The Evolution and Techniques of Metal Casting

The history of casting dates back thousands of years, being one of the oldest metal transformation processes. The discovery and evolution of casting marked significant technological and social advancements, enabling the development of tools, weapons, artifacts, and structures essential to human civilization.

Ancient Origins of Casting

The first indications of metal casting date back to around 5000 BC, during the Copper Age. Ancient civilizations such as the Egyptians, Mesopotamians, and Chinese began experimenting with heating metal ores in rudimentary furnaces to extract copper. The discovery that molten metal could be poured into molds to create specific shapes revolutionized the manufacturing of tools and weapons, inaugurating a new technological era.

Around 3500 BC, the technique of bronze casting was developed by mixing copper with tin. Bronze, a harder and more durable alloy than pure copper, allowed the production of superior weapons and tools, driving the progress of Bronze Age civilizations. Casting skills were refined, enabling the creation of statues, ornaments, and detailed household items.

Advancements in the Iron Age

The next major advancement in casting occurred during the Iron Age, around 1200 BC. Iron casting required higher temperatures than those used for copper and bronze, leading to the development of more advanced furnaces. The discovery that adding carbon to iron produced steel, a material even stronger and more durable, had a significant impact on ancient societies. Steel tools and weapons allowed for the construction of better structures and military achievements.

Middle Ages and Renaissance

During the Middle Ages, casting continued to evolve with the development of high-temperature furnaces, such as the blast furnace. The invention of the blast furnace in China and its later adoption in Europe enabled the mass production of cast iron. This period also saw the introduction of sand molding techniques, improving the accuracy and quality of cast parts.

In the Renaissance, the revival of scientific and technical knowledge led to significant advancements in casting. The invention of typography by Johannes Gutenberg, which used movable type cast in lead, revolutionized printing and the dissemination of knowledge. Additionally, sculptors and artists such as Benvenuto Cellini used precision casting to create intricate works of art in bronze.

Industrial Revolution

The Industrial Revolution, which began in the late 18th century, brought drastic changes to casting. The demand for metal parts increased exponentially with the development of steam engines, railways, and industrial infrastructure. The casting of iron and steel became a central process in industrial production. More efficient furnaces and improved molding methods allowed for the mass production of standardized components, reducing costs and increasing efficiency.

The Bessemer steel casting process, invented by Henry Bessemer in 1856, revolutionized steel production by enabling large-scale, low-cost manufacturing. The ability to produce large quantities of high-quality steel was crucial for the construction of bridges, buildings, and ships, shaping the modern world.

Modern Casting

In the 20th century and beyond, casting continued to evolve with the introduction of new technologies and materials. Die casting allowed the production of complex parts with high precision and repeatability, being widely used in the automotive and electronics industries. Investment casting, also known as precision casting, became essential for the manufacture of aerospace and medical components.

Advancements in materials science and casting technology, including the use of computer simulations and automated process control, improved the quality and efficiency of casting. New methods, such as lost foam casting and centrifugal casting, expanded the possibilities for design and application.

In this step, we will discuss the casting process, a fundamental technique in the manufacturing of various mechanical components. Casting is widely used in the industry to produce complex parts with high precision and versatility. Let’s dive into the description and essential aspects of this process.

Casting is a process that involves melting a metal or metal alloy and pouring the liquid material into a mold, where it solidifies to form a solid part. This process is widely used in the industry due to its ability to produce parts of various sizes, shapes, and complexities.

Main Stages of the Casting Process:

• Mold Preparation: The first step in casting is preparing the mold. This involves choosing the mold material (typically sand), creating a negative pattern of the part to be produced, and assembling the mold.
• Material Preparation: The material to be cast is selected and prepared. This may involve melting metal alloys in casting furnaces, where the material is heated to reach its proper melting point.
• Pouring and Solidification: The molten material is poured into the prepared mold. It fills the empty spaces of the pattern, taking on the desired shape. As the material cools and solidifies, the part is formed within the mold.
• Cooling and Extraction: After the material has fully solidified, the mold is opened and the part is extracted. In some cases, it may be necessary to remove excess material, such as burrs or feed channels.
• Finishing: After extraction, the cast part may undergo additional finishing processes, such as machining, grinding, or heat treatments, to achieve the desired tolerances and properties.

