Lesson Notes By Weeks and Term v3 - Senior Secondary 2
fabrication of ferrous metals (sheet)
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fabrication of ferrous metals (sheet)
Download the Lessonotes Mobile Nigeria 2025 app for faster lesson access on Android and iPhone.
Subject: Welding & Fabrication
Class: Senior Secondary 2
Term: 1st Term
Week: 1
Theme: Practical Works / Projects
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Students should be able to fabricate of ferrous metal in to a required shape or object
height (H) of 300 mm: Body Flat Pattern: Length = Circumference (C) = $\pi \times D = 3.142 \times 200 \text{ mm} = 628.4 \text{ mm}$ Width = Height (H) = $300 \text{ mm}$ Add Seam Allowance: For welding, add 10-15 mm for overlap. So, Length = $628.4 \text{ mm} + 15 \text{ mm} = 643.4 \text{ mm}$. The body will be a rectangle of $643.4 \text{ mm} \times 300 \text{ mm}$.
Base Flat Pattern: Diameter = $200 \text{ mm}$. Need to cut a circle of $200 \text{ mm}$ diameter.
2. Material Selection: Select appropriate gauge mild steel sheet (e.g., 1.5mm - 2.0mm thick).
3. Measuring and Marking Out: Clean the sheet metal surface. Use a steel rule and scriber to accurately mark out the calculated rectangular body pattern and circular base pattern on the sheet. Use a centre punch to mark the centre of the circles before using dividers or a trammel for drawing. Ensure lines are clear and precise.
4. Cutting: Carefully cut out the marked rectangular body piece and circular base piece. For straight lines, use bench shears or a guillotine. For the circle, use tin snips or a nibbler, or a plasma cutter if available. Deburr all cut edges using a file to remove sharp edges.
5. Forming/Bending (Rolling the Body): Teacher Demonstration: Set up the slip roll machine. Adjust the rollers to the desired curve (cylinder diameter). Carefully feed the rectangular sheet metal into the slip roll machine, ensuring even pressure and multiple passes to gradually form it into a cylinder. The aim is to bring the two short edges together to form an overlapping seam. Alternatively, for smaller or less precise cylinders, mallets and a suitable cylindrical former (e.g., pipe) can be used.
6. Joining (Welding the Seam and Base): Body Seam: Align the overlapping edges of the cylinder body. Tack weld the seam at several points to hold it in place. Proceed with continuous welding (e.g., using SMAW) along the seam to create a strong, sealed joint. Grind smooth if necessary.
Base to Body: Place the formed cylindrical body onto the circular base. Ensure the base is concentric with the cylinder body. Tack weld the base to the body at several points around the circumference. Continuously weld the joint between the cylinder body and the base, ensuring a leak-proof seal (if required). Grind off excess weld material and sharp edges.
Alternative Joining: Riveting can be used if welding equipment is unavailable or impractical. Drill holes, insert rivets, and fasten with a pop riveter. For a strong, sealed joint, welding is generally preferred for mild steel.
7. Finishing: Clean the fabricated container. Grind any sharp edges or burrs. Apply a protective coating, such as primer and paint, to prevent rust (especially important for mild steel in Nigeria's humid climate). E. Safety Precautions Always wear appropriate Personal Protective Equipment (PPE) including safety glasses, gloves, and overalls. Ensure the work area is clean, well-lit, and free from obstructions. Use tools correctly and for their intended purpose. Be aware of sharp edges and burrs after cutting. Exercise extreme caution when operating power tools and welding equipment. Ensure proper ventilation during welding. Disconnect power from machines before making adjustments. * Report any faulty equipment immediately.
A. Introduction to Ferrous Sheet Metals Definition: Ferrous metals are alloys containing iron. Common ferrous sheet metals used in fabrication include mild steel (low carbon steel) and galvanized iron sheets.
Mild Steel (Low Carbon Steel): This is the most common ferrous sheet metal due to its affordability, ease of working (cutting, bending, welding), and good strength. It rusts easily if not protected.
Applications in Nigeria: Used for making water tanks, agricultural implements (e.g., hoppers, troughs), roofing sheets (though often galvanized), gates, fences, vehicle bodies, and general workshop fabrications.
Galvanized Iron (GI)
Sheet: Mild steel sheet coated with a layer of zinc to prevent rust.
Applications in Nigeria: Primarily used for roofing, guttering, water storage tanks, buckets, and other applications requiring corrosion resistance. While excellent for corrosion resistance, welding galvanized sheets requires good ventilation due to hazardous zinc fumes. For this practical lesson focusing on general fabrication, mild steel sheet is typically preferred for initial learning unless a specific project requires GI. B. Overview of Sheet Metal Fabrication Process Fabrication involves transforming flat sheets of metal into three-dimensional objects by a series of processes:
1. Design and Pattern Development: Creating a drawing or sketch, then developing a flat pattern (template) that, when cut and formed, will produce the desired 3D shape.
