Injection molding is used to fabricate many medical products. It’s a tried and tested manufacturing process that supports high-volume production while allowing low per-part costs. Injection molding also facilitates design and manufacturing complexity because of its part-to-part integrity. A wide selection of available fabrication materials is another benefit of employing plastic injection molding for medical products.

Medical injection molding allows a choice of various materials with different properties, price points, regulatory approvals, and compliance with established standards. However, it’s not the number of choices that matters—it’s the ability to select a material with the specific attributes needed for a given component, assembly, or device.

A disposable applicator can be made from a cost-efficient, impact-resistant commodity plastic. But some medical products may require a more robust (and expensive) engineering plastic, a biocompatible material, or an antimicrobial polymer.

“Although we utilize commodity grade resins for disposable components, we specialize in high temperature/performance resins (PEEK, PPSU, etc.), which are typically used in implantable, surgical, and dental applications,” said Andy Lesser, vice president of sales at Allegheny Performance Plastics, a Leetsdale, Pa.-based injection molder, manufacturer, and global supplier of technically advanced functional parts and assemblies. “There are various design considerations and molding challenges with each material, which we overcome by partnering with our customers and working through our proven five-step process.” (That process covers discovery, feasibility and analysis, design solution, prototype testing, and production.)

Multi-material injection molding (MMM) is a useful method to diversify development of the plastic molded product fabrication. It combines different materials and colors to create high-quality plastic parts. As with traditional injection molding, MMM fills voids or cavities in a pre-machined mold, thereby taking on the shapes of the designed tooling. The three most widely used methods of MMM fabrication are multi-component, multi-shot, and over-molding.

Generally, MMM’s advantages over other production methods include making parts with an elastic modulus that varies with location on the part, creating a single-structure part with different regional materials, and creating a single part with multiple, independent polymer colors.

“For products that require over-molding or insert molding, we simulate these complex processes to ensure different components fit properly (dimensional tolerances) and the final assembly is structurally sound and functional,” said Harshal Bhogesra, director of sales at Moldex3D, a Farmington Hills, Mich.-based provider of plastic injection molding simulation software. “It’s also crucial to understand how different materials interact, especially in medical devices. We allow manufacturers to analyze and predict material behavior, ensuring compatibility and performance of the final product. By accurately simulating multi-component molding processes, manufacturers can also significantly reduce the need for physical prototyping, saving time, resources, and energy.”

Dip molding is a plastic process that is utilized to create plastic products or parts that have a hollow interior. It involves submerging a mold in a bath of heated plastic, then allowing it to cool. Once cooled, the hardened plastic exterior is separated from the mold. Since the mold fills the space inside the plastic, dip molding fabricates product and components with a hollow interior.

Though typically performed to create plastic parts, some manufacturers use dip molding to add a plastic layer over a metal product or part. Known as plastic dip molding, the process differs from conventional dip molding because it doesn’t need a mold—the metal product or part is submerged in a bath of heated, liquefied plastic.

Plastic dip molding’s purpose is to improve performance of metal products and components. Those parts are susceptible to corroding without a plastic coating. The dip molding adds a weather-resistant layer over the product or part’s surface. The layer of plastic also protects the underlying metal from scratches.

“Dip molding allows for creation of complex geometries in a single component—often those that could not be created in an injection mold, such as a ‘Y’ shape,” said Jeff Charlton, vice president and general manager of dip molding and coating automation solutions at Aptyx, a Tempe, Ariz.-based partner for complex injection molding, extrusion, coating, and medical device assembly. “The process is widely used for a range of medical devices and components such as nasal and spring reinforced arterial cannulae, urinary catheters, stethoscopes, balloons, rebreather bags, and other bladders.”

Most dip molding processes are done using plastisol, a type of plastic made of PVC particles suspended in plasticizer, because it’s cost-effective and generally easy to use. Manufacturers may use other bathing solutions for dip molding, like polyurethane, silicone, or latex.

“The equipment to produce dip molded devices ranges from indexing batch to highly automated systems, and the key drivers as to the choice of equipment are the process, the size of the product being produced, and the overall volume or desired throughput,” said Charlton. “Key inputs to the chosen process are product geometry and the polymer being used. As to whether the equipment is in-house or at a manufacturing partner, that is frequently a business decision although unlike injection molding, dip molding expertise is quite concentrated.”

