Advanced Materials Research Vols. 24-25

Abstract: CVD diamond films have been used in many high-tech fields with the industrial and scientific developments, while the lagging of the polishing technology for the CVD diamond films has limited their widely applications. This paper presents a high-efficient low-cost wheel-grinding technology for CVD diamond polishing, and the two key techniques of this technology are introduced in detail based on thermo-chemical polishing technology. Furthermore, wheel grinding technology exhibits a promising perspective for the widely application in the diamond films.

Abstract: In this paper, multi-linear regression and artificial neural network (ANN) models have been developed to predict surface roughness in high-speed milling of 7050-T7451 aluminum alloy. Surface roughness is taken as the response variable, while cutting speed, feed per tooth, radial depth of cut and slenderness ratio are taken as independent input parameters. An orthogonal experiment design is developed to conduct experiments. The measured values of surface roughness are used to find the regression coefficients and train the neural network for prediction of surface roughness. Predicted values of surface roughness by both models are compared with the measured values.

Abstract: Based on the synthetic analysis of thermal error sources, ICA (Independent component analysis) method is proposed to reduce the number of temperature sensor, and the selected temperature variables is used for thermal error modeling of gear hobbing machine. Finally, the hardware system of thermal error compensation is presented based on SCM (Single chip microcomputer) technique, and which is tested on Y3150K hobbing machine then. The results show that cumulative pitch error is reduced from 80μmto 20μm, and the machining accuracy is improved more than 2 grades.

Abstract: There are some applications of error separation technique in actual measurement. However there exists a series of theoretical and technical obstacles, and the error separation technique lacks the objective assessment. The further discussion about the character of error separation technique by multi-probe method is made in this paper and six criteria for precision measurement of error separation technique by multi-probe method is also advanced. That is, (1) The criterion for veracity of error separation; (2) The criterion for periodicity of combination signal; (3) The criterion for the remnant first-harmonic in combination signal; (4) The criterion for validity of error separation results; (5) The criterion for validity of probes’ fixing angles ; (6) The criterion for nonzero character of weight function. These criteria are significant for the objective evaluation of the measuring apparatus’ measurement precision, the validity of the sampling data, and the confidence level of error separation results. The validity of the measuring condition was proved by the online measurement experiment.

Abstract: The worn surface is usually coated with a layer, which thickness exceeds magnitude of wear. In order to provide required clearances (or tightness) in the assembling of parts, uniform clearances (this suggests the presence of the perfect mating should be provided. In the paper, the effects on the layer were discussed and forecasting the clearance sizes or (when the limit values are specified) determining the assembly life. In the process of repairing, the worn surface is usually coated with the layer, which thickness exceeds magnitude of wear. After the surface is coated it is machined by one of the available methods. During recent years, new so-called “cold” methods of coating have appeared, some of them (particularly galvanomechanical machining) enables to obtain required dimensions and quality metrics of surface layer without complete machining. The final goal of repair is to provide required clearances (or tightness) in the assembling of parts. It is required to provide uniform clearances (this suggests the presence of the perfect mating surfaces before assembly). Depending on accuracy grade, variations in the clearance dimensions may be within the limits from some microns to decile of millimeter. This depends on mating surface accuracies and is independent of the fact whether these surfaces were repaired or not. If the parts were machined separately, thickness of the layer shall be determined subject to the actual size of mating part areas, size and dimensional tolerances of clearance. When developing the process of parts repair, the following shall be considered: - wear degree of contact mating locations; - requirements for quality of surface layer in part assemblies; - permissible errors of mating surfaces; - allowance (or tightness) between mating parts and its variation limits in the assembly. The wear in mating locations is determined by supervision of part defects before repair. The limiting wear of products shall not exceed capability of galvanomechanical method. It is required for qualitative surface coating to limit the thickness to 0,5-0,6 mm. Depending on wear degree, two methods of repair can be used: -smoothing of macrosurface with a galvanomechanical coating, for example with chromium and thereafter application of qualitative surface layer. Such process shall be applied in the case when degree of surface unevenness does not exceed 50%. If wear degree is out of the stated limits, preliminary machining is required. This machining is necessary to reduce surface unevenness up to 50%. After this procedure, effective thickness of coating shall be applied. The acceptable surface unevennesses with different degrees of wear are shown on Fig.1 At the first stage of coating the stock shall be evened. After this, the surface roughness does not exceed the roughness coefficient specified for a new part, but other quality indexes of the surface (residual stress character, wear-resistance) are not in conformance with the requirements for the repaired parts. Therefore, after evening, another “slower” method of galvanomechanical repair with specified contact pressure and mechanical effect conditions is applied. As a result of this method, the following indexes are available. See Table 1.

