Key Engineering Materials Vols. 364-366

Abstract: We have developed optimization methods for generating free-form surfaces. The main applications are in the industrial on-line spectroscopic and machine visions measurements, where spectral and spatial uniformity, good efficiency and pass-line stability are required parameters. We used commercial software for ray-tracing engine. We have developed in-house optimization routines, but used also build-in functions. In this work we have designed a speckle free alternative for laser line generation based on the LED sources. The optical system is based on the collimation part and a free-form mirror. Simulation results are presented.

Abstract: As one of the key factors grinding heat has a significant effect on the ground surface quality in grinding engineering ceramics using diamond grinding wheel. Differences between mechanical and physical performances of ceramic materials and grinding parameters have important influences on the surface temperature distribution. In the present research, experiments with/without ultrasonic assistance were carried out to study the temperature characteristics in the grinding field by thermocouple in grinding ZrO2 and Al2O3 engineering ceramics respectively. Moreover, the theoretical analysis and the experiment confirmation for the relationship between grinding parameters and temperature have been discussed. The results show that the further the heat source keeps against grinding surface, the lower the peak value of temperature, and the surface temperature increases with the grinding depth, grinding speed and work table speed. According to the results of orthogonal experiments on grinding parameters, the grinding depth is the most important factor affecting the grinding temperature on the workpiece surface.

Abstract: Aimed at the precision machining characteristics of nano ZTA engineering ceramics external cylindrical components, ultrasonic aided lapping experiments were carried out adopting inhouse developed ultrasonic external cylindrical lapping device with solid abrasive material. To obtain minimum surface roughness with constraint of the material removal rate, response surface methodology (RSM) was adopted to analyze the experimental data, and suitable experiment design was chosen to fit the response surface in this research. Second-order surface response models of surface roughness and material removal rate were developed respectively, and the influence laws of lapping parameters on surface roughness and material removal rate were clarified according to the built models. Finally, parameters optimization of the ultrasonic external cylindrical lapping process for nano ZTA engineering ceramics was realized using surface response methodology.

Abstract: MgO single crystal is mainly used as substrate for high temperature superconductor film. Surface quality of MgO substrate has significant effect on the function of high temperature superconductor film. MgO single crystal is a typical hard and brittle material, and is easily cleaved along the {100} face, so some defects are always generated on the substrate surface while lapping and polishing, which badly affects the surface quality of the substrate. In this paper, a kind of typical defect, the triangular fracture defect which is on the substrate surface after lapping and polishing, is analyzed in detail. According to the structure characteristics of the MgO single crystal, and based on the dislocation reaction theory, a formation mechanism of the triangular fracture defect in lapping and polishing processes is explored. Through the single grain scratch test in different directions on the polished surface of MgO{100} single crystal substrates, the formation mechanism of triangular fracture defect in lapping and polishing processes is verified. And during the scratch test, the plastic flow of the MgO single crystal material beside the scratch was observed.

Abstract: A new special-purpose optical coordinate measurement machine has been developed with the cylinder coordinates to solve the problem of testing aspherics with full aperture in the stage of grinding and pre-polishing .A full aperture measurement was made by testing several meridians in the point by point manner. In the aspect of hardware, the system is composed mainly by an ultraprecise air guide-way, realizing the linear motion, and a graduator, realizing the rotary motion. In the aspect of software, the mathematical model of the system was analyzed and a new algorithm for the full-aperture testing of rotationally symmetric aspherics was built. The testing software and data-processing software are written on the VC++6.0 and Matlab6.5 platform respectively. The maximum measurement range of the system is 600mm, the maximum sag: 25mm, the minimum sampling step, 1 mm and the accuracy is better than 1um in full scale, after the compensation of the systematic errors. The requirement in the grinding and pre-polishing process for the test of aspheres has been satisfied. The real experiments indicate: the system runs well and has a good repeatability and accuracy.

