Turning of copper parts: techniques, challenges and industrial applications

What you must remember :

• Pure copper has a machinability index of about 20% compared to free-cutting brass (reference 100%): its softness and ductility promote adhesion to the tool and the stringy chips.
• The Cu-Te (copper tellurium) grade brings this index to 85-90% thanks to the Cu2Te precipitates which naturally fragment the chip, without significantly degrading the conductivity.
• The choice of grade depends on the use: Cu-ETP/Cu-OF for maximum conductivity, Cu-DHP for weldability and brazing, Cu-Te for mass production.
• The high density of copper (8,96 kg/dm³) directly impacts the material cost, which is sensitive to copper prices on the metals market.
• Abundant lubrication and chip management are non-negotiable to preserve surface condition and dimensional regularity in series production.

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Copper is the benchmark metal for electrical and thermal conductivity. This property makes it an essential material whenever a part needs to carry current or dissipate heat: connectors, terminals, power bars, heat sinks. But these same qualities make copper a unique material for precision machining, requiring different machining techniques than other metals.

At Jacquemoux Décolletage, we produce copper and copper alloy parts for the electronics, automotive , and precision engineering industries. This article details the properties of copper that determine its machining, the appropriate processes and parameters, its major industrial applications, and the factors that influence the cost and quality of machined parts.

Why copper requires a specific approach in bar turning

Copper does not behave like other common screw-machining metals. Its exceptional conductivity and high ductility, which give it its value in use, are also the source of its main machining difficulties.

Mechanical and thermal properties of copper

• High density: 8,96 kg/dm³, which is about 14% more than steel (7,85 kg/dm³) and more than three times that of aluminum (2,7 kg/dm³). For the same volume, a copper part is therefore significantly heavier and more expensive in terms of material.
• Reference electrical conductivity Annealed copper serves as the basis for the IACS scale (100%). Alloy grades deviate from this according to their composition: the phosphorus in Cu-DHP, for example, lowers the conductivity to approximately 80% IACS.
• Very high thermal conductivity : approximately 390 to 400 W/(mK), just behind silver. This property is desirable for heat sinks, but it also complicates dimensional control during machining, as heat diffuses rapidly throughout the workpiece.
• Low hardness and high ductility Annealed copper has a hardness of around 40 to 50 HB, with an elongation at break that can exceed 40%. This softness promotes adhesion of the material to the tool rather than clean breakage.
• Melting point of 1085 °C and excellent corrosion resistance, with antibacterial properties sought after in certain medical applications, paramedics and sanitary facilities.

Risks and challenges associated with copper machining

• Adhesion on the cutting edge (gluing) Pure copper, being soft and sticky, tends to weld itself locally onto the tool (built-up edge). This phenomenon degrades the surface finish and accelerates edge wear.
• Long, stringy wood chips Unlike other metals, pure copper does not naturally fragment its chips. A poorly controlled, long-running chip can wrap around the tool or workpiece, causing machine stoppages and posing a risk to the operator.
• Work hardening : an incorrectly set cutting speed or feed rate locally hardens the material, which accelerates tool wear and degrades dimensional repeatability.
• Rapid thermal expansion The high thermal conductivity of copper, while facilitating the dissipation of cutting heat, also makes the part more susceptible to dimensional variations during production. Temperature control is recommended for tight tolerances.
• Cross-contamination : copper is particularly sensitive to traces of other metals (zinc, lead, iron) which can alter its electrical properties.

Processes and tools adapted for copper machining

Mastering the machining of copper alloys requires combining the right choice of grade, appropriate cutting parameters and rigorous management of lubrication and chip.

Selection of machines and cutting parameters

Copper machining, like steel or aluminum machining, relies on cam-operated or numerically controlled lathes, fed with round, square, hexagonal or octagonal bars conforming to the EN 12164 standard, which specifically covers copper and copper alloy bars for machining.

The choice of shade directly influences the cutting parameters.

• Cu ETP (CW004A): Electrolytic copper with a minimum of 99,90% copper, the reference grade for electrical conductivity. Its machinability index is approximately 20% lower than that of free-cutting brass (reference 100%): moderate cutting speeds and appropriate tooling are necessary to limit adhesion.
• Cu-OF / Cu-OFE (oxygen-free) Oxygen-free copper of very high purity, reserved for the most demanding electronic and vacuum applications in terms of conductivity. Its machining requirements are similar to those of Cu-ETP.
• Cu-DHP (CW024A): Deoxidized copper with phosphorus, 99,90% copper. Its slight phosphorus content improves weldability and brazing properties, at the cost of slightly reduced electrical conductivity (approximately 80% IACS).
• Cu-Te (CW118C, tellurium copper) This alloy is specifically developed for bar turning. The tellurium (0,4 to 0,7%) precipitates as Cu2Te during cooling, naturally fragmenting the chip. Its machinability reaches 85 to 90% compared to standard free-cutting brass, with a conductivity close to that of pure copper. This is the nuance to prioritize whenever the production rate is paramount.

In terms of tooling, copper requires sharp, polished cutting edges with a pronounced positive geometry, made of carbide or PCD, to shear the material rather than tear it away . Grades optimized for machining (Cu-Te) tolerate significantly higher cutting speeds than pure copper, resulting in substantial productivity gains in high-volume production.

