In-depth analysis of the metal casting process: technology, history and applications

May 25, 2024

Metal casting, as a long-established and highly skilled manufacturing process, continues to play an integral role in modern industry today. In this article, we will take a closer look at how metal casting works, its historical background, classification, material selection and its wide range of applications in industry.

What is metal casting?

Metal casting is a manufacturing process that involves pouring molten metal into a mould (often referred to as a casting die), allowing the metal to cool and solidify to form a part or product of the desired three-dimensional shape and size. The process dates back thousands of years and is an ancient and widely used metal working technique.

The key steps in metal casting include

Design and manufacture of the mould

As the first step in the casting process, mould making is a key aspect of creating a model of the final part. Models are made from a variety of materials, including wood, metal and plastic, and modern technologies such as 3D printing are increasingly being used in this area. SANDY Technology has developed a range of 3D printing equipment for sand and wax moulds, click here to view.

Metal melting and pouring

Choose a suitable metal (commonly iron, stainless steel, aluminium, copper or alloys), heat it to a molten state, pour the molten metal into the prepared mould and the metal will be filled according to the shape of the mould.

Cooling and curing

The molten metal is allowed to cool in the mould and solidify into its final shape.

Demoulding

Once the metal has cooled and solidified, the mould is opened and the metal casting is removed.

Post-processing

After the metal has cooled and cured, the necessary post-treatment processes are carried out, including deburring, cleaning, polishing, and possibly heat treatment, machining, drilling etc.

Classification of metal casting

Sand casting

Sand casting is a common metal casting process, cost-effective, easy to operate, is one of the oldest casting methods. Sand casting uses sand as the primary mould material. This technique is particularly suited to high volume production as it allows for the relatively quick and economical manufacture of simple or complex shaped metal parts. SANDI Technology has launched a variety of sand 3D printers that can print oversized sand moulds, while easily handling structurally complex parts, helping to take the unified sand casting industry to the next level.

Sand 3D printer is printing sand mould for casting
Sand casting parts

Die Casting

Die casting is a precision casting process that uses high pressure to rapidly inject molten metal into a precision metal mould. This technique is primarily used to create metal parts with complex shapes, thin walls and precise dimensions. The die casting process is fast and can be automated, making it suitable for high volume production and capable of producing high quality parts with intricate detail.

Investment casting

Investment casting, also known as lost wax casting or investment casting, is a casting process for the manufacture of complex shaped metal parts. This technique is particularly suited to producing parts with fine detail, thin walls, complex internal passages, or parts that are difficult to manufacture by other casting methods.

LaserCore-5300 Picture
3D printer for printing wax moulds: LaserCore-5300
Four-cylinder-engine-head
Printed wax moulds and finished parts by investment casting

Defects in metal casting: identification, causes and prevention strategies

Metal casting is a manufacturing process in which molten metal is poured into a mould and cooled and solidified to form a desired shape. Although metal casting offers significant advantages in the production of complex parts, some defects may occur during the casting process. The following section will discuss common types of defects in metal casting, their causes, and preventive and remedial measures.

Common types of metal casting defects

Porosity and gas holes

Causes: Gas forms bubbles in the metal or shrinks during solidification to form voids.

Prevention: Optimisation of casting parameters and use of proper venting systems.

Shrinkage and loosening

Cause: Uneven shrinkage of the metal during solidification, leading to the formation of holes inside or on the surface.

Prevention: Adjust the cooling rate to ensure uniform solidification.

Cracks

Cause: Casting stress exceeds the tensile strength of the material.

Prevention: Control casting parameters to reduce thermal and mechanical stresses.

Inclusions

Cause: Foreign materials such as sand, oxides or other impurities mixed into the molten metal.

Prevention: Keep melting equipment and moulds clean, use filtration systems.

Deformation

Cause: Uneven shrinkage during cooling.

Prevention: Optimise the mould design and control the cooling rate.

Surface defects

Cause: Mould surface is not smooth or oxidation during pouring.

Prevention: Improve the surface quality of the mould and control the pouring conditions.

Detection methods of metal casting defects

Visual inspection: Direct observation of the casting surface and interior (by profile inspection).

Non-destructive testing: Use X-ray, ultrasonic testing and other techniques to detect internal defects.

Strategies to prevent metal casting defects

Design optimisation

Optimise mould and casting design to reduce stress concentrations and uneven shrinkage.

Material selection

Selection of suitable alloys to reduce the tendency of defects during casting.

Process control

Strict control of melting, pouring, cooling and post-treatment process parameters.

Quality Management System

Strict quality control processes are implemented to ensure quality standards at every step of the process.

Defects in metal casting can be minimised by careful design, strict process control and an effective quality management system. Understanding the causes of each defect and taking the appropriate preventive measures can significantly improve the quality and consistency of castings, thereby enhancing product reliability and market competitiveness.

Materials used in metal casting

Materials used in metal casting usually include a variety of metal alloys that are chosen for their specific physical and chemical properties. The following are some of the commonly used materials for metal casting:

1. steel (Steel):

   Carbon steel and alloy steel is widely used in casting, because of its high strength, good toughness, suitable for manufacturing a variety of mechanical parts and tools.

2. stainless steel (Stainless Steel):

   Strong corrosion resistance, commonly used in food processing, medical equipment, chemical equipment and other fields. 3.

3. aluminium (Aluminum):

   Lightweight, high thermal and electrical conductivity, commonly used in automotive parts, aircraft components and electronic equipment. 4.

