Solving the World’s Toughest CFD Problems

Continuing with the blog series featuring new developments in FLOW-3D, I will focus in this post on the capabilities of fluid particles, one of the new particle classes in the particle model. Fluid particles directly inherit fluid properties, including evaporation and solidification. There can be a variety of cases where fluid particles can be applied: from a relatively simple rainfall modeling (animation below) to complicated laser metal deposition modeling.

Fluid Particles

Once the fluid particles option is enabled in FLOW-3D, users have the option of setting various fluid particle species with varying diameters and densities. Additionally, the dynamics of fluid particles can be controlled by properties like diffusion coefficient, drag coefficient, turbulent Schmidt number, restitution coefficient and solidified restitution coefficient. Fluid particles can even be assigned thermal and electrical properties.

Users can set multiple sources for fluid particle generation where each source can have a mix of all or some fluid particle species defined earlier. Also, users can choose either a random or uniform generation of particles and define the velocity at which particles are ejected out from the source.

Laser Metal Deposition

Laser metal deposition is a 3D-printing process to create three-dimensional metal parts by fusing fine metal powders together. Laser metal deposition finds wide applications in the aerospace and medical orthopedics industries. A schematic of laser metal deposition is shown below. Control parameters like power intensity distribution, travel speed of substrate, shielding gas pressure and physics like melting/solidification, phase change and heat transfer work together to make laser metal deposition an effective additive manufacturing process.

Laser metal deposition
Schematic of a typical SLM

Setting Up Laser Metal Deposition

The new fluid particles model is an indispensable part of setting up laser metal deposition simulations since it allows for assigning powder intensity distribution and captures the complex particle-substrate interaction that happens in and around the melt pool.

Those who read my blogs regularly may have noticed that I keep mentioning the ease of setting up simulations in FLOW-3D. Well, there is nothing different in the case of laser metal deposition setup either. Setting the physical properties of IN-718, geometry creation, particle powder intensity distribution, mesh creation and finally running the simulation, every setup step is straightforward and user-friendly.

The physical properties of IN-718 are used both for the substrate and the solidified fluid particles. 40 micron fluid particles are injected from the particle source into the computational domain at a rate of 500,000 per second in a random manner. The particle beam is momentarily stopped every time the direction of motion of the substrate is changed to let the molten pool adjust to the sudden change in velocities. This prevents any reflections of the particles from the substrate. Since the substrate turns every 5 seconds, the rate of particle creation drops to zero every 5 seconds as shown in the plot below. The substrate movement itself is specified using tabular velocity data into FLOW-3D. Particles are injected as solidified fluid particles, which, on hitting the hot molten pool, melt and become part of the molten pool fluid.

Rate of particle creation
Rate of particle creation
Substrate velocity
Substrate velocity

Apart from the particles model, FLOW-3D’s density evaluation, heat transfer, surface tension, solidification, and viscosity models are used. More specifically, the temperature-dependent surface tension causes a Marangoni effect that significantly affects the shape of the deposited layers.

To replicate the laser, a very basic setup with 100% porous component is used as a heat source. 100% porosity does not affect the flow dynamics around the component; rather it effectively adds heat to the substrate at a specific region. Ongoing efforts involve replacement of this preliminary heating mechanism with a full-fledged, highly-sophisticated laser module developed by our Japanese subsidiary, Flow Science Japan. The heating porous component is moved up slightly after each layer has been deposited so that each layer gets the same amount of heat.

Results and Discussion

The animation below shows a laser metal deposition process with multiple layer deposition. Notice the momentary pause of the particle beam motion every time the substrate changes its direction. Also, as layers are deposited, the shape of new layers changes due to the unequal addition of heat to each layer from the porous heat source. It is difficult to gauge the amount by which the heat source needs to be moved up after each layer has been deposited. The laser module from Flow Science Japan is expected to mitigate this problem.

Overall, the particle model accurately replicates the powder intensity distribution, a very important process parameter in laser metal deposition. We expect that such a level of control and sophistication with the particle model will help users and providers alike in the field of additive manufacturing to fine tune their manufacturing processes.

Learn more about the power and versatility of modeling additive manufacturing applications with FLOW-3D AM.

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