Additive Manufacturing & Pulsed Electrochemical Machining (PECM)

Nickel-alloy tensile bar samples processed by PECM and achieving local surface finishing where required.

Short answer: PECM may be useful for selected metal additive manufacturing parts when rough downskin surfaces, support-removal remnants, thin-wall limits, thermal distortion, or internal-feature access create production risk. Fit still depends on conductive material, target surfaces, geometry, electrolyte access, tolerance requirements, inspection method, and annual volume.

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Key Takeaways

1. PECM is an effective post-processing method for metal additive manufacturing, improving surface roughness, refining thin-wall features, and correcting thermal distortion without introducing heat or contact-based damage.
   

2. Unlike conventional finishing methods, PECM can selectively machine critical areas of a 3D printed part, removing macro-level roughness from downskin surfaces and support structures while preserving overall geometry.
   

3. Combining faster, lower-resolution additive builds with PECM post-processing can reduce total production cost while achieving high-performance surface finishes and tight tolerances in critical features.

Metal 3D printing, or metal additive manufacturing (AM), is a rapidly growing field, particularly in the aerospace and medical device markets, and pulsed electrochemical machining (PECM) is a viable postprocessing solution able to improve surface finish, refine thin-walled features, and correct geometric inaccuracies without introducing thermal distortion or tool contact, at high volumes.

The most common metal additive manufacturing techniques include powder-bed, powder freeform, and wire freeform. Of the three, powder-bed additive is the most prevalent and uses a laser (e.g. DMLS, SLS, SLM) or electron beam (EBM) to melt or weld metal powder, layer by layer, to create a 3D geometry. The powder and wire freeform additive manufacturing methods can be used to form much larger parts with faster deposition rates-- but at the cost of feature resolution.

These metal AM techniques enable complex geometries, lightweight designs, and consolidated parts that would be impossible (or at least prohibitively expensive) with other manufacturing processes.

A common mistake is treating AM post-processing as a cosmetic finishing step. For many metal AM parts, surface condition affects flow performance, fatigue risk, corrosion behavior, inspection reliability, and whether internal or downskin features can be qualified for production.

PROBLEMS WITH 3D PRINTING

However, metal 3D printing does have a few challenges, such as surface roughness, minimum wall thickness, thermal distortion, and cost.

Surface roughness in a 3D printed metal part can be a function of the powder size and distribution, layer heights, surface angle relative to the build platform, re-deposition of melted material (e.g. micro weld splatter), and layer recoating or powder quality. During the printing processes, surfaces that are overhung or “downskin”(i.e. <90° from the build plate) lead to surface roughness that may be considerably worse than the sidewall or upskin surfaces.

Support structures on 3D printing. Credit: 3dhubs.com

In addition, support structures of thin, removable metal lattices are often utilized to support downskin surfaces to prevent sagging, to help conduct heat, or to stabilize a critical section during the recoating operation or heat-treating steps. Even after removal, these support structures leave remnants or surface irregularities. This surface roughness can negatively affect the part either through incorrect form or fit, creating excess surface flow friction, initiating corrosion, creating crack formation sites via pits or crevices, or making part inspection (e.g. fluorescent penetrant inspection, FPI) more difficult.

Metal additive manufacturing is also an inherently thermal process based on welding principals. The heat generated during the build process can lead to residual stresses in the part which cause distortion and changes in geometry. In extreme cases, this distortion can lead to cracking and build failures. Although simulation and predictive algorithms are improving this issue, thermal stresses will always affect certain parts.

These AM issues do not automatically make PECM the right next step. A rough downskin, support-removal mark, thin wall, or distorted surface still needs review around material conductivity, feature access, removal allowance, tolerance stack, and inspection requirements.

There are also limits to the wall thickness that are achievable with metal additive manufacturing. The free-form AM processes in particular are limited to relatively large thicknesses or order to achieve higher deposition rates but even powder bed AM processes have aspect ratio limitations that can be driven by thermal challenges, powder recoating forces, etc.

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Nickel-alloy turbine vane/nozzle segment finished by electrochemical machining

Thus far, most metal AM parts have found value in the market either for fast-turnaround replacement parts or by creating geometries / eliminating assemblies that improve performance or reduce downstream costs. As metal AM expands to cover broader markets, the cost pressures will increase. In some cases, those costs are driven the surface finish, wall thickness, or thermal distortion challenges. For example, the techniques used to improve the as-printed part surface finish (finer powders, smaller layers and beam sizes, etc.) also slow or add costs to the process.

Early PECM review can help engineering teams identify which AM surfaces actually drive performance and which areas can remain as-printed. That distinction matters because selective finishing is often more valuable than trying to improve every surface equally.

Based on these challenges, post processing of 3D printed parts is a significant aspect of delivering a complete part. It is not unusual to employ multiple post processing methods including hand polishing, electropolishing, vibratory processing, CNC machining, and EDM to address the surface roughness, thermal distortion, or wall thickness limitations. However, one post-processing method that may be underutilized for this work is pulsed electrochemical machining, or PECM.

