12 Different Types Of Casting Processes in Manufacturing
You’re not alone if you find getting the ideal casting process to match your product designs challenging. The casting process can often cause headaches and heartaches alike.
Besides, the many options available can be overwhelming, leaving you questioning whether there is a better way. But worry not—today we’ll talk about the different types of casting processes in manufacturing and help you make the best choice easier when choosing.
What Is the Casting Process?
Casting is a crucial process that shapes raw materials into finished products of incredible complexity and value. Everything from artwork, construction supplies, automotive metal casting parts, mechanical devices, aerospace parts, and electronics to engine parts can be created through this process.
This manufacturing process involves shaping liquefied materials such as molten metal, steel, or other materials into intricate solid shapes by pouring them into the cavities of specially designed molds and allowing them to solidify.
After solidification, the solidified part, also referred to as casting, is ejected from the mold, undertaken through different finishing treatments, or used as a final product.
Types of Casting Processes
There are different types of casting processes in manufacturing industries based on the type of material being cast, quantity of production, the complexity of the part’s shape, and accuracy requirements.
On the other hand, when choosing the right type of casting process for your manufacturing requirements, it’s important to consider their advantages and disadvantages. Here’s a list of different types of casting processes and their pros and cons.
1. Sand Casting Process
Sand casting is a common production process for manufacturing metal parts of different weights and sizes. It can create intricate, detailed parts using any metal alloy type. Automotive products such as cylinder heads, crankshafts, and engine cylinder blocks are manufactured through this process.
Sand casting usually uses molds from green sand, water glass, resin sand, or silica-based materials such as naturally or synthetically bonded sand to form and shape intricate metal castings. The casting is designed to minimize the chances of cracking, tearing, or other defects by allowing a moderate degree of shrinkage and flexibility during the cooling stage of the process. Adding clay helps strengthen the sand by bonding the particles more closely.
This casting process has four main steps: patternmaking, molding, melting and pouring, and cleaning. The pattern is the shape around which the sand is placed. It has two parts: the drag (the lower half) and the cope (the upper half).
After the sand is compressed enough to align with the pattern, the cope is removed and extracted. Then, additional inserts ( also referred to as core boxes) are inserted, and the cope is replaced.
Molten metal is carefully poured into the pattern and left to solidify, taking the intended shape. After solidifying, the casting is removed, extra metal is trimmed, and any sand and scale residue is cleaned.
Pros
It’s economical in terms of production costs
Allows casting of both ferrous and non-ferrous materials
You can fabricate large components
It offers a recycling ability
It is possible to process metals with high melting temperatures
Cons
Using this method for products with pre-determined sizes and weight specifications takes a lot of work.
The final products usually have a rough surface finish
This casting method has a lower degree of accuracy than other casting process types.
2. Die Casting Process
Die casting involves melting metals with low melting points and injecting them into an already-made mold. The molds are made of steel using cutting-edge techniques such as CNC machining, ensuring precision, high levels of accuracy, and repeatability when working with metal components.
The first step in this casting process is the creation of a reusable steel mold with two sections. The two sections are then clamped together tightly. Molten metal is then injected after applying a lubricant, which helps regulate its temperature and ease the casting removal from the mold.
Die casting has two main procedures: cold chamber and hot chamber die casting. Each process can handle different materials depending on their melting points. For instance, the hot chamber die-casting process is used when dealing with materials with low melting points, such as zinc, magnesium, lead, and tin. In contrast, cold chamber die-casting is ideal for aluminum.
Hot chamber die is not recommended for alloys with higher melting points since doing so would damage the pump because the metal would end up getting into direct contact with it. It involves using pressure from hydraulic stems to pour the metal into the chamber die after it has been melted.
Pros
It offers good product quality and high efficiency.
It is perfect for mass production
It provides high precision and dimensional tolerance
The flow rate is fast during the casting
Cons
The cost of the tool is relatively high
Castings are prone to shrinkage and tiny pores.
The die castings have low plasticity
3. Pressure Die Casting
Pressure die casting is a manufacturing process that produces net-shaped, precisely tolerated metal components. The process involves injecting a molten metal (aluminum, zinc, or magnesium) at high speed and pressure into a steel mold (a closed die). One half of the die is moveable while the other half is stationary, both mounted on the casting machine’s platen.
The liquid metal alloy solidifies immediately to create a net-shaped component, which is then extracted.
There are two types of pressure die casting: high-pressure die casting (HPDC) and low-pressure die casting (LPDC), based on the pressure applied. Although about 50 percent of all light metal alloy casting production uses HPDC, it has a wider range of applications.
Furthermore, HPDC is crucial for castings requiring a precise tolerance and complex geometry. Due to the additional pressure, the metal alloy can be forced into the mold’s intricate features. On the other hand, LPDC is often used for larger, less-important components.