Another specialty service involved in medical molding is the advanced material blending of specialty additives. Custom blends are usually proprietary formulations designed for specific customer applications and environmental conditions. There are a variety of choices for how blends are technically constructed including powder/liquid mixing, granulating, pelletizing, and extruding.

The final result is a single product or formulation that contains several different chemical additive components.

“The process of blending specialized additives into a base formulation will vary depending on multiple factors,” said Brian Reilly, director of sales and marketing at ProMed Molded Products, a Plymouth, Minn.-based contract manufacturer of complex, intricately designed molded silicone and plastic components and assemblies for highly regulated industries.
“The main influencing variables may include the type of elastomer system we intend on incorporating the filler into and the viscosity of that chosen system, the solubility of the chosen filler into the base system, the physical form of the filler (liquid, crystalline, powder, gel), the targeting loading level of the filler, and the desired physical properties of the resulting blend. We also have to consider any special handling requirements with fillers such as temperature or humidity restrictions, exposure to levels of shear, and compatibility with the cure chemistry of the elastomer.”

Some of the components that benefit from material blending services include drug delivery devices that incorporate active pharmaceutical ingredients (APIs) like steroids, hormones, or antimicrobials. Other examples include desiccant-loaded components for medical device or aerospace applications.

This encompasses functionality like electrically or thermally conductive fillers, radiopacity with BaSO4, tungsten, or tantalum, and incorporating pigments, colorants, or dyes to accommodate branding or markers, as well as directions for appropriate use.

“Once we’ve identified any potential restrictions, we can then move forward with an appropriate method for homogenizing base and filler,” said Reilly. “Common techniques include milling with two or three roll mills, blade style mixers, and bladeless style mixers or dual asymmetric centrifugal mixers.”

In addition to the molding equipment and services, many medical molders have ancillary capabilities for the OEMs they partner with. Design and manufacturing support is usually chief among these in order to ensure a high-quality and manufacturable medical molding project.

“We offer a wide array of design and engineering services depending on application, ranging from mold flow and other predictive modeling to fully integrated optical design support,” said Brandon Swinteck, chief revenue officer at Carclo, a Latrobe, Pa.-based provider of injection molding and contract manufacturing services for medical, optic, and electronic applications. “The addition of these up-front services offers tremendous value to customers looking to augment their own design capabilities, in addition to providing valuable information about the molding process prior to the start of tool design and validation.”

Automation processes are also included in many medical molders’ arsenal of technologies. In the current landscape of smart manufacturing, it’s a necessity for some processes to be automatic.

“In our manufacturing operations, various automation processes significantly enhance efficiency and quality,” said Matt Bont, Ph.D., silicone engineering manager at EPTAM Precision, a Northfield, N.H.-based provider of advanced precision manufacturing solutions with expertise in polymer machining, precision metal component machining/micro-machining, laser cutting/welding, and plastic injection molding. “For instance, utilizing ejection and robotic systems integrated in the injection machines to extract parts and/or sprues from molds, as well as for sorting in family tooling. Conveyors are strategically employed on machines handling delicate parts to prevent damage during part removal. Furthermore, automation facilitates tasks such as assembling components, heat staking, ultrasonically welding, pad printing, and conducting functional tests and/or inspection on sub-assemblies, contributing to streamlined operations and consistent quality standards.”

Tools of the Trade

Injection molding tooling is essentially the heart of injection molding. Whether the molding project involves a complex application or simple part, tooling design can determine the quality of the injection molding process and the parts fabricated. The main goal for the design of tooling is to create a product with high manufacturability. Accomplishing this requires a high-quality process that is simple and efficient, long-lasting, simple to operate and maintain, and meets OEM specifications at the lowest possible cost.

There is a strong bond between tooling complexity and tight tolerances. Tooling design, materials, and cavitation all affect tolerance—generally, the more simple of a process, the more likely it can achieve and maintain tight tolerances. On the other hand, complex parts can put tight tolerances at risk because there are more variables like the number of cavities in the mold or needing to precisely heat or cool the tools.

