What Is Casting?- Definition | Types of Casting

At its core, casting is the backbone of producing solid metal parts, which are often referred to simply as “castings.” The process itself is pretty straightforward: you start with molten metal, pour it into a carefully designed mold, and let nature do its thing as the metal cools and solidifies, taking on the exact shape of the mold cavity.

One of the big appeals of casting is the sheer flexibility it offers when it comes to forming intricate shapes. If you’ve ever marveled at complex metal components, chances are they owe their existence to this method.

It’s also incredibly efficient for mass production—manufacturers can closely control how much material goes into each casting, so there’s minimal waste and, not surprisingly, a significant cost savings. You might also hear casting referred to as “founding,” especially in older texts.

What is Casting?

In a nutshell, casting involves pouring a liquid most commonly molten metal into a mold shaped exactly like the part you want to make. You then wait for the material to harden, pop it out (or sometimes break the mold to get it out), and voilà: you’ve got your finished piece.

While metals are the stars of the show here, the casting process isn’t limited to them. It’s also widely used with materials that set and harden after mixing, like concrete, plaster of Paris, clay, and certain epoxies.

It’s kind of wild to think about, but metal casting has been around for about 7,000 years. The earliest recorded example is a small copper frog, dating back to 3200 BCE, found in what we now know as Iraq. Whether in manufacturing or the arts, the steps have stayed largely the same: pour molten metal from a crucible into a mold, let it cool, and remove the finished piece for any final touches.

There are several traditional methods for casting metal. These include lost-wax casting, plaster mold casting, die casting, and sand casting, among others. Depending on what’s being made, casting might happen in an industrial foundry or even in a jeweler’s studio.

Over the millennia, casting has played a huge role in producing everything from sculptures and jewelry to transportation parts, weapons, and tools. It’s particularly handy when you need to make complicated shapes that would be a nightmare (or just way too expensive) to fabricate any other way.

For example, massive items like ship propellers or the beds of heavy machine tools are often made in a single casting—saving a ton of time and hassle compared to assembling them from smaller pieces.

Related Posts: What is Metal Casting?

What is the Casting Process?

When we talk about casting processes, what we’re really describing is a method that relies on pouring molten material most often metal into a carefully shaped mold. The mold itself defines the final shape of the part. Once the liquid metal is inside, it’s allowed to cool down, usually as the mold draws away the heat, until the metal hardens into the shape you want.

Broadly speaking, metal casting falls into two main categories: those that use molds which can be reused, and those that use molds designed to be broken or discarded after a single use. In both cases, the basic sequence is pretty similar.

The metal gets heated until it’s melted—usually in a crucible—then poured into the mold. After the metal has cooled and turned solid, you either remove the mold (if it’s expendable) or simply take the new part out (if the mold can be used again).

At its core, metal casting starts with designing a pattern and creating the mold. Once those are ready, you pour in the molten metal, let it solidify, and then extract your finished casting. What’s great about this process is how adaptable it is—you can tweak it to suit different metals, shapes, sizes, and design requirements.

Step 1: Creating the Pattern

Before getting started with mold-making, the first essential task is to develop a pattern—the piece that ultimately decides the shape your mold will take. This pattern acts as a three-dimensional stand-in for your finished casting and can be crafted from a variety of materials, such as wax, sand, plastic, or wood.

Interestingly, some artisans prefer using plaster or silicone to make molds. While these materials can’t handle the extreme heat of molten metal, they do make it easy to produce several identical wax copies, which is especially handy if you’re planning on expendable mold casting.

As you work on shaping your pattern, don’t forget to factor in the shrinkage that typically occurs as the metal cools. It’s also common practice to add gates or sprues essentially channels that help guide the molten metal into every nook and cranny of the mold.

Step 2: Making the Mold

Once your pattern is ready, the next phase is all about constructing the mold itself. Depending on your project, you can opt for a reusable mold usually made of metal or a disposable one, which might be made from materials like sand, plaster, or a ceramic shell.

Each type of mold has its own strengths, catering to different metals and varying levels of design complexity. For example, if you’re working with a wax or plastic pattern, you can place it in a kiln and burn it out, leaving a cavity that’s ready to be filled with metal.

Step 3: Selecting the Metal Alloy

Now comes the decision of which metal alloy to use. Every casting project relies on either ferrous or non-ferrous alloys, each chosen for the specific mechanical properties needed for the end product. Ferrous alloys include materials like steel, malleable iron, and gray iron.

