Numerical Simulation Research On Flexible Clamp Stretching Of Saddle-shaped Part

With the rapid development of aviation industry since1949, it requires morecomplex surface, higher stretching quality and forming efficiency. Traditionalstretching machine has so many problems such as difficulties even defects in forming,low utilization rate of sheets, very complex control system, expensive price, thatrestricts its expansion to other fields. In order to resolve above-mentioned problems,Jilin University has invented flexible clamp stretching machine. This machine canperfectly solve above-mentioned problems, and widen application range for stretchingforming technology.Flexible clamp stretch forming is a new sheet metal forming technology based onthe improvement of traditional stretch technology. In the forming process, the overallclamping mechanism is replaced by discrete clamp mechanism, the tension providedby hydraulic cylinder and the resistance generated by sheet deformation makes theclamps swing around the universal joint. The main contents and conclusions in thisarticle are listed:1. The principle and superiority of flexible clamp stretch forming was analyzed.The theory of finite element was simply introduced. Then the FEM of flexible clampstretch forming was established with ABAQUS.2. The FEM of flexible clamp stretch forming and rigid clamp stretch formingfor saddle-shaped part were set up, then calculated and analyzed the simulation results.The results showed that: comparing with rigid clamp stretch forming, flexible clampstretch forming could improve the stress and strain distribution of saddle-shaped part,shorten the size of transition zone, and improve the utilization ratio of material.3. Related technology parameters such as pretension, friction coefficient andloading amplitude curve shape effect of flexible clamp forming for saddle-shapedparts were studied. The results showed that: the suitable pretension did not onlyimprove the stress distribution, reduce the forming difficulty, but also decrease thespringback after deformation to improve the forming precision. Wrinklingphenomenon would occur when the friction coefficient was too small, but if thefriction coefficient was excessive, the forming quality would be bad because ofuneven distribution of stress and thickness of the forming. Using the right loadingamplitude curves could inhibit the occurrence of wrinkling effectively, especially the saddle-shaped parts with smaller curvature. It was important to avoid wrinklingphenomenon and improve the sheet metal flow with smooth vertical direction andhorizontal direction loading curve at the initial stage.4. Four situations were discussed in different saddle-shape forming effects beforeand after the overturn of objection surface, and the influence on forming quality ofoverturn was compared. The results showed that: when the length of saddle-shapeddie was different with its width, the stress and strain distribution would be differenttoo after objection surface overturn.