TWI Industrial Member Report Summary 934/2009
W He and P A Hilton
Direct metal laser deposition (DMLD) is a well recognised additive manufacturing technique and offers many advantages over other such processes, such as low heat input and the availability of sophisticated systems to accurately control the processing head and deliver the powder. DMLD will only achieve its full potential when a link between the process parameters used, the microstructure created, and the properties of a particular metal deposit can be established. Any advanced numerical modelling of the DMLD process will require a multiphysics solution, ie one that involves multiple physical models, or multiple simultaneous physical phenomena. The significance of developing such a modelling technique for the DMLD process is now more and more recognised by the industry sectors that use and wish to use this process.
The difficulties of a multiphysics approach with the complicated coupled mass and heat flow involved, have not yet been solved, although there have been several models proposed. A novel approach, especially in the use of the numerical tools, is needed to handle the mechanisms operating in the process, as well as the relationship between the diverse process parameters and the resulting quality of the deposit.
This project, 0701-12, is one of the supporting tasks involved in the integrated project (another two major tasks are 0703-7 and 0702-7), which aim at developing a fundamental understanding of the DMLD process through modelling, characterisation and testing of laser deposited material. The project is still in progress and the objectives of this report are to present the progress and the prospects of the next stage of the work.
A series of numerical models using various numerical tools (CFD/FLUENT; Analytical/MATLAB; FEA/ABAQUS) has been designed to simulate the decoupled process aiming to gain more fundamental understanding (Figure i). This report presents the models initiated at this stage compared with the corresponding validation experiment results. These simulations cover the following aspects in the decoupled process:
- Kinematic interaction between the powder stream and turbulent fluid flow in the modelled nozzle.
- Thermal interaction between the powder and the laser beam.
- Melt pool model considering attenuated laser power by the powder and transverse speed.
- Develop numerical models using commercially available software tools to simulate decoupled aspects in the DMLD process including: the kinematic interaction between the powder stream and the turbulent fluid flow, the thermal interaction between the powder stream and the laser beam and a moving melt pool under the influence of a laser beam with power attenuated by interaction with a flow of powder.
- Derive and carry out supporting experiments to assist the validation and calibration of the above numerical models.
- Provide a deeper understanding of the processes involved and provide recommendations for further work.