Casting Process | Definition, Types, Processing, and Uses

Once the mold has been formed, the pattern is removed from the sand, leaving behind a cavity in the shape of the desired part.

If the part requires cores for internal features, these cores are placed into the mold cavity and secured in position. The mold halves are then carefully assembled, and any necessary gating and riser systems are added to facilitate the flow of molten metal and prevent defects.

After that the molten metal is poured into the mold cavity through the gating system. The type of metal used depends on the specific requirements of the part, with common metals including cast iron, steel, aluminum, and bronze.

After the mold is filled, the molten metal cools and solidifies within the mold cavity. The cooling rate is carefully controlled to minimize defects and ensure uniform solidification.

Once the metal has cooled and solidified, the sand mold is broken apart to remove the casting. This process, known as shakeout, may involve mechanical or manual methods, depending on the size and complexity of the casting.

Finally, the casting may undergo various finishing operations to remove any excess material, such as gates and risers, and to achieve the final desired shape, dimensions, and surface finish. Finishing processes may include grinding, machining, shot blasting, and heat treatment.

Advantages of Sand Casting:

The advantages of sand casting are:

• Sand casting can be used to produce parts of various sizes, shapes, and complexities.

• It is relatively inexpensive compared to other casting methods, making it suitable for both small-scale and large-scale production.

• Sand casting can be used with a wide range of metals and alloys, including aluminum, iron, steel, bronze, and brass.

• Since patterns are typically made from readily available materials, tooling costs are often lower compared to other casting processes.

• Changes to the part design can be easily accommodated by modifying the pattern.

Limitations of Sand Casting:

The disadvantages of sand casting include:

• Sand casting often results in rough surface finishes, requiring additional finishing processes to achieve the desired surface quality.

• Achieving tight tolerances can be challenging with sand casting, as factors like sand movement and mold deformation during pouring can affect the final dimensions of the casting.

• Sand casting may not be as fast as some other casting methods, particularly for complex parts that require extensive mold preparation and cooling time.

• The sand used in sand casting can generate waste, and the casting process may produce emissions and waste materials that require proper disposal or recycling.

Investment Casting

Investment casting, also known as lost-wax casting, is a manufacturing process used to create intricate and complex metal parts. It is one of the oldest known metal-forming techniques. The process involves several steps, each crucial to achieving precise and high-quality castings.

The process begins with the creation of a pattern, typically made of wax or a similar material. The pattern is an exact replica of the desired part, including all its intricate details. Skilled artisans or modern computer-controlled machines can produce these patterns.

Multiple wax patterns, known as the tree, may be attached to a central wax sprue to form an assembly. This arrangement allows for multiple parts to be cast simultaneously in a single mold, improving efficiency.

The assembly is then dipped or coated in a ceramic slurry or investment material. This material is carefully formulated to withstand the high temperatures of the casting process and provide a smooth surface finish. After coating, the assembly is covered with a layer of fine sand or stucco to create the mold.

Once the investment material has dried, the entire assembly is heated to melt and remove the wax patterns, leaving behind cavities in the mold corresponding to the desired parts. The mold is preheated to further strengthen it and prepare it for the molten metal.

Molten metal, often heated to extreme temperatures, is poured into the mold cavity. The metal fills the cavities left by the wax patterns, forming the desired parts.

After filling the mold, the molten metal is allowed to cool and solidify within the mold cavity. This process may take some time, depending on the size and complexity of the part.

Once the metal has cooled and solidified, the investment material is broken away or dissolved, revealing the cast metal parts within.

The cast parts may undergo various finishing processes, such as grinding, machining, polishing, or surface treatments, to achieve the final desired shape, dimensions, and surface finish.

Advantages of Investment Casting:

There are many advantages of investment casting include:

• It allows for the production of intricate and complex parts with high precision and detail.

• The process can produce parts with excellent surface finish and dimensional accuracy, often requiring minimal additional finishing.

• It can be used to cast a wide range of metals and alloys, including steel, aluminum, bronze, and titanium.

• Despite being more labor-intensive than some other casting methods, investment casting can be cost-effective for small to medium production runs, especially when producing parts with complex geometries.

Limitations of Investment Casting:

The disadvantages of investment casting include:

• Investment casting can be time-consuming due to the multiple steps involved, especially when compared to simpler casting methods.

• Setting up for investment casting may require specialized equipment and skilled labor, which can increase initial costs.

• While investment casting can produce small to medium-sized parts with high precision, it may not be as suitable for very large parts due to limitations in mold size and handling.

Die Casting

Die casting is a highly versatile and efficient metal casting process used to produce a wide range of parts with high accuracy and surface finish. It involves injecting molten metal into a steel mold, known as a die, under high pressure. Die casting is commonly used in the automotive, aerospace, electronics, and consumer goods industries for its ability to produce complex parts with tight tolerances. Here are the steps of the die casting process:

The process begins with the design and fabrication of the die, which consists of two halves, the cover die, and the ejector die. These dies are typically made of hardened steel and are precision-machined to form the desired part shape.

