FORMING EQUIPMENT

PRESSES*

The amount of pressure needed to form Vical acrylic is much less than that needed to form metal. Presses with a capacity of one ton per square foot of platen area are adequate for forming, including corrugating.

The following rule of thumb can be used to calculate the total force in pounds required to form the average sign face by the plug and ring method: Calculate the perimeter of the basic shape, all letters and copy in inches and multiply the total by 30

Vertical presses may have (a) a fixed lower Platen and a moving upper Platen or (b) moving lower and upper Platens. Horizontal presses in which the Platens move in a horizontal Plane are also available. Such presses may be operated by air or hydraulic cylinders which have a stroke of at least 18U (the stroke should be three times the maximum depth of draw). Platens should have a steady rate of travel of from 5 to 15 feet per minute without chatter. They should be rigid and not deflect more than i/s" when loaded to capacity.

CLAMPING RINGS AND CLAMPS

Some means should be used for holding the edges of the sheet against the form during forming and cooling. For very simple shapes, rubber bands can be fastened to the form and snapped over the edges of the formed Vical acrylic. For more complicated shapes, a clamping ring is made to fit the contours of the form. The clamping ring is brought to bear on the edges of the sheet to hold it in Place. The ring should be hinged or located by guide pins on the form so that it will always be in correct position in relation to the form, allowance being made for the thickness of the sheet. The ring may also be used as a template of the finished part so

that when the Plastic is cool, the "trim line" may be scribed while the part is on the form. The Vical acrylic should not be scribed until it has cooled since the material contracts during cooling.

The surface of the clamping ring which contacts the hot Vical acrylic should provide a non~slip grip. The clamp faces can be surfaced with a variety of materials such as coarse sandpaper, ping pony paddle rubber or perforated metal. The choice of clamping method will usually depend on the number of and rate at which the parts must be formed. If only a few parts are to be formed, wood clamps or "C" clamps may be used. For high production rates, toggle clamps or air cylinder actuated clamping rings are used. Forming presses and clamping fixtures may be combined in many different ways to meet the need for versatile forming equipment or specialized devices capable of high production rates. Forming equipment may be constructed from readily available parts and materials to suit any requirement. A few typical designs are discussed below.

To form parts such as skylight domes with compressed air, the vacuum/pressure table is first covered with kraft paper to block off the vacuum holes, then covered with light flannel to diffuse the air and prevent chilling of the heated Vical acrylic when it is clamped in the press. A dome of any desired height within the daylight opening is formed by admitting compressed air. The front side of the clamping frame is hinged at the top so it may be raised to facilitate removing the part after forming.

Vacuum forming is carried out in a similar manner using a perforated mold on the vacuum/pressure table. Vacuum holes outside the area of the piece to be formed are covered with kraft paper. Heated Vical acrylic is clamped to the mold, in this case, corrugated metal with letters attached, and a vacuum is drawn, forming the sheet.

Forming Acrylic Sheet