Metal Casting

Metal casting has been around for thousands of years and has been used for making jewelry, tools, sculptures, and much more. The first ever known metal casting appeared in 3200 BCE in Mesopotamia; It was a frog made from copper. Later, around 2000 BCE, people discovered iron, and that changed the way of metal casting ever since.

Metal casting is the process in which a metal or alloy is melted down into a liquid form and poured into a mold. The mold is cooled and the metal solidifies into whatever shape of the mold cavity. Once cooled, the newly shaped metal is referred to as a cast or ingot. The cast is removed from the mold and is cleaned up, removing any rough edges. There is an abundance of different types of casting methods including: sand casting, gravity die or permanent mold casting, pressure die casting, investment or lost wax casting, plaster casting, centrifugal or roto casting, lost foam casting, vacuum casting, squeezing casting, and continuous casting. It is safe to say that as this industry grows, more casting processes will become available.

Whether you are a professional metal caster or a new hobbyist, we will explain to you the metal casting process and all the metal casting materials and metal casting mold supplies that you will need required for making casts.

Why consider Metal Casting for your next project?

There are many reasons why you should consider metal casting for your next project.

Cost Effective

If you’ve ever had to cut, weld, and shape some metal together to get the final result you’re looking for, you are aware of how much time is needed, and wasted, to get things looking right. Because casting molds (in most cases) can be used over and over again, you do not have to worry about purchasing another mold after every project. It also saves on costs because each cast is essentially a carbon copy of the other, you don’t have to worry about going back to fix something, or worry about two identical pieces coming out different sizes

Structural Strength

The strongest objects are those that are solid (typically). With metal casting, you do not need to worry about seams or welded connections. In metal casting the cast is one solid chunk making it extremely durable and strong.

Variety of Materials and Properties

There are a variety of different alloys that you can choose from including Aluminum, Brass, Copper, Gold, Iron, Nickel, Silver, Steel, Zinc, and many others. Depending on the material you choose, you can get a wide array of properties with your cast including variations of hardness, strength, ductility, wear resistance, corrosion resistance, machinability, weldability, high and low temperature properties.

Shape Complexity

A specialty of metal casting is the ability to pour large, complex, and hollow shapes. With metal casting, there are no seams, and nothing needs to be welded together. What you pour is what the final product will be, minus some surface imperfections that will need some cleaning up.

Types of Metal Casting

As mentioned above, there is no shortage of different ways to make metal castings. Some of the various metal casting methods include:

SAND CASTING

Sand casting is a versatile and commonly used metal casting method. This process can be used to cast any type of alloy, ferrous or non-ferrous, and is commonly used in the mass production of automotive parts like engine blocks, crankshafts, and more.

The mold is made up of silica-based material like natural or synthetic sand, which form the soft mold surface. Molten metal gets poured into the mold and is left to solidify and take its finishing shape. Once cooled, the cast is touched up, cutting off excess metal.

Pros & Cons

Some pros of Sand casting are its ability to cast both ferrous and nonferrous materials, its ability to be recycled, and the ability to process metal with very high melting points, like titanium. Some of the cons of Sand casting are that it has a lower level of accuracy compared to some other processes and generates products with a rough surface finish.

GRAVITY DIE / PERMANENT MOLD CASTING

Gravity Die or Permanent Mold casting is the process where you use a reusable mold. The mold is made from metal, like graphite or steel. This metal casting process is most commonly used for creating various working parts, like gears or gear housing, pistons, wheels, and more. Because the mold is made of a metal, we are able to cast a lot more materials such as cast iron, lead, aluminum, zinc, and more.

This process works from the bottom up to fill the mold (this is much different than other metal cast processes) and it can be tilted to control the filling. Gravity Die/Permanent Mold casting has a higher production rate, but it is generally more expensive due to the mold materials.

Pros & Cons

Some pros of the Gravity Die/Permanent Mold casting process are that it can produce very thin products, it produces high accuracy products, and delivers better exterior quality due to rapid solidification. Some of the cons of this casting process include higher manufacturing costs and casting complicated objects is more difficult.

PRESSURE DIE CASTING

There are two types of pressure die casting: High-Pressure Die casting and Low-Pressure Die casting. Low-Pressure Die casting is used for the large and simple part production and is the preferred over High-Pressure Die casting because it is a safer process. High-Pressure Die casting is a popular choice for mass production of complex parts that require high precision.

Non-ferrous metals like aluminum, zinc, copper, etc. are put into a reusable mold and pressure is maintained through the rapid injection process, and this process prevents the metal from hardening. Once hardened, the cast is extracted, and excess metal is removed.

Pros & Cons

Pros of the Pressure Die casting process are faster production rates due to rapid cooling, good product quality, and the process can last longer without the need to replace the die as soon. Cons of this process include higher expenses, it can only be used with nonferrous material, and is not used for structural parts because mechanical properties cannot be guaranteed.

