Process of Aluminium Gravity Fed Die Casting




Metal Fabrication

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The process of Aluminium gravity-fed
die casting

The Furnace.

This process begins with adding aluminium ingots to the furnace. The furnace takes 30 ingots which are then heated to 680 degrees centigrade. The ingots need to become molten which takes approximately 3 hours. This is often done overnight so casting can begin first thing in the morning and continue all day.

KJ Precision Engineering has a 400kg electric holding furnace. The furnace is manufactured from steel and fire bricks with a silicon carbide crucible lining which holds the molten aluminium.

Image of molten aluminium in KJ Engineering furnace

The Tooling or Die

Beside the furnace is a hydraulic press which holds the die or mould. The design of the mould is critical to the quality of the casting and must be designed by an experienced and qualified engineer. The mould is made from two blocks of Tool Steel and can vary in size.

Image of cleat die

It is generally made in 2 halves to a very high degree of accuracy (0.02mm) via our CNC Milling machine. The die has a series of risers and runners, into which the molten aluminium is poured during the process. These also must be designed by an experienced engineer to achieve the desired quality of the end product.

The tooling or mould can have many shots run from it but requires cleaning and preparation at regular intervals during a run. It also requires extensive maintenance after many casting runs. This is again achieved in the CNC Milling machine.

Watch video of cleaning the die to prepare for pouring.

The Process

Once the aluminium is molten and the die has been set up in the hydraulic press, a ladle is used to manually transfer the molten metal into the runners in the die. Gravity then takes the aluminium into all reaches of the die. There is a wait on average of 2 minutes while the aluminium cools and solidifies in the mould. This can vary according to the scale of the mould, the shape and the amount of aluminium required. It takes an experienced foundry man to carefully assess each casting and pour the aluminium with precision.

The hydraulic press is then opened and the casting is removed via hydraulic force through the ejector system. The casting is then removed manually via a lifting tool.

Watch video of the pouring process, followed by the cast removal.


The casting must then be dressed and this involves a number of processes beginning with the runners and risers being removed from the casting. The risers will then be recycled back into the furnace. These are manually removed via a bandsaw.

Each casting will then be ground down on the surfaces requiring finishing to create a smooth uniform shape. This is completed on the linisher or belt grinder and performed manually.

Some castings will then each take a turn in the CNC Milling machine to remove any large areas of aluminium. For example the 380mm cleats require the bottoms to be machined totally flat to sit securely and flush on a marina dock. Other castings may need to be drilled or further shaped. Each casting is placed and removed into the CNC mill manually. The final step is for each casting to be wiped free of swarf or residue. Your castings are then ready to be boxed up and delivered.

Watch video of the dressing process from removal of runners and risers through grounding/smoothing to CNC Milling to the final product ready for delivery.

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