جستجوی مقالات مرتبط با کلیدواژه "شکل دهی تدریجی" در نشریات گروه "مکانیک"

Incremental forming of metal sheets is one of the new methods of forming, in which the local exertion of forming forces and the absence of a matrix enhances the forming limit of the sheet and extends the flexibility of process in producing of complex geometries. In this research, the forming limit of aluminum/copper bilayer sheets in the single-point incremental forming of different geometries was studied. Considering the instability mechanism of the sheet, the Xue-Wierzbicki damage criterion was used in the form of the VUMAT subroutine of Abaqus in the numerical prediction of the growth and damage initiation of bilayer sheets. Experimental tests showed that the type of geometry has influences on the forming height limit due to the different induced stress and strain states on the sheet. The prediction of the numerical model of the forming height limit on average for different geometries with difference of 8% compared to the experimental tests, which indicates the validity of the numerical model. Accordingly, using the numerical model, the effect of changes in equivalent plastic strain and triaxial stress as crucial variables on the distribution of surface strains and damage was analyzed. Also, cyclic and nonlinear loading in this process was shown by plotting the strain path for different geometries.

The development of rapid prototyping methods has been very drastic in recent years. One of these methods, with a nature similar to sheet-forming processes, is the incremental forming method. In the last two decades, this technique has attracted much attention in industrial applications. The incremental forming process has been able to play a major role in advancing industrial projects in the production of low-volume prototypes. This process is a suitable alternative to conventional forming processes in the single production of conical geometries because of the low cost of machinery, equipment, and tools. In this paper, the two-point incremental forming of conical parts by three multi-point matrix designs, including single, double, and three-step cylinders, were investigated. For this purpose, the feed rate (400-1000 mm/min) and the penetration step of the tool (0.5-1.1 mm) were investigated in three levels to form the aluminum sheets with a thickness of 0.5 mm. In the following, the effect of the input parameters on the limiting height of the formed specimens, thickness distribution, surface roughness, and geometric accuracy of longitudinal cut specimens was assessed. According to the results, using the multi-point matrixes, despite increasing the final geometric accuracy, friction was reduced compared to the conical matrix. Using a two-step matrix, deeper pieces were formed by increasing the formability of the sheet, in which the average height was improved by an average of 12%. However, no significant change was observed in the roughness of the samples formed by all three types of matrixes. Therefore, the design of the proposed matrix had almost no tangible effect on the final surface roughness output. From the view of geometric accuracy, the matrix design with three steps created the highest geometric accuracy, as well as the least deviation relative to the planned path.

Single point incremental forming (SPIF) is a cost-effective process with high flexibility and as a result, it is a suitable choice for low-batch production compared to traditional metal forming methods. In the present experimental research, the warm SPIF with ball nose tool was used in the forming of aluminum tailor welded blanks (TWB) that were joined together by the argon welding process. Aluminum sheets of 6061 and 5083 with an equal thickness of 1.5 mm were used as base metals and joined together using the butt welding method. In this research, the effect of four parameters of temperature, lubricant, step down, and feedrate were investigated on the formability and appearance of aluminum. The temperature range is between room temperature and 290 degrees Celsius, and three types of lubricants are used in the experimental tests. The Taguchi method was used for the design of the experiment. The results of the tests indicated that an increase in the temperature as the most effective parameter led to an increase in the formability of TWB by 79%. The lubrication, step down, and the feedrate was in the next ranks of effectiveness in the formability of aluminum TWB.

The Incremental forming is an applied production method in rapid prototyping and manufacturing of sheet products in small batches. Usually this process is performed in environment temperature by a computer numerical control machine or a manipulator. Conducting the process in high temperatures, studying the thickness distribution and improving the forming limit of producing parts are the main research contributions in this field. Also, some efforts have been made to increase the accuracy of manufactured parts and two point incremental forming and using of metallic foams have been proposed. In this research, the usage of polymeric foam as a flexible support is proposed to improve the incremental forming of high density polyethylene sheet with the thickness of 2 mm. Wrinkling and tearing defects for both with and without flexible support processing conditions with different spindle speeds and feed rates were investigated. For this, parts with variable wall angle were used. The results showed, the usage of polymeric foam support improves the forming condition by achieving to the parts with higher wall angle. Also, some samples produced in different working condition were selected and the accuracy of them was investigated using a 3D scanner and the improvement of the accuracy in the condition of using the flexible die support was observed.

