| Abstract Scope |
Finite Element codes are widely used to simulate the size and shape of the melt pool and peak temperature during an additive manufacturing process. The accuracy of these simulations depends on the input of material properties which are typically obtained from handbooks, or by physically testing the material. The limitations of such an approach are as follows. Handbook data are:
i) Often not temperature dependent and so constant values are employed.
ii) Not sensitive to compositional variation.
iii) Not typically measured for materials that have been subjected to high cooling rates where metastable phases could form.
iv) Not suited for alloy development where novel materials would need to be physically tested before simulations can be made.
This talk will describe a new Additive Manufacturing Module developed by Thermo-Calc Software for the Powder Bed Fusion process to address the problem of solidification during AM, where a unified treatment is employed of both process parameters and chemistry-dependent thermophysical properties when solving the multiphysics problem of a moving heat source that melts and solidifies metal powder.
Using the CALPHAD approach, alloy dependent physical properties such as specific heat, density, thermal conductivity, viscosity, and surface tension of liquid are calculated from evaporation temperature down to room temperature in lieu of handbook values. Then using an extended SCHEIL calculator these are automatically transferred to the AM Module where the multiphysics simulations treat thermal conduction, fluid flow, evaporation-, radiation- and convective- heat loss.
Process parameters for the simulations include scanning speed, layer thickness, scanning pattern, heat source (power, absorptivity and heat distribution), and base plate temperature. Output includes size of melt pool, peak temperature, velocity of fluid flow, property variations through the melt pool (viscosity, thermal conductivity, density), temperature vs. time response at selected position of the build and how this changes with process parameters.
For validation, simulations have been made comparing this approach to benchmark data from the NIST AM-Bench test series on alloy 718. Good agreement is found when comparing calculated vs. measured melt pool shape. Thermal profiles for selected nodes are then taken and used as inputs to further CALPHAD based precipitation simulations to determine the extent of in-process precipitation of gamma prime and gamma double prime. |