Plating CNC Plastic Machining Services

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  Key takeaways
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  Substrate and plating route by application
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  Which plastics actually accept a plated finish
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  How CNC machining sets up the plate
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  What the plating sequence does to your part
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  How to read a plating CNC plastic machining services quote
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  Common failures and how to design around them
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  Step by step: from CAD to a plated plastic part

Plating sticks to plastic through a chemical etch that opens micro-pores in the surface, then a catalyst deposits onto those pores so the first metal layer has something to hold. That mechanism only works well on resins with a specific molecular structure. ABS is the benchmark because the butadiene phase etches away and leaves a sponge-like surface. PC/ABS blends behave similarly when the ABS fraction stays high enough.

Semi-crystalline resins are a different story. PP, PE and POM have tight, ordered chains that resist etching, so metal sits on the surface instead of anchoring into it. A part may look fine off the rack and fail a tape test or a thermal cycle a week later. If your design needs those materials, plan on a primer-assisted route, or move the cosmetic surface to an ABS cap and keep the structural body in the engineering resin.

PEEK is the exception worth knowing. It costs far more than ABS, but it survives the plating sequence and the service temperatures that go with aerospace and medical hardware. Not every plating line is set up for it, so confirm the bath chemistry before you commit a design to PEEK.

One more input: colorant and flame retardants. Some additive packages interfere with the catalyst. Give the plater the exact grade and color code, not just the family name.

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  PlateableABS, PC/ABS, PC with primer, PEEK with high-temp chemistry
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  ConditionalPMMA for decorative work only; unfilled PA with a primer
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  AvoidPOM, PP, PE, and most glass-filled grades on visible faces

Plating does not hide geometry. It copies it. A 0.02 mm step left by a dull cutter becomes a visible line under chrome, and a chatter mark on a curved face shows up as a ripple. That is why the machining stage matters as much as the bath. We cut plastic with sharp, polished tooling, climb milling on finishing passes, and keep the finishing pass light.

Surface roughness is the parameter to control. For most plateable plastics, aim for Ra 0.8–1.6 μm on cosmetic faces. Below Ra 0.8 μm the etch has trouble forming a uniform pore structure and adhesion drops. Above Ra 3.2 μm the plate follows the tool path and the part looks machined even though it is metallized. Non-cosmetic faces can run Ra 1.6–3.2 μm; nobody sees them.

Wall stock is the second lever. Chrome and nickel build a few micrometers, which is small, but the plating process also amplifies any internal stress in the plastic. Thin walls warp during the hot baths. Keep 2.5–3.5 mm on visible faces and add ribs on the back if you need stiffness.

Finally, plan the datum structure around the plated part, not the bare part. Thickness adds on all sides, so a bore that fits on the machined part may not fit after plating. Machine bores slightly under and mask them, or leave grinding stock and cut them after plating.

A typical ABS chrome sequence runs through cleaning, alkaline etch, neutralization, catalyst activation, acceleration, electroless nickel, then electrolytic copper and nickel, and finally chrome if you want a bright finish. Each bath has its own temperature and dwell time. The part sees heat, acid and mechanical handling before it ever reaches the final rinse.

That sequence explains most field failures. Blisters come from contamination or incomplete etching. Peeling at edges comes from mold release left on the surface. Dimensional drift comes from thermal expansion during the hot stages. None of these are visible on the drawing, and none can be fixed by tightening the CNC tolerance alone.

Ask the supplier which steps are in-house. Shops that machine, etch and plate under one roof can change the etch time when adhesion test results drift. Shops that broker the plating have to send parts out and wait for a batch, which slows down any correction.

For functional parts, specify what you actually need: conductivity, wear resistance, or decoration. A bright decorative chrome and a hard functional chrome are not the same stack. Naming the function up front avoids a mismatch at first article.

A useful quote tells you the resin grade, the pre-plate surface finish, the plating stack and thickness range, the masking layout, and the inspection method. If any of those are missing, you are comparing prices on different scopes. Two quotes can differ by 40% simply because one masks ten holes by hand and the other plates the whole part.

Lead time deserves the same scrutiny. Quoting and DFM feedback within 12 hours is realistic for a shop that runs its own line. Beyond that, ask where the plating happens and whether the chemical baths run daily or weekly. Batch frequency, not machine speed, usually drives the calendar.

Certification matters when the part ships into a regulated product. ISO 9001:2015 covers general quality systems. IATF 16949:2016 applies to automotive programs. ISO 13485:2016 suits medical devices, and ISO 27001:2022 covers information security for your CAD files. Match the certificate to the industry you sell into, not to the longest list.

On volume, no minimum order quantity is normal for a shop that already runs prototypes. You can start with one part, prove the finish, then scale to a 10,000-piece run without requalifying the process.

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  Red flagQuote lists a resin family but not the grade or color code
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  Red flagNo pre-plate Ra value, no masking definition
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  Red flagPlating subcontracted with no stated bath schedule

Blisters and peeling top the list. They usually trace back to mold release, fingerprints, or a gate area with trapped stress. Specify a release-free molding or machining process and keep gate locations off cosmetic faces. If the part is machined from stock, wipe down before the plater receives it, and bag it.

Sink marks and read-through are a geometry problem. Thick bosses on the back of a thin cosmetic wall pull material as the plastic cools, and the plated surface shows a ghost of the boss. Keep wall transitions gradual and avoid abrupt thickness jumps greater than 2:1.

Knife edges and sharp corners plate unevenly. The current density is higher at a sharp edge, so the deposit builds faster there and can look burned or frosty. Break external edges to 0.3–0.5 mm and radius internal corners where the design allows.

Thermal cycling exposes weak adhesion. If the part sees hot and cold in service, ask for a thermal cycle or tape test on the first article. A part that passes visual inspection can still fail after three cycles in a chamber.