GlossaryKind of term: Manufacturing termDesign for cost (DfC)
What is design for cost?
Design for cost is a design approach in which cost is a requirement: choices are tested against a target cost before the design is released.
The abbreviation is DfC. Cost counts alongside function, quality and lead time. In its strict form, also called design to cost, the development team receives a target cost per product, module or part and tests every choice against it: material, the number and kind of operations, tolerances, roughness, finishing and make or buy. Not everyone uses the term this strictly; sometimes it simply means designing with an eye on cost.
What does a design-for-cost estimate depend on?
A DfC decision is made early, often before there is a route, a chosen supplier or a quote. The cost then comes from an estimate: the engineering department's cost model, a cost per kilo or per operation, or a budget price from a supplier. How useful that estimate is depends on what the model takes into account. An average hourly rate and a generic machining time largely leave out the setups, the machine the part fits on, the tolerances between features and the subcontracted steps, even though these can decide the cost of a machined part. The target cost itself is often worked back: the end product's target selling price less the required margin, split across modules and parts.
How does design for cost work in practice?
For a supplier, DfC arrives as a request for a budget price, as a target price in a request for quotation, or as an invitation to comment on the design. An answer that shows what each choice costs, item by item, gives the designer something to work with: a wider tolerance that saves a finishing pass, a feature that saves a setup, a different stock form. What such a change is worth depends on quantities, machines and rates. Before release a change is usually cheaper to make than after, because afterwards it needs a new revision and a new approval.
What is design for cost often confused with?
Design for cost is not value engineering: value engineering breaks a design down into functions and looks for ways to deliver each at lower cost, often on an existing product, though it can also run during development. DfC makes cost a requirement from the start. Nor is a target cost a target price: the target cost is a requirement inside development, the target price the figure the buyer gives the supplier. And DfC is one of the goals within DfX, alongside design for manufacturing and design for assembly, among others.
How do you see design for cost in Blake?
In Blake the cost estimate of a machined part is split into lines for material, machining, finishing, setup and programming, per part and per batch for each quantity break, and labelled as an estimate. A changed design comes in as a new revision of the part, a new price as a new quote version. More on estimating.
Frequently asked questions
How do you set the target cost of a part?
Usually by working back from the market: the end product's target selling price less the required margin gives the allowable cost, split across modules and parts. For a machined part you test that against a cost built up from material, operations, setups and finishing.
What is the difference between design for cost and value engineering?
Design for cost makes cost a requirement from the start and steers the design before it is released. Value engineering analyses the function and cost of a design, mostly one that already exists or is in series production.
How should a supplier respond to a DfC request?
With a cost built up item by item, and the choices that cost most called out separately, such as a tolerance, a setup or a finish. State the assumptions, such as quantity and material, because the result depends on them.
Why does an engineering cost estimate often differ from the supplier's quote?
Such an estimate often works with averages: a generic hourly rate and a standard machining time, without setups, inspection time or subcontracted steps. The quote works from the shop's route, machines and hourly rates, and it is a price, with mark-ups and margin included.