Activity of STEP 1: Types of Casting Processes

In this step of the activity, your task is to research and explore the casting process in the industry in more detail. Focus on different types of casting, such as sand casting, lost wax casting, and metal mold casting. Additionally, highlight the advantages, challenges, and applications of each type of casting.

To conduct this research, consult books, academic articles, specialized websites, and technical materials. Be sure to correctly cite all sources used. When conducting your research, consider the following points:

• Sand Casting: Describe the sand casting process, including the steps involved, such as mold preparation, pouring the molten material, and solidification. Discuss the advantages of this method, such as production flexibility, relatively low cost, and the ability to create large parts. Also, address the challenges, such as the need for post-treatment and the limitations in the complexity of shapes produced. Explain the main applications of sand casting in the industry.
• Lost Wax Casting: Explain the lost wax casting process, which involves creating a wax model, applying a ceramic coating, removing the wax, and pouring the molten material into the mold. Highlight the advantages of this method, such as dimensional accuracy, the ability to produce complex parts, and excellent surface quality. Discuss the challenges, such as the need for longer production time and higher costs, as well as the limitations in terms of part size. Present the main applications of lost wax casting in the industry.
• Metal Mold Casting: Describe the metal mold casting process, which uses permanent molds made of metal, such as steel or cast iron. Explain the steps involved, including mold preparation, pouring the molten material, and extracting the part. Discuss the advantages of this method, such as high dimensional accuracy, good surface quality, and the ability to produce parts on a large scale. Address the challenges, such as the greater complexity and cost involved in making the metal molds. Present the main applications of metal mold casting in the industry.

In this step, we will conduct an experiment on the casting process. To do this, access the virtual laboratory called "FOUNDRY PROJECT." Upon opening it, you will cast a metal part using a green sand mold.

During the experiment, you will follow these procedures:

• Transferring sand to Box 1: Pour water into the basin containing sand and mix it with the ladle. Place Mold 1 in Box 1, then apply talcum powder over the mold. Using the ladle, add a layer of sand over the mold and compact it with the wooden stick. Add another layer of sand with the ladle and compact it again.
• Transferring sand to Box 2: Rotate Box 1 so that the mold becomes visible. Attach Box 2 on top of Box 1 and position Mold 2. Sprinkle talcum powder over the mold and place the PVC pipes. Using the ladle, add two layers of sand, compacting each one with the wooden stick. Remove the PVC pipes and detach Box 2. Carve out the passage with the spatula and remove the molds.
• Transferring sand to the core mold: Apply talcum powder over the core mold. Using the ladle, add two layers of sand, compacting each one with the wooden stick. Remove the core from the mold and place it in Box 1. Reattach Box 2 and position the risers in the box.
• Pouring the molten metal: Use the tongs to remove the crucible from the foundry furnace and pour the molten metal into the mold. Wait one hour, break the mold, and retrieve the finished part.

STEP 2 Activity: Conducting the Casting Process

In this stage of the activity, your task is to perform the "Foundry Project" experiment in the virtual simulator.

To carry out the experiment, open the virtual laboratory and follow the experiment guide. The guide provides a step-by-step breakdown of the necessary procedures to ensure the correct execution of the experiment.

After reading the instructions, start the experiment and follow the steps to cast your metal part.

At the end of the experiment, answer the following questions:

1. Describe how each step of the experiment was carried out, explaining what was done from the beginning to the end of the process.

The casting experiment was conducted following a series of carefully planned steps to ensure the proper formation and evaluation of the cast parts.

1. Transfer of sand to box 1:

   The process began with the preparation of the sand. Water was added to the basin containing the sand and mixed with the scoop until the desired moisture was achieved. Mould 1 was placed in box 1, and talc was applied to the mould to facilitate removal. Using the scoop, a layer of sand was deposited onto the mould and compacted with a wooden rod. After compacting the first layer, another layer of sand was added and compacted again.

