Key Engineering Materials Vols. 304-305

Abstract: Experimental researches on material removal rate and surface roughness of Al2O3 engineering ceramic guide-pulley lapping were carried out using W20 and W5 fixed oilstones by self-developed ultrasonic lapping tool both with and without ultrasonic assistance. Experimental results show that lapping speed, lapping pressure and grain size produce different effects on the lapped surface roughness and material removal rate. The material removal rate in ultrasonic lapping process is two times as large as that in traditional lapping, and the ground surface roughness is superior to that in common machining method. The material removal rate increases along with the average diameter of grains and the lapping speed both in ultrasonic lapping and traditional lapping. In traditional lapping process the material removal rate becomes bigger along with the lapping force, while in ultrasonic lapping it gets the optimal value with the lapping force 450N. The value of lapped surface roughness increases along with the lapping speed in traditional lapping, on the contrary it decreases contrast to the lapping speed until 250rpm in the ultrasonic lapping. The value of traditionally lapped surface roughness decreases contrast to the lapping force, whereas it achieves the minimum with the lapping force 450N with ultrasonic assistance.

Abstract: A brittle-ductile transition lapping mechanism is proposed for the mechanical lapping of ultra-precision diamond cutting tools, and then the critical depths of cut for brittle-ductile transition in different orientations and on different planes are deduced in theory. Combined the critical lapping depth with the contact accuracy between rotating scaife and lapped tool surface, the influences of processing factors on cutting edge radius are studied. Both the theoretical analyses and experimental results indicate that the vibration of lapping machine tool and surface quality of scaife have enormous influences on the sharpened cutting edge. And lapping compression force has an optimal value. Lapping rate should be considered when lapping velocity is selected. But the smaller the lapping velocity is, the littler the cutting edge radius sharpened. Finally, the optimal selections are performed for each influencing factor and a perfect diamond tool is lapped in ductile mode with a cutting edge radius of 30~40nm and a surface roughness Ra of 0.7nm.

Abstract: In this paper, in order to analyze the oxidation, dissolution and corrosive inhibition effects of additives in the slurry for copper Chemical-mechanical polishing(CMP), the slurry(pH5) with the peroxide as an oxidant, the citric acid as a complexing agent and the benzotriazole(BTA) as an inhibitor is studied. The static etching rate and polishing rate of the Cu-H2O2-Citric acid-BTA slurry are measured. The electrochemical behavior involved in the dissolution and corrosive inhibition of copper in the solutions containing additives is investigated by the electrochemical impedance spectroscopy (EIS) studies. The surface roughness is measured using ZYGO 3-D surface profiler. It is observed that when the slurry is with only 5wt% peroxide existing, copper is stable and slight etching rate on the copper is produced, and the etching rate is only 8.7nm/min. When 0.6wt% citric acid presents after adding 5wt% hydrogen peroxide, the etching rate will increase by 5.3 times, with a blue complexing product emerging. When the inhibitor BTA is added, the corrosion will be effectively restrained. From the EIS results, the impedance of copper in 5wt% peroxide solution which is in passivation can be greatly decreased by adding the citric acid as a complexing reagent. And the impedance of copper in the solution containing peroxide and citric acid can be increased by the addition of BTA. The surface roughness of the wafer polished with the slurry of 5wt% peroxide+0.6wt% citric acid+0.12wt% BTA slurry is Ra 4.7 Å.

Abstract: Based on the principle of sphere generating and Electrolytic-Abrasive Machining (EAM), a new EAM method —Electrolytic-Abrasive Sphere Finishing is developed. In the experiments, the tubular cathode is covered by unwoven nylon cloth, and the abrasive grains are provided together with electrolyte which flows through the tool electrode. This paper chiefly clarifies the features of this method, the selecting bases for the running specifications and the ways to control low current density. The experimental results show that the pulse current is conducive to paucity of metal removal, and mirror or quasi-mirror finish can be achieved conveniently.

Abstract: The lubrication properties of the slurry between the silicon wafer and the pad in chemical mechanical polishing (CMP) are critical to the planarity of the silicon wafer. Moreover, the suspending abrasives, which are contained in the slurry, have an extremely important influence on the lubrication properties of the slurry. In the CMP process of the large-sized silicon wafers, the influence of suspending abrasives on the slurry becomes more prominent. In order to explore the effects of suspending abrasives on the lubrication properties of the slurry under the light load conditions, a three-dimensional lubrication model based on the micro-polar fluid theory is developed. The effects of suspending abrasives on the fluid pressure acting on the wafer and the distribution of the slurry film between the silicon wafer and the pad are discussed.

