Why the custom injection moulding process is a marathon and not a sprint

Justin Strike, product manager at Trelleborg Sealing Solutions, discussed the process of customised injection moulding with MPN editor Laura Hughes.

What are some of the key factors to consider when selecting materials for injection moulding, and does this differ for custom injection moulding?

Most of the injection moulding for the medical device market uses either thermoplastics, high consistency rubber, or Liquid Silicone Rubber (LSR). LSR is an increasingly popular elastomeric material for medical device components due to its biocompatibility. The composition of LSR also promotes curability and other advantages, including easily altered durometers, varying textures, resistance to different types of sterilisation and the inclusion of additives.

Determining the ideal material for an application depends on several usage conditions. A moulder must consider the applied stresses, contact and temperature resistance requirements, transparency and opacity, lubricity, wear resistance amongst others. In addition to functionality, consideration must be given to the environment in which the moulded component will be housed to determine the ideal material.

How different is the production process for custom injection moulding compared to non-customised injection moulding?

It is not that the actual moulding process differs, but rather, it is what surrounds the moulding process that differentiates the two. Injection moulding projects inherently require a methodical approach that relies on custom-built tools and engineered manufacturing processes to accomplish the high level of precision and performance required of the complex components.

As a custom moulder, we do not own the design, we own the process. Our focus is on ensuring that the moulding process is efficient, effective, and superior to any alternatives. Accomplishing this does not come without experience. It is this experience with engineering custom-moulded processes that is the difference. Experience aligning the limits of the process with the features of the design acts as an additional tool in our customers’ toolbox.

Utilising a custom moulding versus a non-customised moulding process can have a significant bearing in application, however, in terms of optimised performance, risk in application and total cost of product ownership. Here, an experienced moulder will be able to lend design support both from the aspects of functionality and manufacturability.

What are the main challenges associated with custom injection moulding?

With a custom injection moulding project, the moulder does not own the design. This prevents the moulder from making changes to enhance the process without first gaining approval from the device manufacturer. The challenge for a moulder is to manipulate the design for the most efficient manufacturing process while maintaining the design intent and functionality of the customer’s product. Successful execution requires concurrent engineering and close communication and documentation between the moulder and device manufacturer, ideally beginning with the initial concept stage of a new product. We own and understand the moulding process, so guidance and commitment to the success of the device is what we offer our customers.

Another considerable challenge is in scaling a prototype to production. Doing so while controlling costs, accounting for the tight tolerances, and ensuring consistent quality can be incredibly difficult. This is where Trelleborg’s expertise in Design for Manufacturing (DfM) is essential for our customers. Our team prepares for the scale-up from the onset, all while exploring design improvements and preserving the unique features of the device.

In the end, the success of the project is built on open communication, collaboration, and documentation between the moulder and device manufacturer.

Are there ways manufacturers can simplify the process for custom injection moulding?

It all comes down to having a good relationship with the injection moulding partner. A device manufacturer will have the greatest understanding of the product’s critical and unique design features. It is vital that the moulder is aware of these critical design elements early in the process.

Knowing key features early on ensures a moulder recognises what can and cannot be manipulated, helping to safeguard the device differentiators from being lost through DfM. Once the differentiators are known, the moulder can make enhancements to the moulded component to improve functionality, lower risk in manufacturing and in application, and ultimately lower the cost of product ownership.

Conversely, it is also vital to identify the subtleties of the device design. This can include surface finishes, gate location, ejector pins, split lines and more. An injection moulder will focus on the critical aspects while also considering how the design subtleties can impact the performance of the device. 

What should manufacturers look for in a partner offering custom injection moulding?

Manufacturers should look to the moulder’s history of successfully scaling a prototype to production. From the onset, an experienced moulder will think beyond the prototype to the manufacturing process to facilitate large-scale production. Doing so impacts how the prototype is developed, with the focus being on improving performance while reducing complexity. A moulding partner should also be flexible in terms of the production processes, materials, and production timelines. An experienced moulder will challenge the process, helping to deliver unique solutions for their customers. 

A prototype shop may be able to provide a prototype that meets the device manufacturer’s specifications, but it is unlikely that the shop will consider opportunities to enhance the design. It is also unlikely that the prototype shop will consider the cost and process to scale up to production.

Do you have any tips for medical device manufacturers who are interested in custom injection moulding?

Partner with an experienced injection moulder early in the design process. Collaboration is essential in identifying design elements that can improve the device and expedite time to market. This early partnership will help with the optimisation of a design, the material selection, establishing a production process, and will allow the moulder to gain insight into key design features.

This approach is something that Trelleborg uses to help our customers accelerate time to market while not jeopardising the established differentiators of the devices. Our moulding experience enables us to push technologies to their limits, and, in some cases, to extend the limits. As a fully integrated manufacturer, that also builds the production tools, we are able to explore solutions that may not be known or considered at the onset of the project. Knowing that an experienced moulder is there to provide support enables device manufacturers to be aggressive with their designs, going beyond current market standards.

When approached correctly, the partnership between moulder and manufacturer can increase the performance of the product while reducing time to market and the device manufacturer’s total cost of ownership.

Conclusion

Medical device manufacturers looking to partner with a custom injection moulder should view the process as a marathon, not a sprint. It is important to set aggressive but realistic timelines and to differentiate between having prototype in hand and getting products to market. Early collaboration will help to expedite the timeline and to identify potential design enhancements.