On the other hand, non-ferrous alloys popular in casting work include aluminum, bronze, and copper. If you happen to be casting jewelry, you’ll probably be dealing with precious metals—think silver, copper, gold, or platinum.

Step 4: Melting the Alloy

Every alloy has its own specific melting point, so this stage can look a little different depending on what you’re working with.

The basic idea is to put your solid alloy into a crucible and heat it up—sometimes using a furnace, other times just an open flame will do the trick. It’s important to watch the temperature closely so you don’t overheat the material.

Step 5: Pouring into the Mold

Once your metal is completely molten, it’s time to pour it into the mold cavity you’ve prepared. If you’re making a smaller item, you can usually just tip the crucible and pour straight into the mold.

Larger projects, though, might need more hands sometimes even a small team—to transfer the metal from the furnace into a bigger crucible or ladle before pouring.

Safety should always come first at this stage. I can’t stress enough how essential it is to wear the right gear: stick to natural fibers, cover up with long sleeves and pants, and use insulated gloves and safety goggles.

Make sure your workspace is well-ventilated to keep any nasty fumes at bay, and always have a chemical fire extinguisher within arm’s reach. And, of course, keep the path between your furnace and mold completely clear to avoid accidents. Give the metal time to solidify in the mold before you do anything else.

Step 6: Removing the Casting from the Mold

When your metal has cooled down and hardened, you can finally take it out of the mold. If you used a mold designed for a single use, you’ll likely have to break it open to get to your casting.

In the case of plaster investment molds, once the metal is set, quenching the whole thing in water helps break the plaster away. For molds that you can use more than once, it’s usually just a matter of ejecting the casting, often with the help of ejector pins.

Step 7: Finishing Touches

Now comes the satisfying part—finishing your cast metal piece. This means cleaning it up, whether that’s scrubbing away leftover bits of mold material, snapping off casting gates with a pair of clippers (if you’re working with something small), or reaching for an angle grinder for bigger pieces. Take your time here; careful filing and polishing make a world of difference to the final result.

Different Types of Casting

Different Types of Casting Process:

• Sand casting.
• Investment casting.
• Die casting.
• Low-pressure casting.
• Centrifugal casting.
• Gravity die casting.
• Vacuum die casting.
• Squeezing die-casting.
• Lost Foam Casting
• Continual Casting

1. Sand Casting

Sand casting has stood the test of time—it’s been around for centuries and is still one of the go-to casting methods today. Part of its appeal comes from how simple and flexible it is.

Unlike permanent mold casting, sand casting is ideal if you’re working with smaller batch sizes and want to keep costs in check. It’s not just about saving money, either; this method is also practical for small-scale operations, making it accessible to a wide range of manufacturers.

One of the great things about sand casting is its versatility. Whether you need something as tiny as a part that fits in your palm or something massive, like a train bed, this process can handle it. Plus, as long as you pick the right type of sand for your mold, you can cast nearly any metal you need.

When it comes to the sand itself, most of the time, you’re looking at silica-based materials—either naturally bonded or synthetic sand will do the job. The sand grains are usually ground finely and shaped like tiny spheres, so they pack together tightly and create a smooth mold surface.

Another key detail is how sand casting is designed to handle imperfections. Since the process allows a bit of flexibility and shrinkage as the casting cools down, it helps prevent cracks, tears, or other defects. Manufacturers sometimes mix in clay to make the sand even stronger, helping the grains stick together more firmly.

A lot of familiar products—think automotive parts like engine blocks—are actually made using sand casting. It’s a method that blends old-school practicality with modern manufacturing needs.

2. Investment casting

Investment casting, which is often referred to as “lost wax casting,” relies on a disposable wax pattern for every single part being produced. The process begins by injecting wax directly into a mold to create the pattern, which is then carefully removed.

This wax pattern is coated several times with a refractory material and a binding agent, layer by layer, to gradually build up a durable shell.

What happens next is actually quite methodical: multiple wax patterns are grouped together on common sprues, almost like branches on a tree. Once these shells harden, everything gets flipped over and heated in an oven, which melts out the wax—hence the name “lost wax.”

It’s worth noting that these wax patterns are pretty delicate and require gentle handling, since they’re not built to withstand much pressure during the mold-making process. One nice aspect of this technique is that the melted wax can be collected and used again, reducing waste.

