Metal Casting Explained: Definition, Process and Advantages
Even as new and more advanced manufacturing processes emerge, the traditional use of molten metal stands tall as a reliable, versatile, and cost-effective method. Its suitability for mass production of simple to complex metal parts using molten metal is indispensable.
Imagine the flawless transformation from shapeless molten metal to some of the most exciting metal items on sale. The chemistry of metal and heat, coupled with human creativity is the basis of metal casting.
Innovators and engineers have used metal casting technology for many years to create items of all complex shapes and sizes. The fact that metal casting is still relevant today underlines the ingenious nature of the process.
In this post, we look at the casting industry in detail. We explore the meaning, process steps, and advantages of lost wax casting, sand casting, die casting, and all the other types of metal casting.
What Is Metal Casting?
Before we deep dive into the intricacies of metal casting and how metal is poured, let us first define it.
Cast metal manufacture is a traditional manufacturing process whereby molten metal is poured into a mold to produce a solid metal casting. With some finish, the cast metal is then ready for use.
Casting processes are thousands of years old, with various historical records showing that this practice existed in 3200 BCE in Mesopotamia. From the earliest iron casting in ancient China to the extensive use of blast furnaces in Britain in the 1800s, metal casting has come a long way.
Metal casting is a popular method for the manufacture of complex items that may be difficult to produce with other techniques. Examples of these are engine blocks, marine propellers, hydraulic pump components, and turbine blades.
What Is the Importance of Metal Casting in Manufacturing?
Through the ages, metal casting has been extensively used in manufacturing to produce a wide range of items. It is a big employer, accounting for over 200,000 jobs in the United States. You will agree with the sentiments from the American Foundry Society that “You’re rarely more than 10 feet from a casting”.
Metal casting is so important in manufacturing that technological advancement is only making the process better and more relevant. The prevalence of this manufacturing method is attributed to several factors.
Cost-effective method for complex parts
Compared to alternative manufacturing methods, metal casting is often more cost-effective. This is particularly true in large-volume production. Metal casting offers savings in terms of overhead costs, time, and raw materials. When manufacturers switch from welding and machining to metal casting, they can save as much as 50% on their production costs.
Even where multiple castings are required, the manufacturer can do this at once. Since the casting comes out of the mode in almost perfect shape, minimal effort and time are required to achieve the final desired shape and surface.
The capability to achieve thin walls and the availability of high-grade materials make the process even more cost-effective. Metal casting enables us to manufacture complex parts without the challenge of stress concentrations.
Maintains material properties
A metal casting can be stronger than a welded part because of the differences in material properties. Welded and machined parts tend to weaken as time goes by. In a foundry, alloys are created to achieve the best combination of desirable properties.
The alloy properties can be maintained for ages. This helps achieve the same measurements and shapes over and over again. Furthermore, the manufacturer can comfortably produce replicas of the product with a smooth surface finish whenever required.
Compatible with many materials
The metal casting manufacturing method is compatible with a broad range of materials. For instance, steel is a popular material for metal casting due to its durability and strength. It is used to produce pump housings and many other products.
Metals with low melting points are also applicable in metal casting. These include aluminum, copper, and magnesium. Alloys such as brass are also potential materials for metal casting. Manufacturers may want to use alloys to attain desirable properties such as strength, durability, and corrosion resistance.
For those looking for manufacturing design flexibility, methods such as investment casting and sand casting are very versatile. They are relevant in many manufacturing sectors. They are used to produce items whose shape tolerances are unlike the alternative methods.
How Dose Metal Casting in Manufacturing Work?
There are several types of metal casting methods, from sand casting to die-casting. However, the fundamental steps or process remains the same.
Let us look at the casting process in more detail below.
Steps 1: Pattern Making
A pattern in metal casting is an imitation of what will be produced when the casting process is complete. The manufacturer uses the pattern to form the cavity that will be filled with molten metal or liquid material. The pattern can be made using any suitable material, the most popular ones being metal and wood.
During the pattern-making step of the metal casting process, several pattern options are considered. A pattern could be solid, multi-piece, or two-piece. Other types of patterns that could be used are gated, sweep, match plate, and skeleton.
In this metal casting step, there are a few considerations to make. One of the most important is the potential shrinkage of the metal on cooling. To enhance the smooth flow of the molten metal into the mold cavity, sprues may be added.
Steps 2: Mold Making
With the pattern ready, it is time to take the mold material and make the mold. The mold may be reusable or designed for single use. Reusable or permanent molds are usually made from metal. Permanent molds are typically made from metal. Popular materials for single-use molds are sand molds and plaster.
Given the different properties of casting metals, the single-use and reusable molds must be designed with several considerations in mind. The complexity of the anticipated product can also determine the mold casting process.
Refractory material is also applied to minimize abrasion and heat effects.
