3.1 Impact of Six Sigma Projects on Customers, Suppliers, and Stakeholders
Key Takeaways
- A process change propagates to customers, suppliers, internal downstream processes, support functions, and regulators.
- Tightening an internal tolerance without notifying the supplier converts your improvement into their non-conformance.
- Customers can be harmed by improvements that change lead time predictability, packaging, documentation, or minimum order quantity.
- A stakeholder impact table in the charter forces the team to state the expected effect and the risk for each affected party.
- In regulated environments a process change triggers change control and possible customer or regulatory notification, and that lead time belongs in the project plan from Define.
Impact propagates in every direction
A Six Sigma project changes a process, and processes sit inside a network. The Body of Knowledge asks Black Belts to describe that propagation at the Understand level, but the practical requirement is harder: predict it before it happens and design for it.
| Stakeholder | Typical positive impact | Typical negative impact if unmanaged |
|---|---|---|
| External customers | Fewer defects, shorter and more predictable lead time, lower cost | Changed packaging or documentation; changed minimum order quantity; a transition period with mixed old and new product |
| Suppliers | Clearer requirements, more stable demand signal, longer-term relationship | Tightened tolerances imposed without notice; smaller more frequent orders; new inspection or certification burden |
| Internal downstream processes | Better inputs, less rework, less firefighting | New handling requirements; different arrival pattern; retraining they did not request |
| Internal upstream processes | Clearer specification of what is needed | New data collection duties; changed schedule |
| Support functions | Fewer escalations and corrective actions | New maintenance intervals, new calibrations, new system changes, new reports |
| Operators in scope | Less rework, less frustration, safer work | Changed standard work; loss of familiar workarounds; perceived job risk |
| Regulators and certification bodies | Better documented, more capable processes | An unnotified change to a validated process |
Suppliers are inside the system
The most common and most damaging propagation failure is treating a supplier as external to the project.
A team tightens an incoming dimensional tolerance from $\pm 0.15$ mm to $\pm 0.08$ mm to raise downstream assembly yield. Internally the project succeeds. At the supplier, a process with a Cpk of 1.4 against the old tolerance now has a Cpk of 0.75, so their scrap rate rises from near zero to several percent. Within two months the cost arrives back as a price increase, a delivery shortfall, or an incoming quality problem, and the net effect on the enterprise is negative.
The rule: any change to a requirement that a supplier must meet is a supplier project as well as yours. Practically that means:
- Share the capability data and the reason for the change, not just the new number.
- Confirm the supplier's capability against the proposed requirement before committing to it.
- Consider whether the assembly can be made robust to the existing tolerance instead -- parameter design is often cheaper than buying tighter components.
- Agree the transition: effective date, existing stock disposition, first-article requirements.
The same logic runs the other way for demand: a project that reduces batch size improves your flow and converts the supplier's steady monthly order into weekly orders, which may raise their setup cost. That is a legitimate change but it must be negotiated, not imposed.
Customers can be harmed by improvements
Improvements that look unambiguously good internally can still create customer impact:
| Change | Unintended customer impact |
|---|---|
| Shorter lead time | Customer planning systems and safety stock were tuned to the old lead time; a change in variability matters more than a change in mean |
| Reduced packaging material | Handling or storage at the customer changes; their automation may not accept it |
| Consolidated shipments | Fewer deliveries per week disrupts a customer running to a daily schedule |
| Changed component supplier | Requires customer requalification in regulated or safety-critical applications |
| Revised documentation format | Customer receiving systems and their audit records must be updated |
The test is simple and often skipped: would the customer notice this change, and would they need to do anything about it? If yes, they must be told before it happens, not discovered afterwards.
The stakeholder impact table
Build it in Define, alongside the SIPOC, and revisit it at every toll gate.
| Stakeholder | Internal / external | Current experience | Expected impact | Risk | Mitigation | Owner |
|---|---|---|---|---|---|---|
| Assembly cell 2 | Internal | Receives 4% of kits short | Complete kits; new pick sequence | Operators must learn a new layout | Standard work plus 2-week hypercare | Cell supervisor |
| Moulding supplier | External | Ships to $\pm 0.15$ mm | Requirement tightens to $\pm 0.10$ mm | Their Cpk falls below 1.0 | Joint capability study before commitment | Supply quality engineer |
| Fleet customers | External | 6-day lead time | 3-day lead time | Batch reduction may raise unit price | Model total cost with the customer | Account manager |
| Field service | Internal | Handles miswired-unit rework | Far fewer callouts | Loses visibility of failure modes | Share the new defect data monthly | Service manager |
| Notified body | External | Process validated in 2024 | Process parameter change | Requires change control and possible notification | Regulatory review in Analyze | Regulatory affairs |
The rows that carry a risk entry are the ones worth reviewing with the sponsor. The row types most often missing are the internal downstream process that absorbs the change without being asked, and the support function that inherits a new recurring obligation.
Regulated environments
Where the process is validated -- medical devices, pharmaceuticals, aerospace, food, automotive safety -- a process change is not merely an engineering decision. It triggers formal change control, may require revalidation, and in some cases requires customer or regulatory notification before implementation. Those steps have lead times measured in weeks or months.
The failure mode is discovering this in the Improve phase, when the solution is designed and the sponsor expects implementation. Regulatory and change-control lead times belong in the project plan from Define, and the regulatory function belongs on the stakeholder list from the first charter review.
Measuring the impact
Where impact is expected, measure it rather than assuming. Two mechanisms:
- Consequential metrics in the project's measure set, so degradation elsewhere is visible while the primary metric improves.
- A short post-implementation check with each affected stakeholder, at 30 and 90 days, asking specifically what changed for them. Suppliers and internal downstream processes rarely volunteer that a change hurt them; they absorb it and the cost surfaces later as something else.
A team tightens an incoming component tolerance from plus or minus 0.15 mm to plus or minus 0.08 mm to raise assembly yield. What is the most likely system-level consequence if the supplier is not involved?
Which change is most likely to disrupt a customer even though it appears to be an unambiguous improvement?
In a validated, regulated process, when should the change control and possible regulatory notification lead time be entered into the project plan?