Pros
It reduces the need for post-casting machining
It offers high precision and dimensional tolerance
The casting process provides high efficiency and good product quality
It offers faster production rates
Cons
It is limited to only non-ferrous materials
High tool costs involved
4. Investment Casting
Investment casting, also referred to as lost wax casting, uses a disposable wax pattern coated with a ceramic material, which solidifies into the shape of the casting.
The first step in this casting process is making a wax pattern, often made from wax or plastic. Since this process requires accurate measurements, several trials, and errors make the investment casting an expensive manufacturing process.
The wax is injected into a mold, carefully removed, and then coated with a binding agent or a refractory material to create a thick shell. Besides, multiple patterns are assembled onto the main sprues.
After the hardening of the shells, the patterns are flipped over and heated in ovens to remove the wax. Molten metal is poured into the remaining shells, solidifying into the wax patterns’ shape. Moreover, the refractory shell is broken off to reveal the completed casting.
This casting process is often used to manufacture power generation, automotive, and aerospace components.
Pros
It reduces the need for post-casting machining
It offers high precision and dimensional tolerance
The casting process provides high efficiency and good product quality
It offers faster production rates
Cons
It is limited to only non-ferrous materials
High tool costs involved
5. Permanent Mold Casting
Permanent mold casting is similar to centrifugal and die casting, especially in reusable molds. These molds can be made of graphite, steel, etc, and used to cast materials such as cast iron aluminum, zinc, lead, and magnesium alloy. Besides, it has a variety of applications for projects that require duplication or mass production.
The molds for this casting process have two parts that fit firmly with an opening at the top section for injecting molten metal. When the metal solidifies, the two parts are separated to reveal the finished casting.
The first step in permanent mold casting is heating the mold to ensure it’s moisture-free and prevent any damage to the mold that can occur during thermal expansion when the molten metal is injected. Preheating also prevents the molten metal from hardening during the casting process.
You can use gravity, vacuum-assisted, pressure-assisted, and slush casting methods to inject the molten metal into the mold. The gravity method is usually the least expensive. The low-pressure method is ideal when a mold requires relatively fine details.
When using vacuum assisted method, air is removed from the mold building up a vacuum that sucks the already molten metal into the mold. The low-pressure and vacuum-assisted method is usually for components with fine details and small spaces.
On the other hand, in the slush method, the molten metal is poured into the permanent mold and allowed to harden against the mold’s outer surface. Once the surface material has fully solidified, the remaining molten metal is emptied, leaving a hollow casting.
Pros
It offers enhanced surface finish and dimensional accuracy
The process provides a high production rate
The process produces a wide range of part sizes and shapes
It uses reusable molds
Cons
Higher initial tooling costs
It offers limited complexity
Making design changes can be time-consuming and costly
6. Centrifugal Casting
Centrifugal casting, formerly the deLavaud process, produces long, cylindrical pieces such as cast iron pipes by relying on the g-forces created in a rotating mold.
The centrifugal casting involves pouring molten metal into a mold that rotates vertically or horizontally, enclosed in a water spray or a water jacket. Molten metal is carefully injected into the mold using a ladle through a trough. As the molten metal gets into the casting, it stretches to both ends of the mold. But first, it is ladled into a bell, from which it gets into the casting and continues entering the mold to the full length.
The centrifugal movement forces the molten metal to the mold’s walls, which hardens it into a pipe. Besides pipes, centrifugal casting can manufacture cylinder linings, flywheels, axis-symmetric parts, etc.
Pros
It offers enhanced surface finish and dimensional accuracy
The process provides a high production rate
The process produces a wide range of part sizes and shapes
It uses reusable molds
Cons
Higher initial tooling costs
It offers limited complexity
Making design changes can be time-consuming and costly
7. Vacuum Casting
Vacuum, urethane, or polyurethane casting usually uses silicone molds to produce plastic and rubber components in a vacuum. The silicone mold is made using 3D molding by following the traditional injection molding procedure.
During this casting process, the pattern is fitted with inserts, cores, and gates then placed in the casting box. Afterward, risers are added, allowing air to escape from the mold. Silicone is then poured on the master pattern into the casting box, covering the pattern and filling it.
After curing at 40o C (104o F) for 8 hours or more, the casting box and risers are removed. The cured mold is then cut using a wavy pattern to reveal the negative cavity for the part. The wavy pattern usually ensures the right alignment of the mold halves during casting.
The resin for the part is then prepared in a pouring bowl and mixed in equal proportions. The resin mixture is then poured into the mold under a vacuum to avoid voids or air pockets.
Once the resin is cast, the mold is cured in a temperature-controlled chamber and then removed from the mold. Then, the gates and risers are removed from the casting in the finished part, and any rough surfaces or imperfections are treated and finished.
Pros
It is perfect for low-volume production
It offers improved mechanical properties and surface quality
There is no need for expensive, complex tool finishing
Heat treatment and welding of products is possible
Cons
The mold used in this metal casting process has a short life
The casting might have hollowness issues
8. Plaster Casting
This casting process is quite similar to the sand casting. The pattern is usually coated with an anti-adhesive compound to prevent it from getting stuck against the mold.
