What's the Difference?
Excerpt from the Thomas Register article by Christian Cavallo.
Casting metal is an ancient process now accomplished in a number of ways. It involves pouring molten metal into a mold where, upon cooling, the metal solidifies and conforms to the mold's shape. Casting allows manufacturers to create complex parts without the need for machining, which can be time-consuming and complicated; however, it is far from a simple, cut-and-dry technique in today's industry. There are many types of casting processes used in modern manufacturing, and each has its distinct benefits and disadvantages depending upon the desired characteristics of the end product. To better understand these unique processes, this article will explore two of the most widely used casting procedures: die casting and sand casting. A comparison of these two casting methods will give manufacturers a better idea of when to implement each process, and which one of these popular methods is best suited towards their application. This article will first explore each process, and then compare them to display why certain manufacturers choose one over the other.
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What is Die Casting?
Die casting is a highly-detailed casting process where reusable metal molds–known as "dies"–are filled with liquid metal under pressure to create tight-tolerance, highly accurate parts. The dies are usually made by machining two mold halves out of a tool steel into the desired exterior contour of a part, and they last between 15,000-500,000 castings per die. They are a large capital investment as they are difficult to machine and test, so it is important for companies to ensure their dies are correct. They are also technically complex, containing water-cooled channels, runners, sprue holes, guide pins, cores, ejector pins, and other high-level accessories that help facilitate a quality casting. These features also allow the die casting process to be more readily automated, and die casting is particularly useful when mechanized in such a way. A lubricant must be sprayed onto each die half before casting begins (known as a "releasing agent"), which will allow the final part to be easily removed from the mold, and protects the mold from damage. A casting metal (often aluminum or steel) is then forced in the clamped die halves under high pressure, where the metal will conform to the die's shape. Die casting machines come in both hot and cold chambered machines, which differ fundamentally based on the injection method of the molten metal, as well as the types of metals used in each machine. The quality of die-cast parts are exceptional both in dimensional accuracy and surface finish, making this process most useful for medium-sized parts with complex details such as automobiles, gears, appliance parts, toys, and much more.
What is Sand Casting?
Sand casting is a method of casting that, unsurprisingly, uses sand to create the casting molds for parts. A pattern is first made out of some compatible material (wood, plastics, etc.), which is in the shape of the final exterior of the product. This pattern will then be placed into one of two halves of a mold, known as either a cope (top half) or drag (bottom half), and sand will be packed tightly around the pattern. When this step is finished, gating systems, runners, sprues, and optional cores are added to finalize the mold, and each half is clamped together. After the mold is finalized, molten metal can be poured into the clamped mold and set to cool. When fully solid, the sand can be removed via water jets, vibration, or other methods until the final part is unearthed. It is necessary to do some post-processing in sand casting such as polishing/sanding/excess metal removal, as this procedure does not conform to the mold as accurately as other casting methods. After this cleaning step, the part is finalized and tested for quality assurance. Sand casting, while not as dimensionally accurate as other methods, allows operators to effectively create any sized part cheaply and easily. Sand casting is particularly useful for engine blocks, various hardware pieces, pistons, and more, and is a mainstay in modern industry thanks to its versatility and low set up cost.
Comparing Die and Sand Casting - Similarities and Differences
Both die and sand casting are widespread, efficient, and highly useful casting methods. So, it can be difficult to specify one method from the other when concerning your project. This article has distinguished certain characteristics common across both methods, and has compared them to show where each casting procedure is best suited (see Table 1, below). Each characteristic will be explained below Table 1, to give a better understanding of using one process over the other.
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