A custom plastic part may go through several stages as it evolves from an idea to reality. A 2D drawing of the part provides a base for creating a detailed 3D rendering of the part design. After a custom plastic part has been clearly illustrated and may seem ready for production, there may be some very good reasons to consider prototype injection molding (making injection molded prototypes) before going into mass production. The following considerations will help you in determining your prototyping needs.
Recent news heavily features the advent of 3D printing technology as a solution for many prototype injection molding applications. Plastic injection molding can still be the best alternative for most prototyping scenarios in many cases. You should be aware of each prototyping method’s strong points to understand which is best suited for your application.
In a supporting role, 3D printing is sometimes useful to correct early design flaws and help visualize a finished product. But one clear benefit of using prototype injection molding is gaining manufacturing experience and knowledge that can be applied when starting to prepare for production . Testing the chosen production material along with the injection mold design offers the manufacturer a preview of any potential problems.
Design problems that are not apparent in a 3D model or printed model can create delays and subsequently added production costs. Developing a prototype injection molding solution for your custom plastic part can help you to avoid some of these common mistakes before production begins:
Computer models and 3D printed models are not 100% representative of real-world plastic molded parts. Injection molded parts often have surface and appearance flaws that can only be fully discovered through real injection molding. Many of these flaws, such as, sink marks, flow lines and gate imperfections can be addressed after prototyping.
Many production failures of injection molded parts are the result of part designs with non-uniform or wall thicknesses that are either very thick or very thin by injection molding standards. Plastic molded parts that require any of these conditions for proper function should always be prototyped by injection molding to understand the production challenges that may lie ahead.
Proper gate placement and gate type on a plastic molded part ensures the mold cavity can be filled evenly and the plastic can be held under pressure long enough to produce parts with consistent quality. Testing the results of a proposed gate type or location on a custom molded part can only be done through prototype injection molding.
Injection molded parts designed with dimensionally tight tolerances in order to perform properly are very good candidates for prototyping. All plastic materials and molded parts shrink and even deform after they are removed from the mold during injection molding.
The amount that a plastic part will shrink or warp depends on many factors, such as, the plastic type chosen and a wide variety of mold design and processing factors. The best way to gain insight on how repeatable a plastic part will be on tight dimensions is through real injection molded prototypes.
Unfortunately, in the injection molding industry there are very broad assumptions and cliché names for plastic injection molds. Many of these assumptions and category names for molds are not only untrue and misapplied, but they also confuse engineers and buyers of custom molded parts. Perhaps the most misinformed assumption that resides in our industry is that there is a clear and well-defined difference between a prototype injection mold and a production injection mold. That is incorrect and we can expand on this by giving you some commonly used mold types along with the real scoop about each of them:
Any mold within this category is available at considerably less cost than traditional injection mold tooling. This cost assumption is considered true most of the time. But, any mold that is manufactured by “rapid prototyping” should be assumed as made by 3D printing and 3D printed molds have a very narrow set of advantages. With their relatively quick manufacturing time, they offer a cost-effective way to test a basic design but should only be used for extremely low quantity molding. In most cases, a prototype injection mold made from aluminum is a much better choice for near the same cost.
Beware of “production injection molds”. Engineers and buyers within the injection molding industry blindly specify that production injection molds should be made from steel. The first assumption of most any injection molding company is that production injection molds are made from steel. As mentioned above, the proper reference between a prototype injection mold and a production injection mold should not be the metal that it is made from. A production injection mold should be designed and constructed to accomplish the fastest cycle times, the highest quality parts, and the longest tooling life possible no matter the metal that it is made with!
There is an old school stigma that any plastic injection mold made from aluminum should be considered a prototype mold with a limited tool life. That is incorrect. Customers often ask, “Can you build an aluminum prototype mold for me?” The answer of course is “sure we can build an aluminum prototype mold for you, or we can build you an aluminum production mold.” The point is that the type of metal used for building the mold does not determine if it should be considered a prototype mold or a production mold. The difference between a prototype aluminum mold and a production aluminum mold is the mold design! If the mold is designed with a single cavity for a very specific purpose of making a limited number of prototypes it will be designed for that purpose. Likewise, it can also be designed with one or multiple cavities and all the features required for mass production.
MSI Mold’s team of experienced engineers and technicians can guide you for your specific custom plastic part prototyping needs. We can:
Through our plastic prototyping services we can offer you the same options that exist for long term production projects: