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The origin of metal casting: How can it be traced back to ancient civilizations seven thousand years ago?
Casting is a manufacturing process in which a liquid material is poured into a mold containing a cavity of the desired shape and then allowed to solidify. The cured part is called a casting, and the process is accomplished by ejecting or breaking the mold. Casting materials are typically metals or various aging materials that cure after mixing two or more components; examples include epoxy, concrete, plaster, and clay. Casting is most often used to create complex shapes that are difficult and uneconomical to create by other methods. Components of large machinery, such as machine tool beds, ship propellers, etc., can be easily cast to the required size without the need to manufacture by joining multiple small parts. It is worth noting that the history of casting dates back more than 7,000 years, with the oldest casting being a bronze frog from 3200 BC.
History
Since ancient times, metal casting has been used to create tools, weapons, and religious objects. The history and development of metal casting can be traced back to South Asia (China, India, Pakistan, etc.). South Asian traditions and religions rely heavily on the casting of symbolic statues and relics. These items are usually made from a copper alloy mixed with lead. Since the beginning of metallurgy, most castings have been made from simple one- or two-piece molds made of stone or ceramic. However, evidence of lost wax casting appears in many ancient civilizations. The lost wax casting process originated in ancient Mesopotamia. The earliest known records of lost wax casting appeared in Sparta, Babylon. The amount of wax required to make a key was clearly recorded in the literature.
The earliest castings were made in open stone molds.
There are two methods of lost wax casting: direct lost wax method and indirect lost wax method. The direct molding method is to make the wax material into a wax pattern that is the same as the casting by hand or using other tools; while the indirect molding method is to make the wax pattern through a mold. The direct forming method requires craftsmen to have a high technical level, otherwise the quality of the casting cannot be guaranteed. However, the limitation of manual direct forming is that its efficiency is too low to achieve mass production. In this regard, indirect molding has advantages. Craftsmen typically create models from stone, wood, clay, or other plastic materials. Early civilizations discovered that lead helped make molten copper more fluid, allowing them to cast more elaborate designs. For example, the Dancing Girl of Mohenjodaro is a copper alloy cast, most likely using the lost wax technique. Lost wax casting dates back to 4000 BC or the Chalcolithic Age. The earliest research example of this technology is a 6,000-year-old amulet from the Indus Valley Civilization.
The evolution of casting technology
India is considered one of the first civilizations to utilize minting methods to mass-produce coins. Around the first millennium B.C., coins in use were made of silver, but as the millennium progressed, the coin material gradually shifted to minted copper alloys. The development of new technologies enabled the mass production of new copper coins and the introduction of stackable multi-piece coin template dies. Multiple molds are stacked on top of each other and placed into a cylinder of clay, allowing molten metal to be poured through the center, filling and solidifying in the open space. This process made it possible to produce a hundred coins at the same time.
In the Middle East and West Africa, lost wax technology was used quite early in their metallurgical traditions, while China adopted the technology relatively late. Compared to the Indus Valley Civilization, Western Europe's use of lost wax technology is considered to be very limited. In Anyang during the Shang Dynasty (1600-1040 BC), no actual lost-wax castings were found, but a large number (100,000 pieces) of mold fragments were found. This led to the inference that lost wax casting was not practiced in the capital of the dynasty. However, the discovery of a mask made from investment casting from around 1300 BC suggests that the lost-wax technique may have had an impact on other areas of China. Historians debate the origins of artillery development, but most evidence points to Türkiye and Central Asia in the 18th and 19th centuries.
Diversity of casting technology
In metalworking, metal is heated to a liquid state and then poured into a mold. The mold is a hollow cavity containing the desired shape and contains feed and exit channels that allow metal to flow into the mold. Once the mold and metal have cooled, the metal solidifies. The solidified part (cast) is then removed from the mold, and subsequent operations remove excess material created during the casting process.
The casting process of metals such as pig iron and aluminum has continued to improve over time, and the evolution of technology has promoted the development of industry.
In addition, materials such as plaster, concrete and plastic resins can also be cast using disposable scrap molds or multi-purpose "sheet" molds. The surface of casting is usually flat and opaque, and surface treatment techniques are often used to enhance the appearance. During the casting process, certain chemically made plastic resins can be mixed with powdered stone to impart color, which many times allows the effect of natural marble or travertine to be simulated. As technology improves, the casting process continues to evolve, achieving unprecedented design accuracy.
In today's industry, simulations of casting processes use numerical methods to calculate cast component mass, taking into account mold filling, solidification and cooling, so that the mechanical properties and thermal stresses of the casting can be quantified in advance and deformations can be predicted. This technology enables an accurate characterization of the quality of castings before production begins. With the advancement of technology, the simulation of casting processes has become one of the most important innovations in casting technology, saving time and costs throughout the entire casting manufacturing process.
This letter covers the history and technology of metal casting. The evolution from ancient craftsmanship to today's advanced technology makes us wonder, how will future casting technology change our lives and industrial manufacturing?