Abstract: One of the most applications of HIPSN(Hot-Isocratic Pressed Silicon Nitride) ceramic ball bearings is applied to the high-speed spindle of numerical control machine tools and high-speed precise mechanics. However, it is very difficult to process the HIPSN ceramic ball bearing. In this paper, a new grinding process method, taper rubbing method, is applied to process the HIPSN ceramic ball. Mechanical analysis of taper rubbing method is given, and the influence of grinding parameters on the ceramic material excision rate, surface quality of ceramic ball and wear and tear ratio of diamond wheel is studied by taper rubbing method. The experimental results show that the HISPN ceramic balls of G3 and G5 are obtained with taper rubbing method by properly controlling the motion of HIPSN ceramic balls and selecting reasonable processing technological parameters.

Abstract: Being a high efficient technique for metal surface treatment , centrifugal grinding is widely applied in the field of polishing and burring for small-sized asymmetric parts. During the process of centrifugal grinding, the dynamic characteristics of the abrasive flow, which is determined by the planetary driver ratio of the instrument, has a profound impact on the quality and producing efficiency of the workpiece. Targeting on the massive abrasive, this paper investigates experimentally theinfluence of the planetary driver ratio of the instrument to the producing quality and efficiency. On one hand, a high-speed photograph is employed to record the movement of the abrasive flow in the processing of centrifugal grinding. The dynamic characteristics of the abrasive flow have been investigated for different planetary driver ratios. By qualitative analyzing the high-speed photographing results, the perceptual knowledge of the characteristics and the kinematic rules of the abrasive flow have been obtained. On the other hand, the surface roughness data at different planetary gear ratio and polishing time have been measured. The influence of planetary gear ratio on producing process have been illustrated by plotting the roughness-time curve combined with the high-speed photograph so as to provide a scientific basis for optimizing the parameters of design and technology.

Abstract: Taking plate as the example, this paper studies the effect of tool’s shape and movement on the electrochemical as well as mechanical lapping characteristics in Electrochemical Abrasive Lapping (ECAL). It is assumed that the removal size of electrochemical action at a random point is in direct proportion to the electrical amperage through this point and the removal size of the lapping action is in direct proportion to the relative frictional distance. Based on the assumption above, electrochemical and mechanical lapping characteristics with different tools shape are studied theoretically. The results show that the diameter of the tool should be larger than the width of the workpiece when a discal tool is used and the inner diameter of the tool should be larger than the width of the workpiece when a ringed tool is used, on the other hand the ratio of the revolving radius of the tool to the diameter of the tool as larger as possible avails to improve the precision and so does the ratio of the angular velocity of the workpiece to the rotating angular velocity of the tool.

Abstract: Magnetic abrasive finishing (MAF) is a processing technology using magnetic abrasive grain (MAG) under magnetic field to finish surface of workpiece. The magnetic fields used in MAF include permanent magnetic field and electromagnetic field. Two conditions must be taken into consideration in the finishing surface of workpiece. One is the sufficient cutting force; the other is the relative moving speed between MAG and workpiece. The principle of step-motor rotating magnetic field is used to produce rotating magnetic field (RMF) in this paper. RMF brings MAG to rotate and keeps workpiece immovable. Meanwhile, the coins vibrate within a definite angle range and reciprocate in axial direction so as to process the outer cylindrical surfaces. Yoke iron is made of two halves so that the coins for rotating magnetic field will be keyed to some section of heavy crankshaft, thus realizing cylindrical surface finishing on the heavy crankshaft. MAG are of importance to MAF . Six performance indexes related to MAG are suggested by studying on process parameters.

Abstract: Magnetic Abrasive Finishing (MAF) is relatively a new finishing technique that employs the magnetic force for finishing. In the paper, finishing mechanism of MAF is studied and four self-sharpening modes of abrasive particles are put forward. With the cylindrical magnetic abrasive apparatus designed and made by the author, a series of experiments on finishing the cylindrical surfaces of nonferromagnetic materials and ferromagnetic materials are carried out. The influence of technical parameters (finishing speed, feed speed, finishing time and so on) on finishing performance is analyzed. Choosing the optimized technical parameters, , the surface roughness of ferromagnetic materials changes from Ra 0.825µm to Ra 0.045µm after the 12-minute finishing experiment; the surface roughness of nonferromagnetic materials changes from Ra 0.434µm to Ra 0.096µm after the 20-minute finishing experiment.