Casting production explained in five steps
Mass producing metal parts has several process options. While 3D printing is all the rage, high-production runs are better off with traditional investment casting. Why? Traditional casting production through the investment casting process is more economical and reliable. The modern casting process involves pouring molten metal into mold cavities in order to form a desired shape. The liquefied metal is then cooled and allowed to harden, before being extracted from the mold in a solidified form. There are five steps in the casting process: patternmaking, molding, melting and pouring, shakeout, and heat treatment and inspection. Read on to find out more about each step.
The first step in the casting process involves making a replica of the product to be cast, which can then be used to shape the mold cavity and provide accurate dimensions and characteristics. Patterns can be made from a variety of materials such as wood, metal, plastic, or plaster. Dimensional accuracy and design are extremely important here, as the pattern determines the form the casting will take. Precise calculations are required to ensure the final high-quality cast products fit and work the way they are supposed to.
Investment casting is a specific type of casting production that uses wax patterns. When molten metal is poured into the mold and allowed to harden, it sets in the shape of the wax pattern. The high-quality casting product is then ejected, and the wax pattern may be melted down for reuse.
During molding, the mold is prepped to receive the molten metal. There are two types of mold processes in casting production: reusable and non-reusable. Like the name suggests, reusable molds can be used repeatedly, and are typically made from metal.
Non-reusable molds are destroyed in the casting process. Sand casting is the most common non-reusable molding process. During sand casting, treated sand is packed tightly around the pattern and placed in a support, called a ‘flask’. When the pattern is removed, the cast will remain.
Melting and pouring
Castings can be produced from either ferrous metals (those that contain iron, such as stainless steel) or non-ferrous metals (those that do not contain iron, such as aluminum and copper). Before they can be used in the casting process, these metals need to be melted in a furnace. The molten metal is then poured into the cavity of the mold and left to harden.
Shakeout and cleaning
Once the molten metal solidifies, it’s time for step four: the shakeout. The mold is vibrated in order to remove the sand from the casting. Any excess metal is removed in the cleaning process, frequently by use of a chipping hammer or band saw. Tumbling barrels, pressure washers, and air-blasters may also be used in casting production to clean off any residual sand and smooth any rough edges.
Heat treatment and inspection
The casting that’s left should be identical to the original pattern. Depending on its final usage, the product may then undergo various finishing treatments. For example, castings produced for heavy industrial use are often heat-treated so they will be able to withstand freezing temperatures, wet environments, or extreme weight. During heat treatment, the casting is both heated and chilled to precise – and often extreme – temperatures.
This reduces stress in the casting, and can also alter the physical properties of the metal so that it is fit for purpose.
Finally, the casting will undergo rigorous testing to check its structural integrity and physical properties. Only products of the highest quality will complete the casting process.
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