Over Molding: Improving Comfort and Ergonomics

Over molding, a technique that involves molding one material over another to create a single, integrated part, plays a pivotal role in enhancing user experience and device functionality to achieve optimal comfort and ergonomic design. In this technical post, PDC explores how over molding contributes to improved comfort and ergonomics in medical devices, focusing on key polymers and real-world case studies that demonstrate its efficacy. 

Understanding Over Molding: Over molding allows for the integration of soft, elastomeric materials with rigid substrates, offering numerous benefits in terms of both form and function. By encapsulating hard components with softer materials, over molding enhances grip, reduces vibration, and provides cushioning, resulting in devices that are more comfortable to use and ergonomically optimized for the end-user. 

Key Polymers for Over Molding: 

  1. Thermoplastic Elastomers (TPE): TPEs offer a unique combination of flexibility, durability, and biocompatibility, making them ideal for over molding applications in medical devices. Their soft-touch feel and ability to bond with various substrates make TPEs a popular choice for enhancing grip and comfort in device handles and grips. 
  2. Silicone Rubber: Silicone rubber is prized for its excellent biocompatibility, heat resistance, and hypoallergenic properties. In over molding, silicone rubber can be used to create soft, pliable surfaces that conform to the user’s grip, reducing hand fatigue and discomfort during prolonged use.
  3. Polyurethane (PU): PU offers a wide range of hardness options, allowing for customization of the tactile properties of over molded components. Its resilience and abrasion resistance make PU an ideal choice for applications where durability and long-term comfort are paramount. 

Benefits of Over Molding for Comfort and Ergonomics: 

  • Enhanced grip and tactile feedback 
  • Reduction of pressure points and discomfort 
  • Improved shock absorption and vibration dampening 
  • Customization of surface texture and softness 
  • Ergonomic shaping for optimal user interaction 

Case Studies: 

  1. Over Molded Surgical Instruments: In a recent project, our team over molded surgical instrument handles with TPE to improve grip and reduce hand fatigue for surgeons during lengthy procedures. The soft, textured surface provided enhanced control and precision, leading to improved surgical outcomes and reduced user discomfort. 
  2. Drug Delivery Devices: Over molding has revolutionized the design of drug delivery devices, such as insulin pens and inhalers. By incorporating soft silicone rubber grips, these devices offer patients a more comfortable and intuitive user experience, ultimately improving medication adherence and quality of life. 

Conclusion: By leveraging the unique properties of key polymers such as TPE, silicone rubber, and PU, manufacturers can create devices that meet the functional requirements of your device. Insert molding and Over molding are considered interchangeable terms in the plastics industry and for the following statements should not be included in the same conversation as True 2-shot molding (2K).   

Mastery in Precision Molding – Insights from Our Expertise:

Both operations involve either a manual or robotic placement of  a substrate into a mold, which could be a previously molded plastic component, a single catheter tube, multiple catheter tubes with metal collars for structural integrity or to ease laser welding in assembly, a marker band, a metal hypo tube, a metal cannula, a 100 micron thick film for titer plate backing,  a MIM micro surgical component or an electronic sensor.  The typical failure modes seen in the industry is not having the expertise during the DFM phase to understand the tolerance variation of the substrate.  Therefore, if the substrate is purchased from an external vendor, albeit the purchased component may be within the print tolerances, the steel tolerances that PDC operates to of +/-.0001” may create a situation of excess flash or tool damage if part is at the high end of the tolerance.  What this means is that during the DFM, every input into the project must be assessed and if required, different sets of core pins or shut offs may have to be fabricated and utilized based upon the tolerances of that particular lot of purchased substrates.  Another planning activity is you are over molding with a high temperature and you have a substrate that be .015” in diameter.  How do you handle this if you are dealing with a 380°F tool, what safeguards do you have in place to ensure proper positioning within a .0001” , is it stamped component or a steel rod that may stress relieve when it comes in contact with the hot mold, whereby the part may cross the parting line and damage it upon mold close?  PDC’s stringent PFMEA and DFM process considers all known variables and even goes as far as what could happen during the molding process.  Even if it is something that is “far-fetched”, it needs to be discussed and noted as a failure mode.  PDC operates with automated and manual substrate placement which utilizes precision fixtures/load bars and cameras; therefore, we understand what is going on between the platens every cycle.   

With a passion for miniaturization and implementation of advanced micro molding techniques,  PDC’s attention to detail for insert molding/over molding creates a highly repeatable and scalable process, which allows our clients to rely on us for continuity of supply, ultra-high quality with components that traditionally have tolerances of +/- .001” and below.