Solid-state welding technologies


The study mainly concerns the solid state welding technique, called Friction Stir Welding (FSW), for the joining of similar and dissimilar metal sheets obtained either by a numerical control center  or by a robotic system. This process is based on friction heating and mixing carried out by means of a rotating tool around its own axis, inserted between the edges of the sheets to be welded. The combined effect of rotation and translation of the tool along the welding line allows the obtaining of the joint. The material flow is characterized by an intense plastic deformation at high temperature (always lower than the value of the melting temperature) and by the consequent generation of a very complex microstructure which significantly affects the properties of the joint and depends on the geometry of the tool and the process parameters used.
The approach followed in the study of the FSW is based on the analysis of the relationship between the process parameters (such as the geometry and tilt angle, the tool sinking, the rotational and welding speeds), and the properties of the welded joint, such as mechanical strength and ductility, in order to identify the optimal welding conditions. In this framework, both experimental techniques and numerical simulation methods were used with the aim of developing prediction models of the mechanical properties of the welded joint.
The research activities carried out in the field of the FSW concerned the following aspects:

  • Tool configuration:
    • With pin
    • Without pin (pinless)
  • Machine:
    • Work center
    • Industrial robot
  • Welded material:
    • Magnesium alloys
    • Aluminum alloys
  • ●    Joint configuration:
    • Similar joint (same alloy)
    • Dissimilar joint (different alloys)
    • With sheets characterised by equal thickness
    • With sheets characterised by different thicknesses
    • Double side friction stir welded joint
    • Joint obtained with sheets of variable thickness along the welding line
  • Control strategies based on:
    • constant rotational speed during welding stage
    • in-process control of the vertical force applied by the tool
    • in-process tool rotational speed adjustment aiming at maintaining the vertical tool force constant during welding stage
    • in-process tool rotational speed adjustment in order to keep constant the heat input to the joint

Tool used in friction stir welding and friction stir welding process

Pin and pinless tool configurations

Cold stamped parts obtained by placing the FSWed sheets with the welding line (a) parallel, and (b) perpendicular to the short side of the die

Different sample arrangements for hemispherical punch tests. B arrangement: ‘‘surface 1’’ in contact with the punch. T arrangement: ‘‘surface 1’’ countered with the punch

Thermograph of similar joint in AA6082 in three position of the welding tool (15, 90 and 165 mm respectively from welding start) (1500 rpm; 60 mm/min).

Regions of the stamped component and sheet thickness distribution: (a), (b) and (c) critical region, (d) and (e) central region

  1. D. Ciccarelli, M. El Mehtedi, A. Forcellese, L. Greco, M. Simoncini, In-process Control of Rotational Speed in Friction Stir Welding of Sheet Blanks with Variable Mechanical Properties. Procedia CIRP, Volume 67, 2018, Pages 440-445
  2. F. Gabrielli, A. Forcellese, M. El Mehtedi, M. Simoncini, Mechanical Properties and Formability of Cold Rolled Friction Stir Welded Sheets in AA5754 for Automotive Applications. Procedia Engineering 183, 2017, 245-250
  3. M. El Mehtedi, A. Forcellese, L. Panaccio, M. Simoncini, Design of Stamping Processes of Pinless FSWed Thin Sheets in AA1050 Alloy for Motomotive Applications Using FEM. Procedia Engineering, 183, 2017, 213-218
  4. M. Bevilacqua, F. E. Ciarapica, A. D’Orazio, A. Forcellese, M. Simoncini, Sustainability Analysis of Friction Stir Welding of AA5754 Sheets. Procedia CIRP, 62, 2017, 529-534
  5. M. Cabibbo, A. Forcellese, M. Simoncini, M. Pieralisi, D. Ciccarelli, Effect of welding motion and pre-/post-annealing of friction stir welded AA5754 joints. Materials & Design, 93, 2016, 146-159
  6. M. Cabibbo, A. Forcellese, M. El Mehtedi, M. Simoncini, Double side friction stir welding of AA6082 sheets: Microstructure and nanoindentation characterization. Materials Science and Engineering: A, 590, 2014, 209-217
  7. M. Simoncini, D. Ciccarelli, A. Forcellese, M. Pieralisi, Micro- and Macro- Mechanical Properties of Pinless Friction Stir Welded Joints in AA5754 Aluminium Thin Sheets. Procedia CIRP, 18, 2014, 9-14
  8. M. Simoncini, A. Forcellese, Effect of the welding parameters and tool configuration on micro- and macro-mechanical properties of similar and dissimilar FSWed joints in AA5754 and AZ31 thin sheet. Materials & Design, 41, 2012, 50-60
  9. A. Forcellese, M. Simoncini, Plastic flow behaviour and formability of friction stir welded joints in AZ31 thin sheets obtained using the “pinless” tool configuration. Materials & Design, 36, 2012, Pges 123-129
  10. A. Forcellese, F. Gabrielli, M. Simoncini, Mechanical properties and microstructure of joints in AZ31 thin sheets obtained by friction stir welding using “pin” and “pinless” tool configurations. Materials & Design, 34, 2012, 219-229
Scientific Manager