Today, metal casting is a complex and intricate process which requires exact chemistry and flawless execution. While current methods may be relatively new when compared to the history of human civilization, the first casting of metals can actually be traced all the way back to around BC. In those times, gold was the first metal to be cast because of its malleability, and back then, metal from tools and decoration was reused because of the complications of obtaining pure ore. However, a copper frog is the oldest existing casting currently known; it is estimated that it was made in BC in Mesopotamia (present-day Iraq). Bronze then became the metal of choice to cast with because its rigidity compared to gold, and it was melted and cast into various tools and weapons by way of permanent stone molds. The process of casting made its way to Egypt by BC, and effectively performing this process was tremendously influential on their gain of power during the Bronze Age. Around BC, the Shang Dynasty in China were the first to utilize sand casting when melting metals. Then around 500 BC, the Zhou Dynasty invented cast iron to the world, but it was used mostly for farmers. Cast iron did not become a military tool or decoration until the Qin Dynasty almost 300 years later.
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Fast forward almost years, religion played a major role in advancing and innovating foundry technology during that time. Extraordinary evolution came from the construction of cathedrals and churches, melting and mold-making processes advanced rapidly to keep up with the demand of the dominant Catholic church. This also marked the boundary of the period between casting for the purpose of art and viewing casting as a technology with unknown potential. It was not too long after the advancements of bell casting that, ironically, a monk in Ghent (present-day Belgium) was the first to cast a cannon in with the same technology. Over 150 years after the first cast cannon, Vannoccio Biringuccio, also known as the father of the foundry industry, recorded the first written account of casting and foundry practices. His work, De Le Pirotechnia, was separated into 10 sections that covered many subjects including minerals, assaying, smelting, alloys, casting, as well as alchemy; it is one of the oldest technical documents still around from the Renaissance era.
Around 200 years later, and after the British Colonies were established in the New World, the first &#;American&#; casting facility was started in Saugus, Massachusetts. That casting facility, Saugus Iron Works, was opened in and also enjoyed tax exemption along with a 20-year monopoly on all iron production courtesy of the Massachusetts General Court. Almost 300 years later, this origin of the American iron and steel industry finally became a National Historic Site in after being a private museum ran by the Iron and Steel Institute for 15 years. While the exact year is disputed, sometime between and came the transformation of the rail industry when Richard Reynolds, not the U.S. Foil Company one, started replacing existing wooden rails with cast iron rails for the transportation of iron and coal in Shropshire, England.
Around that same period, seven men with foundry backgrounds have their signatures on the Declaration of Independence. Among the more noteworthy foundry men to sign the most famous document in history, George Taylor was an ironmaster and Colonel in the Pennsylvania Militia, he started his career by shoveling coal into furnaces at Warwick Furnace, Rock Run Furnace, and Coventry Forge before eventually owning Durham Iron Works; his company was the first munitions supplier for the Continental Army, producing grape shot, cannon balls, bar shot, and cannons. George Ross also signed the Declaration of Independence and had significant ties to the iron industry. Ross&#; company was responsible for building many furnaces and forges, including Mary Ann Furnace and Spring Forge. Adding to his resume, Ross was also a Colonel in the Continental Army and was a judge on the Admiralty Court of Pennsylvania where the issue of state&#;s rights became a focal point for the newly-established country. Besides his contribution to ironworking and America&#;s independence, Ross&#; son married Betsy Griscom, who was later known for making the first American flag.
Shortly after the American Revolution, centrifugal casting became the latest innovation for the casting industry. While the general idea of utilizing centrifugal forces to produce castings had been known for some time, A.G. Eckhardt obtained a patent in which unveiled the physics and benefits of this new process. Less than a decade later, Mount Joy Forge, later known as just Valley Forge, was the first to produce cast steel in the US. Besides the dealings of George Taylor and George Ross, as well as steel production at Valley Forge, Pennsylvania has been home to many innovations in metal working not only in America, but around the world. This sentiment continued to be proven true in ; the S. Jarvis Adams Co. developed the first molding machine to be commercially available in markets. Furthering the development of this machine led to the first die casting machine patent in by J.J. Sturgiss, it was used to supply the growing need of lead type in the rising newspaper industry.
