Effect of lubrication and green-compact shape on mechanical properties of mechanically alloyed Zn-22wt%Al powders during hot extrusion of spur gears

We investigated the extrusion behavior of mechanically alloyed Zn-22wt%Al powders with different lubricants and green-compact shapes. The mechanical alloying of powder particles was performed by planetary ball milling for 4 h, 8 h, 16 h, 32 h, and 64 h. The mechanical properties of these powders, as compacted and sintered cylindrical preforms, were estimated by uniaxial compression tests. The alloyed powder with an average particle size of 10 μm obtained after milling for 32 h had the highest compressive strength (288 MPa). Extrusions of miniature spur gears with pitch circles of 1.8 mm using the alloyed powder were carried out at different extrusion temperatures. An extrusion temperature of 310°C resulted in the highest Vickers hardness without surface defects when alloyed powder milled for 32 h was used. To investigate the effect of green-compact shape and lubricant on the dimensional accuracy and cracking regions during the first stage of hot extrusion, extrusion experiments with conical- or cylinder-type green compact shapes and BN spray or a graphite lubricant were performed at an extrusion temperature of 310°C. The results showed that the extrusion of spur gears by using the conical-shaped billet and graphite lubricant resulted in a low extrusion load, good surface roughness, a short cracking region during the first stage, and high dimensional accuracy.     

3D contact analysis of conjugate spur gears by a complete mating process

Instead of applying fixed boundary conditions to constrain and simplify material behavior in 2D models, the point and line contact of tooth surfaces are substituted by a face-contact model of teeth in this study. The inaccurate prediction of load, deformation, and stress in 3D contacts are solved. Most research uses one pair to three pairs of meshing teeth to simulate the mating process. However, describing the entire process of three contact zones during each mating pair is insufficient. By implementing a combined 3D face contact and finite element method, the contact stress analyses between two spur gear teeth are conducted in 11 different contact positions during a full mating process. The proposed approach provides a complete and effective solution to the contact problem in a quasi-dynamic manner. This model not only determines the load-sharing prediction but also verifies the applied boundary conditions.     

Design of nonstandard spur gears cut by a hob

A numerical technique has been developed for determining the individual hob offsets for a pair of spur gears designed to operate at a nonstandard center distance with the maximum ratio of recess to approach action or to balance tooth strengths of the pinion and gear. The numerical technique is based on determining the limit to which the hob is offset to create a full recess-action gearset, to balance the tooth strengths, to maintain a desired contact ratio, and to avoid undercutting. The values of the hob offsets from these design criteria are calculated, and the limiting value selected to produce an acceptable gearset. In this paper, backlash is incorporated into the solution method and a new numerical technique is employed to solve the optimum hob offsets. This paper presents the formulation of the equations for each of the design criteria and the corresponding solution methods, which include backlash, that are used to determine the optimum hob offsets. These design criteria have been incorporated into a Basic program. Example problems and results from the program are presented.     

CAD-based simulation of the hobbing process for the manufacturing of spur and helical gears

Targeting an accurate and realistic simulation of the gear hobbing process, we present an effective and factual approximation based on three-dimensional computer-aided design. Hobbing kinematics is directly applied in one gear gap. Each generating position formulates a spatial surface path which bounds its penetrating volume into the workpiece. The three-dimensional surface paths generated from the combination of the relative rotations and displacements of hob and work gear are used to split the subjected volume, creating concurrently the chip and the remaining work gear solid geometries. The developed software program HOB3D simulates accurately the manufacturing of spur and helical gears, exploiting the modeling and graphics capabilities of a commercial CAD software package. The resulting three-dimensional solid geometrical data, chips and gears provide the whole geometrical information needed for further research, such as prediction of the cutting forces, tool stresses and wear development as well as the optimization of the gear hobbing process.     

