What matters should be paid attention to in the production and processing of ultra-precision ultra-fine copper round wire?

Ultra-precision ultra-fine round copper wire (usually refers to copper wire with diameter ≤0.1mm) requires extremely high precision, surface quality and mechanical properties in production and processing, and any omission in any link may lead to product scrapping. The following are the key points to be paid attention to in the production and processing, covering raw materials, equipment, process parameters and environmental control:

First, raw material control

Copper purity and impurity management

Purity requirements: select high-purity electrolytic copper (purity ≥99.95%), and the content of impurities (such as oxygen, lead, iron, etc.) should be strictly controlled to avoid embrittlement or fracture of copper wire due to impurity segregation.

Surface cleaning: the surface of raw copper rod should be free of oil stain, oxide layer or scratches, and degreasing and pickling should be carried out when necessary to prevent impurities from being brought into subsequent processing.

Uniformity of raw material structure

The copper rod needs to be annealed to ensure uniform and fine grains, and avoid stress concentration and wire breakage during wire drawing due to uneven structure during processing.

Second, the key control of wire drawing process

Mold selection and maintenance

Die material: Diamond (PCD) or tungsten carbide die is used, which has higher wear resistance and is suitable for extremely fine specifications (diameter < ＜0.05mm). It is necessary to regularly check the wear of die aperture (tolerance is controlled within 0.5 μ m).

Design of die taper angle: design the length of sizing belt and taper angle reasonably (usually the taper angle is 12-16) to avoid surface scratch or diameter deviation of copper wire caused by excessive friction.

Wire drawing speed and tension control

Low-speed stable machining: the drawing speed of ultra-fine copper wire (such as 0.02mm) is generally less than 50 m/min to avoid oxidation or plastic deformation of copper wire caused by high-speed friction heat generation.

Tension uniformity: servo motor or magnetic powder brake is used to accurately control the tension (fluctuation ≤ 1%). If the tension is too large, the copper wire will be broken, and if it is too small, the diameter will be uneven.

Lubrication and cooling system

Lubricant selection: Use special ultra-fine copper wire wire drawing oil (low viscosity and strong oxidation resistance) or use water-based lubricant (rust inhibitor is required) to ensure uniform adhesion of lubricating film and reduce die wear and surface scratch of copper wire.

Cooling and temperature control: the mold temperature should be controlled at 40℃-60℃ during wire drawing, and heat can be dissipated by circulating cooling water or oil cooling system to avoid annealing and softening of copper wire caused by high temperature.

Third, the surface quality and oxidation protection

Anti-oxidation treatment

Inert gas protection: nitrogen gas (purity ≥99.99%) is introduced during wire drawing, annealing or storage to prevent copper wire from contacting with oxygen to form oxide layer (oxide layer will affect electrical conductivity and welding performance).

Surface coating: Immediately after wire drawing, apply extremely thin antioxidant (such as fatty acid protective film), or silver and nickel plating to isolate the air.

Surface defect detection

On-line use of laser caliper (accuracy 0.1μ m) and high-definition CCD vision system, real-time monitoring of copper wire diameter, roundness, surface scratches, burrs and other defects, found abnormal automatic shutdown.

Fourth, annealing process control

Annealing temperature and time

Adopt continuous annealing furnace (such as bell jar furnace or mesh belt furnace), the temperature control accuracy is 5℃, and the annealing temperature of ultra-fine copper wire is usually 180℃-250℃ (according to the diameter adjustment, the thinner the temperature, the lower the temperature), so as to avoid overheating leading to coarse grains and strength reduction.

The annealing atmosphere should be pure hydrogen or nitrogen-hydrogen mixed gas (hydrogen content 3%-5%) to ensure the reduction annealing effect and eliminate work hardening.

Cooling rate after annealing

After annealing, it needs to be rapidly cooled to room temperature (cooling time ≤10 seconds) to prevent the secondary oxidation of copper wire during slow cooling, and at the same time maintain the uniformity of structure.

Five, equipment and environmental requirements

Precision of production equipment

The spindle jump of wire drawing machine is less than or equal to 1 μ m, and the repeated positioning accuracy of wire arranging mechanism is less than or equal to 5 μ m, so as to avoid the fluctuation of copper wire diameter caused by equipment vibration.

The winding device needs to take up the wire with constant tension, and the winding speed should be synchronized with the wire drawing speed to prevent the copper wire from loosening or breaking.

Clean workshop environment

The production environment should meet the standard of 10,000-class clean room (ISO 8), and dust and particulate matter (the number of particles ≥0.5μm ≤ 352,000/m) should be controlled to avoid impurity adhesion affecting the surface quality of copper wire.

Temperature and humidity control: the temperature is 23℃ 2℃ and the humidity is 45% 5%, so as to prevent the copper wire from being oxidized by moisture or dimensional change caused by temperature and humidity fluctuation.

Six, quality inspection and process monitoring

Key index detection

Diameter and roundness: use a screw micrometer (accuracy 0.1μm) or a non-contact laser caliper, sample and test each batch, and the diameter tolerance is controlled within 1% (for example, the tolerance of 0.05mm copper wire is ±0.0005mm).

Mechanical properties: tensile strength and elongation are tested. The tensile strength of ultra-fine copper wire should be ≥300MPa, and the elongation should be ≥10% to avoid the influence of brittle fracture on subsequent use.

Conductivity: Resistivity ≤ 1.724× 10 Ω m (20℃), so as to ensure that the electrical performance reaches the standard.

Process tracing and recording

The raw material batch, drawing die number, process parameters (temperature, speed, tension) and test data of each batch of copper wire are digitally recorded, which is convenient for tracing quality problems.

Seven, safety and anti-static measures

Antistatic treatment

Operators should wear anti-static clothing and gloves, the grounding resistance of the equipment should be ≤10Ω, and anti-static rubber should be laid on the workbench to avoid electrostatic dust adsorption or copper wire winding.

Safety protection

Ultra-fine copper wire has high hardness and poor toughness, and may splash when it breaks. Therefore, it is necessary to set a protective baffle in the equipment operation area, and the operator should wear goggles.

summary

The production and processing of ultra-precision ultra-fine copper round wire should be strictly controlled from the whole chain of "material-process-equipment-environment", and the core lies in reducing processing stress, preventing oxidation, and ensuring dimensional accuracy and surface quality. Any slight deviation in any link may lead to product scrapping, so it is necessary to combine automatic detection technology with refined management to realize traceability and real-time monitoring of the whole process.