Lesson Notes By Weeks and Term v4 - SHS 3
WELDING TECHNOLOGY
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WELDING TECHNOLOGY
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Subject: Applied Technology
Class: SHS 3
Term: 1st Term
Week: 13
Grade code: 3.2.2.LI.4
Strand code: 2
Sub-strand code: 2
Content standard code: 3.2.2.CS.1
Indicator code: 3.2.2.LI.4
Theme: METAL TECHNOLOGY
Subtheme: WELDING TECHNOLOGY
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Welcome, future engineers and technicians! Today, we are moving beyond just joining metals permanently with welding. A truly professional and complete metal product, like the burglar-proof windows in our homes or the frame of a "trotro", is more than just welded joints. It requires other components to assemble it and a protective coating to make it last long and look good. This lesson focuses on these two critical aspects: mechanical fasteners (like bolts and screws) and finishes (like paint).
This topic covers what happens before, during, and after welding to create a complete, functional product. We will break it down into three parts: Mechanical Fasteners, Finishes, and the guiding principle of Design for Manufacture. Part A: Mechanical Fasteners
A mechanical fastener is a hardware device that mechanically joins or affixes two or more objects together. Unlike welding, which creates a permanent bond, most fasteners create non-permanent or semi-permanent joints, meaning they can be removed for repair, maintenance, or disassembly.
Common Types of Mechanical Fasteners:
| Fastener Type | Description & Diagram Sketch | Common Ghanaian Application | When to Use It | | :--- | :--- | :--- | :--- | | Bolts & Nuts | A bolt has a head on one end and external (male) threads on the other. It passes through unthreaded holes in two parts and is secured by a nut with internal (female) threads. *(Sketch: A bolt with a hex head, a smooth shank, a threaded portion, and a separate nut)* | Attaching an engine to the chassis of a car; assembling a metal bed frame; fixing a bench vice to a workbench. | When you need a strong, secure joint that can be tightened to a specific tension and disassembled later for repairs. | | Screws | A screw is similar to a bolt but is designed to cut its own thread into the material it is turned into. - Machine Screws: Have a straight shank and are used with a pre-tapped hole or a nut. - Self-Tapping Screws: Have a tapered, sharp point that can form its own thread in sheet metal. | Roofing Screws (a type of self-tapping screw with a rubber washer) used to fix roofing sheets to wooden or metal purlins. Attaching number plates to vehicles. | When joining thin materials like sheet metal, or when one part is too thin to be tapped for a machine screw. Faster assembly than bolts and nuts. | | Rivets | A short metal pin or bolt for holding together two plates of metal. Its headless end is beaten or pressed down to form a second head (a process called upsetting). *(Sketch: A rivet before and after installation, showing the original head and the formed 'shop' head)* | Joining the handles to an aluminium cooking pot ("dadesen"); assembling metal trunk boxes ("chop boxes"); constructing water tank stands. | For a strong, permanent mechanical joint that is resistant to vibration and does not need to be disassembled. It is often cheaper and lighter than a bolt. | | Pins | Simple cylindrical fasteners. - Cotter Pins (Split Pins): Pass through a hole in a bolt or shaft to prevent a nut from loosening. - Clevis Pins: Used with a cotter pin to join parts that need to pivot. | Securing a wheel onto the axle of a wheelbarrow; preventing the castle nut on a vehicle's axle from coming off. | To lock other fasteners in place or to create a pivot point for moving parts. | Part B: Finishes