The Impact of Heat-Affected-Zones (HAZ) on Scalable Medtech

Kirk Abolafia
Apr 24
10 min read

Updated: Jul 20

And how Voxel's PECM process mitigates this issue, at-scale.

Heat-affected zones (HAZ) are not merely cosmetic "burn" regions, but rather, localized areas of thermal damage that are generated when a process melts (or strongly heats) a workpiece and then cools it rapidly. In laser cutting, EDM, welding, and certain grinding operations, that thermal cycle can inherently affect a material's properties:

Grain structure
Hardness
Residual stress
Oxide chemistry & corrosion behaviour

In this article, we'll identify why HAZ is a prohibitively expensive and challenging problem to solve at scale, and how Voxel's PECM process, by avoiding HAZ, can enable new designs and scalability.

HAZ becomes a scalability problem when thermal damage consumes part of the tolerance, surface-integrity, corrosion, or fatigue budget. PECM can remove the thermal-damage mechanism for selected conductive-metal features, but application fit still depends on geometry, cathode access, electrolyte flow, tolerance targets, inspection requirements, and production economics.

Working on a conductive medtech component where HAZ, recast, fatigue risk, corrosion behaviour, edge condition, or post-processing burden is limiting scalability? Send Voxel the material, geometry, tolerance target, current process, and expected volume for a PECM fit review at info@voxelinnovations.com

Key Takeaways

Heat-affected zones (HAZ) alter critical material properties, directly impacting fatigue life and biocompatibility in medical devices
HAZ becomes a scaling problem as features shrink; even micron-level damage can consume a significant portion of the geometry and tolerance budget
Thermal processes like laser and EDM introduce variability at scale (notably feature-to-feature inconsistencies) reducing repeatability across high-density parts
Post-processing requirements increase manufacturing complexity, as secondary steps (polishing, passivation, inspection) become mandatory to remove or mitigate HAZ
Eliminating HAZ via PECM changes the scalability equation: processes that avoid thermal damage remove a major source of variability, enabling more consistent production of complex, high-density geometries

These changes can create significant performance differences, even if they are in a few micrometers-worth of material. For medtech leaders, where small devices can be heavily inspected and extremely fatigue-limited or corrosion-sensitive, these altered properties have considerable effects.

HAZ, fundamentally, is often manageable at the prototype scale but is clearly unmanageable and prohibitively expensive at production scale. Representative studies show laser-cut nitinol HAZ lasers can become substantially large fractions of the very parts themselves. While lower-energy EDM capabilities have been shown to reduce HAZ, it does not eliminate the possibilities of HAZ entirely: even narrow HAZs just a few micrometers wide can change hardness, pitting behaviour, crack susceptibility and more for critical medical devices for 316L and CoCr components.

A HAZ-sensitive part can look like an obvious PECM candidate and still require engineering review. Material sensitivity, feature density, and thermal-damage risk are useful signals, but they do not confirm whether PECM can access the geometry, control the removal zone, protect the required tolerances, and justify process development. The reverse can also be true: a borderline application may still be worth discussing if the current process creates enough inspection, rework, yield, or qualification pressure.

HAZ matters more than ever, as FDA/ASTM frameworks increasingly evaluate the susceptibility of finished devices for corrosion, nickel release, and dimensional integrity as opposed to simply evaluating their chemistry. The FDA's nitinol guidance, in fact, explicitly references how thermal processing and surface finishing changes corrosion and "nickel-leach" behaviour.

How HAZs Form

Small fixture devices like these are inherently susceptible to small surface defects.

When certain materials have extremely localized energy input followed by rapid cooling, their very material structures can change. The material closest to the energy source can melt and re-solidify (such as in recast layers, also known as white layers), but the surrounding material also undergoes transformation: recrystallization or coarsening of the grain structure can still occur away from the direct site of machining.

A common mistake is treating HAZ as a simple surface-cleanup issue. In medical devices, the more important question is often where the thermally altered material sits relative to the functional feature: a fatigue-loaded edge, a corrosion-sensitive surface, a sealing region, a microhole, or an internal flow path. That location determines whether HAZ is manageable through finishing or whether the manufacturing method itself deserves review.

Interested in learning another way? Consider listening to our AI-enabled podcast of this article.

HAZs occur in a wide variety of processes: laser cutting, EDM, and welding all have literature showcasing their susceptibility to producing thermal-created surface defects, most notably HAZs.

Nitinol is especially sensitive to the effects of HAZs, as the alloy's very functionality relies on its "thermomechanical phase transformation", as noted from the FDA paper. It is a "shape memory alloy" and its unique ductility and corrosion resistance can be directly affected by the presence of HAZs, not to mention increased susceptibility of nickel-leaching. Nickel ion release is limited to 0.5 µg/kg/day, an extremely small amount that allows no room for surface irregularities in nitinol devices.

