The brief
Our customer is a German OEM that builds reusable laparoscopic tools under their own brand and private-label. The enclosure is the body of one of their tools — the surgeon’s hand grips it, the internal mechanism mounts to it, and six O-rings seal against machined faces inside the cavity. It is reusable, sterilized between patients by the hospital, and expected to survive at least 300 cycles over its service life before retirement.
Their previous vendor had held dimensional tolerances on first articles but the enclosures walked out of spec after 10 to 15 autoclave cycles — the bore went out-of-round and the O-ring seal failed. Our job was to requalify the part with documented 50-cycle stability as a floor.
Why the previous shop’s parts failed
We requested a used sample from the field and measured it on our CMM. What we saw was classic release of through-thickness residual stress: the sealing bore had ovalized by 0.12 mm after 12 cycles, and the long-axis length had shrunk 0.04 mm. The material was right, the geometry was right — the previous shop had skipped the pre-machining anneal on the plate and had taken finish passes too aggressively, leaving surface stress that released under the thermal cycling.
The lesson we wrote into our own medical-PEEK protocol after this job: anneal the plate, anneal again mid-process for parts with ribs or deep pockets, finish with at least 0.1 mm stock for light removal. It adds roughly 4 hours of oven time per lot. It is the difference between parts that pass validation and parts that come back after 15 cycles.
Process plan
Rough mill from 40 mm annealed plate in a single setup on a 3-axis vertical cell, leaving 0.5 mm of stock on all features. Remove from fixture, post-rough anneal at 150 °C for 1 hour in an air-circulating oven. Return to the cell, re-indicate datums, semi-finish to 0.15 mm stock, finish to final dimension with fresh tools and a light chip load. Final cleaning in isopropanol, visual inspection for any cosmetic defects, dimensional inspection on CMM. Pack in cleanroom-grade pouches.
The 50-cycle validation
The customer specified the validation cycle and we ran it through an accredited lab. Five parts entered the cycle at dimension Zero. We pulled them at cycle 1, 5, 10, 25, and 50 and CMM-measured the same twelve features each time. Bore diameter drifted 0.06 mm over 50 cycles, 0.04 mm of which happened in the first five cycles. All features stabilized by cycle 25. The customer’s acceptance criterion was 0.1 mm total — we passed with 40 % margin.
The lab report plus our CMM data and material cert became the supplier-qualification package. The customer’s regulatory team signed off four weeks later.
Ongoing production
We run 80 pieces per quarter on this part now, on a standing PO. Every lot ships with a DHR packet: material cert to the feedstock lot, CMM report on three parts, visual inspection record, cleaning record, and cleanroom packaging log. Unit price dropped 8 % between first article and third lot as we tuned the fixture and removed a redundant inspection step.
If you are building a reusable device and your current shop isn’t holding dimensional stability through sterilization cycles, send us the drawing plus the cycle spec. We will scope first-article, validation, and standing production and come back with a timeline inside a week.