Injection Moulding & rapid prototyping can also come in the form of injection molded parts. How? Rapid tooling (bridge tooling) delivers low volume production quality parts (up to 100,000) from production resins. Think of rapid injection molding as end use prototype manufacturing. End use because your parts are identical to production parts. Prototype because the lead times and costs of rapid injection molding are significantly reduced compared to full production tooling.
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Rapid plastic molding tools are made from steel or aluminium. We use both options but most of our custom injection molding tools are steel. Why? More value for you. Our steel rapid tool injection molding services will typically deliver more than double the parts than comparable aluminium programs.
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Time to read: 8 min
Is prototype injection molding an oxymoron? If youre like most designers, youve learned that plastic injection molding is for high volumes of production-quality (i.e., non-prototype) parts. Maybe youve also heard that steel injection molds are for higher volumes, aluminum injection molds are for lower volumes, and that both types of molds are too expensive for prototypes.
If any of this sounds familiar, its time to unlearn some of what youve been told and to re-think your prototyping and production options. Yes, plastic injection molding is a high-volume production process. Yet there are also times to use it for prototyping and for low-volume production as well. As for injection molds, theres more to consider than just aluminum vs. steel.
Do prototype injection molds come at a cost? Yes, but there are ways to reduce your expenses, as this article will explain. Do injection molds take a long time to produce? If you expect mold-making to take several months, youll be pleasantly surprised to learn that the right manufacturing partner can produce tooling in just a few weeks. Take a look at the big picture and consider your part design and material selection along with tooling costs and machining times. And remember that help is available when you share your part design with Fictiv. For example, if your design doesnt contain enough draft, our DFM experts will suggest a larger draft angle so that your parts eject smoothly.
Fictivs Injection Molding Design Guide contains advice about draft angles for prototype injection molding. This free resource is available for download.
How mature is your part design? If youre not ready for manufacturing, youre probably still in the prototyping stage. But which type of prototype do you need?
This isnt the only way to categorize prototypes, but the above list provides a framework for what follows.
Most proof-of-concept prototypes and looks-like prototypes dont warrant the cost of an injection-molding tool. Thats because the designer usually needs just one or two parts, and its difficult to justify the expense of an injection mold when youre spreading the total tooling cost across just a few parts.
Works-like prototypes and pre-production prototypes are a different story. Often, a designer needs part volumes that are measured in tens rather than in single digits. Depending on the quantity then, it might make sense to use injection molding instead of 3D printing, which does not require tooling but is not the intended production process.
Consider the difference between molding one proof-of-concept prototype vs. 100 pre-production prototypes. In both instances, lets say the cost of the tool is $10,000. For one proof-of-concept prototype, the per-part tooling cost is $10,000. For 100 pre-production prototypes, the per-part tooling cost is $100. Thats a big difference.
The table below explains what to consider when comparing 3D printing vs. injection molding for prototyping.
Parameter3D Printed PrototypesInjection-Molding PrototypesDesign StateEvolving designs that are still in the concept stagesFinished designs that need real-world testingProduction QuantitiesVery low quantity requirementsPrototype quantities that exceed 100 piecesLead TimesLead times of 1 to 15 daysLeads times of 2 to 5 weeksNow think about design for manufacturability (DFM), the process of designing parts in such a way that theyre easy to manufacture. Lets say you 3D-print some components that you then assemble. They fit together flawlessly and let you test the products functionality.
Thats great, but what if injection molding these same parts results in production failure? How can that happen? Your 3D-printed prototypes might be perfect but dont assume that level of perfection will translate seamlessly into the perfect injection molded part.
3D printing has different design rules, such as minimum wall thickness, than injection molding. Thats important to remember because walls that are too thick, too thin, or non-uniform are a frequent cause of failure in production injection molding. The best way to avoid this problem is to use prototype injection molding to create parts that let you identify any production challenges.
Theres more to consider as well. The file formats for 3D printing and plastic injection molding are different. Specifically, the STL files that are used in 3D printing define objects in terms of a triangle mesh. By contrast, the CAD files that contain the designs for injection molded parts are parameter-driven.To use your 3D printing files with injection molding, youll need to convert them from a mesh to a shape to a solid.
3D printing and injection molding also have different tolerances, or allowable part-to-part variations. In most additive manufacturing technologies, the dimensional tolerance is at least 0.1 mm. Therefore, the deviations in 3D printing are greater than with injection molding. Plus, injection molding has two types of tolerances: commercial and fine.
Ready for some good news? Fictiv provides expert DFM assistance through 3D visualization for injection molded part design. Theres also this handy online checklist so that you can determine if youre ready to go from 3D printing to injection molding. And remember that you dont have to wait until your parts are production-ready to get injection-molded samples.