On surface integrity of miniature spur gears manufactured by wire electrical discharge machining

This paper reports about investigations on some important aspects of surface integrity of the miniature spur gears manufactured by wire electrical discharge machining (WEDM) process. The investigations included study of variation of form errors (deviations in profile and lead) and surface roughness with discharge energy parameters, i.e., voltage and/or pulse-on time for the miniature gears. The effect of WEDM process on flank surface topography, bearing length parameters, microstructure, and microhardness for the best quality miniature gear were also studied. The manufactured miniature gears were of external spur type having 9.8 mm as outside diameter, 4.9-mm thickness, 0.7 mm as module, 12 teeth, and were made of brass. It was found that combination of low discharge energy parameters resulted in better form accuracy, surface finish, and microstructure ensuring enhanced service life and better functional characteristics of the WEDMed miniature gears. The best quality miniature gear had form errors (i.e., lead and profile deviations) as low as 5.4 μm, very little variation in the actual surface topography from the theoretical one, an average surface roughness of 1 μm, and maximum surface roughness within the entire evaluation length as 6.4 μm, showed consistent surface finish measured by other surface roughness parameters, good bearing area curve, and crack-free gear tooth surface without significant alteration in microhardness. Results of the present work demonstrate the superiority of the WEDM process over the conventional miniature gear manufacturing processes.     

Determination of static tooth stresses in nonstandard spur gears cut by pinion cutter

This paper is a continuation of the paper entitled “Determination of Pinion-Cutter Offsets Required to Produce Nonstandard Spur Gears with Teeth of Equal Strength.” Sample charts are presented for determining how closely the static bending stress in the pinion teeth and gear teeth are balanced when gears are designed using the cutter offsets determined from the previous paper. These charts are plots of stress factors for the pinion or gear versus gear ratio for changes in center distance and for a particular diametral pitch and pitch diameter of cutter. This paper also presents a set of sample calculations for the determination of the stresses in the pinion teeth and gear teeth.     

粉末冶金法制备多孔Ni-Ti合金的烧结过程研究

研究粉末冶金法固相烧结多孔体的原理及工艺参数,并对多孔Ni-Ti合金烧结进行实验研究,结果表明,在140MPa压力下压制,在950℃下粉末冶金固相烧结制备的Ni-Ti合金,具有以NiTi为主相的、合适孔隙度的合金.     

Fabrication and evaluation of various types of micro one-way valves through micro rubber molding process

In recent years, research and development on micro fluid systems has become active in the fields of chemical technology and biotechnology. For the realization of these micro fluid systems, micro fluid devices such as micro-valves and micro pumps are very important. This paper reports the fabrication and experimental evaluation of several micro one-way valves. The valves are fabricated through a micro molding process, which makes the fabrication process simple and suitable for mass production. The experimental results indicate that the developed valve has great performance with a normal flow rate of 130.2 ml/min and a leak flow of 2.2 ml/min. The normal flow rate is 1.4 times higher than that of the previous model.     

Analysis and optimization of micro-geometry of miniature spur gears manufactured by wire electric discharge machining

This paper reports about the analysis and optimization of micro-geometry parameters (i.e. total profile deviation ‘F_a’ and accumulated pitch deviation ‘F_p’) of the wire electric discharge machined (WEDMed) fine-pitch miniature spur gears made of brass. Effects of four WEDM process parameters namely voltage, pulse-on time, pulse-off time and wire feed rate on the micro-geometry of the miniature gears were analyzed by conducting the experiments designed using Box–Behnken approach of response surface methodology (RSM). Analysis of variance study found all four input parameters significant. Larger deviations in profile and pitch were observed with higher values of the voltage and pulse-on time, and with lower values of wire feed rate and pulse-off time. Multi-performance optimization of WEDM parameters was done using the desirability analysis to minimize profile deviation and pitch deviation simultaneously. The values of F_a and F_p of the gear obtained by the confirmation experiment conducted at the optimized WEDM parameters were as 11.5 μm and 9.1 μm respectively. These values categorize the WEDMed gear having DIN quality number as 7 and 5 respectively for profile and pitch which are better than those obtained by the conventional miniature gear manufacturing processes.     

