جستجوی مقالات مرتبط با کلیدواژه « نیروی شکل دهی » در نشریات گروه « مکانیک »

One of the forming pipes methods is the rotary draw bending process. Today, bending of thin-walled pipes with low radius of curvature is widely used in the automotive, military and aerospace industries, which is used to bend high-strength pipes. In this paper, at first the necessary models were created to simulate the bending process of the rotary pipe, and then the necessary mechanical and physical properties for stainless steel 304 and elastomers were determined. Then, experimental and numerical study of the forming force and changes in pipe wall thickness were performed. The process simulation was analytically performed using polyurethane elastomeric mandrels and nitrile rubber based on ABAQUS finite element software on 304 steel. The results show a good agreement between simulation and experimental results. Finally, the effects of process parameters including mandrel type, pipe diameter and bending radius were analyzed on the maximum forming force by factorial analysis. The results showed that the maximum forming force for both types of mandrel materials is obtained for pipes with small diameter and high curvature radius. Also, the bending forces increase 5 times by 30%increasing the bending radius, for pipes with smaller diameters. In addition, in equal diameter and radius of bending, the bending forces in the case of using polyurethane mandrel are 25% more than nitrile mandrel.

The equal channel angular pressing process is one of the most effective severe plastic deformation processes to produce ultrafine grained steels metals. Also, the upper bound theory is one of the reliable theoretical tools to forecast deformation strain and forming load. In this research, analysis of equal channel angular pressing technique in an arbitrary channel and corner angles using upper-bound theory was performed and a general and user-friendly equation for predicting the forming force is proposed according to the geometry of process and elastic-plastic properties of work-piece material. By comparing the amount of obtained theoretical load with experimental forming force resulted from applying process on 7075 Al alloy, has been observed very good agreement between the results. This guarantees the reliability of the achieved general equation for equal channel angular pressing force. According to the results of the present research, experimental and theoretical forming load of equal channel angular pressing process on this material under conditions of channel angle 135°, corner angle 20°, billet diameter 10 mm, and billet length 90 mm were obtained equal to 48 kN and 55.04 kN, respectively. Furthermore, by increasing the channel angle from 60 to 150 under a constant corner angle of 20°, process load is decreased equal to 41.3% from 86.4 kN to 50.7 kN. In addition, by increasing the corner angle from 0° to 40° under a constant channel angle of 135°, the negligible reduction of a load equal to 2.5% was observed from 56 kN to 54.6 kN.

In recent years, industrial applications of composite sheets have been increasingly expanded due to their extremely different properties such as high strength, low density, and good corrosion resistance compared to single layer sheets. For this reason, in the current study, it is investigated the flanging of composite metal sheets. Also, the behavior of an aluminum-copper sheet, cladded using explosive welding, during incremental forming of a circular collar have been experimentally and numerically studied. In addition, the experimental results are used to validate the numerical simulation of the forming process. At first, in order to understand collar forming of the perforated sheet, the effect of hole diameter, forming direction or layer arrangement on dimensional accuracy, thickness distribution and forming force were investigated and then, the effect of hole flanging and collar forming were compared using two strategies. The results show that by decreasing the initial hole diameter of sheet, the average vertical maximum force increases by 9%, the minimum thickness decreases and its location shifts toward the center of sheet. Aluminum-copper arrangement also experiences a 7% reduction in average force and a 4% increase in minimum thickness due to the protective property of copper layer in tensile state compares to copper-aluminum. Besides, the multi-step method leads to a 6% minimum thickness increase due to better material flow compared to single-step method.

The Incremental Sheet metal forming is one of the dieless forming processes. In this process, the ball nose tool runs the predetermined path to form the sheet by applying the local pressure on the sheet. One of the disadvantages of the incremental forming process is the springback phenomenon. In this paper, the effect of parameters on the springback in the two layear sheet Cu / Austenite St produced by the Single Point Incremental Sheet Forming has been investigated. The input parameters of this process include the tool diameter, vertical step, sheet thickness, depth of form, forward velocity, and arrangement of layers of the double layer sheet. Using the finite element simulation via Abaqus software and the Taguchi design of experiments method via Minitab software, the effect of input parameters on springback and forming force has been investigated. Also, the results of the simulation were validated by the empirical test and it was determined that the finite element has an appropriate overlap in extraction of the final results. At the end, the effect of each of the parameters mentioned on the springback and forming force was analyzed. It was determined that the thickness of the sheet had the greatest effect on both springback and forming force.

