How to form plexiglass

Written by joshua smyth
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How to form plexiglass
Plexiglas is clear, strong and durable. (nach hause telefonieren image by Oliver Hirte from Fotolia.com)

Plexiglas is the trademark name for polymethyl methacrylate, a polymer introduced in the late 1930s and still commonly used in industrial and commercial applications, especially for windows and skylights. Plexiglass, note the spelling difference, refers to a lightweight material like Plexiglas. As a thermoplastic, Plexiglas softens and becomes pliable when heated. It can then be formed into a desired shape and left to cool. Once cool, it retains the shape it was formed into. There are several techniques for forming Plexiglas, depending on the type and size of the job.

Skill level:
Easy

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Things you need

  • Vacuum pot
  • Air pressure head
  • Air line
  • Molds
  • Clamps
  • Oven
  • Plexiglas sheeting
  • Wooden frame

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Instructions

  1. 1

    Cold-form the Plexiglas by bending the material by hand into a curved frame. The radius of the curve should be at least 180 times the thickness of the Plexiglas sheet in the case of Plexiglas G or 300 times the sheet thickness in the case of Plexiglas MC. This method requires no heat, and the Plexiglas will hold the curve after being bent into the frame.

  2. 2

    Bend the Plexiglas using a strip heater. This is a long, straight heating element that heats the Plexiglas at the point of contact until it is soft enough to bend. The bend point must be notched with a cutting tool first. This type of heating and bending puts a great deal of stress on the plastic and may cause cracking or splitting.

  3. 3

    Drape form the Plexiglas by heating it in an oven to between 143 and 176 degrees C. The exact amount of heat needed depends on whether it is Plexiglas G or MC (with G requiring more heat) and on whether the plastic is encased in a mould. If it is, temperatures closer to 176 degrees C are necessary. For drape forming, 143 degrees C is enough. The plastic is heated in an oven to this temperature, then draped over a form and clamped down at the edges.

  4. 4

    Free form the Plexiglas by clamping a heated sheet of it over a vacuum pot or pressure head. The air can be used to form the pliable plastic without physical contact. Changing the shape of the pot opening allows different shapes to be formed this way. Although vacuum forming is a simpler process, the equipment set-up cost is higher than for pressure forming.

  5. 5

    Form the Plexiglas around a mould using vacuum snapback forming. In this process, a heated sheet of Plexiglas is sucked down into a vacuum pot. A shaped mould is introduced above the plastic, and the vacuum is gradually released. As the plastic tries to resume its original sheet form, it clings to the mould and produces the desired shape.

  6. 6

    Vacuum draw or blow a sheet of heated Plexiglas around a form. In these processes, the sheet of pliable material is first draped over a mould and clamped to its edges. It is then formed to the mould either by pressure from air jets or suction from a vacuum pump.

  7. 7

    Slip form the Plexiglas by clamping it loosely to the mould at the beginning of the cooling process. This will allow it to draw inward a bit as it cools, thickening the centre of the piece. When it has slipped enough to give this extra thickness, the edges should still be clamped down for it to set into shape without further slippage.

  8. 8

    Build an airtight box and insert a piece of heated Plexiglas draped over a form. Seal the box over the Plexiglas and form, then pump air into it. The pressure of the air will force the Plexiglas down over the form in a process called blowback forming. This is especially useful for forming complex drawn shapes, which can be turned into three-dimensional block moulds.

  9. 9

    Billow form the Plexiglas by placing a sheet of heated material over an air pressure head. Turn on the air to make a bubble in the Plexiglas, then set a mould down on top of the bubble. The Plexiglas will be pushed by the air pressure into the interior form of the mould. It is important to install a relief valve to prevent too much pressure from building up under the mould.

  10. 10

    Press a heated sheet of Plexiglas between two plates with wooden or metal ridges along their interior surfaces. This is an open-forming technique called "ridge forming" that doesn't require a sealed form. It can be used to make corrugated sheeting or more complex shapes that map whatever shape the ridges are cut into.

  11. 11

    Stamp a heated Plexiglas sheet between male and female metal dies. This process is called "male and female forming." To get enough pressure, the dies must be attached to a hydraulic or pneumatic press in a machine shop or factory.

  12. 12

    Emboss Plexiglas sheeting by blowing it against a form with a soft or textured surface. This also requires a pneumatic system that can produce positive pressure of 22.7 to 34 Kilogram per square inch. The sheet must be closed into the press very quickly so that it doesn't cool too much before being formed.

Tips and warnings

  • Even heating is the most important thing when heating a sheet of Plexiglas in an oven before forming it. Ovens with forced-air circulation will produce the most even heating gradient and are least likely to overheat the sheet.
  • A Plexiglas object will retain its shape up to a temperature of 82.2 degrees C, after which it will try to revert to its original shape.

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