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Acrylic is a commodity plastic that can be used for injection-molded prototypes
Prototype injection molding and production injection molding can both use the same plastics. However, abrasive materials such as glass-filled nylon will cause prototype injection molds to wear more quickly. (Thats because prototype molds are usually made from softer materials.) Still, if youre planning to prototype 100 parts, wear is less of an issue than it would be with a full-scale production run of 10,000 parts.
If your part design is still in its early stages, you might decide to use commodity plastics that are less expensive, even if they dont have the same mechanical properties as your intended production materials. For example, PEEK is an engineering plastic thats used in some medical devices. It costs significantly more than other polymers and may have a high minimum order quantity (MOQ) if your supplier doesnt buy it in large enough volumes to receive a discount.
For a works-like prototype, you could use a less expensive material like polyphenylsulfone (PPSU). In fact, PPSU might be a fine choice. Yet using anything other than PEEK wont provide a full test of your parts moldability. Since PPSU and PEEK are both available as 3D-printing filaments, could you use additive manufacturing instead? Youd save on tooling costs, and you could use the plastic that you want. Sounds simple, right?
That approach might not provide what you need. 3D-printed materials dont have the same end-use properties as their injection-molded counterparts. For example, 3D-printed PEEK isnt as strong as injection-molded PEEK. And if your part is for a medical device, youll need representative samples for the first article inspection (FAI). The best way to get them is to use the same material and the same process as you plan to use for full-scale production. Thats injection molding.
If you upload your part design to Fictiv, you can ask our DFM experts for more information.
Injection-molded prototyping generally uses less expensive tools.Whats the difference between a prototype injection mold and a production injection mold? Its not about the metal that the mold is made from. Production molds can be made from aluminum or steel and prototype molds can be made from aluminum or steel. And it doesnt end there. There are several different steels that are used in injection molds and there isnt just one kind of aluminum.
There are also SPI classes for mold finish to consider. In the table below, look at SPI Class 105. Thats the one for prototype quantities.
SPI Mold ClassVolumeCycles101HighOver 1 million102Medium-to-High500,000 to 1 million103MediumUnder 500,LowLess than 100,PrototypeLess than 500What about the other SPI mold classes? Ideally, a production injection mold is designed and built for the fastest cycle times, the highest quality parts, and the longest tooling life (i.e., cycles). For prototype injection molds, long tool life is less important than part quality, especially for a few FAIs (first article inspections). Cycle time is also less important, at least if your goal in prototyping is to produce, say, 100 representative pre-production prototype parts.
Aluminum vs. Soft and Semi-Hardened Steel vs. Hardened Steel Molds
Yes, the metal that your mold is made of plays an important role in all of this. But you have more choices than just aluminum vs. steel. Specifically, you can choose:
Aluminum is your least expensive choice, but it wont produce injection-molded parts with tolerances that are as tight, or precise, as those with steel molds. Thats an issue if tight tolerances are required, but it can also affect tolerance stack-ups in assemblies with several injection molded parts. Aluminum injection molds can be machined to tolerances of +/- 0.005 inches, but steel molds can be machined to tolerances as tight as +/-0.001 inches.
Soft and semi-hardened steels typically cost twice as much as aluminum but dont rule them out for prototype injection molds. These steels can achieve tighter tolerances and arent so difficult to machine that it takes months to cut a tool. When you work with Fictiv, you can get prototype steel molds in as little as 10 to 14 days.
Generally, hardened steel is used with production injection molds. Its more expensive than soft or semi-hardened steels, but hardened steel lasts longer (i.e., more cycles) and can achieve tighter tolerances. Prototyping doesnt have to produce millions of parts, of course, but what if you need tight tolerances for medical, aerospace, or other demanding applications? Aluminum just wont do.
Whether its for production or prototype parts, injection-molding complexity adds costs.Fortunately, injection molding supports the use of multiple mold materials. For example, the base of a prototype mold could be made of aluminum or soft or semi-hardened steel. The inserts could then be made of soft, semi-hardened, or hardened steel. If your mold requires moving components such as lifters, those components could be made of steel as well.
There are also master unit die (MUD) inserts with a standard mold frame and customized, removable inserts. MUD molds, as they are called, can lower the cost of initial tooling by as much as 66%. Yet they still support the complexity that many designers need for prototyping. If you need to modify your design, as is often the case with prototypes, a toolmaker can modify just the insert.
Finally, prototype injection molding ensures that your mold uses the right gate type and location so that the mold cavity fills evenly and the plastic is held under pressure long enough to produce parts with consistent quality. An injection molder can use mold-flow-analysis software instead, but that wont put a part in your hands now, will it?
Fictiv operates a global network of highly-vetted and managed manufacturing partners for injection molding s and can help you take your product from prototyping through production. Because we offer a wide range of capabilities through a single platform, including both 3D printing and injection molding, you can use the process that you need when you need it. You wont find that type of one-stop shopping everywhere, and we can produce complex parts (including prototypes) at blazing speeds.
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