Quenching is a common heat treatment technique used in the production of cast or otherwise-produced metal components. In particular, immersion or direct quenching process is a widely adopted procedure in the automotive and aerospace industries to minimize the formation of undesirable thermal and transformational gradients, which may lead to increased distortion and cracking.
AVL FIRE™ offers state-of-the art modeling functionality in the field of quenching. Various quenching approaches can be simulated: air quenching followed by spray and finally direct quenching. Different numerical models cover the different physical specifics of the thermal treatment process, which significantly influence the properties of cast materials. Commonly investigated components include cylinder heads or engine blocks made of aluminum, which can, under certain circumstances, undergo exceedingly high operational loads leading to material failure. Cracks commonly appear as a consequence of downsizing and weight reduction. An example of an everyday application is the weight reduction of passenger cars with a desire to minimize tailpipe emissions. Virtual prototyping, with its short turnaround times, provides a great solution for this problem, which is highly complex and in real life requires a great deal of time to investigate.
Boiling Regimes during direct Quenching
Physically, the most challenging quenching approach is submersion (or direct) quenching where reheated components are submerged in the water pool. Initially, the phenomenon of film boiling is present, slowing down the heat removal, followed by transition in nucleate boiling and finishing in single phase cooling after the solid has cooled down beneath the saturation temperature of the quenchant. Predicting different boiling modes and the transition between them is the key. AVL FIRETM has proven to be an accurate and reliable numerical tool in numerous test configurations and all levels of complexity, such as with cylinder heads. The quenching process is affected by solid piece orientation, initial solid temperature, water temperature and other factors, therefore accurate prediction of local temperature histories within the structure is crucial for the final prediction of residual stresses resulting from the production process.
Thermal Stress Prediction
Solid temperature results obtained with AVL FIRE™ serve as input for Finite Element Analysis of thermal loads and deformations. A simple GUI-based mapping step is performed to produce input data for Finite Element Analyses. Finally, the predicted residual stress levels are compared with operational loads. If residual stresses are greater than the operational loads, the thermal treatment needs to be changed. A different submerging direction or quenchant temperature may completely change the nature of residual stresses in critical areas and thereby improve the quality and safety of the components in operation. This extends the lifetime of the product and reduces the risk and warranty costs of OEMs in the market.