Time to read: 8 min
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If plastic injection molding is fast, how is rapid injection molding different? Traditional injection molding already has short cycle times, aka the amount of time it takes to produce parts. Depending upon a part's size and complexity, a single cycle can take just a few seconds.
That's significantly faster than CNC machining, which can take anywhere from several minutes, to a few hours, to a few days. In terms of cycle times, traditional injection molding is also faster than 3D printing, which typically takes a minimum of several minutes per build.
Rapid injection molding is considered to be rapid because the tools that it uses take less time to produce. With traditional injection molding, a complex tool can take eight weeks or longer to machine. With rapid injection molding, the tooling times are much shorter ' and the mold materials are less expensive.
Yet there are some tradeoffs to consider. Because of their materials of construction, rapid injection molds have a shorter tool life and can't match the part tolerances of traditional high-volume molds, which are often made of expensive hardened steel.
So, how do you know if rapid injection molding is what you need? After all, terms like 'fast' or 'slow' are relative. If shorter lead times are critical for your project, when do you need your parts and which tradeoffs can you make? And can rapid injection molding support design complexity?
Remember: rapid injection molds take less time to produce than traditional injection molds.
There are two main reasons to use rapid injection molding ' and they're not just about speed. One is about rapid prototyping and the other is about bridge tooling.
Unlike traditional injection molding, which has lead times measured in months, rapid injection molding can put parts in your hands in a few weeks. That's what Alea Labs discovered when the developer of smart HVAC systems partnered with Fictiv on a project.
In this rapid prototyping injection molding example, the plastic vents and grilles Alea Labs designed had many ribs at various angles. The company needed a partner that could support design complexity and shorter lead times to accelerate time-to-market. They found it in Fictiv.
Design engineers need to balance rapid injection molding's speed against other requirements.
Before you decide to go with rapid injection molding for prototypes, it's best to understand how it works in terms of part design, tooling, processing, and part samples. Then, make sure you have the right partner. This article is a good place to learn about rapid injection molding, and Fictiv is ready to help when it's time to start molding parts.
3D printing and CNC machining have longer cycle times than injection molding, but you won't have to wait for a tool to arrive before prototyping or production can begin. CNC machines use tools for cutting, milling, drilling, and other operations, and every shop has a suite of tools on hand, but milling a part takes much longer than molding one. So, it might take longer to 3D print or CNC machine a part, but prototyping that starts sooner can put parts in your hands more quickly, enabling you to refine your designs more quickly, too.
Yet there are other considerations. For example, will 3D printing support the same resin you plan to use during production? If not, rapid injection molding is a better choice for prototyping ' and you'll enjoy an easier transition to production since you won't have to redesign your part for a new manufacturing method. CNC machining can produce parts with complex geometries, but so can rapid injection molding ' if you have the right partner.
Rapid injection mold tooling has a shorter tool life and less exacting tolerances than the tools used in high-volume injection molding. But that doesn't mean you have to sacrifice part quality to get a mold more quickly. Fictiv machines rapid injection molds from different metals ' or combinations of metals ' to balance speed against other project requirements, such as support for design complexity. The materials we use are also suitable for rapid heating and cooling injection molding.
We can help you compare traditional injection molding to rapid injection molding, and we also provide 3D printing and CNC machining services if you need them. No matter which process you choose, you'll get design for manufacturing (DFM) help along with your quote. Because there are key differences between traditional and rapid injection molding, the rest of this article covers part design, tooling, processing, and part samples.
Fictiv provides DFM feedback along with your quote so that you get your parts made faster.
There are ten major considerations when designing a part for the rapid injection molding process.
Fictiv's Injection Molding Design Guide examines each of these considerations in detail. They're the same with both traditional injection molding and rapid injection molding, but rapid injection molding raises some special concerns with material selection and part tolerances.
Injection molding materials range from commonly used polymers to specialty plastics and polymer blends. There are hundreds of different plastic resins available, and they each have different end-use properties and processing requirements. Plus, the same plastic material can come in different grades, including resin types with glass or carbon fibers.
Rapid injection molding supports many of the same plastics as traditional injection molding, but abrasive materials such as glass-filled nylon cause softer molds to wear more quickly, which shortens tool life. That doesn't mean you can't use these materials, however. In the case of Alea Labs, the company needed to use a special molding compound with a high glass content.
Corrosive grades of plastic, like PVC or POM, can also cause an injection mold to wear more rapidly. Tool life usually isn't a problem if you need prototypes or lower production volumes, but it's worth considering how many parts you need. If a rapid injection mold requires repairs or replacement, it could affect your project timeline.
Rapid injection molded parts that will be used in larger assemblies need to have correct and consistent dimensions so that parts fit together. Because some degree of dimensional variation is expected in any manufacturing process, you'll need to define part tolerances. These allowable variations are expressed as plus or minus dimensions and are a function of both the resin type and the mold material.
Traditional injection molds made of hardened steel can produce parts with fine tolerances and withstand production of hundreds of thousands of parts. Softer rapid injection molds won't last as long and might not be able to meet the same dimensional standards. The commercial tolerances that rapid injection molds can achieve are less precise, but you'll get lower-cost parts using lower-cost molds at faster speeds.
Let's say that's what you need ' what's the right type of tooling material for your rapid injection molding project?
Rapid injection molded parts need tolerances that support alignment and assembly.
Rapid tooling injection molding uses tools made of aluminum, soft steels, or semi-hardened steels in various grades. They typically have a single cavity because multi-cavity tools take longer to produce. Hardened steel is sometimes used with rapid injection mold inserts, but hardened steels take longer to machine and are more expensive. Rapid injection molds can also use a master unit die (MUD) to deliver tooling quickly and less expensively, but at lower volumes and with less exacting tolerances.