The die is mounted in a die casting machine, which consists of a hydraulically operated injection system. This system includes a molten metal reservoir, a shot chamber, and a plunger. The molten metal is heated to the desired temperature in the reservoir and then transferred to the shot chamber.

Once the shot chamber is filled with molten metal, the plunger is activated, forcing the metal into the cavity of the die under high pressure. This pressure ensures that the molten metal completely fills the mold cavity and solidifies quickly to form the part.

After the molten metal is injected into the die cavity, it rapidly cools and solidifies to form the desired part shape. Cooling channels within the die help regulate the temperature and solidification process, ensuring uniform cooling and minimizing defects.

Once the metal has solidified, the die halves are separated, and the ejector pins or plates push the part out of the die cavity. The part is then removed from the machine, and any excess material, known as flash, is trimmed off.

Depending on the requirements of the final part, additional finishing operations such as machining, polishing, or surface treatments may be performed to achieve the desired surface finish, dimensional accuracy, and mechanical properties.

Advantages of Die Casting:

There are many advantages of die casting include:

• The process allows for high production rates and short cycle times, making it suitable for large volume production runs.

• Die casting can produce parts with intricate shapes and thin walls that are difficult or impossible to achieve with other casting methods.

• The high pressure and rapid solidification of the molten metal result in parts with smooth surfaces and fine details.

• Die casting can be used with a wide range of metals and alloys, including aluminum, zinc, magnesium, and copper-based alloys.

Limitations of Die Casting:

The disadvantages of die casting include:

• The tooling and equipment required for die casting can be expensive, particularly for complex parts or specialized alloys.

• Die casting is generally more suitable for small to medium-sized parts, as larger parts may require larger, more costly equipment.

• Parts must be designed with draft angles, fillets, and other features to facilitate ejection from the die and minimize defects.

Continuous Casting

Continuous casting is a highly efficient process used in the production of semi-finished metal products, particularly steel and aluminum. It involves the continuous pouring of molten metal into a water-cooled mold, which allows for the continuous solidification and extraction of a long strand or slab of metal. This method is widely used in the steel industry to produce billets, blooms, and slabs, which are subsequently processed into various finished products. Here are the steps of the continuous casting process:

The process begins with the preparation of the molten metal in a furnace. The metal is heated to its melting point and brought to the desired chemical composition and temperature for casting.

The molten metal is then transferred to a holding vessel called a tundish. The tundish acts as a reservoir, ensuring a constant flow of metal to the casting mold and allowing for the removal of impurities and slag.

The tundish delivers the molten metal to the continuous casting mold, which is typically made of water-cooled copper. The mold is designed to shape the metal into a continuous strand or slab of the desired cross-sectional shape and dimensions.

As the molten metal flows through the mold, it comes into contact with the cooled mold walls, causing it to solidify gradually. The solidification process begins at the mold walls and progresses inward, resulting in a solid outer shell of metal surrounding a still-molten core.

As the metal solidifies, it is continuously withdrawn from the bottom of the mold at a controlled rate by a series of rollers or withdrawal mechanisms. This pulling force ensures a steady flow of metal through the mold and maintains the desired shape and dimensions of the cast product.

After leaving the mold, the partially solidified metal strand or slab passes through a secondary cooling zone, where it is further cooled and solidified using water sprays or other cooling methods. This helps to control the microstructure and mechanical properties of the final product.

Once fully solidified, the continuous strand or slab is cut into desired lengths or rolled to specific thicknesses and widths, depending on the intended application. These semi-finished products, such as billets, blooms, or slabs, can then be further processed through various metalworking techniques to produce finished products such as bars, rods, sheets, or plates.

Advantages of Continuous Casting:

There are many advantages of Continuous casting include:

• Continuous casting allows for the uninterrupted production of metal products, resulting in higher productivity and lower energy consumption compared to batch processes.

• The controlled solidification process in continuous casting helps to minimize internal defects and segregation, resulting in higher-quality products with consistent mechanical properties.

• Continuous casting produces minimal scrap compared to traditional casting methods, as the process generates a continuous strand or slab of metal with uniform dimensions.

• Continuous casting can be used to produce a wide range of metal alloys and shapes, making it suitable for various industrial applications.

Limitations of Continuous Casting:

The disadvantages of Continuous casting include:

• Setting up a continuous casting facility requires significant capital investment in specialized equipment and infrastructure, which may be prohibitive for smaller producers.

• Continuous casting requires precise control of process parameters such as temperature, casting speed, and cooling rates to ensure the quality and integrity of the cast products.

