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This article contains all the information you need to know about aluminum casting.
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Aluminum casting is a method for producing high tolerance and high quality parts by pouring molten aluminum into a precisely designed and precision engineered die, mold, or form. It is an efficient process for the production of complex, intricate, detailed parts that exactly match the specifications of the original design.
A positive benefit of aluminum cast parts is the layer of aluminum oxide that forms immediately after the part is removed from the mold, which provides a wall of protection against corrosion and rust.
One typical method for casting aluminum is to pour molten aluminum into a steel mold that has been precision processed to ensure that the cast piece will have an exceptionally smooth and refined surface. This particular process is one of several methods used to produce aluminum castings, each of which is used for the creation of specific types of parts.
A variation in the casting processes is the type of mold, which can be permanently made of steel or temporarily made of a non-metallic material. Each of the types of castings have their benefits and are depended on for their reliability and product quality.
In order to discuss the aluminum casting process, it is necessary to examine each of the different distinct methods and how they are used since there isn’t just one process. Though there are manufacturers who specialize in one or several methods, many producers offer customers a choice as to which process they would prefer.
Much of the expense of aluminum permanent mold casting is the machining and shaping of the mold, which is normally made from gray iron or steel. The mold is shaped into the geometric shape of the designed part with the specifications and shape of the part divided into two halves. In the injection process, the halves of the mold are tightly sealed such that no air or contaminants are present. The mold is heated prior to the pouring of the molten aluminum, which can be ladled, poured, or injected.
At the completion of the process, the mold is allowed to cool to allow the aluminum part to solidify. Once cooled, the part is rapidly removed from the mold to prevent the formation of defects.
Regardless of how simple the process may seem, it is a scientifically and technically engineered method for producing high volume parts.
The sand casting process involves packing sand around a reusable pattern that has the shape, details, and configuration of the final product. Included in the pattern are risers that allow the molten metal to be poured into the mold and for hot aluminum to feed the casting during solidification to prevent shrinkage porosity.
Included in the pattern is a sprue that allows molten metal to be inserted into the mold. The dimensions of the pattern are slightly larger than the product to account for shrinkage during the cooling process. The sand has the weight and strength to maintain the shape of the pattern and is resistant to interacting with the molten metal.
Die casting is a process where molten aluminum is forced under pressure into the mold. The products produced are exceptionally accurate and require minimal finishing or machining. The process of die casting is rapid, which makes it ideal for mass production of high volume parts.
The two forms of die casting are hot and cold. The difference between them is related to how the molten metal is injected into the mold. In hot die casting, the hot chamber is connected to the melting pot and uses a plunger to force the molten metal through a gooseneck into the mold. In cold die casting, the melting pot is not attached to the die casting system, and the molten melt is ladled into the cold chamber where it is forced by a plunger into the mold.
In the diagram below, an image of hot die casting is on the left and of cold die casting on the right.
Vacuum die casting uses an airtight bell housing that has a sprue opening at the bottom and a vacuum outlet at the top. The process begins by submerging the sprue below the surface of the molten aluminum. A vacuum is created in the receiver creating a pressure differential between the die cavity and the molten aluminum in the crucible.
The pressure differential causes the molten aluminum to flow up the sprue into the die cavity, where the molten aluminum solidifies. The die is removed from the receiver, opened, and the part is ejected.
Controlling the vacuum and the pressure differential between the die cavity and molten aluminum makes it possible to control the fill rate required by part design and gating requirements. Control of the fill rate enhances the ability to determine the soundness of the finished part.
Having the sprue submerged below the surface of the molten aluminum ensures that the molten aluminum will be the purest alloy free from oxides and dross. Parts are clean and sound with minimal foreign materials.
Investment casting, also known as lost wax casting, begins with wax being injected into the die to create the pattern of the finished product. The waxed patterns are attached to a sprue to form a tree ike configuration. The tree is dipped into a slurry multiple times, which forms a strong ceramic shell around the wax shape.
