Research On New Process And Equipment For Precision Riveting And Assembly Of Automotive Hub Bearing Units

As key components of automobiles, the hub bearing units directly influences theirsafety, comfortability, economy, environmental and energy saving and so on. A hubbearing unit consists of multiple parts and its working clearance formed after theassembly is one of the key factors which influence the performance of the product. Thedevelopment trend of assembly technology of hub bearing units is to rivet the shaft byrotary forging technology. During riveting assembly of the hub bearing unit, its stressand deformation condition are complicated and manufacturing tolerance of each parthas a great influence on the working clearance formed after the assembly. The rivetingassembly processe and equipment adopted by domestic enterprises are relativelybackward, which results in that hub bearing units manufactured by riveting assemblyare difficult to meet usage requirements such as service life of over150000km.Therefore, this paper takes the3rd generation hub bearing unit DAC2F10as anexample and deeply studies the contents including riveting assembly process principle,stress and deformation rules of workpiece, riveting assembly equipent. It proposes andfounds a new precision riveting assembly process based on the volume-varying method.The new precision riveting assembly special equipment is developed. The experimentsare carried out with the new special equipment and the riveting assembly processparameters are optimized. It realizes automatic and high-precision riveting assembly ofthe aotomobile hub bearing unit.The main contents are as follows:(1) The structure and development of hub bearing unit are analyzed and its assemblymethods are introduced. The deformation theory and mechanism of rotary forgingtechnology are discussed with emphasis. Combined with the research status of rivetingassembly process and equipment of the hub bearing unit at home and abroad, the studycontents and route are indentified.(2) The rotary forging deformation priciple and process priciple with applicaiton tothe riveting assembly of hub bearing unit are analyzed. The contact area is studiedwhen the workpieces with different shapes such as ring and cylinder are forged andrelavent mathmatic model is built. The rotary forging torque mathmatic model forriveting assembly of hub bearing unit is also built. The workpiece deformationmechanism during riveting assembly is revealed.(3) The stucture, material and assembly technology requirements of the hub bearing unit are analyzed. A horizontal rotary forging experimental equipment for rivetingassembly is development and compared with the vertical one. The test system for axialrotary forgine force is developed. The performance test systems for the hub bearingunit are built. The performance of the hub bearing unit manufactured by rivetingassembly and velocity impulse during riveting assembly are premarily studied byrotary forging reviting assembly experiments. The axial rotary forging forces in thehorizontal and vertical assembly are compared. The problems existing in availableriveting assembly equipments are pointed out and some possible improving directionsare proposed.(4) The working clearance formation of the hub bearing unit is analyzed. It is foundout the rational negative working clearance is about0~-0.02mm. The reasons whydomestic enterprises cannot realize the negative clearance assembly control of the hubbearing unit are figured out. The influences of the assembly process, partmanufacturing tolerance, process parameter and control method of riveting assemblyon the working clearance of the hub bearing unit are studied. The reasons why thetime-and distance-fixed methods cannot realize the negative clearance assemblycontrol of the hub bearing unit are revealed. The assembly strategy is proposed torealize the negative clearance assembly control of the hub bearing unit. The newcontrol strategy is based on the volume-varying method. Its implementation process isstudied according to the established mathmatic models. The test method for thenegative working clearance of the hub bearing unit is discussed. The releventmathmatic model for the negative working clearance obtained by the moment stiffnessis built.(5) The movement and functional requirements of the new riveting assembly specialmachine tool for the automobile hub bearing unit are analyzed. The overall designscheme is proposed according to the requirement of negative clearance assembly onthe equipment. The power unit, magnetic attachment and precision and adjustablehydraulic working table of the machine tool are designed in detail on the basis of thetheoretical analysis. The elctrical and hydraulic control systems are designed. Thecontrol system software for automatic riveting assembly is programmed with thecontrol algorithm based on CMAC network. The prototype machine tool is developedand its performance is tested. This prototype can realize the real-time measurement andfeedback control during the riveting assembly of the hub bearing unit.(6) The experiments are carried out with the new riveting assembly special machinetool. The inclination angle of riveting head, feeding speed and stop riveting position of the new riveting assembly process based on volume-varying method are optimized.The shapes of riveting head and workpiece are optimized according to the requirementof the new riveting assembly process based on volume-varying method. Theexperiments verify the new riveting assembly process based on volume-varyingmethod is available and capable of realizing the negative clearance assembly of thehub bearing unit. This technology improves the quality of products and has beenapplied successfully in the enterprise.