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: 16
Grade code: 2.2.2.LI.5
Strand code: 2
Sub-strand code: 2
Content standard code: 2.2.2.CS.1
Indicator code: 2.2.2.LI.5
Theme: METAL TECHNOLOGY
Subtheme: WELDING TECHNOLOGY
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In every Ghanaian town and city, we see skilled welders creating essential items that make our lives safer and more convenient – from the burglar-proof bars on our windows to the metal gates that protect our homes, and the market stalls where traders sell their goods. These creations are not made by chance; they are the result of a careful, planned process. This lesson focuses on that process: the step-by-step sequence of operations that turns raw metal pieces into a useful, finished product (an artefact).
The process of creating any welded artefact, whether simple or complex, follows a universal and logical sequence. We can break this down into four main stages:
Stage 1: Planning and Design Stage 2: Material Preparation Stage 3: Fabrication and Assembly Stage 4: Finishing
Let's explore each stage in detail. Stage 1: Planning and Design This is the most critical stage. Mistakes here are costly to fix later. "Measure twice, cut once" starts with good planning. Problem Identification: What is the purpose of the artefact? What need does it solve? *Example:* A classroom window is unsecured, posing a theft risk for school property. The problem is a lack of security. The solution is to fabricate a burglar-proof frame. Conceptualisation and Sketching: This involves drawing the design. Freehand Sketch: A rough drawing to capture the basic idea, shape, and features. Working Drawing: A detailed, neat drawing with precise dimensions (length, width, height) and specifications (e.g., type of metal to use). This drawing is the blueprint for the entire project. Material Selection: Choosing the right materials based on strength, cost, appearance, and resistance to rust (corrosion). *Example:* For a burglar-proof frame, we might choose 20mm x 20mm mild steel square pipe for the outer frame and 12mm solid square bars for the inner design. Mild steel is chosen because it's strong, relatively cheap, and easy to weld. Creating a Bill of Quantities (BOQ): This is a detailed list of all materials and their quantities needed for the project. It helps in purchasing and cost estimation.
Worked Example: BOQ for a 800mm x 600mm Burglar-Proof Frame | Item No. | Description | Material | Dimensions | Quantity | | :------- | :---------------------------------- | :----------- | :------------------------------ | :------- | | 1 | Top & Bottom Frame Members | Square Pipe | 20mm x 20mm x 800mm | 2 | | 2 | Side Frame Members | Square Pipe | 20mm x 20mm x 600mm | 2 | | 3 | Vertical Inner Bars | Square Bar | 12mm x 12mm x 560mm | 4 | | 4 | Horizontal Inner Bar | Square Bar | 12mm x 12mm x 760mm | 1 | | 5 | Welding Electrodes | E6013 | 2.5mm | 1 packet | | 6 | Metal Primer (Anti-rust) | Red Oxide | | 1 small tin | | 7 | Final Paint | Gloss Black | | 1 small tin | Stage 2: Material Preparation This is where we get the raw materials ready for joining. Accuracy is key. Measuring and Marking Out: Using the working drawing, we measure the lengths of metal required. Tools: Measuring tape, steel rule, engineer's try square (to ensure 90° angles), scriber (to scratch sharp lines on the metal). Process: Measure the required length accurately on the stock metal and mark a clear line with the scriber. Use the try square to ensure the cutting line is perfectly perpendicular. Cutting: The marked metal is cut to the required sizes. Tools: For a school workshop, a hacksaw is common. In commercial workshops, an angle grinder with a cutting disc is faster. Safety: Always wear safety goggles to protect your eyes from metal filings and sparks. Secure the metal firmly in a vice before cutting. Edge Preparation: After cutting, the edges are often sharp and rough (these are called burrs). Tools: A flat file or an angle grinder with a grinding disc is used to smoothen the edges. This ensures a tight fit during assembly and is a crucial safety step. Stage 3: Fabrication and Assembly This is the stage where the cut pieces are joined together to form the artefact. Layout and Arrangement: The cut pieces are arranged on a flat, level surface (like a welding table or a clean concrete floor) according to the working drawing. Tack Welding: This is the process of applying small, temporary welds at the corners or joints to hold the pieces together. Purpose: Tacking allows you to check the entire assembly for accuracy (e.g., squareness) and make adjustments *before* committing to a permanent weld. It's like using pins to hold fabric before sewing. Checking for Squareness: It is vital to ensure all 90° corners are truly 90°. Method 1 (Try Square): Use an engineer's try square at each corner. Method 2 (Diagonal Measurement): For any rectangle or square, the two diagonal measurements must be equal. If they are not, the frame is skewed and must be adjusted before final welding. Full Seam Welding: Once you are certain the assembly is accurate, you perform the final, continuous welds (seams or beads) along all joints to create a strong, permanent bond. Stage 4: Finishing This final stage improves the appearance and protects the artefact from the environment. Cleaning and Grinding: The welded joints are often lumpy and have slag (a byproduct of welding) on them. Tools: A chipping hammer is used to remove slag, and a wire brush is used to clean the weld area. An angle grinder with a grinding disc is then used to smooth the weld bead down so it is flush with the metal surface, giving a neat, professional look. Surface Treatment (Painting): This is essential to prevent rust (corrosion). Step 1: Priming: Apply a coat of metal primer (e.g., red oxide). The primer helps the final paint adhere better and provides a crucial anti-rust layer. Step 2: Final Painting: After the primer is dry, apply one or two coats of the desired colour of gloss or emulsion paint. This gives the final appearance and adds another layer of protection.