Once the ceramic has set and hardened, it is heated in an autoclave to complete the dewax burnout. To achieve desirable temperature of the shell, it is preheated before being filled with the molten aluminum, which is poured into the sprue and passes through the series of runners and gates into the molds. When the parts harden, the ceramic is knocked off leaving the tree connected parts to be cut from the tree.
The lost foam casting process is another type of investment casting where wax is replaced with polystyrene foam. The pattern is molded from polystyrene in a cluster assembly like the runner and sprues of investment casting. Polystyrene beads are injected into heated aluminum molds at low pressure with steam added to expand the polystyrene to fill the cavities.
The pattern is placed in densely packed dry sand that is vibration compacted to eliminate voids or air pockets. As the molten aluminum is poured into the sand mold, the foam is burned off, and the casting is formed.
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Aluminum is the third most prevalent element on earth with oxygen and silicon being first and second respectively with aluminum being the most prevalent metal. The difficulty of extracting aluminum from the earth‘s crust is due to the complex and complicated processes that are necessary compared to what is needed to extract iron or other metals.
The sedimentary rock, bauxite, has a 45% to 60% aluminum content and is the metal from which aluminum is processed. Initially, it was difficult to process aluminum, which made it an expensive and rare metal until the end of the first industrial revolution when more efficient methods for refining it were invented.
Though aluminum is processed as pure aluminum, in many cases, it is alloyed with other metals to enhance its properties as well as the properties of the metals to which it is alloyed.
There are eight different aluminum alloys, which are numbered from one to eight. The first three numbers indicate the alloy with which aluminum has been combined. For casting alloys, a decimal is placed between the third and fourth digits with the fourth number indicating the form of the product. As an additional indicator, each alloy is given a crack, corrosion, finishing, and joining number from one to five with one being best and five being the worst. The 1000 series alloys have a rating of one in all categories while series 8000 has a five in all categories.
The descriptions below are for wrought aluminum alloys that have different indicators than those for casting alloys. Wrought aluminum alloys do not have a decimal, which is an easy way of telling the difference between the two grading methods.
The 1000 series is the purest of the alloys with 99% aluminum content. It is soft and ductile with excellent workability. The 1000 series can endure extreme forming since it hardens slowly. It is easily weldable and performs well during the processing.
The 2000 series is alloyed with copper containing 2% to 10% copper and small additions of other elements. The copper enhances the strength and hardness of aluminum but reduces its ductility and corrosion resistance. Series 2000 is difficult to weld but heat treatable.
The primary alloying element for series 3000 is manganese. The combination of manganese with aluminum has good corrosion resistance but is moderately strong. It is a non-reinforced aluminum alloy that has been heat treated. The main benefits of series 3000 is its low density, good plasticity and weldability, corrosion resistance, ductility, and exceptionally smooth finished surface.
The 4000 series is alloyed with silicon, which gives the alloy a low melting point and improves its fluidity. It is one of the more popular casting alloys due to the ease of forming it in its molten state. The 4000 series is used as a welding and brazing filler.
The 5000 series is alloyed with magnesium , which gives it exceptional tensile strength and formability. It is classified as a high strength sheet and plate alloy with high weldability. The preference of the 5000 series for sheet metal applications is due to its resistance to acids and alkali corrosion. These characteristics make the 5000 series adaptable to harsh hostile environments.
The 6000 series is alloyed with magnesium and silicon, which gives the alloy strength, mechanical properties, and corrosion resistance. Some versions of the 6000 series are combined with series 4000 and 5000 to enhance the properties of the 6000 series . The processing of the 6000 series requires specialized technologically advanced equipment, which is complex and expensive. Added to its excellent corrosion resistance and oxidation is the ease with which it can be coated and treated as well as its workability.
