A Method for Decreasing Preheating Time of Thermoforming

Thermoforming is one of the most versatile and economical processes to produce polymer products, and the key drawback is difficult to control the thickness of final products. The temperature distribution after the preheating process affects to the thickness distribution of final products. The cycle time must be decreased in order to improve the competitive power of the products, but the preheating time can not be decreased freely because of the key drawback. In this study, a new method for decreasing the preheating time under the condition of satisfying temperature of forming window was developed. At first, the relationship between temperature difference and preheating time was investigated. In order to check the possibility of decreasing the preheating time under the condition of satisfying temperature of forming window, finite difference method was applied under the condition of considering the effect of natural convection using optimal heating profiles expressed by exponential function form which was developed based on Duhamel´s Theorem and optimization technique in a previous study. The optimal results show that the preheating time can be decreased using the developed method in this study with satisfying temperature of forming window.