مجله مهندسی ساخت و تولید ایران
سال هشتم شماره 1 (فروردین 1400)

In order to evaluate the possibility of the similar and dissimilar welding of 5019 and 7039 aluminum alloys, plates of 3 mm thick from this alloy were welded via Self-Reacting Friction Stir Welding (SRFSW) method. Floating bobbin tool was designed and manufactured from heat –treatable hot working steel to perform the welding process. The effect of various process variables such as the shoulders pinching gap, the tool transverse speed and the tool rotational speed were investigated to establish a defect-free joint. Following the visual inspection and X-ray radiography, it was found that a defect-free joint is obtained at the transverse speed of 22 mm/min and rotational speed of 1120 rpm. The results of tensile test, also, revealed that the joint efficiency of 5019-5019, 7039-7039 and 7039-5019 joints are 72, 76 and 91.5%, respectively. Accordingly, these amounts were more than the joint efficiency of the fusion welding, and comparable with/more than the joint efficiency of Conventional Friction Stir Welding (CFSW). Microscopic evaluation of the fracture surface of welded pieces indicated that the dominant fracture mechanism for similar joints is the soft fracture, while the one for non-similar fracture is the brittle fracture. Assessment of the cross-sectional hardness of the welded pieces near the upper and lower shoulders showed that the degree of hardness near the lower shoulder of the tool is always higher, which can be attributed to the lower temperature of the work piece in this area.

In this study, surface transformation hardening of AISI O1 cold work tool steel was investigated by use of a high power (1600 W) diode laser apparatus. In order to evaluate the effect of laser hardening, different output powers and scanning rates were applied and microstructures and phases were characterized, as well as micro-hardness and wear resistance were measured. The hardening treatment resulted in formation of a hardened zone of about 2 mm depth and up to 10 mm width at the surface of sample. The microstructure of this hardened zone was comprised of martensite and residual austenite; average surface hardness of the samples treated under various set of variable parameters was 650 to 760 Vickers. Increase of heat input caused increase of residual austenite content and formation of coarse martensite structure so that the least hardness was obtained for the sample processed by the highest heat input. Comparing wear resistance of laser hardened samples with traditionally quench-temper hardened and annealed specimens, it was revealed that the laser hardening process improves wear resistance of hardened samples so that wear resistance of the samples hardened via laser was about 10 times of the annealed ones.

Due to the needs of different industries to produce high precision dimensional products and desirable surface properties and the highest effect of final surface quality on product performance, selection of effective and suitable polishing processes for production of quality products is important. Among different methods of polishing, the burnishing process due to low cost, the possibility of installation on different machines and the polishing without chip has been consideration. Therefore, in this study, due to the widespread application of ductile cast iron in various industries, after preparing the samples of ductile cast iron, making the roller burnishing tools and mounting it on the lathe machine, experiments were carried out in accordance to experimental design table and the effect of burnishing force, feed rate and number of passes, on microhardness and surface roughness of samples were evaluated. For statistical analysis, the results of minitab software and response surface methodology (RSM) were used and the statistical analysis performed with the confidence level of 95%, the most effective parameters and their desirable values to increase the microhardness and quality of samples were introduced. The results showed that the effect of the burnishing force, had the greatest impact on the microhardness and roughness of samples and the optimization of samples by (RSM), optimum value for surface roughness and microhardness of specimens, respectively, 0.562 μm and 203.20 Vickers were obtained in comparison with the values for the initial sample, the surface roughness of samples about 58% reduction and microhardness of samples were increased about 12%.

Autonomous submarine robots are significant over the last decades. Since they can replace humans for performing dangerous underwater works. Positioning navigation is the key to guaranteeing that underwater robots can complete their task. The purpose of this paper is to control the linear and angular velocity of fish robot, to convert the robot model to unicycle model for mobile robots, which is make it possible to implement the navigation algorithm on robot. The appropriate dynamic model was simplified as a two dimensions model of robotic fish. Among different types of actuations, the tail-actuated robotic fish or BCF was considered. Also the average model of robotic fish was considered to control and its coefficient was corrected. The parameters of tail-actuating are defined as bias, amplitude and frequency. The frequency of tail-actuating was assumed to be constant but, bias, and amplitude are variable and controllable. After simulation the relations between tail-actuating parameters and rigid body linear and angular velocities was investigated. With this significance linear forward velocity and angular velocity could be controlled simultaneously and independently. This motion control applied on smooth rotation behavior with the constant speed, but it could be generalized for the others robot’s behavior. Eventually, through the amplitude, and the bias control respectively, the linear forward velocity is controlled with PI controller and 1.67% error and angular velocity is controlled with PID controller and 2.5% error.

In this study, the advantages of porous implants compared to conventional implants in order to apply a specific type of porosity to the implant most were investigated. The use of Triply Periodic Minimal Surface (TPMS) in porous implant design due to its curvature has a high potential in designing variable structures both morphologically and in relative density with respect to its implicit structural equations. The equations of Triply periodic minimal surface are solved using the Grasshopper plugin, and finally the surface of a unit cell is obtained to design porous structure. One common dental implant and two porous dental implants with 54% and 65% porosity are modeled on Straumann's catalog according to ITI standard. In static and dynamic loading, forces were inserted into the implant in three different directions according to biomechanical principles. The results showed that after implantation of dental implants, the maximum amount of stress increased in the porous implants compared to the conventional implants so that it increased from 31.82 to 98.93 MPa in the fifth second. And in porous implants, stress distribution in the cancellous bone is increased compared to the conventional implant. Stress Shielding can be counteracted by porosity of dental implants. In this phenomenon, the implant, due to its much greater strength than the bone, prevents the transfer of stress to the bone, which results in weakening of the bone around the implant. By applying porosity and applying the TPMS to the implant. Stress distribution increase in the cancellous bone.

Proper positioning of the blank in the sheet metal forming dies is very important. An error in the initial positioning can lead to the production of a defective part. The number and location of positioning gauges are very effective in positioning the part correctly. In the manual and traditional design of dies for forming large sheet metal parts, two positioners are usually used to position the sheet at each edge, therefore eight gauges are used in the four directions of the sheet, some of which do not seem to be necessary. In the present study, by establishing a relationship between Catia and Abaqus softwares and with the help of optimization methods, an integrated software system has been created that is able to automatically perform finite element analyzes and make changes in the input file according to the output of each analysis and perform the next analysis. At each stage, for a specific arrangement of gauges, the amount of deviation of the sheet during placement and forming is examined, which should not be more than the allowable limit. Applying changes to the input parameters according to the optimization algorithm and performing subsequent analyzes will continue until the problem converges to the best answer that suggests the arrangement of the positioning levels. To compare the results of this system with the traditional design, two examples are presented. The results show that with a smaller number of gauges than the traditional method, the blank can be positioned correctly and accurately in the die.