• The water-cooled mold and associated equipment require regular maintenance and monitoring to prevent equipment failure and ensure worker safety.

Lost-foam casting

Lost-foam casting is a modern casting process that offers several advantages over traditional casting methods. It involves creating a foam pattern of the desired part, embedding it in sand, and then pouring molten metal into the mold. The heat of the metal vaporizes the foam, causing it to "disappear" or "get lost," hence the name. The molten metal then takes the shape of the foam pattern, resulting in a precise casting of the desired part. Here are the steps of the lost-foam casting process:

The process starts with the creation of a foam pattern that represents the final part to be cast. This pattern is typically made from expanded polystyrene (EPS) foam due to its ease of shaping and low cost. The foam pattern can be produced using various methods such as cutting, carving, or CNC machining.

Once the foam pattern is ready, it may be assembled with other foam components if the final part requires multiple pieces. These components are attached using adhesives or other bonding methods to create the complete pattern assembly.

The foam pattern assembly is then coated with a refractory material to improve its surface finish and enhance its ability to withstand the heat of the molten metal. This coating helps prevent defects such as sand erosion and metal penetration during the casting process.

The coated foam pattern assembly is placed in a flask filled with unbonded sand or a mixture of sand and binders. The sand is vibrated or compacted around the pattern to ensure proper packing and support.

Once the mold is prepared, molten metal is poured directly into the mold cavity. The heat from the metal causes the foam pattern to vaporize and decompose, leaving behind a void in the sand that is filled by the metal. The metal solidifies within the mold cavity, taking the shape of the original foam pattern.

After pouring, the metal-filled mold is allowed to cool and solidify. The cooling time depends on factors such as the metal type, mold design, and part complexity. Once solidified, the casting is removed from the mold.

The cast part may undergo various finishing processes such as machining, grinding, and surface treatment to achieve the desired final dimensions and surface quality. Any excess material or imperfections are removed during this stage.

Advantages of Lost-foam Casting:

There are many advantages of Lost-foam casting include:

• It allows for the production of complex parts with intricate details and thin walls that may be difficult or impossible to achieve with other casting techniques.

• Since lost-foam casting produces near-net-shaped parts, there is often less need for secondary machining operations, resulting in cost and time savings.

• The use of foam patterns coated with refractory materials can result in superior surface finishes compared to traditional sand casting.

• Creating foam patterns is generally less expensive than producing metal molds or patterns used in other casting processes, making it a cost-effective option for small to medium production runs.

Limitations of Lost-foam Casting:

The disadvantages of Lost-foam casting include:

• Foam patterns can degrade or deform under the heat and pressure of the molten metal, leading to defects in the casting.

• The use of polystyrene foam in the process raises environmental concerns due to its non-biodegradable nature. Efforts are being made to develop more environmentally friendly alternatives.

• Achieving consistent results can be challenging due to factors such as foam pattern quality, sand compaction, and metal pouring conditions. Strict process control is essential to minimize defects and ensure quality.

Glass Casting

Glass casting is an ancient technique for creating intricate glass objects by pouring molten glass into a mold. It's a versatile method used by artists, artisans, and industrial manufacturers to produce a wide range of glass products, from decorative art pieces to functional items. Here are the steps of the glass casting process:

Like other casting processes, glass casting begins with the creation of a pattern or mold. This can be made from a variety of materials, including plaster, ceramic, metal, or refractory materials. The pattern defines the shape and details of the final glass object.

The pattern is placed inside a mold made of a material that can withstand the high temperatures of molten glass without deforming or cracking. The mold may consist of one or multiple parts depending on the complexity of the object being cast.

In some glass casting techniques, particularly those involving wax or other organic materials, the pattern is first coated with a refractory material and then fired in a kiln to remove the pattern and create a negative space in the mold. This step is known as "lost wax" or "lost mold" casting.

Glass used for casting is typically in the form of frits, cullet (recycled glass), or billets. The glass is heated in a furnace to temperatures ranging from 1100 to 1500 degrees Celsius (2,012 to 2,732 degrees Fahrenheit) until it becomes molten and fluid.

Once the glass is fully molten and homogenized, it is carefully poured into the prepared mold. The pouring process requires precision to avoid air bubbles and ensure complete filling of the mold cavity.

After pouring, the filled mold is allowed to cool slowly to anneal the glass and relieve internal stresses. The cooling rate is carefully controlled to prevent cracking or distortion of the glass. Depending on the size and thickness of the casting, this process can take several hours to several days.

Once the glass has cooled and solidified, the mold is carefully opened, and the casting is removed. This step requires careful handling to avoid damaging the fragile glass object.

Depending on the desired finish, the glass casting may undergo additional coldworking processes such as grinding, polishing, sandblasting, or engraving to refine its surface texture and shape.