2. Transfer of sand to box 2:

   Box 1 was rotated to make the mould visible. Box 2 was then attached to box 1, and mould 2 was positioned. Talc was sprayed onto mould 2, and PVC pipes were positioned to create feeding channels. Two layers of sand were added with the scoop and compacted with the wooden rod. After compaction, the PVC pipes were removed, and box 2 was detached. The passage was excavated with the spatula, and the moulds were removed.

3. Transfer of sand to the male mould:

   The male mould was prepared by applying talc, and two layers of sand were added, each compacted with the wooden rod. The male mould was then removed and placed in box 1. Box 2 was reattached, and the risers were placed in the box.

4. Pouring of liquid metal:

   The liquid metal was poured into the mould after the crucible was removed from the melting furnace using tongs. After solidification, which took approximately one hour, the mould was broken to remove the cast part.

5. Evaluation of results:

   Finally, the cast part was evaluated according to the guidelines established in the "Evaluation of Results" section of the experimental procedure.

2. Did the part have any defects? If so, how could they be prevented?

I have no idea. The virtual lab has poor quality, and the instructions are unclear. I carried out the experiment three times, following all the instructions, and in the end, all I see is just sand. Below is the final photo of the piece I managed to see in this terrible lab.



As I cannot visualise the piece, I will list the possible defects of this type of casting and how to resolve them:

• Shrinkage: The design of the riser must be appropriate, with properly positioned risers and feeding channels to compensate for metal shrinkage.
• Surface defects: Ensure the coating is appropriate to reduce sand adhesion to the piece, control the metal temperature, and ensure the sand is well-mixed and compacted.
• Porosity: Control the moisture of the sand, provide ventilation to the mould for gas escape, and use high-quality sand.
• Shape or dimension defects: Ensure precise mould making and use sand with the proper thermal properties.
• Cracks in the piece: Ensure gradual cooling.
3. What material was used to make the core, and why?

The core was made with compacted sand, a material chosen for its suitable properties to withstand the thermal and mechanical conditions of the casting process. Compacted sand is able to retain its shape during metal pouring and solidification, withstanding high temperatures and providing a good finish on the final piece. The choice of this material ensures that the cast piece has the correct shape and that the moulding is carried out with precision.

After completing the virtual lab experiment, where you cast a part using the green sand molding technique, it is important to reflect on the key aspects and stages of this process. Green sand molding is widely used in the foundry industry due to its versatility and cost-effectiveness. In the experiment, you observed the entire process, from preparing the sand and clay mixture to pouring the molten metal into the mold, followed by cooling and solidification.

Now, to reinforce your understanding of this casting process, you must answer specific questions. These questions will cover both the theoretical foundations of green sand molding and the particular observations made during the virtual experiment. This reflection will not only strengthen the concepts learned but also provide a deeper understanding of the practical applications and challenges of this casting method.

Let’s explore the questions and analyze the details that make green sand molding a fundamental technique in metal component manufacturing.

STEP 3 Activity: Exploring Green Sand Casting

To reinforce your learning, answer the following questions about casting using a green sand mold:

1. A common defect in the casting process is shrinkage, which appears as a depression on the surface or an internal void in the cast part. This defect occurs due to metal contraction during solidification. What is the most common method used to prevent this failure?

The gating system is crucial in the casting process. It ensures that the molten metal is properly fed into the mould cavity and compensates for contraction during solidification. Proper design of the gating system involves optimising the feed system to ensure that the molten metal can flow efficiently and continuously into the main part during the solidification process.

2. Green sand compaction can be done manually or with the help of machines. What is the basic composition of this mixture?

According to Dwang Metals (2022), green sand is composed of sand (75-85%), bentonite clay (5-11%), water (2-4%), and other materials (3-5%). It is the most commonly used type of sand in casting.

