考虑可成形性的先进高强钢板表面损伤演化规律实验研究

The increasing use of high strength steels in a variety of mechanical engineering applications has illuminated problems associated with surface galling in sheet metal forming operations. Surface galling is an important factor limiting the part surface quality, the tool life and the number of processing steps. The surface galling behavior of sheet steel is changed with increasing of the tensile strength, and these approaches obtained only based on tribology method can't effectively solve the surface galling in sheet forming. Therefore, this proposal introduces sheet metal formability as a constraint condition, and investigates the surface galling behavior of advanced high strength steel (AHSS) in forming based on the formability. This proposal mainly focuses on the surface galling mechanics of AHSS with tensile strength of more than 600MPa. A surface galling test device is developed to simulate effectively process parameters and tools condition in AHSS forming based on the formability. Furthermore, the surface galling evolution behavior of the dual phase (DP) steel and the quenching-partitioning (QP) steel with different tensile strength is revealed, and the effect of process parameters on the surface galling behavior of the AHSS is found out by means of experimental method. In addition,the effect of tools factors on the surface galling of the AHSS is also studied in this proposal, and a parameter window which can express reasonable matching among the AHSS, tools condition and production scale is established in order to eliminate surface defect of stamped part in practical engineering. The approaches in this proposal can be use in design of process parameters and selection of tools materials for the AHSS forming, and will promote application of the domestic AHSS in industry.

由于高的成形压边力，导致先进高强钢零件易于出现表面损伤缺陷，是高强钢板成形应用上的难题。随着钢板强度提高，成形接触界面条件发生了根本性变化，已有的表面损伤控制方法不再适用；同时传统摩擦学方法还不能有效地解决此类成形问题。为此，本项目引入成形性这一约束条件，探究强度600MPa以上双相钢板和QP钢板成形表面损伤演化规律。构建用于成形条件下板料表面损伤试验装置，实现考虑成形性条件下的工艺参数和模具条件的有效物理模拟。采用实验手段揭示先进高强钢成形件表面损伤演化机制，查明成形工艺因素对上述钢板表面损伤演化的影响规律，为其工艺设计提供依据；通过开展模具因素对成形表面损伤的影响，建立抑制先进高强钢板成形表面损伤的模具参数匹配窗口，获取适用于双相钢和QP钢的模具表面参数，实现满足成形性条件下零件表面损伤有效控制。该研究将为提高先进高强钢成形表面质量提供技术手段，并促进更高强度等级高强钢板在工程上应用。

先进高强钢具有更高的强度，成形过程中板料-模具界面产生更高的接触压力和温升，尤其是在凹模圆角区域附近，这将导致冲压件表面损伤和模具磨损问题。该问题是当前工程面临的难题，制约着先进高强钢在汽车结构件上应用。揭示冲压成形条件下板料-模具界面摩擦磨损行为，是需要解决的主要科学问题。.针对目前先进高强钢（DP钢和QP钢）冲压过程磨损问题，本项目开展了面向冲压成形条件下滑动摩擦磨损模拟装置研制、冷成形热力耦合数值仿真建模、先进高强钢表面损伤演变规律和先进高强钢磨损预测方法研究。.在综合分析先进高强钢冲压过程中滑动摩擦类型基础上，研制出磨损物理模拟的试验装置，实现了冲压过程钢板表面损伤和模具磨损实验室环境研究。通过引入应变率相关的本构方程，建立先进高强钢冷弯曲成形过程热力耦合数值仿真模型，实现了凹模-板料界面的接触压力和温度场数值计算，显著提高了高速冲压条件下凹模-板料界面的接触压力和温度的预测精度；基于此模型，揭示了板料强度和工艺条件对冷冲压凹模-板料界面的接触压力和温度的影响规律。基于弯曲试验的材料抗表面损伤结果表明：相同工艺条件下，钢板强度越高，在成形过程中越容易产生表面划伤；而对具有相变诱发塑性材料，相变提高了界面接触压力和界面温升提高，引起摩擦系数和试样表面粗糙度升高。对于工艺参数而言，相同材料强度条件下，相对圆角半径越小、压边力越大、拉伸速度越快、润滑条件越差时，板料表面划伤越严重。先进高强钢裸板弯曲实验表明：对于TD热处理改性后的模具材料表现出更优的抗磨损性能；模具磨损形貌分析显示：弯曲成形模具磨损主要集中在凹模圆角0度到15度区域。给出了基于数值仿真的凹模圆角区摩擦功耗散的求解方法，联合模拟实验获得极限冲压次数，建立了基于摩擦功的模具磨损预测方法，实现了先进高强钢实际冲压模具磨损定量评估。.上述研究成果可以系统认知先进高强钢冲压成形磨损演化行为，指导我国汽车用钢冲压件表面质量控制、成形工艺设计与模具选材。