Process Rethink

Question the process itself: a different technology or supplier process can delete cost the design cannot.

Time1 h
FormatSmall group
StageGenerate

Process Rethink: what it is and why it works

Process Rethink questions the manufacturing route itself rather than the geometry it produces. Most design-to-cost work tunes a part inside a process that nobody chose deliberately: a bracket is machined because the first prototype was machined, a housing is welded because the shop has welders. The method lists every process in the cost breakdown, asks whether each one exists by habit, by capability or by genuine requirement, and then tests alternative technologies at the actual production volume. The comparison is made on total cost, meaning piece price plus tooling, qualification, learning-curve losses and the cost of running two routes during the transition.

It works because process choice sets the cost floor. Design refinements can shave a few percent off a machined part, but moving to a casting, a stamping or a laser-cut and formed design can remove whole operations. The method pays off most at volume changes, when a product moves from tens to thousands per year, or when a supplier base offers capabilities that did not exist when the design was frozen. It pairs naturally with Make or Buy, since a new process often means a new supplier, with Material Substitution, since materials and processes move together, and with Activity-Based Costing, which exposes the setup and handling costs a process switch can eliminate.

What you need

Current cost breakdown by operation (routing with times, rates and material)
Annual and cumulative volume forecast, including expected ramp
Functional requirements that genuinely constrain the process (loads, pressure, finish, certification)
Capability data or quotes for at least one alternative process
Qualification requirements: first article, customer approval, code or standard compliance

What you get

Process inventory tagged habit, capability or requirement
Short list of alternative routes with piece cost at forecast volume
Switch cost estimate: tooling, validation, dual running, learning losses
Total-cost comparison with payback and break-even volume
Decision and, if approved, the design changes the new process needs

When to use it

When design is optimized inside a process that should not exist.

How to do it, step by step

List the manufacturing processes in the current cost breakdown.
For each, ask: is this process chosen by habit, by capability, or by requirement?
Identify processes where a different technology could cut cost at the volume: stamping versus machining, welding versus adhesives.
Quantify the switch cost: tooling, validation, learning curve.
Decide with total cost, not piece price.

Worked example: From welded fabrication to ductile-iron casting for a gearbox housing

Illustrative scenario — figures are realistic but not from a real company.

A mid-size manufacturer of industrial mixers builds a gearbox housing as a welded steel fabrication: plate cutting, fit-up, welding, stress relief and full machining. At 150 units a year this made sense. A new water treatment contract will push demand to about 1,500 units a year, and the fabricated housing costs $640 each.

The team listed six operations on the routing and tagged stress relief and heavy machining as habit: they existed only because welding distorted the part.
A foundry quoted a ductile-iron casting at $310 plus $120 of finish machining, with a pattern at $48,000.
Engineering added $32,000 for first-article inspection, a load test and customer approval, and $15,000 for scrap and learning losses during the first 300 castings.
The design needed draft angles, uniform 0.5 in walls and relocated bosses, which the team reviewed with the foundry before committing.

Result. The cast route saves about $210 per unit, roughly $315,000 a year at full volume, against a switch cost near $95,000, so payback comes in under four months. The fabricated route was kept as a qualified backup for spares. The team's lesson: the process had never been reviewed since the product was a low-volume special.

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Common pitfalls and how to avoid them

Comparing piece prices only and ignoring pattern, die or fixture costs.Put tooling, qualification and dual-running costs in the comparison and compute break-even volume explicitly.
Assuming the current design can be dropped into the new process unchanged.Review the design rules of the new process (draft, wall thickness, bend radii) with the supplier before quoting.
Rethinking the process once at launch and never again.Re-run the process inventory at every major volume change or new-supplier opportunity.
Treating certification or code requirements as an afterthought.Check early whether the new route needs requalification under the applicable code, customer specification or site rules, and include that cost and lead time.

Frequently asked questions

How do you choose between machining, casting and stamping for a part?

Start from volume and geometry. Machining has low tooling cost and high cycle cost, so it suits low volumes and tight features. Casting suits complex, thick-walled shapes at medium volume once pattern cost is spread. Stamping needs expensive dies but very short cycles, so it wins on thin sheet parts at high volume. Compute total cost per unit at your forecast volume and find where the curves cross.

What is the break-even volume for a process change?

It is the volume at which the one-time switch cost equals the cumulative piece-cost saving: break-even volume = switch cost / (old unit cost - new unit cost). Include tooling, qualification and learning losses in the switch cost. If the forecast volume over the product's remaining life is well above break-even, and the risk is manageable, the switch is worth pursuing.

Is Process Rethink the same as value engineering?

It is one lever within value engineering. Value engineering examines function and cost across the whole product, including materials, features and specifications. Process Rethink focuses specifically on how the part is made and whether a different manufacturing technology or supplier process would reach the same function at lower total cost.

Origin

Process selection in engineering design — manufacturing process economics (Kalpakjian & Schmid tradition).

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