3. In gravity casting, the metal is poured using only the force of gravity. Considering the process performed in the laboratory, at what stage is it most appropriate to use the casting model?

In gravity casting, the ideal time to use the casting pattern is before compacting the sand mixture. This step is essential because the pattern must be inserted while the sand is still loose and malleable. This allows the pattern to be properly positioned and the sand to mould around it, forming the cavity that will match the shape of the desired piece.

4. Delamination occurs when two portions of molten material meet but do not properly fuse due to premature solidification. What are the most common causes of this defect?

The most common causes of this defect include insufficient fluidity point of the molten material, pouring temperature below the recommended level, pouring speed being too slow, and the cast piece being too thin, which causes rapid solidification. An insufficient fluidity point can prevent the metal from fully filling the mould cavities and bonding properly. An inadequate pouring temperature can cause premature solidification of the metal before it fills the mould completely. Slow pouring can also lead to premature solidification, and very thin pieces may solidify quickly, preventing the complete fusion of the molten material. Therefore, the combination of these factors must be carefully controlled to avoid the delamination defect in casting.

5. Explain the importance of maintaining the metal at the correct fluidity point during the pouring stage. Regarding critical temperatures in the casting process, which ones should be carefully monitored?

Maintaining the correct fluidity of the metal during pouring is important to ensure the quality and integrity of the cast pieces. Proper fluidity allows the molten metal to fill all mould cavities evenly, preventing defects such as porosity, voids, and surface imperfections. If the metal is too viscous, it may not fully fill the mould, resulting in incomplete or defective pieces. On the other hand, excessively fluid metal may cause issues such as shrinkage defects, where depressions or voids form in the piece due to the contraction of the metal during solidification. To ensure the ideal fluidity of the metal, it is necessary to carefully monitor the following temperatures during the casting process:

• Melting temperature: the temperature at which the metal transitions from solid to liquid. The metal must be maintained above this temperature to ensure it remains liquid and has the necessary fluidity to fill the mould.
• Pouring temperature: the temperature at which the metal is poured into the mould. It should be high enough to ensure that the metal is fluid enough to fill the mould cavities, preventing issues such as premature solidification or oxidation.
• Solidification temperature: the temperature at which the metal begins to solidify and change from liquid to solid. Monitoring this temperature is important to ensure that the metal does not solidify before completely filling the mould, which could compromise the quality of the cast piece.

Completing this activity, which combined the description of key casting processes, the practical construction of a green sand mold, and the resolution of theoretical questions, has been an enriching and essential experience for your learning in the Manufacturing Processes discipline.

By describing the casting processes, you reinforced your theoretical understanding of various techniques and their industrial applications, gaining insight into the advantages and challenges of each method. This theoretical knowledge is crucial for identifying suitable processes for different types of parts and materials—an essential skill for any mechanical engineering or manufacturing technician.

The practical stage of constructing a green sand mold and subsequently casting a metal part allowed you to apply theoretical knowledge in a realistic setting. This hands-on experience is vital for understanding the complexities and challenges of the casting process, providing a more complete and tangible grasp of the theoretical concepts studied. Practical application strengthens theoretical learning, enabling you to visualize and handle the studied materials and techniques while addressing real-world manufacturing challenges.

Finally, answering the questions related to the casting process further solidified your understanding, encouraging critical reflection on what was learned. The ability to identify and solve problems, such as delamination and shrinkage, and to understand the importance of melting, solidification, and superheating temperatures, are essential skills developed through this type of activity.

The integration of theory, practice, and critical reflection into a single activity offers a comprehensive and in-depth learning experience, preparing you to face real challenges in the manufacturing industry. Understanding and mastering casting processes are fundamental for the efficient and high-quality production of metal components, and this activity is an important step in that direction. The combination of these elements strengthens your knowledge and skills, essential for your academic and professional success in manufacturing processes.

Congratulations on completing this activity! Keep exploring and enhancing your knowledge in mechanical and production engineering, as they are key to building a strong and successful career in the industry.