Directional solidification (DS) is a process in which materials are cooled and solidified in a direction that is favorable to the desired material properties. Generally, this involves the use of an external heat source, such as a furnace, to cool molten metal from one side to the other. The goal of this process is to achieve a uniform distribution of micro-structures in the as-cast part.
DS is used in a variety of industries, including automotive, aerospace, power generation and medical. It is the preferred method of casting for certain components due to its unique combination of strength and size control. It is used for processing engine blocks, rotors, turbines, intake and exhaust manifolds, and other larger parts that require more intricate shapes.
The process begins with the selection of a proper alloy to be cast. The choice of material depends on the condition of the part to be produced, such as the amount of distortion and potential shrinkage. Once the proper alloy is chosen, the pattern is created to the desired shape and size of the finished product. The location of the inlet and outlet positions is also determined.
Subsequently, the part is placed into a heated furnace and slowly cooled over the total span of the cast. During the process, a temperature gradient is established in which the temperature at the inlet is higher than the outlet. This gradient causes the solidification of the molten metal to start from the inlet and slowly move towards the outlet. The molten metal cools and solidifies at each step along the path, until it reaches the endpoint. The result is a homogenous product with a consistent microstructure throughout.
DS also has several advantages when compared to conventional casting. It offers a more accurate and efficient method of casting, as it eliminates air pockets, pores and other imperfections which can cause problems in the finished product. Additionally, since the cast is completed in one piece, it requires less post-processing compared to traditional methods.
DS can be done in several different ways, including the use of vertical or horizontal directions, or the use of a tilt table. The most common process is the vertical direction, in which the furnace is mounted vertically and the molten metal is slowly cooled from top to bottom. The tilt table method involves the positioning of the pattern in a tilt, allowing for air accommodation as the molten metal cools.
In conclusion, directional solidification is an efficient and accurate process for forming metal components. It eliminates air pockets and other defects, and provides a homogenous distribution of micro-structures in the finished product. This catalyzes shorter production times and more accurate sizing, helping to reduce costs.
