AIM: Understanding and Demonstration of Various Moulding Processes (Demonstration may be Real / Video / Industrial Visits)

Competency and Practical Skills:

1. Identify the materials for sand mould making
2. Understand the basic terminology of sand moulding
3. Select the moulding process as per requirement/application

Relevance to CO:

CO-1: Interpret foundry practices like pattern making, mould making, core making, and inspection of defects.

Objectives:

1. Understanding the moulding processes
2. Understanding the types of moulding processes
3. Ensuring quality control
4. Cost-effectiveness
5. Demonstrating expertise

MOULDING PROCESSES

Mould cavity is formed by ramming moulding sand around the pattern. OR

In sand casting, the moulding process refers to creating a hollow space-called a mould cavity-by tightly packing sand around a pattern. This cavity shapes the molten metal into the final product.
The process of making a mould is called the “Moulding Process”.

Figure-1: Moulding Process

Moulding processes are classified into two groups:

1. Hand Moulding
2. Machine Moulding

Figure-2: Hand Moulding and Machine Moulding

• Hand moulding is the process of making a mould using hand tools.
• Machine moulding uses various moulding machines for production.

Classification of Moulding Processes Based on Moulding Materials Used:

1. Green Sand Moulding

Green Sand Moulding is the most widely used and traditional method of sand casting. In this process, moist (green) sand is used to form the mould cavity. The term “green” refers to the presence of moisture, not the color. It is suitable for small to medium-sized castings and offers low-cost, flexible, and quick moulding.

Figure-3: Green Sand Moulding Process

Key Features:

1. • Prepared from green sand.
   • Sand, clay, and water are added in specific proportions.
   • Green moulds have low strength and can be prepared quickly.
   • Used for mass production of small non-ferrous and ferrous metal parts.
   • Offers easy reuse and low tooling cost.
2. Dry Sand Moulding

Dry Sand Moulding is a casting process where green sand moulds are first prepared and then baked in a furnace or oven to remove moisture and increase mould strength. This method provides better surface finish, dimensional accuracy, and is used for medium to large castings.

Key Features:

1. • Made by adding binders to green sand and baking it.
   • Baking removes moisture and strengthens the mould.
   • Provides a good surface finish.
   • Suitable for large and heavy castings.
   • Reduced gas defects due to low moisture.
   • Dry Skin Sand Moulding

Key Features:

1. • Surface moisture is dried to a depth of about 25 mm using gas torches or heaters.
   • Combines advantages of green and dry sand moulding.
   • Suitable for very large moulds.
2. Loam Moulding

Loam Moulding is a traditional sand casting method used for very large and heavy castings, such as steam engine cylinders, large bells, and big pipes. It uses a special type of loam sand that is applied layer by layer over a rotating spindle or skeleton frame, and the mould is dried before pouring. It is especially suitable for hollow, symmetrical components.

Figure-4: Sample Loam Sand Mould prepared using sweep pattern

Key Features:

1. • Uses loam sand (sand, clay, fire clay, or ganister).
   • Mainly used for large components where solid patterns would be costly, e.g., large gears.
   • Used for extra-large, hollow, and symmetrical castings.
   • Involves a rotating structure (spindle or skeleton).
   • Mould is built up gradually by hand, using loam sand.
   • Requires drying or baking before pouring.
   • High customization and strength.
2. Plaster Moulding

Figure-5: Plaster mould preparation

Key Features:

1. • Metallic patterns and plaster of Paris are used.
   • Slurry is poured over the pattern, and after drying, the shell is used as a mould.
   • Suitable for non-ferrous metal castings.
   • Provides good surface finish and dimensional accuracy.
2. CO₂ Moulding

CO₂ Moulding, also called Sodium Silicate Moulding, is a chemical moulding process where sodium silicate (water glass) is used as a binder mixed with silica sand. The mixture is hardened by passing carbon dioxide (CO₂) gas through it, forming a strong and rigid mould without the need for baking.

Figure-6: CO2 Moulding

Key Features:

1. • A mixture of dry silica sand and sodium silicate is used.
   • Fast hardening at room temperature using CO₂ gas.
   • No need for ovens or drying time.
   • Produces high strength and accurate moulds/cores.
   • Widely used for ferrous and non-ferrous castings.
   • CO₂ gas is passed through the mould to form silica gel, which hardens the mould.

Classification of Moulding Processes Based on Moulding Method:

1. Bench Moulding

Figure-7: (a) Box bench moulding (b) Stack moulding using 3 moulds and common sprue

Key Features:

1. • Moulds are prepared on a workbench of convenient height.
   • Easier mould handling due to table-level work height.
   • Suitable for small and intricate moulds.
   • Used in repair shops, prototypes, and low-volume production.
   • Low-cost setup.
   • Quick pattern changes.
   • High control and visibility of the process.
   • Not suitable for large-scale production.
   • Labor-intensive.
   • Inconsistent quality if not handled carefully.

1. Floor Moulding

Figure-8: Floor moulding

Key Features:

1. • Mold is made directly on the foundry floor.
   • Used for heavy, large castings.
   • Manual process using cope and drag boxes.
   • Requires adequate floor space and strong ramming.
   • Used where mechanized equipment is not economical.
2. Pit Moulding

Pit Moulding is a sand casting process used for very large and heavy castings. In this method, a pit is dug into the foundry floor, which acts as the drag (bottom mould). The cope (top mould) is made separately and placed on top during final assembly.