For example, shrink rates will vary and tight tolerances will be more difficult to reach if tooling isn’t designed for consistent cooling. Mold and part cooling are also integral for determining surface finish.

“In-house tool design and manufacturing provides a higher visibility and accountability for the success of a new product development launch, as the manufacturer has full control of the entire process,” said Rey Obnamia, vice president of technology and regulatory and an operating partner at IRP Medical, a San Clemente, Calif.-based manufacturer of liquid silicone and rubber molded, engineered components for the medical device industry. “Tool design is crucial because there is a very high success of matching the desired outcome of using that tool from ‘Print-to-Part’ utilizing the manufacturer’s array of existing injection molding machines—if not, then compression, transfer, or flashless molding equipment, robots, end-of-arm tooling, product handling, product inspection, and any secondaries. This offers an ‘end-to-end’ solution for a customer who is expecting product launch on very tight timelines to place product into the marketplace.”

Sophisticated, injection-molded components need equivalently sophisticated tooling. Some common added features for this type of tooling can include undercuts and threads. For complex geometries, the tooling might need rotational hydraulic motors, mechanical racks and gears, hydraulic cylinders, floating plates, or multi-form slides.

“In-house, modular tooling speeds up the overall lead time for mold build, design, and maintenance,” said Steve Raiken, founder and president of RenyMed, a Baldwin Park, Calif.-based full-service medical injection molder. “Our modular tooling solution can accommodate same day or next day in-mold exchanges. Even when using a local tooling provider, a quick mold change will require pulling and packaging the mold, completing the paperwork, and scheduling the shipment to and from the vendor. Our ERP system includes all of these steps in addition to project management, validation actions, and production—all within a system that is secure and backed up.”

The techniques of scientific injection molding (SIM) seek to improve molded part quality and consistency as well as optimize process efficiency and performance. The systematic approach—also known as decoupled injection molding—treats the fill, pack, and hold stages separately to minimize fluctuations and improve consistency of product.

SIM relies on controlled, data-driven processes. It accepts the scientific principle of plastic behavior, combining them with known variables that can be controlled to lower cycle times and increase machine efficiency. SIM also focuses on material behavior, allowing machine-independent processes and reducing the need for machine-specific parameters. The process standardizes process development and troubleshooting methods across technicians, presses, molds, and companies.

Cavity pressure sensing technology is used in scientific injection molding. Cavity pressure sensing is a molding process control tool that leverages sensors in order to monitor the pressure inside an injection mold. Using strategically placed transducers in multi-cavity and hot manifold tools allows monitoring and controlling the process in real time. Sensors can either be placed on the tool’s surface as a cooling lines or unit failure backup.

“First and foremost, measuring the plastic pressure at the end of fill ensures that you have a dimensionally correct part on every shot (part) that meets the process curve. It will also alarm and divert (reject) any process that does not fall within the alarm limits,” said John Budreau, director of new business at PTI Engineered Plastics, a Macomb, Mich.-based injection molder and manufacturer of plastic components and subassemblies. “Having the injection mold built with cavity pressure sensors will also prevent running large quantities of bad parts with the potential to send defective parts to the customer. Another major benefit in a production manufacturing environment if there is machine issue or the mold must be moved for some unforeseen issue, the cavity pressure sensors will be used to duplicate the process curve to produce a part consistent to the original validated process.”

Many metal additive manufacturing (3D printing) methods have carved out a niche in their respective applications; tooling has long been a target for various approaches. Metal injection mold tooling has high precision, surface finish, and material property requirements, which lead to high costs, long lead times, and the requirement for highly skilled toolmakers who spend hundreds of hours producing a tool.

The toolmaking industry is in the midst of a significant labor shortage, with the number of toolmakers falling 50% in the last 25 years, according to Mantle’s director of marketing Ethan Rejto. He said metal 3D printing can mitigate these labor shortages by automating 85% and above of the mold insert fabrication. This way, tools can be built with less labor to lower lead times and boost capacity.

