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Building Better Parts with Scientific, Multi-Material Molding

Mark Shortt
Editorial Director
Design-2-Part Magazine

A medical molder's science-based approach isolates the negative effects of process variables, elevating part consistency even at the micro level

A relatively small but growing number of progressive companies, such as MRPC (http://mrpcorp.com), of Butler, Wisconsin, are relying on a data-driven, science-based approach known as scientific molding to develop and refine their molding processes. Their goal: to achieve greater part consistency and manufacturing efficiencies. A disciplined process development practice that employs statistical analysis of key variables, scientific molding enables molders to produce parts with consistently reliable quality and material properties.

In June of this year, MRPC announced it was expanding its use of scientific molding across multiple manufacturing processes, including silicone molding. A specialist in molding small-to micro-sized parts for the medical device industry, MRPC offers manufacturing services that include silicone molding, two-material molding, custom rubber molding, plastic molding, and silicone extrusion. The company also offers materials development capabilities through its in-house Tech Center, where it can formulate elastomeric materials specific to customers' product requirements.

"About 80% of our business is medical device molding," says Mark Brandstaetter, the company's vice president of sales and marketing. "The other parts that we focus on are for aerospace, electronics, and safety components."

Rather than simply molding parts for customers, MRPC aims to build a superior part--one that will do a better job of functioning in the device that it's intended for--by pooling the insights of an engineering team with diverse perspectives and experience. "For the medical device companies we serve, the quality and performance of components are vital factors in their choice of manufacturers," said MRPC President Greg Riemer in a statement in June. "Expanding our use of leading-edge processes such as scientific molding helps demonstrate our leadership in those areas."

Design-2-Part Magazine caught up with MRPC Vice President of Engineering Jeff Randall, Vice President of Sales and Marketing Mark Brandstaetter, and Senior Process Engineer Brunson Parish recently to talk about the company's engineering and manufacturing strengths in areas such as two-material molding, micro molding, and scientific molding.

Design-2-Part (D2P): What sets MRPC apart from other medical molders?

Mark Brandstaetter (MB): The real strength that sets us apart from other molders for the medical device industry is our ability to mold multiple materials. When we talk about multiple materials, we're referring to thermoplastics, silicone materials, and rubber materials. We're talking about the ability to combine those multiple materials together into multi-material components. For example, we'll take a thermoplastic, rigid substrate and bond an elastomeric material to it, whether it's a silicone or a medical-grade rubber. Essentially, it gives you some design latitude from an engineering standpoint, allowing unique properties and characteristics to be built into a part.

D2P: How does your scientific molding approach enable MRPC to produce medical parts with greater precision, consistency, and efficiency?

Jeff Randall (JR): The scientific molding discipline is more than just focusing on the molding process itself; it's understanding how the materials behave and how they like to be treated during the manufacturing process. It considers part design, tool design, and equipment, even in the concept stage of design, as well as material selection and part geometry. It's important to exercise the disciplines of scientific molding throughout the entire process of product development.

The advantage to using a scientific approach, as opposed to not using it, is hard to quantify because it's so ingrained in your methods and the ways that you work. I can't imagine not using a scientific, disciplined approach. I can't imagine how you could be successful without it. As far as the final part at the end of the line is concerned--the precision, consistency, and efficiency--it really is about defining the process. Scientific molding creates a more robust molding process that is more tolerant of lot-to-lot material variations and machine variations. It helps to isolate, or negate, those variables from having an effect on part quality.

D2P: Why hasn't scientific molding traditionally been used with silicone molding?

JR: Scientific molding is really a disciplined scientific approach to the molding of a product, and a lot of the published information uses thermoplastic injection molding as the example. It's the default, the easy answer to use. Unfortunately, a lot of industry takes it this way, that scientific molding is a process for thermoplastic molding. But if you look beyond this, and understand what's behind scientific molding, it's really a deep understanding of the material and the material's behavior, and how that material likes to be processed. It deals with the most effective way to process that material, whether it's thermoplastic, silicone, thermoset, or anything else. You can even apply it to industries other than molding.

D2P: Is it important to apply scientific molding to medical parts molding?

JR: I would say yes, obviously, because of the criticality of the medical market and the risks and liability issues, traceability requirements, and process control requirements. It's not to say that other industries wouldn't also benefit from this, but certainly the medical industry really needs to have these stringent controls in place. It's becoming more and more of a litigious society, so the more work you can do on the front end and throughout your entire operation, the better off you will be. In addition, it affects the useful life of the product in the field.

Scientific molding gives you a very disciplined, logical approach to anticipating and putting measures in place to mitigate or reduce the effects of these risks or other variables on the performance of the final product--whether it's part design, mold design, equipment design, or process design.

D2P: Can you tell us a little about MRPC's silicone molding capabilities?

MB: We specialize in the ability to work with not only silicone, but many other materials. Specific to silicone, we process both liquid and high-consistency silicone, also referred to as HCR silicone, which has more of a gum base, where we actually mill the material and add pigments to it for additional properties. We also extrude silicone into different tubing profiles and shapes.

We can incorporate wires into a silicone extrusion; we can also extrude over a cable type of product to give it electrical insulation properties. So, from a processing standpoint, we have all of the different types of capabilities for silicone materials. Based on the customer's physical property or volume requirements, we can help guide them to the best material for the application.

