Medical Implant Stamping: Grade 23 Titanium and 316LVM

Medical stamping fails on the documentation table before it fails in the field. A stamped clip inside a surgical instrument or an implantable lead fails silently, and the cost is a recall, not a return. That is why medical stamping lives on three things most industrial runs never face: tighter tolerance, certified clean material, and traceability from strip coil to finished lot. A stray inclusion in 316LVM can seed a corrosion pit in chloride-rich tissue fluid. A titanium particulate left from a sloppy blanking edge can trigger a chronic inflammatory response that never settles. And if a lot of bone-screw blanks cannot be traced back to its melt, the entire shipment gets rejected at incoming inspection, ISO 13485 audit or not.

This guide is written the way implant programs are actually engineered: start with the alloy and its governing spec, then the die and the process window, then the surface, then the paper trail. It covers the two alloys that carry most stamped implant work - Grade 23 titanium (Ti-6Al-4V ELI per ASTM F136) and 316LVM stainless (per ASTM F138) - plus the stamping process realities behind thin-stock blanking, electropolishing and passivation, the ISO 10993 biocompatibility evidence chain, melt-level traceability, the failure modes that send lots back, and how to evaluate a stamper before you commit tooling. The numbers cited are the ones that appear on real material certificates, real drawings, and real first-article reports.

The Snapshot

• Implant blanks are stamped from strip in the 0.10-1.0 mm range on precision progressive dies; piloted tooling holds strip positioning to ±0.005 mm and critical features on implant blanks typically hold ±0.01 mm.
• Grade 23 Ti-6Al-4V ELI per ASTM F136 is the load-bearing workhorse: tensile 860 MPa, yield 795 MPa, elongation 10%, modulus about 113 GPa - roughly half the stiffness of stainless, which reduces stress shielding next to bone.
• 316LVM per ASTM F138 is the vacuum-melted stainless of record: tensile 490 MPa, yield 190 MPa, elongation 40%, PREN about 24-26 for chloride resistance.
• Electropolishing per ASTM B912 takes stamped surfaces below 0.2 µm Ra on stents and below 0.4 µm Ra on most implants; passivation per ASTM A967 and ASTM F86 rebuilds the passive film.
• Every coil ships with an EN 10204 type 3.1 certificate and heat-level lot control; a lot that cannot be traced to a melt does not ship.

What We Actually Stamp for Implants

When people hear "metal stamping" they picture fenders and brackets. The medical world is the opposite end of the spectrum. We are talking bone plates and screw blanks in the 0.5 to 3 mm stock range, vascular stent frames cut from tube or strip at 100 to 200 micron wall, and catheter components like marker bands and hypotube segments where a 0.01 mm deviation changes how the device behaves in a coronary artery. These are small, thin, unforgiving parts, and each family carries its own dominant risk.

None of these parts is big, and none forgives a sloppy process. The die that produces them is a precision progressive tool whose clearance, piloting and sharpening schedule are treated as quality parameters, not maintenance trivia. Precision progressive dies hold plus or minus 0.01 mm on good days. That is the playing field, and the buyer's job is to make sure the supplier's process can stay on it for the life of the program, not just for the first article.

Grade 23 Titanium: Ti-6Al-4V ELI per ASTM F136

For load-bearing implant structures - plates, screws, spinal constructs - Grade 23 is the workhorse. It is the Extra Low Interstitial version of Ti-6Al-4V, governed by ASTM F136. The ELI designation matters because the oxygen ceiling drops to 0.13% maximum against 0.20% on standard Grade 5. That tighter interstitial control buys you fracture toughness and fatigue life, which is exactly what a bone plate cycling under every step needs. The chemistry is fixed tight:

• Titanium: balance
• Aluminum: 5.5 to 6.5%
• Vanadium: 3.5 to 4.5%
• Iron: 0.25% maximum
• Oxygen: 0.13% maximum (the ELI line)
• Carbon: 0.08% maximum
• Nitrogen: 0.03% maximum
• Hydrogen: 0.012% maximum

Annealed bar minimums from the spec: tensile strength 860 MPa, yield strength at 0.2% offset 795 MPa, elongation 10%. Density sits at 4.43 g/cm3 and the elastic modulus around 113 GPa - roughly half of stainless, which is a feature, not a bug, because the lower modulus reduces stress shielding next to living bone. Fatigue strength in the 450 to 500 MPa range under rotating-beam testing is what keeps a fracture-fixation screw from failing after a million cycles.