Fabrication of micro rods by twin-mirroring-wire tangential feed micro electrical discharge grinding

In micro electrical discharge machining (micro-EDM), the precision fabrication of cylindrical micro rods is difficult to achieve with a high processing efficiency. In order to overcome this challenge, this paper proposes a new processing method, which is denoted as twin-mirroring-wire tangential feed micro electrical discharge grinding (TMTF-WEDG). The machining principle, characteristics, and realization of the new method are firstly introduced. Then, the advantages of TMTF-WEDG in terms of machining efficiency and accuracy are demonstrated. The experimental results have shown that the machining efficiency can be increased to more than 70% in comparison with conventional tangential-feed wire electrical discharge grinding. It has also been proved that a minimum removal of material corresponding to a reduction of less than 1 μm in the diameter of a micro rod can be obtained by TMTF-WEDG. This considerably helps in improving the accuracy and repeatability of the machining process. A deviation of less than 1 μm on the diameter of a micro rod has been obtained in a length range of 800 μm. The process repeatability in machining five micro rods has been established to be below 2 μm. The proposed method is therefore of great significance for improving the machining efficiency and ensuring a high precision in the shaping process of cylindrical micro rods.     

Undercutting and contact characteristics of longitudinal cycloidal spur gears generated by the dual face-hobbing method

This paper investigated the undercutting of longitudinal cycloidal spur gear generated by the dual face-hobbing method. Sensitivity of transmission errors and contact patterns due to varied assembly errors were studied using the tooth contact analysis (TCA) technique. The undercut of the longitudinal cycloidal spur gear is similar to the regular spur gear except for the fact that the helical angle is varied along the longitudinal direction due to the cycloidal cutting trace. Several numerical examples are presented to validate the derived undercutting of the proposed longitudinal cycloidal spur gear and the tooth contact pattern sensitivity. As expected, the bearing contact and transmission error are insensitive to the assembly error.     

UV-LIA制作超高微细阵列电极技术研究

超高金属微细阵列电极在微细加工领域和生命科学领域有广泛应用。本文采用UV-LIGA技术制作超高金属微细阵列电极,并利用电解置桩的方法辅助去除SU-8胶。通过单次涂胶、提高前烘温度、降低后烘温度的方法制作了厚度达1mm的SU-8胶结构;采取反接电极法在金属基底上电解得到微坑,增强电铸金属电极与金属基底的结合力,保证去胶后电铸金属的完整性。选取优化的工艺参数：单次注射式涂胶;前烘110℃/12h;适量曝光剂量;分步后烘50℃/5min、70℃/10min、90℃/30min;反接电极电解10V/15min等,获得了高900μm、线宽300μm的金属微细阵列电极结构。试验表明,UV-LIGA技术是一种高效、经济的制造超高微细阵列电极的有效手段。     

Mechanical etching of micro pockets by powder blasting

The main objective of this research is to develop a mechanical etching technique to produce micro mould dies having micro pockets of hundreds of μm. A powder blasting technique is applied to stainless steel plates based on predefined process conditions. This paper describes the performance of a powder blasting technique and the effect of the number of nozzle scanning times and the stand-off distance of the nozzle on the depth and width of pockets. Required blasting and measurement steps are performed to extract the relationships between given process parameters and machined results. Experimental results show that increasing the number of nozzle scanning times and decreasing the stand-off distance of the nozzle increase the depth and width of machined pockets. Increase of the width of the pockets results from mask film wear. The results of this research can be a fundamental basis to produce more accurate and smaller micro pockets using the powder blasting process .     

