Die Casting

Aluminum die casting, in simple terms, is a metal forming process in which molten aluminum alloy is injected into a precision mold under high pressure and rapidly solidified. The principle is similar to the injection molding process we are familiar with, but it involves metal — which requires higher temperatures, greater pressures, and tighter precision.

The entire process can be broken down into several key steps:

Step 1: Mold Preparation

Before die casting begins, the mold must be preheated, typically to between 150°C and 230°C. This prevents the molten aluminum from cooling too rapidly upon contact with a cold mold, which would affect its fluidity and forming quality. After preheating, a release agent is sprayed onto the mold cavity surface to facilitate smooth ejection of the casting. The fixed and moving halves of the mold are then tightly closed on the die-casting machine, with sufficient clamping force applied — measured in tons, ranging from a few hundred tons for small parts to several thousand or even over ten thousand tons for large integrated structures.

Step 2: Melting and Pouring

Aluminum alloy ingots are melted in a crucible furnace, typically at temperatures between 650°C and 670°C. During melting, degassing and fluxing treatments are carried out to remove gases and impurities from the molten aluminum, preventing porosity or defects inside the casting. Once the melt is properly prepared, it is poured — either manually or automatically — into the shot chamber of the die-casting machine, ready for injection.

Step 3: Injection and Filling

This is the most critical stage of the entire die-casting process. The injection plunger drives the molten aluminum into the mold cavity at extremely high pressure (10 to 200 MPa) and very high speed. The filling process is extremely fast, typically taking only 0.01 to 0.2 seconds. This high speed is essential to ensure that the aluminum fills every fine detail of the mold — including thin-wall sections and complex geometries — before it begins to solidify. If the filling speed is insufficient, the aluminum may solidify before completely filling the cavity, resulting in short-shot defects.

Step 4: Pressure Holding and Cooling

Once the cavity is filled, the injection plunger continues to apply pressure for a short period to compensate for the volumetric shrinkage that occurs as the metal cools and solidifies. Under this pressure, the casting rapidly cools and solidifies. The duration of this stage depends on the wall thickness and the design of the casting.

Step 5: Mold Opening and Ejection

After the casting has fully solidified, the mold opens. Ejector pins push the casting out of the cavity. At this stage, the casting still has gates, runners, and flash attached — these are byproducts of the process and will be removed in subsequent steps.

Step 6: Post-Processing

The casting removed from the mold is only a semi-finished part. It must go through a series of finishing operations: gates and runners are cut off, flash is trimmed, the surface is improved through sandblasting or shot blasting, and critical dimensions are brought to print tolerance through CNC machining when required. Key castings are also inspected through X-ray or other non-destructive testing methods to ensure there are no internal porosity or cracks.

Compared to injection molding, aluminum die casting involves higher temperatures, different shrinkage behavior, and more demanding equipment requirements. However, its advantages are equally clear: cast parts have high strength, good thermal conductivity, excellent dimensional accuracy, and superior surface finish — making it especially suitable for producing complex, thin-walled metal parts in high-volume production.

Today, with the rapid growth of industries such as new energy vehicles and 5G communications, aluminum die casting is expanding beyond traditional applications like automotive body structures and engine blocks into areas like large-scale integrated die casting and precision heat dissipation components. For Haina, a company with deep expertise in precision mold manufacturing, aluminum die casting represents a direction worth exploring — while the technical barriers are higher than injection molding, the market potential and added value are equally significant.