Use of thermography to calibrate fusion welding procedures in virtual fabrication applications

Abstract

The application of infrared thermography to the measurement of transient temperature fields generated by fusion welding of ship structures is described. The purpose is to capture real data from practical welding situations, which can then be used as input to computational simulation of welding manufacturing operations (virtual fabrication). Workpiece distortion due to thermal mismatch strains constitutes a major technological and economic problem in welding fabrication, and there is worldwide research interest in simulation techniques that facilitate off-line investigation of methods to reduce distortion in real applications. The effectiveness of such methods depends critically on the thermal input stage, where the complex effects of variable arc energy transfer, non-linear material properties, and workpiece / fixture heat-sink variables are present in a practical case. Thermography provides a unique method to measure such parameters on a whole-field basis. The paper presents measurement comparisons made on large welded plate structural components between whole-field thermographic data, thermocouple data, finite-element thermal analysis, and analytical approaches. The paper also addresses relevant thermal imagery problems in this context, such as emissivity calibration and compensation methods for lens distortion. Thermography is shown to be an ideal way to identify the outcomes of practical features such as thermal discontinuities in the workpiece and the effects of weld preparation and process variables on the thermal transfer efficiency of the welding process electrical energy.