Advanced Materials Research Vols. 83-86

Abstract: A CV joint outer race is an important load-supporting part in cars. Its geometry is very complicated. Traditional hot and cold forging methods have their own limitations to produce such a complex shaped part. Therefore, multistage forging may be advantageous to produce this part. The key point of outer race is performing the geometry of ball grooves with negative slope angle. Traditional methods form the ball groove by machining that takes long time and waste many portions of the material. Thus near net shape forging is an attractive option for producing of outer race. In this study, the process sequence in the multistage forging of a CV joint outer race has been investigated by using the rigid plastic finite volume method and forging process sequence is designed which can produce a near net-shape housing without defects within a given press capacity. Finally physical modelling with commercial lead is used to verify the reliability of numerical simulation results.

Abstract: The outer race of a constant velocity (CV) joint is an important automotive component that is difficult to be forged because its shape is very complicated and the required precision is high. Since traditional cold forging methods are not always capable of producing complexly shaped parts, such parts are often made by processes, which require intense machining operations at relatively high costs. Thus near net shape forging is an attractive option for producing of outer race. Actual problems in final ironing sequence are prevention of ductile fracture and surface defects in final product and true formation of internal ball grooves of the workpiece. In this study Cockroft&Latham failure criterion was applied to final ironing sequence. Finally physical modeling is down using lead. In order to investigate the flow of the billet material during forging, the experimentally obtained section profile of internal grooves as measured by a CMM is compared with simulation based profile.

Abstract: Superalloy IN718 large tube is used in critical jet engine applications, while manufacturing such components, the control of temperature during tube hot extrusion is of paramount importance. To determine the relation between technological factors and the temperature rise, extrusion force during tube hot extrusion of superalloy IN718, a numerical model was developed to for the large tube hot extrusion through die and over mandrel. The constitutive behaviour of the material and friction at the extrusion temperatures are established as a thermoplastic process. In order to investigate the influence of technological parameters of extrusion process on the temperatures rise and extrusion force, then the extrusion variables such as friction factor, ram speed, tool and billet preheating temperature are taking into consideration. Besides tool preheating temperature, other parameters have a great influence on temperature rise of billet during the extrusion process. All of technological parameter of study in this paper have a significant influence on the extrusion force. Moreover, based on the simulation results, the case with tool preheating temperature of 300°C should avoid during the technology making.

Abstract: Temperature effect due to varying die opening shapes in the direct extrusion of lead have been numerically simulated and presented. Using upper bound method of analysis the internal heat generation due to plastic deformation and frictional heat at various stages of the extrusion process for different die opening geometry are simulated. A C++ program simulates the deformation and frictional power at die land region which is converted to temperature change using finite difference program. At the extrusion die land region, temperature rises with increasing complexity of die openings geometry with I-shaped section, giving the highest temperature rise, followed by T-shaped section, rectangular, circular shaped die openings with square section die opening, giving the least temperature rise for any given extrusion parameter. The die land zone shows increasing temperature rise with increasing friction coefficient, while increasing friction coefficient has no overall effect on the dead metal zone temperature rise. The proper choice of die land is, therefore, imperative if excessive generation of heat at the emergent section is to be avoided to maintain good quality and metallurgical structure of the product.

Abstract: The unstable shell growth pattern in the early solidification stages results mainly from the unevenness of the heat flux drawn from the mold surface. This heat flux is determined either by the size of the air-gaps formed between the solidifying shell and mold surface or from the value of the contact pressure. Present work examines the role of the mold surface topography on gap nucleation and the contact pressure variation in pure metal solidification. The results of the present study can be used to tune mold surfaces for the control of cast surface morphologies.

