Sensor for tape laying process control: model, validation and case study

Thermoplastic matrix composites can be consolidated during layup by locally applying heat and pressure. The goal is to maximize the material layup rate while achieving good interlaminar bonding. During tape laying, raw material properties can vary (fiber volume fraction, tow width) and part geometry can change (curves, number of layers). Because of these conditions, it is difficult to select one setting for the applied temperature and pressure and achieve consistent bonding. However, real time control of the main process variables, head speed, applied pressure and heat intensity, can ensure final part quality. For adequate bonding, the material must be heated above the melt temperature. A unique sensor has been developed that senses the temperature rise in the material when heat is applied. The sensor consists of a 100 W cartridge heater mounted between two optical pyrometers. The optical pyrometers record the composite surface temperature before and after the heater passes. The change in temperature indicates the material's ability to absorb heat at the current layup speed. Experimental data indicate that the number of plies as well as the tool plate geometry can affect sensor output. These data also agree well with model predictions of sensor function. A case study relating sensor output and tape laying head heat intensity required to reach the melt temperature is presented.