contained by the same plane. That makes the geometrical property of the quick-point grinding different from conventional cylindrical grinding. This paper emphasizes particularly on the abrasive geometry analysis on the quick-point grinding. After founding a model, this paper has educed equivalent wheel diameter, maximum contact length, undeformed chip thickness and so on. In this paper the quick-point-grinding angle is made use of to find a model of grinding force and deduce an expressions.

Abstract: When grinding material compounds, different material properties cause significantly changed cutting conditions. Grinding forces, wheel wear and wear mechanisms as well as temperature load of the system differ due to these changes in mechanism, leading to deviant surface qualities and geometrical errors. If consistent quality at the compound’s transition from one material into the other is needed, these errors need to be compensated. In this paper geometry error sources are evaluated by comparing error cause models to experimental results.

Abstract: This paper presents a new type of drill grinder based on a special universal joint. The special universal joint is composed of a parallel mechanism with three legs as the inputs. One can rotate as a spindle; other two legs can drive a moving platform and make a drill point get an accurate position in workspace. Due to the simple mechanical structure comparing the grinder with the existing conventional CNC cutting tool grinders, it should be easy for the grinder to manufacture at a low cost. In addition, inverse kinematic equations of the special type of universal joint are derived.

Abstract: Spindle-bearing system plays a crucial role in superhigh speed grinding, which directly affects machining precision, but it is complex and difficult to get the dynamic performance in experiment. This leads to study how to accurately simulate dynamic performance of spindle-bearing system. So a method which springs and damping units imitate bearing support is proposed in this paper. The proposed method can predict the regular pattern which bearing stiffness and damping ratio affect natural frequency and harmonic response. The research demonstrates that the method predicts well the dynamic performance of the spindle-bearing system and it is close to actual condition, therefore, it can be a reference for dynamic optimization design of spindle-bearing system in superhigh speed grinding.

Abstract: In this paper the geometry of the grinding wheel effective topography is analyzed. Existing and newly developed abrasive grain geometry models are investigated. Further, different abrasive distribution systems are developed and the grinding wheel surface is generated. The 3D stereomicroscopy at the Scanning Electron Microscope offers the opportunity to measure a three-dimensional profile of the grinding wheel. Hence, the investigations of the real grinding wheel surface can be used as a verification of the developed surface model. Abbott-Firestone-Curves are used as a comparison of the model based topography and the real grinding wheel surface. The variation of the grain geometry and distribution offers the opportunity to adapt the simulation to the grinding wheel specification.

Abstract: Ultrasonic machining (USM) is an effective method for machining of hard brittle materials. In this process, the slurry is supplied to the gap between the workpiece and the ultrasonic vibrating tool, and the materials are removed by the impacts of the abrasive grains that are pressurized by an ultrasonic vibrating tool. The purpose of this research is to achieve precise and efficient microfabrication on hard brittle materials by USM. However, in the case of microfabrication, chipping which is generally observed around the edges of machined micro holes and grooves, deteriorates the machining accuracy. In addition, there is another problem in that the machining efficiency decreases with the progress of the machining. Electrorheological fluid-assisted USM has been proposed as a countermeasure to these problems. In the present study, the problems and countermeasures associated with the machining of high-aspect ratio micro holes in hard brittle materials by electrorheological fluid-assisted USM are investigated. By positioning an auxiliary electrode under the workpiece, it becomes possible to keep the electric field high even when the machining depth becomes large. As a result, high-precision and high-aspect ratio micro holes can be machined on hard brittle materials.

Abstract: Compared to other machining processes, conventional grinding has a low material removal rate and involves high specific energy. A major part of the specific energy in grinding is changed to heat which makes harmful effect on surface quality. A recent and promising method is the use of ultrasonic assistance to increase the material removal rate along with decreasing the thermal damage on the workpiece and reducing cutting forces. The advantages of Ultrasonic Assisted Grinding (UAG) were proved mostly for the brittle material. Our investigations show the improvement on the surface roughness, reduction of the grinding forces and thermal damage in case of using UAG comparing to Conventional Grinding (CG) for a soft material of 100Cr6. The designed and developed ultrasonically vibrated workpiece holder and the experimental investigation show a decrease of up to 40% of normal grinding forces.

Abstract: Although titanium is a very useful material and becoming more in demand, we are faced with difficulties in machining the material. By applying ultrasonic vibration to the tool tip, interrupted cutting can be applied. Using ultrasonic vibration-assisted cutting of titanium alloy, we succeeded in reducing the cutting force. This technology enables us to improve tool wear and surface roughness of the workpiece. In regards to cutting fluid supply methods, it was found that semi-dry cutting was the most suitable for ultrasonic vibration-assisted cutting of titanium alloy.