Aluminum casting methods vary in different manufacturing processes, from sand casting, die casting, pressure die casting, continuous casting, shell mold casting, etc. Each aluminum casting process will have its advantages and disadvantagea. Depending on the casting’s size and complexity, we can choose the most suitable method.
Aluminum is widely applied in different casting parts serving a range of industries, both non industrial and industrial uses. For those who often doubt “How to Cast Aluminum parts”, the answer is that aluminum foundries use various casting technologies, and quality is one of the key factors in deciding which technology is suitable.
The quality of casting is the measure of both inside and outside the casting and its strength and ductility. Engineers must always promote the advantages and overcome the disadvantages of aluminum casting methods to improve product quality and satisfy customers needs optimally.
Compare aluminum casting methods:
Casting processSize rangeTolerancesTooling costRelative cost in large quantityRelative cost in small quantitySurface finishMin draft requestMin section thicknessSand castingAll sizes0-3″ = 1/32″ 3″- 6″=3/64″ 6+”=1/18″. Across parting line add 0.020″ to small castings. 0.090″ to large Castings.$50-$15,000LowLowest175-350 RMS1-5⁰0.125’’-0.25’’Pressure die castingSmall sizeNot less than 0.002″. Additional .010″ on dimensions affected by parting line.$5,000-$150,000LowestHighest20-90 RMS1-3⁰0.050″ Small parts 0.080″ Medium partsShell mold castingNormal maximum 80cm2 usable mold area.1″ =0.004″ 1″-3″ =0.010″ 3″-6″ =0.013″ 6″-12″ =0.016″ 12″-20″ =0.020″. Add 0.005″- 0.010″ across parting lines.$1,500-$25,000MediumMedium75-125Outside: 0 to 1 1/2⁰. Inside: 0 to 2⁰0.100’’Permanent casting0.25kg-50kg0.015’’ to 1″. Across parting line add +/- 0.010″ if Small Casting, +/- 0.030″ if Large Casting.$1,500-$55,000LowLowest125-200 RMS2-4⁰0.100″-0.150″Investment casting1 ounce-100 pounds+/-0.005″-3″ +/- 0.002″ there after$500-$20,000HighestMedium60-120RMSNone0.3’’Centrifugal CastingDiameter: 1 – 120’’. Length: Up to 50 ft. Weight: Up to 5 tons± 0.01″ for Cylindrical shape. ± 0.002″ for complex shape.No informationLowMedium63 – 500 μin for Cylindrical shape 32 – 500 μin for complex shape. None0.1 – 5.0’’Continuous castingUp to 0.2-1m LowHigh NoneDepend on the shapeSand casting is one of the oldest casting methods that appeared about 2000 years ago. Sand casting has been used to cast aluminum since aluminum metal became popular since the beginning of the 20th century.
In the aluminum sand casting, mold is made of sand, and bonding agents; patterns are placed inside the mold and pressed tightly.
After withdrawing the pattern, it is created a mold cavity that is the replica of the aluminum casting shape.
Through the gating system, molten aluminum is poured into the mold cavity and solidifies. As the casting is cooled down, the caster breaks the sand mold, and the casting is collected.
Aluminum green sand castingNowadays, improvements in sand casting technology have increased the weight and average size of the aluminum sand casting. Many sand casted aluminum objects are weighing more than 50kg, even some casting as large as 100m3.
Refer to the article about sand casting here.
How to calculate aluminum casting shrinkage: https://vietnamcastiron.com/aluminum-casting-shrinkage/
It is difficult to mention most aluminum sand casting applications because this aluminum casting process can manufacture almost all parts ranging in any sizes.
If you have a moderate budget and want to cast aluminum products that do not have too high requirements on surface finish, then the sand casting method is the number one choice.
Detail of green sand metal casting:
There are two types of die casting: aluminum high-pressure die casting and aluminum low-pressure die casting.
High-pressure Aluminum Die casting is the aluminum casting process that fabricates casting parts by pressing aluminum fluid under high pressure (approximately 1200 bar) into a steel mold through a cylinder-pistol.
Liquid aluminum is pumped at high speed and solidifies quickly to form the aluminum casting parts.
There are two types of cast chambers in high-pressure aluminum die casting:
Aluminum high pressure die casting is suitable for mass production of small details, weighing about 5kg, thin cutting surface, and about 0.4mm thickness. The larger the aluminum casting part, the higher the cost.
With low-pressure aluminum die casting, the mold is filled with liquid metal from a pressure-adjustable crucible (usually 0.7bar).
The metal annealing furnace is located below (instead of horizontally like high-pressure aluminum die casting), the molten aluminum is pumped directly from the bottom up to fill the mold.
Aluminum low-pressure die casting is suitable for manufacturing aluminum casting parts with wall thickness of 3mm or more, and the volume can be up to 150kg.
In die casting, aluminum alloy is among the most often casted metal, accounting for twice the other metal casting methods use.
This aluminum casting process has a wide range of applications from simple components such as lighting components to complex components such as engines, transmission housings, wheels, automotive suspension and spacecraft.
