Materials Science Forum Vols. 532-533

Abstract: During the process of laser shock processing (LSP), we use high power Nd:Glass laser systems which result in significantly improve fatigue properties and stress corrosion cracking in titanium components. An ablative coating such as black painting and aluminum foil are used to protect the titanium component from surface melting by laser pulse, which adversely affects sample fatigue life. Three different shock-processing configurations are considered: non-ablative exposure, aluminum foil and confined ablation with black painting. We analyzed effect of the coatings on the shock wave propagation into the titanium specimen and the resulting change in mechanical properties versus depth. Near the surface, yield strength and hardness are found to be increased by laser shock, the titanium surface for all coatings increased in yield strength by 16% to 37%. The result have demonstrated that surface hardness can be improved by 31 percent over a machine worked surface with black paintings and be improved by 25 percent with aluminum foil .The experiment aim is to report the effect of the ablative, sacrificial coatings on the laser pulse generation of shock waves and their propagation into the titanium alloys and the resulting change in mechanical properties below the surface versus depth.

Abstract: This paper deals with an application for achieving precision curve grinding by automatic dressing and compensation of diamond wheel wear through non-contact measuring method. A realtime vision measurement combined with vibration analysis method for the wear of a grinding wheel is presented. The wear condition is evaluated by analyzing the topography changes of the wheel surface and the vibration signals in the grinding process. A kind of PC-based integrated control system with dynamic monitoring and automatic dressing function is investigated, and the control algorithm is also proposed. The benefits of the proposed methods are confirmed by the grinding experiments. Dynamic monitoring of the wheel facilitates determining the optimum dressing amount and interval. A much higher abrasive machining precision and efficiency are attained by the real-time error measurement and compensation arrangement.

Abstract: Regular micro-surface structure in the form of micro-pores produced on the face of mechanical seals by laser technology can be used to improve the friction performance of the seal mating rings. A test rig with variable axial load was used to test laser-textured seal rings with micro-pores of various pore depth and pore ratio to study the effect of the laser-textured seal face structure parameters on the friction performance of mechanical seals. It is found that there are optimum texturing face parameters at which the friction torque and the face temperature rise of seal rings are minimum. Results of these tests show that the micro-pores on one of the seal mating faces can generate substantial hydrodynamic effect. Heat generation due to frictional contact on seal-ring surfaces is a major factor that causes deterioration of face seals and shortens their service life[1,2]. Excessive temperature rise can be avoided by improving structure of a seal surface. By means of laser technology return-flow structure, oblique line groove and spherical micro-pores are engraved on the seal face[3-5]. The research shows that substantial hydrodynamic effect can be generated between the seal faces with micro-pores[6-8]. In this study experiments are performed on laser-textured micro-pores seal faces at various axial loads to investigate the effect of the face structure and operating parameters on friction torque and face temperature rise.

Abstract: Polycrystalline diamond (PCD) is an ideal tool material for machining high-pressure laminated (HPL) flooring with ceramics overlay. In this paper, the finite element (FE) model of PCD cutter was built firstly, then stress distribution of PCD cutter for machining wear resistance layer embedded with Al2O3 particles was analyzed. The analysis results showed that the stress distribution was variable in rake and flank face of tool, which leads to the final uneven wear profile. Moreover, the test of cutting load was carried out. From the analysis and test, it was shown that PCD cutter was suffering from the fatigue loading of high cycling while machining. At last, a series machining experiments was conducted and the wear characteristics were examined. The analysis results were verified by the wear characteristics of PCD tool. Machining experiments also revealed that the typical micro crack in wear region had great effects on the wear of tool.

Abstract: With the development of modern industry, the consciousness of quality monitoring increases rapidly. The requirements to the dimensional control and profile monitoring of the products including the mechanical, optical and electric ones become higher and higher. New, non-contact and convenient instruments are needed to enable people to evaluate their products. A new type of dynamic active confocal probe is developed in this paper. The key point of this new method is that the displacement measurement of the vibrating lens located on the tuning fork is converted to time difference measurement, which is much simpler and assures higher accuracy in measurement. System structure and improvement, electric circuit and signal processing system are discussed. Experimental studies of the probe performance and analyses of the experimental results are presented.

