Induction Skull Melting of Ti-6Al-4V: Process Control and Efficiency Optimization

Titanium investment casting is one of the leading and most efficient near-net-shape manufacturing processes, since complex shape components are possible to obtain with a very low amount of material waste. But melting these reactive alloys implies the usage of specific melting technologies such as the Induction Skull Melting (ISM) method. In this work the ISM was extensively studied with the aim of deepening the characteristics of this specific melting method and improving the too low energy efficiency and overall process performance. A 16 segment copper crucible and 3 turns coil was employed for the melting of 1 kg of Ti-6Al-4V alloy. Through the calorimetric balance, real-time evolution of the process parameters and power losses arising from the crucible and coil sub-assemblies was displayed. Results revealed the impact of coil working conditions in the overall ISM thermal efficiency and titanium melt properties, revealing the use of these conditions as an effective optimization strategy. This unstudied melting control method allowed more heat into charge and 13% efficiency enhancement; leading to a shorter melting process, less energy consumption and increased melt superheat, which reached 49 °C. The experimental data published in this paper represent a valuable empiric reference for the development and validation of current and future induction heating models.

Temperature feedback algorithm for efficient electron beam heating of titanium melt

High-quality electron beam melting of titanium requires a uniform heating of the melt in the intermediate container of the electron beam unit and an efficient distribution of the power of the electron beam guns. In this study, we investigated the efficiency of different algorithms to control the electron beam trajectory. Three-dimensional transient heat transfer in the intermediate container was simulated using finite element method. It was shown that the standard algorithm, with a zigzag trajectory provides uniform heating of the melt in the absence of unmelted furnace charge. A temperature feedback algorithm allows heating the melt within the required temperature range in the presence of the furnace charge, but it doesn’t provide temperature distribution uniformity. Based on the mentioned algorithms, a combined algorithm was proposed which allows efficient heating of the melt regardless of the presence or absence of the furnace charge. The implementation of the combined algorithm into the technological process allows a substantial increase in the productivity of titanium melting.

Numerical Simulation of Bubble Migration in Liquid Titanium Melts under Hypergravity Field

Bubble migrations in liquid titanium melt under hypergravity field is modeled using commercial computational fluid dynamics software FLUENT 6.3 (Fluent inc., USA). The two-phase fluid model, incorporated with the Multiple Reference Frames (MRF) method is used to predict the movement of the bubble in the melt. Simulated results are compared with experimental data from the water model measurement and reasonable agreements are obtained. Furthermore, the computed results show that the bubble migration under hypergravity field includes the movement forward to the casting rotating shaft and the movement opposite to the direction of the rotating mould. In addition, the initial bubble size and the surface tension between the melt and the gas bubble have an important effect on the distortion of the bubble.