Advanced Materials Research Vols. 264-265

Abstract: Interest in processing of bulk ultrafine-grained materials has grown significantly over the last years. Severe plastic deformation processes such as twist extrusion have been the essence of these researches and used to decrease the bulk grain size. The bulk gain size can reduce if twist extrusion process combines with a conventional forming technique. In this study, the effects of reduction by employing the rolling process after the twist extrusion method were considered. The twist extrusion process of the commercially pure aluminum sample was carried out using a twisted die with 60º die angle, and the samples were processed through rolling subsequently. As a result of rolling, average microstructure grain size decreased significantly and the hardness amount increased accordingly

Abstract: The present work focuses the attention on the Single Point Incremental Forming (SPIF) of the Titanium (Ti) alloy Ti-6Al-4V. Tensile tests were carried out using the optical strain measurement system Aramis3D, in order to determine the mechanical behaviour of the alloy and to investigate the anisotropy of such alloy. Finite Element (FE) simulations of the SPIF process (using ABAQUS/explicit) were performed using a simple but non-axialsymmetric shape (truncated pyramid) with the aim of investigating the effect of both the tool/pitch ratio (D/p) and the draw angle (α), taking into account the anisotropic behaviour. The analysis of plastic strains and thinning maps, together with the evaluation of shape errors originated by the forming process, highlighted that the parameter D/p plays a key role in the SPIF. Results from the preliminary FE analysis were used for investigating the production by SPIF of an automotive component (car door shell). A specific subroutine was created by the authors for automatically generating the tool path to be used in both the FE simulations and the manufacturing of parts by SPIF on a CNC milling machine.

Abstract: To lighten total product weights, the local increases in sheet thickness of products effectively contribute to decreasing product weights, when appropriate sheet thickness distribution in product by a designer could be performed by using an accurate prediction method by simulation. The designer only could distribute thick part where needed a large moment inertia of area from the view points of the strength of the section. In the sense of the such optical designing for the variable thickness distribution in the products, we do not need to consider that sheet thickness should be constant in a product. This paper is concerned with a forming prediction during deep drawing process. To clarify the mechanism of increase of sheet thickness, a 3-D forming simulation during deep drawing by finite element method was performed. Effects of tool shapes (contacting angles to the original materials, contacting length of punch with a material) which mainly affects the results on thickness change of original materials were investigated. The thickness distribution of drawn cups was measured in order to compare simulation results obtained by the finite element method. It has been found that controlling sheet thickness distribution was possible if an original material was relatively thick, when in choosing an appropriate manufacturing condition could be selected.

Abstract: Growing demand for lightweight products has been increased by the rapid development of automobiles since the global environment conservation meeting at Kyoto. Lighter products have been necessary when considering in taking action to reduce fuel consumption. One of the key is the utilization of high strength and light materials, such as stainless, high-tensile strength steels and magnesium alloys, which are difficult to be formed due to their high strength compared to normal steel pipes. This paper is concerned with the development of pressing technology that copes with forming relatively high strength stainless pipe with screw threads on the surface of pipes. Our new press-forming process in order to obtain accurate screw threads on the stainless pipe was tested. A 3-D digitizer was used for the measurement of the accuracy of manufactured pipes by the proposed pressing method. It is found that the proposed our press-forming was effective to improve decrease of pipe thickness compared to conventional roll forming technology. The maximum decrease in material thickness was 20% using our press-forming process for screw threads in the formed pipe.

Abstract: Procedure of die design is mostly based on iterative try and error to obtain final design with good stamping formability. The stamping formability of sheet metal part is possible to be improved by adding addendum features at die model. In this paper discusses the effect of drawbars toward the formability of stamping process of aluminum AL6063. Effect of addendum size is evaluated Finite Element Simulation to prevent wrinkling and tearing. Simulation model is constructed by designing a simple die, punch and binder using variety drawbar diameters. The model further evaluated using LS-Dyna software interfaced by forming tool of LS-Prepost. Formability of the model is evaluated through yield stress, major strain and minor strain data. From the result of evaluation obtained that without draw beat, major/minor strain is above FLD while the formability is improved by applying 5 mm draw bead diameter.

Abstract: The changes of microstructure in eutectic sn-3.8ag-0.7cu during moderate current stressing have been investigated. The current stressing values were 102 and 103 a/cm2. The tests were carried out for 24, 216, 576 and 1008 hours. Sn-rich phases and eutectic phases appear immediately after soldering process. However, thermal rise during current stressing has coarsened sn-rich phases and altered the microstructure of the solder. Higher current density leads to larger snrich phase coarsening. The microstructures for current stressing test were also compared with the series of microstructure for isothermal annealing test since there is similarity in coarsening effect for both tests. The effect of thermal rising during current stressing as well as during isothermal annealing to sn-rich phase coarsening is established and will be discussed further.

Abstract: The temperature distribution of 6061-T6 aluminum alloy plates under a friction stir butt-welding was investigated by using experiment and numerical simulation. A real-time temperature measuring system was used to measure the temperature change in the welding process. Vickers hardness profiles were made on the cross-section of the weld after welding. A commercial software of FlexPDE, a solver for partial different equations with finite element method, was used to simulate the experimental welding process of this study. Comparison the experimental and numerical results, the temperature cycles calculated by numerical are similar to those measured by experiment. The temperature distribution profile obtained from the numerical simulation is symmetrical to the weld center and has a close correspondence with the hardness configuration and the microstructure of the weld. The region with the temperature over 300 °C is the zone of softening within the boundaries of base material and HAZ. The regions of 350 °C with minimum hardness are located near the boundary of HAZ and TMAZ. The maxima temperature about 500 °C distributes around the upper part of the weld center. However, the region above 400 °C only matches with the upper half of the weld nugget.

Abstract: Explosive welding process is one of the effective methods in order to weld two dissimilar materials. Aluminum-steel composite was undergone heat treatments at temperatures between 2000C-5000C. In this study, the effects of explosive ratio and stand-off distance on the shape of the interface were studied. Moreover, the effects of various heat treatments on the interface strength are studied. The study shows that the type of the explosive, the magnitude of explosive ratio and standoff distance produces various interfaces with or without intermetallic compounds. The results show that effects of heat treatment on the aluminum-steel bond strength is depended upon the type and microstructure of straight, wavy and continuous melt produced at the interface. Moreover, the study shows that heat treatment gives rise to produce the brittle intermetallic compound of FeAl3 which lowers the weld strength. Having produced the smooth interface would reduce the heat treatment effects on lowering the weld strength.

Abstract: In this paper effect of joint groove geometry on the residual stresses in circumferentially butt-welded still pipes is investigated by the finite element simulation. The elements birth and death technique is used for modeling of filling metal and joint groove geometry. The electrode heat power is modeled by a moving heat source which has a Gaussian distribution on a spherical domain. By using a transient region, elements near the welding zone are refined in a good manner. For validation of the proposed model, results obtained from model are compared with experimental data. Then three different joint geometry; V-joint, U-joint and X-joint are studied by the presented model.