Experimental Study On Unilateral Double Four-way Tube Extrusion-bulging Forming

After decades of development, the study of the forming mechanism and manufacturing process of the internal high-pressure forming has made significant progress. Pipe fittings products which formed by internal high-pressure bulging have lots of advantages such as higher specific strength, higher specific stiffness, less stress concentration, better material flow performance, more uniform wall thickness distribution, higher forming limit, when compared with traditional stamping and welding process.Air conditioning condenser pipe belongs to parallel multi--branch tubes. Using traditional welding process to processing parallel multi--branch tubes faces several problems, Such as curved surface transition is not smooth, and surface quality is low, and stress concentration is much, and welding seam quality is not stable, and the working life is not long. By using the method of internal pressure bulging forming air conditioning condenser pipe can improve the shortcomings. Unilateral double four-way tubes belongs to the part of the parallel multi--branch tube. It makes great importance to researching the forming process of parallel multi-branch tubes when researching the rules of forming the unilateral double four-way tubes by internal pressure bulging ways. This paper studied extrusion-bulging forming of unilateral double four-way tube by theoretical analysis and experiment research, for finding several technical parameters and providing references for finding out the process which can forming higher branch pipe.Primarily, make mechanical analysis on unilateral double four-way tube. Under the precondition of neglecting the through thickness stress, plasticity of unilateral double four-way tube is described, and the stress and strain state during the initial forming period and the middle forming period of outside main pipe, inner side pipe and forming area are analyzed. The internal pressure and the feeding force which the tubes need for forming experiments are estimated.Then, prepare for the forming test to build test platform. Comparison of a variety of mold design scheme, choose to use the jack axial loading scheme, and the design and manufacture of forming device. After building the feed force measuring and recording platform, select the feed force measuring device, and measuring and recording. Provide back pressure and the hydraulic system design of hydraulic cylinder use.Secondly, build the forming test apparatus to make preparation for forming experiments. After Comparing several forming apparatus designing program, choose the program that using jack to do axial loading. Then machine the apparatus. Next step is building the feeding force measuring and recording system. Designing the Hydraulic System and using hydrocylinder to provide the back pressure of the back pressure punch.Finally, do experimental study. Introduce common defects which appeared during forming unilateral double four-way tube and analyze the factors. After comparing bulging mediums ubricating grease and industrial plasticine, find that unlike the plasticine, the leakproofness of the ubricating grease is bad, and it’s not easy to control the quantity of the ubricating grease during forming stage. After analyzing the material flowing discipline of the formed tube, find that circumferential stress of the material near the branch pipe are higher than other material on the main pipe. The material flow curves point to the branch. And the curvatures of the flow curve near the branch pipe are larger than the farther. According to the measuring data, the thickest wall locates near the end face of the feeding punch boss, and the thinnest wall locates in the inner side fillet of the top of the branch pipe. Analyze the effects to forming of friction condition, heat treatment temperature, initial length of the tube, back pressure, preset distance of back pressure punch, and loading path from the standpoint of experiments. The experiments results show that, lubricating effect is better when forming. When heat treatment temperature is 450 degree centigrade, the branch height can reach a higher limit. Less long initial tube length bring higher branch height limit. The heavier back pressure brings the lower branch height. The influences of preset distance of back pressure punch to branch height, feeding distance, wall thickness are not significant. Loading path has a great effect on branch height. The feeding level increased, the branch height increased significantly.