Avoid These 10 Common DFM Mistakes in Medical Device Development

The journey of bringing a medical device from a brilliant concept to a market-ready product is fraught with complexities. Every decision, from the initial sketch to the final assembly, carries significant weight, impacting not only the cost and timeline of the project but also the ultimate safety and efficacy of the device. A foundational element that underpins this entire process is Design for Manufacturing (DFM). This proactive approach involves designing products in a way that makes them easier and more cost-effective to produce without compromising quality. When applied correctly, DFM for Medical Devices is a powerful tool for innovation and efficiency. However, when overlooked, it can lead to a cascade of problems, ranging from production delays and budget overruns to regulatory hurdles and even product failure.

 In the highly regulated and precision-driven world of medical devices, the consequences of DFM errors are magnified. A seemingly minor design flaw can have significant repercussions, affecting everything from the biocompatibility of a material to the long-term reliability of a life-sustaining device. Understanding the common pitfalls in Design for Injection Molding (DfIM) is the first step toward avoiding them. This article will explore the top ten DFM mistakes that occur in medical device development, offering insights into why they happen and how a strategic approach, grounded in experience and expertise, can navigate these challenges successfully. By addressing these potential issues early in the design phase, companies can streamline their path to market, enhance product quality, and ultimately, deliver safer and more effective solutions to patients and healthcare providers.

1. Inadequate Material Selection from the Outset

One of the most frequent and impactful mistakes in the DFM process for medical devices is the failure to thoroughly consider material selection at the very beginning of the design journey. The choice of material for a medical device is a complex decision that intersects with biocompatibility, sterilization compatibility, regulatory requirements, and manufacturability. A material that appears perfect on a datasheet might prove to be a significant roadblock during production or regulatory review.

Biocompatibility and Regulatory Hurdles

The human body is a complex and sensitive environment. Any material that comes into contact with tissues or fluids must be biocompatible, meaning it will not elicit an adverse local or systemic response. Standards such as ISO 10993 provide a framework for evaluating the biological effects of medical device materials. Choosing a material without a proven track record of biocompatibility for the intended application can lead to extensive and costly testing, and potentially, a complete redesign if the material fails to meet the necessary standards. Furthermore, different regulatory bodies, like the U.S. Food and Drug Administration (FDA), have stringent requirements for materials used in medical devices. A lack of familiarity with these regulations can result in the selection of a non-compliant material, leading to significant delays in product approval.

Manufacturability and Performance

Beyond the biological and regulatory considerations, the chosen material must also be suitable for the intended manufacturing process. In the realm of Medical Injection Molding, for instance, different polymers have vastly different processing characteristics. A material with a high melt temperature might require specialized equipment, while a material prone to warping could necessitate a more complex mold design with intricate cooling channels. Ignoring these manufacturability aspects can lead to a host of production issues, including defects like flash: a thin, unwanted layer of plastic that can interfere with part assembly and function. The physical properties of the material, such as its tensile strength, flexibility, and chemical resistance, are also paramount to the device's performance. A material that cannot withstand the rigors of its intended use or the chosen sterilization method will inevitably lead to product failure.

2. Overlooking the Nuances of Injection Mold Design

The injection mold, or tool, is the heart of the plastic manufacturing process. Its design and construction are foundational to the quality and consistency of the final parts. A common DFM misstep is to treat the mold design as an afterthought, failing to appreciate the intricate interplay between the part geometry and the mechanical realities of the molding process. Professional injection mold design services can help identify and resolve these issues early. This oversight can lead to a variety of preventable defects and production inefficiencies.

The Importance of the Parting Line

A prime example of a frequently overlooked detail is the parting line, the surface where the two halves of the mold come together. The placement of the parting line can have a significant impact on the part's aesthetics, but more importantly, it can influence the formation of flash. Flash occurs when molten plastic escapes from the mold cavity. A poorly designed parting line can create a pathway for this escape, leading to parts that require secondary trimming operations, adding cost and time to the manufacturing process. Flash can significantly interfere with the sealing surfaces or the fit of assembled components.

Gates, Runners, and Vents

The runner system, which directs the molten plastic into the mold cavity via gates, is another area where DFM expertise is vital. The size and location of the gates can affect how the plastic fills the mold, influencing everything from the part's cosmetic appearance to its structural integrity. Similarly, vents, which are small channels that allow trapped air to escape the mold cavity, are essential for preventing defects such as burn marks or incomplete parts, known as "short shots." A design that does not account for proper gating and venting can lead to a frustrating and expensive cycle of trial and error on the production floor.