The catch with titanium is the springback. It springs back three to five times more than stainless after a bend, so the die has to overbend and the toolmaker has to know the material's actual recovered angle, not a textbook guess. Die clearance runs tight, about 5 to 8% of stock thickness, and tool wear is real because titanium work-hardens and galls against tool steel. That is why a serious titanium program is a die-engineering program: the compensation is built in CAD before the first hit, and the tryout loop is budgeted as part of tooling cost, not discovered on the first article. For the wider family of difficult alloys and their process windows, see our exotic alloy stamping guide.

316LVM: The Vacuum-Melted Stainless per ASTM F138

For non-load-bearing or moderate-load parts - marker bands, certain catheter components, some stent platforms, surgical wire - 316LVM is the stainless of record, covered by ASTM F138. The "VM" is the whole story: vacuum melting, typically vacuum arc remelt (VAR) or electroslag remelt (ESR), drives non-metallic inclusions down versus commercial 316L. Fewer inclusions means better fatigue performance and better pitting resistance in body fluid. The alloy envelope:

• Carbon: 0.030% maximum
• Manganese: 2.00% maximum
• Phosphorus: 0.025% maximum
• Sulfur: 0.010% maximum
• Silicon: 0.75% maximum
• Chromium: 17.0 to 19.0%
• Nickel: 13.0 to 15.0%
• Molybdenum: 2.25 to 3.00%
• Iron: balance

Annealed bar minimums: tensile strength 490 MPa, yield strength 190 MPa, elongation 40%. Density is 7.9 g/cm3 and modulus close to 193 GPa. The molybdenum is what gives the pitting resistance its teeth; the PREN (pitting resistance equivalent number) lands around 24 to 26, enough to resist chloride attack in physiological environments far better than plain 316. The vacuum remelt also shrinks the sulfide stringer population that plain 316L can carry, which is the difference between a stent strut that survives ten years of cyclic bending and one that finds its inclusion in year three.

316LVM stamps more easily than titanium - lower springback, longer die life, friendlier on progressive tooling. Where titanium wins on strength-to-weight and modulus matching bone, 316LVM wins on formability, cost, and corrosion behavior for the right application. If stainless is your material class across a broader program, the stainless steel stamping guide covers the wider grade family and process windows.

Choosing Between Grade 23 and 316LVM

The selection question is not which alloy is better; it is which alloy matches the mechanical duty, the corrosion environment, and the cost ceiling of the device. The comparison below is the table I put in front of every new device buyer, because the wrong choice shows up late - at fatigue testing, not at quoting.

The decision logic is short. If the part carries load and stays near bone, titanium wins on modulus matching and fatigue; that is why fracture-fixation hardware is Grade 23, period. If the part is thin-walled, high-formability, or cost-sensitive and the design tolerates a stiffer material, 316LVM wins - that is why catheter components and many stent platforms stay in stainless.

Cost follows the same fork. Titanium strip commands a multiple of stainless raw material cost, and its tooling costs more because of galling, coatings and springback tryout. On a small part the material premium can move the piece price more than any process efficiency, so the honest question at quoting is not "what is your price per part" but "what is your price per part against which certified melt, and what scrap rate does your process hold on this alloy". A cheap titanium quote is usually a process risk in disguise - thinner coating, looser tolerance, or a material cert that arrived after the order instead of with the coil.

