Controlling costs continues to be a dominant issue in the US healthcare market, and companies are continually finding themselves in the position of being introspective of their organizations’ roles within this call to action. This is particularly felt among medical manufacturers, who face pricing pressures from competition, healthcare providers, and payers, as well as a stricter regulatory environment and unfriendly tax provisions. In the face of these significant challenges, it is hard to imagine that custom molders and contract manufacturers, as well as their customers, are lucky to be doing business today. However, they are. It has nothing to do with these market forces though, and everything to do with being a business in the age of plastics—a period that offers unparalleled design freedom.

From a profitability perspective, the medical manufacturer’s goal is to save time and money by manufacturing parts or assemblies with the least number of components. This is where plastics offer some great value. Specifically, some of the greatest opportunity for cutting medical manufacturing costs come from consolidating multiple parts into one and utilizing the myriad of plastics resins to replace metal parts. Coupled with appropriate processing techniques, both activities can be leveraged for improved economics in the medical manufacturing environment.

Due Diligence

Fig. 1 – Aspects to consider for a part conversion/consolidation.

To achieve success, it is imperative that custom molders and contract manufacturers guide their customers through the consolidation and conversion processes. In order to optimize the process, the customer must be engaged early in the design process to generate an accurate list of part requirements.

First and foremost, it is critical to analyze the part and/or assembly thoroughly, utilizing the following set of questions to evaluate whether there can be a successful consolidation or conversion:

  • Can the part count be lowered by consolidating components?
  • Can metal be replaced while maintaining structural strength?
  • Can the look and feel of the application be improved while meeting all other target requirements?
  • Can the end result be manufactured cost-effectively?

There also are several advantages of a consolidation/conversion to plastic to consider, including:

  • Lowering manufacturing cost,
  • Reduce part weight,
  • Part consolidation resulting in greater design flexibility,
  • System simplification due to the integration of more features into a single part, which results in increased part functionality,
  • Enhanced regulatory compliance,
  • Improved appearance,
  • Elimination of time-consuming and costly secondary operations, and
  • Corrosion resistance.

Additionally, for a successful conversion, the following aspects, as shown in Figure 1, must be evaluated in depth to achieve the desired outcome:

  • Optimize the part design,
  • Choose the right resin,
  • Determine the appropriate process, and
  • Evaluate manufacturability from a tooling perspective.

Design

There are a number of considerations when approaching part design. For instance, the wall thickness of part design is an important factor impacting cycle time and weight. The part size has a significant influence on the molding costs and required tonnage. The complexity of the part requiring ribbing for stiffness, as well as bosses and other functional features, makes the evaluation of the warpage after molding necessary to ensure the parts meet the dimensional specifications on the print. The final part design also is influenced by a number of factors, including, but not limited to, branding, cleaning concerns, and ergonomics.

Fig. 2 – Resin pyramid.

Material

Material selection poses its own challenges, as it must fit all application requirements. There are various key consideration factors for the resin selection— amorphous vs. semi-crystalline— which, in turn, influences shrinkage, mechanical properties, chemical resistance, flow, and in-use continuous temperature, just to name a few. Additives, fillers, and modifiers are being used to change properties of resins. In medical applications, the chosen resin has to comply with a number of regulatory specifications.

There are more than 100,000 different grades of resins in available databanks for all the different resin families, which can be divided in a number of categories as shown in Figure 2. The available resin portfolio is represented as a pyramid. Generally, the higher a resin family is located towards the top of the pyramid, the more likely it can be used in higher performance applications.

Material considerations are often driven by a number of other factors that are characteristic to the application, such as end-use environment, recyclability, repeated sterilization, and durability in higher than ambient temperature under constant load. All of these factors have to be evaluated in order to create an application that fits all the criteria on the list of requirements.

Fig. 3 – Sandcast arm (top) and molded arm (bottom).

Process

Another key element is the selection of the molding process to be used in the conversion approach. It can be injection molding, structural foam process, and external or internal gasassist process. Further on overmolding and insert molding are other variants of the process that can be considered.

