What are the requirements for the machining accuracy of copper bars during stamping?

As the core conductive connector in power system and electrical equipment, the stamping accuracy of copper bus directly affects the conductive performance, assembly compatibility and operation safety. Combined with power industry standards (such as GB/T 5585.1-2018 "Copper and Copper Alloy Busbars"), equipment assembly requirements and practical application scenarios, the precision requirements of copper bar stamping mainly focus on four core dimensions: dimensional accuracy, shape and position accuracy, surface quality and burr control, as follows:

A, dimensional accuracy requirements (core basic indicators)

The dimensional accuracy directly determines the assembly adaptability between the copper bar and other components, and it is necessary to strictly control the deviation range of key dimensions to avoid problems such as poor contact and uneven current distribution caused by dimensional deviation.

1. Dimensional accuracy of plate foundation

Thickness tolerance:

The common thickness range of copper bar is 1.5mm~12mm (the mainstream specification of power system), and the thickness tolerance should meet the requirements of GB/T 5585.1:

When the thickness is ≤3mm, the tolerance is ±0.15mm；;

3 mm < thickness ≤6mm, the tolerance is ±0.20mm；;

When the thickness is greater than ＞6mm, the tolerance is ±0.30mm；;

High-precision scenes (such as precision electrical equipment) should be controlled within 0.05 mm ~ 0.10 mm (high-precision punch+precision die is required).

Width tolerance:

The common width is 10mm~120mm, and the width tolerance is adjusted according to the specifications:

When the width is less than or equal to ≤50mm, the tolerance is ±0.20mm；;

When the width is greater than ＞50mm, the tolerance is ±0.30mm；;

In mass production, it is necessary to ensure that the width deviation of copper bars in the same batch is ≤0.15mm to avoid gaps or interference during assembly.

2. Stamping dimensional accuracy

Punching size (bolt hole/mounting hole):

The core size of copper bar stamping directly affects the tightness and conductive contact area of bolt connection;

Aperture tolerance: usually H12 (for example, M8 bolt corresponds to an aperture of 8.5mm, and the tolerance is+0.18mm/0), and high-precision scenes need to reach H10 (+0.10 mm/0);

Tolerance of hole spacing: the deviation between the centers of two adjacent holes is ≤±0.15mm, and the deviation between the center of the hole and the edge of the copper bar is ≤±0.20mm；;

Verticality of holes: when the aperture is less than or equal to ≤10mm, the verticality deviation is less than or equal to ≤0.1mm/m；/m; When the aperture is greater than ＞10mm, it is less than or equal to ≤0.2mm/m/m (to avoid poor contact caused by inclined bolt installation).

Incision/shear size:

Dimensional tolerance of copper bar end shearing or special-shaped cutting (such as oblique cutting and step cutting):

Tolerance of shear length: 0.20 mm ~ 0.30 mm (batch production consistency ≤ 0.15 mm);

The contour tolerance of special-shaped incision: ≤±0.25mm, and the key mating surface should be ≤ 0.15mm..

Bending size (including stamping and bending process):

After bending, the angle tolerance of copper bar is ≤ 1, the bending side length tolerance is ±0.20mm, and the bending radius deviation is ≤±0.10mm (to avoid assembly interference or reduction of conductive cross-sectional area due to insufficient bending accuracy).

Second, the form and position accuracy requirements (to ensure the stability of assembly and conductivity)

The geometric shape and relative position deviation of copper bars are controlled by the shape and position tolerance, so as to avoid assembly difficulties, uneven current distribution or local heating caused by deformation.

1. Straightness and flatness

Straightness: when the length of copper bar is less than or equal to ≤1000mm, the straightness deviation is less than or equal to 1 mm/m; When the length is more than ＞1000mm, it is less than or equal to ≤1.5mm/m/m (to avoid the gap caused by the failure to fit the conductor bracket during installation).

Flatness: the surface flatness tolerance of copper bar is ≤0.3mm/m (high-precision scene is ≤0.15mm/m), and the overall flatness is ≤1mm (for copper bars with a length ≤ 2,000 mm); If the surface of the copper bar is warped and concave-convex, the contact area with other conductors will be reduced, and the local resistance will be increased, which will lead to the hidden danger of heating.

2. Parallelism and verticality

Parallelism: the parallelism tolerance of both sides of the copper bar is ≤0.2mm/m, so as to ensure the consistency with other parts during assembly.

Verticality: the verticality tolerance between the punching axis and the copper bar surface is ≤0.15mm (aperture ≤10mm) and ≤0.2mm (aperture > 10mm); The verticality tolerance between the shear end face and the copper bar in the length direction is ≤0.2mm/m, so as to avoid uneven stress during bolt connection.

3. Coaxiality (porous scene)

If the copper bar needs to be punched with multiple coaxial holes (upper and lower copper bar butt holes), the coaxiality tolerance shall be ≤0.2mm, so as to ensure that the bolts can penetrate smoothly and avoid deformation or thread damage of the copper bar caused by forced installation.

