Electrolytic copper (Cu-ETP)

Physical properties

Laser processing

Heating copper produces cuprous oxide (Cu2O) and cupric oxide (CuO) as fine particulate. Irritating to the respiratory tract. During high-power cutting, copper fumes are toxic. Mandatory ventilation.

CO₂: Copper reflects approximately 98% of the CO2 laser beam. Not cuttable under any maker conditions. Engraving is effectively impossible: the reflected beam can seriously damage the machine optics.

Diode: Impossible to process with diode laser. Copper reflectivity in the visible and near-infrared spectrum is extremely high.

Fiber: Marking possible but technically challenging. Copper strongly reflects the fiber laser wavelength (1064 nm) as well. Risk of back-reflection toward the laser source: some machines lack sufficient protection. Use only fiber lasers equipped with back-reflection protection. Marking produces surface oxidation (darkening/browning). Cutting requires very high power levels.

CNC / milling processing

Pure copper is one of the most problematic materials to mill despite its low hardness. Extreme softness and very high ductility promote built-up edge: copper literally welds itself to the cutting edges of the bit. High thermal conductivity (385 W/mK) dissipates heat rapidly — a positive property but one that requires parameters completely different from other metals. Use sharp-geometry bits, high rake angle, high cutting speed, and adequate feed rate. Air blast is the preferred coolant to avoid contamination.

Post-processing

Sanding: Easy to sand and polish thanks to its softness. Wet silicon carbide paper. Mirror polishing is easily achievable with fine grits (1200+) and abrasive paste. Beware of fingerprint staining during polishing.

Primer: Copper does not require primer: natural oxidation can be controlled with clear lacquers to preserve the pinkish tone. For coloured painting, apply etch primer for non-ferrous metals.

Gluing: Bondable with structural two-component epoxies after degreasing. The soft surface provides excellent mechanical key with preliminary sanding.

Over time: Progressive atmospheric oxidation: fresh copper's pinkish colour shifts to dark brown (cuprous oxide) and eventually to the characteristic blue-green patina (verdigris or basic copper carbonate) in humid environments with CO2. The process takes years outdoors and can be accelerated chemically.

Common defects

• Built-up edge (copper welded to the cutter) — primary cause of scrap during milling without correct parameters
• Fingerprints immediately visible on the polished surface — always handle finished parts with cotton gloves
• Rapid patina (verdigris) formation in humid environments if not protected with lacquer

Safety

Recommended PPE: eye_protection, mask_p2, gloves_nitrile

Copper fumes and dust are toxic with prolonged exposure. Mandatory extraction during processing. Do not ingest processing residues. The green patina (verdigris) is toxic if ingested.

Availability and formats

Commercial formats: round bars, tubes, sheets, strips, wire

Related materials

Sources

• EN 1652 — Copper and copper alloys (Cu-ETP sheet and strip)
• MatWeb — Copper C11000 (ETP) Datasheet