Metal Casting Production: Common Methods and Quality Control Using Microscopy
Metal casting production, also called founding, is one of the few manufacturing processes that are used in both art and science. It is also one of the oldest practices, dating back to about 6,000 years ago when metals such as bronze, copper and iron were used. Later, metal and nonmetal combinations such as alloys were also included in metal casting.
Metal casting is sometimes a more economical way to produce parts and materials and an even better production method to employ when cutting parts from a solid chunk of material is not only labor-intensive but also difficult.
Methods of metal casting production
One of the most commonly used methods in metal casting production is sand casting, where an object is used to produce a model. This model is then used to produce a mold made of a mixture of clay, sand and liquids. Later, molten metal is poured into that mold and allowed to cool and solidify. When the metal is ready, the mold is taken apart and the metal casting is released.
Another method used for metal casting is die casting. This is commonly used for producing casts of non-ferrous metals. A mold, called the die, is used to form the metal casting. Melted metal is poured using high pressure into the die, which is usually made of steel to withstand the heat of the molten metal. To facilitate a faster production, multiple dies are often used to produce a single design or mold.
Die-casting is often the preferred method today, particularly because it is more economical and the process takes a short time. This makes it ideal as a method for mass producing metal castings. Since die casts are also better molds, metal castings can often show better details and a finer finish compared to sand casting. Die casting is the metal casting method used to produce metal parts for equipment, machineries and automobiles.
Another method is continuous casting. This method involves the use of a wide, long and hollow mold onto which molten metal is poured. Water is used to help cool the molten metal from underneath the mold to create a cross section, while solid steel is extracted continuously from the bottom. This produces an elongated sheet or slab of metal casting.
The lost wax method or cire perdue is also a metal casting process still in use today. This is the preferred method in the production of metal sculptures and statues. A model of the item is first coated with wax and allowed to cool. Once it has solidified, it is then wrapped in two layers of clay or plaster. After the wrapping has dried, the wax is heated to melt it and allowed to run off. It can also be removed manually from the plaster or clay mold.
Molten metal is then poured into the mold, taking the place of the molten wax. Once it cools and hardens, the mold is broken. This method is also often used for the production of jewelry, art works and even dentures. Since the wax mold can take the shape of the original, intricate details can be captured, allowing the copies or metal castings to replicate the original design.
The lost wax method is often adapted as a supplemental step in other types of metal casting production, such as investment casting.
Quality control in metal casting production
Although the process of metal casting production is highly controlled these days, there are some things that can result to an error in the end product. Air pockets, sand, dirt and other contaminants in the mold, for example, can often create a less than ideal casting. This becomes a concern especially when certain manufacturing standards are being followed and maintained. As such, inspection of the finished product is often performed with the use of microscopy, particularly metallographic microscopes.
Metallographic microscopes are capable of producing images that allow observers to view a sample of metal casting. Generally, the surface of the metal is prepared by grinding, polishing and etching in order to observe its properties and physical characteristics. This will help test for errors in production and design and determine whether or not the final product is up to pre-set standards.
A metallographic microscope is also an excellent tool to identify the metals and alloys used in the production of the metal casting. Since certain metals exhibit their own physical characteristics under close inspection, it is easier to determine which metals were used in the creation of a particular cast.
Metallographic analysis is also excellent to examine if the material or metal cast had undergone multiple phases. This is often employed in the study of valuable art works, where the method used in the production is unknown. Another important contribution of metallographic microscopy is in the identification and analysis of any damages or degradation in the metal casting, which are often necessary to investigate and predict materials failure. Once the errors have been identified, appropriate corrections may then be performed.
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