Unit 2: Mechanical Skill

Concept of workshop practice

A workshop is a place where manufacturing and repair of goods take place. Workshop practice is the study and application of the skills, tools, and processes required to make or repair objects, typically from materials like metal, wood, or plastic.

It provides the fundamental "hands-on" knowledge needed by engineers and technicians.

Core Objectives of Workshop Practice:

• Safety: Learning to operate tools and machinery safely is the primary objective. This includes wearing proper Personal Protective Equipment (PPE) like safety glasses, gloves, and boots.
• Tool Familiarity: Understanding the name, function, and correct use of various hand tools (e.g., files, hammers, saws, wrenches) and machine tools (e.g., lathes, drills).
• Material Knowledge: Learning to identify different materials (like steel, aluminum, copper, wood) and understanding their properties (e.g., hardness, brittleness).
• Process Knowledge: Learning the basic manufacturing processes like measuring, marking, cutting, shaping, joining (welding, soldering), and finishing (filing, painting).
• Accuracy: Developing the skill to create a component that matches a given technical drawing and its specified dimensions (specifications).

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Overview of manufacturing methods

Manufacturing is the process of converting raw materials into finished goods. There are several primary methods:

1. Casting (and Foundry)

• Foundry: The workshop where casting is done.
• Casting: This is a shaping process.
  1. A pattern (a model of the desired object) is made, often from wood.
  2. This pattern is pressed into special, moist sand to create a mould (a hollow cavity).
  3. The pattern is removed.
  4. Molten (liquid) metal is poured into the mould.
  5. The metal cools and solidifies, taking the shape of the mould.
  6. The sand mould is broken, and the finished metal casting is removed.
• Use: For creating complex shapes that would be difficult to machine. (e.g., engine blocks, manhole covers, lamp posts).

2. Forging

• Description: This is a shaping process that uses compressive forces (hammering or pressing) to shape metal, usually when it is hot.
• Process: It's like a blacksmith with a hammer and anvil. A metal billet is heated until it is "plastic" (soft but not liquid) and then hammered or squeezed into the desired shape.
• Benefit: Forging refines the internal grain structure of the metal, making the final part extremely strong and durable.
• Use: For high-strength parts. (e.g., wrenches, crane hooks, connecting rods in an engine).

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Specifications and Identifications of Components

Specifications of components

A specification (or "spec") is a detailed description of a component's required properties. This is found on a technical drawing or in a manual. It removes all ambiguity and ensures the part is made correctly.

Key specifications include:

• Dimensions: Length, width, height, diameter. (e.g., "M8 bolt, 50mm long").
• Tolerances: The acceptable range of variation for a dimension. (e.g., "diameter = 10.00 ± 0.05 mm" means the part is acceptable if its diameter is between 9.95 mm and 10.05 mm).
• Material: What it's made of (e.g., "Stainless Steel 304").
• Finish: The required surface texture (e.g., "polished," "matte," "painted").

Identifications of nuts, bolts, screws, etc.

These are common "fasteners" used to join components.

• Bolt:
  • Description: A fastener with external (male) threads. It has a "head" on one end and is threaded on the other.
  • Use: A bolt is designed to pass *through* unthreaded holes in two components and is secured on the other side by a nut. It joins things by "clamping" them.
  • Head types: Hexagonal (most common), square, round.
• Nut:
  • Description: A block (usually hexagonal) with internal (female) threads.
  • Use: Mates with a bolt to fasten components together.
• Screw:
  • Description: A fastener with external threads, similar to a bolt.
  • Use: A screw is designed to be inserted into a threaded hole in one of the components (or to cut its own threads, as in a wood screw). It typically does *not* use a nut.

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Commonly used materials for manufacturing

Metals

• Steel: An alloy of iron and a small amount of carbon.
  • Properties: Very strong, durable, versatile.
  • Use: The backbone of construction, cars, tools, and machinery.
  • Stainless Steel is a type of steel alloyed with chromium, which makes it highly resistant to rust. (Use: Kitchen sinks, cutlery, medical instruments).
• Iron:
  • Properties: Heavy, strong but brittle (if cast).
  • Use: Often as "cast iron" (high carbon content) for heavy, vibration-damping machine bases, pipes, and cookware (e.g., frying pans).
• Copper:
  • Properties: Excellent electrical conductor, excellent heat conductor, ductile (can be drawn into wires), resists corrosion.
  • Use: Electrical wiring, water pipes, motors, pots and pans.
• Metal Sheets: This is a *form* of metal, not a type. It is metal (often steel or aluminum) that has been rolled flat. (Use: Car bodies, appliance housings, roofing).

Alloys

An alloy is a metal made by combining two or more metallic elements to produce new, improved properties (e.g., strength, lightness, corrosion resistance).

• Steel (Iron + Carbon) - already discussed.
• Brass (Copper + Zinc) - Used for decorative hardware, musical instruments, plumbing fittings.
• Bronze (Copper + Tin) - Used for statues, bearings, ship propellers.

Plastics

Plastics (or polymers) are synthetic materials.

• Properties: Lightweight, low cost, easily moulded, waterproof, good electrical insulators.
• Use: Ubiquitous. (e.g., bottles, bags, electronic casings, toys, car interiors).

Composites

A composite is a material made from two or more different materials that, when combined, are stronger or better than the individual components.

• Example 1: Fiberglass. Made from a plastic (polyester resin) reinforced with fine fibres of glass.
  • Properties: Lightweight, strong, stiff, can be moulded into complex shapes.
  • Use: Boat hulls, car bodies, water tanks.
• Example 2: Carbon Fibre. Plastic resin reinforced with extremely strong carbon fibres.
  • Properties: Extremely strong, stiff, and very lightweight.
  • Use: High-performance applications like racing cars, aircraft, and high-end bicycles.