There are different methods of casting aluminium. These methods usually involve melting metals and placing them in a mold.

Two prominent methods of casting aluminium are die casting and sand casting. Each of these two has some distinguishing features. It may be difficult to know which of them to opt for. So, pretty sure you want to know the differences between them. Right?

You are on the right track! In this article, we will show you the differences between aluminium die casting and sand casting. Sit tight!

The differences between aluminium die casting and sand casting

Now, we will consider these differences in details. Follow closely.

(1.) Difference in mold

One striking difference between aluminium die casting and sand casting is the difference in the molds used in their productions.

(a.) Sand casting mold: The mold in sand casting is made from sand and bonding agent such as clay. To make the mold, you have to mix the sand and clay. Also, you need to add some water or any other binder to the mixture.

The common binders are vegetable oil, water, cereal, sea coal, fuel oil, pearlite, molasses, etc.

Green sand is a common sand you can use. This is because it has natural moisture which increases the strength of the mold. You have to divide the sand into sand coat and base sand. Remember to clean the sand if it has any contaminant. Also, ensure that the sand is dry to avoid any possible split and for safety.

You should also make the clay into fine particles. The clay absorbs more water to increase the binding strength of the mold.

You can add some auxiliary substances such as straw or coal powder to the mixture. This is to increase the air permeability of the mold and help the mold mixture resist heat

Mix these ingredients in a moderate proportion. Don’t add excess water. Once your mixture is able to maintain a form, you should stop adding water. Otherwise, it may become watery. So, ensure that the mixture is thick enough to avoid any cracking and burn.

At this point, you will need a pattern or match plate to compact the sand to the desired shape. The pattern can be metal, wood, or plastic. The pattern shapes the mold cavity. To apply the mixed sand on the pattern:

(a.) Place the pattern on the pattern plate, with the parting line touching the pattern plate.

(b.) To prevent the sand from sticking to the pattern, you can sprinkle some chalk dust on the pattern.

(c.) Fill the sand base into the mold using sand sifter.

(d.) Compact the sand in the mold to ensure that it is tight and proper. Ensure the edges are very tight. This will enable the mechanical strength of the sand mold.

(e.) Cut off any excess sand on the mold by flattening the upper surface. You can create sike oblique holes to enable the escape of air. Note that you need to add gating systems, runners, sprues and optional cores to finalize the mold.

(f.) Flip the flask and thereafter remove the pattern. These steps produce the mold to use in sand casting.

(b.) Aluminium die casting: Conversely, the mold used in die casting is different from that used in sand casting.

Here, the molds are made from machined steel, and not sand. You have to use a material with higher strength and melting temperature than aluminium.

To design the mold, you need to use 3D CAD/CAM systems. The mold would have two equal halves so you can open and close it. This will enable you to easily remove the castings from the mold.

The first half is the stationary die half that you will mount on the die casting machine’s fixed plate. The second half is the ejector die that you will fix to the movable fixing plate.

So, as shown above, the mold used in aluminium die casting and sand casting are different. Also, while you have to use pressure in die casting, you don’t use pressure in sand casting.

(2.) Re-usability of mold

You can only use a sand mold once. On the other hand, you can re-use the mold in die casting. This makes die casting suitable for large-scale production. This also reduces production costs.

(3.) Ease in casting

Sand casting molds are relatively easy to make than die casting. Here, you just have to mix the ingredients and use a pattern to compact the sand into your desired shape.

Also, note that the production lead time of sand casting is lower. If the materials are on ground, you can make sand cast product in a day. Although this is suitable for small-scale castings.

Conversely, die casting molds need to be designed, machined, tested and fixed to the equipment. The general lead time of die casting is higher than sand casting. The machining, testing and other processes takes time.

(4.) Time frame of mold production

In sand casting, after preparing the mold, you need to wait for some 8-10 minutes before you can use it. Whereas, for die casting, you can use a mold immediately after preparation.

(5.) Tooling costs

Sand casting does not require many sophisticated machines. It is mostly suitable for small-scale castings.

Die casting requires a higher upfront capital than sand casting. You need several machines and equipment. This is because die casting is more advanced than sand casting. Also, die casting is used for large-scale castings.

(6.) Casting of complex parts

Although you can use sand casting to cast complex parts. However, it is not suitable for casting components with thin wall or delicate geometry.

On the other hand, die-cast parts are suitable for castings that require high precision, such as medical equipment. You can use it to create shapes with closer tolerances.

(7.) Surface of castings

Sand cast parts usually have coarse and rough surfaces. This is due to the compacted sand imprints its texture gives to the cast. Also, the lack of pressure makes sand castings more porous, thereby causing a granular finish.

So, you will always need to do surface finishing on the sand castings. This would increase the post-production costs.

However, you can use some materials such as resins and coatings to improve the surface quality in sand casting. Also, packing the sand grains tightly will produce a more uniform surface. Note that the finer the sand grains, the smoother the surface will be.

If you use shell sands during sand casting, the casting would have a better surface. You know why? It’s because shell sands can combine the highest hot strength and resin level with the finest grain of any chemical sand.

On the other hand, die-cast products have a higher-quality surface finishing than sand casting. This is because of the pressure used in filling the die and the smoothness of the die’s inner walls. Though, this does not mean die-cast parts do not always need surface finishing.

Because die casting has excellent precision dimension, the machining costs is consequently reduced, compared to sand casting.

Note that the various surface treatment options include chemical film, powder coating, anodising, etc.

(8.) Scale of productions

Sand casting is mainly suitable for small-scale productions; usually less than 1,000 castings. This is because each part needs a new sand mold. Definitely, it will be cumbersome to make new molds for each part in large-scale productions.

On the other hand, die casting is suitable for mass production. It involves using sophisticated machines such as CNC machines, die casting machines, etc. If you want to quickly cast aluminium in bulk, consider die casting.

(9.) Wall thickness

Usually, sand castings have thinner walls. Through machining, you can have more space to correct any inaccuracy in your sand castings.

In comparison, even though die castings have thinner wall, they have greater dimensional accuracy.

Which is better between aluminium die casting and sand casting?

Having explained the differences between aluminium die cast and sand cast, you may wonder which is the best option between both.

Well, it is difficult to outrightly say one is better than the other. The right choice basically depends on what you want to do with the castings.

For example, sand castings are more suitable for the furniture industry. Sand cast products usually have textual imprints that improve the aesthetics of a piece of furniture or decór.

On the other hand, die casting is usually used to produce medical equipment. This is because these equipment require complex castings with higher precision.