Advanced Materials Research Vol. 445

Abstract: The effect of tool edge roundness attracts growing attention due to increasing applications of precision, micro-and nanomachining technologies. A new slip-line model and its associated hodograph are proposed for cutting with a rounded-edge tool in this paper. New model considers stagnant metal region called as dead metal zone formed in front of the rake face of tool during cutting process. Dewhurst and Collinss [ matrix technique for numerically solving the slip-line problem is employed in the mathematical formulation of the new model. The unknown slip-line angles were solved depending on the force data obtained from experiments and variation of the sub-regions with cutting edge radius was determined.

Abstract: The paper presents an experimental investigation into the slotting of hardened AISI D2 (~62HRC) tool steel using 0.5mm diameter coated (TiAlN) tungsten carbide (WC) end mills. SEM analysis of tool morphology and coating integrity was undertaken on all tools prior to testing. Tool wear details are given based on resulting cutter diameter and slot width reduction. In addition, cutting forces are also presented together with details of workpiece burr formation. A full factorial experimental design was used with variation of cutting speed, feed rate and depth of cut, with results evaluated using analysis of variance (ANOVA) techniques. Parameter levels were chosen based on microscale milling best practice and results from preliminary testing. Main effects plots and percentage contribution ratios (PCR) are included for the main factors. Cutting speed was shown to have the greatest effect on tool wear (33% PCR). When operating at 50m/min cutting speed with a feed rate of 8µm/rev and a depth of cut of 55µm, cutter diameter showed a reduction of up to 82µm for a 520mm cut length. SEM micrographs of tool wear highlighted chipping / fracture as the primary wear mode with adhered workpiece material causing further attritious wear when machining was continued up to 2.6m cut length. All tests produced burrs on the top edges of the slots which varied in size / width to a lesser or greater degree. Under the most severe operating conditions, burr width varied from approximately 50µm to more than 220µm over the 520mm cut length. Cutting forces in general were less than 12N up to test cessation.

Abstract: This paper describes for verification of bending effect on the performance of the heightwise-asymmetric plunge cutting method, which was composed of an upper-wedge blade and a lower-wedge blade embedded in the lower-counter plate, in order to apply this cutting method for a polycarbonate (PC) thick sheet. By varying the tip angle α_U and the tip thickness w_U of lower blade embedded in the counter plate, and combining a standard steel cutting rule of 42° center bevel blade, the sheared profile of two kinds of PC worksheet (the thickness of which was chosen as t=0.5, 1.0 mm) was experimentally investigated. Through this experiment, it was found that the sheared profile (the necked height η_n, the upper inclination angle β, the lower inclination angle β_U) of PC worksheet was primarily characterized by the normalized lower tip thickness w_U/t. The difference of sheared profile was explained using the Prandtls punching solution for two kinds of PC worksheet. Furthermore, by varying the heightwise position of lower blade tip, the bending effect on sheared profile of worked sheet was experimentally verified.

Abstract: In a roll forming process, a desired profile is produced through continuous bending of a sheet metal strip. Occurrences of spring back, twist, and bow are major defects in roll formed profiles. We developed a dedicated analysis program based on the elastic-plastic finite element method to simulate roll forming processes with asymmetrical shaped rolls. We applied the augmented Lagrangian technique in contact algorithm and a pre-determined deformation region division method for computation efficiency. A simplified cross section produced via three passes of roll forming has been experimented to be measured in the amounts of twist and bow occurred after roll forming. The performance of the developed FEA tool has been verified with measurements in terms of accuracy. The tool has been evaluated in terms of computation efficiency by comparison of without region division method.

Abstract: Vibration Drilling (VD) is one of the advance machining techniques to produce precision holes. In this study the vibration tool of drilling process is made with a new design while drilling tool vibrates by an ultrasonic transducer, it also rotates. The exerted vibration to tool has frequency of 20.6 kHz and low peak-to-peak amplitude. After preparation of process set-up, primary experiments were done on Al2024 workpiece. In these experiments , it was shown that thrust force in vibration drilling process is lower than in ordinary drilling (OD).Then the influence of some machining parameters include cutting speed and feed rate on thrust force in VD process studied and compared with OD process.

