There are hundreds of obstacles that you need to hurdle when doing your "how to make plastic molds" science project. Remember that plastics are quite volatile and it can easily pull out its moisture from the mold. And if this happens, expect cracks to appear and expect your science teacher to give you a low mark as well. So to spare you from these woes, the best solution is to use Silicone RTV. It not only exudes flexibility, it is also tear-resistant and can demonstrate finer points of your molds. Doing your "how to make plastic molds" project will usually take you three days to complete - that's when everything turns out right on the first try.
But doing a plastic mold as a science project and doing prototype products in a larger scale like in a manufacturing business is a whole lot different. In a manufacturing and processing firms, the plastic molds that would be needed should be highly resistant and highly durable. Some of the plastic molds needed are small parts of huge machines that are used for testing purposes. This requires molds that are tough enough to stand the rigors of testing. This could be achieved through the use of more stable Urethane Resin or plastic forms like PVC, PE or Acetal.
On some cases, prototype products are done for presentation or advertising purposes. During a launch of a new product, manufacturers often come up with a high end replica of a product that is yet to hit production. This way, it would make their target market view what the end product would look like before the production takes a full blast. In a way it's like testing the waters whether their future clients are warm on their new product. Remember that full scale production needs a huge investment. It includes purchasing heavy equipment for fast manufacturing and training personnel on its usage. And if their new product doesn't click, then they are in for a lot of trouble.
Making plastic mold science project can expose anyone to different dangers like getting burns. So while casting a plastic molds, ensure to wear protective gears like goggles, gown or gloves. Melted plastics can stick to the skin and embeds quite deep. Ugly scarring is one of the obvious consequences but this could be avoided with presence of mind and alertness especially when the plastic is on its melted form and of course wearing protective gears all the time.