3. The Perils of Inconsistent Wall Thickness

Achieving a uniform wall thickness throughout a plastic part is a cornerstone of good Plastic Part Design Optimization for injection molding. However, designers, particularly those less familiar with the intricacies of plastic flow, might create parts with significant variations in wall thickness. This seemingly simple design choice can introduce a host of manufacturing challenges and compromise the quality and performance of the final product.

Cooling, Warping, and Sink Marks

When molten plastic is injected into a mold, it begins to cool and solidify. Thicker sections of a part will cool much more slowly than thinner sections. This differential cooling can create internal stresses within the part, leading to warping, where the part distorts from its intended shape. Furthermore, as the thicker sections cool and shrink, they can pull material from the surface, creating depressions known as sink marks. These cosmetic defects can be particularly problematic in medical devices where a smooth, easily cleanable surface is often a requirement.

Filling the Mold

Inconsistent wall thickness can also complicate the process of filling the mold cavity. The molten plastic will naturally flow along the path of least resistance, which is typically the thicker sections. This can lead to a situation where the thinner sections of the part do not fill, resulting in a short shot. To compensate for this, a molding technician might be forced to increase the injection pressure, which in turn can increase the risk of flash. A well-designed part with uniform wall thickness promotes a more consistent and predictable flow of material, leading to higher-quality parts and a more stable manufacturing process.

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4. Ignoring the Necessity of Draft Angles

One of the more subtle yet profoundly important DFM principles for injection molding is the inclusion of draft angles. A draft angle is a slight taper applied to the vertical walls of a part. This taper facilitates the release of the solidified part from the mold. Designs that feature perfectly vertical walls, with no draft, can create a situation where the part adheres to the mold surface, making ejection difficult and potentially damaging the part or the mold itself.

Ejection and Surface Finish

The process of ejecting a part from the mold involves ejector pins that push the part out of the cavity. Without an adequate draft, the friction between the part and the mold surface can be substantial. This can lead to drag marks or scratches on the surface of the part as it is being ejected. In more severe cases, the part may deform or even break during ejection. For medical devices, where surface finish can be a functional requirement for sealing or for minimizing friction between moving parts, such a defect can be unacceptable.

Cycle Time and Mold Wear

The difficulty of ejecting a part without draft can also increase the cycle time: the total time it takes to produce one part. A longer cycle time translates directly to a higher cost per part. Over time, the repeated stress of ejecting parts with insufficient draft can also lead to premature wear on the mold, particularly on the core and cavity surfaces. This can result in the need for costly mold repairs and production downtime.

5. Over-Tolerancing and Underestimating Manufacturing Variability

Tolerances define the acceptable range of variation for a part's dimensions. While tight tolerances are often necessary for medical devices to function correctly, a common DFM mistake is to specify tolerances that are tighter than what is actually required for the part's function. This practice, known as over-tolerancing, can significantly increase the cost and complexity of manufacturing without providing any tangible benefit.

The Cost of Precision

Achieving very tight tolerances in injection molding requires a more precisely machined mold, more sophisticated process controls, and more rigorous quality inspections. Each of these factors adds to the overall cost of the part. A designer who specifies an unnecessarily tight tolerance on a non-critical feature may be inadvertently driving up the cost of the product. A thorough DFM analysis involves carefully considering the function of each feature and assigning tolerances that are appropriate for that function.

Understanding Process Capability

Every manufacturing process has an inherent level of variability. A good DFM process takes this variability into account. Designers should work closely with their manufacturing partners to understand the process capability of the equipment that will be used to produce their parts. This collaboration allows for the development of a design that can be consistently and reliably manufactured within the specified tolerances. Ignoring this aspect of DFM can lead to a high scrap rate, as parts that fall outside the overly restrictive tolerance range will have to be discarded.

6. Neglecting Design for Assembly (DFA)

While DFM focuses on the manufacturability of individual components, Design for Assembly (DFA) is concerned with the ease and efficiency with which those components can be put together to create the final product. A medical device may consist of dozens or even hundreds of individual parts. A design that is difficult to assemble can lead to increased labor costs, longer production times, and a higher likelihood of assembly errors.

Simplifying the Assembly Process

A key principle of DFA is to minimize the number of parts in an assembly. This can often be achieved by combining multiple functions into a single, more complex molded part. Other DFA strategies include designing parts with self-locating features that guide them into the correct position, and using snap-fits or other integrated fastening features to eliminate the need for screws or adhesives.