The 20th century was host to the explosion of casting technology and processes that most modern methods are based on. Seven years after the end of World War I, x-ray technology was first used to determine the quality of a casting. After that breakthrough, all castings made for US Military aircraft were required to pass such inspections to be accepted.
The next major innovation to the casting world came half a century later when ESCO Corp. was the first steel foundry to make alloys through the process of Argon Oxygen Decarburization (AOD) in . Until this point in history, there was no widely-available method for simulating metal solidification or filling molds until programs such as MAGMA-soft, ProCast, and Flow3D appeared on the market as mold simulation solutions in the s.
In the early s, MetalTek International pioneered a new process called near-net shaping which combines various shaping technologies, such as sand casting and investment casting, with the high-integrity centrifugal process to maximize the benefits of each. Net-shaping can be readily added to add O.D. profiles to centrifugally cast components through the use of sand, ceramic, or split graphite dies. True net-shaping at investment casting levels of O.D. detail can be added by employing MetalTek&#;s proprietary net shaping technology and special tooling. In addition to reduced cost due to savings because of reduced metal used, near-net shaping and net shaping centrifugal casting enable tighter quality control, especially in applications where alloy solidification behavior is a problem. Finally, since shaping is cast in versus machined in, customers realize savings in machining costs.
Finally, the latest game-changer for the casting industry came from the Department of Energy Metal Casting Competitiveness Research Act enacted by the US Senate and House of Representatives in . This bill focused on providing funding and resources to conduct research on technology in the area of metal casting to ensure industry competitiveness, energy efficiency, national security, and economic well-being in the United States. The CFD (Computational Fluid Dynamics) Project led to the creation of the Arena-Flow software; this software was designed for cutting-edge engineering in pattern formation. While other programs focused mainly on a single aspect of the casting process, like fluid dynamics or solidification, this program combined many adjustable variables together to get a reliable and consistent pour when it came to casting metals in different shapes and alloys.
Casting is the oldest metallurgical technique. The first functional metal components were accidentally refined copper, from chalcopyrite and chalcocite rocks in a fire. The metal could be cast into ingots in the ashes and hammered into a useful shape. Aluminum casting is a critically important group of methods that allow the manufacture of complex parts. The shaping is usually achieved in a single-stage process from liquid metal to finished or near-finished parts. This article will discuss what aluminum casting is, how it works, its importance, types, and applications.
Aluminum casting is the process of introducing molten aluminum into a cavity to create a part. Aluminum and many of its alloys have relatively low melting points and low viscosity when molten, yet cool to form strong, rigid solids. A variety of casting processes make use of these properties by forming a heat-proof cavity (in one or two parts), into which molten aluminum is poured. The metal then cools and solidifies, taking on the shape of the cavity it has filled. The cavities used for this vary in material and construction, and the processes have various names.
Aluminum casting is perhaps the most important cluster of technologies and methods in the aluminum product supply chain. Human technology development has gone through seismic shifts over millennia. The bronze age societies were eventually supplanted by those utilizing iron. In turn, iron gave way to steel in the 19th century and steel began to give ground to aluminum in the s. Aluminum is the third most common element in the earth's crust. It&#;s easy to find its salts in high concentrations&#;and with energy available, it is straightforward to refine. Aluminum is the key to most areas of technology and aluminum casting is one of the key processes that bring the material into mainstream use and appreciation. The ability to produce net shape-finished parts of high precision, low weight, and moderate strength empowers every manufacturing sector.
The aluminum used in casting generally refers to its alloys rather than pure aluminum. The properties of which are as follows:
Aluminum castings are very tough when designed to exploit the strengths and offset the weaknesses of the process. Cast aluminum is of no use as a bearing surface, or under impact loads and must be carefully designed to handle high and cyclic loads. Aluminum castings suffer from stress cracking, creep, abrasion, and shock loading, all of which are factors to be managed in the product design process.
Aluminum casting processes can be broken down into different types as listed below:
Die casting uses a hardened steel, two-part cavity tool, in which molten aluminum is poured or forced. These tools generally have 100,000 to 150,000 cycles of shot life and produce high-accuracy and high-quality parts. Die casting ranges from using simple tools with hand-poured fill-up to completely automated systems for very high volumes.
