Pressure forming lighter, more consistent medical device parts

Surgical Temperature Controller pressure formed cover panels fit together better than rotationally molded parts.

Consistent parts are vital to the success of medical device launches.

An international medical manufacturer changed production methods to ensure proper fit and finish for the cover panels on their new temperature management system. The mobile machine controls a patient’s body temperature during heart surgery.

The initial design called for covers fabricated by rotational molding. However, several issues emerged with early production samples. The OEM approached Profile Plastics, Inc. to consider heavy gauge thermoforming as a possible better solution.

Challenge:
Can you achieve greater dimensional and cosmetic consistency and reduce costs?

Rotational molding (or rotomolding) is a common process for producing plastic parts. However, it has several limitations that make it less practical for applications that demand close tolerances like medical devices.

The central issue for this OEM was the inability of rotomolding to deliver consistent parts.

Pressure formed panels (right) provide better color and more accurate attachment points

Part-to-part variability is a problem when cover panels need to fit the frame of a larger product, like this mobile surgical device. Ultimately, it was determined that rotomolded parts just couldn’t meet the dimensional requirements of the project.

Similarly, the nature of the rotomolding process was unable to produce covers with consistent color between runs. Lack of uniformity is especially noticeable on mating panels. If a side panel is replaced, for example, the new part may not match the color of the original panels it meets.

Another issue was effectively meeting UL 94 V-0 flame rating requirements. The rotomolded parts were produced with LLDPE. To achieve the standard, this material required thicker walls. The resulting panels were much heavier than intended.

Learn how pressure forming compares to rotational molding.

Solution:
Partner with a skilled pressure-former who offers DFM

Pressure forming (top) offers the same V0 protection with thinner wall thickness.

Profile Plastics offers design for manufacturing (DFM) assistance to customers, optimizing designs to meet all their goals. For the medical manufacturer, the engineering team adjusted the cover designs for pressure forming. This provided repeatable part-to-part quality with additional benefits.

Changing the production method required investing in new tooling. Only the inside surfaces of the cover designs changed. However, the process-friendly machined aluminum tool Profile designed would provide a strong return on investment (ROI).

Dimensionally, pressure forming duplicated the exterior surfaces of the covers with a much higher degree of consistency. This allowed the panels to meet each other with a precise line-to-line fit. Mounting blocks added to the backside created precise attachment points to the device frame.

Pressure forming has a shorter cycle time and allows more temperature control for the plastic. Proper heating techniques with custom color thermoplastic sheets minimized color variation.

Profile recommended using KYDEX® T brand PVC/Acrylic blend thermoplastic. This material is denser than the LLDPE used for rotational molding, meeting the UL 94 V-0 standard with less wall thickness. As a result, the pressure formed covers also delivered a 50% weight reduction.

See our visual comparison between pressure forming and rotomolding in this PDF infographic.

Results:
Cover All Your Bases

Profile created medical device covers for this OEM customer that matched the look and feel of the rotomolded parts. The difference was reliable dimensions and cosmetics.

The new set of covers even won an award from the Society of Plastics Engineers’ Thermoforming Division.

Profile’s DFM engineering for pressure forming delivered:

• Higher quality parts
• Better consistency between individual parts and between runs
• Lower total project costs

Profile also provided inventory management. The customer could order all the panels it needed for a year, optimizing run quantities. Units were shipped to match the OEM’s production schedule.