Rapid Prototyping

Rapid Prototyping (RP) expedites the transition from the design concept to a physical model. With RP, objects are created from thin layers, i.e., by Layered Manufacturing (LM). The most common LM technique, stereolithography, uses a liquid photopolymer selectively solidified by an ultraviolet laser.

Mechanical properties of photopolymers can be improved by the addition of short-glass-fibres. In our work, a novel process for Rapid Layered Composites Manufacturing (RLCM) was developed. RLCM overcomes several fabrication problems caused by the introduction of fibres into the photopolymer liquid: (1) thin layer formation from a viscous mixture; (2) fibre settling; and (3) lack of inter-layer fibre penetration. The distinguishing features of the proposed process are: (1) external fibre-resin mixing supply source; (2) precisely controlled liquid deposition from above; and (3) selective solidification by a scanning pattern with layer-to-layer interconnecting features.

As part of the engineering analysis of our LM process, the constituent materials were studied to evaluate the fibre-photopolymer interaction; the high strength of the fibre-solid photopolymer interface was verified by single-fibre pull-out tests; and, fibre-liquid photopolymer interaction was observed through rheological measurements which determined the relationship between the composite liquid’s viscosity and (a) the fibre concentration and (b) the fibre aspect ratio.

RLCM process output was analyzed in terms of parts geometric quality and mechanical properties. The geometric quality was assessed by examining individual layers. Fluid-mechanical layer-formation models were employed to interpret layer-to-layer thickness variations.

Mechanical properties of layered composites are of importance since such parts may directly serve as functional prototypes. These properties were modelled employing the modified rule of mixtures. Modelling mechanical properties of the short-fibre composites, however, requires information about the fibre orientation and length. Thus, three-dimensional fibre-orientation distribution was measured with a novel methodology where two closely spaced consecutive cross-sections are examined. The method’s novelty lies in accurately calculating the transformation between the cross-sections and additionally estimating the fibre length.

The analytical models for mechanical property estimation matched well the tensile test results of parts manufactured on our experimental system, which demonstrated a significant improvement (80%) in modulus with reinforcements.

Due to increased market competition and, in turn, shortened product development cycles, there is a demand to rapidly create functional fully-densed metal parts without hard tooling. A possible solution to this problem is Rapid Layered Metals Manufacturing (RLMM), for example, via laser-beam fusion of metal powder. Our RLMM process is based on this approach. It involves selective laser-beam scanning of a predeposited metal-powder layer. The laser beam melts the powder locally, forming fully-densed claddings, as the basic building block of individual layers.

As part of the engineering analysis of our RLMM process, the theoretical investigation of the process-parameter influence on claddings geometrical properties employed computer modeling and process simulation. The commercial finite-difference, thermal-modeling software I-DEAS TMG was used for the determination of the global temperature fields within the powder layer and the metal substrate due to the application of a laser-beam heat source. The claddings expected geometry was reconstructed using an algorithm based on surface analytical geometry. The relationships between claddings geometrical properties, namely its width and height, and the scanning speed were determined for both laser-working modes.

In order to verify the findings of the process simulations, numerous experiments, involving fabrication of single claddings, were also carried out with varying process parameters. A generic experimental set-up, which can be used for both pulsed and continuous laser-working modes, was designed, built and utilized for this purpose. Comparisons of the process simulations and experimental results showed good agreement in terms of overall trends.