“Traditional injection mold toolmaking is incredibly slow and expensive and can only be performed by scarce, hard-to-find toolmakers,” Rejto told MPO—Mantle is a San Francisco, Calif.-based provider of precision metal 3D printers for the tooling industry. “Printing allows tools to be produced with the push of a button in just days, rather than months, by removing many of the complex steps involved during a tool build.”

During product development, a point can be reached where plastic 3D-printed prototypes are no longer helpful for validation—material properties and part performance differ too greatly from the final part produced via injection molding. One solution involves using aluminum mold tooling, which is quicker and less expensive than steel tooling due to its ease of machining.

“One challenge with aluminum tooling is that its thermal properties are dramatically different from tool steel, the material from which the production mold will be made. This thermal difference leads to risk, as the part will shrink in the aluminum mold differently than in the production tool,” said Rejto. “The shrink difference causes the same problem as when using a plastic 3D-printed part, although not as dramatically, where the prototype part is not an accurate representation of the production part.”

Rejto suggested the alternative option of 3D printing tool steel mold inserts because they’re the same material a production mold will be made from and molded parts are considered production-equivalent. That way they validate the final material choice, manufacturing process, mold design, and mold processing parameters.

Micromolding for Microfluidics

Droplet microfluidics are a recent trend in laboratory automation technologies. They allow exploring the biological world at unprecedented resolution and throughput, enabled by innovative instrumentation, software, consumable reagents, and chips. The plastic chips are crucial for microfluidic applications because they ensure consistent, scalable droplet production.

A higher volume of those chips may be needed when microfluidic channels are tested and confirmed for a specific research objective. In addition to its high productivity, injection molding allows fabrication of non-micro structures like reservoirs, wells, and inlet/outlet gates—together with micro-sized geometries in a single, moldable piece. This comes at a cost that can be challenging for injection molding providers, however.

“The most challenging part of molding a microfluidic device is tooling—a negative part of the device (a mold) must have micro channels protruding, which means traditional subtractive machining methods can be limited as the surface quality is usually required of an optical quality,” said Dominykas Turčinskas, CEO of Micromolds, a Vilnius, Lithuania-based plastic micro injection molding company for medical, automotive, furniture, and other industries. “It’s easy to mirror polish a flat plane but it becomes nearly impossible when some micro protruding features must be worked around.”

“A synergy of different modern technologies must be used in combination to achieve a required quality for microfluidic tools,” Turčinskas went on. “The tooling is critical, but injection molding is of no less importance. The microfluidic devices can be relatively large parts in terms of micro molding; what makes them ‘micro’ are the micro features they have. This condition causes moldability challenges as the molten plastic hesitates to fill these micro cavities. An intricate combination of molding parameters and peripheral equipment has to be found for every individual project.”

Project Size Matters

From the perspective of a medical molding quote, the time required can be significantly different between a small project and a large assembly—particularly if it’s millions of devices per year.

Impact of the new project can be drastic—both positive and negative. Being competitive, yet not losing money, is of crucial importance for larger projects.

“When the project is awarded, the scope of the project dictates the number of team members and the overall approach,” said Joe Szyperski, director of advanced design and development at Medbio, a Grand Rapids, Mich.-based full-service contract manufacturer with expertise in medical molded solutions. “A simple molded part is likely handled by a project engineer, who might have a launch meeting with tooling, process engineering, and manufacturing engineering, but it may not warrant even weekly meetings or a formal Gantt chart.”

While a quote for a single molded component may take a couple of man-hours, a large quote (like an auto-injector) can involve hundreds of hours from an organization.

“The semi-large project demands a comprehensive Gantt chart and regular multi-discipline meetings, typically involving the customer, where concerns and open issues are raised, documented, and tracked on a regular basis, to ensure everyone is on the same page,” said Szyperski. “As delays occur, it is important to adjust the Gantt chart and make sure all parties realize the effect of the delay.”

The two largest threats to a project’s success are inadequate planning and lack of effective and/or timely communication. Regular touchpoints are crucial for both internal and small teams, as is fostering frequent communication in the broader organization.

“The auto-injector project is a different animal, often requiring facility expansion, capital equipment purchases, hiring of resources, and significant planning,” said Szyperski. “There will be multiple teams in the organization to handle the different tasks and it is the full-time job for several on the team to keep all the balls in the air.”