Error-Proofing the Assembly

Another important aspect of DFA is designing parts in a way that prevents them from being assembled incorrectly. This concept, sometimes referred to by the Japanese term "poka-yoke," can involve creating asymmetrical features that only allow parts to fit together in the correct orientation. In the context of medical devices, where a single assembly error could have serious consequences, designing for error-proof assembly is of the utmost importance.

7. Underestimating the Importance of Secondary Operations

The manufacturing process for a medical device often does not end when the part is ejected from the molding machine. Many devices require secondary operations, such as assembly, packaging, and sterilization. A DFM process that fails to consider these downstream activities can create unforeseen challenges and costs.

Designing for Cleanroom Environments

Many medical devices are assembled and packaged in a cleanroom to minimize the risk of contamination. The design of the components can impact the efficiency of these cleanroom operations. For example, parts with complex geometries or textured surfaces may be more difficult to clean and handle in a sterile environment. Designing parts with smooth, easily accessible surfaces can streamline the cleanroom assembly and packaging process.

Sterilization Compatibility

Medical devices must be sterilized before they can be used. There are several common sterilization methods, including autoclaving (steam sterilization), ethylene oxide (EtO) gas sterilization, and gamma irradiation. Each of these methods can affect plastic materials in different ways. An autoclave, for example, exposes the device to high temperatures and pressures, which can cause some plastics to warp or degrade. A comprehensive DFM process will consider the intended sterilization method from the beginning and select materials that are compatible with that method.

8. Insufficient Collaboration with the Manufacturing Partner

One of the most significant DFM mistakes is a lack of early and ongoing collaboration between the design team and the manufacturing partner. Designers are experts in the functional requirements of the device, while manufacturers have a deep understanding of the intricacies of the production process. When these two groups work in silos, valuable opportunities for optimization are often missed.

Leveraging Manufacturing Expertise

An experienced contract manufacturer can provide invaluable feedback on a design's manufacturability. They can identify potential issues with a design before a mold is ever built, saving time and money. For example, they might suggest a change to a part's geometry to improve material flow, or they might recommend a different material that offers better processing characteristics without compromising performance.

A Partnership for Success

The relationship between a medical device company and its manufacturing partner should be viewed as a partnership. Open and transparent communication is essential. By involving the manufacturer early in the design process, companies can leverage their expertise to create a more robust and manufacturable design. This collaborative approach leads to a smoother transition from design to production, a higher quality product, and a faster time to market.

9. Failure to Adequately Prototype and Test

Prototyping is a fundamental step in the product development process. It allows designers to test the form, fit, and function of their designs before committing to expensive production tooling. A DFM mistake is to rush through the prototyping phase or to skip it altogether in an effort to save time. This is almost always a false economy.

Identifying Design Flaws Early

Medical Device Prototypes can be created using a variety of methods, including additive manufacturing, also known as 3D printing. Rapid Prototyping Services enable teams to quickly produce these prototypes, which can be used to identify design flaws that might not be apparent in a CAD model. For example, a physical prototype might reveal that a part is difficult to grip or that two components interfere with each other when assembled. Catching these issues at the prototyping stage is far less expensive than discovering them after the production mold has been built.

Testing and Validation

Prototypes also allow for early testing and validation of a design. This can include functional testing to verify that the device performs as intended, as well as user testing to gather feedback from clinicians and patients. The insights gained from this testing can be used to refine the design before moving into full-scale production.

10. Overlooking the Impact of Post-Processing on Part Design

The final surface finish of a part, as well as any logos or markings, are often created through post-processing steps. A DFM process must account for these requirements. For instance, if a part is to be pad printed with a logo, the design must include a flat, accessible surface for the printing process. Similarly, if a part requires a specific surface texture, this needs to be incorporated into the mold design. Neglecting these considerations can lead to additional manufacturing steps or a final product that does not meet the aesthetic or functional requirements.

At Aprios, we understand the intricate challenges of medical device development and the pivotal role that a well-executed DFM process plays in achieving success. Our team of experienced engineers works collaboratively with our clients from the earliest stages of a project, providing expert guidance on everything from material selection and mold design to assembly and secondary operations. With our Custom Manufacturing Services, injection molding services, and Precision Manufacturing Services, we deliver design for manufacturing solutions tailored to your specific needs. By partnering with Aprios, you can navigate the complexities of DFM and bring your innovative medical devices to market with confidence.

If you are ready to discuss your next project, contact Aprios today to learn how our custom manufacturing solutions can support you from concept to production.