Mechanisms of Joint Formation in Ultrasonic Spot Welding Aluminium Automotive Sheet

Effect of reduced or zero pin length and anvil insulation on friction stir spot welding thin gauge 6111 automotive sheet

“…Refs. [14][15][16][17][18][19][20][21]. All spot welding was carried out under displacement control.…”

“…Refs. [13][14][15][16][17][18][19][20]. The tool had a removable 10u tapered triflat threaded pin with a diameter of 4 mm, made from MP159 material.…”

“…36 This tensile component reduces with sheet thickness as the degree of bending decreases. In general terms, the failure behaviours reported for FSSWs can be separated into three main modes, the first of which has only been reported with thicker gauges (.2 mm): 13,19,20 (i) mode I: shear failure following the join line between the two sheets in the plane of the sheet 19 (ii) mode II: mixed cleavage failure that initially starts by debonding, or cleavage, following the oxide debris delineating the original surfaces between the two sheets. This initiates at the edge of the shoulder contact area, where there is often only a partial bond, before turning upwards and tearing through to the top surface near the keyhole, where the top sheet is thinned by upward flow of the bottom sheet surface as the pin penetrates displacing material 19,20 (iii) mode III: nugget pull out where the interface does not fail and the top sheet tears around the edge of the shoulder contact area leaving the weld nugget attached to the bottom sheet.…”

“…In FSSW a high speed rotating tool, consisting of a shoulder with a probe/pin, is plunged into the upper sheet of a lap joint while an anvil supports the down force. The weld cycle typically lasts 1-4 s. [13][14][15][16][17][18][19][20] In FSSW the heated and softened material below the tool deforms plastically to very high strains, disrupting the oxide at the joint interface, so that a solid state bond can be formed between the upper and lower sheets. However, several problems remain with this technique.…”

“…22 A number of groups have investigated optimisation of the FSSW technique by studying the effect of process variables, such as the FSSW tool design, role of the shoulder plunge depth, rotation speed, plunge rate, weld hold time, probe profile and heat input. [14][15][16][17][18][19][20][21]23,24 The process has also been modelled by the finite element method (e.g. Ref.…”