مجله مهندسی ساخت و تولید ایران
سال سوم شماره 2 (تابستان 1395)

Severe Plastic Deformation (SPD) processes are widely used in order to decrease the grain size and improve mechanical properties of engineering alloys. Equal- Channel Angular Pressing (ECAP) is one of such processes that can be performed on bulk materials. In this paper effect of ECAP and heattreatment coupling on 7075 Aluminum alloy was investigated. ECAP was performed on samples after solution treatment. Considerable grain size decrease was observed. Sample’s hardness was increased after ECAP. In order to investigate the effect of solution treatment time on hardness, samples were solution treated at 500° degrees for 5, 10 and 15 hours. It was shown that increasing the solution treatment time from 5 to 15 hours decreases the hardness in solid solution state from 45 to 39 HRB due to increase in the solution of the initial precipitates. Aging treatment at 80 and 120 degrees was performed to further harden the alloy. It was observed that aging treatment after ECAP increases the hardness of all samples. Increasing the solution treatment time from 5 to 15 hours increases the maximum hardness in aging state at 120 degrees from 92 to 98 HRB.

Cold roll forming is a sheet metal forming process that it looks simple, but the lot of parameters that influence this process and interaction of this parameters over each other's are challenges. One of the defects that affect the quality of the products in this process, is the thinning. This defect occurs mainly in bending zone is affected by the parameters of the process. Parameters such as forming angle, sheet thickness, roller diameter, roller corner radius and distance between stations have a major effect on the occurrence of fructure. In this paper, the roller corner radius, forming angle and sheet thickness have been investigated to the thinning defect in this process. Cold roll forming experiments for this study has been done and the Abaqus finite element simulation software used to predict the thinning in the bending zone. St52 steel sheet was used to experiments. The results showed that from three parameters investigated in this paper the radius of the corner of 5mm with 41.7% and forming angle of 600 whit 40.7% have the greatest effects on this defect. In fact for reduction of transverse strains in bending zone it is better that forming angle decrease so the number of forming stations increase.

AA2024 alloy has high strength but low formability. Therefore there is a difficulty during forming processes of the alloy such as rolling, because high capacity of rolling machine is required. So, achievements in good mechanical properties in this alloy besides the improvement in ductility during cold rolling are the main challenges for industries. The objective of this paper is to improve mechanical properties of 2024 aluminum alloy by using a combination of cold rolling and precipitation hardening. To do this, the hot rolled strip of the alloy first solutionized at495 ̊C for an hour and immediately quenched in cold water. The samples were then subjected to 15, 30 and 50 percent reduction by rolling at room temperatures. The cold worked samples were then natural aged for a week. The tensile test and Brinell hardness test were conducted and microstructural study was carried out by metallography. The results indicate that, the 30% cold rolled sample has the maximum strength and hardness in comparison to the T4 or T3 samples.

Grinding is one of the final processes on the ground part that improves surface quality. Grinding wheel must be sharpened before surface quality damaged. Dressing parameters must be well adjusted in order to achieve the best conditions of grinding wheel surface. In the present research an experimental study has been performed to analyze effect of dressing parameters on surface quality of chrome-molybdenum rolls. Firstly, dressing was performed on grinding wheel and topography of wheel, wheel surface quality and surface quality of ground part were compared before and after grinding process. Further, a parameters study was carried out to determine the effects of dressing speed, feed rate and dressing depth on the surface roughness of the ground part. Here, 20 experiments were designed by use of central composite design and response surface methodology to determine effects of parameters on the final surface roughness and also identify optimal parameters. In the parameters study obtained results indicated that in minimum dressing feed rate and in minimum dressing depth and in maximum dressing speed are the most effective parameters among process parameters. Finally, the desirability approach function has been used to optimize surface roughness simultaneously.

