Abstract
Materials used for Superplastic forming (SPF) are mainly titanium alloys which are good candidates to produce lightweight complex-shaped components for high performance aerospace applications. SPF process has limitations because it involves a high-temperature furnace with poor heat efficiency and expensive tooling with low management flexibility. Enhancing this manufacturing process is a major challenge for the aerospace industry which is facing to important production ramp-up and cost reductions. Direct heating combined with tool heat management result in significant savings of SPF process: production time savings by drastically reduce the heating time, reduction of maintenance costs and energy savings by significant heat efficiency improvement. Aurock developed direct heating by Infrared emitters and succeed in forming series 1.5x1m² Ti6Al-4V blanks. A key point with this new technology is to ensure a homogeneous blank temperature all along the forming. This point is achieved thanks to lamp power modulations and numerical techniques to secure the blank thermal regulation with a full radiative flux control at different forming stages. Results obtained are stable and repeatable regarding to dimensional criteria, post-forming thicknesses distribution and microstructure. Numerical predictions are in very good agreement with the experimental results, enabling robust machine setup for series Infrared SPF parts production.
Highlights
The principle of the Superplastic Forming (SPF) is to homogeneously heat a blank of a superplastic material at its superplasticity temperature and to apply a monitored gas pressure vs. time to form the blank on a die at a controlled strain rate ε
Due to the low conductivity of the insulating panels, the metal casing temperature is lower than 300°C so low-cost low-alloyed tool steel can be use unlike the expensive alloys conventionally used for SPF tools strongly allied with Chrome and Nickel
The number, power and position of the IR emitters are defined thanks to a thermal model assessing the radiative flux needed by the blank to have a homogeneous temperature (870°C for TA6V) all along the forming steps
Summary
The principle of the Superplastic Forming (SPF) is to homogeneously heat a blank of a superplastic material at its superplasticity temperature (around 900°C for TA6V [1]) and to apply a monitored gas pressure vs. time to form the blank on a die at a controlled strain rate ε (classically 5.10-4 s-1 for TA6V [1]). Different materials were characterized with different lubricant coatings such as Boron Nitride With all these input data, a thermal model is built to assess the global thermal behaviour of the system and to find the needed thermal flux in order to ensure: - a uniform and stabilized temperature of the metallic die at the end of the pre-heating and loading sheet phases - a uniform and constant temperature at 870°C of the blank during the forming phase The architecture of the cover is optimized, setting the number, length, maximum power and network configuration of the IR emitters. Microstructure checks with alpha case layer determination have not yet been performed on the four formed sheets, form experience on previous IR forming, Aurock has a high level of confidence on the results due to the fact that thermal measurements with thermocouples indicated no overheating on the blank nor on the metallic die.
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