Lubrication and chip management

Lubrication plays a central role in the success of machining:

• Abundant watering: It dissipates cutting heat, limits material adhesion to the tool and preserves the surface condition.
• Chip breakers These are essential for pure copper alloys (Cu-ETP, Cu-OF, Cu-DHP), whose chips do not naturally fragment. A suitable tool geometry is necessary to avoid stringy chips.
• Cu-Te, a naturally controlled chip : thanks to tellurium precipitates, this grade produces short and brittle chips without requiring a specific chip breaker, which simplifies removal in continuous production.

Effective chip management directly conditions the achievable production rate in large series, as well as the consistency of the surface finish from one part to another.

Industrial applications: where copper makes the difference

Copper is the obvious choice when maximum electrical conductivity and geometric precision are required. In the electronics sector, machined copper ferrules and connectors ensure stable contact resistance over time, a critical criterion for high-frequency or high-voltage equipment. A variation of just a few microns in the diameter of a contact can be enough to degrade the performance of an industrial connector.

In the automotive industry , the transition to electrification is increasing the need for precision-machined copper parts: battery terminals, electric motor commutators, and thermal distribution components. Required dimensional tolerances regularly reach ±0,01 mm on diameters from 5 to 30 mm, with surface roughness requirements of less than 0,8 µm in functional areas.

In the energy sector , machined copper bushings and rings are used in the construction of busbars, circuit breakers, and electrical distribution equipment. The purity of the material (Cu-ETP or Cu-DHP depending on the application) directly determines the conductivity of the finished part – and therefore the certification of the final electrical subassembly.

Factors influencing the price of machining copper parts

The price of a machined copper part depends on several factors combined:

• The price of copper: traded on international metal markets, the price of copper is volatile and weighs heavily on the final price, especially since the high density of the material increases the weight of material per piece for the same volume.
• The choice of grade: pure copper (Cu-ETP, Cu-OF) is more expensive to machine than Cu-Te, due to longer cycle times, increased tool wear and a potentially higher scrap rate.
• Geometric complexity and tolerances: the tighter the tolerances and the more complex the geometry, the more cycle time and quality control weigh on the cost.
• Series volume: as with any machining, fixed costs (setup, tooling) are amortized more effectively the longer the series.
• Secondary operations such as tinning, silvering or nickel plating are common on copper connectors intended for electronics or automotive applications, and add to the machining cost.

Applicable standards and certifications

The industry's quality benchmark remains ISO 9001, published by AFNOR (NF EN ISO 9001, 2015). It structures the quality management system: process control, traceability, non-conformity management, and continuous improvement. Jacquemoux Décolletage has been ISO 9001 certified since 2018, guaranteeing our customers rigorous documentation and complete traceability for each production batch.

For automotive customers, IATF 16949 certification goes beyond basic requirements. It mandates monitoring plans, process FMEAs, and stricter supplier management requirements. Copper components for electric vehicles are directly affected by this standard.

In terms of materials, copper and copper alloy bars intended for machining remain subject to the EN 12164 standard, already mentioned above, which defines the chemical and dimensional tolerances of the bars to be machined. Compliance with this standard at the time of material purchase is essential for the conformity of the finished parts.

Frequently asked questions about machining copper parts

Q1. What are the main difficulties of machining copper?

The main difficulty stems from the softness and ductility of pure copper, which promotes material adhesion to the tool and the formation of long, stringy chips that are difficult to remove. Added to this is the risk of work hardening if cutting parameters are incorrectly set, and dimensional sensitivity due to the material's high thermal conductivity. Choosing a suitable grade (Cu-Te for high-volume production) and using ample lubrication helps to manage these challenges.

Q2. How to evaluate the price of a machined copper part?

The price combines the cost of materials, directly linked to the price of copper and the material's density, the machining cost, which varies depending on the chosen grade (pure copper is more expensive to machine than Cu-Te), the geometric complexity and required tolerances, the production run, and any secondary operations such as tinning or silver plating. An accurate quote requires a detailed specification document, which should be provided to your machining partner beforehand.

Q3. Which industrial sectors use machined copper parts?

Electronics and connectors are the primary users (connectors, terminals, contacts), followed by the automotive industry, particularly with the rise of electric vehicles (busbars, high-voltage connectors, motor terminals). Machined copper is also used in energy, telecommunications, hydraulic and refrigeration fittings, as well as in certain medical applications that take advantage of its antibacterial properties.

Q4. Are machined copper parts reliable over time and in large series production?

Yes, provided that the material grade and machining parameters are chosen carefully from the initial project definition. A well-machined copper part, with a controlled surface finish and rigorous dimensional control, offers stable durability and conductivity over time. It is the combination of material selection, machining expertise, and quality control that guarantees repeatability, batch after batch, regardless of production volume.

Do you have a project involving machined copper parts?

From defining the grade to delivering your finished parts, the Jacquemoux Décolletage technical team studies your specifications and offers you a solution adapted to your dimensional requirements, volumes and time constraints.

→ Contact Jacquemoux Décolletage for a precise quote and expert support for your copper parts.