重卡螺栓连接扭矩-预紧力关系影响因素分析

The Factors Influencing Torque-Preload Relationship of Bolted Joints in Heavy Truck

为了提高重卡装配载荷的一致性水平,开发了一种高精度螺栓装配连接试验台,可模拟不同材料及规格的螺栓装配过程,实现扭矩法、扭矩转角法和屈服点控制等拧紧策略,并实时检测螺栓扭矩和预紧力的变化。试验设计方法规划了6因素2水平螺栓拧紧试验方案,系统研究了6个因素(被连接件材料、螺栓等级、垫片等级、润滑状态、表面形貌及拧紧速度)对扭矩-预紧力关系(扭矩系数)的影响规律,并通过统计学理论分析了各因素的显著性和部分因子的交互作用。试验结果显示:表面粗糙度和被连接件材料为扭矩系数的显著影响因子,被连接件材料与螺栓等级、被连接件材料与润滑情况的交互作用对扭矩系数也有较大影响,扭矩系数随着重复拧紧次数的增加急剧减小,当拧紧次数超过4次时,扭矩系数趋于稳定。该研究优化了螺栓装配工艺,从而给出提高重型卡车装配预紧力一致性的合理建议。

To improve the load consistency in heavy truck assembly, a high-precision fastening instrument is developed to simulate bolted assemblies with various materials and sizes. This instrument enables to control the tightening process with torque, torque-turn, or torque-to-yield strategy. The tightening torque and the preloading force can be measured in real time. Adopting the design of experiment （DOE） method, a tightening tests program, characterized by six variables with two levels each, is designed to investigate the influence of six factors on the torque- preload relationship （nut factor） in bolted joints. These factors include joint materials, fastener class, gasket grade, lubrication, surface roughness, tightening speed and repeated tightening. The effects of these factors on the nut factor and their interactions are evaluated with statistic technique. The results show that the surface roughness and the joint materials are the major factors affecting the nut factor; the interactions between the joint materials and the gasket grade and the interactions between the joint materials and the lubrication also exert considerable influence. The nut factor deereases rapidly with the tightening times, and it remains stable after four tightenings.