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5.9 Joining (assembling) our gearwheel

Whilst we cannot make our food mixer gearwheel just using joining processes, we could assemble it out of several pieces which must be joined together. In practice, any of the joining processes (soldering, adhesion and welding) would allow the wheel to be built up from bits. Wooden gearwheels and waterwheels used in mills many years ago, known as cog wheels, were made by assembling individual parts which could easily be repaired if any wore out after prolonged use. However, these were on a different scale from that of a gearwheel from a food mixer. So although building a gear would be possible, it is not really a practical proposition. Imagine trying to build a gearwheel from parts; each tooth would need to be manufactured individually and then screwed, glued or welded together to the central ring. A great number of hours would be spent manufacturing each one.

Although the gearwheel itself is not suitable for being made through an assembly process, it is itself assembled into the food mixer, which has many discrete parts, made from a range of processes. There is always a stage at which a single product is likely to be assembled in some form into a larger product for a particular use.

SAQ 10

List three advantages and three disadvantages of using joining processes in manufacturing.


Some advantages are:

  • joining enables large objects to be built up from smaller, more manageable components.

  • joining allows dissimilar materials to be joined.

  • practically speaking, most functional objects require joining because they cannot be made in one piece.

  • heat-sensitive materials can be joined at room temperature.

Some disadvantages are:

  • joints may be a weak point in a structure, and even welded joints will not have the strength of the individual materials that are joined.

  • surface preparation can affect the joint properties if adhesives are used, the design life of a joint may be hard to predict.

You may have suggested other, equally valid, factors.