As more industries need better stuff, there’s also a growing need for making intricate and top-notch things. Luckily, there are various ways to create these things through casting. This allows shaping things into what we want. This article gives you a complete guide to the different casting methods.
What is Casting Process?
Casting is a way to make metal parts in the shape you want. You do this by melting the metal and pouring it into a mold. Then, it cools down and gets hard. Casting is great because it can make both simple and very detailed parts, no matter how big or small they are. If you need a lot of metal parts that are all the same, casting is perfect because it can make many at once.
Main Types of Casting Process
Following are the main types of Casting Processes:
Sand Casting Process
Sand casting is a method that is used for producing metal objects. This technique is widely utilized in large scale factories. It is especially used for manufacturing a range of items, such, as engine blocks, cylinder heads and crankshafts.
The process involves using a mold made from sand material comprising two parts known as the “cope” ( part) and the “drag” (bottom part). Molten metal is poured into the mold through a pouring cup. Left to cool resulting in the desired object. To achieve an appearance any excess metal can be easily trimmed away afterwards.
|Used to fabricate huge components||It gives a rough surface finish|
|It has the ability to be recycled||Difficult with pre-determined specifications|
|It can easily cast both ferrous and non ferrous alloys||Lower accuracy|
Gravity Die Casting
Gravity die casting, which is also called permanent mold casting, uses molds made of metal like steel or graphite, which you can use again and again to shape metal and metal mixtures. It is used for making different things like gears, gear housing, pipe fittings, wheels, and engine pistons.
First you pour melted metal into the mold, and it flows down because of gravity. Sometimes, you can tilt the mold to make sure the metal spreads out evenly. Then, the metal cools down and becomes the stuff you wanted. Unlike some other ways of casting, this method fills the mold from the bottom up. It’s faster than sand casting but can be more expensive because the metal molds cost more.
|High Tolerance||Manufacturing cost is high|
|Thin wall products could be easily made||Difficult to make complex shapes|
|Better surface finish due to rapid solidification|
Pressure Die Casting
There are two main types of pressure die casting:
Low-pressure – Low-pressure die casting is better for making large and simple parts.
High-pressure – High-pressure die casting is more popular when you need to make a lot of precise and complicated things.
They use molds that can be used again, and these molds are covered with a slippery substance. They put non-ferrous metals like zinc, tin, copper, or aluminum into the mold and push them in with high pressure. They keep the pressure high during this quick injection process to prevent the metal from getting too hard. After the process is done, they take out the casting and clean it up to get rid of any extra material. The big difference from gravity die casting is how they fill up the mold. In pressure die casting, they use high pressure to push the melted metal into the mold, and it hardens fast to make the thing they want.
|Post casting not needed||Supports only non-ferrous materials|
|It can easily run for long hours||High Tool cost|
|Molten metal cools rapidly||High investment|
Investment casting is also called lost-wax casting. It involves creating a mold from wax and filling it with metal. It allows making various products, including gears, bicycle parts, and more. This method can be expensive and labor-intensive. It’s suitable for complex or mass-produced items.
|It supports castings with 90 degree angle||High manufacturing cost|
|High Accuracy||Longer production cycle|
|Shrinkage allowed||Labor is required|
Plaster casting is like sand casting, but it uses a mixture called ‘Plaster of Paris’ for the mold. Plaster doesn’t cool the metal as quickly as sand, which is good for making precise parts with thin sections. However, it’s not ideal for really hot metals like ferrous materials. This method can make both small castings (around 30 grams) and big ones (up to 45 kilograms) using plaster molds.
|Smooth finish||Aluminum and copper alloys have limited applications|
|High Accuracy||Metals with high melting point are not supported|
|Able to cast complex shapes||Cooling time is high|
Centrifugal casting, also known as roto casting, is a way to make cylindrical parts in industry using spinning forces. Here’s how it works: they heat up a spinning mold, then pour melted metal into it. The spinning makes the metal spread out evenly under high pressure.
There are three types of centrifugal casting:
True centrifugal casting – true centrifugal casting lets the metal stick to the sides as it spins
Semi centrifugal casting – Semi centrifugal casting fills the mold using a sprue
Vertical centrifugal casting – Vertical centrifugal casting works like true centrifugal but is done in an up-and-down way.
|High yield and less waste||Only certain shapes can be made|
|Output has almost no defects||High Cost|
|Gates and risers are not needed||Skilled labor is needed|
Lost-foam casting is a bit like investment casting, but it uses foam instead of wax to make the pattern. They cover the foam with a special ceramic material by dipping, coating, spraying, or brushing. After that, they pour melted metal into the mold to make what they want. This method works for different materials like alloy steel, carbon steel, alloy cast iron, and more.
