Scientific method for determining cooling time in injection molding using infrared thermography

Abstract

Injection molders face confusion regarding accurately determining the required cooling time to produce quality parts. Many methods exist to estimate cooling time, but disagreement among results and fundamental flaws create error that leads to extra work, long cycle times, and a loss of profitability for molders. This research proposes a new method for determining cooling time at the injection molding machine using infrared thermography and Dynamic Mechanical Analysis (DMA) data to relate part ejection temperature to dimensional stability. Experiments exhibited evidence that dimensional stability is linked to material modulus, which would allow molders to choose cooling times based on required dimensional stability by relating measured ejection temperatures to specific modulus values using DMA data and thermal imaging techniques at the injection molding press. For the materials tested in this paper, it was found that at low ejection temperatures, the standard deviation approached nearly zero and part dimensions remained stable. However, as ejection temperatures approached 85%-95% of the glass transition temperature, the standard deviation began to rise and dimensional stability became more unstable.