The 7000 series of aluminum alloys are the strongest and most resilient of the alloys with a strength factor that is two thirds of industrial grade A3 steel. Due to its high hardness, 7000 series have exceptional wear resistance, good mechanical properties, and anode reaction. It is ideal for casting parts that are required to endure a great deal of stress such as aircraft components. Zinc is the alloy of 7000 aluminum, which helps increase its hardness though zinc has the same hardness as aluminum on the Mohs scale.
The primary alloy of the 8000 series is tin with small amounts of copper and nickel. Though this alloy has low strength, it has excellent machinability and wear resistance. The configuration of alloys for the 8000 series changes according to how the product to be produced will be used. Its configuration determines the metal‘s temperature performance, density, and stiffness.
An important benefit of using aluminum for casting is the ability to stipulate the necessary properties. Regardless of the project, there is an aluminum alloy to fit the application. All that is necessary is to determine the required characteristics.
When making the decision regarding the type of alloy for an application, the list below can serve as a guideline for the properties and characteristics that are necessary.
The two charts below outline the distinction between cast alloys and wrought cast alloys. Note that series 600.X does not appear on the cast alloy chart.
Since the inception of the Bayer and Hall-Héroult methods for processing and refining aluminum, aluminum has become a central part of the manufacture and production of a wide assortment of commercial and industrial aluminum products. The development of more practical and economical methods of production opened the door for engineers and designers to rapidly include aluminum in their renderings.
From aerospace to ovens, aluminum‘s multiple properties and characteristics have proven it to be a reliable and strong metal that has a long usage life as well as the ability to be worked and shaped into any form to fit a design. Aluminum can be combined with over 270 minerals to enhance its performance and benefits.
Since the end of the Second World War, the aerospace industry has relied on aluminum parts, which is approximately 80% of the structure of an aircraft. Cast aluminum parts have the properties and characteristics that are demanded by the industry. Aircraft producers have realized substantial savings through the use of cast aluminum components.
As the pressure has increased to improve gas mileage for vehicles, auto manufacturers are continually searching for ways to include high strength aluminum castings in their product designs. To assist in the process, aluminum casting producers have been perfecting and improving their methods and techniques to streamline the production processes to increase output at a reasonable cost.
Aluminum cast parts for automobile manufacturing include oil pumps, water pump housings, connectors, transmission parts, and a wide variety of brackets. The durability and reliability of aluminum cast parts has made them an essential part in auto design improvements and innovations.
Aluminum cast lighting produces lights that are non-toxic and lightweight. The corrosion resistance of aluminum cast light fixtures makes them ideal for outdoor use. Two popular processes for producing light fixtures are permanent mold and gravity casting, which makes it easier to work with the final product and can be used for lighter forms of aluminum. As with the production of automotive components, the production of light fixtures using cast aluminum is economical and time saving.
Each of the many production processes can easily be adapted to produce any design with the stability and characteristics required. The ease of production, weight of the final product, and exceptional resilience of aluminum cast lighting are the main reasons for its popularity.
Many of the aluminum cast parts for agriculture have similar requirements and specifications to those produced for the auto industry. The difference is the increased strength and lasting stability required by agricultural machinery due to the harsh conditions and constant use. An additional factor is cost, which is a major concern for agricultural production. It is for these reasons that aluminum castings are used for crankcase housings, gearbox housings, and motor housings.
The function of a heatsink is to remove heat from parts and components designed for electronic applications. Aluminum cast heatsinks require less machining, which lowers production costs and increases the speed of manufacturing. The extra features of a heatsink, such as cooling fins, are produced at the same time further improving production efficiency.
Aluminum cast heatsinks are electrically conductive, which means they can be grounded. They are cast with additional features included to eliminate secondary operations such as machining and assembly to reduce costs.
A common use for the aluminum casting process is the manufacturing of brackets for heavy duty equipment for industrial use and appliances for home use. The choice of aluminum casting is the near net shape of the final bracket, which eliminates the need for welding or assembly. The single piece construction of aluminum brackets ensures that the bracket will be stronger and less likely to fail. When holes are necessary, they are included in the casting mold to avoid the need for finishing.
