Advanced Materials Research Vols. 264-265

Abstract: In the present study, the effect of cooling condition on hot tearing tendency and hot tearing fracture surface morphology were investigated. Results show that, the hot tear fracture surface characteristics are nearly similar under different cooling conditions. The hot tear surface exhibits two main features; the brittle region and the ductile region. The results also indicate that cooling condition has multifaceted effects on hot tearing phenomenon. Increasing cooling rate increases the thermal gradient, which raises the hot tearing tendency; concomitantly it decreases the grain size and dendrite arm spacing which increases the strength of the material. The occurrence of hot tearing phenomenon under different cooling conditions is discussed and evaluated based on the competition between these opposing factors during the solidification process.

Abstract: In laser welding, the heat input per unit length is determined by the welding speed and the laser output power. Along with these parameters, there are several other important parameters such as the shielding gas composition, shielding gas flow rate, beam angle, defocusing distance, and so forth. In this paper, the effect of each process parameter on the welding quality was investigated to establish a laser lap welding process for Al sheets. Al 5J32 and Al 6K32 sheets were used as the base metal, and a 4kW disk laser was used as a high brightness laser power source. The bead appearance, the cross-sectional bead shape, X-ray images, and the weight of spatters were examined to evaluate the welding quality.

Abstract: Recently, not only robotic welders have replaced human welders in many welding applications, but also reasonable seam tracking systems are commercially available. However, fully adequate process control systems have not been developed due to a lack of reliable sensors and mathematical models that correlate welding parameters to the bead geometry for the automated welding process. Especially, real-time quality control in automated welding process is an important factor contributing to higher productivity, lower costs and greater reliability of the bead geometry. In this paper, on-line empirical models with experimental results are proposed in order to be applicable for the prediction of bead geometry. For development of the proposed predicting model, an attempt has been made to apply for a several methods. For the more accurate prediction, the prediction variables are first used to the surface temperatures measured using infrared thermometers with the welding parameters (welding current, arc voltage, CTWD and gas flow rate) because the surface temperature are strongly related to the formation of the bead geometry. And the developed model has been carried out a learning each time data acquired.

Abstract: Industries such as gas, oil, petrochemical, chemical, and electric power have generally employed for the operation and used to enlarge the equipment or structures that require a high capital investment. In order to meet these requirements, the industries are increasingly moved toward saving the experimental verifications and computer simulation. Therefore industries to reduce the maintenance costs without compromising operational safety have been forced on finding better and more efficient methods to inspect their equipment and structures. It was motivated to meet the industrial needs and to secure and maintain the institute's technical initiative and leadership in the development of this new and exciting technology. Also, the system with many sensors could be detected the weld defects, and was useful for real-time monitoring. This paper is focused on the development of the real-time non-contract monitoring system as an efficient tool for the experimental study of weld defects based on the relationship between the measured voltage and input parameters. The monitoring technology involves the use of Ms S (Magnetostrictive Sensors) for the generation and detection of the guided waves. The developed system was employed to the experimental study in order to fine the weld defects for steel object with artificial defects used in the welding field.

Abstract: This study investigated on the cooling characteristics of AC4C aluminum alloy and AC7A aluminum alloy used as a casting material for manufacturing automobile tire mold by experiment. The metal mold device by gravity casting method was manufactured. AC4C casting material and AC7A casting material were heated in smelting furnace at about 650°C and 670°C, and then they injected into the metal mold device when the melting process was completely finished, respectively. When the melted casting material was completely injected into the metal mold device, the temperature inside the casting was measured by 9 measurement points. Also, when the temperature inside the casting was measured approximately 500°C during the cooling process, the casting is separated to metal mold device and carried out cooling at normal temperature. The separating time from metal mold device of AC4C casting material and AC7A casting material have been taken 25 minutes and 15 minutes, respectively. The final cooling time of AC4C casting material and AC7A casting material have been taken 400 minutes and 380 minutes, respectively. Accordingly, AC7A casting material is able to improve on productivity than AC4C casting material because production time was decreasing.

