مجله مهندسی ساخت و تولید ایران
سال هفتم شماره 3 (خرداد 1399)

Turning is one of the most commonly used material removal processes. The self-excited chatter, which is one of the most common causes of cutting instability, decreases machining efficiency and surface quality extremely. The stable and unstable regions of the cutting are predicted by determining the stability lobe diagram (SLD). With the aid of this diagram and choosing the most suitable spindle speed and depth of cut a higher machining efficiency can be achieved. Despite the importance of cooling with cutting fluid, less attention has been paid to the effect of cooling on the chatter stability in machining processes. Therefore, in the present study, due to the importance of the subject, the chatter vibration in the turning process has been theoretically and experimentally investigated for two cooling conditions including 1- dry machining and 2- wet machining. First, a new model has been semi-empirically developed for prediction of turning force using Genetic Expression Planning (GEP). In this modeling, the turning force is obtained as a function of cutting parameters and cooling conditions. Then, the extracted force model is used to predict the chatter stability limit diagram (SLD) for two cooling conditions (dry & wet). In the next step, the SLDs have been evaluated by empirical data. The results of this research show that there is a good agreement between the SLDs and experimental chatter data. Moreover, the cooling with cutting fluid in the turning process has a significant effect on the displacement of the SLD.

Bone drilling process is one of the essential steps in orthopedic surgeries. If temperature of this process is more than 47 ° C, thermal necrosis occurs. In the event of the thermal necrosis, bone consolidation is not well done. For this reason, a lot of research has been done to reduce the thermal necrosis. In this study, by using an analytical model, bone temperature elevation during drilling was investigated at different feed rates and rotational speeds. To validate the analytical results, the bone temperature elevations were evaluated by comparison with bone drilling process using bovine femurs. With comparison the results, it was found that there are differences between analytical and experimental results that are related to incorrect estimation of the fraction of total heat generated that flows into the bone. Therefore, the correct values of this fraction were obtained after comparing analytical and experimental results. Finally, it was concluded that the fraction is dependent on the feed rate and rotational speed, and also a new equation was presented for it. Experimental results show that within the range of the investigated variables, increase in feed rate causes decrease in bone temperature and with the increase in rotational speed, the bone temperature changes are swinging.

Friction stir process is one of the process that improve the mechanical and metallurgical properties of metals surface. One of the important parameters in this process which affect mechanical and metallurgical properties is rotational speed of shoulder and pin tool. In this study, unlike the other research a new tool was designed and manufactured in such a way that rotational speed of pin and shoulder is seperatable from each other and each one can adopt different speed. Friction stir process was done with constant rotational speed of shoulder (800 rpm) and different rotational speed of the pin(800, 1000 and 1250 rpm). Maximum temperature and mechanical properties of the samples was investigated. The results showed that the maximum temperature does not increase greatly with increasing the rotational speed of the pin (2% increase with 25% increase in the rotational speed of the pin). Mechanical properties of the samples increased with increasing the rotational speed of the pin. The ultimate stress was increased 18% when the rotational speed of the pin was changed from 800 rpm to 1250 rpm.

By the fast growing of electronic related industries, the demand for application of high strength with high conductivity materials is getting increased. In this paper, the accumulative compound extrusion is proposed as a severe plastic deformation method to produce UFG pure copper. An initial copper billet is placed in the die. In the first half- cycle the billet is pressed against the fixed mandrel by an upper punch which results in radial and forward flow of material. In the second half-cycle the billet is regained it's initial shape by pressing down punch. The accumulated plastic strain in each cycle of ACE processing is computed by analytical method and the obtained results showed significant amount of imposed plastic strain. The microstructure evolution during ACE processing was significant grain refinement of 110-240 nm from the initial grain size of 39µm at the end of second cycle. The microhardness examinations showed the increase of ACE processed Hardness to 98HV from the initial value of 57 HV. Also, the results of tensile tests showed the increase of yield and ultimate tensile strength by the factor of 2.07 and 1.13, respectively at the end of ACE second cycle. The flow behavior of material was simulated using FEM in DEFORM 2D software and the model predictions were in good agreement with the analytical results. The electrical conductivity examinations of the ACE processed samples showed the UFG pure copper with high strength and good conductivity in contrast with the alloyed copper parts.

The friction stir welding is a suitable substitute for gas metal arc welding for joining aluminum alloys in aerospace and shipbuilding industries. Recently a new friction stir welding method named floating bobbin tool friction stir welding has been introduced, that enables the implementation of this process with almost zero vertical force. Another advantage of this technique is the simultaneous double sided welding and the symmetry of the stirred region along the thickness. This paper focuses on the use of double sided friction stir welding technology with a floating bobbin tool for joining pure commercial aluminum. The tool used in this process was made from hot working steel with a hardness of 52 HRC. This tool has two shoulders and a threaded cylindrical pin. After performing the welding process, in order to assess the quality of the connection, non-destructive tests of visual inspection, radiography, as well as destructive tests of tensile, bending, hardness and metallography performed on a welded sample. Non-destructive tests confirmed the perfection of a welded sample with optimal parameters. The results of the tensile test showed that the connection efficiency was very significant and reached about 80%. In addition, the fracture strain of the welded sample was 80% higher than that of the base metal. Accordingly, the development and exploitation of this method provides the potential for the development of a low cost, solid state and reliable technology, and the feasibility of designing inexpensive equipment for mobile friction stir welding.

A finite element model has been developed to simulate the laser beam welding (LBW) process, which enjoys the capabilities of ABAQUS in transient thermal analysis. The substance used in this research was AISI 304 which thermal and mechanical properties are introduced to the model as temperature dependent. At first, a non-linear three-dimensional transient thermal model is developed, which calculates the temperature distribution in the local weld area and predicts the keyhole and weld bead size and shape. After the thermal analysis, the FE model is verified through the experimental work. After validation of the model, the effect of laser welding parameters on thermal distribution has been studied. Also, temperature variation on the weld line and on some points of distinct distances from the weld line during the heating and cooling procedure of the laser welding process has been examined. Results indicate that the major laser welding parameters affecting the weld bead geometry are laser power and velocity which have direct and reverse effect on the weld bead geometry, respectively. Also, among the material properties, conductivity is the dominant parameter, affecting the result of simulation.