How the High Pressure die-casting machine functions?

Die-casting is a process of pushing metal into the mold cavity with high pressure. However, this process is generally referred to as ‘High Pressure Die-casting’ where high-grade steel tool is used to accommodate high speed and pressure. Along with these two, high temperature also needs to be maintained around 700ᵒC. This method has a competitive advantage over the other processes as it produces large volumes, polished surface finish and improved tolerances.

It incurs a high tooling cost as it has implanted advanced technologies. The high pressure die-casting machine accounts to maintain considerable pressure while forcing metal into moulds. In this process, the casts possess the characteristics of splendid dimensional accuracy and smooth surfaces due to which it doesn’t require machining.

Almost every machine of this type employs Aluminium. The production rate of these ‘High-pressure die casting machines’ can move up to 1000 per day depending on the appropriate tooling of die-casting and developing designs maintaining an ideal pressure. With these standards a productivity of 20,000 to 30,000 Die Casting parts can be achieved. However, the cost of using high pressure die-casting machine is very high in comparison to low pressure die-casting machines.

The moulds of high pressure die-casting machine are made up of hard steel which are able to with stand extremities of the temperature and immense pressure. These can also be produced from inexpensive inputs that can reduce the overall cost of the machine.

Basically, die-casting machines are two types:

Horizontal cold chamber – Mostly for castings
Vertical – Mainly for electrical motor parts along with encast winding

However, using these high pressure die-casting machines causes turbulence resulting in air entrapment. Molten material enters with a speed of 20-45 m/s in the die. The speed is so high that the infusion takes place in a blink of the eye and there is no time left for the air to escape. Provision for air ventilation also couldn’t solve this problem. Moreover, impurities need to be introduced in the molten metal to avoid the stickiness of castings with moulds. The mouldings ranging from 50g to 50 kg can be produced from these conventional methods.

Irrespective of these drawbacks, HPDC machines are most preferred by the industries because of their merits.

The numerous processes undertaken by these conventional machines are as follows:

Slow shot die-casting process – Along with two sub-processes vis-a-vis Squeeze casting process that reduces shrinkage porosity and gas voids due to slow metal injection and Acurad process that minimizes air traps by slow injection through the first plunger and then pushes it hard through the second plunger.

Vacuum die-casting process – Involves two processes: Ultra-high vacuum process with air and gas content below 5cc per 100g of metal and Vacural process that is similar to the previous but employs low pressure.

Pore-free process – This process replaced air with oxygen gas that reduced the air blow holes, which is called as Otivac process.

Minimum Fill-time process – This uses a multi-runner system that incurs minimal time in filling the cavity.

Semi solid-liquid metal casting process – With the advantages of conducting operations at low-temperature and long-lasting dies.

Thixocasting process – Reheats the solidified die to convert it into a semi-liquid slurry to impart high strength to the end-product.

Rheotech Casting process – Involves an electro-magnetic stirrer in the injection process to prepare a solid-liquid mixture.