As part of prototyping production methods for our mills we tried playing with castible molds and plastic to provide a solution for the rapid production of multiple copies of a part. The results were fairly promising and the company may offer cast kits at some point.
Smoothon.com offers multiple lines of castable plastic resins with lines of compatible mold materials, and release agents. Smoothon.com also supplies tutorials for all their products – but the casting process is fairly simple and we will show what we tried here.
Start by gluing an original part to be copied down to a water proof sheet of flat material, and build a mold box around the parts. When casting multiple parts add small pieces of material connecting the parts. This will leave a channel in the cast mold through which the liquid plastic can flow, allowing the entire mold to be poured from a small number of points. Next add one or more pieces of material that will stick up out of the mold to provide pour points. Also add other pieces of material should also stick up out of the mold to allow places for the air to escape. The air vents can be very small – tooth picks work well.
Pieces mounted in mold box
Once the parts have been glued into the mold box hot glue the mold box to the underlying water proof sheet. This prevents the liquid mold material from leaking out of the box. If using a wooden mold box it is also a good idea to hot glue the interior corners of the mold box to make it liquid tight and able to hold the molding material. Pictured above is a mold ready for casting, and the same mold once cast is pictured below. You can see small pieces of wood used as risers for air and pouring points. Once the mold has hardened, you break down the mold, remove the original pieces and pull out the risers that were added for pour points and air venting.
Mold box filled and drying
To cast parts you just re-assemble the mold treating the inside with a release agent. You want to glue the box down to the underlying sheet again, this time to prevent any liquid plastic from escaping. When casting large pieces you should also put something heavy on top of the mold to prevent the mold material from floating up when you pour in the liquid casting material. At this point you just mix and pour your liquid plastic and fill the mold.
Make sure to have some place to pour off any excess material in case you mix too much plastic. Be sure to carefully read the directions on how the material used should be mixed and handled to avoid air bubbles in the finished casting. Stirring either to vigorously or not enough can both cause defects to result in most cast materials.
Once the plastic hardens break down the mold box and remove the pieces. A sample mold with cast pieces is pictured below.
Pieces in mold
Then just peal the parts out of the mold and cut off the flashing.
Removing pieces from the mold to clean up the flashing
Below are pictured some white sample cast parts next to their black ABS plastic pattern originals. The “wavy-ness” you see on the cast surfaces is because I used aluminum foil as a casting surface. They foil was not perfectly flat and this ended up being reflected in the cast surface.
Cast pieces next to the originals
So in summary casting parts turned out to be very easy and fast once you had an original. We anticipate that our customers who want a large number of a particular part will probably end up making molds or casting off parts made by one of our products.
