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Proceedings of the 7th ICFDM2006 International Conference on Frontiers of Design and Manufacturing June 19-22, 2006, Guangzhou, China THETHETHETHE SWAGINGSWAGINGSWAGINGSWAGING TECHNOLOGYTECHNOLOGYTECHNOLOGYTECHNOLOGY USEDUSEDUSEDUSED ININININ SHAFTSHAFTSHAFTSHAFT CLINCHINGCLINCHINGCLINCHINGCLINCHING ASSEMBLYASSEMBLYASSEMBLYASSEMBLY FORFORFORFOR AUTOMOTIVEAUTOMOTIVEAUTOMOTIVEAUTOMOTIVE HUBHUBHUBHUB BEARINGBEARINGBEARINGBEARING UNITUNITUNITUNIT Xiao Yunya 1, 2 , Zhou Zhixiong1and Lv Jianmin3 1College of Mechanical and Automotive Engineering, Hunan University, China 2Department of Electromechanical Engineering, Shaoguan University, China 3Shaoguan Southeast Bearing Co., Ltd.,China Abstract:Abstract:Abstract:Abstract: Recently, shaft end clinching is being adopted in the hub bearing unit assembly, which will raise as technological trend and gradually replace clamp nut in future. In a machine reconstructed from lathe, the sample of shaft end clinched hub unit is successfully manufactured by swaging technology with given parameters. Some tests confirm that the shaft end clinching hub unit has functions greater than the traditional hub unit with clamp nut. In the end, the future application and the further research direction of the swaging technology are discussed. KeyKeyKeyKey Words:Words:Words:Words:hub bearing unit, swaging, shaft clinching, assembly Hub unit bearings are widely being adopted for cars as they are lighter and stronger and easily to mounting. In the hub bearing unit assembly, the shaft clinching tightening replaces clamp nut and becomes technological trend. It is adopted in the mostly famous international companies of bearing manufacture. However, the deformation of the workpiece in clinching process is complex and difficult to be controlled. It brings phenomenons such as distortion of structure in the connecting area, shortage of supporting rigidity, inadequacy of strength, disqualification of rotational accuracy and lack of life. Thus leads the hub unit to invalidation easily. Up to now, the swaging technology used in shaft clinching for hub unit is not well mastered. With the support from some corporations, the pilot study of the swaging technology is completed. The problems from technics and equipment of clinching are solved, and the sample of swaged edge of hub bearing unit is manufactured successfully. 1. 1. 1. 1. IntroductionIntroductionIntroductionIntroduction Hub bearing unit is assembled from several components, which is pre-adjusted and lubricated for life. The unit was originally designed for use in cars and trucks to replace the traditional taper roller bearings, which is ready to install and free maintenance. With the hub bearing units not only the number of parts, but also the overall weight of the wheel arrangement is reduced. They also reduce assembly time because they do not require any special adjustment. Each unit is self-contained and ready to be bolted in place. This kind of bearing has come through three generations since it was designed by SKF in 1938. The 4th generation hub unit is now under development though it has not yet been mass-produced. Figure 1 illustrates the structure of hub bearing units 3. The 1st generation hub bearing unit is composed of two single-row bearings with their outer rings integrated, where grease is filled with seals. Compared with the 1st generation, the 2nd generation hub bearing unit is much more light weight and miniaturization ， which has integrated flange into the outer ring of 1st generation wheel bearing. The 3rd generation hub bearing unit is an advanced type of 2nd generation, which the outboard inner ring of the inner-ring rotation type hub unit and hub-shaft are integrated. In this generation hub unit, number of built-in high-performance sensor type has increased. 2 Figure.1 Hub unit bearings To further reduce the weight and size of the hub bearing unit and improve its reliability, NSK has recently developed a novel shaft end clinching hub unit. In the new hub design, the clamp nut which fastens the inner and outer rings together is replaced with a swaged edge. The swaging that used in shaft clinching is a technique that deforms the end part of hub shaft by swaging forging in which inboard of inner ring and proper shaft force by this deformation. Figure 2 shows examples of 3rd generation type clinched shaft hub units for a driven wheel and drive wheel respectively. In addition, this technique is also applicable to the inner ring rotation type 2nd generation hub units 2. driven wheeldrive wheel Figure2 Shaft clinching hub unit There are several advantages of the swaged hub unit in comparison to conventional retaining nut assemblies. The nut is saved in the swaged hub unit. The swaged hub unitssize is smaller and weight is less than the conventional retaining nut assemblies. The structure of the unit becomes compact. And the vehicle fuel consumption is reduced 1. The clamping force can be controlled accurately during the swaging process. Then the effect of error from parts is avoided. The fluctuation of pre-adjusted force is reduced greatly. As every hub unit gains the best pre-adjusted force after assembly, the life of bearing unit can be extended. The clinching tightening is an un-reversible assembly. The assembly is not failure though the vibration caused from running process is been loaded on the hub unit. The shaft clinching process is capable to perfectly comply with the problem of “loosening of tightening” that was impossible to be solved for the nut tightening. Then the shaft clinching improves the reliability and safety of the product greatly. This technology enables resource and energy of the manufacture of hub bearing unit to be saved. Due to predigest the assembly process, the cost of the whole vehicle is further reduced. 2. 2. 2. 