Front and back of door for enclosure of Siemens’ Immulite immunoassay medical diagnostic system produced by twinsheet thermoforming using a proprietary thermoplastic alloy from Boltaron Performance Products. The part offers greater stiffness and rigidity, and more detailed geometry, than those previously molded of fiberglass.

The attractiveness and functionality of the thermoplastic enclosure for the Immulite Immunoassay medical diagnostic testing instrument by Siemens Healthcare Diagnostics, Deerfield, IL, is the result of a cost-effective union involving the right thermoplastic alloy and forming method for the job.

The two side doors of the medical device were redesigned in order to take advantage of the twinsheet forming process and a fire-retardant, extruded alloy sheet.

The 4335 alloy by Boltaron, Newcomerstown, OH, has a UL 94 V-0 rating, impact resistance of 15 to 18 ft lbs/in (2.1- 2.5 kg/m), and broad chemical resistance for standing up to concentrated cleansers.

The molder— Kintz Plastics, Howes Cave, NY— uses the sheet in thicknesses of 0.156 in. (4 mm) front side and 0.125 in. (3.2 mm) back side in a twin-sheet thermoforming operation to achieve the detailed geometry (deep recesses and corners) and durable lightweight parts required by Siemens.

Twin-sheet thermoforming consists of two simultaneous vacuum forming operations used to produce an integrally welded, hollow part, similar to one which has been blow molded. The two halves of a twin-sheet part can be of the same or dissimilar materials and thicknesses, with front and back finished surfaces. The process consists of two plastic sheets that are heated in a double framework setup and then transported to the forming station. The two molds are brought together, air is evacuated, and both heated sheets are pressed and fused together at certain predetermined weld points.

The side door enclosures were originally designed in flame-retardant ABS/PVC sheet, but Kintz opted for the rigid proprietary alloy sheet because of its formability, durability, and light weight.

Once molding is complete, several secondary operations are performed including extensive machining and trimming with a three-axis CNC router. Backside mounting blocks for hinges are incorporated, a screw block is bonded to the sheet with an epoxy system, and brass inserts are ultrasonically pressed into the part.

Both side doors are painted in a two-tone off-white, after which Kintz applies a metalbased EMI/RFI spray-shielding component on the interior side for antistatic protection.

The manufacturing cost associated with thermoformed alloy doors are said to be 30% to 50% lower than the previously molded, fiber-reinforced plastic doors. Further, the overall weight reduction of the immunoassay instrument decreases shipping costs and makes the unit easier to move around in the hospital.