Abstract: Aluminum Nitride (AlN) ceramic materials have high thermal conductivity and electrical insulation, prompting consideration of their use as a semiconducting material. Although AlN should be machined with a high accuracy of form and dimension to achieve products and components with requisite precision, mechanical and other machining methods such as the laser method cannot be used because of the brittleness and high thermal conductivity of AIN. Recently, we have succeeded in machining many insulating ceramics by sinking (SEDM) and Wire-Electrical Discharge Machining (WEDM) with the assisting electrode method. We have already machined many insulating ceramic materials such as Si3N4, ZrO2 and Al2O3. However, inferior machining characteristics were obtained with AlN than with other materials. In this study, the effects of several electrical discharge conditions were examined to obtain better machining properties, such as high material removal rate and a low electrode wear ratio. It was found that machining time decreased with an increase in capacitance, while the electrode wear ratio increased. The electrode wear ratio of the W electrode was low, suggesting that it is suited for accurate machining of AlN. Additionally, the electrically conductive layer was analyzed using Energy Dispersive X-ray Spectrometry (EDS) and X-ray Diffraction (XRD). As a result, the architectural component of the EDMed AlN surface is considered mostly Al that is resolution of the workpiece. Therefore, in the EDM of AlN using the assisting electrode method, machinability using deionized water may be superior to dielectric oil. To investigate the effect of the dielectric working fluid, AlN was machined using deionized water and dielectric oil. In the case of machining with deionized water, the removal rate was faster and electrode wear ratio was lower, compared to dielectric oil.
Abstract: The proposed paper aims at the development of extruding seam square tube of AA7075 high strength aluminum alloy by simulation and experiment. There are several factors related to extrusion load such as billet temperature, billet dimension, flow stress, die cavity and product geometry. The extrusion loads and die stresses for hot extruding square tube with respect to different product have been investigated. Since AA7075 behaves high forming resistance comparing to AA6063 and AA6061, the product design and die design should be modified in order to meet with the limitation of extrusion machinery. Moreover, AA7075 has high thermal welding crack behavior by comparing to AA7003. Therefore, In order to provide high contact pressure enough to conduct solid welding for the split AA7075 materials in welding chamber, the specific die cavity design has been finished. Then, the solid welding pressure can be increased. The research results show that under the same forming conditions such as fixed ram speed and billet temperature, the extrusion force for the product with thick thickness is small than the one with thin thickness. The same result was obtained for die stress. A square tube extrusion experiment has been conducted by installing die set into forward extrusion machinery. The experiment and simulation results have been compared and discussed.
Abstract: Forging is simple and inexpensive in mass production. Metallic materials are processed through plastic deformation. This not only changes the appearance but also changes the internal organization of materials that improve mechanical properties. However, regarding manufacturing of plastic products, many processing factors must be controlled to obtain the required plastic strain and desired tolerance values. In this paper, we employed rigid-plastic finite element (FE) DEFORMTM software to investigate the plastic deformation behavior of an aluminum alloy (A7075) workpiece as it used to forge bicycle pedals. First we use Solid works 2010 3D graphics software to design the bicycle pedal of the mold and appearance, moreover import finite element (FE) DEFORMTM 3D software for analysis. The paper used rigid-plastic model analytical methods, and assuming mode to be rigid body. A series of simulation analyses in which the variables depend on different temperatures of the forging billet, round radius size of ram, punch speed, and mold temperature were revealed to confirm the predicted aluminum grain structure, effective stress, effective strain, and die radial load distribution for forging a bicycle pedal. The analysis results can provide references for forming bicycle pedal molds. Finally, this study identified the finite element results for high-strength design suitability of a 7075 aluminum alloy bicycle pedal.
Abstract: The effects of tool geometry on the microstructure and tensile shear strength of friction stir spot-welded A6061-T6 Al alloy sheets were investigated in the present study. Friction stir spot welding (FSSW) was carried out at a tool speed of 2500 rpm, plunging rate of 1 mm/s, and dwell time of 3 s. Four types of tools with the same shoulder shape and size, but different pin profiles (threaded cylindrical, smooth cylindrical, threaded triangular, and smooth triangular) were used to carry out FSSW. The mechanical and metallurgical properties of the FSSW specimens were characterized to evaluate the performance of the different tools. Experimental results show that the pin profile significantly alters the hook geometry, which in turn affects the tensile shear strength of the friction stir spot welds. The welds made using the conventional thread cylindrical tool have the largest elongation and yield the highest tensile strength (4.78 kN). The welds made using the smooth cylindrical tool have the lowest tensile strength. The welds made using the threaded triangular and smooth triangular tools both have a tensile-shear load of about 4 KN; however, the welds made using the threaded triangular tool have a better elongation than those made using the smooth triangular tool.
Abstract: AZO thin films were deposited using a magnetron sputtering system with an AZO target (with 3wt% Al2O3) on polyethylene terephthalate (PET) substrates with pre-strain. The effect of sputtering power on the optical and electrical properties of AZO films was investigated. For samples deposited on pre-strained PET substrates, X-ray diffraction was used to determine the c-axis orientation of AZO films deposited at 60, 80, and 100 W. Results show that resistivity decreased with increasing sputtering power, which might result from the better crystalline structure and fewer grain boundaries obtained at high power. The transmittance increased when the power was increased from 60 to 100 W. The absorption edge thus decreased for AZO film deposited at 100 W.
