A brief but succinct explanation of the underlying metal casting processes as well as a short history of metal casting.
A majority of people use, put on, or exchange intricately made metal items daily, but only a precious few know, in detail, how those items are made. The level of sublime craftsmanship and experience that goes into crafting metal goods is really astonishing – but our consumer-driven lifestyle has meant that we just buy and use these items without paying any attention whatsoever to how they are made.
Metal casting is how a large portion of the demand for metal products is filled. Mostly applied in the metalworking as well as the jewelry industry, it is a process where liquid, molten metal is poured into a cast containing a negative image of the intended shape of the finished item. Following this, the entire mold is cooled, and because the mold is usually made of a breakable material like clay, broken to reveal the fully formed item inside.
During the casting process, the molten metal is poured into the cast through a channel called the sprue.
Casting is one of those processes that have remained unchanged for hundreds of years. Civilizations dating back to biblical times have been discovered to have, in one form or another, engaged in metal casting. Some even depended on it as a major source of income and foreign trade.
Historically speaking, the oldest known evidence of ancient metal casting traditions is in the form of a frog that was made from copper. This was believed to have been made around 3200BC when copper was the preferred material for use in metalwork. At around 700BCE, cast iron was developed for use in China. Sand molding was also invented in the Ease Asian country.
The crucible method is a popular technique commonly used in the production of fine steel implements. It first appeared in the 1st millennium and subsequently, made its way across the globe. From Asia to Europe, the method was i=even a mainstay in the manufacture of early Viking swords. The trick to it was achieving a high enough temperature in order for the steel to melt, and the English Benjamin Huntsman was able to achieve this at around the year 1750.
A Step-by-Step Breakdown of the Inherent Processes
- Patternmaking: This is the first step to casting. Here, a replica of the casting exterior is made from plastic, metal, or wood (depending on the unique requirements for the finished item).
- Coremaking: Cores typically are strong but collapsible, allowing for easy removal when the cast is finished.
- Molding: This is perhaps the first real challenge when it comes to metal casting. Simply put, it is a process that ensures that a case is formed around a particular pattern – usually with molding sand. The flask usually houses the mold and is filled in with casting sand all around the intended pattern. With the sand packed extremely tightly enough, the cast remains tightly in place whilst the pattern gets removed.
- Molten stage: This is literally the hottest part of the process, and certainly the most dangerous. It does help that conversely, it is the easiest to explain on paper. Here, molten metal is carefully poured in through the sprue, into the mold. It is left (depending on the cooling time of the particular metal in use) to cool down and solidify. While all this happens, the metal slowly but surely takes the shape of the mold and at the time of removal, is completely shaped into the required form. Waste sand istypically recycled for use in future projects because as we all know, sand doesn’t degrade.
- Fettling: Here, the final item is taken and separated from the mold. Unwanted materials such as leftover sand are removed and the object is sanded over, with intricate final additions applied to ensure that it is as close to perfect as possible.
In our modern world, a literal barrage of consumer goods, parts, and electronics rely on metal casting for a large part of their product demands. Simply put, modern metal casting differs from that of the 19th century only in the material precision as well as tolerances that unlike before, can easily be achieved thanks to our modern automated design, as well as modernized core and mold production processes. The same innovation that revolutionized other industries also made its way into the spheres of metal casting as well.
It is important to note that aside from the method mentioned above, there also exist other processes that, although closely relate to the sand casting method, differ ever so slightly. Some of these are plaster casting, die casting, and investment casting. Plaster casting simply replaces the sand with a plaster mold.