2. Material Selection: Choosing the appropriate type and thickness of sheet metal.
3. Measuring and Marking Out: Transferring the pattern dimensions accurately onto the sheet metal.
4. Cutting: Separating the required shape from the main sheet.
5. Forming/Bending: Shaping the cut metal through bending, rolling, or stretching.
6. Joining: Assembling multiple pieces or closing seams (e.g., by welding, riveting, bolting, soldering).
7. Finishing: Cleaning, deburring, and applying protective coatings (e.g., painting). C. Tools and Equipment for Sheet Metal Fabrication Teachers should demonstrate and explain the use of these tools.
Measuring Tools: Steel rules, measuring tapes, vernier calipers.
Marking Out Tools: Scriber (for lines), centre punch (for hole centres), dividers (for circles/arcs), protractor, combination square, surface gauge.
Cutting Tools: Hand Shears/Tin Snips: For cutting thin gauge sheets (straight, left, right cut types).
Bench Shears (Lever Shears): For cutting thicker sheets and longer straight lines.
Guillotine (Shearing Machine): Mechanical or hydraulic, for precise, high-volume straight cuts on large sheets.
Nibblers: For cutting intricate shapes and internal cuts.
Angle Grinder with Cutting Disc: For heavy-duty cutting.
Forming Tools: Hand Bending Machine (Folding Machine/Brake Press): For making straight bends.
Slip Roll Machine (Rolling Machine): For forming curves and cylinders. Mallets (Hide, Plastic, Rubber): Used with stakes for manual shaping without marring the surface. Stakes (Bench, Hatchet, Beakhorn): Anvil-like tools providing support for shaping and forming.
Joining Tools: Arc Welding Machine (SMAW): For strong, permanent joints (mild steel).
MIG/MAG Welding Machine (GMAW): Faster, cleaner welding.
Spot Welding Machine: For joining overlapping sheets (often for car bodies, but also general fabrication).
Pop Riveter and Rivets: For mechanical fastening.
Drilling Machine: For creating holes for rivets or bolts. Bolts, Nuts, and Washers: For temporary or dismountable joints.
Safety Equipment (PPE): Safety glasses/goggles, welding helmet, leather gloves, ear defenders, safety boots, overalls. D. Step-by-Step Fabrication of a Cylindrical Container (e.g., a simple refuse bin or water holder) This section focuses on fabricating a cylinder, as specified in the evaluation guide.
1. Design and Pattern Development: Teacher Explanation: A cylinder consists of a rectangular body and two circular ends (one base, one lid or top opening).
Example Calculation: To make a cylinder with a diameter (D) of 200 mm and a height (H) of 300 mm: Body Flat Pattern: Length = Circumference (C) = $\pi \times D = 3.142 \times 200 \text{ mm} = 628.4 \text{ mm}$ Width = Height (H) = $300 \text{ mm}$ Add Seam Allowance: For welding, add 10-15 mm for overlap. So, Length = $628.4 \text{ mm} + 15 \text{ mm} = 643.4 \text{ mm}$. The body will be a rectangle of $643.4 \text{ mm} \times 300 \text{ mm}$.
Base Flat Pattern: Diameter = $200 \text{ mm}$. Need to cut a
A. Teacher Activities: Introduction (10 minutes): Introduce the topic of sheet metal fabrication, its importance in Nigeria, and the types of ferrous metals used.
Briefly discuss the project: fabricating a cylindrical container.
Concept Explanation (20 minutes): Explain key concepts: flat pattern development (with the cylinder calculation example), major tools, and steps of fabrication (measuring, marking, cutting, forming, joining, finishing). Tool Identification & Safety Demonstration (25 minutes): Display and identify common sheet metal tools and equipment. Demonstrate their correct and safe usage, emphasizing PPE and general workshop safety rules. Highlight specific hazards associated with cutting, bending, and welding. Demonstration of Cylinder Fabrication Steps (45 minutes): Pattern Layout: On a large piece of paper or actual sheet metal, demonstrate the marking out of the body and base of a cylinder. Show calculation.
Cutting: Demonstrate safe use of tin snips/bench shear to cut out patterns.
Forming: Demonstrate the use of a slip roll machine (if available) or manual bending techniques with a mallet and former to shape the cylinder body.
Joining (Welding): If a welding machine is available, demonstrate tack welding and seam welding of the cylinder body and base. Emphasize proper technique, current settings, and safety (welding helmet, gloves). If not, demonstrate riveting.
Finishing: Briefly discuss deburring and painting.
Guided Practice Setup (10 minutes): Divide students into groups. Provide materials (pre-cut sheet metal if time is limited, or allow students to cut small pieces) and supervise the initial stages of marking out.
Circulation and Support: Move around the workshop, observe student activities, provide individual guidance, correct errors, and reinforce safety procedures. Answer questions as they arise.
Wrap-up and Review (10 minutes): Summarize the key steps, review safety, and preview the next steps for students' independent practice.
B. Student Activities: Active Listening and Note-taking: Students pay attention during explanations and demonstrations, taking notes on key concepts, tools, and procedures.
