Systems: Processes, scales of production and quantity techniques

Introduction to Systems Production

Welcome! In this chapter, we are exploring how electronic and mechanical systems move from being just a single idea to a product that thousands of people can buy. We will look at scales of production (how many items we make) and the specialist techniques used to ensure every single one works perfectly.

Whether you are building a custom robot in your shed or manufacturing millions of smartphones, the "how" and the "how many" are vital decisions for any designer.

1. Scales of Production

The scale of production depends on how many items the market needs and how much money is available for machinery. There are four main types you need to know:

One-off Production

This is when only one product is made at a time. It is often a "bespoke" or custom-made item for a specific client.
Example: A custom-built control system for a one-of-a-kind experimental satellite.
Characteristics: High cost per item, highly skilled workers, and uses general-purpose tools.

Batch Production

This involves making a specific number of identical products (a "batch"). Once the batch is finished, the machines might be changed to make something else.
Example: Making 500 circuit boards for a boutique guitar amplifier.
Characteristics: Uses jigs and templates to speed things up; flexible enough to change designs later.

Mass Production

This is for making huge quantities of identical products over a long period.
Example: Producing thousands of identical TV remote controls.
Characteristics: High initial cost for automated machinery, but the cost per item becomes very low. Most work is done by robots or low-skilled workers monitoring machines.

Continuous Production

This runs 24 hours a day, 7 days a week. It is usually for raw materials or very simple, high-demand components.
Example: A factory producing standard copper wire used in electronic systems.
Characteristics: Extremely expensive to set up; stopping the production line can cost thousands of pounds.

Key Takeaway: As the scale of production increases, the cost per item usually goes down, but the cost of machinery goes up!

2. Techniques for Quantity Production

When making more than one of something, designers use "production aids" to make sure every part is identical. This is called accuracy and repeatability.

• Templates: A shape you can draw around to mark out a pattern onto material. It ensures every piece is cut to the same size.
• Jigs: A device that holds the material and guides the tool (like a drill) so that holes are always in the exact same place.
• Fixtures: These hold the material firmly in a set position while it is being worked on, but they don't guide the tool.
• Moulds: Used to shape materials (like plastic casings) into a specific form every time.
• Patterns: A replica of the object to be made, often used to create a mould.

Sub-assembly

In "Systems," we often use sub-assembly. This means different parts of the system (like the circuit board, the plastic case, and the wiring loom) are made separately and then "assembled" at the very end. This makes production much faster.

3. Systems-Specific Manufacturing Processes

How do we actually put a "System" together? Here are the official processes you need to know for your exam:

PCB Mounting

Printed Circuit Boards (PCBs) are the "brains" of most systems. There are two ways to attach components:

1. Through-hole: Components have long wire "legs" that go through holes in the board and are soldered on the other side. This is great for parts that might be pulled (like switches) because it is very strong.
2. Surface-mount technology (SMT): Components are tiny and are soldered directly onto the surface of the board. This allows devices (like smartphones) to be much smaller and is perfect for mass production using robots.

Digital Manufacture (CAM)

Computer-Aided Manufacturing (CAM) is essential for modern systems:

• CNC Laser Cutting: Uses a high-power laser to cut or engrave sheet materials (like acrylic cases) with extreme precision.
• 3D Printing: Builds up a 3D object layer by layer from a digital file. Great for one-off prototypes or complex shapes that are hard to mould.

Cable Management

A "System" isn't just a board; it often involves lots of wires. Good production uses:
- Looms: Bundling wires together so they don't get tangled.
- Sleeving and Ties: Protecting wires and keeping them neat for safety and reliability.

4. Quality Control and Tolerance

In the world of Systems, things have to be exact. If a resistor is the wrong value, the circuit fails!

Working within Tolerance

Tolerance is the "allowable margin of error." No manufacturing process is 100% perfect.
Example: If a wire needs to be \(100mm\) long with a tolerance of \(\pm 1mm\), any wire between \(99mm\) and \(101mm\) is acceptable. Anything else is "waste."

Quality Control (QC)

This involves checks during production. In systems, this might include:
- Visual checks of solder joints.
- Using a multimeter to check for continuity (making sure the electricity can flow).
- Testing the finished system to see if it performs the correct function.

5. Efficiency and Minimising Waste

Manufacturers want to make as much money as possible, which means wasting as little material as possible.
- Nesting: Arranging shapes on a sheet (for laser cutting) so they are as close together as possible.
- Standardised Components: Using the same type of screw or the same value of resistor across many different products to save money on buying in bulk.

Quick Review:
- Jig: Guides the tool.
- Fixture: Holds the work.
- SMT: Modern, small, surface-soldered components.
- Tolerance: The "acceptable error" (e.g. \(\pm 0.5\%\)).
- Batch: Making a specific set number of items.

Don't worry if the technical names for PCB mounting seem confusing; just remember: "Through-hole" goes through the board, "Surface-mount" stays on top!