1) Analysis of current solutions
Several analyses have been carried out in order to make a state of the art, know about the tools and machines currently available on the market and intended for FSW process and eventually select the CNC machine:
- Analysis of tools available related to an adjustable pin and a stationary shoulder configuration,
- Analysis of dedicated CNC machines and industrial robots available for FSW.
2) The design of special welding head for FSW process compatible with CNC machines whose dimensions are sufficient to fit the head in and whose nozzle has the necessary surfaces to be interfaced with it has been completed. The head as designed allows automatic adjustment of the pin, force control system modifications and concave-convex geometries welds.
3) The manufacture of the special welding head is achieved and set up on a 5-axis CNC machine.
4) Optimization of FSW process parameters
FSW Process parameters (welding tools, forging force, advance and rotation speeds...) have been determined on butt and lap joint welds of 2024 T3 and 7075 T6 aluminium alloys with thicknesses ranging from 0.5 to 3 mm.
Weld qualification tests have been performed such as:
- Tensile tests
- Microstructural analyses
- Microhardness measurement
The results show that mechanical properties reached for 2024-T3 welds with thicknesses of 0.5 to 3 mm are between 75% and 95% of the base metal. For 7075-T6 alloy welds, a change of behaviour with the base metal was observed. Yet, 7075-T6 welds remain ductile with mechanical properties of 70% of base metal.
Microstructural observations reveal the failure through the weld and allow to identify different parts of the weld such as nugget, heat affected zone (HAZ) and thermo-mechanical affected zone (TMAZ). A scientific paper had been submitted on the subject.
At the same time, numerical simulations of the temperature during the welding process based on the FSW parameters were performed to help find optimized process parameters. Numerical calculations of the Heat Flux and temperature with different FSW parameters were carried out on 2024-T3 alloy sheet with 1 & 3 mm thicknesses. Results of numerical approach according to process parameters were presented in a FSW comission.
5) Performance tests of the retractable pin and force control have been carried out. For example, exit hole closure was performed.
6) A temperature measurement tool has been added on the FSW head. Tests of the tool and a comparison of the results with the thermal numerical model have been realized.
7) Final tests on concave and convex welds have been performed.
Capacities of this FSW head will increase joint design possibilities and better weld quality for applications such as cold plates or stiffened panels.
