مجله مهندسی ساخت و تولید ایران
سال ششم شماره 4 (مهر 1398)

The purpose of this study is to investigate the effect of using bobbin tool on the mechanical properties of aluminum alloy 6061-T6 in friction stir welding. The friction stir welding method is one of the suitable process to welding aluminum alloys to reducing welding defects and increase joint strength. In this process, the welding parameters such as the rotational speed of tools and travel speed, beside the type and geometry of the tool also has a great effect on the quality and strength of the weld. In this study by using the typical tool and bobbin tool the effect of welding parameters on the mechanical strength of the welded joint are investigated. The results of this study show that the bobbin tool has a higher performance and capability in connection with this type of alloy. The main advantage of the bobbin tool is welding the both sides of the weld zone at one stage of the welding process compared to the typical tool. Also in terms of mechanical strength of connection, the use of bobbin tool has resulted in improving the tensile strength of the connection and resistance to a better impact. The effects of welding parameters show that by increasing the rotational speed of the device from 900 to 1100 rpm as well as increasing the travel speed of the tool from 25 to 32 mm/min of the joints shear strength has increased.

The use of clad material as a structural material is increasing in many industries because it has material properties that cannot be obtained from a single material. For the present study, a hot forward extrusion process was applied to fabricate aluminum/copper (Al/Cu) clad composite rod. The different of extrusion ratios and die angles were applied to obtain the best extrusion condition. Finally, hot forward extrusion process was applied at a temperature of 480 ◦C with extrusion ratio of 4 and Die angle of 45 ⃘. The purpose of this paper was fabrication of Al-clad Cu rods by hot forward extrusion. Materials that used in this research were aluminum alloy of AA7075 and pure commercial copper as clad material. There were some experiments among pure copper, AA7075 (both without any extrusion and cold work) and Al-clad Cu rods that included Mechanical Tensile Tests, Micro Hardness tests and Microstructure compare. Microstructure characterizations of the Al/Cu interface and the neighboring regions revealed the formation of a suitable and adhesive bonded layer with thickness of 22 microns and acceptable Microhardness. The mechanical properties results of AA7075, copper and two layer Al/Cu rods reveal that the Yield strength, Ultimate Tensile strength and Formability of extruded Al/Cu rods are suitable in compare to single material rods consist of AA7075 and copper rods.

In recent years, various ways have been used for productions of square tube by reshaping processes. Mainly, it is expected that forming of a square tube that does not have any defects for using in industrial application, should be investigated during the design stage, before trials begin. In this paper, the elasto-plastic deformation of a circular pipe into a square tube without any defects, during the cold re-shape rolling process, is examined by Abaqus finite element software. The occurrence of collapse defect (parameter C) in the flat part of square tube during the forming process is one of the influential negative factors in the final quality of these tubes. Accordingly, the effects of various process parameters such as geometric ratio, roll gap reduction, friction coefficient, roll radius and the material of the pipe, on the occurrence of collapse defect in the squaring process are discussed. The findings show that with increasing the roll gap reduction, the amount of parameter C increases for constant geometric ratios. The geometric ratio is a major factor on the occurrence of collapse defect in the process of squaring circular tubes. In order to verify the simulation results, several experimental tests were performed. Obtained results of simulation showed good agreements with the experiment results.

In this research, the method of mechanical alloying and subsequent sintering has been used to obtain Zr-based MAX Phases compounds with nanocrystalline structure. For this purpose, a stoichiometric mixture of high purity elemental powders of ZrH2, Al and C (Graphite) was subjected to intense mechanical alloying in a planetary high energy ball mill under different milling conditions (5, 10, 20, 40 and 60 h). The fabricated compounds were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and microhardness measurements. Experimental results exhibited that after an optimum milling time of 40 h, Zr2AlC MAX phase with the crystallite size of less than 25 nm and high microhardness of 971 HV can be obtained. Also with milling time, morphology of pre-alloyed powders changed from lamella to globular. Sintering of milled powders at 1300 °C for 2 h resulted in the production of nanometric Zr3AlC2 and Zr4AlC3 MAX phases, increase the crystallite size (grain growth), and release of internal strain. The results revealed that this route (high energy milling followed by sintering) is a powerful, cost effective and high productive technique for preparing Zr-based MAX phases compounds with nanometric structure and homogenies morphology.

Due to the high length to diameter of the tool and its high flexibility, internal turning process is very prone to chatter vibrations. Different methods have been used to increase dynamic stiffness of tools; the most effective method is active control method. In order to analyze and design a control system, a dynamic model of the system is required. Obtaining a system model using finite element modeling technique is complicated and time-consuming, thus, a method that can quickly and accurately estimate the response of the vibration control system is very important. The aim of this study is to propose a method for dynamic modeling of the internal turning tool using the experimental modal analysis, which can be used to predict and simulate vibration reduction. In this method, using the experimental modal test, a linear matrix model of the system dynamics was extracted and then the actuator-tool model was identified using sweep frequency method. Thereafter, by using the obtained models, the active vibration control loop of the internal turning tool was simulated in MATLAB/SIMULINK software and the controller performance was investigated. Finally, the simulation results were compared with the experimental results, which indicate good performance of the proposed method for dynamic modeling of the system and controller design. The proposed method in the identification frequency range accurately estimated the system response, and this method can be used to optimize the controller's gain.

One of the most important factors affecting the mechanical, physical and chemical properties of metals, are crystal structure and grain size. Ultrafine metals with an average grain size of 1000-100nm and nanostructured metals have an average grain size of less than 100nm. Ultrafine and nanostructured materials are known as a new generation of metal products, which have remarkably mechanical and physical properties in comparison to coarse-grained metals. In the last two decades, due to good properties such as high strength, high ductility and toughness, good corrosion resistance and high superplasticity properties, these materials have been considered by many researchers. In recent years, many methods have been proposed for severe plastic deformation and are now being developed and expanded. In these processes, in spite of the high hydrostatic pressure and the unaltered dimensions of the sample during the process, it is possible to apply very high strains, which results in the desired mechanical properties and ultrafine grained and nanostructured materials. The accumulative roll bonding process is one of the methods of SPD. ARB process is simple, extensive use, low-cost, industrially capability method that can produce ultrafine and nanostructured metals. In this research, light metals such as aluminum, magnesium and titanium and also extremely used metal such as copper and steel are discussed. Also, mechanical properties, fractography and microstructural properties of ultrafine and nanostructured metals produced by ARB are compared with initial samples and the mechanisms governing of ARB process that cause changes in mechanical and microstructural properties are analyzed.