When we talk about die casting, there are two processes followed – HPDC (High-Pressure Die Casting) or Gravity die casting (Low-Pressure Die Casting). Both of them cater to different situations but utilize a similar process to achieve the final output.

Gravity die casting is one of the earliest die casting processes invented by human beings. With time, it received massive improvements in respect to the equipment and the overall process efficiency.

In this article, we discuss gravity die casting, its advantages, and its process.

Definition of gravity die casting

Gravity die casting is a type of die casting process useful for large series production. It finds usage in several industries owing to minimal costs and high-quality output it achieves with minimum human interference. The process is used for non-ferrous alloy parts, typically aluminium, copper, and zinc-based ones.

The modern gravity die casting process can be automated to a great extent. It is best suited for large, thick parts requiring high detail levels. The products from this process offer superior finish and mechanical properties compared to sand casting. It also has a higher casting rate compared to aluminium sand casting.

How is it different from high-pressure die casting?

High-pressure die casting uses pressure after injecting the liquid into the die. It requires complex machinery and follows an entirely automated process to achieve the result. Gravity die casting is not a fully automated process, leading to lower flexibility. Gravity die casting is also the cheaper of the two.

Applications of gravity die casting

Gravity die casting finds usage in a myriad of industries, such as kitchen tools, automotive, lighting components, and others, with several use cases. It is ideal for producing parts, such as knuckles, engine cylinder heads, engine blocks, pistons, etc. The production process is uncluttered and best suited for making items in large numbers.

Gravity die casting process

Gravity die casting is very popular because of its clutter-free and comparatively straightforward approach. It requires minimum machinery, and you can tweak the output to an extent. If you are looking for high volumes, you can automate a significant part of the process. 

Here are the elements involved in a traditional gravity die casting process –

1. Preparing the die

The process begins with heating the die using gas burners and sprayed with a refractory coating. It can be used multiple times and helps in the removal of the casting. It also manages the temperature levels. The die parts are then assembled and clamped.

2. Liquid injection

The operator pours the molten metal into the die. The liquid metal is left to set and assume the shape of the cast for a few hours. In gravity die casting, the machine operator uses bottom pouring, and he fills the liquid using a down sprue.

3. Ejection

Once the metal is set, the die is opened, and they eject the castings. The next part involves the removal of cast parts and ejection pins manually. The scrap, including gates, sprues, runners, and flash, are removed from the cast.

4. Shakeout and polishing

The castings are then fettled and heat-treated (wherever necessary). The processing helps in the removal of any sharp edges and excel material. The final process involves blast cleaning to give the requisite polish to the end products.

Advantages

Here are the reasons why gravity die casting is gaining a lot of popularity –

• It is one of the most cost-efficient processes for die casting
• It is useful for simple castings, preferably smaller ones, with uniform wall thickness and no intricacies
• Good dimensional accuracy with faster production times
• It is most suitable for high volume levels
• The coating can be used multiple times and requires minimum investment once the initial investment is in place
• It can produce parts with top-notch mechanical properties (such as low gas porosity and fine grain) most suited for heat treatment
• The final product requires less finishing and fettling due to its inherent advantages

Wrap up

There are several factors to be considered before deciding on the precision die casting process you choose. It includes quality requirements such as complexity, integrity, surface finish, and mechanical properties. We also need to consider the lead time, production rate, and other commercial aspects. Metals with higher melting points are not the best for gravity die casting.