2. ProcessProcessProcessProcess andandandand ExperimentExperimentExperimentExperiment The swaging process is an applied “rocking die forging”. Figure 3 illustrates the principle of the rocking die forging 3. On the center point of a workpiece, the axis OY of a conical upper die, which is titled by an angle from the centerline OX of the work, is turned about the OX axis. This gives rocking motion to the upper die, and the workpiece is continuously formed as the upper die continues the rocking rotation. The motions needed by the shaping principle can be achieved from a lathe. As Figure 4 showing, a rolling head is fixed on the end of the lathe shaft. The head is tilted an angle from the centerline of workpiece and self-rotating. The workpiece is fixed on the worktable restructured from the tow- board which is drived by hydraulic pressure. During the rolling process while the tilted rolling head is rotated on the bearing assembly, the shaft end of the flanged inner ring (workpiece) will receive a pressure provided from hydraulic-driving worktable and yield plastic deformation until it is firmly fixed to the smaller inner ring. Photo 1 shows the reconstructed machine. Figure3 Principle of the rocking die forging Figure4 The motions needed by the shaping principle The rolling head is the key unit device for the swaging experimentation. Figure 5 illustrates its structure. It is consisted of a roll-wheel, a bearing, a nut, 3 inner hexangular bolts and a joining- tray. The bearing is a double row angular contact ball bearing, actually a hub bearing unit, which supports both of the double-direction axial forces and the radial force. It ensures the roll-wheel to be self-revolving with the effect of friction from the contact area between the roll-wheel and the workpiece during the swaging process. The rolling head is fixed on the lathe shaft with the joining-tray which can adjust its gradient angle to meet the angle needed between the r Photo 1 The reconstructed machine for swaging In order to ensure the quality of the clinching assembly, the shape of the rolling head used in the experimentation should be optimized. It is not enough to only have purely axial grinding- pressure but also to keep the perfect radial grinding pressures in the process of the clinching assembly. The key is that the diameter of the ball-head of the rolling head should be larger than that of the inner hole of the bearing, and keep an appropriation touching angle. At the same time, the rolling head must be grinding with no slippage in the process of the swaging so as to avoid the hub unit rotation caused by the friction when touching each other, thus reducing the quality and the precision of the clinching assembly The swaging process is executed in the reconstructed lathe machine. Although the processing load is small as a result of the rolling head inclination angle , axial and radial loads are applied to the assembly during the swaging process. This can result in potential adverse effects that influence bearing performance, such as deformation or stiffness of the rolling elements and raceways. To eliminate or reduce these adverse effects, it thus becomes necessary to confirm the technical parameter through the swaging experimentation. After repetitious experiments on swaging, the parameter is confirmed at last. Under the integrated effect of the given parameters which includes pressure, loading speed and rotating speed, the sample of swaged end hub unit is successfully manufactured. Photo 2 shows the real product. Figure5 The rolling head Photo 2 The sample of swaged end hub unit 3. 3. 3. 3. ConclusionConclusionConclusionConclusion andandandand DiscussionDiscussionDiscussionDiscussion In order to examine the static strength of the swaged edge, a static strength test was carried into execution. A moment load was applied until the bearing failed. At the end, neither the swaged bearing nor the bearing assembled with a clamp nut failed at the fastening joint. Failure occurred in the flanged inner ring at the corner of the mating face with the smaller inner ring. The test determined that the swaged edge was not the weak point of the bearing. Photo 3 shows the failure of hub bearing unit. In addition, the sample of swaged hub bearing unit also passed the running endurance test under heavy load. It verified that the swaged edge is sufficient for fatigue strength. It is indicated on the result of the test that swaged hub bearing unit has functions greater than the traditional hub bearing unit with clamp nut. Although the feasibility of swaging used in shaft clinching for hub bearing unit assembly is confirmed on the experimentation and the sample of swaged end hub unit is manufactured successfully, but still there are many problems waiting to be solved before mass-produce. In order to master the swaging technology entirely, a general research should be demanded to perform. It includes analyzing the potential failure mode of swaging, simulating the plastic deformation course of the hub unit during the swaging process and optimizing the geometric shape of the shaft edge and roll-wheel. Based on these studies, many base theories of swaging can be constructed and some key technologies for swaging the hub unit can be mastered. Using these theories and key technologies, a novel high efficient and precise special swaging machine for shaft clinching hub units will be developed. Photo 3 The failure of hub bearing unit It is quite important to master the swaging technology for manufacture either the 2nd generation and 3rd generation hub units or the new generation hub unit. As a hub unit, it should includded bearing assemblies. These new generations of hub bearing unit are not exceptions. Figure 6 shows the structure of hub 4, hub 5 and hub 6 designed by SKF. Because the bearing assemblies are composed of outer ring, rolling balls, flanged shaft and inner ring, it is pivotal to adopt the swaging technology when assemble them into a unit, thus itssignificant to develop the swaging technology for the shaft clinching assembly. Hub4Hub5Hub6 Figure6 New generations of hub bearing unit It is discovered by analyzing the conFigureuration of the hub bearing unit in detail that the number of parts of the hub unit can be further reduced with the swaging technology used in shaft clinching. The shaft end of theflanged inner ring may be directly swaged to raceway, and the smaller inner ring can be saved, then the parts of the unit are decreased. Thus it will predigest the structure of the hub unit, improve the reliability, reduce the cost of manufacture. One reason of this design is that the tightening position is not the weak point of the hub unit, but the root of the flanged inner ring. The other is informed by the FEM analysis that small inner ring receives not