Abstract: In this study, the influence of different electro discharge machining parameters (current, pulse on-time, pulse off-time, arc voltage) on the electrode wear ratio as a result of application copper electrode to hot work steel DIN1.2344 has been investigated. Design of the experiment was chosen as full factorial. Artificial neural network has been used to choose proper machining parameters and to reach certain electrode wear ratio. Finally a hybrid model has been designed to reduce the artificial neural network errors. The experiment results indicated a good performance of proposed method in optimization of such a complex and non-linear problems.

Abstract: The surface roughness model in the turning of 34CrMo4 steel was developed in terms of cutting speed, feed rate and depth of cut and tool nose radius using response surface methodology. Machining tests were carried out using several tools with several tool radius under different cutting conditions. The roughness equations of cutting tools when machining the steels were achieved by using the experimental data. The results are presented in terms of mean values and confidence levels.The established equation and graphs show that the feed rate and cutting speed were found to be main influencing factor on the surface roughness. It increased with increasing the feed rate and depth of cut, but decreased with increasing the cutting speed, respectively. The variance analysis for the second-order model shows that the interaction terms and the square terms were statistically insignificant. However, it could be seen that the first-order affect of feed rate was significant while cutting speed and depth of cut was insignificant.The predicted surface roughness model of the samples was found to lie close to that of the experimentally observed ones with 95% confident intervals.

Abstract: The control of blank-holder force (BHF), is one of the main parameters in deep drawing. Fracture, wrinkling and inappropriate draw-in of sheet edges on certain locations are the main defects that occur due to insufficient and not well distributed restraining force of sheet flow into die cavity by BHF. It was demonstrated that appropriate utilization of draw beads with appropriate geometry and location in die could reduce or even eliminate these defects. Achieving an optimum geometry and location of draw beads are main issues in tooling stage that would cause high cost due to trial and error. In this paper, 2D FE analyses to reach draw bead restraining Force (DBRF) for several usual draw beads geometries were performed. 3D FE analyses of deep drawing process of a rectangular automotive panel with complex and parametric geometry with the presence of draw beads were simulated by the use of ABAQUS6.9 commercial FEM package to reach an optimization of best location and also best geometry. Response surface method with full factorial case was employed for optimization. Simulation results were validated by experimental data of deep drawing.

Abstract: The state of the surface, whatever the metal or alloy used is of paramount importance. Hand disc grinding operation is difficult to master in terms of results on the surface due to its manual nature. From this, comes the great importance to the mastery of the consequences induced by this abrasive process. A previous experimental study on hand disc grinding revealed several consequences on the surface integrity in terms of residual stresses, micro-hardness, hardening of the material etc. Numerical simulation can be a good way to prevent manufacturers of very time consuming experiments for the prediction of residual stresses due to grinding. The purpose of this study is to predict the consequences in terms of induced temperature fields and the state of residual stresses. The action of the disk-grinding wheel on the Workpiece is modeled by a moving heat flux on top of the part surface. All the difficulties lie in the quantification of the heat flux and more precisely in the heat flux density that gives the way the thermal load is distributed in the contact disk grinding/workpiece area. In this paper, an original analytical model for the determination of the heat flux density has been developed. For each step, the thermo-mechanical calculation is performed. Finally, the distribution of temperature and residual stresses will be carried out with the FE software SYSWELD 2010®.

Abstract: A Proton Exchange Membrane Fuel Cell (PEMFC) is a type of fuel cell being developed for automotive applications as well as for stationary fuel cell applications and portable fuel cell applications. Its performance such as power density can be improved by the use of the bipolar plate with a new lightweight material which is one of core components making up PEMFC stack. Aluminum alloy has good mechanical properties not only in terms of density, electrical resistivity and thermal conductivity, but also in terms of corrosion resistant compared with stainless steel and graphite composites bipolar plate. Furthermore, the use of aluminum for a bipolar plate reduces simultaneously the cost and weight of it, and it contributes to the ease of machining. For these reason, an aluminum alloy is selected in this study. This study presents the feasibility of the simulation for the development of aluminum bipolar plates that consists of multi array micro channels. The analytical solutions obtained by the simulation are validated by the comparison with the experimental results. From the results, it is ensured that the stamping processes for the bipolar plate could be predicted and designed by the results of the by FE-Simulation.