Steps 3: Core Making
In cases where the mold casting has an opening, the next step of the metal casting process would be the creation of a core. A core is placed in such a way that no molten material fills the space.
Steps 4: Selecting the Cast Metal
Metal castings are typically products of alloys (ferrous and non ferrous metals). There are ferrous options such as grey iron and steel. The non-ferrous alloys include copper and bronze. Considering your product requirements, choose the appropriate metal from the numerous options.
Steps 5: Melting the Metal
The metal, in solid form, is put in a crucible ready for heating. Heating the solid metal creates a liquid metal that is ready to be poured into the permanent mold or expendable mold. The most common heating options are furnace and flame.
Steps 6: Pouring Molten Metal
At this point, everything is set for the pouring of the molten material into the mold cavity. Remember that there are different types of metal casting processes. Investment casting or lost wax casting method uses a wax pattern. Other casting processes are centrifugal casting, die casting, sand casting, and plaster casting.
Others are vacuum casting, lost-foam casting, and gravity die casting methods.
After pouring molten metal into the mold, it is important to wait until the liquid metal cools. A variety of cooling methods exist for permanent mold casting. These include water cooled mold designs.
Steps 7: Removing the Part from the Mold
As the part is being removed from the mold, there are several considerations to make. For instance, in the sand casting process, one may need to shake or vibrate the setup. This helps get rid of sand around and within the cast components after the casting processes.
Steps 8: Finishing
You do not have the final product from sand casting and others until you have performed the surface finish operations. One of the surface finish requirements is trimming. The casting has excess material that should be removed.
The Common Materials Used in Casting
Because of different design requirements, cast parts have varying requirements. Some parts need more weight, while others need to be light.
The preferred metal for a particular cast part may not be suitable for another one. Therefore, it is important to note these differences before you contact a supplier for metal casting items. You want to go with the most optimal material for the best casting results.
Here are the most common metals used in metal casting for manufacturing:
Aluminum
As the third most available material, aluminum is often a popular consideration in manufacturing processes. Fortunately, this material works excellently in all types of metal casting – sand casting, die casting, pressure die casting, and others.
Before the process of casting aluminum can begin, bauxite must be cleared of all the impurities. A special chemical process comes in handy here.
The properties of aluminum are good strength, excellent electrical conductivity, corrosion resistance, and visual appeal. It doesn’t spark and contains no toxins. With its high thermal conductivity, aluminum is perfect for processes where fast heat dissipation is necessary.
Aluminum casting presents several advantages due to its chemical and physical properties. It is a versatile material that can be cast into whatever shape or size. Its lightweight nature is also attractive for products that need to be lighter than steel or iron. Despite being lightweight, aluminum provides durable castings because it has incredible strength. At our company, we also like the recyclability of aluminum casting.
For these qualities, aluminum casting works for many sectors. The automotive, food & beverage, aerospace, and appliance sectors are just examples. For instance, in automotive, engine blocks are made from aluminum casting.
Copper alloy
Copper has been available for human use for over 10,000 years. There are numerous deposits of copper in the Earth’s crust. However, only a small portion of this can be drawn out cost-effectively.
The metal has excellent electrical and thermal conductivity, only second to silver. That’s why you will find it extensively used in industrial and residential wiring projects. The corrosion resistance of the casting material is another notable feature. Pure copper may be soft, but copper based alloys can be significantly strong.
When the raw copper is combined with other materials, it produces alloys such as bronze and brass. Usually, the alloys have better physical and chemical properties.
Copper alloy castings make perfect products for items such as bearings, fittings, and gears. Like the raw aluminum, the alloys have suitable properties for these products. High thermal conductivity and corrosion resistance are obviously on top of the list.
Steel
Steel metal casting plays a big role in the manufacturing of important items in industries. The process has a rich history of providing manufacturing efficiency. Steel is renowned for durability and strength, so the casting products last longer and bear heavy loads.
Steel metal casting has many advantages, but it also comes with some challenges. In steel casting, temperature regulation is necessary. The specialist handling the process must ensure that the molten steel remains at the required temperature throughout the process.
Even the smallest temperature deviations can introduce flaws in the cast item. These flaws can bring significant challenges to the final product, including lost strength. Related to this challenge is shrinkage, which results in dimensional inaccuracies.
The specific properties of the cast steel depend on a wide range of factors and as intended for the planned application. But generally, cast steel is hard. That means it is capable of withstanding abrasion. The exact hardness depends on the percentage of carbon in the cast steel. Cast steel is also strong, and this element also depends on the carbon content.
Cast steel can be either alloyed cast steel or carbon cast steel.
Iron
Three versions of iron metal are commonly used in cast iron manufacture: White iron, grey iron, and ductile iron. Gray iron is the most common of the three, particularly in industrial metal casting. It has excellent density and strength. It is a versatile material. Its properties can be adjusted during the casting process to suit different industrial uses.
