Performance of sinking EDM electrodes made by selective laser sintering technique

Electrical discharge machining (EDM) is a nonconventional machining process widely applied for the manufacture of intricate shapes in hard materials which are not easily machined by conventional machining processes. The production of geometrically complex EDM electrodes is difficult, time consuming, and it can account for about 50 % of the total process costs. Selective laser sintering (SLS) can be an alternative technique to produce EDM electrodes in a faster way. This work conducted an experimental study on the performance of EDM electrodes made by SLS using pure copper, bronze–nickel alloy, copper/bronze–nickel alloy, and steel alloy powders. Important EDM performance measures such as material removal rate and volumetric relative wear were investigated and discussed for finishing, semifinish, and roughing regimes. This work contributes with an insight into the production of EDM electrodes via selective laser sintering, as an alternative technique to conventional machining processes, as well as to evaluate the performance of the electrodes, and also provide directions for future research on this field.     

Design of thread surface finish using ultrasonic-aid in electrochemical leveling

In most manufacturing systems the contribution of human labour remains a vital element that affects overall performance and output. Workers’ individual performance is known to be a product of personal attitudes towards work. However, in current system design processes, worker performance variability is assumed to be largely insignificant and the potential impact of worker attitudes is ignored. This paper describes a field study that investigated the extent to which workers’ production task cycle times vary and the degree to which such variations are associated with attitude differences. Results show that worker performance varies significantly, much more than is assumed by contemporary manufacturing system designers and that this appears to be due to production task characteristics. The findings of this research and their implications are discussed.     

Optimal parameter settings for rough and finish machining of die steels in powder-mixed EDM

The present study was undertaken to identify the appropriate parameter settings for rough and finish machined surface for EN31, H11, and high carbon high chromium (HCHCr) die steel materials in a powder-mixed electric discharge machining process. The effect of seven different process variables along with some of their interactions was evaluated using a dummy-treated experimental design and analysis of variance. Material removal rate (MRR), tool wear rate, and surface finish were measured after each trial and analyzed. The parameter settings for rough and finished machining operations were obtained. EN31 exhibited maximum MRR as compared to the other two materials at similar process settings. Copper (Cu) electrode with aluminum suspended in the dielectric maximized the MRR. Suspending powder in the dielectric resulted in surface modification. Graphite powder showed a lower MRR but improved the surface finish. HCHCr require higher current and pulse on settings for initiating a machining cut and works best in combination with tungsten–Cu electrode and graphite powder for improved finish. The MRR for H11 is lower than EN31 but significantly higher than HCHCr under same process conditions.     

宏指令编程提高加工表面质量

针对数控机床加工周期性循环的曲面或曲线时出现的进给速度突变，提出了一种利用宏指令编 程来控制循环的解决方案。     

A study on helical surface generated by the primary peripheral surfaces of ring tool

Often in the engineering practice, cutting tools bounded by primary peripheral surfaces of revolution are used because of their effectiveness. Among these, ring and tangential tools can be used for the generation of constant pitch cylindrical helical surfaces. In this paper, we present an algorithm for the profiling of these types of tools. The algorithm is based on the topological representation of the tool’s primary peripheral surface. The main goal is to devise a methodology for the profiling of tools whose surfaces are reciprocally enveloping with cylindrical helical surfaces. We present a numerical example for the numerical determination of the axial section form for this type of tools. The application method for this algorithm was developed in the CATIA graphical design environment within which the procedure is developed as a vertical application. In addition, we present a solution for the shape correction of the tool’s axial cross-section by considering the existence of singular points on the profile of the helical surface to be generated where multiple normals to the surface exist.     

电火花加工变质层对模具成形表面的影响

电火花加工是模具制造的主要加工手段之一,其物理本质决定了用该手段加工的模具成形表面存在表面变质层.分析表面变质层的形成机理、变质层对模具质量和寿命的影响,并提出对策.     

