Medical Device Precision Parts: Cleanliness, Traceability and Material Proof — Which One Gets Dropped From the Quote

Article

June 15, 2007

A surgical instrument joint may only need plus or minus 0.02mm, which plenty of industrial shops can hold. What they cannot always do is produce the evidence behind each unit. Here is what that evidence is, and how to write it into a request for quotation so the answers are comparable.

Precision Is Not the Gate; Evidence Is

Medical parts are often quoted as if they were simply high-precision parts, which misses the point. A stainless joint in a surgical instrument may hold plus or minus 0.02mm, while industrial shops routinely hold five microns. The real gate is not the tolerance but what can be produced as evidence behind every unit: material certificates, cleanliness records, sterilisation compatibility validation and change control records.

That explains why the same drawing can quote at more than double for a medical customer. An industrial customer accepts the part; a medical customer accepts the part plus the record of how it travelled. The first can rely on an experienced operator's feel. The second requires process, and the manufacturer has to be able to reproduce that record years later. So when qualifying a supplier for medical work, the useful question is not what machines they own but whether their inspection records are searchable by batch.

Material Proof: A Mill Certificate Is Not Enough

The 316L stainless, titanium and PEEK used in medical parts all need material certificates, but a mill certificate alone is usually insufficient. What a medical customer needs is the linkage proving this heat went into this batch of parts — a mapping from melt number to finished lot. One mixed bundle in the middle breaks the chain.

Sound practice is to tag on receipt, scan on issue, and isolate remnants separately. It sounds like a warehouse detail, but it decides whether an affected lot can be locked down within four hours when something goes wrong. This is the point most often skipped on bulk orders: the larger the lot, the higher the chance of mixing and the higher the traceability cost — which is part of why small medical batches are not cheap.

Cleanliness: The Requirement That Cannot Be Drawn

Cleanliness is usually expressed as residual particles per unit area or total residual mass, yet many drawings simply say the surface must be clean and free of oil. That is not actionable at acceptance, so it degenerates into a customer wiping the part with a white cloth to look for a dark mark — unscientific, and guaranteed to end in argument.

The workable approach is to split cleanliness into three written requirements: the cleaning process (ultrasonic, spray or vapour phase), the test method (particle count or gravimetric), and the packaging (double bag under vacuum or a cleanroom box). For parts that will later be sterilised, confirm that cleaning-agent residue will not conflict with the sterilisation method: ethylene oxide is sensitive to residue, while irradiation cares more about the material's own radiation tolerance.

Sterilisation Compatibility: Wrong Material Wastes Everything

The most commonly skipped step in medical material selection is asking whether the material can survive the sterilisation method the customer has chosen. The same PEEK changes dimensional stability after repeated autoclave cycles; some polycarbonate grades yellow and embrittle after irradiation; metal parts can pit after repeated cycles.

These problems are invisible at the prototype stage and tend to surface when the customer has finished sterilisation validation and is preparing for volume. For medical parts made by injection molding or investment casting, three questions belong in the quotation stage: which sterilisation method, what is the maximum number of cycles, and is dimensional data before and after sterilisation required. Answering those three well matters far more than a few cents on the price.

Change Control: Even a Chamfer Goes Through the Process

Changing a chamfer on an industrial part can be agreed in a single message. On a medical part it cannot: any change affecting form, material, process or supplier goes through change control, is assessed against completed validation, and is re-validated where necessary. That is not bureaucracy; it exists because validating once costs far more than changing once.

The practical consequence is that a medical quotation must include change management as a real cost: controlled process documents, change review records, and sealed storage of superseded tooling. It is also why bespoke medical parts typically take twice as long to develop as industrial parts of similar complexity. The time is not spent machining; it is spent confirming whether a change invalidates earlier validation.

Low Volume, High Mix: Why Medical Work Is Priced by Batch

Medical programmes are typically low volume and high mix: a platform may run a few hundred units a year split across a dozen variants, each with its own sterilisation method, packaging and labelling. Orders like these cannot be quoted as unit price times quantity, because the cost sits in changeover — a new cleaning programme, a different sterilisation pouch, a fresh batch record, a repeated first-article inspection.

A supplier that quotes medical parts at volume pricing will almost certainly run into trouble during execution: either a price increase mid-programme, or records quietly dropped. The workable approach is to state annual volume, variant count and minimum batch size in the RFQ, and ask for a two-part quote — batch cost plus unit cost — so that procurement can see which part was squeezed.

There is a scheduling consequence too. Medical parts usually cannot share a line with industrial work; cleaning, assembly and packaging need dedicated windows, which means reserved capacity rather than filling gaps. A useful audit question is how many shifts that line reserved for medical work last month. A specific number usually means real medical experience; we can always fit you in usually means none.

Putting It Into the RFQ

Compressed into four lines a buyer can actually use: material certificates must map to finished lot numbers; cleanliness must state cleaning process, test method and packaging; sterilisation compatibility must be confirmed at quotation stage including cycle count; and change control must fix a review deadline and name who owns re-validation. Written into the RFQ, those four lines separate suppliers immediately.

One more caution: sourcing medical parts on price alone is a trap. On the same batch, the lowest quote usually comes from a shop that has never done medical work, and what it left out is exactly those four items. The cost returns during validation, and the total ends up higher. Split the supplier quote into machining cost and compliance cost, and it becomes obvious who has actually done this before. View the manufacturer's product details