Investment casting has found its place in high-demand industries such as automotive, power generation, and aerospace. For instance, turbine blades are often made using this method because it offers impressive precision and repeatability, along with versatility in design and structural integrity.

3. Die Casting

Die casting is another popular manufacturing process, and it works by forcing molten metal into a mold cavity under high pressure. The majority of die-cast products are made from non-ferrous metals—think zinc, copper, and aluminum alloys though there are cases where iron-based parts are also produced.

What makes die casting particularly appealing is its ability to produce a large number of small to medium-sized parts with excellent detail, smooth surfaces, and consistent dimensional accuracy. This process is a go-to choice in situations where quality and efficiency need to go hand in hand.

4. Low-pressure casting      

Low-pressure casting is a fascinating process where molten metal gets introduced into the die from a furnace kept under slight pressure—usually around 0.7 bar.

The setup is such that the holding furnace sits at the bottom of a vertical die casting machine, so the metal moves upward, injected directly into the base of the mold. What keeps the metal in place is that steady pressure, which is maintained until the metal solidifies.

What really sets this method apart is how much control it gives over how the die fills up. Because the molten metal moves quickly and evenly through the feed lines, there’s less chance for oxides to form, and porosity is kept at bay—both common headaches in casting.

Originally, this technique found its niche in making axially symmetrical pieces, like car wheels. But there’s some flexibility built in: by using sand cores inside the die, it’s also possible to create parts with hollow sections and more complicated shapes.

5. Centrifugal Casting

Centrifugal casting is pretty clever in its simplicity it’s how we get those long, hollow, cylinder-shaped pieces, like cast iron pipes. The secret? Using the force from a spinning mold. When the molten metal is poured in, the rotation pushes it outwards against the inside surface, so you end up with a casting that’s free of voids or bubbles.

Historically, this method goes back to the de Lavaud process, which used water-cooled molds. It’s a go-to for making symmetrical pieces such as soil pipes and even heavy-duty cannon barrels, partly because you don’t need many risers (those extra features that help feed metal into the mold).

Now, when it comes to parts that aren’t symmetrical and can’t just be spun on their own, there’s a workaround. A type of centrifugal casting called pressure casting lines up several molds around a shared sprue, then spins the whole setup.

This approach is handy for things like large gear rings, too. Depending on what you’re casting, you might use a metal mold or even a sand one—the method adapts to the job at hand.

6. Gravity Die casting

Gravity die casting is a method that uses a permanent mold, where molten metal is simply poured—usually from a ladle—into the mold cavity. Unlike other techniques that rely on external pressure or force, here it’s gravity that does the job of filling the mold. Operators can control how the metal flows by tilting the die if needed.

If the final part needs any undercuts or internal cavities, these are created using sand cores that are placed inside the mold. One of the main reasons manufacturers favor gravity die casting over sand casting is the noticeably better surface finish and improved mechanical properties it offers. This is thanks to the faster cooling, which allows the metal to solidify quickly and uniformly.

While gravity die casting can produce parts at a faster rate than traditional sand casting, it does require investment in metal molds, which are costlier than sand molds. However, the process brings advantages like reduced gas porosity and the ability to achieve finer grain structures in the metal.

Post-casting cleanup is usually minimal, which means less time is spent on finishing the part. Despite the higher upfront cost for the molds, the resulting products generally have a higher and more consistent quality compared to those made by sand casting.

7. Vacuum Die Casting

Vacuum die casting takes things a step further by introducing a vacuum into the process. At Kennedy Die Casting, for example, a vacuum system pulls air out of the die cavity right before the molten metal is injected.

This helps to minimize trapped gases and keeps porosity in the finished parts to a minimum, which directly improves overall quality.

It’s important to remember, though, that using a vacuum is not a cure-all. The basics of good die design—careful planning of the cavity, runners, gates, and overflow channels—are still essential. The vacuum system acts as an additional tool to boost quality but can’t compensate for poor engineering choices in the mold itself.

8. Squeezing die casting

Squeeze casting, which some people also refer to as liquid forging, offers a unique blend of two classic techniques: permanent mold casting and die forging. The process itself is fairly straightforward yet highly effective.

It starts with pouring a measured amount of molten metal alloy into a die that has already been heated and lubricated. What makes squeeze casting stand out is that the metal isn’t just left to cool on its own—instead, it’s forged and allowed to solidify while under significant pressure.

