Aluminum casting refers to the casting process using aluminum alloys. Compared to steel casting & iron casting, the most typical feature is its light weight. The typical alloying elements of aluminum material are copper, magnesium, manganese, silicon, tin and zinc. Aluminum is lightweight, has excellent strength, high thermal and electrical conductivity, high reflectivity, good corrosion resistance, excellent workability, and attractive appearance. It can be given almost any finish. It is nonmagnetic, nontoxic, and non-sparking.
The high thermal conductivity of aluminum is a marked advantage in any application where it is desirable to conduct or dissipate heat quickly and uniformly. On a weight basis, aluminum is the most efficient heat conductor of the common metals.
Casting is the original and most widely used method of forming aluminum into products. Technical advances have been made, but the principle remains the same: Molten aluminum is poured into a mold to duplicate a desired pattern.
Aluminum Casting Methods
High-Pressure Die Casting (HPDC) is an extremely efficient manufacturing method for producing various product forms. The process forces molten metal at high speed, and high pressure into a closed steel die cavity. The die has a stationary and moving half, both of which are mounted to the die casting machine’s platens. The die casting machine has an injection end that uses hydraulics and pressurized gas to move a piston forward, injecting the molten metal into the closed steel die. The die casting machine also has a clamping end that utilizes hydraulics and mechanical toggles to absorb the injection pressure and hold the die shut while the part solidifies. The process is capable of turning molten metal into a solid near-net-shape part in seconds.
Advantages of High-Pressure Die Casting
-Fast filling, high production efficiency.
-High compactness, high product strength and surface hardness, low elongation.
-Good surface finish, generally up to RA6.3 or even Ra1.6.
-Fit for Products with thin wall thickness (the thinnest to 0.5mm).
-Much gases in Internal , poor porosity .
-Not allow heat treatment, small machining allowance (better less than 0.25mm ).
-High cost and short time life for molding
Low Pressure Aluminum Die Casting
Low-pressure die casting is a method of production that uses pressure – rather than gravity – to fill molds with molten metal such as aluminum and magnesium. In this process, the holding furnace is located below the cast and the liquid metal is forced upwards through a riser tube and into the cavity. The pressure is applied constantly, sometimes in increasing increments, to fill the mold and hold the metal in place within the die until it solidifies. Once the cast has solidified, the pressure is released and any residual liquid in the tube or cavity flows back into the holding furnace for “recycling.” When cooled, the cast is simply removed.
Advantages of Low-Pressure Die Casting
-Precise control of the filling process.
-Reduces oxide formation and porosity.
-Ensure superior consistency of the partsfrom top to bottom
-Exceptional density , strength values and excellent dimensional accuracy.
-Fit for parts with simpler, symmetrical forms, complex geometries
-Uncomplicated machinery and technology, well to automation.
Aluminum Gravity Die Casting
Gravity Die Casting ( called Permanent Mold Casting in USA and Canada)is a permanent mold casting process , where the molten metal is poured from a vessel or ladle into the mold. The mold cavity fills with no force other than gravity, filling can be controlled by tilting the die. Undercuts, and cavities can be incorporated into the component form with the use of sand cores.
It specifically refers to metal casting, however, sand casting, metal casting, investment casting, lost mold casting can also be included generally .
Advantages of Gravity Die casting
-Less pores and can be heat treated.
-Low density
-Product finish is not high.
-Low production efficiency.
-Molding with long lifetime and low cost
-Simple technic process
-Not suitable for parts with thinner wall.
Aluminum Sand Casting
Sand casting is the most versatile method for producing aluminum products. The process starts with a pattern that is a copy of the finished casting. Virtually any pattern can be pressed into a fine sand mixture to form the mold into which the aluminum is poured. The pattern is slightly larger than the part to be made, to allow for aluminum shrinkage during solidification and cooling. As compared to die and permanent mold casting, sand casting is slow process but usually more economical for small quantities, intricate designs or when a very large casting is required.
Comparison of Aluminum Casting Methods
| Sand casting | Gravity die casting | Low pressure die casting | High pressure die casting | |
| Weight of the casting, kg | 0.1 … 500 | 0.01 … 50 | 1 … 70 | 0.01 … 30 |
| Annual volume | 1 … 5000 | 100 … 50 000 | 100 … 10 000 | 5000 … 1 000 000 |
| Pattern / tooling cost | Relatively low | Moderate | Moderate | High |
| Cost of changes | Low | Moderate | Moderate | High |
| Flexibility of design | High | High | Relatively high | Relatively high |
| Minimum wall thickness, mm | 4 … 6 | 3 … 4 | 3 … 4 | 0.8 … 1.5 |
| Dimension accuracy | Fairly good | Good | Good | Very good |
| Possible surface roughness, Ra | > 6.3-12.3 | ≥ 3.2 (2.5) | ≥ 3.2 | ≥ 1.6 (0.8) |
| Delivery time for samples, weeks | 3 … 5 | 4 … 5 | 5 … 6 | 4 … 5 |
| Special features | Also with sand cores and heat-treated | Also with sand cores and heat-treated | Also with sand cores and heat-treated | Also heat treated (in special conditions) |
Advantages of Aluminum Casting
Now that we know aluminum casting methods, the next question you are probably asking is, “What are the advantages?”
Aluminum casting is especially important in the manufacturing industry for commercial and industrial products. Therefore, let’s share with you the advantages of aluminum casting.
First, aluminum castings can allow the attainment of complex designs and forms for die cast parts. This means that manufacturers can easily order customized castings that will be suitable for their production needs.
Second, aluminum castings allow producers to manufacture parts at an extremely higher and faster rate than other alloy materials. Aluminum die casting can also achieve near net shape so the process of machining can be eliminated to produce finished parts.
Third, aluminum castings have the strength of steel but very lightweight. The appearance and aesthetic value of aluminum parts are also superior to other metal alloys. However, aluminum die cast parts are cheaper so end consumers can get high quality metal products at very affordable prices.
Lastly, castings made from aluminum are versatile, corrosion resistant, and can be used for different purposes. These qualities allow manufacturers to produce multiple products using aluminum parts. The finished products also have longer lifetimes thus giving consumers more value for their money.
Applications of Aluminum Casting
Aluminum castings are an ideal decorative element and can be used in many applications. Aluminum is light-weight, rust-free and durable, lending itself to both indoor applications and outdoors applications in almost any climate.
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