Advanced Materials Research Vols. 69-70

Abstract: Parallel grinding is an effective method of aspheric moulds machining which is usually made of industrial ceramic such as silicon carbide (SiC) or tungsten carbide (WC), but if the spherical grinding wheel is not being with precision truing and dressing, the roughness and form accuracy of the ground aspheric surface should get worse, for this reason, in this paper, the influence factors of thoroughness and form accuracy induced by the wheel truing and dressing are studied firstly, and a new 3-axis CNC Ultra-precision grinding system which is based on the PMAC (Programmable Multi-axes Controller) is developed, through simultaneous motion of the controlled X, Z and B axis, the form errors which is induced by the grinding wheel can be improved theoretically, and the aspheric mould machining test shown that the surface roughness of Ra 0.025μm and the form accuracy of P-V 1.15μm are achieved.

Abstract: Camshaft is one of the key components of vehicle engines. In this paper, an independent optimization and simulation module for camshaft grinding was developed. First an optimization algorithm based on the least square method was proposed according to the constant linear velocity mathematical model of the camshaft. The algorithm can be used to smooth speed curves and improve machining efficiency and accuracy. Then the real time dynamic simulation of the camshaft grinding process was finished to perform the machining status according to the optimized motion path of the process system components.

Abstract: ELID (electrolytic in-process dressing) grinding was proposed by one of the authors for automatic dressing the grinding wheel while performing grinding for a long time. It offers a high effective way and has been widely used for grinding hard and brittle optical materials. However, those surfaces produced by fixed abrasive grinding are characterized by considerable sub-surface damage, micro-crack. Magneto-rheological finishing (MRF) is a novel precision finishing process for deterministic form correction and polishing of optical materials by utilizing magneto-rheological fluid. In this paper, an ultra-precision synergistic finishing process integrated MRF and ELID grinding is proposed for shorten total finishing time and improve finishing quality. A lot of nano-precision experiments have been carried out to grind and finish some optical materials such as silicon, silicon carbide, etc. ELID grinding is employed to obtain high efficiency and high surface quality, and then, MRF is employed to improve further surface roughness and form accuracy. In general, form accuracy of ~ λ/20 nm peak-to-valley (P-V) and surface roughness less than 10 Angstrom are produced in high efficiency.

Abstract: The technological parameters of laser direct metal deposition (DMD) were researched by DMD forming experiments using 2Cr13 powder. Fixing other parameters, the lower of laser power, the smaller the characteristic sizes of cladding layer are. Increasing of laser power, cladding height would firstly increase and then decrease, cladding width would firstly increase and then almost maintain constant, while cladding depth would gradually increase. When other parameters are invariable, with increasing of powder feeding speed, cladding height would increase, cladding width and cladding depth would decrease. When other parameters are invariable, cladding width, cladding height and cladding depth would decrease with the adding of scanning speed. The microstructure of single track cladding had three typical patterns, cellular dendritic, column dendritic and equiaxed crystal. The patterns depended on the temperature gradient and the solidification velocity. Under different technical parameters, the average hardness of specimens would change from 300HV0.2 to 550HV0.2.

Abstract: When the pocket in die and mould is machined by high speed milling (HSM), the cutting forces increase and vibration fluctuates at the pocket corner because of the sudden change of cutting direction in general. It will cause serious wear and possible breakage of cutting tool, and poor quality of parts. By means of experiments, the cutting forces and vibration at the pocket corner with different HSM conditions are measured. The results show that the sharper pocket corner, higher cutting speeds, larger feed rate per tooth and radial depth of cut, will result in increasing of cutting forces and vibration amplitude. Thus, it will lead to be unstable during the process of high speed milling pocket corner.

Abstract: This paper presents a research on the attenuation of cyclic stress amplitude and the variation of microstructure under the action of ultrasonic vibration in crack propagation for Al2O3-ZrO2 composite nano-ceramics. To interpret this phenomenon, the nonlocal theory is introduced to establish the constitutive model under the ultrasonic condition based on the specified 2D attenuating function. The mechanics behavior of the ceramics under the action of ultrasonic vibration is analyzed according to the relationship between the internal character length and the external character length (i.e. ultrasonic wave length). In addition, the variation law of the cyclic stress amplitude and microstructure with different ultrasonic frequencies is also studied in this paper. It is shown that the cyclic stress amplitude is attenuated under the action of ultrasonic vibration, and this attenuation phenomenon becomes more and more evident by increasing the ultrasonic frequency. The results of experiment are in accordance with the theoretical conclusions drawn from the nonlocal theory, which verifies that the action of ultrasonic vibration can actually accelerate the ceramic crack propagation.

Abstract: Ceramic balls have become an important component in advanced bearings, and the sphericity of balls is a key qualification focused in lapping process. An investigation on the effect of dynamic behavior of ball support system on the performance of ball lapping in rotated dual-plates lapping method is carried out. Sinusoidal waveform in terms of Fourier analysis is employed to express the shape error of the ball surface, and a dynamic model for support is setup. It is found with numerical calculation that the variation of lapping load lags behind the variation of the shape error for the damping of support. A lower natural frequency of the support system, higher spin speed of balls and a larger value of spin angle in RDP lapping are better to rectify the shape error of balls and reduce the lagged effect. It is concluded that dynamics of lapping system must be taken into consideration in order to understand comprehensively the spherical surface generation mechanism.

Abstract: A multi-axis micro-EDM machine tool for small hole is developed. It mainly includes marble base, precision servo and linear-motor platforms, RC pulse power supply, CCD microscope and so on. Superiority of linear motor used on the Z axis is analyzed. Primary experiments, in which small electrodes with different materials are used to machine 3mm thickness TC4, are carried out. Histograms of open-circuit voltage and capacitance to machining efficiency and electrode relative wear and small-hole samples are given. Influence rules of open-circuit voltage and capacitance to machining efficiency and electrode relative wear are analyzed according to experimental results.

Abstract: In the paper, in order to overcome machining limits in throughput and precision because of positioning error and tool wear of a single tool electrode, a method for the microelectrode array fabrication by micro-WEDM is described and assessed. Characteristics of the microelectrode array fabrication by micro-WEDM, such as machining open voltage, pulse peak current, discharge duration and servo feed rate so on, are investigated through a series of experiments. A 10 10 squared electrode array is machined by micro-WEDM and the width of each squared electrode is about 40µm. The microelectrode array with good quality is obtained by applying decreased open voltage and peak current, increased discharge duration and optimized machining speed. Then micro hole-array is processed by applying obtained electrode array in micro-EDM method. The diameter of each squared hole in the array is about 50 µm due to appropriate control strategy that per micro pulse energy is decreased and periodic jump-down is applied during the machining process. Experiments have demonstrated that the combination process of microelectrode array fabricated by micro-WEDM and micro-hole array done by micro-EDM is a novel method of process which makes it more feasible and efficient to fabricate microelectrode array and high-density hole-array.

Abstract: Free abrasive particle plays a crucial role in material removal and quality improvement of curved surface mould. In order to observe and investigate the general distribution state, fractal dimension and movement characteristic of abrasive particle in gasbag polishing process better, an abrasive particle stroboscopic photography system is established and polishing experiment is carried out. The abrasive particle contacts with not only the rubber gasbag enwrapped by polishing cloth full of mesh-like structures, but also the mould surface. Contact analysis of abrasive particle including the discussions of contact state, material removal mechanism and advantage of precession polishing is helpful to hold the optimal polishing process parameters combination and establish ideal abrasive particle field for higher polishing efficiency and more well-proportioned surface quality.