How to control the dimensional deviation of copper sheet during processing?

To control the dimensional deviation of copper sheet processing, it is necessary to control it from multi-dimensional systems such as material characteristics, equipment accuracy, process parameters, operation specifications and quality inspection. The following are specific control strategies and practical methods:

First, the material pretreatment control

1. Material state selection

Hardness matching:

Semi-hard parts (such as H65 brass semi-hard, hardness HV80-100) are preferred for high-precision parts (tolerance within ±0.03mm), giving consideration to formability and deformation resistance;

Complex bending parts are annealed (HV50-70) to reduce springback, and hard materials (HV120+) are only suitable for simple stamping.

Flatness detection:

Incoming materials shall be measured by flatness detector, and plates exceeding 0.1mm/m²/m shall be treated by leveler (rolling times ≥3 times, pressure 8-12MPa).

2. Material stress release

Pre-stretching treatment:

Before processing the thick plate (> ＞2mm), carry out 1-3% plastic stretching to release the rolling stress (for example, 500mm wide copper plate, stretching speed of 0.5m/min, load of 20-30kn);

Aging treatment:

Keep the precision parts in a 150℃ thermostat for 2 hours before processing to eliminate internal stress (the deformation can be reduced by more than 60%).

Second, equipment precision and mold control

1. Calibration of processing equipment

Stamping equipment:

The verticality error of the punch guide rail is less than or equal to ≤0.02mm/m/m, and it is detected by a laser interferometer;

The mold closing height error is ±0.01mm, which is monitored by electronic height gauge in real time.

CNC machine tool:

The positioning accuracy is less than or equal to ≤0.005mm, and the repeated positioning accuracy is less than or equal to ≤0.003mm, and the clearance of the screw rod is detected by the ball rod instrument every week;

Spindle runout is less than or equal to ≤0.002mm, and the tool is calibrated with a dynamic balance instrument.

2. Mold precision design

Clearance compensation:

The unilateral clearance of the stamping die is 5-8% of the thickness of the material (such as 0.5mm copper sheet and 0.025-0.04mm clearance), and the upper limit of the hard material is taken;

The R angle of the bending die is designed according to the springback compensation formula: actual R angle = theoretical R angle× (1+k), and k is the springback coefficient (H62 brass K=0.03-0.05).

Wear detection:

After every 5000 pieces of dies are produced, the wear amount of the cutting edge is detected by a secondary imager, and it needs to be repaired if it exceeds 0.01mm (grinding amount is 0.005-0.01mm/time).

Third, process parameter optimization

1. Cutting processing

Laser cutting:

Sheet (≤1mm): power 80-120W, speed 5-8m/min, pressure of auxiliary gas (nitrogen) 0.8-1.2MPa, and thermal deformation controlled within ±0.02mm；;

Thick plate (> 3 mm): pulse laser (frequency 200-300Hz) is used to cut in layers (each layer is 0.5-1mm), and water cooling is used to reduce the heat affected zone.

Numerical control stamping:

When the punching speed is 100-150 times/min and the hole spacing accuracy is ±0.05mm, the punching shall be carried out step by step (punching the positioning hole first and then punching the forming hole).

2. Forming processing

Bending process:

Bending angle compensation: after the measured rebound angle, the die angle = theoretical angle-rebound angle (for example, theoretical 90, measured rebound 5, die set to 85);

Control of pressing force: monitored by pressure sensor, pressing force = material shear strength× bending length× thickness× 1.2-1.5 times (H65 brass is about 80-100kN/m).

Stretching process:

Tensile coefficient ≥0.5 (pure copper can be 0.45), radius of concave die fillet =(5-8)× material thickness, and multi-layer stretching is adopted (for example, if the stretching depth is more than 3 times the diameter, it will be stretched in 2-3 times).

Iv. Operation Specification and Process Control

1. Three-inspection system for first article

Detection process:

After processing the first article, the operator shall conduct self-inspection → the team leader shall conduct re-inspection → the quality inspector shall conduct special inspection, and mass production can be carried out only after the dimensions (with micrometer and projector), form and position tolerance (straightness ≤0.05mm/m, flatness ≤0.03mm) are qualified.

2. Process inspection and adjustment

Sampling frequency:

During mass production, 5-10 pieces are sampled every hour, and the mean-range diagram is drawn by SPC statistical process control. When 5 points exceed 1 σ continuously, stop the machine immediately and adjust the parameters.

Real-time compensation:

For the size drift caused by die wear in continuous machining (such as the aperture gradually increasing), the coordinates are corrected in real time by the CNC system of the machine tool (the compensation amount is 0.002-0.005mm each time).

Five, advanced detection and feedback technology

1. On-line detection system

Visual inspection:

Install an industrial camera (resolution ≥ 5 million pixels) in the stamping production line, and cooperate with AI algorithm to detect the size in real time. When the deviation is more than ＞±0.02mm, it will automatically trigger the shutdown (response time is less than 0.5 seconds).

Laser thickness gauge:

Continuously monitor the change of copper sheet thickness with an accuracy of 0.001 mm. When the thickness fluctuation exceeds 0.5%, it will be fed back to the uncoiler to adjust the feeding tension.

2. Fixture optimization

Positioning accuracy:

The positioning mode of two pins on one side is adopted, the spacing tolerance of positioning pins is ±0.005mm, and it is matched with a precision vise (the clamping force uniformity error is ≤ 5%);

Anti-deformation fixture:

When processing thin-walled parts, use vacuum adsorption fixture (suction ≥0.08MPa) or elastic rubber pad (thickness 2-3mm) to reduce clamping deformation.

Six, typical size deviation solution

Solutions to common causes of deviation types

If the die with large aperture is worn and the blanking gap is too large, repair the punch (single-side grinding amount is 0.005mm) and reduce the gap to 5% t.

If the bending angle is insufficient, the rebound is not compensated, and the pressing force is insufficient, the die angle compensation will be increased (+3-5), and the pressing force will be increased to 120 kn/m.

The servo feeding system (accuracy ±0.01mm) is installed to optimize the cooling process if the feeding position is inaccurate in the length direction and thermal deformation.

If the leveling of wavy edges is not complete and the uneven shear stress increases the leveling times (≥5 times), oblique edge shearing (angle 3-5) shall be adopted.

Seven, continuous improvement mechanism

Establish process database:

Record the processing parameters of copper sheets with different brands and thicknesses (for example, the stamping gap of H62 brass is 0.8mm and 0.04mm) to form enterprise standard process cards.

PFMEA analysis:

Failure mode analysis is carried out for high-risk processes (such as precision stamping), and preventive measures (such as regular flaw detection of molds) are formulated.

Employee skill certification:

Operators need to pass practical assessment (e.g. the control error of bending angle is ≤ 2), hold relevant certificates and receive regular retraining (twice a year).

Summary: The control of dimensional deviation should follow the principle of "prevention first, process monitoring and quick response". Through the closed-loop management of the whole process of material-equipment-process-detection, combined with digital detection technology, the dimensional tolerance of copper sheet processing can be stably controlled within ±0.03mm (general precision) or ±0.01mm (precision grade). The key is to establish a standardized workflow and optimize process parameters through continuous data accumulation.