Casting

 What is Casting?

Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Casting materials are usually metals or various time setting materials that cure after mixing two or more components together; examples are epoxy, concrete, plaster and clay. Casting is most often used for making complex shapes that would be otherwise difficult or uneconomical to make by other methods.Heavy equipment like machine tool beds,ship's propeller etc. can be cast easily in the required size rather than fabricating them by joining several small pieces.

What is the History of Casing?
By the time molding reached the Greeks and Romans, it had become an artform used to cast bronze statues using a hollow wax casting. Each part of a piece was cast separately. The core of the mold was made of clay and covered with wax followed by a layer of clay that was heated to melt the internal wax, which was heated a second time to burn out the remaining wax. Once the mold was stable and prepared, the molten metal was poured into the area where the wax had been removed, a method that is similar to modern day investment casting.

Artisans of the Renaissance period were fascinated by the works of the Greeks and Romans. They continued and perfected the casting process with improved molds made from wood, terracotta, or plaster. The most difficult part of the process was the creation of the mold to produce a correctly proportioned form.

The present use of casting to produce tools, bowls, and other practical items was begun in China around 1000 BCE. Using iron, the Chinese mass produced farm tools and weapons. The technique did not reach European cultures until several centuries later and was used to make cannon, cannon balls, and bullets. With the advent of the industrial revolution in America and Europe, casting became a standard manufacturing process much like it is today. As new metals were discovered and techniques improved, the products produced were of higher quality and endurance. Today, a variety of casting methods are used to make everyday items for commercial and industrial use.

With the advent of the industrial revolution in America and Europe, casting became a standard manufacturing process much like it is today. As new metals were discovered and techniques improved, the products produced were of higher quality and endurance. Today, a variety of metal casting methods are used to make everyday items for commercial and industrial use.

The evolution of metal casting took place over several thousand years. As methods for heating and melting metal improved, casting processes rapidly improved. The first metal to be cast was gold, due to its malleability and low melting point. Of the many original metal casting, the oldest to survive is a copper frog from 1500 BCE. China added to the advancement of casting with the discovery of sand casting and iron or pig iron as it was known.

Several events during the first industrial revolution significantly impacted the growth and development of casting. In 1809, A G Eckhart introduced centrifugal casting as a method for evenly distributing the molten metal by rotating the mold. In 1837, Jarvis Adams introduced the first casting machine, which was used to produce letters for printing presses. In 1856, Sir Henry Bessemer discovered that blowing oxygen into molten metal removed excess carbon and impurities to make pouring molten metals easier.

What Are the Different Types of Casting?

The basic methods from ancient times have been transformed into a vast array of casting techniques designed for specialized and specific purposes. Each of the different processes can produce quality parts and have manufacturing benefits. An understanding of the advantages and disadvantages of each method can help in choosing a method designed to meet individual production requirements. Some of the popular kinds of casting processes include sand, die, investment, and plaster. The basic principles of each method may seem similar. How the processes are completed and the quality of what they produce differs greatly.

1. Sand Casting
The versatile metal forming technique of sand casting uses non-reusable sand molds to produce intricate metal castings. It's an essential method for creating metal parts in various sizes, ranging from ounces to tons. This technique is indispensable in many different industries because it excels at shaping alloys with high melting temperatures, such as: steel, nickel, and titanium. Inexpensive and recyclable materials are combined to make up molding sand with exceptional heat resistance. Silica is the preferred casting sand, though chemically bonded systems and green sand are also used. The effectiveness of the mold in maintaining its shape and producing high-quality castings depends on key characteristics like strength, permeability, and flowability. To learn more, see our guide on Sand Casting Manufacturing. A sand casting diagram is below:

2. Die Casting (Metal Die Casting)
Die casting is a precision-focused manufacturing process that involves melting a metal with low melting point and injecting it into a long-life die-casting mold. These steel molds, which are created using cutting-edge techniques like CNC machining, guarantee high levels of accuracy, precision, and repeatability when creating metal components. The process has a long history that dates back to the 19th century. It has developed into two separate procedures: hot chamber and cold chamber die casting. Based on their different melting points, each process can handle a variety of materials, including: aluminum in cold chamber casting and alloys of zinc, tin, lead, and magnesium in hot chamber casting. Die casting finds extensive use in industries ranging from consumer and automotive products to aerospace components, making it an indispensable part of modern manufacturing. To learn more, see our guide on What is Die Casting Used For.

3. Investment Casting
Investment casting, a meticulous method, crafts ceramic molds around wax patterns, in order to serve as encasements for molten metal. Multiple wax patterns can be melted onto a gate system, and then a layered casing is created by submerging the pattern(s) in slurry and sand. After the wax is removed, molten metals like stainless steel or aluminum are poured in to create intricately detailed copies. Investment casting efficiently creates complex parts that are difficult for other processes to produce; the advantages include: undercuts, fine detail, and smooth finishes. Investment casting has developed from its ancient roots to modern applications to become an essential technique used in a variety of industries, preserving fine craftsmanship and enabling effective large-scale manufacturing. To learn more, see our guide on What is Investment Casting.

