Research On The Manufacture Of Small-diameter Straight Split Sleeve

Split sleeve cold expansion can significantly improve the fatigue life of structure fastening holesfor various materials. With high interference, simplify operation and high quality strengthening effect,it has been widely used in aircraft fastener holes strengthening and achieved good results. Split sleeveis the important part of split sleeve cold expansion, ensures the strengthening effect. But the researchon split sleeve is still scarce, especially for small-diameter split sleeve. The basic need of it indomestic market depends on imports to meet. This limits the promotion and development of the splitsleeve cold expansion technology in China. Therefore, with straight split sleeve as the object, thispaper uses experimental analysis, theoretical research and finite element numerical simulation toaccomplish the research on manufacture of small-diameter straight split sleeve. The main researchwork and achievements are as follows:1. The impact on the curvature radius of the straight sleeve made by two-axle bending atdifferent processing parameters has been analyzed through single-factor experiment. It has beenproved that the smallest forming radius of curvature is decided by the diameter of the rigid axle. Andthe increasing of the elastic wheel hardness and the feed of the rigid axle, the releasing of theworkpiece width can change the forming curvature radius of straight sleeve at some degree. But theinfluence of the outer-diameter of elastic wheel is not obvious.2. The common problems and the reasons which cause these problems are analyzed by comparingthe result of two-axle roll-bending experiment and the theory of roll bending technology. Straightedge and skew are the most common problem in the process of manufacturing small-diameter splitsleeve by two-axle roll-bending. For solving the problem that the length of the edge is difficult tomeasure, the image recognition system on split sleeve is developed. This system can identify thecurvature radius, the length of straight edge and its ratio in sleeve accurately and conveniently. So it ishelpful to improve the accuracy and speed of measurement on the length of the straight edge.3. A theoretical study on the straight edge of split sleeve has been done, the analysis of the planestress; and its analytical model have been completed. After analyzing the process of the straight sleeveforming, it is found that the straight edge occurs in both the initial and end stage. It also proves thelength of straight edge mainly relates to the elastic wheel hardness, the size of elastic wheel and therigid axle, the rigid-axle feed and the workpiece thickness.4. Based on the analytical model of the straight-edge length in two-axle roll-bending, the effects of processing parameters on the length of straight edge were discussed. The result shows thatincreasing the elastic wheel hardness and the rigid axle feed, reducing the thickness of elastic wheeland the diameter of rigid axle can cut down the length of straight edge effectively. Considering thestress and transformation of straight sleeve in the process of the split sleeve cold expansion, it is betterthat the length of straight edge is shorter than that of landing edge.5. Based on the dynamic explicit algorithm of ABAQUS software, the three-dimensional finiteelement model of metal forming on two-axle roll-bending was build up. And the post-processing ofsimulation results about the forming curvature radius was successful completed by nonlinear fittingbased on MATLAB. Simulation value is smaller than the experimental value about15%to20%.Theoretical and experimental verification shows that the model is able to meet the requirements foranalysis.6. Based on the three-dimensional finite element model of metal forming on two-axleroll-bending, the effects of processing parameters on the forming curvature radius were discussedsystematically. By changing the elastic wheel hardness and the size of elastic wheel and workpice, theforming curvature radius can be adjusted, but it can’t affect the smallest forming curvature radiusobviously. In actual machining process of the small-diameter split sleeve, the elastic wheel shouldselect the hardness of about95A. The diameter of rigid axle should be smaller than that of straightsleeve; the thickness of the elastic wheel should be fit, as usual select around24mm and on this basis,increasing the wheel size appropriately can be beneficial to small-diameter split sleeve preparation. Atthe same time, it is better to keep the width radio of elastic wheel and workpiece up1.5times.