Development of medical devices that are molded from thermoplastics or that have plastic components should begin with collaboration between the OEM’s engineering team and the mold manufacturer. While 3D solid modeling, as well as other forms of developing plastic components, can be useful tools for generating a visual representation and even “touchy-feely” parts, medical devices and components require something more.
Today’s mold manufacturers that specialize in supplying the medical device market — including disposables and durable products such as medical diagnostic, treatment devices, and instrumentation — can provide the insight that will help eliminate some of the hurdles and/or manufacturing challenges that often occur with product development.
Some mold manufacturers offer an extensive range of services such as product development, which includes plastic part design assistance. This ensures that the product or components that the OEM’s new-product design engineers have drafted are actually designed for “mold-ability” or manufacturability. A part that looks good on the screen might not, for a variety of reasons, be suited for the injection molding process.
Additionally, the mold manufacturer can also provide innovative and creative input into the design of the product or component that can offer benefits such as reduced cost-to-manufacture by combining various components into a single component. That means that instead of two or three separate molds, the product or its various components can make use of advanced mold technologies such as in-mold labeling, inmold decorating, and in-mold assembly, or new molding technologies such as multi-shot or overmolding, in which two or three different materials or colors of material can be injected into the same mold to produce a complex part. Components can have a rigid thermoplastic substrate over-molded with a thermoplastic elastomer (TPE) for ergonomic or aesthetic purposes.
Mold manufacturers with good R&D capabilities can provide product development assistance in a variety of ways. They can provide recommendations that can reduce overall cost not only in the prototype phase, but looking forward to the production tooling, they can also — through the use of 3D modeling or simulations — provide very useful conceptual images of the part or product. However, for a simulation to provide good, accurate data, the information must be filtered through a mold maker with the experience and expertise needed to understand that data. The output of a 3D simulation is only as good as the engineer’s input. Simulations, while a good start for a concept, are not the best for every scenario, especially where functionality of a product and the dynamics of injection molding are concerned.
Additive Manufacturing and Prototyping
Additive manufacturing (AM) can be useful in several ways. First, through processes such as stereolithography (SLA) or Fused Deposition Modeling (FDM), the product design engineers can achieve a relatively good prototype model. The drawback to these types of prototypes is that in many cases, the material required for the end-use part are not available for the AM process. While many new materials have been developed over the past few years as AM has evolved — such as ABS, PC-ABS, and acetal, among others — there are many more material requirements for medical applications for which no material would be available in AM to create an exact prototype.
However, one of the benefits to AM for prototypes is that complexity of the geometry is of no consequence. That said, while geometry complexity is not an issue for the AM process, the part may have complexities that make it impossible to mold through the injection molding process. The mold manufacturer’s engineering team and the OEM’s engineers need to collaborate during the development stage to evaluate what can be done to achieve what the OEM needs or wants in the product’s functionality, and what can realistically be done in a mold with the injection molding process.
A prototype using the AM process is also beneficial in that it gives the engineer a part to hold and to present to marketing for evaluation, and perhaps to perform some form and function testing prior to advancing to the development phase. There are a number of AM service bureaus that a mold supplier can work with to provide these types of prototypes. Some mold companies may have prototyping capabilities in-house using one or more of these AM processes.
For the medical device market, designing a medical product or component requires complex levels of design, development, and testing prior to actually building the multi-cavity, high-volume mold. Because of this, one of the most optimum ways of getting a prototype part, particularly for the medical industry, is to build a prototype mold with a toolmaker that has multiple hightech manufacturing tools available. This will enable them to produce a core and cavity insert that can be dropped into a mold base that the moldmaker may have on hand for tryouts, allowing parts to be produced fairly quickly. The advantage of this is that the parts can be molded in the actual plastic material required for the product or part. This makes functional testing more accurate and provides the best data for further development.
Another benefit to developing a product or component in a single-cavity prototype mold is that the molding process can also be tested. The molding process may not be optimized in a prototype mold; however, it does allow the engineering team to determine if there are design issues that would challenge the molding process — for example, are there areas in the part that would inhibit a fast cycle time, or possibly cause a part to get “hung-up” in the mold on ejection?
Another AM technology that has been determined useful in creating cores and cavities for a prototype mold is the Direct Metal Laser Sintering (DMLS) process. Developed by an additive manufacturing equipment maker in Germany, (EOS GmbH), core and cavity can be created from powdered metal that comes in a variety of steel and alloys, and even titanium. A single core and cavity can be produced in about a day, depending on the size of the part. The DMLS process is only limited by part size; however, the newer equipment from EOS can handle larger parts.
The benefit of using DMLS for creating a core and cavity insert is that parts can be molded in the required material within about three days, depending on how much post-sintering work needs to be done, such as polishing. However, there are some limitations to the number of parts that can be molded using DMLS cores and cavities, depending on the polymer material used. Some test runs have gotten as many as 50,000 parts. As with any AM process, there are a number of variables that determine how many parts can be molded from a DMLS core/cavity set.
One of the disadvantages of using the DMLS process for medical devices and components is that medical parts may require a level of dimensional accuracy that DMLS cannot provide (for example, to create a core and cavity in 10ths instead of +/- a thousandth or two). While this process can generate a good representation of the part, secondary machining is typically still required to get the part dimensionally correct.
Today, using 3D solid modeling, CAD/CAM software, and high-speed machining, a single-cavity insert can be built in a fraction of the time that it used to take, depending on the geometry of the part. While that is longer than a core/cavity set in the DMLS process, the benefit of a single cavity prototype mold allows the OEM to get closer to the actual part accuracy required in the actual material required. It will produce parts that can be tested and evaluated for form, fit, and function in the actual material chosen. However, if the exact material has not been pinned down, more than one core/cavity insert may be required to test various materials.
The disadvantage of a single cavity prototype mold is that while it allows the OEM to test/qualify a sample of one piece, it doesn’t give a range of cavities to predict the quality throughout the entire mold. In some instances, Tech Mold builds what it calls a “pilot” mold, typically a 1-4-cavity mold that can be a better predictor of the part’s final characteristics. The pilot mold will mimic the production mold in design, venting, and cooling. It will also enable the company to perform process development and provide solid data that will be a valuable foundation for decision making — two critical factors when building high-cavitation production molds.
With medical devices and components, the entire process is longer and more intense with a longer mold and process development time — which is precisely why the development phase is critical to the success of the project. All of the prototyping methods are useful tools, but they are just tools — just first steps in the long process of developing medical components. Choosing which method is best, i.e. which prototype process will allow the medical device OEM to gather the best data, enable optimum testing and manufacturability, and ultimately provide faster time-to-market, is critical to the success of the project.
This article was written by Vince Lomax, Vice President of Tech Mold Inc. in Tempe, AZ. For more information, Click Here .