The formation of sub-surface defects during friction stir welding has limited the adoption of the process in high volume production. A potential exists to eliminate/reduce the need for costly post weld inspection of such defects through the development of an in-process defect detection method based on a measured process output. The current state of in-process defect detection consists primarily of applying “black box” methods of correlating process outputs to defect occurrence without a fundamental physical understanding of what is producing the change in the output. This approach constrains the application of such methods when altering any aspect of the friction stir welding process. The current study seeks to provide a fundamental physical explanation as to what is driving the oscillation of friction stir welding process forces at the tool rotational frequency, as well as what is occurring when the tool interacts with defects and the oscillatory process forces are altered. A novel understanding was enabled through the synchronization of force measurements with angular position measurements of tool features. The results suggest that the eccentric motion of the tool and/or the rotation of a slanted shoulder surface are the primary drivers of process force oscillations. A fundamental explanation of the interaction between features on the tool probe and defective volumes has been proposed. The physical understanding helps to explain how altering the process will alter the force transients on which the detection method is based, which will enable a more robust and transferable method.

搅拌摩擦焊接过程中表面缺陷的形成限制了该工艺在大批量生产中的采用。通过开发基于测量的过程输出的过程中缺陷检测方法，存在消除/减少对此类缺陷进行昂贵的焊后检查的潜力。过程中缺陷检测的当前状态主要包括应用“黑匣子”方法将过程输出与缺陷发生相关联，而没有对造成输出变化的基本物理理解。当改变搅拌摩擦焊接过程的任何方面时，这种方法限制了这种方法的应用。当前的研究试图提供基本的物理解释，以解释在工具旋转频率下驱动搅拌摩擦焊接过程力振荡的原因，以及当工具与缺陷相互作用并且改变振荡过程力时发生的现象。通过使力测量与工具特征的角位置测量同步，实现了新颖的理解。结果表明，工具的偏心运动和/或倾斜的肩部表面的旋转是过程力振荡的主要驱动力。已经提出了对工具探针上的特征与缺陷体积之间的相互作用的基本解释。物理上的理解有助于解释改变过程将如何改变检测方法所基于的力瞬变，