Abstract: Resistance spot welding was used to join low carbon steel and A5250 Aluminum alloy sheets. Mechanical properties and failure behavior of the spot welds in terms of peak load, failure energy and failure mode, were evaluated using tensile- shear test. Relationship between welding current and mechanical properties was investigated. It was found that the formation of brittle intermetallic compounds in the weld fusion zone is the key governing factor for mechanical properties of dissimilar Al alloy/low carbon steel resistance spot weld. Increasing welding current, increases both peak load and energy absorption due to increasing overall bond area and transition in failure mode from interfacial to pullout failure mode.

Abstract: Studies on the weldability of ferritic stainless steel grades suggests that low heat input rate and better heat transfer dynamics are appropriate for the control of grain size and microstructural feature in thin sections. However, the optimal welding conditions to achieve combination of such characteristics are yet to be established. In the present investigation, AISI 430 ferritic stainless steel is TIG welded using energy input between 0.205 and 2.05kj/mm and characterized in terms of microstructure and hardness. The microstructural characterization of the welds with varying heat input rates suggests the presence of interdendritic martensite in the fusion zone and grain boundary martensite in the HAZ in conjunction with some intermetallics in varying proportion. The hardness values across the welds indicate that grain growth and the presence of intermetallics are minimized when welded with increased heat input rates that permits transformation within the dual phase regions. The study provided a new insight into the contribution of heat input rate in the production of unwanted weld microstructural features and assisted in the design of methods and techniques for tailoring weld microstructures with optimum properties.

Abstract: The purpose of the present experimental investigations is to study the effect of work piece dimensions on reducing the shell wall thickness of mould cavity for cost effective, hybrid rapid casting solution of aluminum alloy. Starting from the identification of component/benchmark, technological prototypes with three different work piece dimensions (volume/ weight) were produced, at different shell wall thickness of mould cavity using hybrid rapid prototyping technique (combination of three dimensional printing and conventional sand casting). Measurements on the coordinate measuring machine helped in calculating the dimensional tolerances of the castings produced. Some important mechanical properties were also compared to verify the suitability of the castings. The study suggested that the shell wall thickness, having value less than the recommended one is more suitable from dimensional accuracy and economic point of view, for all three work piece dimensions (volume/ weight). Further best shell wall thickness of the mould cavity for different work piece dimensions of the selected benchmark has been highlighted for rapid casting solution of aluminum alloy.

Abstract: Compressor is a part of turbocharger approaches that utilize the exhaust gas of an automobile to drive the compression device. The purpose of turbocharging is to increase the intake pressure and the amount of air into the combustion chamber to improve the efficiency of the engine. Compressor impeller determines the service life of the turbocharger. This paper proposes the new methodology of producing the compressor impeller using Metal Matrix Composite (MMC) material by investment casting. In general, this study presents the tasks pertaining to metal matrix composites and their interactions in designing of compressor impeller. This study presents the use of genetic algorithm (GA) and computer programs for designing a new compressor and determined the wax pattern dimensions based on three-dimensional finite-element simulations as a preliminary study by using investment casting method. The model of thermal and mechanical analysis was developed by ANSYS. As the results, the simulation model was generated and it could be used for improving the design of turbine-compressor assembly through the bottom geometry changes of the compressor.

Abstract: In this investigation, the effect of heat treatment parameters on the microstructure and impact energy as a measure of toughness of the austempered ductile cast iron (ADI) was studied. Yblocks were casted from ductile cast iron with following composition: 3.2% C, 2.5% Si, 1.09% Ni, 0.87% Cu, 0.5% Mo and 0.16%Mn. Charpy specimens (un-notched) were machined from the straight part of Y-blocks. All of specimens were heat treated with different conditions. Some of them were austenitized at 900°C for 60 min and then austempered at 250, 300, 350 and 400°C for various durations. Then, hardness test, impact test, optical microscopy and X-ray diffraction (XRD) were performed on the heat treated ductile iron samples. The results reveal the highest impact energy (105 J) for the sample austenitized at 900°C and austempered at 350°C for 150 min. The microstructure of this sample consisted of 28% austenite and broad ferrite needles.