Friction Flash to Tube (F2T) is an innovative friction based manufacturing technique to produce seamless tubes based on open die forging, invented at Aalto University. These tubes can be produced economically in small sizes and batches, envisaging applications of high value materials that are not available in the market. The objective of this Master thesis was to develop the experimental condition of F2T as well as the proper parameters in F2T by approaching Taguchi method. The pre-defined parameters to investigate in Taguchi method were established as forging force, tool rotation and initial transient plunging depth and the investigating of geometrical and metallurgical characteristics were done. Cold rolled high strength and low alloy structural steel S355 is the material used in this research work. The parameters of the F2T process were developed based on design of experiments, with geometrical and hardness properties as performance parameters. The optimized conditions and parameters were applied to produce tubes for extensive evalua-tion of the mechanical and metallurgical material properties.
The F2T process has specific components and control demands that cannot be met by the existing manufacturing systems. This challenge was overcome by developing one first version of a dedicated system based on an existent Friction Stir Welding equipment. One additional challenge was to produce tubes longer than 40 mm because of buckling. The buckling was prevented by implementing a lateral support system constraining the consumable rod during the initial transient plunging period. The test specimens for extensive mechanical test and metallurgical analysis were extracted from tubes produced with 80 mm in length. These longer tubes were manufactured using the support system to prevent buckling. The results on tensile test, flattening test and flare test of F2T tube reveal that the mechanical properties of produced tubes are as good as tube of similar material produced by another manufacturing technique.
The temperature during the application of the F2T process was monitored with thermo-couples. The mechanical properties of produced tubes were evaluated by hardness meas-urement of cross and longitudinal sections. Tensile test were applied to sub-sections of wall of the tubes, and flare and flattening test to the whole tubes. The metallurgical analysis encompasses optical microscopic analysis, and SEM/EBSD with grain size evaluation. The research work demonstrate the feasibility of producing seamless tubes by F2T in structural steel. A correct design of a dedicated system to prevent the buckling, enables to produce long tubes