Aluminum alloys have been widely used in various industries, due to its special characteristics. On the other hand, due to its low formability, the forming of these alloys is difficult at room temperature. Therefore, in order to facilitate the forming, warm forming methods can be used, which will lead to the oxidation of the material. In Single Point Incremental Forming (SPIF), a sheet metal is formed by a progression of localized plastic deformation using a hemispherical-head tool. In this study, by applying ultrasonic vibration to the tool, Ultrasonic Vibration assisted SPIF (UVaSPIF) process was developed that improved the sheet formability at room temperature. In present paper, the effect of ultrasonic vibration and lubricant on behavior of the forming force has been investigated. Consequently, a hemispherical-head tool (D = 20 mm) with natural frequency of 20.4 kHz was designed and manufactured. The occurrence of longitudinal mode and resonance phenomenon has been confirmed by the results of modal analysis and experimental test. Then, Al 1050-O sheet was used as a work material. Experimental results obtained from straight groove test, indicate that in UVaSPIF, imposing of vibration without lubricant has the greatest impact on reducing the vertical component of the forming force whereas in SPIF, the lubricant has the greatest impact on reducing the vertical component of the forming force.

Bipolar plates are one of the most important parts of the fuel cell which have the highest production cost for the system. In this study, the formability of SS 316L bipolar plates with an active area of 100 cm2 by the stamping process is investigated. With respect to various types of the forming process, stamping process has the advantages of simplicity, higher production speed, and lower production. In this process, the sheet is considered to be between two rigid die slabs, and applying force to the die set results in forming the plates. The important issue of bipolar plates is the dimension accuracy of the channels. In this paper, the width and flatness of the channels and ribs of the produced plates are investigated. If the tolerances of the formed channels are not in the desirable range, the performance of the fuel cell is disturbed and the fuel cell efficiency is considerably decreased. The results of this study demonstrate that increasing the stamping force results in an increase of the width of channel and rib. Moreover, the flatness due to the spring-back of the sheet is in the desired tolerance range and these plates can be utilized as metallic bipolar plates in the fuel cell stacks.

In this paper, the performance of electric hot incremental forming process is investigated on the Ti-6Al-4V sheet by FE simulation and experimental method. Ti-6Al-4V titanium alloy sheet has extensively used in aerospace industries. Therefore, forming of this lightweight alloy is very important. Ti-6AI-4V sheet has poor formability at the room temperature and can be well-formed in high temperature. In this paper, the geometrical shape of final part was a cone frustum that obtained from forming of rectangular sheet, and the effect of processing parameters, such as wall angle, step size and tool diameter, on the forming forces were investigated. The results demonstrated that the forming force are increased by increasing of step size and decreasing of tool diameter. Also, to form parts with larger wall angle, the required force is lower. The process was simulated in the ABAQUS software to investigate the process using finite element analysis. The modeling was performed using local heat on the sheet. It showed a good agreement between the experimental and numerical results of forming force and deference between both of them is about 5.7%.

Investigating the effects of process parameters on forming forces and defects formation in tube spinning process of AA6061
˜یÏå [English]
Tube spinning or flow forming process is used for manufacturing of seamless tubes widely put into service in advanced industries. The ideal flow for materials entering the deformation zone in this process is extrusion-type flow in axial direction. Very localized deformation zone which is confined by outer materials and forming tools is very important aspect of this process. Therefore, development of defects during the deformation process with undesirable flow of materials can be easily occurred. The main reason of undesirable flow of materials is choosing inappropriate process parameters which results in arising various geometrical and dimensional defects. In this paper, the effects of process parameters on formation and growth of different defects and their correlations with material flow and forming forces in tube spinning of AA6061 was investigated by using design of experiment (DOE) method. The results of experiments show that by applying the optimized values of reduction and feed rate per revolution, these defects can be controlled. Also, by comparing the experimentally measured and theoretically calculated forming forces it can be shown that the larger the deviation of measured forces from calculated ones gets the more severe formation of defects and undesirable materials flow becomes.

