Papers by Keyword: Grinding

Abstract: The machining methods such as waterjet cutting, milling, grinding, lapping, etc. are usually used to manufacture glass fiber reinforced composites (GFRCs) parts. Damages will be produced unavoidably in the machining process, no matter which machining method is employed. Subsurface damage is one of the important parameters to evaluate the surface layer damages. The detection method for the subsurface damages of glass fiber reinforced glass matrix (glass/glass) composite after machining is researched. The characteristics of subsurface damages of glass/glass composite after waterjet cutting, milling, grinding and lapping are investigated mainly, when the fiber direction is either perpendicular or parallel to the cutting surface.

Abstract: Superalloys are widely used in the aeronautic and astronautic industries owing to their excellent properties in aspects of high-temperature strength, heat stability and thermal fatigue resistance. However, the severe loading of grinding wheel and the poor integrity of grinding surface usually become the problem in grinding of superalloys with conventional grinding wheels. In this paper an experimental study was carried out to investigate the grinding characteristics of superalloys with microcrystalline alumina abrasive wheel. The roughness of grinding surface was tested, on which the effects of the grinding parameters were analyzed. Study results indicated that low loading of grinding wheel and high quality of grinding surface (Ra 0.2 μm) were obtained. The grinding parameters were optimized based on the experiment results.

Abstract: As a typical multi-functional single crystal material, Lithium tantalate (LiTaO₃ or LT) exhibits its excellent electro-optical, pyroelectric and piezoelectric properties, and has now been widely applied into many applications, especially in the telecommunication field. However, the most critical issue in the process is its pyroelectric effect and piezoelectric effect which potentially leads to crack initiation during grinding. Because it is rich in plasticity, LT demands larger specific energy for material removal. As the most machining energy is eventually converted into heat, LT undergoes a rapid rise in temperature during the grinding process, thus highly risks in thermal shock. In order to clarify the thermal influence on the grinding process of LiTaO_3, the effects of coolant temperature, diamond grinding wheel geometry and material of substrate are investigated in this research. The experimental results show that the increasing rate of grinding torque (or force) and surface roughness are two major factors dominating the crack initiation during grinding of LT wafers. Via a DOE (design of experiment) analysis, coolant temperature and wheel type stand out as the main factors influencing on the increasing rate and wafer surface roughness.

Abstract: The purpose of this paper was to investigate the silicon wafer surface roughness ground by the micro pellet grinding tool and the electroplated disc grinding tool with diamond grit size of 4-6 μm and 10-20μm under the spindle rotation speed of 500-2500 rpm and the feed rate of 1-5 μm/min. The results showed that the micro pellet grinding tool can get a better surface roughness of the silicon wafer than the electroplated disc tool. When the tools containing a larger diamond grit were employed, selecting a higher spindle rotation speed and a lower feed rate can obtain a better wafer roughness. However, when the tools of a smaller diamond grit were used, the spindle rotaion speed operates properly at a optimal value to obtain a best wafer surface roughness, which achieves Ra = 0.03-0.06 μm for the micro pellet tool. Besides, the material removal mechanism during the grinding silicon wafer for these two tools displayed mainly ductile grinding behavior.

Abstract: In order to increase tool life and workpiece surface quality, cutting processes with geometrically defined cutting edges demand inserts with a targeted prepared edge. For example, chamfers are largely used in many processes to provide edge strengthening without damaging the chip flow. In order to achieve a stable and reliable cutting process, small and uniform chamfers are necessary. In this context, the influence of grinding parameters on the edge quality and on the chamfer width deviations is investigated. It was found that larger abrasive grains increase edge chipping and that elastic deformation during chamfer grinding at insert corner radius is the main responsible for chamfer width deviation.

Abstract: The hydrostatic seal rings are one of the most important components used in reactor coolant pumps. They are generally made of hard materials such as silicon nitride, alumina, silicon carbide and tungsten carbide. Meanwhile, the form error should be within the length of one to two helium light bands and the surface roughness should be in the scale of nanometers, which make them difficult to machining. In order to solve this problem, a high accuracy grinding method using a large cup wheel had been proposed and the tilt angle of the cup wheel spindle become a crucial factor affecting the ground form errors. This paper addresses a novel method for high-accuracy calibrating the tilt angle of the cup wheel spindle to fit the extremely shallow taper angle of the seal ring conical surface, and the mathematical model is established incorporating a standard optical flat with a high-accuracy laser displacement sensor. The practicability of this method is verified by grinding a seal ring sample with the outer diameter is 200 mm and the taper angle is 700 μrad. It is found that the taper angle error is only 1.72 μrad and the radical profile error of the conical surface is about 0.22 μm.

Abstract: Double-substrate angle polishing is presented for detecting depth of sub-surface damage layer during sapphire substrate grind process. Bimorph overlap bond is used in the double-substrate angle polishing, and when measuring the beveled corrosion crack, measurement errors caused by the traditional angle polish which results in fussy boundaries between polished bevel and the edge of the original wafer plane is avoided. Also digital length measurement is used to measure specimens polished bevel machining contours, then calculate accurate slant angles, eliminate errors of inaccurate angle values and improve measurement accuracy. This experiment has tested the length of mono-crystal polished bevel crack is 175um, the angle of slant is 4.85°. According to theoretical calculation, the double-sided grinding substrate subsurface damage layer is 15um, and the depth of double-sided crystal surface is about 30um. Grinding parameters: 320# boron carbide aqueous solution, lapping pressure 110g/cm², grinding speed 30r/min.

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: t is challenging to achieve good surface quality and high efficiency simultaneously when machining thin film solar panels. In this study the machining characteristics of a multilayered thin film structure were investigated using diamond wire sawing and grinding. It was found that the efficiency in sawing was significantly greater than that of the employed grinding process, but the machined surface quality was much worse. The results indicated that grinding could still be the solution for such processing and sawing must be improved before this technology could be further progressed for machining thin film multilayered structures.

Abstract: An experimental investigation is reported on the grinding of a titanium alloy using electroplated CBN wheels with water-based grinding fluid and wheel surface cleaning fluid applied at high pressures. This work was motivated by applying grinding fluid and wheel surface cleaning fluid both at high pressures for avoiding wheel loading, which is commonly seen in titanium alloy grinding. The objective is to explore the feasibility to grind titanium alloys with electroplated CBN wheels and high pressure wheel surface cleaning fluid for enhancing material removal rates. Straight surface grinding experiments were conducted on titanium alloy blocks in both shallow depth of cut and creep-feed modes. Grinding power, forces, and surface roughness were measured. Specific material removal rates of 8 mm²/s in shallow cut mode and 3 mm²/s at a depth of cut as high as 3 mm in creep-feed mode were achieved without burning and smearing of ground surfaces. It was showed that it is feasible to grind titanium alloys with electroplated CBN wheels at enhanced removal rates by applying grinding and wheel cleaning fluid at high pressures.