This article will discuss Brake Forming and Strip Heating of Polycarbonate Sheet. Brake forming is done with a metal brake press. It is done cold and no pre-drying of the polycarbonate sheet is required. Brake forming alone is not recommended above 0.118 inches (3 mm) because the sheet may crack or fail due to induced stress.
To brake press thicker sheet, a combination of strip heating and brake pressing is recommended. A strip heater is a single long heating element, such as calrod or a nichrome wire placed in a heat resistant housing. Heat the polycarbonate surface along the area that is to be bent using the strip heater. Heat the area in the 300 F (149 C) to 350 F (177 C) range when combining with brake pressing. Sheet below 0.177 inches (4.5 mm) can be heated single sided. Sheet having a thickness above 0.177 inches (4.5 mm) must be flipped on the strip heater to prevent burning and to evenly heat the sheet to avoid stress being built up in the part. Once the sheet is heated, then place it on the brake press.
Strip heating alone typically results in warpage of the part. Strip heating only heats the narrow strip that is to be bent. Because the heated portion of the material is prone to shrinkage and the adjacent unheated material is not, this results in warpage. Combining strip heating with brake pressing often alleviates the warpage problem. For strip heating alone, the sheet surface temperature along the area to be bent should be approximately 500 F (932 C). Strip heating is still heat forming and pre-drying is recommended.
By following these recommended process conditions you should be able to improve your Brake Forming and Strip Heating of polycarbonate sheet. Our next blog post will cover trouble shooting of forming problems.
For additional information on polycarbonate sheet, contact Liz Grimes – Technical Director 215-872-3532/lgrimes@highlinepc.com