MATERIAL AND MANUFACTURING PROCESSES , Mechanical Engg 3rd Semester Notes, ME3001

 

4. MATERIAL AND MANUFACTURING PROCESSES

This section deals with engineering materials, metal casting processes, and various types of metalworking processes that are used in manufacturing industries to shape and form materials.

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4.1 Engineering Materials

Engineering materials are substances used in the manufacturing and construction of products or structures. The selection of materials is critical in engineering design, depending on factors like strength, weight, cost, and environmental conditions.

4.1.1 Classification and Their Properties

Engineering materials can be classified into the following major categories based on their characteristics and composition:

1. Metals: Typically strong and ductile materials that conduct heat and electricity well. Metals are often used in structural applications and for machinery components.

   • Ferrous Metals: Contain iron (e.g., steel, cast iron).
     • Properties: Strong, good tensile strength, magnetic.
   • Non-Ferrous Metals: Do not contain iron (e.g., aluminum, copper, brass).
     • Properties: Corrosion-resistant, lightweight, good conductivity.

2. Polymers (Plastics): Materials made from long chains of molecules (e.g., polyethylene, polystyrene).

   • Thermoplastics: Can be melted and reshaped (e.g., PVC, polythene).
   • Thermosetting Plastics: Harden irreversibly when heated (e.g., Bakelite, epoxy).

3. Ceramics: Inorganic, non-metallic materials such as clay, glass, and cement.

   • Properties: Hard, brittle, heat resistant, electrical insulators.
   • Examples: Bricks, tiles, and glass.

4. Composites: Made from two or more materials to improve properties like strength, toughness, or resistance to environmental factors.

   • Examples: Fiberglass, carbon fiber composites.

5. Semiconductors: Materials that have conductivity between conductors and insulators, used primarily in electronic devices (e.g., silicon).

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4.2 Metal Casting: Moulding, Patterns

Metal Casting is a manufacturing process in which a liquid metal is poured into a mold and allowed to solidify into the shape of the mold cavity.

Moulding:

• Moulding is the process of creating a mold into which molten metal is poured. Commonly used moulding materials include sand, plaster, and ceramic. The mold is made by packing the molding material around a pattern.

Patterns:

• A pattern is a replica of the object to be cast, used to form the mold cavity. Patterns are typically made of metal, wood, or plastic.

  • Types of patterns:
    1. Solid Pattern: Made from a single piece, used for simple shapes.
    2. Split Pattern: Made from two or more pieces, used for complex shapes.
    3. Shell Pattern: A thin shell pattern used for detailed casting.

  Diagram:

         +-------------+
         |  Pattern   |  ← Made of wood/metal, etc.
         +-------------+
               ↓
    +---------------------+
    |    Molding Sand     |  ← Packed around pattern
    +---------------------+
               ↓
    +---------------------+
    |   Mold Cavity       |  ← Where molten metal is poured
    +---------------------+
  

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4.3 Metal Working Process: Hot and Cold Working (Introduction Only)

Metalworking processes involve shaping and forming metal materials into desired shapes through mechanical processes.

Hot Working:

• In hot working, the metal is heated to a temperature above its recrystallization point (typically above 50% of its melting point). This makes the material more ductile and easier to shape.
  • Examples: Rolling, forging, extrusion, and drawing.
  • Advantages: Can produce larger parts and reduce material hardness.
  • Disadvantages: High energy consumption and surface oxidation.

Cold Working:

• Cold working involves shaping metals below their recrystallization temperature (at room temperature or slightly above). This increases the strength and hardness of the material due to strain hardening.
  • Examples: Rolling, bending, drawing.
  • Advantages: Increased strength, improved surface finish, no heat required.
  • Disadvantages: Increased material hardness and brittleness, limited to smaller shapes.

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4.4 Metal Forming Processes (Introduction Only)

Metal forming processes are a subset of metalworking that specifically involves shaping metals by plastic deformation. The material flows under the application of force without breaking.

Common Metal Forming Processes:

1. Rolling: Reduces thickness or changes the shape of the material by passing it through rollers.
2. Forging: Shaping metal using localized compressive forces, typically performed at high temperatures.
3. Extrusion: Forcing material through a die to create long shapes of uniform cross-section.
4. Drawing: Pulling metal through a die to reduce its cross-section.

These processes are used to create products such as bars, plates, sheets, and wires.

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4.5 Press Working Process (Introduction and Working)

Press working refers to a variety of processes that shape and form materials using a press machine. These processes are generally used to make metal parts in large quantities with precise dimensions.

Working Principle:

• A press machine uses a die to shape a workpiece. The press applies force on the material, which is deformed into the shape of the die.
  • Common types of presses include mechanical presses and hydraulic presses.
  Diagram:

   +----------------------+
   |    Press Machine     |  ← Applies force to the material
   +----------------------+
          ↓
   +----------------------+
   |      Die             |  ← Shapes the material
   +----------------------+
          ↓
   +----------------------+
   | Workpiece (Metal)    |  ← Shaped part
   +----------------------+
  

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4.5.1 Press Working Operations: Cutting, Bending, Drawing

Press working involves several distinct operations, including:

1. Cutting: The process of shearing or cutting the material into smaller pieces or specific shapes. Common cutting operations are:

   • Blanking: Cutting out a blank from a sheet metal.
   • Piercing: Punching a hole in the material.

2. Bending: The process of deforming a material along a straight axis, typically by using a die and punch. This operation is used to create sharp angles or curves in metal parts.

3. Drawing: Involves pulling a metal sheet into a mold to form a cup or bowl-like shape. It is commonly used in the production of containers and deep-drawn parts.

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4.5.2 Press Working Operations: Punching, Blanking, Piercing, Notching, Lancing

Here are specific press working operations in detail:

1. Punching: Creating holes in a workpiece using a punch and die set. The punched material is discarded as scrap.

   • Diagram:

     +--------------+
     |   Punching  |  ← Punch applies force to create hole
     +--------------+
           ↓
     +--------------+
     |   Material   |  ← Workpiece with hole
     +--------------+
     

2. Blanking: Cutting out a blank or a disc from a sheet material. The blank is usually used in further operations.

3. Piercing: Similar to punching, but the material is removed as a separate piece (e.g., holes for bolts or rivets).

4. Notching: Removing a portion of the edge of the material to create a notch, often used to prepare parts for bending.

5. Lancing: A special case of notching where slits or cuts are made in the material to relieve stress or form patterns.

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4.5.3 Effect of Clearance

Clearance in press working refers to the gap between the punch and die. The clearance affects the quality of the cut, and it must be chosen based on the material's thickness.

• Effect of clearance:
  • Too little clearance: The punch may not cut through the material completely, leading to poor separation or distortion.
  • Too much clearance: The material may fracture or deform excessively, leading to rough edges.
  The optimal clearance is usually a percentage of the material thickness (typically 5-10%).