Qualification of a Low Force FSW Process for Portable FSW to be Applied to Assembly of Large Structure

摘要

Friction Stir Welding (FSW) is now being implemented in production applications throughout the world. However, the scope of the FSW applications has been relatively limited. Many applications involve linear welds, for example, joining of extrusions. A smaller percentage of FSW applications involve multi-dimensional paths, but most of these applications are components that are small in size. The current production applications represent a relatively small portion of the total available market. This limited market penetration can be attributed to the high process forces which are required to perform FSW. These high forces tend to require use of high-cost, custom engineered equipment and fixturing solutions. To minimize welding cost, many of the existing applications fall into three categories; they are relatively simple to fixture, they are small components, or they have high production volumes. However, the potential market for friction stir welding is much larger. If lower force and/or simpler clamping techniques could be developed, FSW could be more widely implemented. This would allow manufacturers to utilize FSW in additional applications and allow them to realize the associated benefits, such as improved weld quality and repeatability, significantly lower distortion, and lower manufacturing costs. One such application area is for assembly of large complex structure. These applications have clamping and out-of-position welding requirements that would otherwise require equipment and fixturing for traditional FSW processes that are either too costly or not practical. This paper will describe development and qualification of a production-capable low force FSW process that will enable FSW to be implemented in the assembly of larger complex structures. First, a process development task was initiated with the objective of developing a nominal FSW process that would provide significant axial force reductions versus typical production processes in 5 mm 5083 Aluminum. Various FSW tool designs and a range in the critical FSW parameters were used to understand the significant controlling factors in reducing the force. The initial process development was also performed with consideration for the production variation (e.g. gaps, mismatch, offseam conditions, etc.) that could be expected to be experienced in production. Once a nominal process was developed, a series of additional experiments were performed to understand the stability of the process and the affect of the production variation, with the objective of confirming a robust and stable process and to establish production control limits for gap, off-seam, mismatch, and material thickness variation. Finally, repair welding studies were performed to qualify repair processes.