What Is Casting?Types Of Casting
What Is Casting?
Casting is a manufacturing process in which a liquid material is usually poured into a mold that contains a cavity of the desired shape and then allowed to solidify. The solidified part is also known as the casting, which is ejected or broken from the mold to complete the process.
Types Of Casting
Types of Casting Process:
●Sand casting.
Sand casting is one of the most popular and easiest types of casting and has been used for centuries. Sand casting enables smaller batches than permanent mold casting and at a very reasonable cost. Not only can manufacturers use this method to produce products at a low cost, but sand casting also offers other advantages, such as very small operations.
The process allows castings that are small enough to fit in the palm of the hand to castings or large enough like train beds. Sand casting can also cast most metals, depending on the type of sand used to make the molds.
Sand casting is typically based on silica-based materials, such as synthetic or naturally bound sand. Cast sand generally consists of finely ground, spherical grains that can be tightly packed together to form a smooth mold surface.
The casting is designed to reduce the risk of cracks, tears, or other defects by allowing a moderate amount of flexibility and shrinkage during the cool-down phase of the process. The sand can also be strengthened by adding clay, which will make the particles more closely bond. Automotive products such as engine blocks are made by sand casting.
●Investment casting.
Investment casting is also known as lost wax casting, it uses a disposable wax pattern for each cast part. In this type of Casting, wax is directly injected into a mold, removed, and then coated with refractory material and binding agent, usually in several stages, to build a thick shell.
Several samples are put together to form common sprues. Once the shells have hardened, the patterns are inverted and heated in ovens to remove the wax. These patterns require extreme care as they are not strong enough to withstand the forces involved in making molds. One advantage of investment casting is that the wax can be reused.
Investment casting is widely used to make parts for the automotive, power generation, and aerospace industries, such as turbine blades. These castings ensure that high-quality components are made with key benefits of accuracy, repeatability, versatility, and integrity.
●Die casting.
Die casting is a method of molding materials by forcing molten metal under high pressure into a mold cavity. Most die castings are made from non-ferrous metals especially zinc, copper, and aluminum-based alloys. However, iron metal die-cast parts are possible.
The die casting process is particularly suitable for applications in which many small to medium-sized parts with good details, fine surface quality, and dimensional accuracy are required.
●Low pressure casting.
In low-pressure casting, the die is filled with metal from a pressurized furnace, the pressures typically being around 0.7 bar. The holding furnace is located in the lower part of the vertical die casting machine, with the molten metal being injected straight up into the bottom of the mold. The pressure holds the metal in the die until it solidifies.
One of the main advantages of this process is precise control of the die cavity filling. Molten metal flows quickly and smoothly through the feed lines, reducing oxide formation and preventing porosity.
This process was developed for the production of axially symmetrical parts such as car wheels. By using sand cores in the die, however, it is also well suited for the production of parts with hollow profiles and complex geometries.
●Centrifugal casting.
Centrifugal casting is used to make long, cylindrical parts like cast iron pipes by relying on the G-forces developed in a spinning mold. Molten metal introduced into the mold is flung against the inside surface of the mold, creating a cast that can be void-free.
This types of casting were originally invented as the de Lavaud process using water-cooled molds, the process is applied to symmetrical parts such as soil pipe and large cannon barrels and has the advantage of making parts with a minimal number of risers.
In the case of asymmetrical parts that cannot be rotated around their own axes, a variant of centrifugal casting called pressure casting arranges several parts around a common sprue and rotates the molds around this axis.
A similar idea is used in casting very large gear rings, etc. Depending on the material being cast, metal or sand molds can be used.
●Gravity die casting.
Gravity Die Casting is a permanent mold casting process, where the molten metal is poured from a vessel or ladle into the mold. The mold cavity fills with no force other than gravity, filling can be controlled by tilting the die.
Undercuts and cavities can be machined into the component shape using sand cores. This type of casting offers a better surface quality than sand casting as well as better mechanical properties, both due to the rapid solidification.
In addition, this process has a higher casting rate than aluminum sand casting, but metal molds are more expensive than sand. The advantages of this process include the possibility of low gas porosity and fine grain sizes can be achieved.
Compared to sand casting, this process requires less post-processing and cleaning, and gravity dies casting tends to result in a higher quality product. The gravity dies casting manufacturing process is generally less cost-effective in making tooling compared to sand casting.
●Vacuum die casting.
Vacuum-assisted die casting is an important process capability at Kennedy Die Casting. The vacuum evacuation of the die cavity reduces gas entrapment during metal injection and decreases porosity in the casting. The result is die casting with a higher level of quality.
Vacuum systems are only a supplement. They do not substitute for good die casting design practice in the engineering of the die cavity, runners, gates, and overflows.
●Squeezing die casting.
Squeeze casting, also called liquid forging, is a hybrid metal forming process that combines permanent mold casting with die forging in a single step where a specific amount of molten metal alloy is poured into a preheated and lubricated die and subsequently forged and solidified under pressure.
●Lost Foam Casting
Lost-foam casting (LFC) is a type of evaporative-pattern casting process that is similar to investment casting except foam is used for the pattern instead of wax. This type of casting takes advantage of the low boiling point of polymer foams to simplify the investment casting process by removing the need to melt the wax out of the mold.
●Continual Casting
Continuous casting is a refinement of the casting process for the continuous mass production of metal profiles with a constant cross-section. Molten metal is poured into a water-cooled, open-ended mold that allows a “skin” of solid metal to form over the still-liquid center, gradually solidifying the metal from the outside in.
After solidification, the strand, as it is sometimes called, is continuously withdrawn from the mold. Predetermined lengths of the strand can be cut off by either mechanical shears or traveling oxyacetylene torches and transferred to further forming processes or to a stockpile.
Cast sizes can range from the strip (a few millimeters thick by about five meters wide) to billets (90 to 160 mm square) to slabs (1.25 m wide by 230 mm thick). Sometimes, the strand may undergo an initial hot rolling process before being cut.
Continuous casting is used due to the lower costs associated with continuous production of a standard product, and also increased quality of the final product. Metals such as steel, copper, aluminum, and lead are continuously cast, with steel being the metal with the greatest tonnages cast using this method.
