Gravity die casting is a permanent mould casting process: molten metal is poured into a precision-machined steel die, fills the cavity under gravity, solidifies, and is then extracted when the die is opened. The same die is used repeatedly, producing castings with consistent dimensions and a better surface finish than sand casting.
The word 'permanent' is the key difference from sand casting. In sand casting, the mould is destroyed to retrieve the casting. In gravity die casting, the mould stays, and its quality improves with use as the die surface conditions. This repeatability makes gravity die casting well suited to components that need to be produced in identical form across a production run.
How Gravity Die Casting Works
The process begins with die preparation: the steel tool is coated with a refractory wash to prevent the aluminium from bonding to the die surface, and heated to the working temperature for the alloy being cast. This temperature control is important: a die that is too cold produces poor fill and cold shuts; too hot, and the casting's mechanical properties suffer.
Molten aluminium is poured from a ladle into the die. Gravity draws it through the running system and into the cavity. Sand cores can be set into the die before pouring to create internal features, undercuts, or hollow sections that the die alone could not produce.
After solidification and a controlled cooling period, the die is opened, the casting extracted, and the running system removed. The casting then moves to inspection and, where required, post-process operations.
Advantages of Gravity Die Casting
- Superior surface finish: the steel die produces a smoother surface than sand, reducing finishing time
- Improved mechanical properties: faster solidification produces a finer grain structure and higher tensile strength
- Dimensional consistency: permanent tooling delivers repeatable accuracy across a production run
- Reduced porosity: lower gas content compared to sand, important for pressure-tight applications
- Sand cores: complex internal geometry is achievable within a die casting, combining the benefits of both processes
Gravity Die vs Sand Casting: Choosing the Right Process
The choice between the two processes depends on the component, the volume, and the requirements. Gravity die casting offers better surface finish and mechanical properties, but the tooling cost is higher and the process is better suited to aluminium than to iron or copper-based alloys.
At Maybrey we offer both processes from the same facility, which means we can advise on the right approach for each application without any bias towards one process over another.
Gravity Die Casting at Maybrey
Our gravity die casting operation produces aluminium castings to 25 kg in a full range of alloys, from commercial grades through class one aerospace-specification aluminium. All dies are designed in-house by our engineering team. We cast the die blocks themselves in our iron sand foundry, giving us control over material quality and lead times from the start.
Many gravity die castings leave our facility fully machined and heat-treated, reducing your supply chain to a single point of contact. For aerospace and defence work, our die casting operation is certified to AS9100 Rev D, with unbroken aerospace approval since 1936.