Stamping Process Realities

Thin Stock and the Die Window

Thin stock is the rule. We run strip from 0.1 mm up to about 1.0 mm for most implant blanks, with the progressive die carrying the part through blanking, forming, and cutoff in one pass. At those thicknesses the die clearance is a fraction of a hair, and the difference between a clean shear and a torn edge is measured in microns of clearance and hundredths of a millimeter of pilot wear.

Piloting matters more on medical work than on any commercial part. The strip is fed by pilots into bushes every pitch, and the pilot holes are cut in the first station. If the pilot wears, every downstream station drifts together - a 0.005 mm positioning error on the press becomes a 0.01 mm feature error on the part. That is why piloted progressive dies with ±0.005 mm positioning are the baseline for implant blanking, and why the tolerance map on the drawing must name which features are pilot-located before the die is cut.

Burr and Edge Quality

The risks are edge quality and burr control - a ragged blanking edge is a particulate source and a stress raiser. We hold burr under 10% of stock thickness and verify it on the lot. On a 0.2 mm stent strut, 10% is 0.02 mm, and a burr that size on a fatigue-critical edge is a crack that has already started. Burr direction is fixed by the die layout - the burr follows the punch side - so the drawing must state which face is functional, and the supplier must build the die so the burr lands where the print says it does.

Edge condition is verified per lot, not per die. The first article tells you the die is capable; the lot tells you it stayed capable. That means burr height belongs in the inspection plan with a gage and a limit, and the limit is written by the buyer on the RFQ, not invented at the first rejection.

Work Hardening and Tooling

Work hardening is the other variable. 316LVM cold-works fast, so over-aggressive forming hurts ductility and the final elongation. Titanium work-hardens too and galls against tool steel, so we coat dies and watch for transfer marks. Neither material forgives a dull punch, and a worn section of a progressive die throws off edge geometry across the whole strip before anyone notices. Tooling for implant work therefore runs on a sharper schedule: coated die inserts, documented regrind intervals, and a maintenance log that the auditor can read. A stamper that cannot show you the regrind history of the die that made your lot is asking you to trust the process instead of verify it.

Lubrication and Cleanliness

Stamping lubricant is a biocompatibility variable in disguise. The lubricant that keeps titanium from galling is the same residue that shows up on a surface analysis after the part is stamped, so the lubricant choice, the cleaning step, and the acceptance limit for residue have to be fixed before production - not discovered when the device maker's surface test comes back. Clean handling after stamping matters just as much: film-interleaved packaging, gloves, and segregated lines so implant work never shares a bin with oily commercial parts.

Surface Engineering: Electropolishing, Passivation and Cleaning

You can stamp a perfect blank and still fail biocompatibility on the surface. Electropolishing is the step that removes the damaged, contaminated surface layer and leaves a smooth, passive finish. We follow ASTM B912 for the electropolishing process and ASTM F86 for surface preparation and marking of metallic surgical implants. A machined or stamped surface at roughly 0.8 micron Ra comes down below 0.2 micron on stents and below 0.4 micron on most implants after a proper polish. That finish removes embedded iron, reduces crevice sites, and improves the passive chromium-oxide layer that the body reads as inert.

What Electropolishing Actually Removes

The stamped surface is not the bulk material. The shear zone at a blanked edge is cold-worked, and the surface carries embedded tool steel particles, lubricant residue, and a disturbed grain structure. Electropolishing dissolves the high points preferentially, which is exactly what a mechanical polish cannot do - it removes the disturbed layer without smearing it. On 316LVM the benefit is measurable: fewer inclusions exposed at the surface, lower surface area for protein adhesion, and a chromium-enriched passive film after passivation.

Passivation and Verification

After polishing we passivate per ASTM A967 and ASTM F86 to rebuild the passive film, then verify with a citric or nitric bath and, where the customer requires, a corrosion test. Surface finish is not cosmetic here - it is the difference between a part the body tolerates and a part it rejects. A rough surface also collects proteins and cells you do not want adhered to a stent. The passivation step is the one most often skipped in a cheap quote, because it is invisible until the corrosion test; ask specifically how passivation is verified, because "we passivate" is not the same as "we test passivation".

