Almost all manufacturing machinery and 90% of manufactured durable goods rely on metal castings. Many types of metal casting is available to meet the needs of applications ranging from automobiles to wind turbines to nuclear power plants.
Learn more here about the different types of metal casting. You can find the method that will give you the best results.
How Does Metal Casting Work?
Metal casting is the process of making objects by pouring liquid metal into a mold with a hollow cavity of the desired shape. The metal cools and hardens into the form of the mold.
Metal casting follows several basic steps. First, the manufacturer makes a pattern of the outside of the part you’re going to cast. Then they form material around the pattern to make the mold. If the final part will be hollow, sand or metalcore shapes the internal form.
Next, the operator melts the metal. Many metals are suitable for casting. Some of the most common ones are iron, steel, aluminum, magnesium, and copper-based alloys like bronze.
After the metal melts, the operator pours it into the mold and lets it harden.
Finally, the operator removes the cast metal object from the mold. If the mold is expendable, operators will just break it away from the casting. Special coatings help keep the part from sticking to a reusable mold.
Most cast parts will then need finishing processes like cleaning or heat treatment.
You can only use an expendable mold once. They’re usually made of sand, plaster, or ceramic. Bonding agents help improve their stability.
Expendable molds let you cast complex, intricate geometries.
Reusable molds are usually made of metal. They open and close to let you remove the castings.
The high temperatures necessary for metallurgy put a lot of strain on the mold. Alloys with a lower melting point like zinc, aluminum, and copper are the best candidates for reusable molds.
Castings from reusable molds have a finer surface finish than castings from expendable molds.
Types of Metal Casting with Expendable Molds
Although you can only use an expendable mold once, they’re cost-effective. This is because they don’t need to be as durable as permanent molds. Several types of castings are possible with single-use molds.
Sand casting is the most common type of metal casting and is the primary method used here at Faircast, Inc. The mold is made of compressed sand with a bonding agent to strengthen it. The metalworker pours molten metal directly into the mold.
After the casting solidifies, the operator breaks away the sand mold and shakes out the core. Much of the sand can be reused for future castings and eventually recycled.
Shell Mold Casting
Shell molding is a type of sand casting. It gives you closer dimensional tolerances than standard sand casting.
The operator pours a mixture of sand and resin over each half of the mold. This mixture cools into a shell. The resin gives extra support to the interior surfaces.
One common use for shell mold casting is to make cores for traditional sand casting.
Types of Metal Casting – Plaster Mold Casting
Plaster casting uses a mixture of gypsum, strengthening agents like talc, and water to make the mold. The plaster sets in approximately 15 minutes. Then the operator dries the mold in an oven to remove any excess water.
The operator pours molten metal into the mold. After the metal hardens, the operator can remove the casting by breaking the mold.
The metal cools slower in plaster than in sand. The casting will shrink very little, so you get more precise sizing.
Full Mold Casting
Full mold or foam casting uses both foam and sand. The manufacturer coats a foam polystyrene pattern with sand. The foam will vaporize when the operator pours hot metal into the mold.
The combination of foam and sand makes full mold casting very accurate. You can make complex shapes.
Reusable and Expendable Molds
The two main types of metal casting are processes with reusable molds and processes with expendable molds. Reusable molds let you make many items from the same mold. The casting process destroys expendable molds. You can only use them once.
Types of Metal Casting with Reusable Molds
Several casting methods are possible when you use permanent molds. Choosing one over another depends on the requirements of the castings you want to make.
Die casting is a process that forces the molten metal under pressure into a reusable mold. The mold or die has at least two parts to allow removal of the castings.
A pressure nozzle injects the liquid metal into the closed mold. The die reopens when the metal has cooled enough. Ejector pins push the part out.
Two methods for injecting the metal into the die are possible: cold chamber and hot chamber. Cold-chamber die casting is similar to a syringe. An injection chamber fills with molten metal and then a piston pushes the material into the die.
With hot-chamber or gooseneck die casting, the chamber of the injection system is immersed in the molten metal. The shape of the system lets the injector refill itself.
Gravity Die Casting (Permanent Mold Casting)
Gravity die casting is similar to regular die casting except that the liquid metal pours into the mold using only the force of gravity. It isn’t under pressure. This means that the tooling is simpler and less expensive.
Semi-permanent mold casting has expendable sand cores instead of permanent ones. The core can have a more complex shape.
Centrifugal casting rotates a water-cooled mold around its central axis at high speed while the molten metal is added. The centrifugal force pulls the metal along the surface of the mold. For centrifugal casting to work, the molds should be cylindrical or circular in shape.
Continuous casting makes the raw material for worked steel. It can create any length of simple metal shapes.
Molten metal flows into a funnel that fills a mold below. Water flows along the outer surface of the mold to cool it. The exterior of the casting solidifies, but it’s still pliable when it comes out of the mold.
Sets of rollers move the casting out of the mold. Gas jets cut the continuous metal strand into manageable lengths.
Types of Metal Casting – Choosing the Right One
You have many types of castings to choose from. Using the right one will help ensure the success of your project. An experienced foundry will work with you to find the best solution for your needs.
Faircast is your go-to Midwest gray iron and ductile iron casting foundry. Our dedicated staff will answer your questions, give you a competitive quote, and cast the high-quality parts you expect.
Contact us today for a quote and let’s get started.