Properly formed Vical acrylic parts will retain their shape if kept below 180°F. If exposed to higher temperatures, they tend to revert to the original flat sheet form. This property, called "elastic memory," prevents forming Vical acrylic parts in several stages as in sheet metal pressing, but permits the fabricator to reheat and reform the sheet if he makes an error in forming. When reforming, the sheet should be heated for flattening and reforming at the same time to keep at a minimum the total time the sheet is exposed to oven temperature.

COLD FORMING

Vical acrylic can be bent while cold to simple shapes by springing the material into a curved frame. The radius of the curvature should be at least 180 times the thickness of the sheet.

Cold forming Vical acrylic beyond these limits may result in crazing of the material due to stresses beyond those recommended for a continuous load.

SLIP FORMING

Vical acrylic is usually clamped around the edges after heating before it is formed. This puts the whole sheet in tension and it stretches more uniformly and wrinkles are not apt to form. In some cases, in order to obtain a thicker finished part, a pre­determined amount of Vical acrylic is allowed to slip under the clamping ring to reduce thinning out of the sheet.

Wrinkles tend to form outside the ring around the edge of the piece, limiting the amount of material which can be allowed to slip in. When sufficient material has slipped in, the rings are clamped more tightly and the draw is completed. Hot or insulated clamping rings may be used to avoid chilling the material.

Forming Temperatures and Cycles