Controlled solidification of aluminium castings: the path to higher-quality components for aviation
The quality of aluminium castings depends on a number of factors, among which the way the metal solidifies and cools after casting plays a crucial role. It is precisely the management of this process that has become the main topic of a development project implemented at the foundry of MESIT machinery (MEMBER OF OMNIPOL GROUP).
The aim of the project was to develop and apply controlled solidification technology for extremely demanding castings for the aerospace industry. The goal was to achieve significantly better internal quality, increased mechanical properties and, at the same time, reduced deformations after casting. The result is an innovative solution that is now being implemented in serial production and delivers measurable improvements in both quality and process stability.
Why is the method of cooling so important
From previous projects, it was clear that one of the key limiting factors for the quality of aluminium castings is precisely the cooling rate. In order to fully control the process and predict the final properties of the castings, it is necessary to keep the solidification process under control.
During cooling, a number of metallurgical phenomena occur that affect the final microstructure of the material. Uneven cooling of individual parts of the casting leads to the formation of temperature gradients, which cause internal stresses, deformations or the formation of microcracks. These defects subsequently have a negative effect on both the strength and the service life of the part.
The risk is particularly high for thin-walled and geometrically complex castings, which are typical in the aerospace industry.
When the mould acts as an insulator
The mould itself also plays a significant role in the cooling process. Ceramic shell moulds, commonly used in investment casting, provide high accuracy and surface quality, but also act as a thermal insulator. The dissipation of heat from the casting is therefore slower and less controllable.
When cooling in air, the entire process is relatively slow, which has a negative impact on the resulting properties. Therefore, the use of liquid cooling is an option, which enables more intensive heat dissipation.
In practice, however, it is not suitable to use water. Its cooling effect is too intense and leads to rapid temperature changes, which cause the formation of internal stresses and deformations. Therefore, it is necessary to use controlled cooling media with precisely defined properties.
What happens during cooling in a liquid
To understand the principle of heat transfer, a water-cooling model is often used, which can clearly demonstrate the different boiling modes.
When hot metal comes into contact with a liquid, three basic modes of heat transfer occur:
- film boiling – a continuous layer of vapour forms on the surface, which limits heat transfer,
- nucleate boiling – intensive heat transfer occurs due to the direct contact of the liquid with the surface,
- convective cooling – at lower temperatures, the process shifts to the standard cooling mode.
From the perspective of process control, it is essential to minimise abrupt transitions between individual cooling modes, which cause an uneven temperature field and lead to the formation of internal stresses within the material.
Simulation as the basis of process management
An integral part of the development was the numerical simulation of mould filling and solidification of castings, carried out using the MagmaSoft software. Simulations made it possible to optimise the gating and riser systems, predict defect formation, and set appropriate process parameters.
The modelling results were experimentally verified by measuring the temperature fields in the castings and subsequent analyses. This made it possible to calibrate the process precisely and ensure its repeatability.
From experiment to serial production
In the experimental phase, various cooling methods were compared, including water and polymer baths. The results clearly demonstrated that the polymer medium provides lower cooling intensity, but at the same time significantly reduces stress and deformation of the castings.
The technology was subsequently implemented into real operation through a robotic workstation, which ensures precise handling, stable process conditions and high repeatability.
Better properties, more stable production
The development of controlled solidification technology has brought several practical benefits. Above all, it led to:
- improved internal quality of castings,
- better mechanical properties,
- reduced deformation after casting,
- a more stable and repeatable production process.
The quality of the castings was also verified by radiographic tests according to the AMS E155 standard, which confirmed a high level of internal material quality. The developed technological solution is also protected by utility model No. 37129.
Significance for modern engineering
Controlled solidification is an example of how the combination of industrial research and experimental development can bring concrete improvements to manufacturing processes in practice.
For manufacturers of aluminium castings, this means not only higher production quality, but also greater efficiency and competitiveness when supplying components for technologically demanding sectors – especially aerospace, defence or energy.