In this study, conventional methods of the groove test on an incremental forming process by finite element method have been investigated in order to analyze the forces imposed by the spindle of CNC machine. Initially, the finite element method analysis using ABAQUS software was validated by empirical research in the published paper. In this analysis, tool and clamping are supposed rigid body and the sheet is deformable body. When using the side fixture for constraining of side edge of sheet was investigated, it was found that the use of the side fixture increase force between 2 to 2.5 times. However the number of tool sweeps would be halved and groove test would be completed with 1 tool sweep. Also by smoothly graded loading for prevention of traumatic force peaks to the machine, this test can be done at a lower cost. For example, for AA7075-0 sheet with 80mm forming path between two different steps 0.25 with 2 sweeps and 0.5mm with 1 sweep, using lower slope and 2 tool sweeps, the maximum vertical force peaks decrease and process is very proper for low load capacity CNC machine.

Incremental sheet forming process (ISF) is a dieless forming method capable to produce small-batch of sheet metal components economically. This makes ISF attention-grabbing for research and development. Use of ultrasonic vibration is a modern approach implemented to improve ISF process. In this article¡ the effects of process parameters of ultrasonic vibration assisted incremental sheet forming (USVAISF) such as tool diameter¡ pitch size and vibration amplitude on forming force¡ fracture depth and percent reduction of forming force is investigated experimentally through response surface method. Results indicate that decreasing tool diameter and increasing ultrasonic vibration amplitude decrease the forming force and make the ultrasonic vibration more effective (increase the percent reduction of forming force) in USVAISF process. Fracture depth decreases with increasing pitch size and vibration amplitude. The influences of tool diameter on fracture depth and pitch size on forming force are complicated and different effects are seen in various conditions. Results show 33% to 63% reduction in forming force and 2% to 29% reduction in fracture depth in ultrasonic vibration assisted incremental sheet forming (USVAISF) compared with conventional ISF (without ultrasonic vibration). Eventually¡ optimal process parameters are predicted for ultrasonic vibration assisted incremental sheet forming and validated experimentally.

Incremental sheet metal forming process is considered as one of methods which able manufacturer to produce parts without dedicated die in low and rapid prototype production, and many researches have been done to improve it. Using of ultrasonic vibration is one of the modern approaches in forming processes which reduce friction and forming force. The purpose of this study is to investigate the effect of ultrasonic vibration applied to the tool in single point incremental sheet metal forming process. For this, first theory of single point incremental forming has been studied; its principle has been investigated and analytical relations have been modified then analytical relations in the case of applying ultrasonic are derived from those. To practical evaluation of applying ultrasonic to this process a set can be installed to the head of CNC milling machine is designed and manufactured. According to results of analytic compared to experimental results a reasonable approximation of forming force variation in normal single point incremental forming process and applying ultrasonic can be offered. Based on tests results forming force in applying ultrasonic compare to normal mode reduces between 33 to 63.5 percent depend on test circumstances.

Incremental Sheet Metal Forming (ISMF) is based on localized plastic deformation. In this process, a hemispherical-head tool, controlled by a CNC milling machine, shapes a sheet metal according to a defined path. Study of the forming force is one of the most important topics in this process. Increasing of vertical step size, tool diameter, wall angle and sheet thickness together with using of high strength sheet metals and lightweight alloys, leads to an increase in the forming force. In this paper, the performance of a novel forming process, named Ultrasonic Vibration assisted Incremental Sheet Metal Forming (UVaISMF) has been investigated. The procedure of design, manufacture and test of vibratory forming tool, is presented. The occurrence of longitudinal mode and resonance phenomenon has been confirmed by the results of modal analysis and experimental test. Furthermore, the effect of ultrasonic vibration on the vertical component of forming force and spring-back has been studied. Aluminium sheet of grade Al 1050-O is used as a work material. Experimental results obtained from straight groove test, indicate that ultrasonic excitation of forming tool, will reduce the average of vertical component of forming force and spring-back in comparison to conventional process.

Single point incremental forming is a sheet metal forming process that has more flexibility than another methods. This process don''t require to die and could formed various shape white use the simple tool and CNC machine. In this paper the influence of process parameters on the forces and dimensional accuracy and thickness distribution in single point incremental forming is investigated. These parameters include the feed rate، tool rotation، vertical step، movement strategy of tool and lubrication. Beginning with the design and construction of the fixture and clamping it on the dynamometer and create of tool (tungsten carbide)، the preparation process was done on a CNC milling machine. Then، the experimental tests were carried out on Aluminum alloy sheets (Al-1200) with creation of pyramid frustum; after the measuring of force in different directions، the influence of parameters on the forming force was investigated. Also parts were measured with CMM devices and compared. The results showed that with increasing the feed rate، the vertical force decreases and with increasing tool rotation speed، horizontal force decreases. The use of lubricant، is effective on the improvement of process.