4. Gravity Die Casting
The time-tested metal casting method known as gravity die casting uses gravity to introduce molten metal into a mold's cavity. This approach, which has roots in antiquity, offers simplicity and economics. Manufacturers coat the cavity, melt the metal, pour it in, and then wait for the metal to solidify. The process uses automatic or manual machines. Positive mechanical characteristics, lower costs, and improved finishing are all advantages. The drawback of gravity die casting, however, is the length of time required to make intricate parts. Despite technological advancements, this seemingly crude method is still effective for smaller parts, finding use in a variety of applications including: kitchenware, lighting, and automobiles. Alternatives like aluminum die casting and sand casting are preferable for complex, high-volume production.

5. Continuous Casting
Continuous casting creates uniform, fine-grained, solid shapes with superior physical properties by quickly cooling molten metal inside a vertical or horizontal mold. This technique minimizes contaminants while maximizing yield because it uses gravity to ensure a steady flow. Although various configurations like squares and hexagons can be made, tubes and solids are the most typical shapes. When the metal has cooled after entering the mold and reached the desired length, it is continuously extracted. Continuous casting excels at producing high-density, pressure-resistant products for applications requiring precision and structural integrity. While continuous casting provides benefits like effective stock utilization and dimensional consistency, mold costs and suitability for particular alloys and quantities should be taken into account.

6. Shell Molding
A thin mold is made around a heated metal pattern as part of the precision casting process known as shell molding. Dry silica sand combined with a thermosetting resin forms a shell—that is about 6 mm thick—around the pattern. This shell is then dried, stripped, and joined to form a cavity for pouring molten metal. For the mass production of thin-walled castings, shell molding is the best option because it offers dimensional accuracy and a superior surface finish. Despite being more expensive than green-sand molding, it produces metallic patterns with high-quality results that guarantee intricate details and reliable results.

7. Lost-Foam Casting
In lost-foam casting, molten metal is poured into a foam mold (that evaporates during the pour) which is encased in sand. The mold is made of carved, machined, or injection-molded polystyrene foam. The waste gas can escape into the sand because the ceramic refractory coating is made permeable to a degree. The lost-foam casting process allows for complex shapes and thin walls at a lower cost and with less lead time and machining requirements than many other casting methods. Complex CAD designs and constrained part sizes, however, present difficulties. This process is used by a variety of industries, including: the arts, defense, and automotive, to produce a wide range of parts, including circuit boards, sculptures, and automobile components.

8. Pressure Die Casting
Modern metal processing methods like high-pressure die casting involve quickly and rapidly filling a mold with molten metal to create castings. It boasts strong mechanical properties, minimal machining, high production efficiency, and excellent surface finish. Key process parameters include: time, temperature, speed, and pressure. Filling capacity and specific pressure have an impact on compactness. Mold temperature has an impact on cooling speed and surface quality. The manufacturing of toys, appliance parts, and automotive housings are just a few examples that make use of pressure die casting.

9. Centrifugal Casting
The centrifugal casting method, also referred to as roto casting, is used to create thin-walled cylinders from materials like metal, glass, and concrete. It produces a fine-grained casting with rotational symmetry by rapidly rotating a permanent mold while pouring molten material. Instead of producing custom-shaped parts, the centrifugal casting method is often employed to produce standardized stock materials for further machining. It was created in 1852 by Alfred Krupp and is used to make things like pipes, flywheels, and cylinder liners. A semi-centrifugal casting diagram is below.

10. Permanent Mold Casting
Permanent mold casting is a method of casting metal that produces accurate, high-quality castings using reusable molds made of materials like steel or iron. It is widely used in sectors like automotive and aerospace that demand complex shapes, large volumes, and superior mechanical properties. Cost-effectiveness, fine-grained structures, smooth finishes, and intricate designs are some of its advantages. Initial costs, a lack of material compatibility, and problems with heat transfer are obstacles. Innovations include CAD, hybrid processes, and 3D printing for making molds. Applications benefit from improved durability, accuracy, and customization in the automotive, aerospace, and medical industries. To learn more, see our guide on Permanent Mold Casting.

11. Vacuum Casting
Vacuum casting, also known as polyurethane casting or urethane casting, uses silicone molds to produce rubber and plastic components in a vacuum. This adaptable method creates bubble-free castings with smooth surfaces by mimicking injection molding. Rapid prototyping and low-volume production of complex parts benefit the most from its use. Numerous resin options are available for vacuum casting, which also has uses in the automotive, aerospace, and product design verification industries. Vacuum casting has advantages in terms of flexibility and cost-effectiveness, but it's important to take mold wear and shrinkage rate into account. The ability to produce intricate features and additive manufacturing are examples of innovations.

