ELID磨削试验电解参数对光学玻璃表面质量的影响研究

随着国防尖端技术的迅速发展,许多具有独特性能的新材料得到了日益广泛的应用,如光学玻璃、硬质合金.但采用传统磨削工艺加工这些材料很难得到良好的表面质量.在线电解砂轮修整(ELID)磨削技术是一项新的、高效的磨削方法,它有效实现了许多难加工材料的超精密加工和高效加工.针对光学玻璃的特性,将ELID磨削方法应用于光学玻璃的精密加工,通过试验研究ELID磨削中电解参数对加工表面的影响规律,找到了在一定条件下优化的电解参数.试验结果表明,在ELID中,工艺参数对磨削质量及磨削效率有着显著影响,优化工艺参数对ELID镜面磨削有着重要的意义.     

A fundamental study on the mechanism of electrolytic in-process dressing (ELID) grinding

Demands for high quality surface finish, dimensional and form accuracy are required for optical surfaces and it is very difficult to achieve these using conventional grinding methods. Electrolytic in-process dressing (ELID) grinding is one new and efficient method that uses a metal-bonded diamond grinding wheel in order to achieve a mirror surface finish especially on hard and brittle materials. However, studies reported so for have not explained the fundamental mechanism of ELID grinding and so it has been studied here by conducting experiments to establish optimal grinding parameters to obtain better surface finish under various in-process dressing conditions. In this research the results show that the cutting forces are unstable throughout the grinding process due to the breakage of an insulating layer formed on the surface of the grinding wheel; however, a smoother surface can be obtained using a high dressing current duty ratio at the cost of high tool wear. ELID grinding is efficient for feed rates of less than 400 mm/min, and surface cracks are observed when it exceeds this limit.     

ELID grinding and tribological characteristics of TiAlN film

This paper presents the results of electrolytic in-process dressing (ELID) grinding experiments performed on TiAlN film and characterization of the tribological characteristics of the produced films. In advanced films coated by physical vapor deposition, such as CrN and TiAlN, the low surface roughness required for attaining superior tribological characteristics is difficult to attain by use of only a coating process. ELID of grinding wheels improves wheel performance, enabling the attainment of specular finishes on brittle materials, with surface roughness on the nanometer scale (4 to 6 nm). In the present study, high-quality TiAlN film surfaces were fabricated by the ELID technique, typically achieving a surface roughness of around Ra 0.0024 μm by employment of a SD#30,000 wheel. Scanning electron microscopy reveals that ELID improved the finish, as indicated by the shape of grinding marks. Chemical element analysis by an energy-dispersed x-ray diffraction system suggests that ELID grinding formed an oxide layer in the machined surface of TiAlN film. Therefore, in addition to the highly smooth surface, an oxide layer formed by ELID grinding imparts superior tribological properties to ELID-ground TiAlN film.     

Wheel curve generation error of aspheric microgrinding in parallel grinding method

In aspheric grinding of hard brittle material, in-process wheel wear is a crucial factor affecting the profile error of the ground surface. To suppress wheel wear, parallel grinding is adopted. Since the wheel and workpiece contact point changes during parallel grinding, geometric wheel error influences machining accuracy significantly. In the wheel truing process with a cup truer, the wheel radius is determined by the angle and distance between the wheel and the truer. Through geometric analysis, this paper presents a new equation of wheel radius, which enables process parameters, such as setup error or thermal error, to be determined easily. Simulation results show that wheel radius error is predominantly affected by vertical deviation between the wheel rotation center and the truer center. Experimental results show that wheel radius errors match those from simulation well.     

非球面磨削加工设备现状与发展趋势

高效、低成本光学玻璃、陶瓷、硬质合金等硬脆材料非球面的超精密磨削加工一直是先进光学制造领域的研究重点.本文介绍了国内外硬脆材料非球面磨削加工设备的发展及最新研制情况,并对其发展趋势进行了总结.     

