Thermoforming vs. injection molding considerations for medical robotics enclosure cost and efficiency

Thermoforming vs. injection molding considerations for medical robotics enclosure cost and efficiency

As the medical robotics industry continues to advance, considerations surrounding the selection of the thermoforming or injection molding process play an important role in ensuring the safety, efficacy, and reliability that development teams work so hard to realize and refine.

Given the complexity and cost of attaining FDA approval for a medical device, companies want to maintain that initial manufacturing investment for as long as possible before the inevitable redesign and resubmittal process. Therefore, your enclosure manufacturing process selection should consider startup cost vs materials vs anticipated growth of product sales.

In the thermoforming process, a plastic sheet is heated and drawn over (male tool), or into (female tool) a mold to form a rigid shape. This process is assisted by pulling a vacuum from the underside, and optionally adding pneumatic pressure on the top side. The excess sheet material is then trimmed off and, if necessary, screw bosses or other features are bonded on to the back side of the part. Color and finish can be integral to the process or added as paint secondarily.

In the injection molding process, molten plastic material is injected into a two-part tool (core & cavity) to form the rigid part. Metal screw threads can be added either before or after molding. Likewise, parts can be painted or color/finish integral to the process.

Production Quantity

The primary consideration when determining which process is best for a project is production quantity. For those companies manufacturing expensive capital medical equipment, clinical trials and initial ramp-up may mean very low quantities (low hundreds annually) for the first few years as they build up sales. Low quantities (50-1,000) are typically the domain of thermoforming, whereas higher quantities (500-10,000) are often provided by injection molding. ThermoFab, located in Shirley, MA provides both thermoforming and injection molding capabilities, often working with customer development teams in making decisions about which process to choose.

In addition, thermoformed parts typically require secondary operations, such as trimming, machining, or gluing. These additional operations impact production quantity since fewer parts can be made in an 8-hour day. Injection molded parts rarely need secondary operations, and each part takes only seconds to a few minutes to mold.

Size, Material, & Cost

Smaller products (less than lunch box size) are more easily adapted to injection molding, whereas larger parts (over 5’) can sometimes only be possible via thermoforming. ThermoFab can produce injection molded parts up to 1.8m (70″) x 1.2m (47″) x 1m (40″), and thermoformed parts up to 1.5m (60”) x 2.4m (96”) x .3m (11”).

If your designs require intricate or precise details like snap fits or complex rib structures, injection molding is the superior choice. Not only does it enable customization for human interaction by incorporating precise ergonomic features, but it also facilitates the use of exotic materials like translucents, transparents or elastomerics, resulting in a distinctive product design. Both thermoforming and injection mold processes provide material options that meet the typical medical device needs for chemical resistance (for frequent wipe-downs) and fire retardancy (60601-1 requirements).

The secondary operations required by thermoformed parts, often manual in nature, tend to make part unit costs higher than injection molded parts. When considering tooling options, thermoformed aluminum tools often come at a lower cost compared to steel injection mold tools. This discrepancy largely stems from differences in tool complexity (such as male or female single-sided tools versus core-cavity double-sided tools) and the machinability of aluminum vs steel.

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