Injection molding vs. additive manufacturing

Features - AM/Injection molding

Nigel Flowers, UK managing director of Sumitomo (SHI) Demag, examines additive manufacturing and injection molding, noting each has distinct advantages and when used for the right application, they complement each other well.

Today’s injection molding machines are designed to deliver quality parts with a high cosmetic finish, often in just a few seconds.
The possibilities of 3D printing (3DP ) were showcased during the COVID-19 pandemic to shore up PPE supplies.

In the last 18 months, additive manufacturing (AM) has crossed over from hype into reality, with a proliferation in prototyping as the world struggled with the COVID-19 pandemic and challenges of rapidly sourcing personal protective equipment (PPE). Global communities embraced its potential, with innovators, entrepreneurs, and even students printing items.

While many cite AM as the next big disruptive trend, it’s still commonly used as a prototyping tool to test engineering designs. It’s neither fast nor cost effective enough to manufacture plastic precision parts in large volumes.

Growing at a compound annual growth rate (CAGR) of 9.8%, by the end of 2027, AM is expected to exceed $15.3 billion. Agility and real-time manufacturing are AM advantages that can be attributed to many factors including the development of new concepts, product personalization, and prototyping. In comparison, a new study by Polaris Market Research estimates that the global injection molding plastics market will be worth $425.7 billion in the same time.

Comparing the two technologies is a moot point. Each has distinct advantages. And when used for the right application, they complement each other well. Even if AM is coming of age, it doesn’t mean traditional injection molding has had its day,” comments Nigel Flowers, UK managing director of Sumitomo (SHI) Demag. “The COVID response was quite unique in that 3DP [3D printing] helped to shore up supplies. Yet, many viewed it as a temporary measure to complement the efforts of injection molders working night and day to maintain critical suppliers.”

Patient safety first

Healthcare is naturally one of the environments where rising use of AM is forecast. Some groups use the technique for pre-operative planning or as alternatives to medical educational cadavers. Additionally, there have been huge advances in using AM to make replacement bones, prosthetics, dentures, organs, and bioprinting tissue and muscles. For these functional parts, injection molding wouldn’t be financially viable due to the level of personalization and the cost of creating a mold tool.

Yet, for mass-produced medical devices components, injection molding wins on cost, quality, and processing repeatability. Today’s injection molding machines can quickly deliver quality parts, consistently, with tight tolerances and a high cosmetic finish. Molded medical parts can be created thousands to millions of times in succession. For in vitro diagnostic medical devices, pipette tips and PCR-plates, this precision and repeatability cannot be compromised.

For short-run commodity parts that don’t have critical dimensions or demanding mechanical-performance requirements, AM can deliver functional parts. However, finish remains a key sticking point because the parts are printed in layers and the surface finish can be rough. Currently, most AM components need some post-processing work to smooth the edges, adding to the overall processing time.

Conversely, in plastic injection molding, finish and surface textures can be created by the mold tooling. Additionally, new generations of all-electric machines have brought vastly increased levels of precision, made possible thanks to advanced direct-drive technology.

“We are now able to achieve very high levels of repeatability while a specific 14mm screw design improves the dosing, which is critical when molding precision medical components,” Flowers explains.

Of course, patient safety comes first. There’s a drive toward using new and more innovative regulated materials with a better flow and high impact strength to mold components and meet European Union Medical Device Regulation (EU MDR) and In Vitro Diagnostic Regulation (IVDR) regulations.

Counterfeiting and intellectual property (IP) protection in AM is also a big factor. For AM suppliers operating in the high-liability medical and automotive sectors, the risks can be especially significant. However, any product in any sector could be counterfeited.

Given that injection molding has been around for more than 70 years, traceability in this sector is more advanced. Most machinery suppliers provide secure data capture and documentation. Authentication of individual medical components requires a fingerprint-style approach to traceability. However, it’s not purely about mandatory information and supply chain tracking. Real-time traceability is about being able to call up data and verify the exact settings used on the injection molding machine when that individual plastic part was made. That’s where connectivity to a management execution system (MES) is vital.

Mold tools can create special surface textures and blend materials and colors for numerous consumer products.
The ability to 3D print functional organs and medical scaffolds on demand is a rapidly growing field.

Making obsolescence obsolete

As the speed of technology accelerates, so too does obsolescence and the consequence of non-available parts. Rather than stockpiling discontinued parts, AM offers a practical and strategic inventory solution.

Aerospace manufacturers were among the first to use AM to upgrade components and create replacement parts for maintenance, repair, and overhaul (MRO). For aircraft parts with long lead times, complicated supply chains or obsoletion, AM offers an ideal alternative.

From a sustainability perspective, producing legacy parts reduces environmental waste and extends product lifespans. Signs suggest this trend will continue, with AM producing parts with complex geometries and features previously deemed impossible.

Rather than viewing injection molding and AM as competing technologies, when used for the right applications they are complementary technologies.

“AM is great for iterating designs and we are increasingly seeing molders using them to test out new concepts and create tooling prototypes. Rather than pitching the two against each other, recognize that they each have distinct advantages and that the level of innovation will continue to accelerate for both,” Flowers concludes.

Sumitomo (SHI) Demag