Research On Bulging And Cold Push Bending With Small Radius Of Thin-Wall Tubes

The tube bending forming has a wide range of applications as a typical plastic forming technology in the aerospace, automotive, shipbuilding and other manufacturing industries. Now the thin-wall elbow with small bending radius has being a research focus as the result of its characteristic of light weight, high strength and low consumption. This elbow produced by the half tube stamping and then welding forming technology, but the traditional technology cannot achieve the purpose of weight reduction and based on the feature of complicated procedures, the production forming quality was reduced. In order to solve all of these problems, the cold push-bending was adopted. Although cold push-bending has its own advantages, it yet faced such problems as out wall thinning, inner wrinkling and cross section distortion flaws, compared with other elbows, these flaws caused by the thin-wall elbow with small bending radius was higher. At present, there are few examples of success.In accordance with these proble ms, The internal-bulging process of thin-walled elbow with small bending radius by the polyurethane packing used as medium for conveying was adopted which based on the traditional cold-push bending process in this paper. The aluminum tube of LF2 M of ?50mm×1mm forming with 1 times relative(R=D R:the relative bending radius,D:outer diameter of the tube) bending radius have been investigated through experimental and combine with theoretical analysis and finite element numerical simulation. The main research content and results are as follows:The theoretical basis that the internal-bulging process is more beneficial to the forming has been obtained by analyzing the principle of forming process, and the basic performance parameters of tube were obtained by the uniaxial tensile at room temperature,and the value of enhancement coefficient is 423 MPa,the hardening exponent value is 0.35,and the plastic strain ratio is 0.82.The forming results of three kinds of tube blanking are compared. The results show that both compensation of two ends is more beneficial to the elbow formation which has a small bending radius. By means of applying the reverse method in the blank design of sheet forming, the finite element mode is established by ABAQUS.Based on the final forming elbow product size and in reverse push simulation to get the optimized size of the tube.The influence law of process parameters on wall thickness distribution and cross section distortion are studied on the forming quality. The results show that with internal pressure increasing, the wall thickness of the tube increase; Both inner wrinkling and cross section distortion become more serious with a too lower internal pressure, on the other hand,end wrinkling and the lack of forming on the elbow will be caused by a higher internal pressure; By properly increasing the friction coefficient can effectively reduce the outer wall thickness thinning and the forming results is the same to a higher internal pressure when the friction coefficient is too large; With die clearance value increasing, the cross section distortion increase,but the inner wall thickness reduces. By using orthogonal experiment method, the optimal combination of process parameters is when friction coefficient take 0.1、inner pressure take 15 Mpa and die clearance is 0.1mm.The polyurethane packing push bending experiments have been investigated. effect of reverse pressure、the feed rate of the spherical core shaft 、friction and lubrication on the forming results are mainly researched. It’s shown that 0.8MPa reverse pressure,60°feed rate of the spherical core shaft and MoS2 lubrication are the best, the maximum thinning rate below 7% and cross section distortion 3%.