12. Low-Pressure Casting
Low-pressure die casting (LPDC) is a metal casting process in which molten metal is poured into a die-cast mold at low pressure, typically 20 to 100 kPa. This method continuously fills the die cavity to account for volume shrinkage during solidification, maintaining high accuracy. The castings are pure due to LPDC producing little slag and less oxidation. LPDC is particularly adept at creating intricate geometries with sharp contours and smooth surfaces. It has limitations in the production of thin-walled parts and slower cycle times, despite its benefits in accuracy and formability. Automotive parts like cylinder heads, blocks, and wheels, as well as everyday kitchen appliances like pressure cookers, are just a few examples of the many applications in which LPDC can be used. To learn more, see our guide on Low-Pressure Casting.

13. Squeeze Die Casting
Squeeze die casting, a combination of casting and forging processes, uses high pressure to solidify molten metals between hydraulic press plates. It produces nearly net-shaped casting that is almost pore-free and highly dense. The two primary types, direct and indirect, each have unique advantages. Indirect casting is similar to high-pressure die casting, whereas direct casting involves pouring metal into the die and pressing it under pressure. The process results in improved mechanical properties, shorter production cycles, and better metallic properties. Material selection varies, with aluminum, magnesium, and copper as common choices. Squeeze casting finds applications in automotive parts, aircraft components, and more.

14. Plaster Casting
Plaster casting, also known as plaster mold casting, creates molds using a gypsum mixture and additives. A rubber or metal pattern coated with anti-adhesives serves as the mold's basis. The mold is created by pouring, setting, and removing the pattern from the plaster. The plaster is removed after the metal has cooled after being poured into the mold. It allows for intricate parts and provides precise shapes with little scrap. Plaster molds produce smooth surfaces, are disposable, and work best with non-ferrous metals. Applications include: prototypes, short-run aluminum/zinc production, gears, valves, ornaments, and lock components.

What Is the Process of Casting?
The casting process, specifically sand casting, involves the following steps:

1.Place the mold pattern, which determines the size and shape of the casting, in the sand. The sand (which includes additives) will take the shape of the pattern.
2.Establish a gating system, consisting of a pouring cup and gates, to direct the molten metal into the mold cavity.
3.Remove the mold pattern from the sand once the sand has taken its shape.
4.Pour the molten metal, heated to the appropriate temperature, into the mold cavity through the gating system. The metal can be one of many elements or alloys such as: iron, steel, aluminum, and bronze.
5.After pouring, the molten metal is left to cool and solidify within the mold. The cooling time varies depending on the type of metal used.
6.Once the metal has cooled and solidified, open the mold to remove the newly formed metal casting. The mold patterns are typically reusable, but the molds themselves need to be remade for each casting.

What Casting Materials are Used in the Casting Process?
In the metal casting process, different metal parts have different requirements and standards, such as strength, durability, appearance, and complexity. The list of specifications requires that the correct metal be chosen for a part to perform properly. The selection process necessitates an understanding of the properties and characteristics of certain metals.

Aluminum
Alloys of aluminum are very castable with a high level of machinability and lower cost. The natural properties of aluminum make it ideal for a wide range of applications. Aluminum is cast using all of the different casting methods with the parts being produced used for industrial and commercial products.

Carbon Steel
Carbon steel has a high level of machinability and weldability but always retains its toughness. Castings made of carbon steel are able to operate in conditions with high pressure where wear resistance and strength are required. The mechanical properties of carbon steel are determined by the amount of carbon it contains with higher percentages making the steel harder and stronger. Carbon steels with low to medium carbon are cast using investment casting.

Copper Based Alloy
Copper is a highly malleable metal that has been cast for centuries. It is never cast in its pure form since pure cast copper can have porosity problems. Common copper alloys that are cast are C80000 up to C9999, which are chosen for their tensile and compressive strength, wear resistance, machinability, conductivity, and corrosion resistance. Copper alloys are placed into three groups according to their solidification or freezing range. The most popular copper alloys are brass, which is made up of copper, zinc, and bronze, and bronze, made up of copper and tin.

Magnesium
Magnesium is widely used as a base material for numerous alloys with magnesium alloy AZ91D being the most common alloying form. The use of magnesium as an alloy is due to its lightweight, durability, good castability, and exceptional toughness. Magnesium is 75% lighter than steel but with steel’s strength. What makes magnesium ideal for casting is its ability to be shaped into complex parts with thin walls and superior dimensional stability. Magnesium is cast using injection molding where the mold is immersed in a reservoir of molten magnesium and a piston forces molten magnesium into the mold.

