Key takeaways
- Cleanliness is designed into the part and the process, not inspected into the final lot.
- Passivation removes free iron and supports the oxide layer, but it cannot remove embedded iron or heat tint.
- Validation covers the process that makes the part, so a change of wire, lubricant or bath is a validation event.
- Agree the document pack, the cleanroom class and the acceptance limits at RFQ stage.
What makes a medical wireform different
A medical wireform is still a bent piece of wire, but the consequences of a bad one are different. It may be a basket that holds instruments through a wash cycle, a spring clip on a single-use device, a retainer inside a diagnostic instrument or a component that ends up near a patient. In every case, the part has to be clean, traceable and made by a process that has been shown to work.
That shifts the centre of gravity of the project. On an appliance part, the first question is cost. On a medical part, the first question is what the device has to demonstrate and which of those claims depend on the wireform. The answers decide the material, the surface finish, the forming route, the cleaning steps and the packing.
The commercial conversation matters, but it comes after the quality plan. A supplier who quotes without asking for the grade, the cleanliness call and the document pack is quoting a different part.
Cleanliness starts on the drawing
A geometry that traps liquid will trap it through every cleaning step. Closed loops, overlapping legs, tight crevices between two wires and blind gaps at a weld are all places where residue, polishing compound or cleaning fluid can sit. The drawing should open those features or remove them.
Radius calls matter for the same reason. A tight inside radius is hard to clean and hard to passivate evenly, because the surface is compressed and the bath has less access. A larger radius, or a bend that stands off the part, costs little in forming and saves effort downstream.
The surface call is the other half. A medical wireform may need a specific Ra, a bright finish, an electrophished surface or a deliberately matte one. Each of those routes creates its own residue, so the drawing should name the surface condition and the cleaning step that follows it.
Finally, say whether the part is supplied clean and packed, or clean and ready for a sterilisation step the device maker controls. Those are different specifications with different evidence.
A trap is a design decision
If a feature can hold a droplet, assume it will. Open the loop, add a drain path or move the joint. Cleaning a trap is more expensive than avoiding one.
Passivation: what it does and what it cannot do
Passivation is a chemical treatment that removes free iron from a stainless steel surface and encourages the chromium oxide layer that gives the alloy its corrosion resistance. For stainless wireforms it is usually specified against ASTM A967 or ASTM A380, with a citric or nitric acid process. The standard, the acid, the concentration, the time and the temperature all belong in the process record.
Passivation is not a cleaning step that fixes everything. It will not remove embedded iron left by carbon steel tooling, it will not remove heat tint from a weld or a heat set operation, and it will not close a scratch. Those need pickling, mechanical removal or a change in the upstream process. A part that is passivated over embedded iron can still show rust at the inclusion.
The practical consequence is that tooling and handling have to be controlled before the bath. Dedicated stainless or coated tools, gloves, clean bins and a ban on carbon steel brushes are cheaper than reworking a lot. Lubricant from the former has to be removed before passivation as well, or the bath will not reach the surface.
Nitinol and other speciality alloys need their own route. Heat setting creates an oxide that has to be removed, and the surface preparation call is different from a 316L part. Do not assume a stainless passivation line is the right line for a nickel titanium component.
The records a medical lot should carry
The exact pack depends on the device classification and the quality agreement between the device maker and the supplier. The list below is a starting point for the conversation, not a claim that every programme needs every line.
| Document | What it records | When it is issued |
|---|---|---|
| Material certificate | Heat number, grade and chemistry, typically to EN 10204 3.1 | With each lot of wire |
| Passivation record | Standard, bath, concentration, time and temperature | Per passivation batch |
| Cleanliness verification | Method, limit and result for residues or particles | Per batch or per validated run |
| First article inspection | Every drawing call, with the measurement method | Before the first production release |
| Process validation report | Installation, operational and performance evidence | Before routine production |
| Bioburden result | Count against the agreed limit, where the device requires it | Per batch or per sterilisation lot |
| Change notification | What changed, the risk assessment and the revalidation plan | Before the change is implemented |
The pack should be agreed in writing at RFQ stage. A supplier that cannot list its records before the order is placed will not produce them after it.
Validate the process, not only the part
A first article can pass and the process can still be out of control. Medical device quality systems, usually built on ISO 13485, expect the manufacturing process to be validated where the output cannot be fully verified by inspection alone. Forming, cleaning, passivation and packing are the usual candidates.
Validation is normally staged. Installation qualification confirms the machine, tooling, utilities and software are as specified. Operational qualification challenges the process across its window: the smallest and largest wire diameter, the shortest and longest bend, the top and bottom of the bath temperature range. Performance qualification runs production conditions and shows the output meets the specification across consecutive lots.