The durability, stability, and the ability to produce variable shapes is the reason that manufacturers have turned to aluminum casting for the production of golf equipment. The goal of producers is to assist players improve their game with higher quality equipment at a lower cost. The types of golf products include golf ball warmers, golf clubs, handles, and brackets.
Aluminum cast enclosures are designed for housing sensitive electronics in any type of environment. An advantage of using aluminum for an enclosure is its natural level of shielding against radio frequency interference (RFI) and electromagnetic interference (EMI). The seamless construction provided by aluminum casting creates a watertight sealed enclosure capable of withstanding any type of conditions.
The requirements for cast aluminum enclosures have been established by the National Electrical Manufacturers Association (NEMA), which provides the standards and specifications that producers must meet to market their products.
There are any number of parts and components produced for the military using aluminum casting, which are required to meet specific government requirements. The production and processing of military parts is outlined in detail that includes the characteristics and properties of the materials. The specialized nature of military components offers a challenge to producers since all military parts require precision engineering and close attention to details.
Two unique military components are described below.
The purpose of a fire suppression housing is to suppress fires in armored vehicles such that the vehicle can take a direct hit without endangering the occupants.
A missile nose piece is attached to the nose of a missile and is required to be precisely cast in order to withstand the G forces a missile launch produces. The casting process is closely monitored to ensure it is pressure tight and precisely engineered to meet the required specifications.
The many benefits of aluminum casting are evidenced by its wide use by manufacturers. The excellent surface finish of cast aluminum parts as well as their extraordinary endurance and stability are a few of the reasons that engineers turn to aluminum and its alloys when creating new designs.
The developments of aluminum casting are constantly changing and advancing as new and improved technical innovations create additional options for manufacturing and design.
Aluminum casting can produce any size, shape, configuration, or form imaginable. From the smallest electrical component weighing less than a gram to transmission casings and clutch housings for automobiles, casting produces each part precisely to the requirements of the design, flawlessly with little need for finishing.
The advent of aluminum casting has offered engineers the opportunity to design any type of configuration with the assurance that the part will perform up to expectations. Aluminum cast Components maintain their integrity through assembly, disassembly, repair, and reprocessing.
The wide range of possible design factors provides engineers with the ability to take advantage of the exceptional characteristics associated with aluminum casting. The versatility of aluminum casting allows for the flexibility of dreaming up any type of custom creation, regardless of how unique or unusual, and making it possible to make it a reality.
Producers are constantly looking for faster and more efficient methods for producing high quality products. Computerization has enhanced the pressure to be capable of on time deliveries to meet customer needs. As the demand for increased efficiency and performance grows, aluminum die casting has been more than capable of meeting and exceeding what has become required. Parts, components, and workpieces are produced at a high rate of speed that is faster than any other type of alloy.
One of the most notable characteristics of aluminum cast parts is their strength to weight ratio, which exceeds any other metal or alloy. Aluminum products are lightweight but have the strength of steel. This factor adds to their endurance and life expectancy, a crucial factor for 21st Century products.
Though aluminum castings are exceptionally strong and lightweight, they have a very positive appearance and aesthetic value. There are several uses for aluminum casting that do not require them to be seen or have a pleasant appearance. In applications where they have to perform and be appealing, they do not have to be adjusted or re-engineered.
Every industry is seeking means and methods to lower costs but produce high quality products. The low cost of the aluminum casting process is a major factor in why companies are choosing it for product development. Much of the cost savings is due to the speed of production and the elimination of the need to finish completed products. The lower cost of materials, fast production runs, and elimination of finishing are passed on to customers and consumers.
When aluminum castings are exposed to the air, their surface becomes oxidized, which is a characteristic of the metal. This one factor is the reason that aluminum castings have longevity and reliability. This enhanced lifetime provides users with greater value.
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