Cleaning and Packaging

Post-passivation handling is a process step, not a courtesy. Parts leave the line clean and must arrive clean: film-interleaved packaging, segregated lots, and no bare-hand contact. Particulate control is the thread that runs through stamping, polishing and packaging - every operation that touches the part either adds particles or removes them, and the audit question is which one the supplier's process does on purpose.

Biocompatibility, Traceability and Quality Gates

ISO 10993 Evidence

Material cert is step one. The biological evaluation follows ISO 10993 - cytotoxicity per ISO 10993-5, sensitization and irritation where the device contacts tissue, and hemocompatibility per ISO 10993-4 for anything that touches blood, which is every stent and catheter part we make. We supply the material history and the clean-surface evidence; the device maker runs the full biocompatibility dossier. Our job is to make sure nothing in our process - lubricant residue, embedded abrasive, smeared metal - adds a variable they cannot control. A clean, passive, fully documented surface is the contribution stamping makes to that dossier.

ISO 13485 and Lot Control

ISO 13485:2016 is the quality system behind this. The practical requirement is simple to state and unforgiving to miss: every stamped part must trace to its heat and its lot. We tag material with the mill heat number, hold an EN 10204 type 3.1 certificate per incoming coil or bar, and maintain lot control through blanking, forming, polishing, and shipment. If a single stent lot cannot be tied back to its 316LVM melt, it does not ship. The audit trail - inspection records, process parameters, calibration of the gages that measured it - is as much a deliverable as the parts. Auditors do not look at your best part; they look at your worst documented one.

Inspection and First Article

First article inspection on implant work covers dimensions, edge condition, surface finish and material identity, with the dimensional data generated on calibrated CMM and optical measurement equipment. Production lots run under the same discipline: capability studies on critical features with Cpk targets, SPC on the features that drive assembly or fatigue, and a release gate that ties the lot record to the heat certificate before shipment. The same quality infrastructure that runs IATF 16949 programs - documented APQP-style planning and PPAP-style submissions - is what makes medical documentation credible, which is why the IATF 16949 explainer is worth reading even for non-automotive buyers: the documentation discipline transfers directly.

Failure Modes and Root Causes

Case 1: Embedded Iron on a 316LVM Surface

A catheter component lot failed surface analysis when the device maker found iron transfer on the outer diameter. The root cause was a die section wearing on the form station and smearing tool steel onto the strip; the electropolish step had been specified at a depth that removed the disturbed layer on the flats but not in the radius where the smearing concentrated. The fix was a coated insert at the wearing station, a shorter regrind interval, and a surface test on the first article of every subsequent lot. The lesson is that surface contamination is a die-wear problem as much as a cleaning problem, and the surface spec belongs on the drawing.

Case 2: Burr on a Bone-Screw Blank Edge

A screw-blank lot was rejected at incoming inspection for a burr of roughly 0.04 mm on a 1.2 mm blank - over the 10% acceptance line. The die had run 80,000 strokes past its regrind schedule because the maintenance log was not tied to stroke count. The fix was a documented regrind interval and burr verification on every lot. The lesson is that burr is a process-control indicator: it climbs with wear long before the part looks wrong, and the buyer who puts a burr limit on the RFQ gets a supplier who manages the die instead of hoping.

Case 3: A Lot That Could Not Find Its Melt

A distributor received a shipment of implant blanks where the coil certificate could not be reconciled with the lot record. The parts were dimensionally perfect and the material was almost certainly correct, but the lot was quarantined because the traceability chain had a gap. The lesson is the one that opens this guide: medical stamping fails on the documentation table before it fails in the field. The DHR (device history record) is the product.

Case 4: Springback Shift on a Titanium Form

A titanium clip drifted out of bend-angle tolerance between tryout and production because the die had been compensated with a textbook springback value, not the recovered angle of the actual coil. Coil-to-coil variation in titanium temper moves springback enough to matter at ±0.5° bends. The fix was a springback check at tool tryout on the production coil, with the compensation recorded and the bend angle verified per lot.