PECM: A Viable Solution

Pulsed electrochemical machining (PECM), also referred to as precision electrochemical machining, is a process that is neither heat- nor contact-based. With a gap between a custom tool and the metal workpiece, PECM uses a current and an electrolyte solution to machine the surface of the 3D printed part, atom by atom. Because of this precise material removal, PECM can create pristine surfaces in areas where finish is important while leaving other areas in their as-printed state. This is where Voxel’s vertically integrated process model matters. AM post-processing with PECM depends on cathode/tooling strategy, electrolyte methodology, fixture design, machine behavior, inspection planning, and production assumptions working together. The value is not simply improving roughness; it is determining where selective finishing changes the manufacturing path.

Particularly when applied to volume production of additive parts, PECM can be a cost-effective post-processing technique to address surface roughness. Although PECM has many similar attributes to electropolishing, the use of locally small gap between the electrode and workpiece is particularly efficient at removing the macro-level roughness characteristic of support structure remnants, downskin surfaces, EBM powder bed, or freeform AM methods.

The table below summarizes common process tendencies. It should be used as a starting point, not a universal process-selection rule. Actual outcomes depend on AM process, material, surface location, feature access, tolerance requirements, removal target, and inspection method.

Capability	PECM	CNC	EDM	Electropolishing	Vibratory
Improves downskin / support roughness	Yes	Limited	Limited	Limited	Limited
Maintains tight tolerances	Yes	Moderate	Moderate	Low	Low
Processes internal geometries	Yes	Limited	Limited	Limited	No
Non-contact process	Yes	No	Yes	Yes	No
Minimal thermal impact	Yes	Moderate	No	Yes	Yes
Scalable for production	Very	Moderate	Low	High	High

Given some of the thin-wall and thermal distortion challenges, PECM can also be an effective secondary machining operation. Instead of trying to work within the wall thickness constraints of existing metal 3D printing methods, PECM could be used to readily create thin-walled features where they are critical to the design. In addition, if thermal distortion is a known potential challenge to achieving the correct profile tolerances, it may be more cost effective to add extra stock material to the surface while utilizing PECM to dissolve the extra material into the correct shape.

Thin walls possible with electrochemical machining

Finally, with effective post processing methods such as PECM, it may be more cost efficient to focus on increasing the 3D printing speed at the expense of surface roughness or feature size (e.g. thicker layers, larger powders, larger beam sizes, freeform AM methods) while utilizing a rapid post-processing technique like PECM to create the critical geometries where necessary. Utilize 3D printing to create internal lattice structures or organic shapes while PECM can help reduce surface roughness, minimize rib thickness, or perform other value-added operations.

Metal 3D printing and PECM can be utilized in tandem to achieve lower costs or better performance than either could achieve on their own. Particularly for additive manufacturing applications which are producing medium to high part volumes, PECM should be considered as an effective post processing tool. In addition, Voxel is continuing to develop this technique such that PECM could be effective at improving surface roughness on single part applications.

PECM fit signals for metal AM parts

Stronger signals: Conductive metal, rough downskin surfaces, support-removal remnants, internal channels, thin walls, high-value features, post-processing burden, surface-finish requirements, or repeatable production needs

Review variables: Material, target surfaces, feature access, electrolyte flow, removal allowance, tolerance stack, inspection method, fixture strategy, annual volume

Weaker signals: Non-conductive materials, simple cosmetic finishing, low-value prototypes, loose tolerances, or geometries where PECM cannot access the target surface

Working on a metal AM part where downskin roughness, support remnants, internal features, thin walls, thermal distortion, or post-processing cost is limiting production? Send Voxel the material, AM process, target surfaces, tolerance requirements, current finishing method, and expected volume for a PECM fit review. Contact us at info@voxelinnovations.com.

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Mini-FAQ

So how does PECM help metal-AM?

PECM can selectively remove material from conductive metal AM parts to improve critical surfaces, refine thin features, or correct certain geometric inaccuracies. It is most relevant when the target area can be accessed and controlled through the PECM process.

What areas are ideal for PECM to postprocess?

Support structure remnant areas and downskin surfaces, often when the material is conductive and the geometry supports electrolyte access and controlled material removal. The result depends on the surface location, removal allowance, roughness target, and inspection method.

Can PECM replace all AM postprocessing?

No. PECM is best evaluated for selected critical surfaces or features where roughness, internal access, thin walls, or production repeatability create meaningful risk. Some parts may still be better served by CNC, abrasive, vibratory, electropolishing, or hybrid routes. Furthermore, the material must be conductive.

What are some example metal-AM components PECM could postprocess at-scale?

Certain aerospace components (printed out of Inconel 625, for example) such as turbine blades or vanes, as well as medical device components like spinal cages.