The filament fusion process works by utilizing the temperature dependent phase behavior of polymer, i.e., the solid phase and the melt/flow phase. At the polymer’s glass transition temperature, the material becomes rubbery and forms a plug in the channel between the solid phase above and the melt phase below, allowing the solid polymer filament to push down the melt phase through the nozzle onto the build plate. The temperature gradient in the printer head must be tightly controlled to maintain the three phase zones -- solid, glass transition, and melt -- to enable reliable printing.
A closed-loop adaptive heating and cooling system can be deployed that maintains precise control of the three phase zones, regardless of extrusion speed. Nozzle geometry is optimized for two different settings, one for filled material and one for unfilled material, resulting in a higher extrusion rate and hence a higher printing speed. The control of melt flow rate allows a consistent extrusion of materials with different viscosities. This extruder design can be programmed for various unfilled and filled materials and results in reliable operation without any clogging of material in the nozzle.
A closed-loop adaptive heating and cooling system maintains precise control of solid, glass transition, and melt phase zones, regardless of extrusion speed. Controlling melt flow rate allows consistent extrusion of materials with different viscosities.
(Source: Arevo Labs)
Test methodology and intelligent software for end production
Existing test methodologies for the characterization of materials developed for injection molding and extrusion are not fully applicable to the 3D printing process. For example, an ASTM 638 tensile bar can be made in many different ways using 3D printing by varying characteristics such as nozzle diameter, fill ratio, fill pattern, layer thickness, and fiber orientation. Further complexity is introduced by a complex part with a spatially non-uniform fill pattern, as well as multi-material parts for which no test methodology exists today.
A new test methodology is required to characterize a polymer for the 3D printing process that takes into consideration the variability of processing parameters. But that’s not enough: intelligent software must also be developed that makes the properties of printed objects more deterministic. Arevo Labs' intelligent software is delivered as two functional components: an analysis & optimization component, and a printer management component. The analysis & optimization component is a set of client-facing tools that enable an engineer to specify the constraints for a printed part, such as material type, stress tolerance, and mechanical properties. A series of simulations are then run to determine the optimal material deposition strategy required to construct a part that meets the desired constraints.
The optimization tool speeds up the design process, as it evaluates several possible construction schemes in software, including optimal fiber orientation. 3D-printed parts can also be optimized for the least possible weight and/or the highest possible strength. This capability is highly efficient, as it does not require the printing and testing of several different versions of the part with varying parameters.
The second component of the Arevo software is 3D printer-specific. This printer management module takes the 3D model file, the engineer’s constraints, and the resulting data from the analysis & optimization component, and maps them to an optimal tool path for a specific printer.