Research On Flanging Process And Cold Expansion Strengthening Performance Of Small-diameter Split Sleeve

At present,in the cold expansion technology,split sleeve cold expansion is more advanced,and its application is more widely in the field of aviation.Our current military and civil aircraft’s fastening holes are required to be strengthened,the split sleeve cold expansion has a significant strengthening effect on these fastening holes.Therefore,split sleeve is an important part of this technology.After years of exploration and research,the manufacture of split sleeve has become increasingly in foreign country.At present,some researchs have been done on the preparation technology of split sleeve,however there is a big gap when compared with foreign mature technology.A method with combination of experimental and finite element is adopted to research on flanging process and cold expansion strengthening performance of split sleeves.The main work and achievements were as follows:1.The flanging tool for small diameter straight split sleeve was redesigned based on top principle,the dynamic process of the tool is analyzed by ADAMS to research its spindle and its bearing centroid shift and their own lives,and the feasibility of the new tool for flanging was ultimately verified.Using the new flanging tool and flange-specific molds to flange different sizes of split sleeves,the flanging part were done well and the flanging sides were in good condition,so the new tool is capable of flanging work with different sizes of split sleeves.2.The flanging process of the split sleeve based on the new tool was simulated by ABAQUS,and the flanging angle,the flanging length and the derived flanging coefficient were used to study the flanging process of the split sleeve instead of the original single parameter--fillet radius of external mold,the diameter identification procedure by the VS2010 was compiled to obtain the inner and outer diameter values of the split sleeve.And the following conclusions were obtained from the simulation results,that is,the stress on the inner and outer surfaces of the split sleeve’s flanging part were larger,and the stress on the upper edge was the largest.All sizes of split sleeve flanging angle selection of 45 degrees were more appropriate,and the flanging length had to be increased with the split sleeve size increasing.Based on the results of finite element analysis,the flanging die was redesigned,and the split sleeve was flanged.After flanging,the flanged part of the split sleeve was well bonded with the outer die,and the quality of the split sleeve flanging part was better.3.A new three-dimensional finite element analysis model was established for the cold expansion strengthening experiment,and the model adjusted the structure of the mandrel bar and plate.Theresults of finite element analysis showed that the distribution of stress and strain around the hole in the plate were the same as that described in the literature.Two sets of orthogonal analysis were carried out for the cold expansion strengthening process,the results showed that the results of cold expansion strengthening of different sizes of split sleeves were the same,that is,the order of influence factors of cold expansion strengthening was bush thickness,bushing hardness and side width;extrusion volume,hole chamfering and extrusion speed.The residual stress around the hole after extrusion was analyzed,and it could be seen that the strengthening effect of the extrusion experiment was obvious.4.According to the results of finite element analysis,the structure of mandrel was modified,and the different cold expansion experiments were carried out by different sizes of self-prepared split sleeves.It was found that the compressive force of the mandrel increased and then decreased with time and increased with the increase of relative squeezing amount.The extruded pore walls were smooth and the material of the extrusion face was very small,which proved that the split sleeve played a significant role in protecting the hole wall during extrusion.Split sleeve extruded plastic deformation occurred,it was no longer usable.The changes of microstructure and micro hardness around the hole after cold extrusion were analyzed,and the grains around the pores were elongated and the micro hardness increased obviously.This showed that the strengthening effect of the cold extrusion experiment on the hole of the plate played an important role,and the result of the finite element analysis was accurate.