Abstract: An investigation on the mechanism of flexible sheet metal forming using plasma arc have been performed in this paper. The experimental results show that temperature gradient mechanism (TGM) is caused by a steep temperature gradient across the sheet metal thickness, which will generates bending towards the plasma arc, while buckling mechanism (BM) usually causes sheet metals to bend away from the plasma arc on the condition that the plasma arc diameter is large compared to the sheet metal thickness and the scanning speed is low. The strain-hardening effects and phase transformation effects were also conducted in the investigation, which can be of great significance for the micro hardness and deformation of sheet metal in the heated area. The investigation reveals the mechanisms of sheet metal forming using plasma arc, and provides theoretical foundation for its industry application.

Abstract: As an important factor in composite fiber winding, fiber winding tension influences the product quality directly, and therefore tension control is a key technique in fiber winding techniques. This paper introduces a closed loop tension control system with the PIC single chip computer as the kernel, a function module with TLC5615 D/A converter as the output, AC servomotors as the actuator, and a radius-following arm to measure the real time radius of the scroll. The mechanism of the tension control system is analyzed and the mathematical model is set up. Then the paper expatiates the design of main control circuit, the voltage transformation circuit and the analogy filter circuit. In addition, the paper presents digital filter and control algorithm of the PIC software. The system is proved to have high control precision and rapid time response through performance experiments of the tension control system in different working states, which well meets the anticipated design requirements.

Abstract: Carbide tools play key roles in present machine manufacture. The mechanical property and cutting performance of carbide tools are improved obviously when adding micro rare earth (RE) elements into carbide tools. By means of some apparatus, such as materials testing machine, Scanning Electron Microscope (SEM), dynamometer, microscope and electron probe microanalyser, the traditional and RE carbide tools, P30 (YT5 and YT5R), P20 (YT14 and YT14R), M10 (YW1 and YW1R), K30 (YG8 and YG8R), are studied and compared by doing a lot of experiments. These experiments show that the bending strength, fracture toughness and anti-impact capability of RE carbide tools are improved remarkably, and their hardness increased a little. Moreover, the cutting force, tool-chip friction coefficient and wear of RE carbide tools decreased in cutting. In addition, the effect and cutting principium of RE element to carbide tools are analyzed and discussed, which is beneficial to the research and application of RE carbide tools.

Abstract: In the modern manufacturing of sophisticated parts with 3D sculptured surfaces, die/mold making operations are the most widely used machining processes to remove unwanted material. To manufacture a die or a mold, many different cutting tools are involved, from hole-drills to the smallest ball nose end mills. Since the specification of each tool is very different from each other, each die/mold is specific with their complicated shapes and many machining rules exist to consider, a great deal of expertise is needed in selecting cutting tools for the die/mold machining operations. An intelligent system developed by using case-based reasoning (CBR) technology for this purpose is described in the present work. The geometry of the workpiece, workpiece condition, and operation type are considered as input values and various recommendations about the tool material, tool type, tool specifications, and cutting parameters are provided.

Abstract: The high precision balls are requested in national defense, astronautics and high-tech commercial domain urgently. Conventional precision machining methods are sensitive to uniformity of abrasives and machining environment. After precision machining, there are easily to produce thick damaged layer on the ball surface because of machining stress and chemical conversion. On the basis of the floating polishing mechanism, a new scatheless ultra-precision polishing method of ball surface can solve the problems of abrasives uniformity effectively and damaged layer. In order to ensure that the new polishing method polishes ball surface equally, the appropriate angular velocities of the ball should be selected. This paper sets up the mathematical model about the motion of ball. By analyzing and simulating the relationship of the angular velocities, the best processing parameters are acquired.