Abstract: Conventional ductile fracture criteria are not applicable in the vicinity of maximum friction surfaces for several rigid plastic material models because the equivalent strain rate (second invariant of the strain rate tensor) approaches infinity near such surfaces. In the present paper, a non-local ductile fracture criterion generalizing the modified Cockroft-Latham ductile fracture criterion is proposed to overcome this difficulty with the use of conventional local ductile fracture criteria. The final form of the new ductile fracture criterion involves the strain rate intensity factor which is the coefficient of the principal singular term in a series expansion of the equivalent strain rate in the vicinity of maximum friction surfaces. When the velocity field is not singular, the new ductile fracture criterion reduces to the modified Cockroft-Latham criterion. The strain rate intensity factor cannot be found by means of commercial finite element packages since the corresponding velocity field is singular. In the present paper, the new fracture criterion is illustrated with the use of an approximate semi-analytical solution for plane strain drawing. It is shown that the prediction is in qualitative agreement with physical expectations.
Abstract: This paper is to investigate the optimization of mechanical properties for the maximum tensile strength, elongation, and impact strength of Polycarbonate and Polymethyl methacrylate (PC/PMMA) blends by injection molding process. The PC/PMMA plastics composites with different blending percentage are first blended have been injected as the tensile and impact specimens designed according to ASTM, type V by injection molding machine. Taguchi’s method is then used to find the optimal parameters for the maximum tensile strength, elongation and impact strength. The control factors selected in this study are melt temperature, packing pressure, mold temperature and cooling time. An ANOVA table has been used for determining the significance of injection molding parameters. Results of experiments show that the melt temperature is the most significant parameter for improvement of mechanical properties of PC-PMMA plastics composites. Blends with high PC concentrations result in low tensile strength and high impact strength. Illumination testing of the tatol internal reflection (TIR) of PC/PMMA blends has been proceeded and the TIR lens illumination intensity is compared with three compositions of the PC/PMMA blends. Illumination results show that the PC/PMMA 80/20 blend has the highest intensity of illumination. Results of this study can be applied on the optimization of injection molding parameters for polymer blends of LED lens.
Abstract: Fixed diamond wire saw has the advantages such as higher cutting rate and clearer operating environment over the slurry wire saw in wafering. However, the higher cost and poor sliced wafer surface are still the obstacles for the diamond wire saw to totally replace slurry wire saw. In this study, the distribution of diamond grits on the wire was investigated by numerical simulation. The results show that there is a critical value of the abrasive interval to transfer the machining mechanism from plastic plowing to brittle indentation cracking for the material removal. The value depends on both the wire tension and bow angle during the operation.
Abstract: The drilling of the printed circuit board (PCB) is a critical process due to occupying a third of the total PCB production time. This study integrates the K-nearest neighbor (K-NN) algorithm and the bi-objective multi-population genetic algorithm (BMGA) for deriving a near-optimal drilling path to reduce the drilling time, to protect product from overheating, and to balance the loading of the drill axes. Firstly, the holing coordinates are parsed from a CNC drilling program, clustered with the K-NN algorithm, which divides the global holes into several areas with local holes. Next, the local holes are classified and reconnected using 1-NN algorithm and BMGA, respectively. The BMGA fitness function is adjusted to eliminate overheating and unbalancing through drill jumping to ensure product quality. Finally, the near-optimal drilling paths can be derived within the time limit by checking a stable factor. The practical values of BMGA have already been demonstrated in 20 PCB samples. By including the thermal protection and the load balancing constraints and resolving the optimal path within an acceptable time limit, i.e. 30 min, this method can reduce the drilling length by an average of 15.5% compared to the original drilling length if the number of holes to be drilled is less than 5k. For cases with the number of holes between 5k and 20k, the average length of the drilling paths can be reduced to 25.6% of the original length. Moreover, the thermal protection maintains the samples with mean yield 99.8%.
Abstract: This paper presents an experimental investigation on the turning of Inconel 718 using tungsten carbide and cermet insert tools with ultrasonic-assisted. The Taguchi method as well as an L18 orthogonal array, signal-to-noise (S/N) ratio and analysis of variance (ANOVA) are employed to examine the performance characteristics of the turning operations. The effect of the machining parameters (cutting tool, depth of cut, cutting speed, feed rate, working temperature and ultrasonic power) on roundness and flank wear in the turning operations are studied. For roundness, depth of cut (σ = 38.40 %) and feed rate (σ = 22.59 %) were recognized to make significant contributions. For flank wear, the significant contribution order was cutting tools (σ = 51.16 %) for different materials, follow working temperature (σ=22.37 %), depth of cut (σ = 13.59 %), and ultrasonic power (σ = 5.79 %). Cutting with ultrasonic-assisted improves roundness by 17.78 % to 45.73 %, and improves flank wear by 26.52 % to 46.26 7%. Finally, turning experiments with 5-20 nm nano-particles cutting fluid were investigated. The experimental results indicated the cutter-workpiece friction force is noticeably reduced and cutter service life is prolonged.