Acrylic is a synthetic polymer and is also called PMMA (Polymethyl Methacrylate). It is an engineering plastic and a transparent thermoplastic. It is classified as a type of glass called Acrylic glass.
To make acrylic products first the small parts are manufactured and then they are assembled together. This process is called acrylic fabrication. It involves processes like masking, cutting, sawing, drilling, milling, routing, machining and finishing.
One of the processes used to make three-dimensional parts from acrylic sheets is called thermoforming. The forming starts at the glass transition temperature of 105° C and goes up from this. Thermoforming is known for moderate equipment investment and low tooling costs. It is one of the most economical methods.
Acrylic Fabrication
Vacuum forming
In this, the acrylic sheet is heated and dropped on the mould. A vacuum is applied to allow the sheet to take the shape of the mould.
A negative or a positive tool selection is done based on the application. When the geometry of the outside part is more important than the surface finish, a negative tool is used. Positive tools are used for applications that require inside geometry detail and a perfect surface finish.
Pressure forming
In this, compressed air is used to apply pressure to force the sheet into the mould. It provides greater dimensional and part definition control. This method offers a greater mould surface detail than any other method. It is used for applications that require texturing or lettering.
Plug-assisted forming
This method prevents excessive thinning of the material when used with deep mould cavities. Parts produced using this method have a more uniform thickness in the walls.
Twin sheet forming
In this method twin acrylic sheets and two negative moulds are used in a single clamp setup. A blow pin is inserted between the two sheets. It is used to pump hot air between the sheets to avoid sticking and sagging. Air pressure is applied through the needle and sheets form against the mould interior. This method is suitable for producing hollow parts or when the parts are made up of different materials.
Free forming
This process is used to make dome shapes. The procedure and the equipment are the same that are used in vacuum forming but the mould used is different. Compressed air or vacuum can be used to make parts.
Drape forming
This is used to make products that require a slight contour like face shields, vehicle windscreens and more. A felt-covered piece of plywood or a heat-resistant sheet is placed on the oven rack. The acrylic sheet is heated on the oven shelf. The heated sheet is removed from the oven and placed on the mould. Pressure is applied to allow the sheet to take the form of the mould.
