Design for manufacture

Design for process — does the shape suit the way it is made? Design for assembly — how many parts and how do they go together? Design for disassembly — can it come apart?

Every DfM change is a change to the drawing. Once the tool is cut the same improvement costs a new tool.

Assembly wants snap-fits, adhesive and the fewest parts; disassembly wants screws, one fastener type and separable materials.

A released snap-fit a tool can open at a named point, or screws where the product must be opened and clips where it need not be.

Draft on every face so it releases, uniform wall thickness so it cools evenly, radii at internal corners, and no undercuts the tool cannot open past.

It cools more slowly than the thin wall beside it and shrinks after the surface has set, pulling the skin in. The fix is a rib at the same wall thickness.

A feature the tool cannot open past, such as a hook on an internal face. It needs a side-action or lifter, or a window in the wall beneath it.

A part designed for machining is a different shape from the same part designed for moulding, so choosing afterwards means redrawing the product.

Does it move relative to its neighbour? Must it be a different material? Must it be separable for assembly or service? If all three are no, combine it.

Combine parts into one moulding; snap-fits instead of screws; symmetrical or un-mistakable parts; and assembly from one direction.

It takes a purchase order, a stock line, an inspection, an assembly operation and a chance of error with it.

When the parts are bonded into an inseparable lump, or when combining them needs a tool so complicated that the saving disappears.

What fails first, and how deep is it buried? In almost every powered product the answer is the battery.

Screws or released clips instead of adhesive; the shortest-lived part reachable first; one fastener type throughout; and materials marked and not bonded together.

It avoids a whole new product — all its extraction, manufacture and distribution. No material substitution comes close.

It costs assembly time on every unit, paid by the manufacturer, for a benefit somebody else receives years later — which is why it is regulated.

Process changes manufacture; assembly changes manufacture and distribution; disassembly changes use and disposal.

Design for disassembly, because repair and upgrade extend the use stage. A three-year life becoming ten avoids two whole products.

Bonding two different materials to reduce the parts count: assembly is faster and cheaper, and neither material can be recovered at the end.

Find the dominant life-cycle stage, remove parts, make the shapes easy to produce, then check it can still come apart.