What Is Metal Casting?- Definition, Types, and Process

What is Metal Casting?

Metal casting, at its core, is the practice of pouring molten metal into a mold shaped to fit the desired final part. Once the metal cools and solidifies, the mold is removed, leaving behind a finished component. Interestingly, the word “casting” doesn’t just refer to the process—it also describes the finished piece that comes out of the mold. This ancient technique goes back more than 6000 years, and while modern methods have evolved, the fundamental principles remain the same.

Over the centuries, casting has been the go-to method for producing complex or massive parts—things that would be nearly impossible or just too expensive to make with other manufacturing techniques. It’s one of those processes that quietly underpins much of our daily life: from car parts and train wheels to lamp posts and even something as simple as school bus pedals, there’s a good chance casting played a role in getting those items into the world.

What’s also worth noting is how sustainable the process can be. Foundries often turn to recycled metal as a primary raw material, which not only keeps costs down but also cuts back on waste—metal that might have otherwise ended up as landfill gets a second life as something new.

The Metal Casting Process

1. Patternmaking

A pattern essentially serves as a model of the external shape of the intended casting. These patterns are commonly fabricated from materials such as wood, metal, plastic, or plaster, depending on the requirements of the project.

In industrial manufacturing, the process of patternmaking holds significant importance because it demands precise measurements and careful planning to ensure that each component fits together properly and functions as intended.

2. Core making

When a casting needs to be hollow inside, a separate insert known as a core—usually made of sand or sometimes metal—is used to create the desired internal cavity.

These cores are specially designed to be both sturdy enough to maintain their shape during the casting process and sufficiently fragile so that they can be removed without difficulty once the metal has solidified.

This allows manufacturers to produce complex hollow structures while ensuring that the core does not become a permanent part of the finished piece.

3. Molding

To better understand the metal casting process, consider the experience of walking along a beach and observing the footprint you leave behind in the damp sand. In this analogy, your foot acts as the core, while the impression in the sand serves as a mold of that core.

The process of molding involves several steps designed to form a cast around a pattern, typically using molding sand. In practice, the mold is held within a frame known as a flask. Molding sand, often referred to as greensand, is carefully packed into the flask, surrounding the pattern.

This technique is called sand casting. After the sand has been firmly packed and the pattern is carefully removed, the resulting cavity remains, ready for the casting process. Alternatively, for industrial purposes, a reusable two-piece metal mold can be produced, allowing manufacturers to create identical cast parts repeatedly and efficiently.

4. Melting and Pouring Molten Metal

Once the metal has been fully melted, it is carefully poured into the mold cavity and allowed to solidify. After the casting has hardened, the next step is known as shakeout. At this stage, the molds are subjected to controlled vibration, which helps dislodge and remove the sand from the finished casting.

In industrial settings, equipment such as the Two-Mass Shakeout plays a key role in maintaining high production levels. Its reliable and efficient operation ensures that output remains steady without unnecessary delays.

The sand that is separated during this process isn’t wasted; instead, it is gathered, cooled down, and often recycled for use in future casting cycles. This not only conserves resources but also supports more sustainable manufacturing practices.

5. Cleaning

At the conclusion of the casting process, the metal object is carefully extracted from its mold. Following this, a process known as fettling takes place, during which any remaining traces of the molding material are thoroughly cleaned away and rough edges are smoothed out. This ensures that the final product meets the required standards of finish and quality.

Types of Metal Casting

When we talk about metal casting, it’s helpful to know that the process falls into two main categories based on how the mould is designed: expendable mould casting and permanent mould casting.

Within these broad groups, there’s another level of classification that depends on the material used to create the pattern. This means the kind of pattern material you start with—whether it’s wood, metal, or something else—can further distinguish one casting process from another.

• Reusable molds:
  • Permanent molds
  • Semi-permanent molds
  • Slush casting
  • Centrifugal casting
  • Pressure casting
  • Die casting
• Expendable molds:
  • Sand casting
  • Shell molding
  • Investment casting (lost-wax)
  • Full mold or foam

Expendable mould casting

Expendable mold casting is a process where the mold used to shape the final product is intentionally made to be destroyed after a single use. In other words, once the casting is formed, the mold has to be broken apart to release it. Usually, materials like sand, ceramics, or plaster are chosen for these molds because they’re easy to shape and remove.

To make sure the mold holds its shape and has enough strength, a binding agent—often called a bonding agent—is mixed in with the base material. This technique is particularly useful when manufacturers need to create parts with complicated shapes or fine details that would be tricky or impossible with other casting methods.

Permanent mould casting

Permanent mould casting—also known as non-expendable mould casting—involves the use of moulds that can be used again and again, rather than being discarded after each casting. One of the main advantages of this process is that the same mould can be reused for multiple production cycles, which helps ensure that each part comes out consistently.

However, there is a trade-off to consider. Because the mould needs to be opened up to remove each finished piece, this method is best suited for relatively simple shapes. More complex castings are generally not feasible with permanent mould casting, as the mould design must allow for easy removal of the solidified part.

Composite mould casting

As you might guess from the name, this method makes use of both disposable and reusable casting moulds to create various castings. Typically, materials like sand, wood, graphite, and metal are involved in the process.

Application of Metal casting

A sector-wise casting consumption is given below which highlights the importance of casting in any industrial setup.

• Transport: Automobile, aerospace, railways and shipping
• Heavy Equipment: Construction, farming and mining
• Machine Tools: Machining, casting, plastics molding, forging, extrusion and forming
• Plant Machinery: Chemical, petroleum, paper, sugar, textile, steel and thermal plants
• Defense: Vehicles, artillery, munitions, storage and supporting equipment
• Electrical Equipment Machines: Motors, generators, pumps and compressors
• Hardware: Plumbing industry pipes, joints, valves and fittings
• Household: Appliances, kitchen and gardening equipment, furniture and fittings
• Art Objects: Sculptures, idols, furniture, lamp stands and decorative items

Advantages of metal casting

• Metal casting can produce complex shapes
• Features like internal cavities or hollow sections can be easily achieved
• Large components can be produced in one-piece cast
• Materials that are difficult or expensive to manufacture using other manufacturing processes can be cast
• Compared to other manufacturing processes, casting is cheaper for medium to large quantities
• Almost all metals can be cast
• Near net shape often without or very minor post-processing

Disadvantages of metal casting

• Relatively coarse surface finish and hence wider tolerance has to be allowed and is not suitable for mating interfaces
• Metal casting such as shell molding has a limit in terms of size and the pattern
• Patterns are time-consuming and expensive to make although additive manufacturing processes such as binder jetting are being used lately to make a mold
• Die casting can be very expensive for smaller to medium quantities due to the high die cost
• Part size and material choices depend on the casting process chosen. For instance, only non-ferrous metal can be used for permanent mold castings

FAQs