Computers and automatic machinery have given us the ability to produce a wide range of complex metal parts. But even with all of our high-tech resources, there are times we encounter a challenge any modern machine shop would find daunting.
Recently a client came to us with a part that had been designed in a CAD (computer-aided design) program. They needed a number of reasonably priced bronze prototypes in varying sizes, which could be used in a special application. It was possible to mill them, but not without extensive setup time. Since we were unsure which final configuration of the bronze "orbs" would suit the clients needs, we did not want to waste valuable time building fixtures to produce parts that might not be ultimately useful. Another possible choice that could work for prototyping the small metal parts was investment casting.
Investment casting, also known as the "lost wax process", is a venerable art used to make intricate metal parts that would be difficult or impossible to produce any other way. It is the method jewelry designers most often choose to produce their artwork. Typically, patterns or forms used in investment casting are fashioned from a special wax that has been carved by hand. In this case, hand carving could not offer the required tolerances.
Jewelers are now using high-tech equipment to make wedding rings and pendants.
This was a perfect opportunity to use our high-resolution, rapid prototyping machine, the SolidScape Modelmaker II™. First, we designed the master orb patterns in SolidWorks™, our CAD program of choice. Afterwards, we transferred the 3D files to the machine and programmed it to build physical models in a high-tech investment casting wax. The Modelmaker II constructs the wax forms with micro droplets, layer upon layer, until the envisioned part is complete. Since the layers are only 0.003 of an inch thick (the width of a human hair), the final dimensions are very close to the original CAD files. The resultant wax models are the master patterns used in the investment casting process. In a modern twist we had combined the lost wax method with our high-tech CAD program to fabricate the bronze orbs, which would be costly and time consuming to produce any other way.
Below are the steps we took to cast the bronze orbs:
The mold is oven-cured at 1350 degrees for 3 1/2 hours.
Heat vaporizes the wax tree, leaving a tree-shaped void in the plaster.
We combined the old and the new, investment casting and a state-of-the-art RP machine, to produce these intricate parts. Mike achieved the desired level of quality and accuracy in a relatively quick and cost-effective manner.
Investment casting is not a process we use frequently. It is simply another "tool" we have available for specific circumstances. As mentioned before, it is common for jewelers to use investment casting when creating their art, but it is rare for a product development firm to offer the process as an option.