By Carrie Ellis
Simply put, rapid injection molding is another option for manufacturing parts from plastic materials—fast—using automated processes. Depending on the application of the part, it could be a viably quicker, more efficient, cost-effective way to generate parts as prototypes, bridge tooling or even for actual production.
| Braemar Leverages Rapid Injection Molding
By Greg Kagan
Today’s cars may be complicated, but for complexity they can’t hold a candle to that little pump in your chest, the human heart. That simple “thump-thump” is the result of an intricate and sophisticated interaction of chemical, electrical and mechanical processes, any of which could potentially cause malfunctions. Like a car, the heart isn’t always cooperative in presenting its problems when a specialist is watching. Fortunately, also like a car, the heart produces a variety of well-understood electrical signals indicative of its operation. Unlike a car, however, the heart has no built-in recording equipment, but doctors have figured out how to provide that capability, and that’s where Braemar, Inc. of Eagan, MN, can help.
Braemar manufactures a variety of heart-monitoring devices, which use electrodes attached to the patient’s body to pick up impulses generated by the heart. The devices record these impulses while the patient goes about his or her daily activities, and upload the recorded information to centralized medical systems at regular intervals. There, the data is analyzed so that specialists can identify problems that may have shown themselves for mere seconds at a time over a period of days or even weeks.
For orders under 5,000 units, Braemar usually stays with Protomold, anything above 5,000, the company will typically go to hard tooling.
According to Gary Swenson, senior mechanical engineer at Braemar, designs are primarily customer-driven. Even the colors of the plastic and the shape, size and type of switches can vary to meet customer requirements. “We always want to be first to market with anything we introduce, so product development has a very short window,” says Swenson. “Whether we’re developing a product for our own use or for another company, once we’ve got the parameters, we want to be ready for market in three to six months. And because users wear our devices, we want them to be as compact, lightweight, tough and reliable as possible. That’s where Protomold comes in.
“Before Protomold, we were using stereolithography (SLA) for most of our prototypes. The problem was that SLA doesn’t use the same resins we use for production. There are significant integrity differences in the resins, so stress testing of those prototypes couldn’t give us useful results. We tried urethane molds, but that limited the number of prototypes we could produce, so we were still looking for a way to get inexpensive, molded prototype parts in a reasonable timeframe. Fortunately, with Protomold we now have a process that gets us to market fast with plenty of opportunity for rigorous functional testing.”
Standard product development at Braemar begins with development of a 3D CAD model using SolidWorks software. Models are carefully evaluated for producibility, eliminating, wherever possible, problematic features like undercuts. SolidWorks also supports finite element analysis, a method for calculating the strength of a design and specific material from a 3D CAD model before the first solid model is produced. Braemar developers then make multiple SLA prototypes to be evaluated in hands-on design reviews. The models are modified as necessary in CAD and re-prototyped as final SLAs. Only then are they sent to Protomold for production of injection-molded prototypes for functional testing.
“Designs have been pretty thoroughly evaluated at that point,” says Swenson, “but because SLA doesn’t necessarily identify moldability issues, Protomold’s ProtoQuote still makes occasional recommendations for design changes. These are usually minor–a change in a radius or the thickness of a wall. We use the Protomold parts for functional testing based on Association for the Advancement of Medical Instrumentation testing protocols, but we usually test to twice the recommended standard. We may do up to three iterations with Protomold to finalize designs for production.”
In some instances, Braemar also uses Protomold for production. “Under 5,000 units, we usually stay with Protomold,” says Swenson. “Above 5,000, we go to hard tooling. With orders for specially designed monitors, Protomold’s fast turnaround for testing and production can be a big help. To move products quickly into the market, we sometimes end up making modifications on-the-fly in the later pre-production stages.
“We’ve found that, with careful planning, Protomold’s standard turnaround times of two to three weeks fits our schedule well. We have had a few situations, though, where we’ve had to use their faster three or five-day turnaround. Besides fast turnaround at affordable prices, we’ve also found Protomold helpful with ideas and information. They’ve got a lot of expertise on staff, and can provide useful ideas and solutions based on that experience. The one thing we’d really like from Protomold that we haven’t gotten is a walk through their plant. We’d like to see how they do what they do, but enough of their process is proprietary that we haven’t been able to arrange the tour. I guess, for the time being, we’ll just have to settle for fast, affordable prototypes.” |
Injection molding as a process involves using high levels of pressure to inject liquefied plastic into a mold, which is the inverted shape of the product. Precision-machined from metal, these molds are made up of two halves, labeled the core and cavity. Much consideration must be put into the mold-making process to verify that parts can be safely released from the mold, and the molten plastic can sufficiently fill out the mold before solidifying to avoid imperfections in the final product. Rapid injection molding is differentiated only in that it incorporates the use of automation in the process.