Nitinol is a useful example because the manufacturing route can affect more than geometry. Edge condition, oxide state, corrosion behaviour, fatigue response, and post-processing burden can all influence whether a feature is production-ready. PECM may be relevant for selected conductive nitinol features, but the fit still depends on the specific cut geometry, surface requirement, tolerance stack, and validation path.

As one study noted comparing CoCr, Nitinol and 316L, "Across all three alloy systems, the recurring material-specific lesson is the same: HAZ does not merely “roughen” the edge. It perturbs the very microstructural and surface states that medtech alloys are chosen for in the first place..."

Why Are HAZs Harmful?

In short, we can identify 4 key reasons:

The first is fatigue. Medical devices operate under millions to hundreds of millions of cycles, often in corrosive physiological environments. Tensile residual stress, microcracks, recast (white) layers, and local hardness mismatches all act as crack initiators or crack-growth accelerants. FDA’s stent guidance ties fatigue failure to loss of radial support, thrombosis, restenosis, and vessel perforation risks, and it explicitly warns that manufacturing flaws not fully removed by polishing can contribute to clinical complications.

Fatigue is a key issue for medical devices like this bone fixture.

The second is corrosion/biocompatibility. Metallic implant surfaces are treated specifically to improve corrosion resistance, and that embedded foreign matter or post-marking surface disturbance can require additional treatment. Where HAZs change, say, oxide thickness, composition, segregation, contamination, etc., it lowers pitting resistance and increases ion release: especially important for nickel-heavy materials such as Nitinol.

The third is tolerance and inspection burden. If a thermally damaged layer must be removed to recover performance, then the true manufacturing problem becomes a compounded issue of the thermal process and its re-passivation before inspection. Microfeatures (like a 10 µm-class HAZ) can consume a large portion of the tolerance budget for manufacturers: the amount of material removed in cleanup and the inspection effort both rise with feature count.

The fourth is regulatory risk. The FDA’s Nitinol guidance makes finished-form corrosion and surface finish key regulatory hurdles. A supplier cannot rely on conventional alloy guidances alone if the manufacturing route has created an inherently different material surface.

Why early review matters: HAZ risk is not uniform across a device. Early manufacturing review can help engineering teams identify which edges, surfaces, or microfeatures drive the highest fatigue, corrosion, inspection, or regulatory risk. In some cases, PECM may provide a cleaner path by avoiding thermal damage at the machining step. In others, improved thermal-process control, finishing, or design changes may remain the better route.

The Scalability Problem

Laser manufacturing, for instance, is attractive for its highly automated, digitized capabilities, able to cut stents and other fine geometries at scale. But when geometries become denser, with tighter tolerances and harder-to-reach internal areas, scalability becomes a nightmare. Consider geometries: as features continue to shrink (miniaturization is a prevalent trend across nearly all medtech devices), a fixed HAZ thickness occupies a larger fraction of the geometry, and this only worsens at-scale. Laser machining is inherently a serial process, meaning each feature adds incremental cycle time. At the same time, each feature introduces its own thermal history. Variability in beam interaction, assist gas flow, and local heat accumulation leads to feature-to-feature inconsistency in HAZ formation, even within the same part.

A common scaling mistake is evaluating HAZ from a single-feature prototype. A process can look acceptable when one feature is inspected, then become harder to control when the same thermal history must be repeated hundreds or thousands of times across dense geometry. For medtech programs, the production question is whether the process can hold edge condition, surface integrity, dimensional control, and inspection confidence across the full device family.

High-density feature devices like these are challenging to scale.

For EDM, there's an opposite trade-off, as those processes are capable of accurate geometries, but the economic appeal degrades very quickly with both high-volume components and high-feature-density components (such as stents, or microhole arrays in drug delivery devices). Debris accumulation in the spark gap, electrode wear, and flushing limitations introduce variability that becomes more difficult to control as geometries become deeper, denser, or more complex. In practice, this means that scaling EDM to high-density arrays or high-throughput production environments introduces nonlinear increases in cycle time, maintenance burden, and process variability.

Ultimately, HAZs force manufacturers into a difficult position: either accept altered material properties or remove the affected layer through secondary processing, which directly impacts dimensional control and yield.

This is where Voxel’s vertically integrated process model becomes relevant. Avoiding HAZ through PECM depends on more than choosing a non-thermal removal mechanism. Cathode/tooling design, electrolyte methodology, fixturing, machine behavior, inspection planning, and production assumptions all affect whether the process can move from a promising feasibility path to a repeatable manufacturing route.

