Advanced Materials Research Vols. 418-420

Abstract: Seam tracking is significant to obtain good welding quality. Aiming at establishing a model to detect and calculate the seam tracking offset during high-power fiber laser welding of Type 304 austenitic stainless steel plate butt joint welding, an infrared sensitive high-speed camera arranged off-axis orientation of laser beam was applied to capture the dynamic thermal images of molten pool. Six parameters such as the keyhole configuration parameters (include four parameters), keyhole centroid parameter and heat accumulation parameter were defined as the eigenvalues of seam tracking offset to determine the seam tracking offset between the laser beam and the desired welding trajectory. A BP neural network model was built to reflect the correlations between the defined eigenvalues and the seam tracking offset. The welding experiments confirmed that the seam tracking offset between the laser beam focus and the welding seam could be monitored and calculated by the BP neural network model effectively.

Abstract: The researches of non-oriented silicon steel are mainly focused on the effect of main processing parameters on the microstructure and magnetic properties, but there have been few studied about its flow stress until now. In this paper, the non-oriented silicon steel 50A1300 of hot forming is studied by thermal-mechanical simulation method. The hot deformation behavior of the steel is explored and the flow stress model of the steel is established based on the creep mechanism. The model has good accuracy and is feasible.

Abstract: To solve the best-fit sphere (BFS) accurately is one of the technological keys for the generating and testing of optical aspherical surfaces. This paper presents a new algorithm for solving the BFS of aspherical surfaces to suppress some deficiencies in the existing BFS algorithms. In the proposed approach, a BFS is constructed, which passes through both sides of endpoints in the section of the aspherical surfaces, the center of the BFS is shifted along the x-axis, and its radius of curvature is automatically computed. The variable step size method is proposed to speed up the convergence of the iteration. Through numerically solving the BFS of conic and cubic surface, the advantages of the proposed approach are verified. The results show that the proposed approach is of rapid convergence, and high accuracy; it is not only suitable for the conic surface, but also for higher order aspheres. The obtained asphericity and material removal function is more suitable for the machining and test.

Abstract: Abstract: Ti-6Al-4V are used extensively in aerospace, medical, marine and surgical implants etc. but it is hard to machine. Machining of advanced difficult-to-machine very hard materials (Ti-6Al-4V, composites and ceramics) is a big challenge. By conventional machining processes, their machining is not only costly but results in poor surface finish and shorter tool life. To meet these challenges, new hybrid machining process (HMP) has been developed. This article is focused on hybrid machining process comprising of conventional surface grinding along with electro-discharge machining between the periphery of metal bonded diamond grinding wheel and flat rectangular shape workpiece. This process has the advantage of shaping advance engineering materials and difficult-to- machine very hard materials. The experimental investigations of various input parameters like wheel RPM, duty factor, current and pulse on-time on material removal rate of Ti-6Al-4V in EDDSG process have been reported here on newly self designed & fabricated set up. Keywords: Electro-Discharge Diamond Surface Grinding (EDDSG), Hybrid Machining Process (HMP), Ti-6Al-4V.

Abstract: The current work presents the development of cost model for tooling during high speed hard turning of AISI 4340 hardened steel using regression analysis. A set of experimental data using ceramic cutting tools, composed approximately of Al₂O₃ (70%) and TiC (30%) on AISI 4340 heat treated to a hardness of 60 HRC was obtained in the following design boundary: cutting speeds (175-325 m/min), feed rate (0.075-0.125 m/rev), negative rake angle (0 to -12) and depth of cut of (0.1-0.15) mm. The output data is used to develop a new model in predicting the tooling cost using in terms of cutting speed, feed rate, depth of cut and rake angle. Box Behnken Design was used in developing the model. Predictive regression model was found to be capable of good predictions the tooling cost within the boundary design.

Abstract: Residual stresses resulted from localized non-uniform heating and subsequent cooling during welding processes enact an important role in the formation of cracks and welding distortions and have severe effect on performance of welded joints. The present research performs a three dimensional transient thermo Elasto-plastic analysis using finite element technique to simulate welding process. Welding simulation procedure is developed using the parametric design language of commercial code ANSYS for single pass T and butt welded joints. The procedure verified with predicted residual stress field found in literature to confirm the accuracy of the method. The material of the weld metal, HAZ and the base metal are assumed to be the same. With regards to high temperature gradient in weld zone, temperature dependant thermal and mechanical properties have been incorporated in the simulation. Also in this work the technique of element birth and death was employed to simulate moving heat source and the weld filler variation with time. Temperature and residual stress fields were discussed.

Abstract: The effects of brazing temperature on microstructure and mechanical properties of vacuum brazed joints of 316L stainless steel were studied. Choose three soldering temperature. After soldering, observed the microstructure, element distribution, microhardness and shear strength of welding clearance. The results show that the welding temperature for 940 °C, the brazing clearance organization mainly by Ni-Cr-P phase composition. Joint performance is poor, element can't get enough spread. P element does not spread easily, mainly in the brazing clearance; Cr element can spread along the grain boundary into mother material; the ability of spread of Ni elements is less than the Cr element. While welding temperature of 970 °C, the shear strength is the highest, and the comprehensive performance is the best.

Abstract: The Ti/TiC/C laminated composite material was fabricated with the sheet of Ti and C by spark plasma sintering (SPS) technology. The effects of thickness ratio on the interface characteristics and mechanical properties of interfacial reaction were studied. The results show that: the reaction layer thickness increases with the thickness ratio. When the thickness ratio was 3:1, the degree of interfacial reaction was better in the case of other conditions are the same. The thickness of reaction layer achieved 33.58μm. The laminated composite bending strength and fracture power reached the maximum 3494.52MPa and 614.89×103J/m2, respectively. The greater fracture power, the more energy absorbed in the process of damage, the higher toughness improved.

Abstract: Custom-built Miniature Machine Tools (MMTs) are now becoming more popular with the demand for reduced energy consumption and workshop floor when machining small/medium batch size micro-components. This paper investigates the capability of a custom-built 4-axis MMT through machining a micro-component demonstrator. The experiments have been carried out in Titanium Alloyed (TiAL6V4) using 0.6mm solid carbide flat end mill cutters. From here, the surface quality and geometrical accuracy of the machined testpiece are evaluated and analysed. The investigation has shown that acceptable geometrical accuracies and surface quality of the machined micro-demonstrator can be achieved using the in-house developed MMT. These results show that the use of the custom-made MMT does not hinder the micro-milling process to produce a good and satisfactory surface quality and acceptable geometrical accuracy.

Abstract: Well-aligned crystalline ZnO nanorod arrays were synthesized on the glass substrate via an aqueous solution route, and the effect of the pH value on structural properties and morphology of ZnO nanorod arrays was investigated using XRD and FESEM. FESEM micrographs show the formation of ZnO nanorod arrays at different pH values. XRD patterns confirm that the ZnO nanorods were wurtzite structure preferentially oriented in c-axis direction and the highest quality of nanorod array was formed at high pH value.