Lesson Notes By Weeks and Term v4 - SHS 2
WELDING TECHNOLOGY
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WELDING TECHNOLOGY
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Subject: Applied Technology
Class: SHS 2
Term: 1st Term
Week: 15
Grade code: 2.2.2.LI.4
Strand code: 2
Sub-strand code: 2
Content standard code: 2.2.2.CS.1
Indicator code: 2.2.2.LI.4
Theme: METAL TECHNOLOGY
Subtheme: WELDING TECHNOLOGY
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Welcome, learners! Today, we are exploring the foundational skills of sheet metal fabrication. Before we can weld pieces of metal together to create useful items, we must first be able to cut and shape them accurately. Think about the metal trunk boxes (chop boxes) many of you use, the cooking pots in our kitchens, or the bodies of 'tro-tro' buses. All these start as flat sheets of metal that are carefully marked, cut, and formed. This lesson focuses on the key operations that make this transformation possible: drawing, and using dies and presses. Mastering these skills is the first step to becoming a skilled fabricator, able to create everything from simple tools to complex machine parts.
This lesson covers the preparatory stages of metalwork, which are crucial before any welding can begin. We are shaping the parts that will later be joined. A. What is Sheet Metal? Sheet metal is simply metal that has been formed into thin, flat pieces. It is one of the most common forms of raw material in metalworking. The thickness is called its gauge. A smaller gauge number means a thicker sheet of metal (e.g., 16 gauge is thicker than 22 gauge). In Ghana, you will commonly find mild steel, aluminium, and galvanised iron sheets. B. Drawing Operations The term "drawing" has two important meanings in sheet metal work. It is crucial to understand both. Drawing as Marking Out (Layout) This is the most fundamental step. It is the process of accurately transferring a design or pattern from a plan onto the surface of the sheet metal. It is like drawing with a pencil on paper, but we use special, durable tools for metal. Purpose: To create precise guidelines for cutting, bending, folding, or drilling. Accuracy here prevents waste of material and ensures the final product fits together perfectly. Common Tools and Their Uses: Steel Rule: For measuring lengths accurately. Scriber: A sharp, pointed steel tool used like a pencil to scratch fine, permanent lines onto the metal surface. Engineer's Try Square: Used to draw lines at a perfect 90° angle to an edge. Essential for making square and rectangular shapes. Dividers: Looks like a compass with two sharp points. Used for scribing circles, arcs, and stepping off equal measurements. Centre Punch: A pointed tool struck with a hammer to create a small indent (a 'pop') in the metal. This helps guide a drill bit or serves as a centre point for dividers. Marking Blue / Layout Dye: A special blue ink painted onto the metal surface. When the scriber scratches it, a very clear, bright silver line appears, making it easy to see.
Example: Marking out a simple metal tray Imagine you need to make a small rectangular tray (200mm x 150mm) with 30mm high sides. Step 1 (Develop the Pattern): You would first draw the flat pattern, which is called the "development". This would be a larger rectangle with squares cut out of the corners. The central rectangle would be 200mm x 150mm. The corner squares to be removed would be 30mm x 30mm. Step 2 (Prepare the Metal): Clean the sheet metal and apply marking blue for clarity. Step 3 (Establish a Datum): Use a file to make one edge straight and smooth. This is your 'datum edge' or reference point. Step 4 (Marking): Using an engineer's try square and scriber, draw a line at 90° to your datum edge. Measure and mark all the dimensions from your pattern onto the metal using the steel rule and scriber. Use the centre punch to mark any points for drilling if needed. Drawing as a Forming Process (Deep Drawing) This is a more advanced industrial process. It involves using a punch to force a flat sheet metal blank into a die cavity, stretching and shaping it into a cup-like or boxy form. Process: A circular blank of sheet metal is placed over a die opening. A punch then pushes the metal into the die. The metal is pulled inwards, or "drawn," to form the shape. Example: This is how seamless cooking pots, drink cans, and kitchen sinks are made. The flat metal is *drawn* into its deep, final shape without any welding on the sides.
*(Image shows a punch pressing a flat metal blank into a die to form a cup shape)* C. Die and Press Operations These operations use specialised tools (dies) and powerful machines (presses) to cut and form sheet metal with high speed and precision. This method is ideal for mass production. What is a Die? A die is a specialised, hardened steel tool used to cut or shape material. It works like a very strong and precise cookie cutter or mould. A simple die set has two parts: Punch: The top part that moves down to cut or form the metal. Die Block: The bottom, stationary part that has a shaped cavity or hole. The punch fits into the die block with a very small, precise gap (clearance). Key Die Operations: Blanking: This is a cutting operation where the punch is used to cut a shape out of a larger sheet of metal. The piece that is punched out is the desired part, called the blank. The rest of the sheet is scrap. *Example:* Cutting out circular discs to be formed into the lids for paint cans. Piercing (or Punching): This is the opposite of blanking. It is a cutting operation where the punch removes material from the inside of a part. The material punched out is the scrap (called a slug), and the sheet with the hole in it is the desired part. *Example:* Making the holes in a metal sieve or a 'kebab' grill mesh.