Characterization of the heat transfer coefficient at near solidus forming condition using columnar pressing test

Abstract

This study addresses the significant gap in the literature regarding the heat transfer coefficient (HTC) under near-solidus forming (NSF) conditions, where materials are shaped close to their solidus state, presenting complex behaviour compared to traditional hot forming processes. Despite the pivotal role of heat transfer in developing a reliable material model for the digital twin (DT), limited data exist particularly regarding HTC characterization at NSF. Additionally, testing methodologies suitable for the high-temperature conditions, crucial for NSF processes, have not been adequately addressed. To fill this gap, this study aims to characterize HTC under NSF conditions using a columnar pressing test. The test was conducted at three different temperatures such as 1250, 1300, and 1360 °C and two different pressures, 2 and 8 MPa. During the test, temperature data was collected at the centre of the sample using a k-type thermocouple. Furthermore, the DT of the pressing test was developed and the three-dimensional finite element model of 42CrMo4 steel was constructed using FORGE NxT® 4.0 FEM software. The simulations were performed with varying HTC values to replicate the experimental test data. Inverse modelling techniques were then applied to compare experimental and simulated data, enabling the characterization and optimization of HTC values under NSF testing conditions. The results demonstrated that HTC in the NSF process is primary impacted by the forming pressure, whereas temperature change showed no variation at the studied ranges. The HTC value of 500 W/m2K and 800 W/m2K was identified at 2 MPa and 8 MPa, respectively. The conclusion of this study aims for a better understanding of heat transfer phenomena in NSF processes, enhancing the reliability of DT for industrial applications.