Nowadays, dieless and flexible sheet forming methods are gaining much interest in prototyping and low production. In this research, a new method is developed to change the cross-sectional area of metal tubes in a longitudinal direction without using special dies. This technique is based on the force applied by a rotary tool to the inside/outside surface wall of a tube. The forming tool is mounted on a CNC milling machine and moves spirally with a specific pitch. In order to study the effects of process parameters on the product quality, a full factorial design of experiments was designed and performed. The input parameters were the feeding depth, forming pitch and tool velocity. Three responses including roughness, minimum thickness and production time were precisely measured for this purpose. The results showed that surface quality and minimum thickness is reduced with increasing the forming pitch and feeding depth. Tool rotational velocity does not have a significant effect on the forming parameters except for production time. Using a multi-objective response optimization, forming pitch of 0.25 mm, feeding depth of 1.25 mm and velocity of 800 mm/min were found to be the best configuration. تفاصيل المقالة

Two main problems exist with friction stir spot welded joints; remaining of a keyhole after welding and low strength of joints. In this paper, a novel method is proposed to address both problems in a simple and cost-effective way. This process is named “Reinforced Friction Stir Spot Welding” or “RFSSW” which is based on recently introduced “TFSSW” process. SiC powder was added to the friction stir spot joints of polyethylene sheets with a thickness of 3 mm. First, the sheets were welded using conventional friction stir spot welding tool with a cylindrical pin. Then, the keyhole was filled with SiC powder. In the second stage, for stirring of SiC particles in the nugget and refilling the keyhole as well, a pinless tool was utilized. A homogenized distribution of reinforcing powder was obtained in the nugget. The effect of welding parameters including refilling tool shoulder diameter, refilling dwell time, and refilling tool rotational speed were evaluated in both TFSSW and RFSSW. In both processes, the refilling tool shoulder diameter was the most effective parameter. The strength was increased by 40% applying TFSSW and a further increase by 20% was obtained by reinforcing. Optimized parameter levels are refilling tool shoulder diameter of 24 mm, refilling tool rotational speed of 800 rpm, and refilling dwell time of 50s which result in shear strength of 1079 N. تفاصيل المقالة

In the present study, a 3D finite element model was developed using DEFORM commercial software to analyse the material flow and phase transformation, as two key phenomena affecting the joint properties in friction hydro-pillar processing of 1045 steel alloy. The microstructure changes significantly due to the high temperature and strain rate. The final microstructure was intergranular pearlite and grain boundary allotriomorphic ferrite. Pearlite was the dominant phase at the final microstructure; thus, its volume fraction was used to validate the model where a good agreement was obtained with the experiment. According to the model, the pearlite volume fraction varies from 100% to 70% moving from the bottom of the stud to the top. The model suggests an inverse relation between the strain rate and pearlite volume fraction. The highest temperature which was experienced in the welding step was 1490 ºC while it dropped to 890 ºC in the forging step. Downward and then radial material flow was detected in the welding step while upward extrusion of material was the dominant material flow pattern during the forging step. Flash was formed mainly in the forging step from stud side material. تفاصيل المقالة

In this paper, a new production method of aluminium/steel double-layered wire is proposed using a modified friction stir extrusion process. The core and coating were made of St37 steel and aluminium alloy, respectively. For extruded specimens, the effects of the main process parameters including tool rotational speed and feed rate were investigated on adhesion strength and surface cracks. The tool rotational speed was studied at two levels of 300 and 600 rpm, and the feed rate at two levels of 4 and 12 mm/min. Pull-out test was carried out using a tensile test machine to evaluate the adhesion strength. Surface cracks were evaluated by the liquid penetrant test. The results suggest that the modified friction stir extrusion process can be used successfully to produce dissimilar double-layered wires. With the right combination of tool rotational speed and feed rate levels, a dissimilar double-layered wire can be produced with a high adhesion strength and good surface quality. No cracks were observed in specimens produced with the feed rate of 12 mm/min and rotational speed of 600 rpm. The maximum adhesion strength was 2867.13 N that was achieved with a tool rotational speed of 300 rpm and feed rate of 12 mm/min. تفاصيل المقالة