Figure-9: Pit Moulding

Key Features:

1. • The pit is part of the foundry floor, used for moulding large parts.
   • Suitable for large castings requiring a large amount of sand.
   • Commonly used in machine base, lathe bed, and heavy structural casting industries.
   • Characterized by a greater depth in the drag portion compared to the cope.
   • Suitable for heavy, bulky, and low-volume castings.
   • Often uses sweep patterns for shaping symmetrical cavities.
   • Pit walls may be lined with refractory bricks for stability and heat resistance.
2. Sweep Moulding

Sweep Moulding is a moulding process used to create large, symmetrical, and round mould cavities without using a full solid pattern. Instead, a sweep pattern (a wooden template shaped to the desired profile) is rotated around a central axis to shape the mould cavity in sand.

Figure-10: Sweep Moulding

1. • Suitable for cylindrical, symmetrical shapes (like bells, flywheels).
   • Eliminates the need for large, costly 3D patterns.
   • Used mainly for large castings with rotational symmetry.
   • Involves a rotating arm (sweep) to carve the mould shape.

1. Plate Moulding

Plate Moulding is a semi-mechanized sand moulding process where the patterns are mounted on a match plate or metal plate, which simplifies and speeds up the moulding process. It ensures high accuracy and consistency and is widely used in mass production of small to medium-sized castings.

Figure-11: Plate moulding

1. • Patterns are fixed on a metal or wooden plate (match plate).
   • Plate carries both cope and drag patterns on opposite sides.
   • Used with moulding machines for faster, repeatable production.
   • Often involves squeeze moulding or jolt-squeeze moulding machines.

MACHINE MOULDING

Machine moulding processes are used to produce better quality and large-scale moulds at lower cost than hand moulding.
Moulding machines are available in various sizes and designs.

Types of Moulding Machines:

1. Squeeze Machine
2. Jolt Machine
3. Jolt-Squeeze Machine
4. Sand Slinger

Figure-12: Moulding Machine

ADVANTAGES AND DISADVANTAGES OF MACHINE MOULDING OVER HAND MOULDING

Advantages:

1. Machine moulding produces moulds much faster than hand moulding.
2. Requires less skill from the moulder, reducing operating costs.
3. Produces identical and consistent quality moulds at lower costs.
4. Preferred for mass production.
5. Requires less allowance on the pattern (e.g., taper, machining), reducing overall costs.

Disadvantages:

1. High initial cost.
2. Cannot produce large-sized castings.
3. Not a fully automatic process—some operations must still be performed manually.
4. Not economical for small-scale mould production.

MCQ Exercises

1. What is the most common type of molding used for casting metals?
2. a) Sand casting
3. b) Investment casting
4. c) Die casting
5. d) Centrifugal casting Answer: a) Sand casting
6. Which of the following is NOT a step in sand casting?
7. a) Creating a pattern
8. b) Preparing the sand mold
9. c) Filling the mold with molten metal
10. d) Pouring molten wax into the mold

 Answer: d) Pouring molten wax into the mold

3. What is the purpose of gating in metal casting?
4. a) To direct the flow of molten metal into the mold
5. b) To provide a pathway for the molten metal to escape the mold
6. c) To create a textured surface on the casting
7. d) To prevent the molten metal from cooling too quickly

Answer: a) To direct the flow of molten metal into the mold

4. Which type of casting method uses a ceramic shell to create the mold?
5. a) Sand casting
6. b) Investment casting
7. c) Die casting
8. d) Centrifugal casting

Answer: b) Investment casting

5. Which of the following is NOT a step in die casting?
6. a) Preparing the mold
7. b) Pouring molten metal into the mold
8. c) Applying pressure to fill the mold
9. d) Adding a ceramic shell to the mold

Answer: d) Adding a ceramic shell to the mold

6. Which molding process uses a machine to apply pressure to the sand mold?
7. a) Sand casting
8. b) Investment casting
9. c) Die casting
10. d) Squeeze molding

Answer: d) Squeeze molding

7. Which molding process uses a machine to jolt the sand mold?
8. a) Sand casting
9. b) Investment casting
10. c) Die casting
11. d) Jolt molding

Answer: d) Jolt molding

8. Which molding process uses a combination of jolting and squeezing to create the mold?
9. a) Sand casting
10. b) Investment casting
11. c) Die casting
12. d) Jolt squeeze molding

Answer: d) Jolt squeeze molding

9. Which molding process uses a machine to fling sand at a pattern to create the mold?
10. a) Sand casting
11. b) Investment casting
12. c) Die casting
13. d) Sand slinging

Answer: d) Sand slinging

10. Which of the following is NOT a common metal used in casting?
11. a) Iron
12. b) Copper
13. c) Aluminum
14. d) Plastic

Answer: d) Plastic

Assignments

1. Explain the purpose of a mold in casting.
2. What are the different types of mold materials used in casting?
3. How is a mold prepared for investment casting?
4. What is the difference between a permanent mold and a temporary mold?
5. Explain the difference between a one-part mold and a two-part mold.

📊 Rubric Categories

1. MCQ Exercises
2. Assignment Completion
3. Attendance
4. Submission
5. Attention in Laboratory

🎯 Rubric-Wise Marks Table