High Speed Friction Stir Spot Welding: A New Approach to Spot Joining of Ultra High Strength Steel

该奖项的研究目的是验证超高强度钢搅拌摩擦点焊的接头结合面积主要由界面压力、界面温度和焊接时间决定的假设。将考虑在每分钟5，000至10，000转范围内的焊接速度，并且焊接过程将被限制为8千牛顿的最大垂直焊接载荷，目标是实现所需水平的接头强度。一种新的方法来模拟摩擦搅拌点焊将被用于拉格朗日有限元框架内，其中的联合界面将表示虚拟和联合接触压力，温度和焊接时间之间的拟议关系将被用来估计债券面积。在模型中将使用Archard定律来估计刀具磨损。一个实验项目将测量接头强度和工具磨损随时间的变化，而接头的微观结构评估将提供洞察工具磨损对粘结机制的影响。如果成功，该项目将使搅拌摩擦点焊在许多工业环境中用于连接超高强度钢板。建模方法将提供更多的了解工具设计和工艺条件对接头强度和工具寿命的作用。找到超高强度钢的点连接解决方案非常重要，因为这些合金有可能使汽车车架更轻、更硬，从而提高车辆燃油经济性并减少碳排放。超高强度钢的广泛应用目前受到传统电阻点焊产生的脆性焊缝显微组织的限制。

The research objective of this award is to test the hypothesis that joint bond area in friction stir spot welding of ultra-high strength steel is determined largely by interface pressure, interface temperature, and weld time. Welding speeds in the range of 5,000 to 10,000 revolutions per minute will be considered, and the welding process will be constrained to a maximum vertical welding load of eight kilonewtons, with a goal of achieving a desired level of joint strength. A novel approach to modeling friction stir spot welding will be used within a Lagrangian finite element framework, where the joint interface will be represented virtually and where a proposed relationship between joint contact pressures, temperatures, and weld time will be used to estimate bond area. Archard's law will be used within the model to estimate tool wear. An experimental program will measure joint strength and tool wear over time, while microstructural evaluation of the joints will provide insight into the effect of tool wear on bonding mechanisms.If successful, this project will enable the use of friction stir spot welding for joining ultra-high strength steel sheet in many industrial settings. The modeling approach will provide increased understanding of the role of tool design and process conditions on joint strength and tool life. Finding a solution to spot joining of ultra-high strength steels is important because these alloys have the potential to make car frames lighter and stiffer, improving vehicle fuel economy and reducing carbon emissions. The widespread use of ultra-high strength steel is currently limited by brittle weld microstructures produced by traditional resistance spot welding.