Abstract: Finite element modeling of Charpy impact test was performed for a normalized carbon steel specimen based on plane strain geometry and bilinear isotropic hardening plasticity. As the suggested approach takes into account all aspects of nonlinearity such as geometric, material and contact nonlinearities, it may describe the conventional destructive impact test accurately with much less effort and cost. A failure criterion is assumed to be at 10 % of plastic strain based on the tensile experiment data. Impact energy was estimated at different testing temperatures. It was found that impact energy required for fracture of the selected steel specimen at room temperature (i.e. 25 °C) is to be 65.9 Joul. According to simulation results, it is found that the ductile to brittle transition temperature (DBTT) equals 0 °C. In order to validate the numerical model, a comparison study was established by comparing the numerical results with the corresponding experimental tests at the same conditions, which shows good match with maximum deviation of 5 % for all computer runs.

Abstract: This paper presents the results of experimental investigations conducted on a vertical machining centre (VMC) using spindle speed, feed rate, and depth of cut as machining variables to ascertain the effectiveness of TiAlN insert in end milling of hardened steel AISI H13, under work-piece preheated conditions and hence a statistical model was developed using the capabilities of Response Surface Methodology (RSM) to predict the tool life. Sufficient number of experiments was conducted based on the small central composite design (CCD) concept of RSM to generate tool life data for the selected machining variables. The adequacy of the model was tested at 95% confidence interval. Meanwhile, a time trend was observed in residual values between model predictions and experimental data, reflecting little deviations in tool life prediction. A very good performance of the RSM model, in terms of agreement with experimental data, was achieved. The model can be used for the analysis and prediction of the complex relationship between cutting conditions and the tool life in flat end milling of hardened materials.

Abstract: This paper presents a inverse method to derive the material properties from the resonance frequencies of a free-edge test specimen based on modal vibration test. A mixed numerical experimental identification procedure is used for this purpose. Finite element models of the test plate is simultaneously updating and reproduces the updating frequencies, then optimal procedure is running. The sum of the squared differences between the experimental and the finite element method numerical resonance frquencies is the objective function. To seek practical solutions, here presents a global optimization method--simulated annealing method for the determination of the elastic properties. The inverse method is applied to determine the elastic constants of aluminum , carbon/epoxy , Glass/PP composite material and double coated steel plate. The results indicate that the method can obtain very accurate elastic constants for aluminum , Glass/PP , carbon/epoxy composite material ,but for double coated steel plate , if the individual layer of the three different layers is as isotroptic material having six elastic constants , the method can obtain very accurate results , but if it is as transversely isotropic material having twelve elastic constants, the evaluating elastic constants are bad.

Abstract: Generally, impact and shock to portable electronic products can cause significant functional and physical damage in the form of internal component failure or package-to-board interconnection breakage. Therefore, this paper provides a dynamic simulation of shock impact to investigate the internal stress and strains of a printed circuit board (PCB) with ball grid array (BGA) chipset. The tin balls will be simulated with a minimum element size as 0.0536 mm in LS-DYNA finite element software. The corresponding strains of dynamic analysis on PCB board will be compared with those of the experimental measurements using the strain gauge. Finally, the model established has values of peak strain and impact duration close to those measured in the actual shock test. The comparison results of the experimental and numerical strain show that the smallest difference is 0.70%. Furthermore, we also investigate the signal curves of experimental error source on the accelerometer and strain gauge. The measurement results show that the capabilities of the repetition and stability both the input signals and output signals are excellent. This result provides researchers in relevant fields with an excellent example and model for further study of PCB with BGA chipsets.

Abstract: Recent trends of welding system have been focused on the development of new process in order to achieve better quality, higher productivity and friendly to the environmentally in welding process. The Magnetic Pulse Welding(MPW) process is based on the principle of a tremendous amount of energy compressed and discharged for an extremely short period of time. The purpose of this paper is to investigate welding characteristics according to the distributions of an electromagnetic force on the weldment using a finite element method and to find the optimal process parameters such as input current and frequency. To successfully accomplish this objective, a 2-dimensional axisymmetric electromagnetic numerical model has firstly been developed. The equation was solved using a general electromagnetic mechanics computer program, ANSYS code. The comparison between the calculated and measured results has been carried out to verify the developed system.