Nickel Based Alloy
Nickel is another metal that was used in ancient times for casting. Monel is a name for alloys composed of nickel and copper with small amounts of iron, manganese, carbon, and silicon. It is stronger than pure nickel but difficult to machine once it has been cast. Inconel is an austenitic nickel chromium alloy that is resistant to oxidation and corrosion. Nickel alloys are cast using investment casting and produce components for high temperature or corrosive environments. The right combinations of nickel and its alloys can have the tensile strength of carbon steel with good ductility and wear resistance.

Iron
As with nickel, gold, and copper, iron has been cast for many centuries and originally was in the form of the very brittle metal, pig iron. Iron comes in several forms, which include gray iron, white iron, malleable iron, ductile iron, and graphite iron. Each of the various types have properties and characteristics that are appropriate for certain applications. Cast iron has a carbon content of 2% to 4% and other alloys including 1% to 3% of silicon. The high carbon content of cast iron means it solidifies as a heterogeneous alloy with a single microcrystalline structure.

Stainless Steel
Stainless steel is a general term used to describe a family of metals that contain chromium and are known for their resistance to corrosion and bright silvery appearance. The most common grades used for the casting process are the 300 series, 400 series, 14-4 PH series, 15-5 PH series, 17-4 PH series, and series 2205. The main differentiation between stainless steel grades is determined by their carbon. Stainless steel grades with low carbon content are highly resistant to corrosion while grades with a high carbon content are heat resistant. These two factors determine which grade will be used for casting with investment casting being the most common process.

Zinc
Zinc is a very popular metal for casting due to its lower tooling cost. Due to zinc's low melting temperature, zinc casting dies can last ten times longer than aluminum die casting dies and five times longer than magnesium dies. Zinc is cast using fast cycling hot chamber die casting where the molten zinc enters the die through a gooseneck that is connected to a tank of molten zinc. A plunger draws zinc from the molten tank and forces it under pressure into the die. Parts rapidly solidify and are ejected.

What Are the Industrial Applications of Casting?
The industrial applications of casting are diverse and extensive. Here is a list of common applications:

Chemical Process Equipment: Employed in the production of chemical process equipment such as: reactors, heat exchangers, and pumps.
Automobile Casting: Produces engine blocks, cylinder heads, transmission cases, and other critical components.
Plant Machinery: Casting plays a crucial role in the manufacturing of various components. Plant machinery refers to a wide range of equipment used in industries such as: manufacturing, power generation, oil & gas, and shipbuilding. Some specific applications of casting in plant machinery include: impellers, casings, and valve bodies.

What Are Examples of Casting Products?

Casting is a versatile manufacturing process that produces a wide range of products for various industries. Here are some examples of casting products:
Hydrants, used for water supply systems.
Firefighting equipment such as: fire hydrants, couplings, and fittings.
Plumbing components like: pipe fittings, valves, and connectors.
Components for military vehicles and transportation equipment, such as: engine parts, brackets, and structural elements.
Electrical hardware components, including: electrical enclosures, connectors, and terminal blocks.
Precision machinery parts, such as: gears, housings, and brackets.

How Durable Are Casting Products?
Cast metal products, especially those that have undergone heat treatment, are durable. Depending on the metal alloy and application, their service life might range from a few months to several decades. Once the service life of a casting ends, the cycle begins again. It is collected by a scrap yard, recycled, and recast into a new object.

Does the Casting Product's Thickness Vary?
Yes, the thickness of casting products can vary. The casting process allows for the production of components with varying wall thicknesses, depending on the design requirements and the capabilities of the casting method. Different sections of casting can have different thicknesses to achieve the desired strength, weight, and functionality of the final product.

What Is the Future of Casting?
The future of casting holds significant potential with the integration of advanced technologies. Optical measuring systems, such as the ATOS 3D Digitizer, are revolutionizing the industry by enabling efficient and accurate measurement of complex surfaces. These systems eliminate the laborious and time-consuming nature of traditional measuring methods, providing full-field measurements and faster validation. Embracing such technological advancements will enhance productivity, quality control, and overall efficiency in the casting process.

What Are the Advantages of Casting?
Advantages of the casting process include:
Ability to produce complex shapes easily.
Versatility—a wide variety of metals and other materials can be cast.
Cost-effectiveness, especially for small quantities.
Capability to produce large-sized castings up to 200 tons.
Cost and time savings compared to other manufacturing methods.
Suitable for materials that cannot be mechanically worked.
Simplifies the production of large and heavy components.

What Are the Disadvantages of Casting?
Disadvantages of the casting process include:
The surface finish may require additional finishing operations.
Limited mechanical properties compared to wrought materials.
The possible presence of casting defects like porosity.
The dimensional accuracy of castings can be compromised due to shrinkage during the solidification process.
High initial tooling and equipment costs for certain casting methods.
The casting process is typically restricted to metals with lower melting points.

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