Abstract:
The main aims of this study are to generate a methodology for the optimisation
of welding procedures for plasma welding of thin sheet aluminium alloys and to
investigate weld quality modelling. Emphasis is focused on the recognition and
evaluation of the consecutive stages of welding procedure development and on the
formulation of a generalised procedural methodology that is potentially applicable to
other processes and materials.
The materials under investigation were 1.6 mm thick sheet 6013, 2024 and 7475
alloys, representing the major medium and high strength heat treatable aluminium
groups used in the aerospace industry. Initial experimentation generated procedures
relating to specimen and equipment pre-weld preparation. Bead on plate and square butt
joint trials were performed in the downhand position. The plasma keyhole mode was
operated autogenously while filler wire addition was employed for the melt-in mode.
Arc monitoring techniques were used to log the arc voltage and welding current values.
The effect of background and control parameters on process performance and joint
quality was studied and used to generate operating envelopes and reveal optimum
welding conditions. Geometrical data from the melt-in joints of all alloys were
employed to build joint geometry prediction statistical models. Numerical algorithms,
based on the information generated by the statistical models, were used to create joint
geometry optimisation techniques. Calorimetric experiments and x-ray examination of
joints revealed the relationship between major operating parameters and arc efficiency
and the incidence of porosity, suggesting desired welding conditions that were
incorporated in the optimisation process. Finally, two software tools for Joint Geometry
Prediction and Welding Procedure Optimisation were developed, incorporating the
knowledge and information created during the modelling and optimisation stages. These
provide the end user with a means of process parameter selection and visualisation of
the influence of parameter variation on weld bead geometry.