This process uses a sacrificial positive model of the required part. Before molten aluminum is poured into the plaster form, the wax is vaporized or driven out by baking the plaster tool. The cavity retains its shape and is then filled with molten metal that cools quickly.
In a more up-to-date approach, the positive model used to cast the cavity can be cut from expanded polystyrene, or 3D printed in wax and potentially polymers such as PET and PLA. In the case of plastic &#;positives&#;, they must also be burned out of the cavity to leave no residues. This process tends to be reserved for high-value and intricate parts. The tool is destroyed to extract the finished part.
Sand casting uses a stronger pattern part, generally from wood, and then packs this into two box halves, using sand with a binding agent, and talc as a release and separating agent. Cavities are usually filled by hand pouring, though automation is possible. This is usually referred to as sand casting and is widely employed in the manufacture of lower-volume and/or larger shot-weight castings. While good precision is possible, the destruction of the cavity tool makes this a one-shot process.
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This process is analogous to die casting in that two permanent (often cast steel) mold halves are clamped together and the cavity filled, generally by hand pouring.
Lost foam casting is identical to investment casting. The pattern, however, is made from low-density foamed polymer rather than wax.
A refinement of basic sand casting uses resin-bonded sand cast around the pattern to form a strong shell. Two shells are fixed together to form a sacrificial (single-use) cavity that is filled with molten aluminum. This process makes casting cavities faster and at a lower cost than ordinary sand casting and is used for medium to large casts needing higher precision.
Vacuum die casting differs from pressure or gravity die casting in that it uses a reservoir below the casting tool and pulls the molten material up by a vacuum applied to the tool. This results in lower porosity and higher-quality parts and is slowly displacing older die-casting methods.
This process casts a silicate slurry around a pattern and then either burns the volatiles from the slurry (Osborn-Shaw process) or bakes them off (Unicast process), leaving a ceramic cavity into which molten metal can be poured. In many regards, this process is analogous to shell mold casting.
This process is similar to shell mold and ceramic mold casting, but gypsum plaster is used to form the cavity tool.
This process uses a fast-spinning steel cavity tool to cast aluminum. Larger parts with rotational symmetry lend themselves to this process. The tool is spun once filled and centripetal force fills the extremities very cleanly, with no inclusions of porosity. Centrifugally cast aluminum is fine-grained, and defect-free, with improved hardness and strength, compared with other processes. It's used for asymmetrical parts that require the best possible properties and are not cost-sensitive.
Some more primitive casting in aluminum is performed using open cavities made from brick, stone, or steel, or pressed into sand. This is usually a method for producing simple billets for later forge/machining. It can be referred to as a branch of permanent mold casting.
Some examples of the different applications of cast aluminum are:
Aluminum die-cast parts can be expected to serve indefinitely under optimum conditions. It is common for automotive die-cast aluminum parts, for example, to remain in a functional state after 50+ years in service.
Aluminum die casting offers a range of benefits, including:
Aluminum die casting has limitations, including:
There is no difference between cast aluminum and aluminum. Cast aluminum is the same base material (aluminum) that has undergone a process. However, due to the various casting methods which exist, it is possible that the cast material will have inclusions and porosity that were not present in the raw feedstock.
The primary difference between forged and cast aluminum is the crystalline structure. Casting imposes very little control on the cooling and resultant crystal growth, making crystal structure within cast parts highly variable and disorientated. This makes thicker sections lower strength, as they cool more slowly, forming larger crystals.
Forging is often performed on cast billets. The upset process disrupts the microstructure by breaking up crystals into smaller units, without creating disjoints between them. This causes the material to become both harder and stronger, to a considerable degree. It also causes a &#;flow&#; of material around obstructions and corners which gives the crystal microstructure a &#;grain&#; that enhances strength and stress distribution.
Inclusions (non-solution contaminants such as oxide slag) are generally aggregated to some degree in cast aluminum parts, often creating severe weakness. In forged parts, any inclusions (from the billet casting process) are smashed and distributed, reducing their influence. Aluminum castings are capable of great detail and fine sections, whereas forging is a brute-force process best suited to simple shapes.
This article presented aluminum casting, explained what it is, and discussed its various applications and benefits. To learn more about aluminum casting, contact a Xometry representative.
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