Numerical Simulation For Defects In Single-Point Incremental Forming Process

Single-point incremental forming (SPIF) is a flexible forming technology which is used for sheet metal parts'processing. In the process, a series of contours is generated by computers according to the dimensions of parts, through controlling the forming tool move along the specific forming trajectory, thus completing the forming process of the parts point by point. Compared with traditional stamping process, SPIF has the following advantages: First of all, SPIF does not need special designed die, it saves the costs on the mold designing and manufacturing, while also saving many time on debugging the die; Secondly, by using of computer and special software, it can easily achieve the automation of sheet metal forming; Lastly, in the forming processing the sheet metal deformed by the local effect, it can fully play the forming capabilities of sheet metal, greatly increase the forming limits of sheet metal. The contact between the forming tool and the sheet metal is concentrated on one point, the stress on the point is very high, and so there are many defects in the process, such as crack, impression, low dimensional accuracy. The numerical simulation on the forming process could analyze the causes of defects and provide solutions.In this paper, using the finite element simulation software ANSYS / LS-DYNA as a research platform to establish the finite element model of single point incremental forming process, analysis a variety of process defects of the single point incremental forming technology, comparing different process parameters and methods on the suppression and improvement of process defects, provide a reference for the manufacturing. The research work and conclusions are as follows:1) Gave a brief analysis of the forming mechanism of SPIF process and introduced the general process to establish the FE model of SPIF by using of ANSYS / LS-DYNA software, and established the finite element model both of the Die less SPIF and the SPIF with support device. In the forming process, the deformation of the sheet metal is very large, when simulating the forming process we choose SHELL163 unit based on Hughes-Liu algorithm as the sheet metal. Hughes-Liu algorithm has higher accuracy, and is more applicable to simulate the complex sheet metal deformation. Through the simulation we can prove that the wall thickness of the parts consists with the Sine law, and the forming angle is a key factor to impact the formability of the sheet metal. At the same time, a new method to measure the dimensional precision of the parts was introduced in detail.2) Stimulated the forming process with spiral trajectory and contour trajectory, compared the stimulated resulted and demonstrated that the spiral trajectory is more reasonable. Simulated the SPIF process with different feedrate and analysis the simulated results, found that downsize the feedrate can improve the formability of the sheet metal and will help to reduce the risk of crack. Analysis the reason why the thickness of the sheet metal decrease with the feedrate downsize, and the dimensional precision of the parts has no relationship with the feedrate, surface quality of the parts is highly related to the feedate, compared the simulated results can found that the surface quality is getting better while the decrease of the feedrate.3) Simulate the SPIF process with different forming tools, the size of these forming tools is gradually become smaller. Through the study we found that the size of forming tool is very important to the formability of the sheet metal. Increase the size of forming tool can greatly decrease the stress of the contact point, so the crack phenomenon can be avoided. The dimensional precision of the parts is highly related to the radius of the forming tool. The smaller tooling radius is, the better machining accuracy will be at the corners of the parts.4) Simulated the multi-process forming of SPIF, demonstrated the possibility of multi-process technology using in SPIF. Compared the simulated results of single-process forming and multi-process forming and found that the multi-process technology can effectively improve the formability of the 3D parts. The more processing pass, the more uniform distribution of the part thickness. At the same time, multi-process technology can also effectively improve the dimensional precision of the part, we should consider using the multi-process technology when forming complex shape parts and high quality parts.5) Using different BHF to simulate the forming process, By comparison the simulated results found that the BHF has a little influence on the sheet metal formability, use smaller BHF can improve the formability of the sheet metal. But the SIPF is a shear deformation forming process, therefore, the reduction of BHF has no obvious effect on improve the formability of the sheet metal. BHF has very large impact to the dimensional precision of the parts, if the BHF is too small, part will rotate during the forming process.6) Simulated the forming process with support device, compared the simulated results with the Die-less forming process, and found that the support device can effectively support the sheet metal in the processing, this could decrease the stress of the sheet metal, tensile behavior over the edge of the part was significantly reduced, the support device could greatly improve the formability of the sheet metal. The support device can also effectively improve the dimensional precision of the part.