This combination leads to castings with improved mechanical properties and a finer microstructure, making it a go-to method when both strength and precision are key requirements.

9. Lost Foam Casting

Lost foam casting (often abbreviated as LFC) is an interesting twist on traditional investment casting. Rather than using wax for the pattern, LFC relies on foam, which makes a surprising difference.

The real advantage comes from the low boiling point of the polymer foam—when the molten metal is poured in, the foam simply vaporizes, leaving behind the desired cavity.

This essentially skips the entire “melt the wax out” step of investment casting, streamlining the process and opening up new possibilities for complex shapes. It’s an elegant solution, especially when intricate details are involved.

10. Continual Casting

Continuous casting has transformed the way we produce metal profiles, especially when there’s a need for high volumes and consistent cross-sections. Here’s how it works: molten metal is carefully poured into an open-ended mold that’s both water-cooled and designed to start solidifying the metal from the outside inward.

This means a thin shell forms right away, while the inside remains molten for a bit longer. The newly solidified “strand” is slowly and steadily withdrawn from the mold—almost like pulling taffy, but on a much bigger scale. As it moves out, it can be cut to whatever length is needed, either with shears or an oxyacetylene torch.

Sizes range widely: from thin strips only a few millimeters thick and up to five meters wide, to billets and slabs much chunkier in size. In some cases, there’s even an initial hot-rolling step right after casting, before cutting to length.

Why has continuous casting become so popular? The reasons are practical: it’s more cost-effective for producing standard products in large quantities, and the resulting metal is typically higher in quality. Today, continuous casting is the method of choice for materials like steel, copper, aluminum, and lead—though steel is by far the most common, thanks to the sheer scale of global demand.

Advantages of the casting process

Casting has the following advantages over other manufacturing processes.

• It can create any complex structure economically.
• The size of the object doesn’t matter for casting.
• The casting objects have high compressive strength.
• All structure made by casting has a wide range of properties.
• This can create an accurate object.
• All materials can be cast.
• It creates an isotropic structure.
• It is the cheapest among all manufacturing processes.
• Composite components can be easily made by casting.

Disadvantages of the casting process

The disadvantages of the Casting Process are as follows.

• Dimensional accuracy: Because of shrinkage in the casting, the dimensional accuracy might be at risk. So, the designers must take care of providing the allowance to the product (Pattern) before pouring the molten metal.
• Low strength: Due to high porosity compared to a machined part.
• Post-processing: It requires Secondary machining operations to improve the surface finish.
• Lower Melting Point: Generally limited to metals of the lower melting point.
• Not suitable for low-volume production.

Applications of the Casting process

The casting process finds its way into all sorts of industries, sometimes in places you might not expect. Let’s look at some of the areas where casting really makes a difference:

• Transport: Whether it’s cars, airplanes, trains, or even ships, casting plays a key role in producing a variety of parts that keep these vehicles running safely and efficiently.
• Heavy Equipment: You’ll also see casting at work in the world of big machinery—think construction sites, agricultural fields, and mining operations. The durability and strength provided by cast components are hard to beat in these demanding environments.
• Machine Tools: From machines that cut and shape metal, to those used in plastic molding, forging, extrusion, and other forming processes, casting is often behind the sturdy frames and precision parts that make these tools reliable.
• Plant Machinery: Factories in sectors like chemicals, oil and gas, paper, sugar, textiles, steel, and power generation rely on cast parts for their heavy-duty equipment. The process allows for custom shapes and robust materials, which are essential in these tough applications.
• Defense: In the defense sector, casting helps create everything from military vehicles and artillery pieces to munitions, storage units, and various kinds of support equipment. The ability to produce complex, strong parts is particularly valuable here.
• Electrical Machines: Motors, generators, pumps, and compressors all make use of cast components. These parts are often crucial for the machines’ performance and durability.
• Municipal Castings: If you’ve ever looked closely at manhole covers, water pipes, valves, or joints in a city’s infrastructure, chances are you were seeing cast products in action. They’re built to last, even under constant use.
• Household Items: The casting process isn’t just for industry. You’ll find it in many everyday things, like appliances, kitchen tools, gardening equipment, and even certain types of furniture and fittings.
• Art and Decor: Beyond the practical, casting is also a favorite in the world of art. Sculptures, idols, ornate furniture pieces, lamp stands, and various decorative items are often brought to life using this age-old technique.

FAQs.