Tooling

The importance of the tooling considerations as the major contributor to the ability of molding the desired part cannot be overemphasized. The effect of adequate tooling for the application is a key factor for success. That said, factors like tool life expectation, production quantity, tool steel, gating, and cooling are essential factors for the overall success of the process. The highest attention is required from the tooling concept phase all the way through all the details of the tool construction into the tool build.

All these aspects are interrelated and require an evaluation by themselves, as well as among each other, to be successful. When executed properly, this approach can ease the transition from product development to full-scale manufacturing, cutting both time and cost out of the project.

There are several advantages coming out of the consolidation and/or conversion process that are usually application or part specific. The following real-life examples of part consolidation and/or metal substitution will demonstrate the above mentioned advantages, illustrating how these techniques not only meet part requirements, but produce better parts at lower cost.

Fig. 4 – Side view of underside of molded shelf.

Example A: Nine into One Part Consolidation and Assembly to SF IM Molded Part

The first example is a part that prior to conversion into a low-warpage, single- piece molded functional frame was a multi-component assembly. The components of the original assembly were made from machined acetal parts, screws, and pins. All together, this part originally had more than 30 components. Utilizing the structural foam process, it was converted to one part molded in a PPO-PS resin with all attachment features. The overall cost savings were around 80 percent, resulting in a quick payback for the required tooling expenses.

Example B: Aluminum Sand Cast Converted into HM-Filled Resin IM Part

The second example illustrates a metal-to-plastic conversion. Prior to conversion, the part was manufactured by metal sand casting with secondary additional machining and painting. After the conversion, the arm is an in-color, injection-molded structural high stiffness part. (See Figure 3)

Due of the structural requirement, a high modulus glass-filled nylon-like material was chosen as the metal replacement resin. Chemical resistance and operating temperature were other criteria on the requirement list as well.

Example C: Seven into One Part Consolidation and Assembly to EGA IM Part

The next example is the conversion of a thermoformed shelf part, which had added metal stiffeners, machined plastic brackets, and a several-step assembly with gluing, into a single molded part. The process chosen for this conversion was external gas-assist injection molding. The resin used is ABS. After conversion the part was structural with significantly higher stiffness than the prior assembly. The molded part also was cosmetic, with no secondary finishing required. The overall cost reduction for this conversion was more than 60 percent. (See Figure 4)

Example D: Eleven into One Part Consolidation of IGA/EGA IM Part with Handles

The final application demonstrates how a combination of different processing techniques in a single molding operation helped develop a cosmetic, unpainted structural part with integrated side handles. The process techniques used were external and internal gas-assist injection molding. The part was molded in ABS. Conversion resulted in a single molded part, which replaced an assembly made up from a minimum of 11 parts, including 3 separate molded parts, a top cover, and 2 handles. There were also 4 screws and 4 metal inserts to connect the 3 parts as an assembly. The single molded part has a high stiffness by design, and low warpage due to the external gas-assist process. Handles on either side were hollowed out by the internal gas-assist process, saving part weight and molding cost.

Summary

To be successful in a consolidation or conversion effort for any application, it is imperative to look at the important aspects as mentioned in the beginning of the article:

  • Part design
  • Resin selection
  • Process selection
  • Tooling

The critical steps for a consolidation and/or conversion are as follows:

  • Review current application aspects,
  • Assess cost and cost savings, return on investment,
  • Define molded application requirements,
  • Select appropriate material and molding technique,
  • Use computer-aided engineering (CAE), finite element analysis (FEA), and rapid prototyping (RP) as needed, and
  • Analyze cost savings and part performance.

Not every application or product is necessarily a good choice for a conversion, and it is critical to understand the customer’s goals for the conversion in order to be able to provide the best solution.

Fully understanding the limitations of process, resin, and tools before a final commitment to a conversion is crucial for the conversion process, including the ability to mold the part within the expected tolerance range, as well as the passing of certain application specific regulatory standards. CAE and FEA can assist to give insight into a number of part or structure related challenges.

This article was written by Michael Hansen, PhD, Senior Technical Development Engineer, Mack Medical/Mack Molding Company, Arlington, VT. For more information, Click Here .