Process modelling and simulation uses computational techniques to design, analyse and optimise engineering processes. Physical effects considered in simulations include elastic and plastic deformation, creep, fluid flow, heat transfer, diffusion and electromagnetic effects.
Usually several physical phenomena occur simultaneously in a process. A relatively simple example is that of current flowing through a conductor. Electrical resistance heats up the conductor causing its temperature to rise, and therefore the resistance changes. In addition an electromagnetic field develops due to the flowing current. Thus both electromagnetism and heat transfer should be coupled in the simulation.
Welding is a particularly complex process, including coupled phenomena taking place over length scales from microns to tens of metres and over time scales from milliseconds to several weeks. Even with many simplifications, simulations are challenging and require plenty of computer power.
TWI has been at the forefront in simulating welding and joining processes for over 40 years. Commercial software and in-house codes are used to simulate welding and joining processes including arc welding, friction stir welding, power beam welding, and deposition processes. The predicted thermal, fluid and structural responses from these simulations are used for optimising processes and carrying out structural integrity calculations.
The benefits of process modelling include:
- Reduced cost of product development by minimising the number of physical trials required for process optimisation and robustness assessment.
- Increased manufacturing flexibility and reponsiveness via exploration of “What If?” scenarios
- Prediction of thermal response and residual stresses in complex structures for engineering critical assessment
TWI investigated the direct metal laser deposition (DMLD) process. A fundamental understanding of the process was developed via modelling, characterisation and testing of laser deposited material. A series of models was developed to establish the relationship between the laser spot size and distribution of powder particles. The models were validated against experiments and new process conditions were identified yielding improved deposit quality.
TWI assisted the Atomic Energy of Canada Limited (AECL) to develop methods for the highly specialised repair of an aluminium reactor vessel. TWI reviewed simulations of the repair process and carried out additional modelling highlighting the importance of the welding sequence on the properties of the repair, including residual stresses. The repair was successfully implemented over a period of six months.
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