The Simplicity of Gravity Casting

Posted on Nov 5, 2020

gravity casting

The process of gravity die casting is a specialized manufacturing process to mold molten metal. Metal is poured from a vessel or ladle into a casting The tool cavity fills with no force except that of gravity. This fills the tool and it can be controlled by other means like tilting the die.

Undercuts and specialized features like recesses can be realized in the form of the element using sand cores. This process can lead to impressive and more refined surface finish than sand casting And it also has better mechanical properties, both due to the rapid solidification.

In addition, the process has a higher casting rate than aluminum sand casting, however metal molds are more expensive than sand. The advantages of this process include the possibility of a low gas porosity and a fine grain size can be obtained.

Compared to sand casting, the process requires less finishing and cleaning, and gravity die casting tends to produce a higher quality product. The method of producing gravity die casting is generally less cost effective in producing tools as compared to sand casting.

:: Read more : Casting Sand For Industrial Use


The Gravity Die Casting Process Explained

In gravity die casting it is usually a laborious manufactung method. with the molten metal added via a ladle. The speed and the flow of the filling can also be controlled by tilting the die. But in some more advanced cases, for some high volume applications, it is also possible to use an automated ladle to introduce the molten metal.

Some other ways of producign casted parts, the molten metal is poured into the die cavity, and the gravity die material, the casting process is essentially the same as sand casting. It involves four steps which we explain in detail below.

The die is heated and then sprayed with a refractory coating, and closed. The coating both helps control the temperature of the die during manufacture and it also assists in the removal of the casting.

Molten metal is then manually poured into the die, (although in some cases a machine can be used) and allowed to solidify. The die is then opened and the cast parts either removed by hand or in some cases ejector pins are used on the mechanized machines.

The final step is for the waste material and that includes the gate, flash, runners, plugs and the tab, is trimmed from the castings. The workpieces then need processing to remove extra sharp edges and excess material, then blasted before shipment to the customer.

Gravity die casting is a natural partner for sand casting and allows us to offer the customer the most cost effective method of producing castings.


How Does Gravity Casting Work?

If you are new to the foundry industry, gravity die casting may appear to be a highly technical and complex process, however, in reality, it is quite simple. Let us introduce you to a step by step method to easily understand gravity casting.


Preparation for Gravity Casting

Before the gravity casting process begins, the first step is to prepare the die itself. It basically involves heating it to the right temperature and spraying it with a refractory coating or grease.

This lubricant not only maintains the die temperature during the manufacturing process, it also prevents premature solidification and helps to remove the casting after it solidifies. The die halves can then be closed and clamped firmly using high pressure.


Material introduction by Pouring or Injection

After this preparation step, the molten metal is then drawn from the furnace and charged directly into the die through a downward spout. This can be done manually or, under certain circumstances, using an automated vat; but either way, the process uses gravity.

No additional forces or pressures are applied. The molten fluid is simply introduced into the die from vertical and vertical positions and flows down into the casting due to the natural action of gravity.

By avoiding the use of high pressure, turbulence is greatly reduced, which in turn helps to prevent and lead to porosity the production of much smoother components and parts.


Casting Cool Down Period

After the molten metal is inserted into the casting, it is allowed to cool and solidify. The metal should be given sufficient time to take the shape of the mold and it should be completely solidified before releasing the die. Premature plaster removal can lead to irreversible damage.

Part Removal and Ejection

After sufficient time has elapsed, the die halves are then released and opened, and the cast parts are carefully removed. This can be done by hand or, in some situations, ejector pins are used to safely push the casting out of the die casting machine.


Secondary Processing and Trimming of Parts

The final step in the gravity casting process is trimming. As the metal cools, any scrap - including gate, rails, lugs and blemishes - is expertly removed from the casting.

Various tools are used to remove sharp edges and excess material, thus creating the desired shape of the element and the part is normally cleaned prior to shipment to the customer. This is the final process for gravity casted parts and we hope you got a good understanding of this useful process.


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