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: 14
Grade code: 2.2.2.LI.3
Strand code: 2
Sub-strand code: 2
Content standard code: 2.2.2.CS.1
Indicator code: 2.2.2.LI.3
Theme: METAL TECHNOLOGY
Subtheme: WELDING TECHNOLOGY
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Welcome, learners. Today, we are delving into a very practical and essential part of metal technology: sheet metal fabrication. Look around you in Ghana; from the body of a trotro to the "chop box" you take to school, from the roofing sheets on our homes to the pans used to sell roasted plantain, we are surrounded by objects made from cut and bent sheet metal. These skills are the foundation for many careers, including welding, auto body repair, and construction. Mastering how to accurately cut and bend sheet metal allows us to transform a simple flat sheet into a strong, useful, three-dimensional object.
This lesson focuses on the fundamental hands-on skills required to shape sheet metal. We will cover the entire process from planning to the final form. A. Safety in the Workshop
Safety is NOT optional. It is the most important part of our work. Before we touch any tool, we must remember these rules: Personal Protective Equipment (PPE): Safety Goggles: ALWAYS wear them to protect your eyes from sharp metal fragments. Thick Leather Gloves: Sheet metal edges are extremely sharp and can cause deep cuts. Never handle sheet metal without gloves. Workshop Apron/Coat: Protects your clothes and body. Strong, Closed-toe Shoes: Protect your feet from dropped tools or materials. Safe Environment: Keep your work area clean and tidy. Remove any tripping hazards. Tool Handling: Always carry sharp tools with the point facing down. Pass tools to others handle-first. B. Understanding Sheet Metal Definition: 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. Common Types used in Ghana: Mild Steel: Strong, affordable, and easy to work with. Prone to rust if not painted or coated. Used for car bodies, gates, and general fabrication. Galvanised Iron (GI): This is a steel sheet coated with a layer of zinc to prevent rusting. It is commonly used for roofing sheets, water tanks, and buckets. Aluminium: Lightweight, corrosion-resistant, and easy to shape. Used for cooking pots ("dadesen"), window frames, and food containers. Sheet Metal Gauge: This is a number that indicates the thickness of the metal. A smaller gauge number means a thicker sheet. For example, 18-gauge steel is thicker and stronger than 24-gauge steel. For most of our school projects, we will use gauges between 20 and 24. C. Stage 1: Marking Out (Pattern Development)
This is the planning stage. Just like a tailor uses a pattern to cut fabric, we use a pattern to mark out our shape on the metal before cutting. This process is called development. Marking Out Tools: Steel Rule: For measuring lengths accurately. Engineer's Try Square: Used to draw lines at a perfect 90-degree angle to an edge. Essential for making sure our boxes are square. Scriber: A sharp, pointed steel tool used to scratch lines onto the metal surface. It creates a much finer and more permanent line than a pencil or pen. Dividers: Used for marking out circles, arcs, or stepping off equal measurements. Centre Punch: A pointed tool struck with a hammer to create a small indent (a 'dot') in the metal. This is used to mark centres for drilling or to make layout lines more permanent. Example: Marking out a simple 100mm x 50mm rectangle Establish a Datum Edge: Ensure one edge of your sheet metal is straight and smooth. This is your starting point. Place the Engineer's Try Square firmly against the datum edge. Use the scriber to draw a line 90 degrees to the edge. This is your first side. Using the steel rule, measure 100mm along the datum edge from your first line and make a small mark. Measure 50mm up the first line you drew and make a small mark. Move the try square to your 100mm mark and draw another 90-degree line. Measure 50mm up this new line and use the steel rule as a straight edge to connect the two 50mm marks. You now have a perfectly square 100mm x 50mm rectangle marked on your steel. D. Stage 2: Cutting
Once the shape is marked, we cut it out. Precision here is key. Cutting Tools: Hand Shears / Tin Snips: These are like strong scissors for metal. Straight Snips (Yellow Handle): Best for cutting straight lines. Right-Cut Snips (Green Handle): Best for cutting curves to the right (clockwise). Left-Cut Snips (Red Handle): Best for cutting curves to the left (anti-clockwise). Bench Shear / Guillotine (Machine): A large machine used for making long, straight cuts quickly and accurately. It has a long blade that is brought down onto the metal with a lever. Safety is paramount when using this machine. How to Cut with Tin Snips: Wear your gloves and goggles. Secure the sheet metal piece in a vice or hold it firmly on a workbench. Open the snips wide. Start the cut at the edge of the metal, carefully following the scribed line. Use long, smooth strokes. Do not close the blades completely at the end of a stroke, as this can create a jagged edge. Stop about 80% of the way through the blade length and then take the next cut. Be careful of the sharp cut edge and the off-cut piece. E. Stage 3: Bending (Folding)