Inline Quality Measurement of Preheated Thermoplastic Composite Parts Using Passive Thermography

Thermoplastic composites play an increasingly important role in lightweight design. The composite industry employs several production techniques for thermoplastic composite parts. A novel approach utilizes a fully automated thermoplastic composite production cell which consists of five processing steps: (a) tape laying, (b) consolidation, (c) preheating, (d) forming, and optionally, (e) overmolding. To optimize process efficiency of the manufacturing chain and increase product quality it is important to gain real-time information of the quality of the intermediates between each processing step. This holds particularly for the preheated plate prior to injection molding. We developed an inline quality inspection method for the preheated part, including (a) a passive thermography camera for the measurement of thermal images and (b) a statistical data analysis approach to predicting critical quality attributes from the pictures. Several experiments with different set temperatures were performed using an industrial-scale infrared oven with consolidated plates made from polycarbonate and carbon fibers. To test our quality inspection approach, we used consolidated plates of different input qualities. The experiments confirmed the usefulness of the approach to assessing the process stability of the preheating step and the quality of the preheated plates.