case studies
How Flexiversa Eliminated Recurring Dimensional Rejects for a Medical Device OEM's Plastic Mouldings
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Flexi Versa Group
How Flexiversa Eliminated Recurring Dimensional Rejects for a Medical Device OEM's Plastic Mouldings
The rejection notice arrived the same week as a scheduled customer audit. A mid-volume medical device OEM, sourcing a family of precision-molded housing and closure components for a diagnostic instrument line, had just failed incoming inspection on a production lot — not because the parts were out of spec, but because nobody could agree on what "in spec" actually meant. The moulder's inspection report showed passing dimensions. The OEM's quality team, measuring the same features on the same parts, showed failures. Two data sets, one part, no shared definition of how it should be measured or accepted.
The Challenge
The root of the problem wasn't the tooling or the moulding process — it was that tolerances and acceptance conditions had never been fully reconciled between design intent and shop-floor measurement practice. Drawings specified dimensions and general tolerances, but critical details — datum structure, measurement temperature and conditioning time, gauge type, sample size, and how bowed or warped features should be handled — were either assumed or left to interpretation. That gap is common in plastic moulding, where dimensions shift with mould shrinkage, cooling rate, and material lot variation in ways that don't apply to machined metal parts.
For this client, the stakes were specific and immediate:
A production lot on hold, threatening a customer delivery commitment already tight against a device launch date
Conflicting inspection data between OEM and moulder, with no agreed method to resolve it
Risk that the disagreement would surface during the upcoming customer audit as a quality-system gap, not just a supplier issue
Engineering time being consumed re-measuring parts that should have shipped weeks earlier
A growing concern, unspoken but real, that this pattern would repeat on every future lot unless the underlying ambiguity was fixed
For a regulated medical device supply chain, an unresolved dimensional dispute isn't just a scheduling headache — it's a documentation gap that an auditor can flag, and a supplier relationship that starts to look unreliable at exactly the point it needs to look dependable.
The Solution
Flexiversa's engineering team didn't start by re-measuring the disputed lot. They started by getting both sides' measurement methods on the table, side by side, to find out where they actually diverged.
Joint measurement review. A Flexiversa quality engineer walked through the OEM's CMM program and the moulder's own inspection setup together, feature by feature, to identify exactly where the two methods disagreed — datum selection, fixturing, and post-mould conditioning time before measurement all turned out to matter more than either side had assumed.
Drawing and acceptance criteria clarification. Where the print was ambiguous, Flexiversa worked with the OEM's design team to formally define the missing conditions: measurement temperature and stabilization period, datum structure consistent with how the part actually functions in assembly, and clear pass/fail sampling criteria tied to the process capability of the tool.
Process capability study. Rather than treating the disputed lot as pass or fail in isolation, Flexiversa ran a short-term capability study across the feature set in question, giving both sides real data on where the moulding process was stable and where tolerance bands were tighter than the process could reliably hold.
Updated inspection protocol. The findings were written into a shared, documented inspection method — not a verbal agreement — specifying gauge type, fixturing, sample plan, and acceptance conditions, so future lots would be measured the same way by both parties.
Requalification of the held lot. With the corrected method applied, the disputed lot was re-measured jointly and the actual disposition — release, rework, or scrap — was based on data both sides trusted.
Technical Support & Collaboration
What moved this from a stalled dispute to a resolved issue in days rather than weeks was direct access to the people who understood the moulding process, not a queue. The OEM's quality lead worked straight with a Flexiversa process engineer from the first call, with no account manager relay in between slowing down technical back-and-forth.
Every measurement discrepancy was documented as it was found, so the OEM's own quality system had a clear paper trail heading into their audit — not a verbal explanation after the fact. Flexiversa also flagged, proactively, two additional features on the same part family that showed the same ambiguity risk, before they became separate disputes on a future lot. That kind of forward-looking communication is what separates a supplier fixing a single complaint from one closing out the underlying pattern.
The Outcome
The held lot was released against the corrected, jointly-agreed inspection method, clearing the delivery commitment ahead of the device launch. More importantly, the updated tolerance and acceptance documentation became the standard reference for every future lot of that part family, removing the recurring source of disagreement rather than papering over one instance of it. When the OEM's customer audit took place, the documented resolution process was cited as evidence of active supplier quality management rather than a gap. The client avoided what would otherwise have been a repeat cycle of holds, re-measurement, and schedule erosion on every subsequent order.
Why It Worked
In-house measurement and process engineering expertise, so tolerance disputes could be resolved with data rather than opinion
Direct engineer-to-engineer communication, removing the delay of routing technical questions through account management
A documented, repeatable inspection protocol that survives beyond any one person's memory of a verbal agreement
Proactive identification of related risk features, addressing the pattern rather than just the immediate complaint
Closing
Dimensional disputes in plastic moulding are rarely about a part being genuinely out of tolerance — far more often, they're about two organizations measuring the same feature under different, unstated assumptions. Resolving that gap requires a supplier willing to open up their measurement method for scrutiny and put the agreed criteria in writing, not just resolve the immediate lot and move on. That's what good technical support looks like for OEMs sourcing precision-molded components: not just a passing inspection report, but a shared, documented understanding of what "acceptable" actually means.
Facing a dimensional dispute or unclear acceptance criteria with a plastic moulding supplier? Contact our team at contact@flexiversa.com to talk through your specific tolerance challenge.
Frequently Asked Questions
What are acceptance conditions in plastic moulding, and how are they different from tolerances?
Tolerances define the allowable dimensional range for a feature. Acceptance conditions define how and under what circumstances that feature is measured to determine pass or fail — including gauge type, fixturing, datum structure, sample size, and post-mould conditioning time. Two parts can have identical tolerances but produce different pass/fail results if the acceptance conditions aren't clearly defined and shared between buyer and moulder.
Why do plastic parts show more dimensional variation than machined metal parts?
Plastic parts shrink and can continue to relax dimensionally for hours or days after moulding, depending on material, wall thickness, and cooling rate. Machined parts don't have this post-process movement. That's why measurement timing and conditioning period are often as important as the tolerance value itself for moulded components.
Does a process capability study fully resolve a dimensional dispute?
Not on its own. A capability study shows how consistently a process can hold a given tolerance, which is essential data — but it needs to be paired with a jointly agreed measurement method. Without agreement on how a feature is measured, even solid capability data can be interpreted differently by each side.
How should an OEM evaluate whether a moulding supplier's measurement claims are trustworthy?
Look for a documented, repeatable inspection protocol rather than a verbal description of "how we check it." Ask whether the supplier is willing to run a joint measurement review with your own quality team and put the agreed method in writing. A supplier confident in their process will welcome that scrutiny rather than resist it.
Can unclear tolerances on a print cause quality issues even if the moulding process itself is capable?
Yes. A capable process can still produce disputed rejects if the print or inspection method leaves room for interpretation — ambiguous datums, unspecified measurement temperature, or undefined sample plans are common gaps. The fix is usually documentation and communication, not a process or tooling change.
What should happen when a lot is placed on hold due to a dimensional disagreement?
The priority is establishing a measurement method both parties trust before disposing of the lot, rather than defaulting to scrap or an informal override. A joint review that reconciles the measurement approach protects both the immediate lot and every future lot from the same dispute recurring.