INVESTMENT / LOST WAX CASTING

Investment or Lost Wax casting is an expensive and labour intensive process and can be used for mass production or for complex metal castings. The process works by using a wax pattern with refractory (heat resistant) material and a binding agent to create and shape a ceramic mold. The molten metal is poured into the mold and follows the same process as other castings. Investment / Lost Wax casting can be used to make gears, jewelry, bicycle bases, and other parts.

Pros & Cons

Pros of the Investment/Lost Wax casting process include producing thin-walled objects with high surface quality and accuracy and can be used for difficult to melt metal, like steels. Cons of this process include expensive costs for molds, production time takes longer, and more on hand labour is required.

PLASTER CASTING

Similar to Sand casting, Plaster casting uses a mold made from a blend called “Plaster of Paris”  Plaster of Paris is a quick-setting gypsum plaster that consists of a fine white powder called calcium sulfate hemihydrate.

Plaster molds cool casts at a much slower rate compared to Sand casting. It is this slow cooling process which assists in obtaining high accuracy parts. This casting process is not suitable for high temperature ferrous metals.

Pros & Cons

Pros of Plaster casting method include a smooth exterior finish and high accuracy, as well as creating objects with thin walls. Cons of this process include higher costs, longer cooling times, and it is not suitable for alloys with high melting points.

CENTRIFUGAL / ROTO CASTING

Centrifugal or Roto casting is specifically for manufacturing cylindrical parts with circular forces. This casting process uses a preheated spinning die, where the liquid metal is poured in. It is the centrifugal forces that help distribute the molten metal at a high pressure.

Centrifugal or Roto casting produces parts that rotate like bush bearings, washers, or piston rings. This process helps reduce defects in the final product but is not suitable for all types of metals.

Pros & Cons

The pros of Centrifugal or Roto casting include producing products with almost no defects and it reduces waste and improves yield. Cons of this process include the requirement of skilled labourers, high costs, and produces very specific shapes.

LOST FOAM CASTING

Lost Foam casting is similar to Investment or Lost Wax casting, the difference is that one uses wax and the other uses foam. The rest of the process is similar; the mold gets coated with a refractory ceramic and the liquified metal is poured in.

This casting process can be used with a variety of materials such as various steels and ferrous alloys. Lost Foam casting can mass produce materials and generates high accuracy pieces, but is not ideal for low volume production as the molds are expensive and labour intensive to produce.

Pros & Cons

Pros of the Lost Foam casting process include the manufacturing of high accuracy casts as well as clean production. It is also economically efficient for large volume production. Cons of this process include high costs for low volume production, longer delivery time, and low strength of the cast.

VACUUM DIE CASTING

Vacuum Die casting is the process in which molten metal is poured into a mold cavity. This mold cavity is kept inside a vacuum chamber, which helps to eliminate air pockets and gas bubbles. The vacuum chamber reduces the amount of trapped gasses while the molten metal is injected into the mold cavity.

Vacuum Die casting is a popular process in industries like automotive, aerospace, telecoms, and more.

Pros & Cons

Vacuum Die casting pros include improved mechanical properties and surface quality, the ability to weld and heat treat products is an option, it is suitable for low volume production, and it removes air pockets at beginning stage of production. Cons of this process include short mold life and high tooling costs.

SQUEEZING CASTING

Squeezing casting is a hybrid metal cast process that combines a permanent mold, and die forging (die forging is the process of shaping metal by hammering or pressing between flat or simple curved dies). A specific amount of liquid metal is inserted into the die and pressure is applied to form it.

This casting process merges the benefits from metal casting and forging. When high pressure is applied during the cooling process, it helps prevent shrinkage and other defects. Because of specific instrument requirements, it is not as commonly used as other metal casting processes.

Pros & Cons

Pros of the Squeezing cast process include preventing casting cracks, no wasted materials, and it eliminates internal defects. Cons of this process include lower production rates, high machining requirements, and it requires accurate controlling, which slows down the production process.

SQUEEZING CASTING

Squeezing casting is a hybrid metal cast process that combines a permanent mold, and die forging (die forging is the process of shaping metal by hammering or pressing between flat or simple curved dies). A specific amount of liquid metal is inserted into the die and pressure is applied to form it.

This casting process merges the benefits from metal casting and forging. When high pressure is applied during the cooling process, it helps prevent shrinkage and other defects. Because of specific instrument requirements, it is not as commonly used as other metal casting processes.

Pros & Cons

Pros of the Squeezing cast process include preventing casting cracks, no wasted materials, and it eliminates internal defects. Cons of this process include lower production rates, high machining requirements, and it requires accurate controlling, which slows down the production process.

Common Metals for Casting and their Melting Point

There are many different types of metals and alloys out there to cast. Some of the most popular ones, and their melting points are found below.

