What is the process flow of copper wire processing and production?

The production process of copper wire is usually different according to the shape of raw materials (such as copper rod and copper ingot), product specifications (such as diameter and performance) and application scenarios (such as electronics, electricity and machinery). The following is the general process of typical copper wire processing, covering the main links from raw materials to finished products:

First, raw material preparation

Raw material selection

Common raw materials: electrolytic copper (purity ≥99.9%) and copper alloy rod (such as brass and bronze).

Raw material form: copper rod (usually 8~20 mm in diameter, used for large-size copper wire) or copper ingot (which needs to be cast into copper rod first).

Raw material inspection

Check the composition (spectral analysis), hardness and surface quality (such as scale and crack) to ensure that it meets the processing requirements.

Second, the copper rod pretreatment (if necessary)

If the raw material is copper ingot, it needs to be cast into copper rod first:

smelt

Put the copper ingot or waste copper into a smelting furnace (such as a medium frequency induction furnace) and heat it in a protective atmosphere (such as nitrogen) until it melts (melting point is about 1083℃).

Adding alloying elements (such as zinc, tin and aluminum) to adjust the composition (suitable for copper alloy wires).

Cast rod

The molten copper is cast into a copper rod by a continuous casting machine, usually with a diameter of 8~20 mm, and the surface is cleaned (oxide scale is removed) after cooling.

Third, stretch forming (core process)

The copper rod is gradually thinned to the target diameter through a multi-pass drawing die, which is divided into two processes: discontinuous drawing and continuous drawing:

1. Pretreatment before stretching

Peeling (peeling): Remove the oxide scale on the surface of copper rod by mechanical or chemical methods (such as sulfuric acid pickling) to avoid die wear or scratch on the surface of copper wire during stretching.

Lubrication treatment: the surface of copper rod is coated with lubricant (such as soap solution and lubricating oil) to reduce tensile resistance and prevent fracture.

2. Stretching process

Single stretching: Small copper wire (such as diameter < 0.1 mm) may need dozens of stretching, and the diameter will be reduced by about 10%~30% after each stretching.

Mold selection:

Die material: cemented carbide (such as tungsten carbide) or diamond (used for ultra-fine copper wire, such as below 0.01 mm).

Mould aperture: arranged in sequence from large to small, and decreased step by step (for example, from 8 mm to 4 mm to 2 mm to target diameter).

Stretching equipment:

Discontinuous drawing: single-mode drawing machine is used, which is suitable for large-size copper wire or small-batch production.

Continuous drawing: multi-mode continuous drawing machine (such as pulley type and in-line type) is used, which has high efficiency and is suitable for mass production of fine copper wire.

3. Intermediate annealing (key link)

Objective: Work hardening (hardness increasing, plasticity decreasing) occurs in the process of copper wire drawing, so it is necessary to restore plasticity through annealing to facilitate subsequent drawing.

Annealing process:

Air annealing: put the copper wire in an annealing furnace and heat it for 0.5~2 hours at 300~600℃, which is suitable for ordinary copper wire.

Bright annealing: annealing in protective atmosphere (such as nitrogen and hydrogen) to prevent oxidation of copper wire surface, suitable for copper wire with high surface requirements (such as electronic leads).

Annealing times: determined according to the drawing passes, usually annealing is needed after every 3~5 times of drawing.

Four, surface treatment (according to the demand)

wash

To remove the lubricant and oil residue in the stretching process, ultrasonic cleaning or chemical cleaning (such as degreasing with alkaline solution) is often used.

Coating treatment

According to the application requirements, tin plating, nickel plating, gold plating, etc. (refer to "Surface Treatment of Narrow-band Copper Sheet" above for the process) to improve the conductivity, corrosion resistance or weldability.

Anti-oxidation treatment

Coating antirust oil, anti-tarnishing agent (such as benzotriazole) or passivation treatment to prevent oxidation during storage and transportation.

Five, finished product processing and testing

Length and winding

According to customer's requirements, the copper wire should be cut to a fixed length (such as copper wire for wire harness) or wound into a coil (such as copper wire for coil), and the winding tension should be uniform to avoid deformation of the copper wire.

Performance testing

Physical properties: diameter tolerance (measured by micrometer), tensile strength (tensile tester), elongation, hardness (Vickers hardness tester).

Electrical properties: resistivity (four-probe method) and conductivity (eddy current conductivity meter).

Surface quality: visual inspection or optical microscope to detect surface scratch, oxidation and coating uniformity.

Dimensional accuracy: use laser caliper to monitor the diameter fluctuation in the drawing process online.

Six, packaging and warehousing

package

Small copper wire: wound on a plastic spool or paper tube, and packaged with moisture-proof paper or plastic bag.

Large-size copper wire: rolled into large coils, tied with steel belts and covered with waterproof film.

sign

Indicate the product specification (diameter, material), batch number, production date and implementation standard (such as GB/T 3953 and ASTM B172).

store

Store in a dry and ventilated place to avoid damp and acid fog environment and prevent copper wire from rusting.

Key process variables and control

Drawing speed: High-speed drawing (such as the speed of continuous drawing machine can reach 10~20 m/s) needs to be combined with high-efficiency lubrication to avoid overheating of mold and fracture of copper wire.

Mold finish: the roughness of the inner hole of the mold should be controlled at Ra≤0.2 μm, otherwise the surface of copper wire will be rough or broken easily.

Annealing temperature and time: too low a temperature can not eliminate work hardening, while too high a temperature may lead to coarse grains and affect strength.

Process differences corresponding to typical application scenarios

Electronic leads (such as semiconductor leads): ultra-fine drawing (diameter ≤0.05 mm)+ bright annealing+silver/gold plating, with tolerance accuracy of ±0.001 mm

Copper wire for power cable: large-scale drawing (diameter 1~5 mm)+ continuous annealing, paying attention to conductivity (≥100% IACS) and surface cleaning.

Copper wire for spring (such as phosphor bronze): after stretching, it needs aging treatment (low temperature tempering) to improve the elastic limit.

Through the above process, the transformation from coarse copper rod to high-precision copper wire can be realized, and the diversified requirements of different industries for the performance of copper wire can be met.