Then there is white iron, which is more expensive but more versatile and durable. For projects that require machining and welding, white iron is a more suited option. Specialized industrial projects will most likely use this metal casting.
Even stronger and more versatile is ductile iron. It shrinks the least after cooling and has a higher strength-to-weight ratio. As the name suggests, this metal is very ductile. The metal can stretch thin and still retain its pliability and strength. For these properties, it is popular for various industrial applications.
Magnesium
Magnesium is a lightweight material that finds use in many manufacturing applications. Casting alloys of this metal is popular when a top consideration of a product is low weight. Magnesium casting is a cheaper option compared to aluminum casting.
Magnesium castings can be manufactured by virtually any traditional casting technique. However, you still need to consider a few factors when choosing a casting method for aluminum casting. The factors include the number of products, complexity of the design, use of the part, and so forth.
Apart from the lightweight advantage, magnesium casting is also highly available and easier to machine. It is also easier to die-cast.
Advantages and Disadvantages of Casting
Here are the advantages of metal casting:
Easier to create complex shapes
Metal casting is an ideal manufacturing method for complex parts because it is characterized by design flexibility. Castings can be available in different shapes and sizes. It doesn’t matter if a design has internal hollow sections; metal casting is capable to provide all that.
The size of the part is also not a concern. It could be too large or tiny, but the quality of the results doesn’t change.
Higher-quality product
Metal casting is renowned for producing items with incredible quality compared to many other manufacturing methods. Specifically, the compressive strength in the products is unmatched. As long as the foundry is of the best quality, even metal casting with thin walls will be sturdy and durable.
Recyclable Products
Many manufacturing companies that use metal casting often engage in recycling, either individually or in partnership. That’s a great way to further the green agenda by minimizing waste. On the economic front, recycling is a great way to reduce power consumption as compared to alternative manufacturing methods. Businesses can make more profits by option for the recyclable metal casting manufacturing.
More Cost-Effective
Metal casting is largely cost-effective. This manufacturing method is less complicated and uses less resources. Many other manufacturing methods use a lot of energy and time. With casting, you only need to pour molten metal in a mold and wait for it to cool.
Superior surface finish
Compared to forging and other manufacturing methods, metal casting results in a smoother surface finish. The surface flaws in this method are minimal. Whatever surface imperfections are there can be removed easily and fast with some grinding or painting.
A few disadvantages:
The accuracy and dimensional consistency of the parts can be poor
Can produce toxic emissions
Its manual nature can endanger workers
Can be costly where expendable molds are involved
Applications of Casting
As seen above, metal casting presents many advantages in manufacturing. That explains why many industries use this manufacturing method extensively. Here are some industrial applications of metal casting:
Automobile Casting
The relationship between metal casting and the automobile industry is strong and olden. Many automobile assemblies and components are metal casting. A good example is the engine block. It is typically aluminum alloy or cast iron. Zinc and magnesium castings are also increasingly becoming part of automobile manufacture. Metal casting in automobile casting presents several benefits including fuel efficiency and reduced emissions.
Plant Machinery
Plant machinery need to be rust and chemical resistant. On top of that, the machinery should be lightweight for fuel economy. A high strength-to-weight ratio is also desirable. For these reasons, metal casting is often picked for these applications.
Titanium casting is prominent for plant machinery, where it is used to manufacture pressure vessels, filters, and many other plant components.
Electronics Casting
The electronics industry has built a strong affinity to metal casting over the years as its variety of products grows. This industry needs parts and components that are lightweight and durable. Metal casting offers these attributes, for instance, in the form of aluminum and magnesium casting for telecommunication equipment. Popular electronic casting items include smart watch, camera parts, and antenna components.
Medical Metal Casting
The hygiene, lightweight, and strength requirements of medical equipment calls for a suitable manufacturing method. Metal casting is a popular option for these applications. Aluminum and stainless steel castings are common feature for this industry.
The need for prompt manufacture and low volumes makes metal casting a perfect method for medical metal items. Metal casting, when done by an expert, can also meet the other strict requirements of this industry. Common products in this category include stethoscopes, pacemakers, and pumps.
In Summary
We have learnt the basics of the metal casting process and reviewed the relevance of the process in various industries. The capabilities of metal casting in different applications make it a reliable manufacturing process.
Since this is not exhaustive, we are ready to attend to any of your queries about the metal casting processes. We are the epitome of the relevance of metal casting for modern needs. Our team continues to offer clients the quality and efficiency that defines metal casting. Call us today for the most reliable metal casting services.
Author
Gavin Leo is a technical writer at Aria with 8 years of experience in Engineering, He proficient in machining characteristics and surface finish process of various materials. and participated in the development of more than 100complex injection molding and CNC machining projects. He is passionate about sharing his knowledge and experience.