Statistical modification analysis of helical planetary gears based on response surface method and Monte Carlo simulation

Tooth modification technique is widely used in gear industry to improve the meshing performance of gearings. However, few of the present studies on tooth modification considers the influence of inevitable random errors on gear modification effects. In order to investigate the uncertainties of tooth modification amount variations on system's dynamic behaviors of a helical planetary gears, an analytical dynamic model including tooth modification parameters is proposed to carry out a deterministic analysis on the dynamics of a helical planetary gear. The dynamic meshing forces as well as the dynamic transmission errors of the sun-planet 1 gear pair with and without tooth modifications are computed and compared to show the effectiveness of tooth modifications on gear dynamics enhancement. By using response surface method, a fitted regression model for the dynamic transmission error(DTE) fluctuations is established to quantify the relationship between modification amounts and DTE fluctuations. By shifting the inevitable random errors arousing from manufacturing and installing process to tooth modification amount variations, a statistical tooth modification model is developed and a methodology combining Monte Carlo simulation and response surface method is presented for uncertainty analysis of tooth modifications. The uncertainly analysis reveals that the system's dynamic behaviors do not obey the normal distribution rule even though the design variables are normally distributed. In addition, a deterministic modification amount will not definitely achieve an optimal result for both static and dynamic transmission error fluctuation reduction simultaneously.     

A study on the mirror surface machining by using a micro-energy EDM and the electrophoretic deposition polishing

In order to achieve a mirror-like workpiece surface by EDM, a micro-energy EDM or a manual lapping is normally used. However, both methods are time consuming and economically unattractive. To have better performance, a sinking EDM machine was first used in this research on SKD 61 for a micro-energy discharge process followed by the electrophoretic deposition (EPD) process to coat Al₂O₃ particles uniformly on a rotation electrode. The precision polishing process was then applied on the discharged workpiece with suitable parameters including the voltage, electrode rotating speed, pH value of electrolyte, and abrasive concentration. After the EDM process, the surface roughness and the recast layer thickness of a workpiece could also be reduced. The experimental data showed that when 0.3 μm of Al₂O₃ particles was used for the EPD polishing process, the initial roughness of a discharge surface could be improved from 0.52 μm Ra (6.50 μm Rt) to a mirror-like surface of 0.068 μm Ra (0.742 μm Rt). Also, the total working time could be reduced significantly to within the range of 5 to 10 min.     

Animation of the evolution of surface finish with wear

In recent years one of the most significant developments in surface metrology has been the three-dimensional characterization of engineering surfaces. The impetus for this development was primarily motivated by a need for a more realistic visualization of surfaces than the traditional two-dimensional surface profile could provide. There have been several approaches to three-dimensional characterization of engineering surfaces including using time series and fractals. A significant application of these mathematical models would be to use them as the basis for the animation of the evolutionary changes of the surface with wear. By considering simple wear models, this paper demonstrates how computer animation illustrating the evolution of a three-dimensional surface with wear may be realized. Non-Gaussian fractals and time series are used as the basis for three-dimensional characterization and the animation is achieved using the standard morphing techniques provided by Autodesk 3D Studio.     

A novel method for improving surface finish of stereolithography apparatus

Stereolithography apparatus (SLA) is one of the most famous and versatile additive manufacturing techniques and has been widely used in many industrial fields. However, the surface quality of SLA parts is unsatisfactory for the precise parts due to stair stepping caused by the layered manufacturing process. In this study, the stair stepping of SLA parts was relieved by ultrahigh pressure atomizing coating with the polyethylene wax emulsion using a group of optimum coating parameters. The experimental results showed that polyethylene wax film with the thickness less than 0.1 mm bonded to the SLA parts adequately and the surface roughness of the SLA parts can be significantly reduced; the Ra of SLA parts was decreased to less than 2.5 μm. This method can be applied to improve both the outer surface and the inner surface of complex SLA parts with good dimensional accuracy and no damage to SLA parts, implying potential for fabrication of precise components. Expected advantages of this method include economical, operator-friendly, and time-saving for the manufacturers.     

