In the metalworking industry, casting refers to the process of pouring molten metal into a pre-designed mold. When the molten metal has cooled down, it will turn into a solid metal object with your customized shape. Casting can be accomplished by using a different variety of metals. When forming the molds, there are also different types of materials that can be used. Since the casting process requires multiple variables, such as molten metal, molds, etc., it is important that extreme safety precautions must be observed and make sure that only trained specialists are allowed to operate the equipment.
Casting manufacturing refers to the process in which a liquefied material will be poured into a mold and allowed to solidify. Once it is hardened, the finished product will be removed from the mold. It could either be used right away or it could undergo several finishing treatments. Generally, casting processes are used in creating complicated hollow and solid shapes. Cast products are used in a variety of applications. For instance, they can be used for aerospace and automotive components. There are various types of casting processes that are used in manufacturing.
Different Kinds of Casting Processes
Casting is considered one of the oldest ways of manufacturing. But today, modern techniques are used in casting technology, resulting in a wide array of specialized casting methods.
Some examples of hot forming casting processes include die-casting, sand casting, plaster casting, and investment casting. Each of these has their own unique advantages. By comparing both the benefits and drawbacks of the different types of casting processes, you can select the best type of method that is well-suited for your production.
Also known as Metal Casting Process, this method involves molding materials under extreme pressure and typically uses alloys and non-ferrous metals including tin, zinc, aluminum, and copper. The mold will be applied with a lubricant to help in regulating the temperature and removing the workpiece easily.
Molten metal will be embedded into the die under extreme pressure. This will continue until such time that the workpiece has hardened. The pressurized injection is done quickly to prevent any portion of the material from solidifying before being cast. Once the process is done, the workpiece will be removed from the die as well as any scrap material.
What Are the Benefits of Die Casting?
- There is a close tolerance on the size and shape of the component.
- There is a minimal requirement for post-casting machining.
- There is high consistency and uniformity in the dimension and design of the component.
Generally, sand casting is dependent on silica-based materials including artificial or naturally-bonded sand. Casting sand consists of finely ground grains that are securely congested into a flat molding surface.
The casting is created in such a way that the risk of cracking, tearing, and other flaws can be prevented by providing a sufficient level for shrinkage and flexibility during the cooling stage. Adding clay to the sand can provide more strength. It can also help in bonding the particles more closely. Sand casting is usually used in manufacturing automotive components such as engine blocks.
The sand casting process includes a lot of steps such as designing a pattern, molding, melting, pouring, and finally cleaning up the component. The pattern is the shape where the sand is packed together. Typically, it is composed of two elements which are the cope and the drag. Once the sand is congested enough to duplicate the pattern, the cope is taken off and the pattern is extracted.
Afterward, more inserts, also known as core boxes, are placed and the cope will be replaced. Once the metal has been poured and hardened, the casting is taken off. All the risers and gates that were utilized during the pouring process will also be removed. Any stuck sand and scale should be cleaned up.
What Are the Benefits of the Sand Casting Process?
- It has the capability of fabricating large components.
- Its production costs are relatively low, most especially for lesser volumes.
- The post-casting tooling costs less.
- It is capable of casting ferrous and non-ferrous materials.
- What are the drawbacks of the sand casting process?
- Despite having several advantages, sand casting is less accurate compared to its alternate methods.
- Components which have predetermined size and weight are difficult to sand cast.
- This process tends to produce components that have a relatively rough surface finish.
Plaster casting is just the same as the sand casting process. The main difference is that plaster casting uses a combination of strengthening compound, gypsum, and water rather than sand. Basically, an anti-adhesive compound is coated on the plaster pattern to prevent the component from being stuck to the mold.
Also, the plaster has the ability to fill in any gaps that exist in the mold. After using the plaster material in casting the component, it usually cracks or becomes defective. That is why it has to be replaced with new material.
What Are the Advantages of the Plaster Casting Process?
- It can cast intricate shapes with thin walls.
- Your component will have a very smooth surface finish.
- It has a higher level of dimensional accuracy compared to sand casting.
- Plaster casting can produce large components with lesser costs compared to other processes.
- The casting process tends to be more effective and cost-efficient when one of the important requirements is the quality of the surface finish.
What Are the Disadvantages of the Plaster Casting Process?
- The plaster casting process is more expensive compared to sand casting.
- The plaster molding must be replaced more often.
- Generally, its application is only restricted to casting copper-based alloys and aluminum.
Investment casting, also known as lost-wax, is utilizing a disposable wax pattern in casting each component. The wax will be inserted into the mold, taken off, then coated with a binding agent and a refractory material. Usually, this is done in multiple phases in order to create a thick shell. Several patterns are arranged to develop common sprues. After the shells have hardened, the patterns are turned upside down and placed in the ovens so the wax can be removed.
The remaining shells will be poured with molten metal so it can solidify into the form of the wax patterns. The refractory shell will be cracked so the completed casting will be exposed. Most often, investment casting is used for producing components for aerospace, power generation, and automotive industries.
What Are the Advantages of the Investment Casting Process?
- It is capable of creating thin-walled components with intricate geometries.
- Components will have a high level of preciseness and accuracy in dimension.
- The final components will have unique details and a high-quality surface finish.
- It has the ability to cast ferrous and non-ferrous materials.
- The expense might be expensive, yet it has lesser machining and tooling costs since it has high-quality surface results.
What Are the Disadvantages of the Investment Casting Process?
- Although it is very precise and accurate, it is usually more expensive compared to the other types of casting techniques.
- It can only be considered as a cost-efficient option if plaster or sand castings are not applicable.
Centrifugal casting is usually used for generating long, cylindrical components such as a cast-iron pipe. This technique relies on the g-forces produced by the spinning mold. Molten metal is poured into the interior surface of the mold, so the casting is free from any empty spaces.
Originally known as the de Lavaud process, this technique utilizes water-cooled molds and applicable only to symmetrical components such as soil pipes and large gun barrels. One of its greatest advantages is it can generate components by utilizing a lesser number of risers.
If you have asymmetric components which are not capable of spinning around their own axes, then you can use the modified version of centrifugal casting known as pressure casting. It can set up multiple components around a common sprue while spinning the molds around this axis. The same application is also used when casting extremely large gear rings. Metal or sand molds might be used depending on what type of material is being cast.
Permanent Mold Casting
Permanent Mold Casting has a similarity with centrifugal casting and die casting, since it also uses reusable molds which can either be made of graphite, steel, etc. Basically, they are used for casting materials such as aluminum, zinc, lead, magnesium alloys, cast iron, and bronzes. This process only requires low pressure. Pouring is usually done by hand by utilizing several molds on a turntable.
As the molds make a rotation through the different stations, they will be coated, closed, then filled, opened, and finally emptied. This technique is also known as slush casting, wherein the mold will be filled, then later on it will be emptied before the metal is completely solidified. Molten metal is discharged from the casting to create a hollow, cast shell. This is the same concept being used in producing hollow chocolate products, for instance, Easter bunnies. Using metal molds can encourage quicker heat transfer through the mold. It allows the shell to solidify while the core is still in the form of liquid.
We hope that this article has helped you in gaining more knowledge about the different types of casting processes. For more information about die casting products, you can visit SEI CASTINGS. We can produce custom castings, enclosures, and many more. If you want to request a quote, then just give us a call at (408) 374-1031.