Our presentation ( Laura West and Mark Ganter) at Ars Mathematica in Paris was a great success and as promised we are jointly releasing our cemetenous metal casting formula for you to play with. What follows is a series of tips along with the formula. Of course we found that it also works quite nicely for sculptural forms and has the unique quality of not needing an infiltration.
The formula simply is:
1000 parts VersaBond
250 parts Maltodextrin
250 parts PVA powder
These molds should be approached much like sand molds. They will have similar surfaces and strengths, you will also need to think of venting them in a similar way. For smaller molds, you should not let the thickness get less than 1/2″ and for larger molds you should increase it to 1″ or more. You will either need to build them as open face molds or as 2 part molds to get the powder out of the center. As time goes I will post more mold making tips on either on this blog or on rpsculpt . (this site is dedicated to the sculpture side of additive manufacturing as well as its use in metal casting, it is relatively new).
You will find that you need to print adjust your powder setting to be fairly wet, but not so wet that the part pulls away from its surroundings. The first few layers may tend to slide, so you should orient your part to account for that (put the bottom of your mold on the bottom of the build) and put it at least 1/4″ up into the build. Placing a few test bars below your build is also a good idea. Creating your patterns on a textured build plate also seems to help. You may find that you need to adjust the anisotropic scaling on x-plane in your print program, which is easy enough to do. Baking the mold on warm (do not go above 125 degrees F or the sugars will start melting) will help with de-powdering. If you spray your mold with a light misting of alcohol, the form will strengthen significantly. This will make the surface of the print hard enough to file your nails – seriously I have filed several broken nails in the lab with this material!
For a finer surface on your cast you may want to paint or spray a thin layer of mold wash on the surface. You can buy a commercially available recipe (Porter Warner) or you can create a mixture 50/50% zircon flour and graphite stirred into either alc0hol or naptha. Fused silica flour can also work as part of the recipe. A mold wash, depending on the pattern, can allow for a second pour if it is an open face mold. If you have a two part mold, you will need to join the two sides. Any 5 minute epoxy will work for small molds. For larger molds you should use a professional grade core paste and/or mold weights/metal clamps to hold the mold together.
A good resource for sand casting techniques is “The Complete Book of Sand Casting” by C. W. Ammen. It can be found on Amazon for less than $15 and should be in every metal caster’s library. Although I will eventually post tips and rules for gates (the channels to get the metal to the pattern) and vents (the pathways for air to escape from the mold) as well as things like metal temperatures and types, this book is an old classic and will give you a head start.
I have attached a Rhino 3d and a stl file which you can use as a base for a mold. You can take a stl and “cut” or “Boolean” it from the form just below the tapered hole to create a negative space to pour into. Depending on your form, you may have to first cut it from one side, then the other. If you are having difficulty with your cut in Rhino, use the “analyze” tab and check your direction. Often this is the cause of the problem. If you have a choice you should place thicker forms over thin ones and you may need to add vents – which you could cut by hand. You should note that this is a two part keyed mold form, even though it appears to be a single object. Link to down load for stl and 3dm files.
I (Laura West) was lucky enough to return as a visiting artist again at Solheim lab for the last week. During the last few weeks, first at my lab in Fresno and then especially at UW some significant breakthroughs have been made, which we will be discussing soon. There is a great deal to be said for artist/scientist/engineer collaborations (expect some posts soon from both of us on the topic). One of the most amazing things that was accomplished was printing a mold and pouring it within 3 hours – one hour before I left for Fresno. I am leaving you with teaser shot of one of these new materials below: