The big idea: Design for manufacture means changing the DESIGN so the product is easier to make, put together and take apart.
Three strategies: design for process asks whether the shape suits the machine. Design for assembly asks how many parts there are and how they go together. Design for disassembly asks whether it can ever come apart again.
The three strategies, and the conflict between the last two.
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| Strategy | Typical changes to the drawing | What it gains |
|---|---|---|
| Design for process | Draft angles, uniform wall thickness, radii instead of sharp internal corners, no undercuts, features a cutter can reach | Fewer rejects, a cheaper and simpler tool, shorter cycle times, and a part that comes out right first time |
| Design for assembly | Combine parts into one moulding, snap-fits instead of screws, symmetrical parts that cannot be fitted wrongly, assembly from one direction | Fewer parts to buy, stock and inspect; faster assembly with less training; far fewer mistakes |
| Design for disassembly | Screws and clips rather than adhesive, one fastener type, materials marked and grouped, the shortest-lived parts reachable first | Repairable products, recoverable materials, a longer working life, and compliance with tightening end-of-life regulation |
All three happen before the tooling is ordered: Every change on that list is a change to the drawing.
After the tool is cut, the same improvement costs a new tool — which is why DfM is a design activity with a deadline, not a review carried out at the end.
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| Design for assembly wants | Design for disassembly wants | |
|---|---|---|
| Joints | Snap-fits and adhesive — fast, light and cheap | Screws and released clips — openable, at the cost of time |
| Parts count | As few as possible, ideally one moulding | Separable materials, which sometimes means more parts |
| Materials | Whatever is fastest to mould and bond | Compatible materials that can be recycled together, and no bonded sandwiches |
| Direction | Everything assembled from one direction | The shortest-lived part reachable first, which may be from another direction |
The resolution, not the compromise: A released snap-fit — one a tool can open at a named point — gives most of the assembly speed and most of the disassembly.
Otherwise: screws where the product will need to be opened, clips where it will not, and never a glued sandwich of two different materials.
How this is tested — outlining design for process, assembly and disassembly strategies. It comes up two ways:
Paper 1 — multiple choice
- Identify which DfM strategy a described change belongs to.
- Choose the strategy that addresses a stated problem.
Paper 2 — analysing a product
- Outline the three DfM strategies for a named product.
- Explain how two DfM strategies conflict, and resolve it.
The trap: Treating DfM as a principle to agree with. Every mark is a specific CHANGE to the design — a draft angle, a combined part, one fastener type.
A moulded electric toothbrush is being redesigned. Outline how each of the three DfM strategies would change it, and where two of them conflict.
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