Shell molding is a molding technology with a mold made of thermosetting phenolic resin.
First, the two halves of patterns are design and created from metal, and then being heated and coated with lubrication. Then place the pattern into the thermoset sand chamber prepared above and then turn it upside down. The mixture of resin sand sticks to the pattern hardens to form a shell.
The pattern is removed, leaving a shell. Two halves of the pattern will form two shell molds about 10-20 mm thick. These two shell molds are assembled to form a complete mold. Liquid aluminum is poured into the mold and solidified into a casting shape.
At this point, just breaking the shell of the mold then we can collect the casting.
Shell mold aluminum casting is one of the aluminum casting methods that is suitable for the fabrication of hollow-core or die castings.
This aluminum casting process is applicable for casting Cylinder heads, connecting rods, engine blocks and manifolds, machine bases, truck hoods, valve body, etc.
Permanent mold aluminum casting, also known as metal mold casting, is one of the aluminum casting methods that use metal as the mold material similarly to the pressure die casting. Accordingly, the liquid aluminum is pushed into the mold by its gravity, so the pouring speed is quite low.
Due to the metal-made mold, the casting cooling speed is fast. Molds have a long service life, so they are called permanent molds.
Aluminum permanent castingPermanent mold aluminum casting is suitable for casting masses greater than high-pressure die casting, about 10kg. The higher the volume, the more expensive the cost.
If combined with the heat treatment methods, the mechanical properties of metal molds will increase. Small castings will cool quickly, so no heat treatment is required.
For maximum mechanical properties, treat with a special solution at high temperatures, then cool and allow natural or artificial aging.
In automotive industry, creating parts like gears, castings, suspensions, fuel injection housings, and engine pistons. Aircraft parts are also often made via permanent mold aluminum casting.
This aluminum casting process is used in the automotive and aircraft industries to create parts, such as gears, suspensions, pistols, fuel housing, etc.
Aluminum Investment casting, also known as aluminum lost wax casting, is the casting aluminum method by inserting wax or thermoplastics into a prefabricated metal or rubber mold.
Wax pattern are collected and assembled to form a tree branch connected to the gating system to cast in the same batch. The wax pattern will now be applied investment with a refractory materials. This process is repeated until the outer sheath reaches a thickness of 5-15mm. This shell is the investment mold.
Then dry and heat the tree so that the wax inside is melted out, leaving the inner chamber of the mold in the shape of the desired casting.
The investment mold is then heated before pouring aluminum fluid. Any cracks that appear in the mold can be repaired with ceramic or special materials.
Molten aluminum is poured into the mold, after it dries up only to destroy the outer ceramic shell. The casting is removed from the tree and passed to finishing process.
Lost wax casting technology has many applications such as manufacturing aluminum casting parts in the aerospace industry, electricity industry, weapons, automobiles, military, gas and oil, …
Aluminum Centrifugal casting is the aluminum casting process in which a mold is made of metal, plaster, or graphite. The mold is rotated on a centrifugal casting machine, while on the outside the molten aluminum is poured into the mold. Liquid aluminum will be evenly distributed onto the mold wall based on centrifugal force and hardens according to the shape of the mold.
There are two types of centrifugal casting molds: vertical centrifugal casting with a vertical axis and horizontal centrifugal casting with a horizontal axis. The rotational motor of the mold rotates the mold to spread the metal evenly onto the mold surface.
Centrifugal casting is employed by aluminum foundries to produce aluminum casting parts of the jet engine compressors, petrochemical furnace tubes, and many military and defense pieces of equipment.
Aluminum Continuous casting is a casting process in which an aluminum alloy is continuously poured into a mold with a circulating water cooling system. Wherever the casting is made, it is immediately cooled and removed.
Arranging right after the casting system will be a continuous stamping and rolling line. Cast products are aluminum bars, plates, or pipes with sizes up to 0.2x1m.
It is a very efficient casting system and is widely used in aluminum and steel foundries.
Aluminum Continuous casting is used to cast metal bars, metal pipes of different sizes.
Besides, there are also several other aluminum casting methods used to fabricate the aluminum casting applications such as Vacuum sealed molding process, Ablation casting, lost foam, etc. They also have many advantages similar to the above casting processes.
Each aluminum casting process has its advantages and disadvantages. After carefully referring to the information comparing different aluminum casting methods in the article, make a choice for your foundry based on your budget, the type of aluminum casting products you want to target, requirements for accuracy, and annual output.
Many other factors are affecting the choice of aluminum casting technologies. However, hopefully through the information provided in the article, VIC has partly helped readers better understand the aluminum casting methods as well as make the right decisions.
At VIC, we have a system of metal foundries with various processing technologies. Especially in aluminum casting, VIC uses green sand and lost foam casting technologies and is on track to expand production line with other casting technologies that match on market requirements.
VIC is pleased to cooperate with partners worldwide to help customers sell metal casting products with reasonable quality and price.
Contact information:
Vietnam Cast Iron Company Limited
Address: Lai Xuan, Thuy Nguyen District, Hai Phong city, Vietnam