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Twin-Sheet Forming of Thermoplastic Alloy Boosts
Performance of Siemens' Immunoassay System Enclosure

Twin-Sheet Forming of Thermoplastic Alloy Boosts Performance of Siemens' Immunoassay System Enclosure

Front and back of door for enclosure of Siemens' Immulite® Immunoassay medical diagnostic system produced by twin-sheet thermoforming using a proprietary thermoplastic alloy from Boltaron. The part offers greater stiffness and rigidity, and more detailed geometry, than those previously molded of fiberglass.

Family-owned Kintz Plastics Inc., in Howes Cave, N.Y., a leading manufacturer of heavy-gauge thermoformed products, turned to twin-sheet thermoforming with a proprietary thermoplastic alloy to produce heavy-duty enclosures for an Immulite® Immunoassay medical diagnostic testing instrument from Siemens Healthcare Diagnostics.

The two side doors of the medical device, previously molded of fiber-reinforced plastics (FRP), were redesigned in order to take advantage of twin-sheet's unique manufacturing and cost advantages, according to Kintz, a long-time specialist in this high-productivity process. Among twin-sheet's primary advantages is the ability to make lighter parts with better performance using less expensive capital equipment, less expensive tooling, and more flexible production. These parts offer excellent stiffness, lighter weight, and more detailed geometry than the labor-intensive fiberglass versions, says Michael Righi, Engineering Manager of Kintz Plastics.

The previous solid, fiber-reinforced plastics doors, says Righi, were heavy, and required long lead times because of their labor intensiveness.

"The twin-sheet process gave us greater control in manufacturing and more consistent shape and size," explains Righi. "Unlike fiberglass, there was virtually no variation and we realized a significant weight reduction." The smooth and finely detailed surface finish, part of Siemens' redesign on both sides of the doors, also results in a highly attractive appearance.

Twin-sheet thermoforming consists of two simultaneous vacuum forming operations which are 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.

Twin-sheet thermoforming can replace two processes with one, saving labor, reducing weight and yielding greater strength compared with separately formed parts that are mechanically fastened or bonded with adhesives. 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 pre-determined weld points.

The side door enclosures were originally designed in flame-retardant ABS/PVC sheet but Kintz opted for a rigid proprietary sheet from Boltaron, Newcomerstown, OH, for improved properties and cost/performance benefits. Boltaron 4335 is a fire-retardant, extruded alloy sheet offering 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, allowing cleaning using concentrated cleansers. The company uses the sheet in thicknesses of 0.156 in. (4 mm) front side and 0.125 in. (3.2 mm) back side, and reports extreme formability with minimal thin-out in deep recesses and on outside corners.

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 for a two-tone color, after which Kintz applies a metal-based EMI/RFI spray-shielding component on the interior side for antistatic protection.

Along with the front doors, Kintz manufactures a large front bumper enclosure which is pressure formed of Boltaron 4335 sheet.

Wynn Kintz, president of Kintz Plastics, says twin-sheet thermoforming lowered the cost of the doors by 30-50%. The overall weight reduction of the immunoassay instrument decreases shipping costs to customers, and makes the unit easier to move around in the hospital.

Kintz operates a 120,000 sq ft (2790 sq m) manufacturing facility in Howes Cave, NY, which handles thermoforming, trimming, and finishing under one roof. The company is reportedly the only thermoformer in the Northeast that can produce parts up to 9 x 13 ft (274 x 396 cm).

Kintz Plastics Inc.
+(518) 296-8513


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