Design for Manufacturing: 10 Engineering Mistakes That Increase Production Cost

Manufacturing cost depends on the route used to make a part repeatedly, not only on material volume. A successful design review considers setup effort, cycle time, tooling, inspection, scrap risk and assembly. The ten mistakes below frame a cost discussion with the supplier. Savings should be demonstrated through comparable quotations or process estimates rather than promised as a universal percentage.

1. Choosing geometry before choosing a process

A shape suited to additive manufacturing may be expensive to machine from solid stock. Compare candidate processes against quantity, material, quality and lead time before freezing geometry. Include finishing operations that the initial process cannot deliver.

2. Ignoring batch size

A dedicated fixture or mould spreads its cost across the production volume. For a small batch, a more flexible process may be preferable even with a longer per-part cycle. Compare total delivered cost at the actual expected quantities.

3. Requiring avoidable setups

Features on multiple faces may introduce extra locating and inspection steps. Investigate whether shared datums, accessible orientations or a revised assembly reduce setup count. Preserve functional relationships across features when consolidating operations.

4. Using tight tolerances without a functional reason

Precision can require slower cuts, specialised tooling or additional inspection. Allocate tolerance to the interfaces that need it, using a fit and stack-up assessment. Review a supplier's proposed relaxation against function rather than accepting it solely for cost.

5. Specifying unnecessary surface finish

A sealing face and a nonfunctional external face may have different finish requirements. Match the requirement to contact, wear, sealing or appearance. Avoid extending a critical finish callout across the whole part through an ambiguous drawing note.

6. Designing fragile machining features

Deep pockets and slender walls can increase chatter, distortion and rejection risk. Consider local stiffness, cutter reach and material-removal sequence. The cheapest nominal geometry may have poor repeatability in production.

7. Proliferating custom features

Unnecessary fastener sizes, unusual hole depths and unique inserts increase tool changes and purchasing complexity. Standardise where it preserves function. Verify that a standard substitute has the required strength, environmental resistance and access.

8. Leaving inspection until the end

A critical internal feature may need specialised measurement or destructive sectioning. Define how acceptance will be demonstrated while designing the part. Supplier inspection capability should inform the drawing and production plan.

9. Overlooking assembly and service

A low-cost component can create expensive assembly if tools cannot reach fasteners or orientation is ambiguous. Review installation order, handling, error-proofing and replacement access. Assess the complete product rather than optimising an isolated part.

10. Changing revisions without updating the process

A small CAD edit can invalidate fixtures, toolpaths, inspection programmes and purchased stock. Link each released revision to its manufacturing package and identify which downstream items require review. Rework caused by stale information is a design-control problem.

Compare options with a simple cost model

For illustration, route A has a 600-unit setup cost and costs 20 per part; route B has a 2,000-unit setup cost and costs 12 per part. Ignoring other differences, their total costs are equal at 175 parts: (2,000 − 600)/(20 − 12). Tool life, scrap, inspection, financing and delivery could change the real choice.

Use such a model to expose assumptions, then request supplier evidence. Autodesk's DFM guidance supports early process selection; the engineering task is to evaluate which change improves the actual production route without weakening functional performance.