Aluminum can be machined twice as fast as steel and doesn't require post-machining heat treatment ' together, these two factors shorten tooling times significantly. Aluminum also has excellent heat transfer properties, which can support faster cycle times. Aluminum doesn't polish as well as steel, however, and that can affect the appearance of rapid injection molded parts that need to be glossy or optically clear. And if you need tight-tolerance parts, an aluminum mold probably isn't the best choice.
Typically, aluminum molds can handle 10,000 shots or less. That might be enough for your rapid injection molding project, but aluminum molds can't handle the high clamping pressures from large injection molding presses. PEI, PEEK, and other plastics that require high processing temperatures aren't recommended for aluminum molds either because aluminum doesn't maintain high temperatures well.
That's why Fictiv generally recommends soft and semi-hardened steels instead of aluminum for rapid injection molds. Although aluminum tools can be cut in just a few days, P20 steel tooling has lead times of two weeks or less ' and P20 can be easily welded to support engineering change orders (ECOs), which are common during prototyping or early-stage production. For glossy or optically clear rapid injection molded parts, NAK80 semi-hardened tool steel is the best choice.
The Society of the Plastics Industry (SPI), the trade association now known as PLASTICS, defines five classes of injection molds. These classes provide a convenient way to compare plastic injection molding tooling in terms of production volume and cycles, but they're also useful when considering rapid injection molds.
SPI Mold ClassVolumesCycles101HighOver 1 million102Medium-to-High500,000 to 1 million103MediumUnder 500,LowLess than 100,PrototypeLess than 500Based on volumes and cycles, SPI classes 104 and 105 might provide what you need. SPI Class 104 molds have hardened steel inserts for tighter tolerances, but have bases made of less expensive cast metal. SPI Class 105 molds sometimes use hardened steel inserts and are the least expensive SPI mold classification.
Rapid injection molds can also use master unit die (MUD) inserts with a standard mold frame and customized, removable inserts. MUD molds, as they're called, can be produced relatively quickly while lowering the cost of initial tooling by as much as 66%. If cost is a consideration, a MUD mold may provide the right combination of advantages.
Ultimately, it doesn't matter how fast a mold maker can machine a tool if an injection molder can't use it to process your parts without defects. That's why Fictiv's global Quality Management System (QMS) ensures our network of carefully vetted manufacturing partners keep quality standards high, regardless of whether you need traditional injection molding or rapid injection molding.
And Fictiv can provide you with T1 samples for functional testing and dimensional measurements in just a few weeks. You can also get T2 and T3 samples if your design changes ' and if your design changes require mold changes, then a steel mold that supports welding could make the difference between keeping your tooling or starting over.
There's a lot to consider with rapid injection molding, and it pays to have expert guidance to make the right decision.
With Fictiv, it's simple to create a free account, upload your part drawing, and get a quote along with detailed DFM feedback. And our in-house injection molding experts will guide you from prototyping through production, making recommendations that will help you leverage the speed of rapid injection molding and meet your other requirements.
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Time to read: 8 min
Is prototype injection molding an oxymoron? If you're like most designers, you've learned that plastic injection molding is for high volumes of production-quality (i.e., non-prototype) parts. Maybe you've 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, it's time to unlearn some of what you've 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, there's 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, you'll 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 doesn't contain enough draft, our DFM experts will suggest a larger draft angle so that your parts eject smoothly.
Fictiv's 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 you're not ready for manufacturing, you're probably still in the prototyping stage. But which type of prototype do you need?
This isn't 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 don't warrant the cost of an injection-molding tool. That's because the designer usually needs just one or two parts, and it's difficult to justify the expense of an injection mold when you're 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, let's 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. That's 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 they're easy to manufacture. Let's say you 3D-print some components that you then assemble. They fit together flawlessly and let you test the product's functionality.
That's 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 don't 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. That's 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.
There's 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, you'll 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. There's also this handy online checklist so that you can determine if you're ready to go from 3D printing to injection molding. And remember that you don't have to wait until your parts are production-ready to get injection-molded samples.
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. (That's because prototype molds are usually made from softer materials.) Still, if you're 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 don't have the same mechanical properties as your intended production materials. For example, PEEK is an engineering plastic that's used in some medical devices. It costs significantly more than other polymers and may have a high minimum order quantity (MOQ) if your supplier doesn't 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 won't provide a full test of your part's moldability. Since PPSU and PEEK are both available as 3D-printing filaments, could you use additive manufacturing instead? You'd 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 don't have the same end-use properties as their injection-molded counterparts. For example, 3D-printed PEEK isn't as strong as injection-molded PEEK. And if your part is for a medical device, you'll 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. That's 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.What's the difference between a prototype injection mold and a production injection mold? It's 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 doesn't end there. There are several different steels that are used in injection molds ' and there isn't just one kind of aluminum.
There are also SPI classes for mold finish to consider. In the table below, look at SPI Class 105. That's 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 won't produce injection-molded parts with tolerances that are as tight, or precise, as those with steel molds. That's 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 don't rule them out for prototype injection molds. These steels can achieve tighter tolerances and aren't 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. It's more expensive than soft or semi-hardened steels, but hardened steel lasts longer (i.e., more cycles) and can achieve tighter tolerances. Prototyping doesn't have to produce millions of parts, of course, but what if you need tight tolerances for medical, aerospace, or other demanding applications? Aluminum just won't do.
Whether it's 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 won't 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 won't find that type of one-stop shopping everywhere, and we can produce complex parts (including prototypes) at blazing speeds.
Ready to get started? Create a Fictiv account and upload your part design.
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