Papers by Author: Zeng Wen Liu

Abstract: Potassium Dihydrogen Phosphate (KDP) crystal is widely used in laser frequency multiplications and electro-optical modulators, but its soft-brittle property and thermal sensitive characteristic make it a very difficult-to-machine material. In this paper, an in-house made diamond tool with one tooth is used to face-mill KDP crystal specimens on a high-speed micro CNC machining centre, based on a statistically designed experiment. The morphology and roughness of the milled KDP crystal surfaces are analyzed with respect to the process parameters. It has been found that cutting speed has the largest effect on surface roughness, while axial depth of cut and feed per tooth show a comparable effect on both the Ra and PV roughness measures. From this study, 3 m/s cutting speed, 3 μm axial depth of cut and 1 μm/z feed per tooth are recommended for single point diamond milling of KDP crystal.

Abstract: Abrasive waterjet machining (AWJ) is one of the fastest growing non-conventional machining methods. However, low pressure and fine abrasive implemented in AWJ precision machining for reducing the surface damage reduce the efficiency. Therefore ultrasonic vibration is considered to apply on the workpiece to improve the machining efficiency. In order to analyze the effect of the vibration on erosion in AWJ machining, smoothed particle hydrodynamics (SPH) is used to simulate the erosion process for avoiding the mesh distortion in finite element method (FEM) when simulating large deformation and high strain rate problems. The results show that the application of ultrasonic vibration can effectively improve the erosion rate due to the dynamics variation of the erosion process.

Abstract: This paper conducts a study on a pre-mixed micro abrasive water jet machining system. A new kind of abrasive mixing tank and the jet system are designed and tapped for the pre-mixed micro abrasive water jet machining system. The performances of the pre-mixed micro AWJ machining system are tested, and some polishing experiments are conducted for hard-brittle materials such as silicon nitride. The results show the feasibility and the advantage of the pre-mixed micro abrasive water jet machining system for polishing hard-brittle materials.

Abstract: A study on the radial-mode abrasive waterjet turning (AWJT) process is presented and discussed. An experimental investigation is carried out to explore the influence of process parameters on the depth of turning and material removal rate (MRR) when turning 96% alumina ceramics. The experiment is designed by the multifactor orthogonal experiment methods. The effect of feed speed, water pressure, abrasive mass flow rate, nozzle tilted angle and surface speed are investigated by the range analysis and variance analysis. The results show that the feed speed is the most significant variables affecting the depth of turning. Based on the test conditions, it is found that the most efficient conditions to maximize depth of turning are at a jet angle of 105 degree, a water pressure of 310MPa, an abrasive mass flow rate of 11.5 g/s, a surface speed of 5.5m/s and a feed speed of 0.05mm/s. At last, the effect mechanism of process variables on the depth of turning is analyzed qualitatively.

Abstract: Abrasive waterjet (AWJ) turning is an emerging technology, which plays an important role in machining cylindrical parts with the distinct advantages of negligible thermal effects and extremely low cutting force. This paper presents an experimental study of abrasive waterjet turning (AWJT) of Al₂O₃ ceramics. The machining process and performance in terms of the depth of penetration (DOP), surface roughness (Ra) and actual impact angle (β) are discussed to understand the effect of standoff distance (SOD) on the processing performance at two different turning modes. Based on the results of these investigations, there is a significant change of DOP and Ra at different SOD in radial mode turning and the optimal SOD of gaining maximum DOP and the minimum Ra is about 5.5mm.However, the DOP is nearly independent on the SOD in offset mode turning. Smaller Ra and DOP can be obtained in offset mode. Furthermore, the results indicate that the roundness error of cylinder parts is probably improved with the proper SOD interval in radial mode turning and it is suitable for machining cylinder part with considerably different radial size. The offset mode turning as the next operation after radial mode turning is recommended to process workpiece with excellent roundness. In this way, by understanding the effect of SOD on processing alumina ceramics, the paper establishes a good basis for developing strategies for optimizing processing parameters in order to generate the desired part geometry and achieve better surface quality.

Abstract: Abrasive water jet (AWJ) technology, due to its potential advantages, is a promising machining method for precision machining brittle materials. In this research, the AlN ceramics was polished using an AWJ machining system. A considerable processing quality has been achieved and a reduction up to 62% of the surface roughness has been obtained. Effects of different process parameters on the surface roughness of the polished workpiece were analyzed. Under the current conditions of the experiments, using a lower impact angle, smaller abrasives and a lower nozzle traverse speed may be appropriate for polishing AlN ceramics.

Abstract: Ultrasonic vibration-assisted machining (UVAM) is an effective and promising technology for processing hard and brittle materials, it has been explored in many experimental and theoretical investigations. In this paper, a study on the erosion performance of monocrystalline silicon with UVAM is presented and discussed. In the erosion experiments, monocrystalline silicon wafers were eroded by the abrasive water jet machine assisted with an ultrasonic vibration system. A contrast experiment was carried out firstly to study the influence of the ultrasonic vibration, and then an orthogonal experiment investigation was carried out to understand the effect of process variables (the abrasive particle diameter, jet impact angle, standoff distance, abrasive mass flow rate and ultrasonic vibration power) on the depth of erosion and material removal rate (MRR). The experimental results revealed that ultrasonic vibration-assisted abrasive water jet erosion (UVA-AWJE) can obviously improve the depth of the erosion and MRR compared with those in traditional AWJE and the variation trends of the effect of the abrasive particle diameter, jet impact angle, standoff distance and abrasive mass flow rate on the erosion performance in UVA-AWJE are very similar to those effect in the traditional AWJ machining.

Abstract: High pressure abrasive water jet (HPAWJ) machining has many advantages in hard brittle material processing. In this paper, the hole formation on stone by HPAWJ is analyzed based on brittle and plastic fracture theories. The formation and construction of jet are studied. The distribution of jet velocity, abrasives and energy in the jet-beam section of HPAWJ is analyzed. It is shown that the cross-section of the hole is characterized by a ‘Reverse-bell’ shape on stones by a HPAWJ. The jet velocity of HPAWJ gets lower from jet center to jet margin and it’s distribution is consistent with normal distribution function along with jet center. The concentration of abrasives becomes smaller from jet margin to jet center and it’s distribution is consistent with normal distribution function along with jet margin. The distribution of jet velocity, abrasives and energy in the section of HPAWJ is modeled.

Abstract: Micro abrasive air jet (MAAJ) cutting technology is being increasingly used in the precision machining of hard and brittle materials, due to its distinct advantages of negligible heat effect zone and small cutting force. In this paper, an experimental study on the kerf characteristics, especially for the effect of cutting parameters on the top edge definition, is presented. It shows that the top kerf edge is straight but not sharp. The top edge definition of the kerf improves with a decrease in the air pressure, while the effect of abrasive flow rate and nozzle traverse speed are hardly discernible. The optimum jet incidence angle for highest top edge definition of the kerf is 60°. The results of this paper may be useful for the cutting parameters optimization in the precision three-dimensional micro-structural machining.

Abstract: Micro abrasive air jet machining technology is being increasingly used in the fields of micro cutting. Since the aspect ratio is a major interest characteristics of kerf in micro cutting, an experimental investigation is carried out to study the effect of cutting process parameters on the aspect ratio in this study. It is found that the aspect ratio increases with an increase in air pressure, abrasive flow rate and jet incidence angle, while decreases with an increase in nozzle traverse speed. Furthermore a predictive model for aspect ratio is developed using the dimensional analysis technique. It is shown that the model predictions are in good agreement with the experimental results. The research results may be meaningful to efficiently control the aspect ratio.