Forming TUFFAK® GP Polycarbonate sheets.

TUFFAK® GP Polycarbonate Sheet can be brake bent to 90° angles in gauges = .100". Attempts at bending heavier gauges can result in cracks or breakage at the time of bending or later due to high-stress levels in the bend area. For this reason, strip heat bending is recommended on all gauges = 0.118".

Cold Bending

TUFFAK® GP® Polycarbonate Sheets may be cold-bent with the minimum radius based upon the sheet thickness. As a guideline, the material can be radiused to 100 times the thickness: (R=T x100).

Cold Bend Radii

Drying Time Hours

Thermoforming

TUFFAK® GP Polycarbonate Sheet can be thermoformed on standard equipment. Vacuum forming, free-blown forming, and line bending are the most extensively used processes.

While most standard forming techniques can be used, critical process modifications specific to polycarbonate are necessary to ensure uniform and repeatable formed parts.

Predrying TUFFAK® GP Polycarbonate Sheet

TUFFAK® GP Polycarbonate Sheet must be dried before thermoforming because polycarbonate absorbs moisture at a high rate. Trapped moisture forms vapor above 250°F, and the vapor expansion creates bubbles in the sheet. Sheets of TUFFAK® GP Polycarbonate sheet should be placed in a dehumidifying air-circulating oven for predrying. The temperature should be 250°F and monitored with controls. Recommended predrying periods are shown below. Be cautious. The polycarbonate sheet begins absorbing moisture immediately upon removal from the predrying oven. The rate of absorption is dependent upon the ambient dew point. For this reason, it is crucial to transfer the sheet directly to the forming machine as quickly as possible.

Forming Equipment

The thermoforming machine should be capable of generating and maintaining a vacuum of 20 in. Hg pressure throughout the thermoforming cycle. Vacuum-forming machines with infrared heating elements perform well for TUFFAK® GP Polycarbonate Sheet forming. Rotary and shuttle designs with automatic or semi-automatic controls are most suitable. Key features of this type of equipment are timer control accuracy, uniform heating sources, and sufficient vacuum power. Single-sided heating has proven effective for TUFFAK® GP Polycarbonate Sheet in gauges up to .177". For thicknesses above .177", it is recommended that dual-sided heating ovens be used for effective radiation penetration.

Heaters

Infrared cal rod, coiled nichrome, or ceramic heating elements provide the best heating sources. Gas-fired heaters or convection ovens are not normally used with polycarbonate. Uniform heating of the sheet is critical. Radiation absorption graphs for polycarbonate are available. These graphs help match the emissivity of the heating element with the sheet for the most efficient heat penetration.

Heating Cycle

Heating TUFFAK® GP® Polycarbonate Sheet for vacuum forming requires heat penetration to achieve a 350°F to 360°F. The heat required will be higher for more complex shapes. When TUFFAK® GP Polycarbonate Sheet reaches forming temperature, uniform "sag" occurs. The amount of sag depends on the size and thickness of the sheet. A 12" x 12" x .060" sheet will sag approximately 1". A 36" x 36" x .177" sheet may sag 4"- 6" at the center. Once the uniform temperature has been achieved, timers can accurately reproduce the condition and maintain part-to-part consistency.

Procedure:

• Sheet thicknesses up to 0.177" gauge can be heated from one side. Above 0.177" gauge, two-sided heating is normally required to enhance productivity significantly.
• Heat source is removed, and the heated sheet is forced over or into a mold where a vacuum is applied.
• Helpful Hints:
• TUFFAK® GP Polycarbonate Sheet "sets up" very quickly compared to other thermoplastics and can be removed from the mold quickly.

Caution:

• TUFFAK® GP Polycarbonate Sheet remains hot during this cycle, and care must be observed when handling finished parts.
• Throughout the vacuum forming process, dust and dirt must be controlled. TUFFAK® GP Polycarbonate Sheet has a static charge that attracts foreign particles, which can create surface imperfections. Molds also attract dust particles and should be cleaned to avoid creating surface defects.

Shading and Screening

Shading is often used to balance out hot spots in an oven for uniform temperature. Shading may also be used to control the sag of the TUFFAK® GP Polycarbonate Sheet during heating.

Procedure:

• Use heavy-duty metal screening to shade the major portion of the clamped sheet, leaving several inches along the edges unshaded to compensate for cooler areas.
• Screens can be installed permanently or placed loosely above the sheet, depending on how much shading is required.

Helpful Hints:

• Use slow heating. This is particularly important with heavier gauges to prevent gradient heating.
• Allow the heat to reach uniformity at the center of the sheet.
• The heating rate may be reduced by lowering the heat intensity or moving the sheet farther away from the heaters.

Thermoforming Troubleshooting