Abstract: The mechanism of electrochemical mechanical finishing (ECMF) process was investigated. The ECMF experimental system and control unit were developed and some vital procedure parameters such as operating voltage, electrolyte component and concentration, machining temperature, electrode gap and current density were also evaluated and optimized, then the optimal procedure parameter match was obtained. Furthermore, the important surface roughness characteristics before and after ECMF process such as height and spacing characteristics of surface roughness, surface waviness characteristics, surface microscopic appearance and light reflection characteristics were compared. The experiment and measurement results indicate that ECMF process can distinctly improve surface quality, eliminate the surface scratch marks and defects and reduce surface roughness.

Abstract: The experiments are performed to study the hardness layer depth at work piece different surface zone in grinding. The result is that hardness layer depth is various at work piece different surface zone. The hardness layer depth is thinner at cutting-in grinding zone, deeper at middle grinding zone and deepest at cutting-off grinding zone. In order to analyze the cause of hardness depth variation, the grinding temperature field is simulated by means of finite element method. From the temperature field and heat flux simulation, the cause of the hardness depth variation is that the grinding heat flux is variable at different grinding zone along the work piece surface in grind-hardening. At cutting-in zone, most of grinding heat flows into the front-below work piece part inverse to table speed, the depth that temperature of surface layer higher than austenite temperature is thin and there is slim martensite transformation layer. At middle zone, the temperature of surface layer is higher than austenite temperature because of grinding heat accumulated in the surface layer, and martensite transformation takes place after cooling. At cutting-off zone, most of grinding heat flows into the below work piece part because of work piece boundary, and hardness depth is deeper than that at middle zone.

Abstract: The abrasive jet finishing process with wheel as restraint is a kind of compound precision finishing process that combined grinding with abrasive jet precision machining, in which inject slurry of abrasive and liquid solvent to grinding zone between grinding wheel and work surface under no depth of cut feed condition when workpiece grinding were accomplished. The abrasive particles are driven and energized by the rotating grinding wheel and liquid hydrodynamic pressure and increased slurry speed between grinding wheel and work surface to achieve micro removal machining. The micro removal machining with grinding wheel as restraint, not only to attain higher surface form accuracy but also to can efficiently acquire defect-free finishing surface with Ra0.15~1.6$m and finally achieve high efficiency, high precision and low roughness values, furthermore, integrating grinding process and abrasive jet finishing into one features. In the paper, surface topography finished by abrasive jet with grinding wheel as restraint was analyzed and evaluated with power spectral density function. Experiments were performed with plane grinder M7120 and workpiece material 45 steel. The machined surface morphology was studied using Scanning Electron Microscope (SEM) and the microscope and microcosmic geometry parameters were measured with TALYSURF5 instrument. The experimental results show that microcosmic geometry parameter values were diminished comparing with ground surface. Furthermore, the mean ripple peak distancing was decreased and, ripple and peak density were increased. The results indicate that surface qualities by machined with abrasive jet precision finishing were improved obviously.

Abstract: With the development of machine manufacture science and technology toward precise, quality evaluation of precision parts has put forward higher request. Problems are pointed out in this paper based on comparison and analysis of burr standard at home and abroad. This study suggests the viewpoint of edge quality of precision parts and provides the fundamentals for enhancing edge (burr) quality according to items such as economic cost, technology level, manufacture level, personnel technological capability and production management level. These have important theoretical value and applied prospects for further enriching and perfecting burr standard, promoting precision machining and automatic machining technology.

Abstract: The functional crystal material Potassium dihydrogen phosphate KH2PO4 (KDP for short) is widely used in navigate, spaceflight, national defenses, energy sources and information technology fields because of its excellent non-linear optical property. However, KDP crystal has some disadvantages such as soft, fragile, hygroscopic, anisotropy, thermally sensitive and low rigidity, which make it a most difficult processing material. In this paper, KDP crystal was machined by the wheel grinding. Some equipment, such as Optic microscope, SEM, ZYGO and Raman spectroscope were used to observe and analysis the KDP crystal surface which was damaged during grinding. The results shows that serious nicks, crashes and the press stress appeared on the surface of the KDP crystal after grinding.