Single point incremental forming is one of the novel processes in forming of metallic sheets that has created high forming levels in sheet by local plastic deformation. In this paper, new tool based on incremental forming principles is introduced for production of cylindrical flange. Using this tool for forming of the flange, the manual milling machine is used instead of milling machine equipped with computer numerical control (CNC). Forming of flange wall is accomplished by a new tool that includes two forming punches. Tool shank is fixed on milling machine spindle and the value of eccentricity determines the final diameter of flange. Movement of rotary tool is simple and downward with defined step. The results show that flanges with specified diameters can be formed by using this method very fast. Increasing the diameter of the primary hole created on the sheet increases the flange height but also increases the thinning. Increasing rotational speed results in forming flanges with higher height but increasing vertical feed rate of tool decreases the flange height.

Incremental forming of metal sheets is one of the new methods of metal forming with high flexibility in batch production of complex geometries. Due to the absence of a matrix and the gradual applying of forming forces, the forming limit in this process is increased compared to conventional ones. In this research, formability, forming, and finally fracture of aluminum/copper bilayer sheets produced by explosive welding method in the single point incremental forming process are studied. In the numerical prediction of growth and onset of fracture of sheets in this process, the Xue-Wierzbicki damage criterion was used as the VUMAT subroutine in Abaqus software. Using the numerical model, variations of the stress triaxiality and equivalent plastic strain as the variables affecting the damage growth in the incremental forming process were analyzed and explained, and the effect of cyclic and nonlinear loading in this process was shown. Experimental results show a different failure height of various geometries due to different loading conditions. Also, using the verified numerical model, in addition to predicting crack growth location, the fracture height in the formed geometries was predicted by 4.06% difference with respect to the experimental results.

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.

In this paper, the single point incremental forming (SPIF) of friction stir welded (FSWed) 5083 aluminum alloy sheets are investigated experimentally and numerically. The aluminum sheets with 2mm thickness are friction stir welded with the same FSW parameters. In order to obtain the effect of FSW on the formability of SPIF, the base sheets and FSWed sheets are formed to conical shapes with different forming angles and then the limiting wall angles are determined for each condition. The experimental results indicate that the limiting forming angle of FSWed sheet is not so much different than the base sheet and FSW does not have a negative effect on the sheet metal formability in SPIF. To study the effect of SPIF and FSW in mechanical and microstructural properties of the formed parts, the effects of these process on the grain size and micro-hardness is investigated. Furthermore, the incremental forming is numerically simulated using the ABAQUS software and the sheet thickness distribution, obtained from the simulation, is compared with the experimental results. After verification of the numerical simulation model, the effect of FSW on the thickness distribution and strain distribution in SPIF is studied. The results indicate that in weld region and base metal region, the distributions of thickness and major strain are uniform while the distribution of minor strain is non-uniform.

New trends have been observed in recent years for rapid prototyping of sheet metal parts by Incremental Forming process particularly at low quantity production. Recent ideas have been presented for a new type of this process known as Incremental sheet metal hammering (ISMH) method. In ISMH process, by sequence moving of a hammering punch over a clamped sheet metal, a three-dimensional work piece is produced without using a die. In this paper, the effect of tool parameter on the formability of Al-1100 will be studied. To investigate this issue, the sheet is clamped. Then by considering the cone angle, hammering is applied at a certain diameter and frequency until the failure happens. By recording the angle and the height values at failure point, a correlation has been extracted between the diameter and the frequency. Analysis of the results shows that by decreasing the diameter of the punch, maximum strain in the direction of thickness is observed at higher height. Also, by increasing the diameter of the punch, formability of Al-1100 increases. Also, it is shown that by increasing the impact frequency, the formability of the sheet will be decreased.

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.