Do-It-Yourself: Plastic Molding

Setting up my own system?First you have to put together your mold. There are several ways this can be achieved. Many people use RTV in either poly or silicon based units to create their two part molds, by making a negative of the part you are going to copy. Take for instance the question in my comments: broken lawn darts. This casting set should likely be in three pieces to allow for easy separation of each Fletch vane. I would use the best of the darts. Oil them with WD-40 or other slippery substance that silicone would not stick to. Next smear a very liberal amount of RTV on six small pieces of quarter inch paneling board. Make sure there will not be any bubbles.Then carefully place each wet silicone piece onto the fletch vanes, making - remove mildew smell - sure that all areas of the lawn dart are covered. It would be good to mark the individual pieces now with a marker. Wait a day or so for the RTV to cure. Using a utility knife, carefully separate the individual pieces. Hindsight in my own mistakes says to make sure you have also bonded the six pieces into three with a bracing piece. This can be siliconed in place as well, but make sure that your vanes are spaced evenly. Doing this properly will help in making sure your parts align properly for the next steps.Once you have removed the original lawn dart from the mold, use your knife to open three small weep holes on the fletching edge of each vane. Next clamp your mold pieces together in the proper order. Then using a liquified plastic solution, usually created by dissolving the proper plastic into a solution of plastic weld glue. For the thin vanes of the fletching, particulate powder can be used, but being consistent in the fletching will be next to impossible. The ideal scenario would be to use the injection method after softening the injected plastic.With this said, metal tipped lawn darts have been banned from use in the US and Canada because of injury and death. Parts can be imported, but kits and complete units are impounded by customs. This is not something to make to sell. However, this product is like the proper handling of a handgun. Education is essential for proper use. Use common sense. Anyone participating in a lawn dart game must understand that in 1988 the Trade Commission banned them after three deaths and a seven year old boy in Indiana suffered irreparable brain damage due to the metal tipped lawn darts.Other IdeasYou could also use a ceramic or metal form to pour your liquid or powdered plastic into then heat or let set. Now let me be clear I'm not only saying a form made from metal or ceramic. I'm saying that the form could be made of anything as long as it with stood the heat of the molding process. Scrap wood can easily be shaped by standard wood working tools and made into the negative of your part. Of course, RTV Silicone mentioned above is a decently cheap method if you do not mind the smell.For one piece molds, there are any number of ways to vacu-form your molds, using old vacuum cleaners and ovens to soften the plastic you will use for your mold. This might be handy for making a repair piece for an old doll or action figure. It is a method used often times by the plastic modelling community for numerous parts.The four basic types of molding (particulate, pour, vacuu-forming and injection) could be used for a long time for manufacturing.But are you going to mass produce your project? Are you going to need a quick setting system for a more rapid production?Injection molding alone is used for many different industries. In essence, Injection Molding is using a machine to squeeze the hot or chemically melted plastic into the mold. Injection molding mated to the particulate molding process, can speed your production considerably, as well as, as mentioned before, quite possibly making a stronger product. Keeping your equipment clean helps keep the fumes at bay as well. Stray plastic material can out gas for a long time after it has melted, and every time it is heated releases even more fumes.I had thought that by this time I would have figured out a better system but arc heating and torch/flame heating are out of the question because of keeping the fumes to a minimum. So for now I use an array of several old soldering irons that are placed strategically around the mold to help in the even heating. However, that is a very inefficient system so I have been working on a new one that uses a small chamber and - - direct blown heat from that chamber.