JR: The ability to combine these multiple materials and molding processes with other materials and molding processes is a very significant added capability. It doesn't matter if it's a liquid silicone, injection-molded component that's bonded with an extrusion, or whether it's a thermoplastic component that's overmolding a titanium insert. It's beyond just being able to mold silicone--it's all of the various things we can do with it to provide part functionality and high quality.

D2P: How is it that micro molding is able to produce parts with physical properties superior to those produced through conventional molding?

JR: The micro molding term can be interpreted in a number of different ways. It's really the ability to create very small features and/or parts. It could be a feature on what someone might call a small part, or it could be a part where the material usage is less than the size of a pellet. So the term is pretty broadly used.

Being able to produce a part through a robust micro molding process requires you to be able to maintain material properties and characteristics, even in very small part geometry. Without a good, disciplined approach to the molding process, you might still be able to form a part of very small size, but you might be compromising some of the material properties. For example, if you fill a part at the wrong speed, you might have more residual shear stress in the part than is desirable. So, being able to understand and process a micro molded part, with a scientific molding approach throughout the entire process, is critical to achieve the most robust, consistent part, with the best physical and material properties.

D2P: When molding micro-sized medical components, how does it help to have your experienced engineering team?

JR: MRPC's early approach with a customer, for any product, is to try to understand as much as we can about the part and its function. We want to know about the parts that it will be interacting with, either in assembly or end use; its environment; the chemicals it might be exposed to; or the temperature and humidity. We don't want to just be a part molder. You can buy a plastic part from a lot of different molding companies around the world, but our approach is that we want our customers to be as successful as possible. We try to understand the function of the device that the part is going into--its end use--so that we can bring different perspectives to the design team. If we're involved early enough in the process, we can bring some insight from our experiences into the design for a better solution.

Having an engineering team on staff that has experience in different markets, different applications, different materials, and different molding and manufacturing processes, we as a team can provide a resource that is affordable to our customers. To try to duplicate the amount of experience and expertise we have at MRPC, a company would have to hire several individuals, which would not be a very practical solution.

D2P: Can you tell us about the material development capabilities of your in-house Tech Center?

MB: We have an on-site chemist, some of whose primary responsibilities are to develop and formulate new materials. When we initially meet with a customer, we evaluate their design and try to find out the critical requirements for part function. A lot of times, depending on what they're looking for from a functionality standpoint, some of the basic off-the-shelf materials are not capable of achieving those types of properties. This is when we bring our Tech Center into the mix to develop custom formulations to meet customers' desires and needs, and to improve some of the physical properties of the material to meet those needs.

JR: An additional benefit of having our Tech Center Lab on-site is the ability to validate incoming materials. Our lab will evaluate materials, lot to lot, to determine whether they are within the processing parameters. Without such a resource on-site, we would really be totally dependent on material suppliers. We would really have no documentation for validation or verification that the materials are correct, other than the piece of paper that comes with the material.

D2P: How are MRPC's capabilities suited to producing some of the new types of medical parts required by today's medical devices?

JR: With micro molding and minimally-invasive surgery, the focus and emphasis has been reducing size. By having a scientific approach and being able to combine materials and being able to use less material for micro molding, we can fit more features into a smaller amount of space. We offer more part functionality by combining materials, and a more creative approach to part geometry to achieve the desired function.

Some customers are a little leery of sharing a lot of information about how the part or component or product is going to be used. But after they've worked with us for a while, they understand that we're asking certain questions not just because we're here to mold a part for them, but we're here to partner with them so we can give them the most successful product that we can. By understanding the product's desired performance, and bringing to bear all the different experiences we have, we can help them achieve a better design or a more robust design.

D2P: Would a medical manufacturer feel better about sourcing to a company like yours, and have more confidence in the quality, than if the work was done overseas?

MB: Yes, that's true. Any intellectual property protection and control of proprietary types of issues is very critical, especially with the medical companies.

Brunson Parish (BP): I would say the other big [reason] is probably the level of validation, both on development and also on process development and manufacturing. Medical customers are very stringent in showing evidence of how things are validated and documented fully all the way through the process--more so than in any other industry. Evidence files must be developed and be readily available at any point in time.

D2P: Is this something that you would be able to provide better than an overseas supplier?

BP: I believe so. Another concern that an OEM may have about going overseas is communication. There are different levels of sophistication and communication overseas, depending on where they are located, and from company to company.

There are a lot of comments about development cycles. Some say that if it takes six months to develop a product in the U.S., it will take 18 months overseas. And specifying a specific grade of steel in a mold can be a bit of a risk with an offshore supplier. The validation, verification, and understanding of the strictness of the requirements is not just a suggestion, but a requirement.

D2P: As a supplier/partner to OEMs, what is your company's greatest strength?

MB: Our core strength is our wealth of experience with multiple materials--specifically the thermoplastics, silicones, and rubbers--and the ability to combine those into multiple material combinations. Another strength is our nimbleness as a smaller company, which allows us to react to our customers' requirements quickly. We're able to develop a product in a short time line to help customers get their products to market very rapidly.

David Gaines contributed to this report.