In this paper, friction stir back extrusion process is proposed for producing ultra-fine grain (UFG) tubes. In this process, a rotating tool is plunged into round bar specimens and then forming tubes. The influence of design parameters such as heat treatment, applied strain and material flow behavior was determined by finite element simulation. Various tests including optical microscopy, tensile test and microhardness test were carried out to evaluate the metallurgical and mechanical properties of processed tubes. The optical micrographs of the microstructure demonstrate that this process is capable to form a tube with a significant fine grained structure resulting from dynamic recrystallization phenomenon. Reduction in grain size and grain refinement occur across the inner wall of the formed tube as well. Hence, the grain size with an initial value of ~ 110 µm was decreased to ~ 33 µm in the inner side of formed tube wall. The obtained results from tensile tests illustrate that the ultimate strength and elongation to failure were increased from the initial value of 153 MPa to 195 MPa and 10% to 13%, respectively. Thus the ultimate strength increased by 13%. The average hardness along thickness has reached to 82 Hv from 63 Hv. The results show that this method is suitable for fabricating a kind of ultrafine-grained tube which own an acceptable combination of strength and ductility.

Nanomanipulation process using atomic force microscopy is one of the new methods in manufacturing. This process has been seriously considered by researchers. Due to very high precision in the manufacture of devices for micro/nano-exist, accurate modeling process will have a significant impact on the construction of the devices. Also, due to the high cost of using atomic force microscopy manufacturing micro/nano-devices, it is necessary to first model this process was carefully done and then enters the construction areas. So far, many researchers have focused on modeling manipulation, most of their research, in conjunction with the 2D manipulation and been made using simple models of friction. Since the real manipulation in micro/nano-devices manufacturing is done in 3D environment and also given that the transition from the macro to the micro/nano, surface forces such as friction are important, therefore, in this paper, for the first time, LuGre friction model, in 3D manipulation modeling has been used. The results, indicating a decrease critical force and time manipulation using LuGre friction model versus the simple models, this is due to the fact that the LuGre friction model contained actual contact area, while other models involve nominal contact surface. Also, compare the 3D results obtained by 2D results show an increase in critical force and time that was due to the increase in surface area is proof of the accuracy of modeling.

Bone drilling process is the most prominent process in orthopedically surgeries and curing bone breakages. It is also very common in dentistry and bone sampling operations. Due to complexity of the material that is machined, bone, and the sensitivity of the process, bone drilling is one of the most important, common and sensitive processes in biomedical engineering field. Developed a three-axis robotic bone-drilling system and mechatronic bone-drilling tools improved the orthopedic operations. Furthermore, imposing higher forces to bone might lead breaking or cracking and consequently serious damage in bone. In this paper a mathematical second order linear regression model is introduced to predict process force behavior during bone drilling process as a function of tool drilling speed, feed rate, tool diameter and effective interactions. This model can predict carefully force behavior during bone drilling within the acceptable range. Moreover, applying design of experiments, modeling and optimization of effective parameters using response surface method in bone drilling process optimized drilling speed, feed rate and tool diameter were obtained to minimize force. Results show that to minimize force increasing the drilling speed would decrease the thrust force, whereas decreasing the feed rate and tool diameter would decrease the Thrust force.

Nowadays, one of the very important issues in the aerospace and automotive industries is reduction of weight of structures and preventing the corrosion. The use of aluminum alloys could help a lot to produce lighter components, resulting in reduced fuel consumption. In this project, the process design and producing of a sample part using rubber-pad bulging process was done. Aluminum alloy used for the production of aluminum pipes was AA1050A alloy and polyurethane rod with Shore A 85 hardness was used as rubber. Mechanical properties of aluminum and polyurethane were obtained from mechanical tests. Experimental tests were conducted to produce sample part on the hydroforming machine. In the experimental tests, only the punches of the machine were used to apply both internal pressure and axial feeding. Applying different loading curves was possible with changing the initial tube length and using a urethane rod with a constant initial length. By varying the length of initial tubes and thus change in the onset of applying axial feeding, production of sample parts without fracture was possible. It was shown that with a beneficial wrinkling in first forming step, it is possible to produce a sample with higher bulging ratio and lower maximum thinning. Samples produced using the modified loading curve, had the maximum bulging ratio of 24.83 percent and maximum thinning of 6.5 percent.