Production Aids With Electrical & Mechanical Components (AQA GCSE Design & Technology): Revision Note
Exam code: 8552
The use of production aids with electrical and mechanical components
Production aids help electronic and mechanical components to be positioned, drilled, soldered, wired and assembled accurately
Components may be small, directionally-sensitive or required to align precisely
This means clear reference systems are essential
Specialist fixtures can be used to protect components from:
movement
heat
static electricity
accidental damage during assembly (typically soldering)
Measuring and reference points for electrical and mechanical components
Electronic circuit diagrams use reference designators such as R1 (resistor), C1 (capacitor) and LED1 (Light emitting diode) to identify each component and its position in the circuit
Printed circuit boards use the following as reference points:
Grid spacing
Pad centres
Component outlines
Pin 1 marks
Direction symbols
Measurements for components include:
Pitch
Diameter
Shaft size
Hole spacing
Voltage
Current rating
The correct property must be checked before assembly
Mechanical systems use datum faces, centre lines, pitch circles and alignment marks to position shafts, bearings, gears, pulleys and linkages
Vernier callipers, micrometers and gauges may be used where small dimensional errors would prevent components fitting or moving correctly
Colour codes (often found on resistors) are reference systems that reduce assembly errors
Templates and patterns for electrical and mechanical components
A drilling template in a product casing can show the positions of:
PCB mounting holes
Switches
Displays
Motor shafts
Cable openings
A PCB artwork pattern defines the copper tracks, pads and component positions used when a circuit board is manufactured
A front-panel template can be printed at full size and attached to a casing before holes and cut-outs are made
Mechanical templates can be used to mark:
Repeated hole patterns
Gear centresBearing positions
Linkage pivot points
A wiring template or harness board shows the route and length of wires and the position of connectors in a repeated cable assembly
Templates reduce layout errors and help the electrical or mechanical assembly fit the casing and other components
Worked Example
Explain why polarity markings are important when fitting an LED to a PCB.
[2 marks]
Answer
An LED only works when connected in the correct direction. [1] The polarity marking helps the maker place the anode and cathode in the correct holes and prevents assembly faults. [1]
Jigs for electrical and mechanical components
A PCB drilling jig holds the board and guides very small drill bits through the centres of component pads
A soldering jig or PCB holder supports the board and components so they cannot move while joints are soldered
A programming or test jig makes temporary electrical contact with a PCB so software can be loaded and the circuit tested quickly
A wiring-harness jig uses pegs or clips to route wires to the correct length and position before connectors are fitted
A mechanical assembly jig aligns shafts, bearings, gears or frames while fasteners and spacers are added
Worked Example
Explain two ways a PCB assembly jig can improve production.
[2 marks]
Answer
It holds the board and components securely so they remain correctly positioned during soldering. [1]
It also speeds up repeated assembly and reduces faulty joints or incorrectly placed components. [1]
Examiner Tips and Tricks
Remember to keep template and jig clearly separate in your answers.
A template, such as a drilling template or a PCB artwork pattern, only marks out or shows positions; you still have to drill, solder or wire the component yourself afterwards.
A jig goes further: it physically holds the component and/or guides the tool during the operation itself, for example a PCB drilling jig that guides the drill bit through the pad centres, or a wiring-harness jig that fixes the wire route and length.
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