42 Drape Forming

Drape forming is used to fabricate, sockets, flexible inner sockets, orthoses, and other devices that have a seam or are open at one end. It may be used with various types and thicknesses of thermoplastic sheets. Common plastics used in P&O are LDPE (low density polyethylene), HDPE (high density polyethylene), PP (polypropylene), Copolymer, Surlyn, Proflex with Silicone, Subortholene, PETG, Kydex, as well as foams, such as Pelite and Plastizote.

PPE

• Always wear dry gloves and forearm protection while working with hot materials.
• Close toe shoes should be worn in all lab areas.

General Technique Tips

Preparation

• Turn on oven and check oven temperature: Melting temperatures vary by type of plastic. The manufacturer’s recommended thermoforming temperature for each plastic (noted in the SDS) is recorded in our “thermoforming” notebook in the black cabinet. Check for the appropriate temperature and set the oven temperature to match. Beware that overheating plastic may cause some plastics to release fumes that may be harmful.
• Turn on/check vacuum pressure at the gauge located on the center post of the thermoforming station: for polypropylene, polyethylene, PETG and Kydex, a low vacuum of about 20 in. Hg. is satisfactory
• Set up the positive model:
  • securely position it horizontally in the vacuum pipe
  • fill gaps between the top of the mold and the vacuum pipe.
  • place nylon over the mold avoiding wrinkles inside trimlines. securely attach the nylon to the pipe.
  • cover the pipe with 3/16″ aliplast and secure in place with black tape. Ensure that there are no areas for air to leak between the vacuum pipe and the top edges of the aliplast.
• Ensure the work area is clear of obstacles.
• Locate and ensure you are familiar with the operation of the vacuum lever.
• Have additional tools accessible and ready for use, e.g., scissors, utility blade.
• Consider potential problems:
  • Loss of suction – always have clay available to plug holes.
  • No suction – always check that there are no areas for the air to leak between the vacuum pipe and the top edges of the aliplast.

Thermoform

• Place plastic in oven
  • Double check vacuum
  • Predict potential problems
  • Prep with your partner
  • Ensure scissors and clay are easily accessible
• After the plastic has turned clear, pull it out of the oven and drape over the mold as illustrated.
  • Grasp plastic at the ankle and gently pull toward the heel to avoid wrinkles at ankle.
  • Grasp plastic at proximal end and secure smoothly to the pipe. Avoid bunching.
  • Seal plastic on bottom surface of mold
  • Do not touch the plastic within the trimlines or your glove marks will imprint the plastic. This is the finished product, unlike the test socket.
• Slowly turn on the vacuum while securely holding the plastic to pipe (avoid loss of vacuum).
• Cut off excess plastic about 2cm from seam.

When complete

• Store all gloves and tools properly.
• Turn off the oven and the compressor.
• Do not use anything but a dry cloth to wipe off the oven tray.

Additional resources

Draping Polypropylene AFO with compcore

Fabrication Of Microcell Puff Innerboots For Use In Pediatric AFO’s

Introduction to Clinical Thermoforming 1 by Gary Bedard