The 3D Systems Thermojet wax modelling system is a well established and reliable method of manufacturing accurate-to- CAD wax patterns for use in the investment casting process.
Thermojet wax patterns are generated directly from your CAD model without the need for tooling. Any metal contraction allowance required can simply be added to the CAD model prior to building, automatically increasing the overall size of the finished wax pattern to compensate.
As with most rapid prototyping systems, the Thermojet wax pattern modelling system is a layer-build technology, printing liquid wax in sequential layers to construct a 3D shape. The layer building is computer controlled and driven by an stl file (Standard Triangulation Language), the standard file format for most rapid prototyping machines. The software divides the stl file into 0.025mm thick slices and then the machine effectively re assembles the model by sequentially layering these slices on top of each other until the model is complete.
Due to the technology employed, the Thermojet can print in very fine layers so intricate surface detail such as lettering, fine geometry and surface decoration can be reproduced in 2.5D relief. Although the build envelope of the Thermojet is 250mm x 190mm x 200mm, larger waxes can be built in sections and easily joined together.
In a similar way to SLA (Stereolithography), the Thermojet requires a structure to support any overhanging geometry being built, but this merely crumbles away during the post finishing process. The remaining surface, adjacent to the support structure (all down-ward facing surfaces) is less smooth in appearance, but this can be addressed with skilled hand finishing as required. Due to fact that the support structure is so easy to remove, very complicated hollow shaped patterns such as tubes or manifolds for instance, are no longer impossible to manufacture.
Because the print head travels the whole length of the build platform, regardless of whether it is building one part or ten, our customers also benefits from an economical build configuration in which arrays of parts are grouped to maximise the build volume. Our customers only pay for the additional wax consumed, as the time difference for multiple builds is marginal. Thick sections can also be made hollow with an internal matrix support structure, which can reduce wax content, shortening build time and ultimately reducing the cost of the wax pattern.
The Thermojet wax is robust enough to withstand careful handling, but can be brittle if unduly stressed. The wax will soften at body temperature, so prolonged handling is to be avoided. The melt temperature of the Thermojet wax is 85-95°C and so can be successfully burnt out of the investment casting shell to leave only 0.01% of ash.
One interesting use of the Thermojet wax patterns is in the manufacture of complex hollow metal components like heat exchangers or manifolds. By modelling the internal void of a hollow component, rather than the component itself and building this in wax on the Thermojet system, we effectively produce a part which is devoid of its surface. This surface is then replaced by electroplating directly onto the wax with copper, nickel or chrome.
Following the plating process the wax is finally melted away to produce a thin walled hollow metal component.