Numerical Simulation On The Combined Forming Technology Of Sheet Metal Using MPF And SPIF

Nowadays, the sheet metal plastic forming has become more and more important in the industrial manufacturing. With the rapid development of the technology, the market requires more products of high quality to meet the customers'demands. Therefore, how to improve the forming quality and accuracy is becoming a hot research field. This paper puts forward a new combined forming technology based on multi-point forming and single-point incremental forming which could not only avoid their deficiencies of each other, but also improve the forming quality. It is a new branch of the digital forming and additions to the flexible sheet metal forming technology. It is applicable to the complex 3-D surface production manufacturing, especially in the small quantities of automobile and aircraft parts, which has great application prospect and market space.The main contents and conclusions are as follows:1. Study on the combined forming technology and its applicationThis paper illustrates a combined forming technology of the sheet metal based on multi-point forming and single-point incremental forming. It is applicable to achieve the digital forming of the complex 3-D surface parts. According to the characteristics of the forming method, two ways of process have carried out, multi point performing-incremental postforming and the incremental forming using MPF. With the contrast of the SPIF, this paper points out the efficiency and the advantages of the new technology.2. Study on the numerical simulation of the combined forming processThe relevant principles and basic equation of the plastic deformation are given to discuss the numerical simulation of the metal forming. The 08 Al material and elastic pad stress-strain curves are also illustrated. This paper utilizes the commercial finite element method software ANSYS to build the model and selects the dynamic explicit theory to solve the issues. In order to obtain the precise simulation results, it is necessary to study the boundary conditions setting such as the element selecting, contact and friction. Two kinds of models are built and solved.3. The analysis of the numerical resultsIn order to illustrate the process of the multi-point performing-incremental postforming, this paper takes the spherical part into the numerical situation. The numerical simulation results illustrate that the stress and strain distribution in the sheet still meets the rule of the incremental forming, but due to the influence of the glacis made by multi-point press forming, the max of the stress and strain decrease and the plastic flow of the material is more reasonable. Corresponding to the over-thinning area in the incremental forming process, the thickness distribution of the combined forming is more reasonable on the whole, effectively avoiding crack and wrinkling forming defects. Moreover, the forming accuracy in the effective area also reaches a high standard.4. The influence of the parameters on the forming resultsIn order to study the influence of various process parameters on the forming effect, this paper takes the spherical part with a cross segment for example. Numerical simulation results show that: a small radius of the tool can provide a high forming accuracy, but stress concentration is likely to happen; Less than 100N of the blank holder force can not provide a stable clamping, but when it is larger than 400N, the material flow will be limited; The vertical feed-in distance of the tool is inversely proportional to the forming precision, when it is greater than 2mm, serious wrinkling will happen. Considering the above factors on the whole influence of the forming process, the reasonable parameters are as follows: tool radius r=4mm, blank holder force F=200N, vertical feed-in distance h=0.2mm, virtual forming speed v=10m/s. The simulation results were compared with the experimental data to verify the accuracy of the numerical simulation.5. The cause and prevention of the forming defectsThere are three major forming defects in the combined forming process: crack, wrinkle, metal accumulation. Crack is mainly due to the stress concentration made by small size radius tool and too large BHF. Wrinkle is mainly because of the instability of the press in the thickness direction, too small BHF and large vertical feed-in distance can lead to this result. Metal accumulation is a unique form defect in the combined forming process, especially in the thick sheet. This thinning-thickening periodical changes are mainly due to the tool trajectory. Therefore, in order to avoid various forming defects, a all-around consideration of the parameters must take into account.