|High precision||High cost for low volume|
|Flexible design||Can cause distortions|
|Less waste||High delivery time|
Vacuum casting, as the name suggests, is a casting method where they make things under low vacuum pressure (less than 100 bar) to get rid of gas from the mold. Here’s how it works: they pour melted metal into a mold inside a vacuum chamber to prevent bubbles and air from getting trapped. This avoids the final product from having unwanted gaps. This method is used in different industries like cars, aerospace, electronics, marine, and telecommunications. It’s used to make things like chassis parts and car body pieces.
|Thin wall products can be made||Short life span|
|Low volume production is supported||High Cost|
|Improves properties of die casting||Hollowness problem|
Liquid forging or squeeze casting is a unique way of shaping metal. It combines permanent mold casting and die forging into one step. Here’s how it works: they inject a certain amount of melted metal alloy into a mold and use pressure to shape it. After that, they heat the metal part past its melting point and take it out of the mold. This method is handy for making important parts like aluminum steering knuckles, chassis frames, and nodes.
|Internal defects are eliminated||Low productivity|
|Less waste||Less flexible|
|High strength||More requirements of machining|
Continuous casting, as the name suggests, is a method to consistently make metal shapes with the same cross-section. It’s commonly used for producing steel bars and other shapes like billets, ingots, and bars. They pour melted metal into a mold that’s open on one side and cooled with water. This forms a solid surface on the outside while the metal inside is still liquid. The metal then solidifies from the outside in. Once it’s done, they can pull out continuous strands of metal. They can cut these into specific lengths using mechanical shears or oxyacetylene torches that move along with the metal.
|Low cost||Needs continuous cooling of the casting molds|
|Less wastage||Involves continuous cross sections|
|High efficiency||Need large space and maintenance|
Shell molding is a casting process where they make molds from sand that’s mixed with resin to create a hardened shell around the pattern. It’s a bit like sand casting, but the mold is made differently. This method is used to make gearbox housing, connecting rods, small boats and truck hoods.
|Semi skilled labor required||Small scale production not supported|
|No post processing needed||Size limit|
|Can cast thin walled products||Special patterns can cost more|
Steps Involved in Casting Process
Following are the main steps involved in Casting Process:
Pattern making : First you need to decide the shape of the mold to make a pattern. You can use materials like wax, sand or plastic.
Choose metal alloys : Metal castings can be made from either ferrous or non-ferrous alloys. This is important for the final casting’s intended use. Ferrous alloys comprise steel, malleable iron, and gray iron, while non-ferrous metals include aluminum alloys, bronze, and copper.
(Note : Alloys are blends of different elements chosen for their mechanical properties
Mold making : When it comes to casting, you need various types of molds. Single-use molds can be crafted from materials like sand, plaster, or ceramic shell. These have a unique manufacturing process. Additionally, patterns created from foam or wax are typically subjected to high temperatures in a kiln to prepare them for casting.
Melt and pour the alloy : This process usually begins by putting solid metal in a crucible and heating it until it becomes liquid, either with an open flame or inside a furnace. For small castings, you can pour the melted metal directly from the crucible into the mold. However, for larger castings, you might need to transfer the molten metal into a larger ladle before pouring it into the mold.
Finishing : Once the casting product has solidified, it’s taken out of the mold, and then metal surface finishing is performed. This finishing process may involve removing any excess material. This is done through scrubbing or machining.
Video on the main types of Casting
Advantages of Casting Process
- Achieves a sleek surface finish
- Accelerates production speed
- Maintains precise tolerances
- Offers cost-effective tooling and machinery
- Accommodates a wide range of sizes, up to 200 tonnes
- Works with various materials
- Allows for intricate and complex shapes
- Provides an economical means to produce diverse shapes, sizes, and mechanical properties.
Disadvantages of Casting Process
- High likelihood of defects, and in some cases, defects cannot be rectified.
- Casting does not achieve highly precise dimensions when compared to precision machining methods.
- Sand casting, a widely used casting technique, often demands significant manual labor.
Application of Casting Process
- Industries use this to manufacture various products. This includes hollow cylindrical cylinders, automotive pistons, pulleys, engine manifolds, valves, nuts, and defense equipment.
- The casting process finds applications across diverse sectors, such as aerospace, defense, automotive, railway, construction, agriculture, mining, and chemicals.
- Cast steel is a primary material for continuous forging.
- Metals like copper, aluminum, silver, cast irons (including white cast irons), aluminum bronzes, oxygen-free copper, and others undergo continuous casting.
- Metals are cast as ingots for rolling, extruding, or forging purposes, and long shapes with basic cross-sections take the form of round, square, hexagonal rods, and more.
The safety guidelines for casting include: Ensuring Adequate Ventilation, Avoiding Contact with Liquids, Wearing Personal Protective Equipment, Heating Metals in Advance, and Restricting Access to the Area.
Molding is the manufacturing process in which a rigid frame called a mold or matrix is used to shape liquid or pliable raw materials.
In general, casting materials are composed of metals or a range of materials that require longer curing times. These materials include epoxy, concrete, cement, and clay, among others.
Thus we have successfully discussed about the main types of casting process. If you have any questions, feel free to write in comments below.