These scaling limitations create three key issues:

Yield and scrap rates: Variability in HAZ thickness or removal leads to out-of-tolerance features, especially in micro-scale geometries
Process complexity: Additional steps (polishing, passivation, inspection) become mandatory
Validation burden: Regulatory expectations require demonstration that surface integrity (corrosion resistance and fatigue performance, for instance) is consistent across production batches

PECM: Eliminating HAZ and Changing the Equation

Processes that avoid thermal interaction like PECM entirely remove this constraint at its source. By eliminating HAZ formation, PECM fundamentally changes the relationship between geometry, material behavior, and scalability. Instead of managing or removing a damaged layer, the process preserves the base material state throughout machining. This has several downstream effects that are particularly relevant for medtech applications:

Feature size is no longer coupled to thermal damage: Microfeatures and thin walls can be produced without a proportionally large affected zone
Feature-to-feature consistency improves: Without localized thermal variability, arrays of features behave more uniformly across the part
Post-processing requirements are reduced: The need for aggressive secondary removal processes diminishes, simplifying the manufacturing chain
Internal geometries become more viable: Since no thermally altered layer needs to be removed, inaccessible features are no longer penalized

These advantages are strongest when the part geometry supports a controlled PECM process. Feature access, electrolyte exchange, masking or isolation needs, removal target, tolerance stack, and inspection method still determine whether PECM is practical for a specific medtech component.

To reinforce that point, it’s important to recognize that eliminating HAZ essentially removes an entire failure mechanism from the process chain. In thermal machining, even well-optimized processes still rely on downstream steps to “repair” the surface: be it recast layer removal, electropolishing, passivation, or chemical etching. Each of those steps introduces its own variability and, critically, its own interaction with complex geometries.

When those steps are no longer required, the manufacturing process becomes inherently more stable, impacting yield (as fewer parts fall out of tolerance due to over-removal), uneven finishing, or inaccessible regions. At production scale, that translates into more predictable output, tighter process windows, as well as reduced dependence on operator intervention.

The table below summarizes common process tendencies. It should be used as a process-selection starting point rather than a universal rule. Actual outcomes depend on material, parameters, feature geometry, post-processing strategy, inspection criteria, and production requirements.

Process	HAZ Formation	Surface Integrity Impact	Scalability Challenges	Internal Feature Capability
Laser Machining	Inherent (thermal melting & rapid cooling)	Recast layer, residual stress, oxidation, microcracks	Serial processing increases cycle time; feature-to-feature variability; HAZ becomes large relative to microfeatures	Limited by line-of-sight; difficult to post-process internal HAZ
EDM / µEDM	Inherent (localized plasma discharge)	Recast layer, tensile stress, microcracks (reduced at low energy but not eliminated)	Low material removal rates at fine settings; electrode wear; debris/flushing issues increase variability at scale	Better than laser for complex shapes, but limited by flushing and electrode access
Grinding (Thermal Damage Cases)	Possible under high heat (“grind burn”)	Surface tensile stress, localized thermal damage	Difficult to control consistently on delicate or micro-scale features; risk of rework	Poor for internal or complex geometries
Chemical Etching	None (non-thermal)	No HAZ, but isotropic material removal	Limited control at depth; undercutting; struggles with high aspect ratio features	Good for thin, planar geometries; weak for deep/internal precision features
PECM	None (no thermal interaction)	No HAZ; preserves base material properties and surface integrity	Scales via parallel processing; minimal reliance on post-processing; high repeatability	Strong capability for internal, non-line-of-sight, and high-density features

There is also a design-level implication that becomes more apparent as device geometries evolve with new designs. When engineers are no longer constrained by the need to avoid or later remove thermally damaged material, they can begin to treat internal surfaces and microfeatures as genuine design elements, rather than liabilities. This is particularly relevant for emerging device categories (such as microfluidic drug delivery systems, high-density microhole arrays, or especially AM additively manufactured implants) where performance is dictated, largely, by internal geometry and surface condition. In these cases, avoiding HAZ enables a more direct path from design intent to production reality, reducing the need for compromise between geometry and long-term device performance.

Mini-FAQ

What is a heat-affected zone (HAZ)?

A heat-affected zone is a localized region where thermal processing changes the material near a machined, welded, or cut feature. In medtech, that change can affect fatigue behavior, corrosion resistance, edge condition, and inspection burden.

Why is HAZ more challenging to manage in production environments?

HAZ becomes more difficult to manage when features shrink, repeat counts rise, and post-processing has to remove or mitigate thermal damage without compromising tolerance. A few micrometers of altered material can become significant on microfeatures or thin medical components.

Why doesn't PECM create a HAZ?

PECM removes conductive metal electrochemically rather than thermally, so it does not create a thermally generated HAZ at the machining step. Application fit still depends on geometry, electrolyte access, tolerances, inspection needs, and production economics.

I might have an application idea-- what do I do next?

Use a contact form on our site or email us at info@voxelinnovations.com. Useful inputs include drawings/models, tolerance goals, your current processes, and annual projected volumes.