计算机控制多个微型步进电动机的原理

在一种自动测量调整系统中有5个供调速用的微型步进电动机,每个电动机有7种状态。在任一时间内每个电动机必须取7种状态中的一种,因而共有16807种组合,在指定时间内5个电动机的状态取何种组合,取决于测量系统所测到的数据,测量系统的数据由计算机进行采集、分析处理以确定各个电动机当时应选择的状态,然后由计算机控制使各电动机按要求的状态运作,各个电动机不同状态的运作,将改变所测到的数据。数据的改变又将反馈使电动机状态的改变,直至最后将参数调整致规定的范围内。文章介绍了计算机接口和步进电动机运转的控制线路及有关软件核心编程的要点。     

Research of production times and cutting of the spur gears by end mill in CNC milling machine

In the current study, differently from the conventional manufacturing methods, cutting of spur gear by the end mill in the computer numerically controlled (CNC) vertical milling machine was purposed. For this aim, two different approaches, radial and axial cutting methods, were introduced. However, the cutting process is performed by use of only the radial cutting method. Parametric equations of tool paths for cutting the spur gear were derived. Regarding those equations, by using the macro-program of the Dyna 2009 Myte type CNC milling machine, a CAM program is developed. By varying the parameters in the tool paths such as module, number of teeth, face width of the spur gear, cutting depth, and cutting angle, spur gear was cut and the production time was obtained. Furthermore, the dimensions of new manufactured spur gear were measured by gear tooth vernies. The dimensions were also calculated by using mathematical expressions and it was concluded that the measured values are well agreeable with the calculated values. It was observed that the production time increases with increasing the module value or number of teeth and decreasing the cutting angle or the cutting depth.     

利用体块PZT制备膜片式压电微泵

利用锆钛酸铅(PZT)的逆压电效应,设计并制备了膜片式压电微泵。通过将电能转换为机械能,实现了液体的微流体控制。微泵由微驱动器与单向微阀两部分组成;微驱动器主要为液体流动提供驱动力,单向微阀则用于精确控制液体的流动方向。通过对PZT-Si膜片的位移量、位移形状的仿真分析,确定了微驱动器的设计尺寸,并估算其液体驱动性能。利用共晶键合工艺、研磨减薄工艺、硅深反应离子刻蚀工艺和准分子激光加工工艺等制备出了微驱动器和单向微阀。最后,设计了驱动测试实验,检测了微泵的液体驱动性能。测试结果表明:所制备的膜片式压电微泵驱动的谐振频率约为70kHz,能驱动微米量级的液体位移或运动。当微泵驱动电压为30Vp-p、频率为600Hz时,液体的驱动流速约为65μL/min。该微泵具有体积小,线性度好等特点。     

采用过电铸工艺制造金属微细阵列网板

针对制作尺度10μm的超小微细阵列网板非常困难的问题,提出了采用过电铸工艺制造超小尺寸微细阵列网板的方法。建立了过电铸工艺过程的电场模型,利用有限元分析技术对过电铸工艺过程进行模拟仿真。选取优化的工艺参数(烘胶120℃/60min,曝光3000mJ/cm2,显影2min等)利用光刻制作了高度为50μm、直径为50μm的AZEXP125nXT-10A光刻胶群柱结构,以此胶膜结构作为模具进行了过电铸工艺实验,并与仿真结果进行对比,结果证明了有限元仿真的正确性。最后,通过过电铸缩孔2h获得了厚度达70μm,孔径为4μm的微细阵列网板结构。实验表明,过电铸工艺是一种低廉、安全、可批量生产的制作超小阵列网板的方法。     

Small-hole arrays of ceramic material manufactured by micro powder injection molding

Ceramic substrate with three kinds of small-hole arrays (the minimum diameter is 400?μm) was manufactured by micro powder injection molding. The homogeneity, thermal, and rheological properties of the feedstock was characterized by means of SEM, Archimedes method, TGA, DSC, and capillary rheometer, respectively. The feedstock has good uniformity and the viscosity of feedstock accords with the pseudo-plastic behavior which is suitable for micro powder injection molding. The test results also show that the linear shrinkage of small holes is lower than the substrate which is important to mold design and size contraction of the sample. Moreover, the porosity of the sintered substrate is lower than that of the thin wall between two neighborhood small holes. Good surface roughness of the sintered samples is obtained by using sub-micron ZrO₂ powder which is even lower than molded surface. The relative density and hardness of the ceramic substrate with small-hole arrays sintered under 1,500°C for 2?h is 98.3% and 13.68?GPa, respectively.