Tool Identification: Students identify and name various sheet metal tools and state their functions.
Safety Observation: Students observe safety demonstrations and ask clarifying questions about safe practices.
Pattern Sketching: Students sketch the flat pattern for a simple cylinder based on given dimensions.
Practical Application (Under Supervision): Measuring and Marking Out: Students practice measuring and marking out lines and curves on scrap sheet metal or the project material.
Cutting: Students (under strict supervision) practice using tin snips and files to cut and deburr small pieces of sheet metal.
Forming/Bending: Students observe and, where appropriate, practice using mallets and simple formers to bend metal. If a slip roll machine is available and safe for student use, they can practice rolling under direct supervision.
Joining: Students observe welding demonstrations and, if permitted and safe, practice basic tack welding under very close supervision, or practice riveting.
Discussion: Students discuss observed techniques, challenges, and solutions within their groups.
Questioning: Students ask questions for clarification during and after demonstrations.
Question 1: A student needs to fabricate a simple cylindrical water container with an internal diameter of 150 mm and a height of 250 mm from mild steel sheet. If a 10 mm overlap is required for welding the longitudinal seam, what are the dimensions of the rectangular sheet metal required for the body of the cylinder? (Use $\pi = 3.142$).
Solution 1: Step 1: Calculate the circumference (C) of the cylinder. $C = \pi \times D$ $C = 3.142 \times 150 \text{ mm}$ $C = 471.3 \text{ mm}$ Step 2: Add the seam overlap allowance. Length of sheet = Circumference + Overlap Length of sheet = $471.3 \text{ mm} + 10 \text{ mm}$ Length of sheet = $481.3 \text{ mm}$ Step 3: Determine the width of the sheet. The width of the sheet corresponds to the height of the cylinder. Width of sheet = $250 \text{ mm}$ Answer: The dimensions of the rectangular sheet metal required for the body are approximately $481.3 \text{ mm}$ (Length) by $250 \text{ mm}$ (Width).
Commentary: This question directly assesses the student's ability to perform the initial calculation for pattern development, a critical first step in fabrication. It is relevant to making common containers found in Nigerian homes and workshops.
Question 2: Identify three different cutting tools used in sheet metal fabrication and briefly state when each would be most appropriately used in the fabrication of a cylindrical container.
Solution 2: Tin Snips (Hand Shears): Best for cutting out the circular base and for trimming small irregular shapes or excess material from the cylinder body after rolling. They are ideal for thinner gauges and curves.
Bench Shears (Lever Shears): Most appropriate for making long, straight cuts on the rectangular body piece of the cylinder from a larger sheet, especially for thicker gauges where hand snips would be too difficult.
Angle Grinder with Cutting Disc: Suitable for quickly cutting thicker sheet metal or for making rough cuts if precision isn't paramount, or for separating large pieces of stock before finer cutting with other tools. Also useful for deburring rough edges quickly.
Commentary: This question tests knowledge of practical tool application, which is essential for efficient and safe work in a workshop environment common in Nigeria.
Question 3: Outline the correct sequence of steps involved in forming the rectangular sheet metal into a cylinder using a slip roll machine.
Solution 3: Adjust the Rollers: Ensure the slip roll machine's rollers are adjusted to the approximate radius required for the cylinder. The upper roll should be slightly raised to allow the sheet to pass through.
Initial Pass (Pre-bending/Crimping): Feed one end of the rectangular sheet (the leading edge) into the rollers to create a slight curve (pre-bend). This helps to avoid a flat spot at the start of the roll. Repeat for the other end of the sheet.
Continuous Rolling: Feed the sheet through the rollers, gradually tightening the top roll to increase the curvature with each pass. Ensure the sheet is fed squarely to maintain a consistent curve.
Forming the Cylinder: Continue rolling until the two short edges of the rectangular sheet meet, forming the desired cylindrical shape with the necessary overlap for joining.
Remove the Cylinder: Release the top roller and carefully remove the formed cylinder.
Commentary: This guides students through the practical skill of operating a key forming machine, which is fundamental to fabricating cylindrical shapes.
Local Manufacturing and Entrepreneurship: Students can apply sheet metal fabrication skills to start small businesses. Examples include fabricating custom-made refuse bins for homes and communities, water storage tanks for households, animal feeders for local farmers, local stoves (e.g., "adogan" or improved wood stoves), or protective casings for machinery in small-scale industries. This directly supports the "buy Nigeria" initiative and youth empowerment. Agricultural Equipment Repair and Production: In Nigeria's largely agrarian economy, the ability to fabricate and repair parts for agricultural machinery (e.g., hoppers for grain mills, protective covers for irrigation pumps, parts of wheelbarrows) is highly valuable. This skill can reduce reliance on imported components and support local farming communities.
Community Development Projects: Fabricated sheet metal products can directly benefit local communities. Students can use their skills to produce items like signboards for local businesses, roadside advertising panels, public waste bins, or even simple shelters/kiosks, contributing to local infrastructure and aesthetics.