Papers by Keyword: Material Removal Mechanism

Abstract: Abrasive water jet machining is a process that removes material using sand and water. This versatile process uses a high-pressure water jet loaded with abrasive particles of mineral origin. It allows the machining of all materials and is particularly suitable for machining or stripping applications on hard metal sheets. Due to a local action, the abrasive water jet limits heating and deformation. During machining, the removal of material occurs abrasion and erosion [1]. The identification of the respective importance of this abrasion and this erosion conditions the precision of the modeling of the machined depth. In this study, these mechanisms are presented and characterized for machining on 6mm thickness TiAl6V titanium alloys sheets with or without inclination of the jet. It is possible to model an elementary passage and it allows predicting the pocket bottom profile obtained after a succession of passages. During machining, two mechanisms appear. Abrasion occurs when machining an elementary pass. Erosion will characterize the effect of repetition of passages. The analysis of the machined profiles makes it possible to characterize the influence of the abrasion mechanism and abrasion mechanism. The variation of the coefficients associated with these mechanisms can be characterized as a function of the angle of inclination of the jet.Keywords: Abrasive water jet machining, Material removal mechanism, Abrasion, Erosion, Titanium alloy, Abrasive particles

Abstract: Fcc-TiBCN powder synthesized by boronizing of Ti was pressured into monolithic block by hot pressing (HP) method. Then the block material was machined by wire-cut EDM. The machinability and the material removal mechanisms were discussed of Fcc-TiBCN block in wire-cut EDM. Results show that the machinability of Fcc-TiBCN is satisfying. The discharge current has little relationship on surface roughness in the range of factory-adjusted optimum settings. The discharge duration and pulse interval time play an important role on the quality of machined surface and EDM machining efficiency. In order to obtain excellent quality of the machined surface, the number of power tube turned on can not exceed 6, and the pulse interval time must be as long as possible. The mini roughness of machined surface is 0.4μm～0.6μm as the number of power tube turned on is 5, the pulse interval time and discharge duration is set in the range of 20～22μs and 65～75μm, respectively. There are three material removal mechanisms of TiBCN conductive ceramic in the EDM machining process: spalling, melting and evaporation. Spalling is the main mechanism resulted by thermal stress superposing.

Abstract: In order to respond to market rapidly, save design time, reduce the cost and particularly design the machine in a predictable and reliable manner, an approach based on the integration of virtual machine tool and workpiece material removal mechanism is proposed in this article for the investigation of centerless grinding process, the prediction of workpiece roundness generation and the evaluation of dynamic characteristics of grinding system. In this approach the machine structure model is firstly presented by incorporating the kinematic relationship of the feed drive system and the material dynamic parameters of the grinding system. Then the virtual machine tool model is built by the combination of the machine mechanical structure and the control loop. Finally the virtual centerless grinding is realized by integrating the virtual machine and the workpiece material removal mechanism through their coupled surface regeneration mechanism. The comparison of the experimental and theoretical results demonstrates that this virtual centerless grinding approach can investigate the workpiece roundness generation accurately.

Abstract: The Quartz substrates are widely used in various fields, and the requirement for the surface quality of quartz substrate is higher than ever before. This paper focuses on the ultra-precision polishing technology for the quartz substrates, and the material removal mechanism in the process of ultra-precision polishing is discussed. The results showed that an extremely smooth surface of quartz substrate was obtained in the ultra-precision polishing process, and the best surface roughness reached Ra 0.82nm. Meanwhile, the thickness can be controlled very well.

Abstract: Alumina is a material that is frequently used in high performance applications. Grinding of alumina is usually associated with micro-cracks which deteriorate surface quality. In order to get a deeper knowledge of the characteristics of material removal mechanisms in alumina during grinding with and without ultrasonic vibration of the workpiece, single grit scratch tests were performed in this research. The effect of the ultrasonic vibrations and cutting speed on the material removal mechanism of alumina was investigated in the chip thickness range of 0.53 μm which is common in precision grinding operations. It was shown that the material pile-up decrease with higher cutting speed. On the other hand, the transition from ductile to brittle mode of material removal occurs earlier in higher cutting speeds. The ultrasonic vibrations showed great influence in the cutting speed 30 m/s in reducing the pile-up values.