Surface finishing of Ni–Cr–B–Si composite coatings by precision grinding

A Ni–Cr–B–Si/10vol%WC coating material has been precision ground to an optical quality surface finish (<10 nm R_a) using a combination of a very stiff precision machine tool, Tetraform “C”, 76 μm CBN grinding wheels and electrolytic in-process dressing (ELID) assisted grinding. When grinding without ELID, surface finish has been shown to be limited by damage to primary and secondary carbides. This damage may be in the form of carbide pull-out or localised fracture and removal of the larger primary WC particulate. ELID assisted grinding helps maintain CBN grit protrusion and sharpness and thus promotes efficient cutting during grinding, minimising pull-out and localised damage to the harder phases within the coating microstructure. ELID therefore improves both the overall surface finish and surface integrity of the workpiece.     

A study on optimum grinding factors for aspheric convex surface micro-lens using design of experiments

As the consumer market in the optics, electronics and aerospace industries grows, the demand for ultra-precision aspheric surface micro-lens increases. To enhance the precision and productivity of ultra-precision aspheric surface micro-lens, we present an ultra-precision grinding system and process for the aspheric surface micro-lens. In this paper, an ultra-precision grinding system for manufacturing the aspheric surface micro-lens was developed by considering the factors affecting the grinding surface roughness and profile accuracy. This paper deals with the mirror grinding of an aspheric surface micro-lens by resin-bonded diamond wheel and with the spherical lens of BK7. The optimization of grinding conditions with respect to ground surface roughness and profile accuracy is investigated by design of experiments.     

The effect of ELID grinding on the flexural strength of silicon nitride

Advanced structural ceramics, such as silicon nitride-based materials, are of significant interest due to their excellent physical and mechanical properties. However the cost of grinding these ceramics, an integral part of their fabrication, is very high and can result in surface and subsurface damage to the material. These defects can significantly reduce the strength and reliability of the finished component and are sensitive to grinding parameters. In this investigation, the effect of finish electrolytic in-process dressing (ELID) grinding on the flexural strength of silicon nitride specimens were studied. Kyocera's silicon nitride SN 235, in the form of Modulus of Rupture (MOR) specimens, were ground using the application of ELID grinding with a # 6000 grit sized cast iron bonded diamond (CIB-D) grinding wheel. A significant improvement in the strength of the Si₃N₄ specimens was noted when finish ELID grinding was performed. This was the result of ductile regime grinding using the application of finish ELID grinding. Another method to improve the flexural strength of silicon nitride specimens will also be addressed in this paper.     

用金刚石磨头数控加工轴对称非球面光学玻璃透镜

为了提高轴对称非球面透镜的形状精度,降低其精加工成本,用金刚石小磨头在不同的加工参数和数控走刀轨迹条件下对K9光学玻璃透镜进行铣磨实验加工。透镜的轮廓精度用三坐标测量机测量,通过测量的数据点计算非球面透镜的法向轮廓度误差,并用数控加工时磨头的有效切削半径进行补偿。实验结果表明:当数控走刀轨迹为平行精加工和等高精加工时,加工后非球面透镜的面型精度最大轮廓度偏差PV和误差平均值RMS分别为54.48 μm和22.88 μm、98.46 μm和28.88 μm;通过优化金刚石磨头的有效切削半径可以提高非球面透镜加工的面型精度,平行精加工后优化的非球面透镜面型精度PV和RMS值分别为44.52 μm和7.37 μm。      

Profile error compensation in ultra-precision grinding of aspheric surfaces with on-machine measurement

A compensation approach based on the on-machine measurement was developed for the grinding of tungsten carbide aspheric moulds. In this approach, the on-machine measurement was employed to eliminate the profile error caused by the re-installation of the workpiece. A new method was proposed to reconstruct the actual ground profile based on the measured profile data. The overall profile error after grinding was obtained by subtracting the target profile from the actual ground profile along normal direction and was then used to generate a new tool path for compensation grinding. The experimental results showed that after three compensation grinding cycles the aspheric surface had a profile accuracy of 177 nm (in PV) with a roughness of 1.7 nm (in R_a). The on-machine measurement was in excellent agreement with the off-machine measurement by commercially available profilometers.