Abstract: A novel profilometer for three-dimensional (3D) surface topography measurement is presented. The profilometer has large measuring range, high precision and small measuring touch force. It is composed of a two-dimensional (2D) displacement sensor, a 3D platform based on vertical scanning, measuring and control circuits and an industrial control computer. When a workpiece is measured, the vertical undulation of the profile at a sampling point leads to a zero offset of the 2D displacement sensor. According to the zero offset, a piezoelectric actuator and a servo motor drive the vertical scanning platform to move vertically to ensure that the lever returns to its balance position. So the non-linear error caused by the rotation of the lever is very small even if the measuring range is large. When the stylus barges up against a steep wall, the horizontal resistance force results in another zero offset of the 2D displacement sensor. If the zero offset exceeds a quota, the vertical scanning platform descends to make the stylus climb the steep wall successfully. According to the theoretical and experimental analysis, the profilometer can measure roughness, profile of sphere, step, groove and other 3D surfaces with curvature precisely.

Abstract: Ion beam Figuring (IBF) of optical mirror is a polishing process based on CCOS with the application of ion sputtering effects. The material removal mechanism is in the atom scale, which can enhance the precision of the target surface to tens of nanometers. Without contact, this process can also promote the subsurface quality. In this paper, the Ion Beam Figuring Machine (IBFM) is introduced，which realizes the relative motion between the target surface and the ion source. Firstly, we describe the design method, the machine configuration and principal technical parameters. With the configuration and motion ability described, we introduce different scanning modes for surfaces of different scales respectively. Secondly presented is the precision analysis method for IBFM. Based on the CCOS principle, the relation between the convergence rate and positioning errors are deduced. This relation describes the precision requirement of machining process. Finally, the postposition algorithm of IBFM is analyzed. According to coordinate transition and rotation, the general transfer model for different scanning modes is given.

Abstract: Traditionally, Argon (Ar) is used as a working gas to deposit MgF2 thin films in ionbeam assisted deposition (IAD) process. It improves the quality of the films, but cannot reduce the loss of F- ions during the process which also results in other impurities appearing in MgF2 thin films. The contaminants in MgF2 film such as C, O and Ar atoms are identified by X-ray photoelectron spectroscopy (XPS). In this study, sulfur hexafluoride (SF6) was chosen as a working gas in which more F– ions were created from the dissociation of SF6 in the IAD process in order to increase the content of F and eliminate the contamination. In our knowledge, very few reports have been published on IAD used SF6 as a working gas in optical coating process at around room temperature. Deposition of unwanted sulfur atoms was the concern when SF6 was used in the IAD process, however, no sulfur was observed in XPS spectra. The XPS spectra of Mg 2p, O 1s and F 1s were decomposed and analyzed with some Gaussian sub-peaks. The transmission spectra of films were measured in UV and visible ranges. The water absorption phenomena in the films were also measured by Fourier Transform Infrared (FTIR) spectrometer. Compared to the films fabricated by other methods, using SF6 as a working gas in IAD is a good choice to deposit MgF2 films.

Abstract: Precision positioning is an essential basis for precision mechanical engineering, such as positioning for precision manufacture, or positioning control of robot arms. Due to the increasing demand for precision in the submicrometer range, precision positioning plays an important role for precision manufacture. In this investigation a nano-positioning stage is developed. With the positioning system, high precision positioning and large displacement range can be achieved simultaneously. Advantages of this developed system are positioning driver with single actuator, uncomplicated mechanical structure, low cost and lower hardware requirement. A laser interferometer is used for displacement measurements of the translation stage, and a mini-autocollimator serves as angle sensor for tilt angle measurements. The tilt angle can be minimized with piezo translators and control operations. By the displacement measurements of laser interferometer, the feedback control is performed for positioning in large travel range. High precision positioning in nanometer-order can be achieved with the positioning system. With this development, individual sensor modules are self-accomplished and dominating technologies for the complete nano-positioning system are established.

Abstract: This study employs finite element simulations to investigate the relationship between the equivalent mass and the real mass of end masses adhered to the tip of the cantilever beam of an atomic force microscope. The equivalent mass was determined by analyzing the variation in the resonant frequency of the cantilever beam caused by the addition of the end mass. The analysis considered five different adhesive mass materials, namely copper, aluminum, S45C steel, titanium alloy and magnesium alloy. Furthermore, the analysis also considerd the effect of the position of the adhesive mass on its equivalent mass value. The numerical results indicate that the equivalent adhesive mass is less than the real adhesive mass. The ratio of the equivalent adhesive mass to the real adhesive mass is approximately constant for a given adhesive position and adhesive material and has a value of approximately 0.6361 for a high-density material. Finally, the results show that an offset of the adhesive mass from the tip position causes a slight change in the value of the equivalent mass to real mass ratio.