Third, the surface quality requirements (to ensure electrical conductivity and corrosion resistance)

The surface quality of copper bar directly affects the conductivity, contact resistance and corrosion resistance, so surface damage should be avoided during stamping.

1. Surface roughness

The roughness Ra of the conductive surface (the surface in contact with other conductors) of the copper bar is ≤ 1.6 μ m, and the non-conductive surface Ra is ≤ 3.2 μ m;

The contact surface should be smooth and level, without obvious scratches, indentations and pits (depth ≤0.05mm, area ≤ 5 mm), otherwise the contact resistance will be increased, leading to local heating.

2. Surface cleanliness and oxidation

After stamping, the surface of the copper bar should be free of impurities such as oil stain, iron filings, burrs, etc. (which should be removed by cleaning process) to avoid impurities from affecting the conduction or causing electrochemical corrosion;

There is no obvious oxidation discoloration on the surface (slight natural oxidation is allowed, which can be improved by passivation treatment), and the thickness of oxide layer is ≤0.005mm, otherwise it needs polishing treatment.

3. No crack and deformation

There should be no cracks in the punching cut, bend and punching edge (invisible to naked eyes, and detected by magnifying glass if necessary) to avoid crack propagation caused by current impact or thermal expansion and contraction during operation;

There is no obvious plastic deformation (such as warping and depression), and the deformation should be controlled within the form and position tolerance.

Four, burr control requirements (key safety and performance indicators)

Burrs after stamping of copper bars will cause difficulties in assembly, scratch operators, increase contact resistance, and even cause arc discharge, which should be strictly controlled:

1. Burr height

The height of burr on the shear plane is ≤0.05mm (≤ 0.03 mm for high-precision scenes);

The burr height at the punching edge is ≤0.08mm (aperture ≤10mm) and ≤0.10mm (aperture > 10mm);

The burr height at the bend is ≤0.05mm, and sharp corners need to be removed (the fillet R is ≤ 0.5 mm).

2. Burr handling requirements

In batch production, deburring procedures (such as grinding wheel grinding, vibration grinding and electrochemical deburring) are needed to ensure that the burr height meets the requirements;

Key contact surfaces (such as bolted contact surfaces and conductive contact surfaces) should be free of burrs, otherwise it will lead to poor contact and fire when local heating is serious.

Five, the accuracy of the special scene supplementary requirements

According to the application scenarios of copper busbar (such as high-voltage equipment, precision instruments and outdoor environment), the following accuracy requirements shall be additionally met:

1. Copper bars for high-voltage equipment

The dimensional tolerance needs to be improved by one level (for example, the thickness tolerance is ±0.08mm~±0.15mm, and the aperture tolerance is H10);

Surface roughness Ra≤0.8μm, without any scratch or oxidation;

Form and position tolerance (straightness and flatness) ≤0.1mm/m to avoid corona discharge caused by uneven electric field distribution.

2. Copper busbar for precision electrical equipment (such as new energy vehicles and aerospace equipment)

Dimensional tolerance ≤±0.05mm (key dimension), and hole spacing tolerance ≤±0.10mm；;

Flatness ≤0.1mm/m, parallelism ≤ 0.1 mm/m;

The burr height is ≤0.03mm, and the surface is free of oil and impurities (it needs to be cleaned by ultrasonic wave).

3. Copper bars for outdoor/corrosive environment

Passivation, tin plating or silver plating are required after stamping, and the surface roughness Ra before treatment is ≤ 1.6 μ m, without oxidation and burr;

The coating thickness is even (tin plating ≥8μm, silver plating ≥3μm), and there is no missing plating and peeling. The coating at the punching cut should be completely covered (to avoid the invasion of corrosive media).

Six, accuracy testing standards and methods

In order to ensure that the stamping accuracy of copper bars meets the requirements, the following testing methods and standards should be adopted:

Dimension detection: use vernier caliper (accuracy 0.02mm), micrometer (accuracy 0.001mm), projector (accuracy 0.005mm) and coordinate measuring instrument (accuracy 0.003mm) to detect key dimensions;

Form and position tolerance detection: flatness and straightness are detected by level ruler, dial indicator and laser leveling instrument; Use verticality tester and coaxiality tester to detect relative position deviation;

Surface quality inspection: detect cracks and burrs by naked eye observation (no obvious defects), roughness meter (detecting Ra value) and magnifying glass (10 times);

Standard basis: Strictly follow GB/T 5585.1-2018 Copper and Copper Alloy Busbars, GB/T 11984-2018 Copper Busbars for Conductivity, IEC 60287 Current Rating of Cables and Busbars and other industry standards.

Summary: the core significance of copper bar stamping accuracy

As the key component of power transmission, the stamping accuracy of copper bar is directly related to: ① assembly compatibility (avoiding the inability to install due to dimensional error); ② Conductivity (contact resistance, current distribution uniformity); ③ Operation safety (to prevent local heating, corona discharge and fire hazards); ④ Service life (avoiding corrosion and crack propagation). Therefore, in the production process, it is necessary to ensure that all precision indexes meet the industry standards and customer needs through "high-precision mold design, CNC punching machine processing, strict process inspection, deburring and surface treatment".