• Aluminum – 661 °C (1221 °F)
• Brass – 965.5 °C (1700 °F)
• Copper – 1084 °C (1983 °F)
• Gold – 1064 °C (1948 °F)
• Iron – 1538 °C (2800 °F)
• Nickel – 1455 °C (2651 °F)
• Silver – 961.7 °C (1763 °F)
• Steel – 1399 °C (2500 °F)
• Zinc – 419.4 °C (787 °F)

Metal Casting Mold Supplies and Tools

MELTING FURNACES

Melting furnaces are an essential part of the metal casting process. They produce the required heat needed to melt the alloy down into a liquid form. There are different types of melting furnaces for casting, each uses a different technology.

Cupola Furnace

The Cupola furnace is one of the oldest melting furnaces still used today. The Cupola furnace works by lining the inside with clay, bricks, or blocks that protect the inside of the furnace from higher levels of heat. Several layers of ferrous alloys, limestone, and coke are put in the furnace. The sedimentary rock reacts with the metal and causes impurities to rise to the surface.

Induction Furnace

An Induction furnace uses an alternating electric current to apply heat required to melt the metal. This process is much more common in global foundries as it is more energy efficient than a Cupola furnace.

Because the furnace uses induction rather than combustion, the thermal energy required to melt an abundance of metal is quite lower and therefore cost effective.

Open Hearth Furnace

Open hearth furnaces are used to melt nonferrous metals in smaller amounts. It works by using natural gas or heavy oil to create heat and turn the metal to a liquid. This furnace makes use of wasted heat, by redirecting furnace fumes through stonework, for various purposes. Open Hearth furnaces are mostly used in industrial applications as an oxygen based or electric arc furnace.

CRUCIBLES

Crucibles are heat resistant containers used to hold your metal during the melting process. Crucibles can come in a huge variety of materials, shapes, and sizes. The below crucibles are commonly used for casting and may be good options to consider if you are looking to metal cast at home.

Porcelain Crucibles

Porcelain crucibles are made from high purity clay and are designed to withstand unexpected temperature changes without cracks or warping. Porcelain crucibles are typically low in cost, have good chemical and acid resistance, and come in a variety of sizes.

Ceramic

Ceramic crucibles are also made from a high purity clay and are great for casting smaller pieces. They can melt a variety of different alloys and can melt precious materials up to approximately 1200 °C

PTFE

PTFE Crucibles are a good substitute for Porcelain crucibles because they have good surface finish, create low friction, have a high working temperature, have corrosion resistance and more. These crucibles are compatible with cryo (sub-zero) temperatures.

Graphite

The Graphite crucible is another commonly used crucible for melting precious metals. Graphite crucibles are thermally conductive, have a high temperature resistance, and can handle the strain of rapid heating and cooling.

MOLDS

Molds can be made up of an infinite number of materials, however, the materials used will dictate the types of liquid metal or material that you can put into it. There are various types of casting processes out there, and some of the mold materials used can include:

• Ceramic
• Graphite
• Various steels
• Clays
• Sand
• Wax
• Many more

Some of these materials are used together to create the molds, for example, sand and clay are mixed together in the Sand casting process.

Important Tools and Gear for Metal Casting

We have already talked about some of the major tools/gear you will need for metal casting, including your material to melt, crucibles, furnaces, and molds. Some of the other tools and gear that you should always have on hand include:

Safety Gear

Safety gear should be one of your top priorities when metal casting. You will want to make sure that all of your gear is heat resistant since you are working with extremely high temperatures. Some gear to make sure you have includes: eye goggles, gloves and sleeves, an apron, and proper foot wear.

Tongs

Tongs are a must when it comes to handling anything heated. Make sure you use proper steel tongs to help you hold hot objects or to remove the crucible from the furnace.

Ventilation

You will want to make sure your workspace has proper ventilation. Proper ventilation is important for several reasons including helping hot air and fumes escape and letting potentially harmful fumes escape instead of inhaling them.

Heat Resistant Workspace

Because you will be working with a variety of extremely hot tools and objects, it is important that your workspace is heat resistant. For example, after you remove your scalding hot crucible from your furnace with your tongs, where will you put either tool? Once you pour the metal into your mold, you will need a space for your crucible as well as your tongs. These are things to consider before beginning your project.

Research

Nobody should be performing at-home casting without the proper knowledge and training. Metal casting can be a rewarding hobby but is also quite dangerous. We recommend learning from someone who has previous foundry or metal casting experience. It is also beneficial to read some books and watch some videos on at-home casting.

In conclusion

Whether you are looking for metal casting information for your own production at home, metal casting information for personal knowledge, information about metal casting mold supplies or materials for molds, or different casting processes, the above information, paired with your own research, can provide all kinds of useful tips, tricks, and data that you weren’t aware of.

If you would like to learn more about metal casting at home, what a foundry is, or who some of the top metal casting companies in Canada are, visit Mira Alloy Steel’s website www.miraalloys.com.