The mold is created with gypsum or calcium sulfate plaster mixed with asbestos, talc, sodium silicate, sand, and water. The mixture of these components creates a slurry sprayed on the pattern, which has already been sprayed with an anti-adhesive to prevent the plaster from sticking to the pattern.
The molds are removed from the pattern and allowed to dry. After drying, the mold and cores are assembled, and the molten metal is poured into them. The mold is carefully broken to reveal the final casting when the metal solidifies and hardens.
Pros
It can cast complex shapes with thin walls.
It produces casting with a smooth surface finish.
It offers a higher level of dimensional accuracy.
Cons
Limited applications to copper and aluminum-based alloys
Not recommended for high melting materials
The plaster mold casting process is a bit expensive
9. Continuous Casting
There are two methods of continuous casting: horizontal and vertical. Both methods produce hexagonal, rectangular, square shapes, gear teeth, and several other shapes. With this casting process, molten metal is poured directly into a mold from an induction furnace through holes at the top of the die.
The mold is usually surrounded by a water-cooled jacket, making the molten metal solidify quickly. Besides, the molten metal above the die serves as a riser, keeping the die filled to prevent shrinkage.
The molten metal is ejected out by mechanical equipment after solidifying through the bottom of the die. The metal’s ejection is usually controlled until it reaches the desired length and is cut off. This process results in a casting with even, fine-grain structures, great physical properties, and high density.
Pros
The process saves metal, increasing the yield
Lower costs involved due to continuous production
It offers various size ranges of casting products
Cons
Casting of only simple shapes
It requires continuous cooling of the molds
10. Gravity Die Casting
Gravity die casting involves pouring molten metal directly from a ladle into the mold cavity. The main concept of this casting process is to use gravity to fill the mold cavity. The mold is loaded with minimal turbulence through one or more channels to reduce foaming and oxidation.
The minimal turbulence also helps reduce inclusions and porosity, which gives optimum properties to the final product. Besides, mold tilting results in denser, high-quality castings with stiffness and high strength, making the casting process ideal for suspension and brake systems.
Although this process has horizontal and vertical mold openings, tilting technology is the most used. The tilting inclination at 0/90° or 0/120° determines how much metal flows into the die during casting.
Pros
It offers an enhanced surface finish and mechanical properties
Casting products have tight tolerance and high precision
Production of thin-walled products
It uses reusable molds, saving time and increasing productivity.
Cons
Manufacturing costs of molds used are higher
Casting complex products is not easy
11. Lost-Foam Casting
The lost foam casting process is similar to investment casting, but the foam is used instead of wax to create the mold. The casting mold is created from polystyrene foam, formed from foam blocks, or made from the injection molding process.
The tooling for this casting process includes a split chamber aluminum die where the foam pattern is formed. The foam pattern is usually coated with a porous ceramic refractory coating to create a barrier between the green sand used and the surface of the foam. Also, the coating allows the gas from the vaporizing foam to escape.
As soon as the sand is firmly pact and the impression of the foam pattern is encased in the sand, the molten metal is injected into the mold, causing the foam pattern to vaporize as the mold is filled. Cooling starts immediately, and the molten metal forms crystals until the whole pattern is solidified.
After the casting has hardened enough, the cooled metal is removed from the sand mold. The fully formed part is then taken to post treatments to perfect the cast piece. In this casting process, there are different types of post-treatment, which include removing the risers and runners and grinding or sandblasting the cast piece to achieve the desired shape, smoothness, and tolerance.
Pros
It is relatively cost-effective for high-volume production
The process offers clean production
It allows for flexible design
The process provides high-precision casting
Cons
Low-volume production results in high pattern costs
Many production processes result in longer delivery time
12. Shell Molding
As the name suggests, Shell molding involves a hardened shell of sand and a two-piece metal pattern created in the form of the intended casting.
The first step of this process entails heating the two-piece pattern and coating it with a lubricant to ease removal. The heated pattern is secured to a dump box containing a mixture of sand and heat-treated resin. The dump box is flipped, allowing the sand-resin mixture to coat the two-piece pattern.
When the surrounding shell and half of each pattern are completely cured, the shell is removed from the pattern. Furthermore, both shell halves are clamped together to create a complete shell mold.
Molten metal is conveniently poured into the mold cavity from a ladle through the gating system. After filling the mold cavity, the molten metal is allowed to cool and harden into the form of the final casting.
The last step involves breaking the mold to reveal the casting. Trimming and cleaning are done to remove any sand from the mold and any excess metal from the feed system.
Pros
It allows the casting of thin and complex parts
The process requires less labor
Produces casting with smooth surface finish and dimensional accuracy
Suitable for both ferrous and non-ferrous metals
Cons
Not ideal for small-scale production
Weight and size limitations of casting
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Author
Gavin Leo is a technical writer at Aria with 8 years of experience in Engineering, He proficient in machining characteristics and surface finish process of various materials. and participated in the development of more than 100complex injection molding and CNC machining projects. He is passionate about sharing his knowledge and experience.