According to
Accumold’s marketing manager, Aaron Johnson, “Rapid injection molding is more than just a machine. In our experience, many of our customers and prospects don’t always know exactly what they want or need. Many of them are new to injection molding as well. Their prime objective is more about speeding up the process to create new products, which involves our expertise in manufacturing, as well as our experience as molders. Rapid injection molding is therefore more of a description of the marketplace demand that all molders face.”
According to Protomold, their rapid injection molding process is ideal for:
- Prototypes. Rapid prototyping processes are great for testing form and fit, but many times fused deposition modeling (FDM), stereolithography (SLA) and the others are no substitute for testing with real injection-molded parts.
- Bridge tooling. When your production tooling won’t be ready for another three or four months, it’s great to have a way to make those 100, 1,000 or 10,000 parts for pilot production
- market testing.
- Production. If your volume requirements don’t justify expensive steel production tooling, injection-molding service providers can supply production parts to meet your requirements.
When To Consider Rapid Injection MoldingSpeed to market is one of the major factors in choosing rapid injection molding over conventional methods. Protomold’s president and CEO Brad Cleveland feels that, “Rapid injection molding is the name we have given to our automated process of designing and manufacturing molds based on customer-supplied 3D CAD part models. Due to this automation, we typically cut lead time for the initial parts to one-third of conventional methods. Worldwide competition continues to drive accelerated development schedules, and rapid injection molding can dramatically reduce the time required to obtain functional injection-molded parts.” When looking for a service provider, take into account their turnaround times, as some offer options that vary from days to weeks.
In some cases, rapid injection molding can save money as well. This savings is attributed to avoiding the costs associated with expensive steel tooling, which is why many companies that specialize in customization or otherwise low-volume production runs may desire this process over conventional manufacturing. “Cost savings vary with the number of parts being produced, but rapid injection molding may also have a substantial cost advantage in runs that are in the thousands of parts,” Cleveland says.
Another reason why many designers are moving to rapid injection molding, as opposed to other manufacturing processes, FDM, selective laser sintering (SLS) or 3-D printing, is that this process is capable of handling miniature parts in greater accuracy. In fact, most companies that provide rapid injection molding services only accept orders for small parts. Rapid injection molding also can produce better surface finishes, including texturing, when compared to other processes.
Johnson explains, “The types of parts that Accumold sees on a daily basis are often so small and detailed that [FDM, SLS, 3D printing] methods can’t produce enough resolution to make the part perform. If a customer only needs a certain amount of fit and form, these [other methods] can work well. However, most of the micro-molding we do is because it can’t be done elsewhere. Rapid injection molding is capable of achieving higher resolution, and in our case, produces production-like parts.”
Dan Scullin, design manager of Matrex Mold and Tool, Inc. in Portage, WI, says that despite lower costs and turnaround times, rapid injection molding is best implemented “when it is critical to test and evaluate finished parts with respect to the properties that will be exhibited in the final injection-molded part.” When considering what company to use as a service provider, Scullin recommends delving into each prospective service provider’s “design capability, analysis capability, experience, software, equipment, review of completed projects, and cost and delivery of those projects as good benchmarks for comparison.”
Rapid Injection-Molding Limitations
While there are numerous benefits to rapid injection molding, the process does have its constraints. The material of the injection-molded product can be plastic, aluminum or brass, but not all service providers offer the same materials mix.
Additionally, although most providers operate within the same range of products, they don’t always provide the same sizes. For example, Johnson says, “At Accumold, we can handle parts from one ounce down to features measured in microns. We are always pushing the edge when it comes to the extreme nature of micro-molding: smaller features, tighter tolerances and faster output.”
According to Protomold’s website, “Ideally your part should be designed with minimal undercuts, but the good news is that the design of many parts which appear to require them can be easily ‘tweaked’ to eliminate the need for undercuts. However, our rapid injection molding process can support many types of undercuts.” Accumold also offers expertise in the area of design for manufacturability.
Scullin admits, “Often the parts are simplified and designed with no sharp corners that would require electric discharge machining” (EDM). However, in cases in which the simplification doesn’t negatively affect the design’s application, these modifications have been known to improve a product.
Johnson gives engineers this advice,”Ask yourself if this service is providing me a part or a solution? Can this service take what was learned from the prototype process and handle my production?” Another potential problem can be CAD compatibility, but yet again, most service providers, whether it be conventional or rapid injection molding, offer a wide selection of the most popular CAD software options in facilitating the process.
Furthermore, some injection-molding providers furnish inspection services. Accumold has a 24-hour quality lab with three high-powered optical microscopes, one with laser measurements. Plus, each project gets a control plan with the critical dimensions noted, and a special team checks them.
Johnson adds, “The use of ‘rapid anything’ is not slowing. We are a demanding society that has little tolerance for slow. Whether it’s microwave popcorn or the latest cell phone design, speed has permeated our society at all levels, including manufacturing.”
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