© 2008 Dream Merchant • 2309 Torrance Blvd. #104, Torrance, CA 90501 (310) 328-1925 email: Jkm316@aol.com MAKING CAST MODEL PROTOTYPES
By Ken Tarlow
PART FOUR
If your product idea is very sculptural and has lots of ins and outs, and it's just impossible to make out of flat sheets and cylindrical tube shapes, you will need to basically sculpt your final shape.
You can use a variety of materials for sculpture. You can use plastileen, which is a clay that never hardens. It's a soft clay which, as it gets warmer, gets easier to work with. After you have sculpted that clay into the shape you want, you can put it in the refrigerator, harden it up, and then cast that piece in plaster.
Once you have the female plaster mold, you can cast it in a variety of materials. If you want to get a shell piece, that is, not a solid piece, but a thin-walled shell of the final design, there are various Urethane mixtures that you can mix and brush into that plaster mold. The urethane hardens and forms a thin plastic shell which you can pop out of the mold. Be sure not to have undercuts in your design, otherwise the part won't come out of the mold. You've got to use a mold release material like Vaseline or one that you can buy in a plastics store to make sure that the Urethane, or whatever it is that you're putting in the plaster mold, doesn't stick.
For clear parts, you can use clear casting resins. These you can buy at the plastics store. You can get them in clear, or you can put colored tints in to produce different colors. It comes as a hardener and a resin which you mix up and pour into the mold. They take about a day to harden.
Another great mold-making material is RTV silicone rubber, which is available in a good plastics store. This silicone mold material is rubber-like, so when you cast into it, it is easy to get the part out because the mold flexes a bit.
In conclusion, you will use a sculpting and casting technique when your design is an irregular sculpted shape. I don't use it that often because it's amazing what I can accomplish with flat plastic sheets, cylindrical tubes and Bondo blending techniques.
Sometimes, if I need a special shape, I'll go to a department store or a toy store and I'll look for a shape that's very close to what I want. I'll buy that product and, using the cut-off wheel on the Dremmel, I will cut the actual piece or shape that I want out of an already-existing product and put it into my prototype. Just splice it in! All is fair in love and model-making. You can use whatever techniques work. What you want to do is be as efficient with your time as possible and do as much of the work yourself so that you don't have to spend lots of money for a professional model maker to construct your prototype.
MATERIALS FOR CAST MODELS
These materials include: plaster-of-Paris, plastileen (a sculpting clay), and Bondo (for making molds and also casting into molds). Silicone casting material is nice because it's somewhat soft, so you can cast a hard shell into that soft material and it's easy to pull it out. After you've made your original shape, you can cast it in the silicone.
NEXT ISSUE: More on Prototypes
The above article was excerpted from Ken Tarlow's MIND TO MONEY, a workbook package that can help you develop a new product from the idea stage to the marketplace. MIND TO MONEY may be ordered from the Dream Merchant at $59.95 plus $4.95 CA sales tax and$5 shipping and handling ($69.90 total). Send orders to the Dream Merchant, 2309 Torrance Blvd., Suite 104, Torrance, CA 90501.
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