A study of the Taguchi optimization method for surface roughness in finish milling of mold surfaces

The objective of this paper is to develop a Taguchi optimization method for low surface roughness in terms of process parameters when milling the mold surfaces of 7075-T6 aluminum material. Considering the process parameters of feed, cutting speed, axial-radial depth of cut, and machining tolerance, a series of milling experiments were performed to measure the roughness data. A regression analysis was applied to determine the fitness of data used in the Taguchi optimization method using milling experiments based on a full factorial design. Taguchi orthogonal arrays, signal-to-noise (S/N) ratio, and analysis of variance (ANOVA) are used to find the optimal levels and the effect of the process parameters on surface roughness. A confirmation experiment with the optimal levels of process parameters was carried out in order to demonstrate the effectiveness of the Taguchi method. It can be concluded that Taguchi method is very suitable in solving the surface quality problem of mold surfaces.     

混粉电火花加工工件表面质量影响因素分析

基于混粉电火花加工的对比试验,解释了表面缺陷产生的原因,获得峰值电流、脉宽、伺服电压等放电参数对白层形成的影响规律。研究结果表明在电火花加工中工件表面白层的形成是引起表面裂纹的主要原因,将峰1直电流IP降低至2A可有效减小白层的厚度,峰值过小反而会增加白层的厚度;脉冲宽度Ton的减小能降低白层的厚度且使其分布更均匀;合适的伺服电压能够使白层的表面缺陷减少。在此基础上,完成大面积工件的加工,分析热影响层的特点。     

一种利用WC电极的电火花表面改性技术

研究了1种在普通电火花加工机床上实现金属工件表面改性的新方法。它是在传统电火花加工方法的基础上，采用WC烧结体电极和普通煤油工作液，在工件表面形成1层硬质陶瓷层，从而达到改善工件表面性能的目的。系统地对放电沉积原理进行了探讨，在大量试验的基础上，总结了放电沉积的工艺方法。通过扫描电镜、电子探针、X射线衍射分析、摩擦磨损等一系列试验手段，对形成的沉积层特性进行了定量和定性的分析。试验与分析表明，用电火花加工的方法进行表面处理是1种极具潜力的改性方法。     

An investigation into the assessment of surface finish by microwave reflection

Non-contact methods are ideal for in-process monitoring of surface finish. In this context, the application of microwave reflection for the assessment of roughness assumes significance. It is well known that surface roughness affects the reflection of microwaves, and the energy loss in their transmission is considerably influenced by the finish of the wave guides. Experimental investigations were conducted with a sweep oscillator and reflectometer to find the feasibility of this technique in monitoring the roughness of manufactured surfaces. A number of surface specimens produced with different machining operations were measured for the return loss, and these compared with the normal roughness values. This paper deals with the experiments conducted and results obtained in these investigations.     

Analysis of surface finish in milling by power spectral density measurement

The power spectral densities (psd) of surface profiles of milled steel samples have been determined by analogue measurement techniques, ie by a spectral analyser. The recorded psd curves indicate the presence in the surface profiles of some periodic components. Increase of cutting speed during milling causes the spectral density values to decrease. By psd measurement it was possible: to distinguish between surface profiles with the same R_a value, but milled under different cutting conditions; and to detect axial run-out of the milling cutter, which results in waviness of machined surfaces.     

模具型腔表面复合精密光整加工参数优化

利用回归方程建模的方法,建立了模具型腔表面超声电火花复合加工效果预测模型,并采用组合遗传算法实现加工参数的优化设计,给出了仿真实例,为超声电火花复合加工参数选择的可靠性和应用的可行性研究提供了新的研究方法与途径.     

温度对螺旋定子内腔曲面挤压成型的影响分析

对螺旋定子内腔曲面的形成原理及啮合方法进行了研究,并对国内外螺旋曲面的加工方法及应用做了一定的了解后,提出了挤压成型加工螺旋定子内腔曲面的方法。以螺旋定子为研究对象,通过建立其三维实体模型,利用有限元软件对其加工过程进行分析,得到不同温度下加工螺旋定子时所需推力,产生的内部应力及其导程的变化等重要参数,为使用挤压法制造螺旋定子提供了参考和依据。