Abstract: This paper introduces the micro-abrasive suspension jet polishing technology in precision machining technology. In order to understand the micro-abrasive suspension jet erosion morphology and material removal mechanism, the erosion experiments of micro-abrasive suspension jet on 40CrMnMo7 special steel work-piece were taken. We found that when the incident angles are 90°, 60°, 30°, the polishing area is respectively annular shape, horseshoe shape and blade shape. During the erosion process, as the incident angle becomes smaller, most amounts of abrasive particles impact angles will also be small, and these cause more material removal. When the particles impact the work-piece with small angles, most particles play shearing action on the work-piece and leave the work-piece nanoscale scratches; while the particles impact the work-piece at large angles, extrusion and blow are formed by the majority of the particles on the work-piece, leaving different small size pits.

Abstract: The mechanical properties and microstructure characteristics in nano-ceramic coating material determine largely their grindability, there are a variety of wear mechanisms existing in grinding process, wear resistance of nanoceramic coatings are higher than normal ceramic coating, processing zone in ceramic materials can be divided into inelastic deformation zone and elastic deformation zone. In the process of nanoceramic coatings materials removal, inelastic deformation removal and brittle removal is the coexistence, the grinding force, existing in nanostructured ceramic coatings, is bigger than it in general structure ceramic coating. In plastic deformation materials removal mode, the grinding surface roughness is low, while in brittle removal , surface grinding roughness is high , prone to grinding surface/subsurface damage.

Abstract: Chemical mechanical polishing (CMP) has become the most widely used planarization technology in the semiconductor manufacturing process. In this paper, the distinguish method of lubricating behavior in wafer CMP had been analyzed in theory firstly. Then, the tests of wafer CMP with silicon wafer and deposited copper wafer at different polishing pressure had been done. By the test results, the Stribeck curves obtained showed obvious smooth. But in normal wafer CMP conditions, the friction coefficient of polishing area was above 0.1. By analyzing the experimental results, it was concluded that the lubrication state in CMP interface is belong to the boundary lubrication and the material removal is the process of bringing and removed of the chemical reaction boundary lubricating film on wafer surface constantly. The contact form between the Wafer and the polishing pad is the solid-solid contact. These results will provide theoretical guide to further understand the material removal mechanism of in wafer CMP. Keywords: Chemical mechanical polishing, material removal mechanism, lubrication form, boundary lubrication.

Abstract: Chemical mechanical polishing (hereinafter referred to as CMP) which is to provide the best global planarization technology has been researched and applied in the field of ultra-precision surface finish. This article outlines the principles of the CMP process, focusing on the development of the major theoretical models such as phenomenological model, contact mechanics model, fluid dynamics model and hybrid model based contact mechanics and fluid dynamics in chemical mechanical polishing process. The hybrid model based contact mechanics and fluid dynamics has been a good developed in recent years. The model based on the molecular / atomic scale is proposed the further research methods of CMP's theoretical model.

Abstract: Based on the analyzing ultraprecision grinding process of hard and brittle materials, taking ELID grinding of silicon nitride ceramic as an example, active control technology of passivating films state was introduced in this paper. ELID ultraprecision grinding process respectively at adaptive dynamic balance mode, discontinuous electrolyzing mode and discontinuous grinding mode had been comparatively studied. By means of AFM used for analyzing surface topography of parts, studies show that material removal method for ELID grinding is always a combination of micro brittle fracture, plastic shearing, lapping and polishing action, and which is the main material removal mode depends on the actual grinding contact state. Finally, finishing surface generating mechanism for silicon nitride in ELID ultraprecision grinding was summed up.