Medical insert molding is an established and developed strategy for producing world-class devices in an efficient and cost-effective manner. A key element in this process involves the anticipation of manufacturing solutions prior to the actual design stages of the part itself. Production advantages quite often are overlooked during this critical phase by the engineers in charge of the project, who discover only later that certain improvements could have been achieved had these factors been anticipated beforehand.
Because medical devices often combine delicate items such as cannula, tubing, wires, metal instruments or porous membrane with thermoplastic resins, manufacturing techniques need to be evaluated carefully. Often, the basic device is injection molded first, with one of the aforementioned items to be attached later by gluing, welding, assembling, heat staking, press fitting, or similar operations. These procedures often are time-consuming, for example, gluing/solvent bonding, which requires an overnight post-cure step. Other operations leave open the possibility of mishandled or damaged components, such as a heat staked part that does not attach properly, or a broken or compromised weld joint. In addition, some requirements of secondary processes often can work against Just-in-Time or Lean Manufacturing protocols, or at the very least hamper attempts to streamline workflow in the plant. In any event, quality issues and/or cost factors associated with these activities can present substantial challenges for medical device manufacturers.
Insert molding offers an effective solution to these challenges. By placing components directly into the mold, and injecting thermoplastic resin into the cavity, a finished part is fabricated immediately and is ready for inspection. In many cases, the part has greater structural integrity and performance than devices requiring secondary operations. Sand blasted cannula, for instance, when molded directly into a needle hub, typically are found to have almost twice the pull strength of those that are solvent bonded in place. Tubing that is insert molded into a catheter manifold will hold greater burst pressures than glued or welded assemblies because the thermoplastic resin actually melts the outer surface of the tubing, causing a strong thermal bond that is able to withstand forces equal to the tensile strength of the tubing. In the case of medical instruments such as scalpels and trocars, placing a swedge on the shaft of the instrument that can be gripped and encapsulated by plastic will insure zero movement of the unit during its intended use.
With the recent development of liquid silicone (LSR) insert molding, even greater possibilities exist to manufacture devices that previously had not been thought feasible. Very small guide wires down to .005 in diameter can be held in a concentric position in a mold while LSR is injected carefully around them. Even tiny glass capillary tubes can be insert molded into housings that contain them in parallel layers. In cases like this, the outside surface of the tube often needs to be treated with a liquid primer, to insure a chemical bond between the glass and plastic. This same technique also allows inert materials like Teflon to be considered for insert molded applications. More recently, medical devices have been designed that actually mold LSR onto a thermoplastic base or structure. One example incorporates a polycarbonate substrate with perforations that is placed in a mold while LSR is injected over the surface, forming liquid-tight “drums” that act as pumps in drug delivery systems. Even silicone catheters and angioplasty devices are becoming more exotic in their design and functions, using similar methods.
Device manufacturers familiar with the opportunities afforded by insert molding can begin during the initial design stages to plan the right approach to manufacturing their products. Many companies specialize in both mold tooling and production insert molding for these critical, close-tolerance applications. It often is better to utilize a company that is proficient with this technology to assist with the project at the very beginning. The expertise that can be gained may yield substantial long-term benefits in both quality level and cost maintenance.
Aberdeen Technologies, Inc.
Carol Stream, IL
If you’d like to learn more about how insert molds and other molding technologies can help provide superior production results and quality control for molding of medical devices, contact us at 1- 800-323-8095.