Research On The Manufacture And Property Of Small-diameter Split Sleeve

Split sleeve cold expansion can significantly improve the fatigue life of fastening holes, and has been widely used in aerospace, aviation, and railway. Split sleeve is an important part of split sleeve cold expansion, with high preparation requires and great difficulty in making. The manufacture technology of split sleeve is quite mature in USA, while this research in our country is still scarce, especially for small-diameter split sleeve. Therefore, this paper researches the manufacture and property of small-diameter split sleeve, based on two-axle bending technique, using experimental analysis and finite element numerical simulation. The main work and achievements are as follows:1.The improved design on rigid-axle fixture has been completed, then dynamics simulation of this fixture through ADAMS, verified the stability of holding and feasibility of operation. This fixture can be used in bending split sleeve in the range of 20mm~10mm. The effects of the rigid axle diameter, elastic wheel external diameter and work-piece width on the limiting diameter has been analyzed through two-axle bending experiments, by the improved fixture. It has been proved that the limiting diameter can be smaller with the smaller rigid axle diameter. The limiting diameter decreases with smaller elastic wheel external diameter and work-piece width, when rigid axle diameter is less than 8mm. While this impact is not obvious by using diameter over 8mm of rigid axle.2.A finite element model of flanging process of small-diameter split sleeve has been built, and flanging radius was obtained by an MATLAB image identification program. The results showed that the flanging cannot fit with the die fillet completely, especially for too small or too large flanging radius. Stress, strain distribution and force of bearing have been obtained through simulation. The results showed that the stress increases with the increase of flanging radius. The flanging shape is better when flanging radius equal to 1mm and 5mm, and it is decided by the external deform of flanging. Flanging wrinkle appears when flanging radius over 2mm, and deform of flanging is different. Force of bearing increases with the increase of flanging radius. The flanging experiments were accomplished according to the simulation results, and good flanging shape is obtained.3.Experiments of cold expansion with small-diameter split sleeve have been done, the mandrel and special fixture also been designed and manufactured. It indicated that extrusion force increases firstly and then decreases by the movement of mandrel, and increases with bigger extrusion. a ridge appears on the hole by split sleeve cold expansion, split sleeve deformed after cold expansion, and cannot be used again. Then measurements of residual stress and micro-hardness around the cold-worked hole have been taken. There is a residual compressive stress field around the cold-worked hole, and it increases with bigger extrusion. Increasing micro-hardness had been found around the cold-worked hole, and it becomes harder with bigger extrusion. Test results indicated the strengthening effect of cold extrusion, and small-diameter split sleeve plays a good performance.4.A finite element model of cold expansion with small-diameter split sleeve has been built. The simulation results showed that stress on the sample surface distributes symmetrically, and the maximum stress is in the middle along the thickness direction. Stress and strain of split sleeve mainly distribute on the contact part between split sleeve and hole wall, and the maximum plastic strain is mainly in flanging and split. This model was verified by residual stress test and literature. The stress distribution, extrusion force and deform of split sleeve have been analyzed by this model, under different cold extrusion method, relative extrusion, split width, thickness of split sleeve and hole diameter. It proved that split sleeve effect is unavoidable by split sleeve cold extrusion, but it makes extrusion force more uniform. Residual compressive stress and its distribution range increase with bigger relative extrusion, split sleeve effect also becomes more obvious. Split sleeve effect enhances when split width increased, so the width should not exceed 3mm. Thicker split sleeve may diminish radial stress a little, and weaken the deform of split sleeve. Residual stress increases with a bigger hole, extrusion force becomes larger, and split sleeve deforms greatly when hole diameter increased.