Risk management, usually to ISO 14971, decides where the effort goes. A part that could injure a patient or compromise a sterile barrier deserves more evidence than a bracket inside a lab instrument. The risk file should name the wireform, the failure modes and the controls that address them, and the validation plan should trace back to it.
Do not treat a supplier certificate as a substitute for the validation record. A certificate says a system exists. The validation report says this process, on this line, with this tooling, produces a part that meets this specification.
Cleanroom packing and the sterile barrier
The forming area and the packing area do not need the same class. Forming is dirty by nature: lubricant, metal fines and handling. Packing a clean part is a different operation and should be separated, with a controlled transition between the two.
Cleanroom classification is usually stated to ISO 14644-1. A device maker may ask for a particular class for bagging, and the class should be written into the drawing or the quality agreement along with the gowning, the entry procedure and the environmental monitoring that supports it. The class is only meaningful if the room is monitored and the monitoring records are kept.
The pack itself is part of the design. If the wireform goes into a sterile barrier, the bag, the seal and the labelling fall under ISO 11607. That means a seal strength and integrity check, a defined fold or pouch size that does not puncture on the wire ends, and a label that carries the lot and the part number. Wire ends should be deburred or capped so they cannot pierce the film.
Change control and the triggers for revalidation
In a validated process, a small change is not small. A new wire supplier can change the surface condition, the inclusion content and the forming behaviour. A new lubricant changes what the cleaning step has to remove. A new passivation bath or a new acid concentration changes the surface. Each of those is a change notification and a risk assessment, and some of them need revalidation.
The trigger list should be agreed early. Typical triggers include a change of wire grade or supplier, a change of forming tool, a change of lubricant or cleaning chemistry, a change of passivation line, a change of cleanroom class or packing material, and a move of production to another site. Cosmetic changes such as a new bin colour do not belong on the list.
Where the device maker holds the design, the supplier should not approve a change alone. The notification goes to the device maker, the risk file is reviewed and the decision is recorded. That is slower than a phone call, and it is the reason a validated supply chain holds together.
Sending a medical wireform out for quote
Send the drawing and the CAD file, the alloy and temper, the wire diameter, the surface and cleanliness requirement, the packing and cleanroom class, the annual volume and the release size. Add the document pack and the standard each document must meet.
Say which operations the supplier owns and which the device maker owns. If sterilisation, final cleaning or biocompatibility testing sits with the device maker, the drawing should say so. If the supplier is expected to provide bioburden data, the sampling plan and the limit have to be agreed before the first lot.
Then ask two questions that separate a capable supplier from an optimistic one. Ask which changes would require a new validation, and ask to see a redacted example of the record pack. The answers tell you more than a price.
- Drawing revision, CAD file and the surface call
- Alloy, temper and wire diameter with tolerance
- Cleanliness limit, test method and cleanroom class for packing
- Document pack and the standard behind each record
- Annual volume, release size and sterility route
- Change notification and revalidation expectations
Frequently asked questions
Does a medical wireform always need passivation?
Not always, but it is common for stainless parts. Passivation supports the corrosion resistance of the alloy by removing free iron. Whether it is required, and to which standard, depends on the alloy, the device and the surface specification. Nitinol and coated parts follow different routes.
Can passivation remove rust from a stainless wireform?
It can remove light free iron contamination, but it is not a repair process. Embedded iron, heat tint and deep scratches need pickling, mechanical removal or a change upstream. Passivating over a defect can leave the defect in place under a thin oxide layer.
What cleanroom class is needed for packing medical wireforms?
It depends on the device and the agreement with the device maker. The class is stated to ISO 14644-1 and should be written into the specification along with gowning and monitoring. Forming and packing are usually separated, with a controlled transition between them.
Does a new wire supplier trigger revalidation?
It can. A new supplier may change surface condition, inclusions and forming behaviour, which affects cleaning and passivation. Treat it as a change notification, assess the risk and decide whether revalidation is needed. The decision should be recorded, not assumed.
Sources and further reading
- ASTM A967, Standard specification for chemical passivation treatments for stainless steel parts
- ISO 13485, Medical devices, quality management systems
- ISO 14644-1, Cleanrooms and associated controlled environments, classification of air cleanliness
Qumek Engineering Desk
Engineering team
The engineering team behind Qumek drawings, DFM notes, tolerances and inspection standards. Every guide is reviewed against the drawings and processes used on live programmes.
Have a medical wireform drawing to review?
Send the drawing, the alloy, the cleanliness call and the document pack. The engineering desk will reply with a written note on the forming route, surface preparation and validation points.
Send a drawing