What processes should be paid attention to in the process of copper sheet processing?

In the process of copper sheet processing, it is necessary to strictly control the process parameters according to the material (such as pure copper, brass and bronze), specifications (thickness and width) and application scenarios (such as electronics, hardware and decoration) of copper sheets to avoid problems such as cracks, size deviation and surface defects. The following are the key process points and precautions:

A, raw material preparation and inspection

Raw material selection

Ensure that the purity or alloy composition of copper meets the standards (for example, the copper content of T2 pure copper is ≥99.9%, and that of H65 brass is 65% 1%), and the content of impurities (such as Fe and Pb) should be strictly controlled to avoid brittle fracture during processing.

Raw material form: copper strip/copper plate in rolled state is preferred, with high surface flatness and good thickness uniformity (tolerance ≤±0.005 mm).

Raw material inspection

Surface quality: Visually check whether there are defects such as scale, scratches, pits, cracks, etc., especially whether the edge is burr or rolled (which may lead to cracking during cutting).

Mechanical properties: confirm the state of raw materials (soft state, semi-hard state and hard state) through hardness test (such as Vickers hardness HV) to match the subsequent processing technology.

Second, the cutting/cutting process (determine the dimensional accuracy)

1. Selection of cutting equipment

Disc cutter cutting: suitable for narrow-band copper sheet (width ≤200 mm). The cutter is made of cemented carbide or high-speed steel, which needs regular grinding to keep sharp (edge roughness Ra≤0.8 μm).

Laser cutting: it is suitable for high-precision and complex copper sheets (such as electrodes of electronic components), with an accuracy of ±0.02 mm, but attention should be paid to edge oxidation caused by heat affected zone.

Stamping and cutting: used for mass production of rectangular copper sheets, the die gap should be strictly controlled (generally 8%~12% of the material thickness) to avoid edge burrs.

2. Key control points

Tension control: the copper strip needs to maintain a constant tension (5 ~ 20 N/mm) when cutting. If the tension is too small, it is easy to deviate, and if it is too large, it may be stretched and deformed.

Tool alignment: the axial runout of the disc cutter is ≤0.01 mm, and the radial runout is ≤0.005 mm, otherwise, the edge of the copper sheet will be wavy or dimensional deviation.

Burr treatment: after cutting, the edge burr (height ≤0.01 mm) should be removed by brush, sandpaper or electrolytic deburring process (voltage 5~15 V, time 10~30 seconds).

III. Rolling/Calendering Process (Controlling Thickness and Properties)

1. Rolling equipment and technology

Cold rolling: used for thin copper sheet (thickness ≤1.0 mm), the roll material is cemented carbide or hardened steel (hardness ≥HRC60), and the rolling oil should have high lubricity (kinematic viscosity 40~100 cSt) and coolability.

Hot rolling: used for thick copper sheet (thickness > 1.0 mm), it needs to be heated to 500~800℃ (adjusted according to alloy type) to eliminate casting structure and improve plasticity.

2. Key control points

Pass reduction: the reduction rate of single cold rolling is usually 10%~30%, and excessive reduction rate is easy to cause cracks (for example, intermediate annealing is needed when the reduction rate of hard brass exceeds 20%).

Shape control: control the flatness of copper sheet (waviness ≤1 mm/m) through roll crown adjustment (such as CVC roll profile) or hydraulic roll bending system to avoid buckling.

Intermediate annealing: if the hardness exceeds the target value (such as HV≥120 in semi-hard state) during rolling, it needs to be annealed (the annealing temperature of pure copper is 300~400℃ and the heat preservation is 1~2 hours) to restore plasticity.

Four, surface treatment process (affect the appearance and performance)

1. Cleaning and degreasing

Chemical cleaning: use 5%~10% sulfuric acid solution (temperature 40~60℃, time 5~10 minutes) to remove the scale, or use sodium hydroxide solution (concentration 10~20 g/L) for degreasing.

Ultrasonic cleaning: suitable for precision copper sheets, with water-based cleaning agent to remove micron-scale pollutants (such as rolling oil residue).

2. Coating and passivation

Electroplating: Tin plating (thickness 1~5 μm) needs to control current density 1 ~ 3 A/dm and temperature 20~50℃ to avoid missing plating or uneven thickness; Gold plating (used for electronic components) requires nickel plating as a primer (thickness 2~3 μm).

