Casting With Zcorporation 3D Printers
Patterns machined, or made by hand, often require a trained CNC operator or skilled craftsman. If the production is outsourced, patterns can be expensive and time-consuming. With Z Corp 3D Printers users can go from a CAD design directly to a pattern quickly, inexpensively and with very little training. This process can be adopted in foundries, design centers, or pattern shops.
Direct metal casting requires an engineered pattern sent to a Zprinter for printing. This process has four stages: Data Prep, Printing, Reinforcement and Finishing. These stages are required to produce of the strongest, most durable, long-lasting patterns possible. A 3D CAD package to export their pattern to STL is also necessary. The pattern should be “shelled out” using the STL editor of Magics RP. The result should be a 5-9 mm thick shell, strong without infiltration, yet thin enough so the epoxy infiltrant will fully penetrate through the plaster. First, import the STL file into Magics RP. Then, select the parting (Select: Tools and then Offset Part).
Another step in prepping your data is called “adding ribs”. This is an important step that provides some additional strength to the part after epoxy infiltration. Dividing the shell into sections improves the curing of the epoxy. The ribs do not have to be very thick; only 2-3 mm preferably. First, start with an STL file. Next, import the STL file of your shelled pattern into the ZPrint software. Make certain the cavity is facing down and aligns to the bottom of the build chamber.
Before you send the file to be printed, you must always check it to make sure it is complete with no gaps or errors in the geometry. When you are ready to print send your STL to the printer. Printing time depends on the model, but generally is multiple hours, plus anytime for curing. Printing patterns should be done with a plaster series powder that will provide the greatest strength potential. This will also provide the best finish and accuracy. After printing, remove the parts from the print bed, the bulk of powder and prepare to reinforce with epoxy.
The two stages of reinforcement are crucial to a completely reinforced build. First, users must infiltrate the pattern using Z-Max epoxy. Next they must backfill the pattern’s cavity with a semi-rigid epoxy. Z-Max is the best choice for a very strong, thin epoxy that can penetrate deep into a pattern. The shell requires as much impact strength as possible. The Z-Max epoxy should be applied according to its instructions for use. As a general rule of thumb, you can use 20-25% of the weight of the plaster part in Z-Max. Make sure to not let the epoxy cure completely before going on to the next step.
Backfilling with epoxy helps solidify the pattern, and gives it a strong anchor point if the pattern is to be screwed to a match plate. Users can do this by simply propping up the pattern and filling the back with epoxy. Make certain that the cavity is filled as close to the top as possible. Once they are infiltrated with epoxy, patterns can be finished. First, sand the cured epoxy-infiltrated pattern with 100-grit sand paper by hand or using power-sanding tools. Next, sand the part until there are few pits in the surface. Finally, coat the part with surface filler making certain to fill in any remaining pits. The pattern can then be mounted to a matchplate by threaded anchors or high strength adhesive.