For clients who are unfamiliar with these processes, we’ve put together a basic overview in order to make informed decisions. Rapid prototyping for plastic parts is an essential part of the product development process minimize risk, compress timelines, brainstorm ideas, and troubleshoot concepts. However, each method has its strengths and weaknesses and is better used in a specific part of the process.
1. Fused Deposition Modeling (FDM). A thin thread of hot plastic .010” diameter gets laid down in layers to form the part. The material is ABS so you can create snap fits and inserts and it will behave like a molded part. It’s great for testing the grip of hand held products and to see if switches can be reached early in the design process. It also works well for fitting an assembly together to test functionality. The parts have visible small lines of the layers.
2. Stereolithography (SLA). A bath of liquid resin is cured by a laser in layers. Much finer resolution that FDM is possible, and the parts can be sanded and painted to look like the real thing. A great use for SLA is a trade show or presentation to gain venture capital funding. Unfortunately the parts are not dimensionally stable and the lack of UV stabilizer in the resin causes the parts to warp in the sun and get an orange color. The parts are also brittle, and a beautiful model can shatter if dropped.
3. Urethane Casting. A two part rubber mold is poured around SLA or FDM master, then the master is removed and a urethane plastic is poured into the mold. After curing, the part is removed, sanded and painted. The molds are good for 15-20 parts then must be remade to make more parts. The parts are more expensive than injection molded parts, but the molds are much cheaper. The parts can look like real production parts but the urethane does not have the characteristics of molded plastic. Urethane castings are great to test the appearance and functionality of a product, and could be used for low volume production of under 500 parts depending on the application.
It’s important to state that whichever prototyping method works best for your part of the process, multiple iterations will most likely be required. Just because everything fits together in a SolidWorks database doesn’t mean the prototypes will work perfectly. Each process has tolerances, as as do the internal components, and those tolerances can stack up and cause an assembly to not fit together. Dynamic systems always require one or more prototypes. It may seem like a lot of money and time to do prototypes, but it’s much cheaper and takes less time to make changes to the design in the prototype stage than it is to make changes to the injection molding tooling. Happy prototyping!