4. copper (Copper):

   High thermal and electrical conductivity, commonly used in casting electrical equipment and heat exchanger parts. 5.

5. brass (Brass):

   Copper and zinc alloy, with good wear resistance and corrosion resistance, commonly used in valves, pumps and pipe fittings. 6.

6. Bronze:

   An alloy of copper and tin with excellent resistance to abrasion and seawater corrosion, commonly used for ship parts and sculpture.

7. Magnesium Alloys:

   A lightweight alloy with good mechanical properties, often used in aerospace and portable electronics. 8.

8. Zinc Alloy:

   Corrosion-resistant, easy to cast, commonly used in die-casting parts, such as automotive parts and hardware. 9.

9. lead alloy (Lead Alloys):

   Good X-ray shielding properties, commonly used in the field of medical and radiation protection. 10.

10. titanium alloy (Titanium Alloys):

    High strength, low density, corrosion resistant, commonly used in aerospace, medical devices and high performance sports equipment. 11.

11. Nickel Alloys:

    Good high-temperature strength and corrosion resistance, commonly used in high-temperature applications and chemical equipment.

The selection of metal casting materials depends on the application needs of the end product, performance requirements, cost-effectiveness, and the suitability of the casting process. Casting engineers use these factors to determine the type of alloy best suited for a particular part. In addition, specific elements may be added to the alloy or subsequent treatments such as heat treatments may be performed to improve the quality and performance of the casting.

Reasons to choose metal casting

There are multiple reasons for choosing metal casting, including cost-effectiveness, design flexibility and sustainability, and the following are some of the key benefits and considerations:

1. Design Flexibility:
 Metal casting is capable of producing parts with complex designs, fine details and unique geometries.

2. Cost-effectiveness:
For high-volume production, metal casting can significantly reduce unit costs because moulds can be reused.

3. material utilisation:
metal casting allows precise control of material usage, reducing scrap and waste.

4. High strength and durability:
Metal castings typically have excellent mechanical properties, including high strength and durability.

5. Close proximity moulding:
metal casting can produce parts close to their final shape and size, reducing the need for subsequent machining.

6. Multiple material options:
A wide range of metal materials can be selected for casting, including steel, iron, aluminium, copper alloys, etc., to meet different performance requirements.

7. Small batch production: 
Although metal casting is suitable for mass production, it can also be adapted to small batch production, especially when certain modern casting techniques are used.

8. Rapid prototyping:
metal casting allows for rapid transition from design concept to physical prototype, accelerating the product development process.

9. Recyclability:
Scrap and defective products generated during the metal casting process can be recycled and reused, reducing the environmental impact.

10. Wide range of industry applications:
 Metal casting is used in a variety of industries, including automotive, aerospace, construction, industrial machinery, consumer products, and more.

11. Quality control:
Through rigorous quality control processes, it can be ensured that each casting meets high standards of quality.

12. Technological advancement:
With technological advancements such as computer-aided design (CAD), 3D printing and simulation software, the metal casting process has become more precise and efficient.

As a manufacturing technology, metal casting is widely used in modern industry due to its unique advantages. However, the choice of metal casting also requires consideration of product-specific requirements, production scale, cost budget and market conditions.

The importance of metal casting

As one of the basic processes of modern industry, metal casting is of utmost importance and widely used. The following are several aspects of the importance of metal casting:

1. The basis of industrial production:
metal casting for automotive, aerospace, construction, machinery manufacturing, energy, transport and many other industrial sectors to provide key components.

2. the promotion of technological innovation:
the development of metal casting technology to promote the development of new materials, new processes, and promote the improvement of product performance and industrial design innovation.

3. the enhancement of economic benefits:
metal casting can achieve mass production, reduce unit costs, improve production efficiency, and create economic benefits for enterprises.

4. The realisation of product diversity:
metal casting process can produce parts with complex shapes and precise dimensions to meet the needs of different products.

5. Sustainable use of resources:
metal casting process materials can be recycled, reducing the waste of resources, in line with the requirements of sustainable development.

6. Creation of employment opportunities:
The metal casting industry provides a large number of employment opportunities for the society, including foundry workers, engineers, designers, and so on.

7. Guarantee of national defence and security:
in the military field, metal casting is used to produce key components of various weapons systems and defence equipment, which is vital to national security.

8. Carrier of cultural heritage:
metal casting technology has a long history and is an important part of human civilisation, many historical relics and works of art are made by casting technology.

9. Development of technical standards:
the development of the metal casting industry promotes the development and improvement of relevant technical standards, and improves product quality and safety.

10. Enhancement of international competitiveness:
the level of development of metal casting technology reflects, to a certain extent, a country’s industrial strength and international competitiveness.

11. Environmentally friendly production methods:
With the improvement of environmental awareness and technological progress, the metal casting industry is moving towards a cleaner, more environmentally friendly direction.

12. Emergency response capacity:
in emergency situations, such as natural disasters or military conflicts, metal casting can quickly produce the required materials and equipment.

The importance of metal casting is not only reflected in its contribution to industrial production, but also in its far-reaching impact on economic development, social progress and national security. As technology continues to advance, metal casting will continue to play a key role in global industrial development.

Conclusion

Metal casting is not only a technology, it is an art, a science and an integral part of modern industry. As technology continues to advance, the metal casting process will continue to evolve, bringing more high-quality products to society.

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