Passivation treatment: use chromate (such as trivalent chromium solution) or chromium-free passivator (such as silane coupling agent) and soak for 30-60 seconds to form an anti-oxidation film (thickness ≤0.5 μm).

3. Anti-scratch treatment

During the processing, the rollers and fixtures that contact the copper sheet should be coated with polyurethane or nylon (Shore A 80~90 hardness) to avoid scratches caused by direct metal friction.

The finished products should be isolated with polyethylene film or neutral paper (thickness 50~100 μm) to prevent surface indentation.

V. Forming and deep processing (such as bending, stamping and etching)

1. Bending process

The bending radius should be ≥1.5 times the material thickness (for example, the bending radius of 0.5 mm thick copper sheet should be ≥0.8 mm) to avoid cracks caused by right-angle bending.

The die needs to be preheated to 50~80℃ (for hard copper sheet) to reduce springback (the springback angle is usually 5 ~ 10, which needs to be corrected by die trial).

2. Stamping and forming

The die gap is 10%~15% of the material thickness (for example, the gap of 0.3 mm thick copper sheet is 0.03~0.045 mm). If the gap is too small, it is easy to chew the die, and if it is too large, it is easy to produce burrs.

The stamping speed should be controlled at 50~100 times/min, and a lubricating device (such as stamping oil spray, the dosage is 0.1~0.3 mL/piece) is required for high-speed stamping.

3. Chemical etching

For precision electronic components (such as flexible printed circuit board), the etching solution is usually ferric chloride (concentration 300~400 g/L, temperature 50~60℃) or acidic copper chloride solution.

The etching time needs to be accurately controlled (for example, it takes about 5~8 minutes to etch a copper sheet with a thickness of 0.1 mm) to avoid line width deviation (±0.01 mm) caused by excessive etching.

VI. Testing and Quality Control

Size detection

Thickness: use a micrometer (accuracy 0.001 mm) to measure at multiple points (edge, center and diagonal), and the tolerance shall conform to GB/T 2059 and other standards (for example, the tolerance of 0.2 mm thick copper sheet is ±0.012 mm).

Width/length: use laser caliper or image measuring instrument with accuracy of ±0.02 mm

Surface quality inspection

Visual inspection or optical microscope (magnification of 50~100 times) are not allowed to have scratches, pits with a thickness of more than 5% or oxidation spots with a length of > 10 mm.

Mechanical property testing

Tensile test: the yield strength and tensile strength shall meet the standards (for example, the tensile strength of H62 brass shall be ≥305 MPa) and the elongation shall be ≥10% (in soft state).

Hardness test: the fluctuation range of Vickers hardness HV value is ≤ 10, such as HV 80~100 of semi-hard pure copper.

Seven, special material processing matters needing attention

Brass (containing zinc)

It is easy to produce "quarter crack" (stress corrosion cracking) during processing, so it is necessary to avoid residual stress. After processing, stress relief annealing can be carried out (150~200℃, heat preservation for 1~2 hours).

Phosphor bronze (containing tin and phosphorus)

When rolling, roll temperature should be strictly controlled (≤60℃) to prevent tin segregation, and after cutting, it should be cleaned in time to avoid residual rolling oil from corroding the surface.

Ultra-thin copper foil (thickness < 0.05 mm)

Adopt a multi-high mill (such as a twenty-high mill), the rolling tension shall be ≤ 5 N/mm, and the ambient humidity shall be controlled at 40%~60% to prevent electrostatic adsorption of dust.

Summary: Core process control objectives

Accuracy: the dimensional tolerance is controlled within ±0.01~±0.1 mm (according to product requirements), and the surface roughness Ra is ≤ 1.6 μ m..

Surface quality: no visible defects, the coating adhesion is tested by the method of marking (ISO 2409), and the peeling area is ≤5%.

Stable performance: mechanical property fluctuation ≤5%, electrical conductivity ≥100% IACS (pure copper), salt spray corrosion resistance ≥24 hours (tinned copper sheet).

Through the above process control, it can be ensured that copper sheet processing can meet the application requirements of high precision and high reliability, such as electronic components, aerospace components, high-end hardware products and so on.