Manufacturing Technology Portfolio

Shape Memory Polymer (SMP) Bladders for Composites Manufacturing
(US Patent No. 7,422,714)

The smart tooling process using SMP Bladders is being commercialized through SmartTooling.com.

Conventional silicone or latex bladders are not rigid enough to support composite lay-up before custom molding. Often material must be applied to the inside of a female mold first, an inflatable bladder inserted, the mold closed, and the bladder pressurized and inflated to consolidate the material against the mold surface. This process is labor intensive, can produce seams, wrinkles and bridging, and often results in inaccurate part shapes. These drawbacks have led to the theory of an inflatable bladder core used as the mandrel, but conventional bladder cores lack the structure required for the composite lay-up process.

SMP bladders operate first as mandrels and later as inflatable bladder cores. First providing a rigid, durable surface for composite layup, SMP bladders then provide flexibility and inflatability when the part is formed against the interior of the final mold.

When heated above their activation temperature, SMP bladders become flexible and can be molded into a near-net bladder shape. When cooled while still under pressure in the near-net mold, they become rigid in the new shape. The resulting rigid bladder is used as a mandrel for lay-up or filament winding of a composite part.

The composite lay-up on the SMP bladder is then inserted into a clamshell mold and subjected to air pressure and heat. The heat softens the SMP bladder, so it becomes flexible and inflates, consolidating the composite material against the mold, ensuring even expansion and precise outer surface dimensions on the part.The part is then cured while pressurized. Since the cure temperature of the composite is higher than the rigid-to-flexible transition temperature of the bladder, the bladder remains flexible and provides consistent pressure on the interior of the part.

Once the part is cured, the flexible SMP bladder is depressurized and contracts from the inner surface of the part. Because of its flexibility when heated, it can be removed easily and reused. Since the mold was completely closed when forming the part, wrinkling, bridging and pinching are less likely. The resulting precision part is seamless and requires no taping, sealing, or pleating.

Benefits:

   • Suitable for hand and mechanical lay-up, filament winding, fiber placement,
      over-braiding, and more
   • No waste, no EPA restrictions, clean process
   • Eliminates the need for part-specific tool retention and storage
   • Easily extracted
   • Reusable
   • Reduces cycle time