Friction Bit Joining (FBJ) is a new technology that can be used to join dissimilar materials together. This ability makes it a good candidate for creating light weight structures for the automotive industry by combining lightweight materials such as aluminum to stronger materials like advanced high-strength steels. The automotive industry and many other industries have great interest in reducing structure weight to increase fuel efficiency. The purpose of this research is to make FBJ of GADP 1180 to AA 7085-T76 a production ready process by (1) better understanding the effects of process parameters, bit design and tool design on joint strength and reliability especially as they relate to different joint configurations; (2) determining if consecutive FBJ joints on a part will be additive in strength; (3) improving surface finish for better coating adhesion so that joints can be made to withstand extended corrosion testing; and (4) determining the failure modes and fatigue life of joint components at high and low load amplitudes. No universal parameter set for optimizing peak load for T-peel, cross tension, and lap-shear tension configurations were found. Due to the extreme load conditions of T-peel and the smaller margin of safety it is better to optimize for T-peel. However, strength and reliability were still improved across the board. Cutting features and tapered shanks were found to not always be necessary. Removing cutting features from the bit design increased peak weld cycle loads, but a stiffer machine can overcome this. Consecutive FBJ joints on a part are mostly additive in nature. When the weakest joint fails, its load is distributed to the remaining joints and will limit the peak load of the whole part. If all joints are "good" then the peak load will be approximately additive. Most of the stress is localized on the side of the bit opposite of the pulling direction. Failure modes in lap-shear tend to change from weld nugget pullouts in single weld specimens to aluminum material failures in multi-weld specimens. This is because of the added stiffness that additional material and welds provide to resist coupons bending and creating a peeling action. Surface finish was improved by development of a floating carbide cutting system which cut aluminum flash as it was generated around the head of the bit. A new internal drive design provided the ability to drive bits flush with the aluminum top layer if desired with minimal reductions in strength. Flush bits provided benefits in safety, cosmetics, and coating adhesion.

Friction Bit Joining (FBJ) is a new technology that can be used to join dissimilar materials together. This ability makes it a good candidate for creating lightweight structures for the automotive industry by combining lightweight materials such as aluminum to stronger materials like advanced high-strength steels. The automotive industry is putting significant effort into interest in reducing vehicle structure weight to increase fuel efficiency and reduce greenhouse gas emissions. Joining of dissimilar materials is a challenge they face in the light weighting the body of the vehicle. The purpose of the current research is to employ FBJ in the joining of a very challenging material combination: GA DP 1180 to AA 7085-T71. In accomplishing this purpose, the goal is to move FBJ toward a more production ready process by better understanding the effects of tooling, bit design, and process parameters on joint strength and reliability as they relate to load profiles captured during the joining process. It was found that the joint strength variation was influenced strongly by the hardness and the geometric consistency of the consumable bits. Bit hardness below 45 HRC led to joint strength that was less than the required specification (5kN in lap shear tension, and 1.5kN in cross-tension and T-peel). Variation in bit height and diameter also led to excessive scatter in joint strength values, where it was not possible to meet the standard for 10 consecutive specimens (for each of the three tests). Implementation of high-speed data acquisition (1000Hz) enabled the capture of load curve profiles generated during FBJ. Load curve profiles were correlated with destructive testing results to discover the impact of process parameter combinations. Analysis of load curve profiles led to improvements in parameter selections of spindle speeds (revolutions per minute) and spindle feed-rates (inches per minute). Process parameters of 5000 RPM and 15 IPM reduced variation in load-curve profiles and destructive testing. Satisfactory joint strength was achieved in lap shear tension, cross-tension, and T-peel testing configurations with values of 10.1 kN, 4.1 kN, and 1.8 kN, respectively. The presence of wet adhesive had little impact on joint performance. Finally, the analysis of a load-curve profiles resulted in a criterion that allowed for distinguishing "good" welds from "bad" ones, where a threshold load of 6kN, or higher, during the dwell phase of welding was required in order to meet joint strength standards.