The big idea: The DfM strategies change the environmental impact of manufacture, use and disposal — and they do it by changing the drawing, which costs nothing once the product is redesigned.
Process cuts waste and energy in making. Assembly cuts parts, material and transport. Disassembly decides whether anything is recovered at the end.
Three strategies, each reaching a different part of the life cycle.
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| Strategy | Life-cycle stage it changes | How |
|---|---|---|
| Design for process | Manufacture | Fewer rejects, less scrap, shorter cycles and therefore less energy per part — and ribs instead of thick sections use less material for the same stiffness |
| Design for assembly | Manufacture and distribution | Fewer parts means less material, less tooling, less stock and often a smaller, lighter product that ships denser |
| Design for disassembly | Use and disposal | Repair and upgrade extend the USE stage, which is the largest saving of all — and separable marked materials are actually recovered rather than shredded |
The largest saving is the product not made: Extending a product's life from three years to ten avoids two whole products — all their extraction, manufacture, packaging and transport.
No change of material, no efficiency in the factory and no packaging improvement comes close to that. Which is why design for disassembly is the strategy with the largest environmental leverage, even though it is the one that costs the manufacturer most.
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In this order, on any product
Find the dominant life-cycle stage
For a powered product it is use; for a passive one, extraction. That decides which strategy is worth the most before any change is made.
Remove parts and material
Design for assembly first, because a part that is not there has no impact at any stage of its life.
Make the remaining shapes easy to produce
Design for process: fewer rejects and less scrap, and a shorter cycle means less energy per part.
Then make sure it can come apart
Design for disassembly, checked against the assembly decisions just made — because that is where the two conflict.
DfM is not automatically green: A design-for-assembly change that bonds two materials together reduces the parts count and makes the product unrecyclable.
So each strategy has to be checked against the life cycle rather than assumed to help. A lower parts count, a faster cycle and a cheaper tool are cost improvements first, and environmental ones only when the end of life is checked too.
How this is tested — discussing how DfM strategies reduce environmental impact. It comes up two ways:
Paper 1 — multiple choice
- Identify which life-cycle stage a DfM change affects.
- Choose the strategy with the largest environmental effect.
Paper 2 — analysing a product
- Explain how DfM strategies reduce a named product's impact.
- Evaluate a DfM change against the whole life cycle.
The trap: Assuming every DfM change is an environmental improvement. Bonding two materials to reduce the parts count helps assembly and ruins recycling.
A manufacturer redesigns a kettle: the parts count drops from 22 to 12, the body is now one moulding with the handle bonded on, and the element plate is welded rather than screwed. Evaluate this against the whole life cycle.
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