Supplier Evaluation and Cost Considerations

Capability Filter

Score candidates against this matrix before tooling, because medical programs are too expensive to qualify twice:

Audit Questions

Ask questions with numbers attached. Which ASTM spec governs your material purchase, and who signs the certificate? What is your burr limit on a 0.3 mm blank, and how do you verify it? What is the regrind interval on the die that will make my part? How many strokes since the last regrind? Where is the first article generated, and who signs it? What was your scrap rate on the last titanium program? What happens when a dimension drifts above 90% of tolerance? The answers separate a medical-grade process from a commercial stamper with a certificate on the wall.

Cost Structure

Implant stamping costs divide into three buckets: certified material, precision tooling, and surface finishing. Material is the largest variable because implant grades carry a premium and scrap is expensive - a 60-80% strip utilization target on a titanium coil is a cost lever, not an efficiency slogan. Tooling is the second bucket: a precision progressive die for thin medical stock with coated inserts and springback compensation is a multi-station tool with a five-figure price. Surface finishing is the third: electropolish, passivation, cleaning and inspection are process steps with their own cost, and a quote that leaves them out is a quote for a part you cannot use.

Red Flags

Three answers end the conversation. No ISO 13485 certificate. A material certificate that arrives after the parts instead of with the coil. Or a surface spec answered with "we polish it" and no Ra target, no ASTM reference, and no verification method. Also flag quotes priced so far below the material curve that the grade is being swapped - the audit for implant material is the melt certificate, not the price.

FAQ

Can implant-grade parts be stamped, or are they always machined?

Stamping is standard for high-volume implant blanks - bone-screw blanks, plates, marker bands, instrument components - where the tolerance, edge and surface requirements can be held in a progressive die. Machining wins for one-off prototypes, very thick cross-sections, and geometries that need 5-axis work. The crossover depends on volume and tolerance, and a DFM review on the drawing settles it in a day.

What is the difference between Grade 23 and Grade 5 titanium?

Both are Ti-6Al-4V. Grade 23 (ASTM F136) is the Extra Low Interstitial version with an oxygen ceiling of 0.13% versus 0.20% on Grade 5 (ASTM B265 / AMS 4911), which buys fracture toughness and fatigue life for implant duty. If a drawing says Grade 5 on an implant part, question it - implant-grade material is Grade 23.

Is 316LVM the same as surgical 316L?

Not quite. 316LVM is vacuum-melted (VAR or ESR) per ASTM F138, which drives non-metallic inclusions down versus commercial 316L. The cleaner microstructure is what carries the fatigue and pitting performance that implant service demands. A certificate should state the melt practice, not just the grade.

What does an EN 10204 type 3.1 certificate actually certify?

It certifies that the material conforms to the specified standard and that the manufacturer documents it - tested and released by the mill with full chemical and mechanical results. For implant work it is the minimum document that ties a coil to its heat. Anything less than 3.1 should be questioned.

Why does surface finish matter for biocompatibility?

A rough or contaminated surface is where crevice corrosion starts, where proteins and cells adhere, and where embedded iron from the die provokes a local response. Electropolishing removes the disturbed layer and passivation rebuilds the passive film; Ra targets and a verification method belong in the spec.

Can the same press line run implant and non-implant work?

Yes, with segregation. The line must be cleaned between programs, tooling dedicated or fully stripped, and lot records must separate implant work from commercial work. The audit question is not whether the press is shared; it is whether the controls around it are tight enough that a commercial lot can never contaminate an implant lot.

Let's Talk About Your Implant Program

If you are sourcing stamped bone-screw blanks, stent frames, or catheter components and need a supplier who speaks ASTM F136 and F138, runs ISO 13485, and can show you the heat certificate before the first sample, that is the work. Send over the drawing and the alloy requirement and we will walk the process - material, die strategy, surface finish target, and the full traceability package - before a single part is cut. For the wider medical picture, see our medical stamping overview and the medical industry page, then send your drawing for a DFM review and quote.