先进高强钢板成形中摩擦行为及拉毛损伤机理研究

The strength upgrade of advanced high strength steel (AHSS) requires higher forming pressure, which results in surface galling defects in vehicle structural parts made by stretch bending of AHSS. Till now, the study on mechanisms of their friction behavior and galling damage confined to the traditional pure friction device, which neglected the tensile deformation in the forming process. To this end, the project uses a self-developed Tribo-tester that can synchronously implement friction sliding and tensile deformation in sliding between die and sheet strip. The experiments will be carried out with AHSS of different strength and different coating in order to study the tribological behavior and surface galling damage, which will reveal the influence of forming parameters on the dynamic behavior of friction for AHSS in sheet metal forming and galling damage under the coupling condition. On that basis, the friction surface morphology and wear debris morphology, roughness and phase composition will be analyzed to explore the mechanism of AHSS surface galling under condition of friction coupling deformation; Based on the formation of and evolution of friction induced hardened layer, the dynamic evolution mechanism of surface galling damage for AHSS forming will be investigated. The galling characterization matrix between different surface modification and different kinds of AHSS will be built in order to understand the influencing mechanism of the die-surface modified layer on the surface galling in AHSS forming. Then optimization matching of die and process will be indentified for each kind of AHSS and verified through actual U-shape stamping by stretch bending.

板材强度上升带来的高成形压力，导致通过拉伸弯曲冲压的先进高强钢汽车结构件成形中易产生表面拉毛缺陷。对其摩擦行为和拉毛损伤机理的研究，较多还局限于传统纯摩擦装置，忽略了成形中的拉伸变形。 为此，项目采用自行研制的摩擦耦合拉伸变形试验机，模拟先进高强钢板与模具对偶之间滑动摩擦的同时施加拉伸变形，研究不同强度和镀层先进高强钢板与模具对偶之间的摩擦行为和拉毛损伤行为，揭示耦合条件下各成形因素对摩擦过程动态摩擦行为和拉毛损伤的影响规律；通过表面形貌及磨屑形貌，粗糙度和相组成结构分析，探讨先进高强钢成形过程摩擦对偶表面拉毛萌生机制；基于摩擦表面影响层硬化的形成和演变与摩擦学性能的响应关系，明晰塑性变形下先进高强钢成形过程摩擦对偶表面拉毛损伤的动态演化机制；构建不同表面改性层模具与不同类型先进高强钢表面拉毛损伤表征矩阵，分析并解释模具表面改性层对拉毛的影响机制，输出可抑制拉毛的优化匹配并以实际冲压验证。

板材强度上升带来的高成形压力，导致通过拉伸弯曲冲压的先进高强钢汽车结构件成形中易产生表面拉毛缺陷。对其摩擦行为和拉毛损伤机理的研究，较多还局限于传统纯摩擦装置，忽略了成形中的拉伸变形。为此，采用自行研制的摩擦耦合拉伸变形试验机，模拟先进高强钢板与模具对偶之间滑动摩擦的同时施加拉伸变形，研究不同强度和镀层先进高强钢板与模具对偶之间的摩擦行为和拉毛损伤行为，揭示耦合条件下各成形因素对摩擦过程动态摩擦行为和拉毛损伤的影响规律。. 通过表面形貌及磨屑形貌，粗糙度和相组成结构分析，弄清了先进高强钢成形过程摩擦对偶表面拉毛萌生机制，将拉毛萌生划分定义为三个阶段：第一阶段，首先在预紧作用下板材表面锌层开裂，板材表面的微凸体在较短的滑动距离内被磨平；第二阶段，板材表面开裂的锌层剥落脱离转移至模具表面，在模具表面形成固体润滑薄膜；第三阶段，锌层继续脱落转移，在反复的摩擦挤压作用下积聚长大，在模具表面形成黏结瘤。. 基于摩擦表面影响层硬化的形成和演变与摩擦学性能的响应关系，明晰塑性变形下先进高强钢成形过程摩擦对偶表面拉毛损伤的动态演化机制，提出了一种拉毛损伤的定量判断标准及相应测试方法，根据板材表面拉毛损伤的几何特征，选择粗糙度变化量ΔRy作为拉毛损伤的定量评价参数，并通过表面形貌的微观分析验证了该方法的可靠性。. 采用不同表面改性层模具与不同类型先进高强钢表面拉毛损伤表征，分析模具表面改性层对拉毛的影响机制并以实际冲压验证，研究表明采用金属碳化物扩散覆层TD处理的模具表面具有最优抗拉毛性能。可为冲压成形中模具拉毛现象提供技术积累，为改善模具表面损伤提供理论依据。