What should we pay attention to when processing stamping parts for copper products?

For the processing of copper stamping parts, the core needs to focus on the characteristics of copper, such as high ductility, low hardness, easy die adhesion and good thermal conductivity, and formulate targeted measures from the dimensions of process design, die selection, parameter control and quality control. The following are detailed precautions:

First, the preliminary process and mold preparation (basic guarantee, to avoid late rework)

Optimization of product and layout design

Reasonable design of blanking gap: the blanking gap of copper material should be 10%~20% larger than that of steel (the upper limit is soft copper, and the lower limit is hard copper). For example, the gap of low-carbon steel is 5%~8% of the plate thickness, and the gap of soft copper (such as T2) can be adjusted to 6%~10%, so as to avoid die sticking and excessive burr caused by too small gap, or warping and edge collapse caused by too large gap.

Reduce the concentration of complex processes: copper has good ductility, but is prone to plastic deformation, avoiding the concentration of narrow grooves, acute angles (minimum internal corner radius ≥ 0.5 times of plate thickness), deep holes and other structures in single stamping. It is recommended to punch in multiple times to reduce the risk of cracking caused by material stress concentration.

The material flow direction is considered in layout: using the anisotropy of copper, the stamping direction is consistent with the material rolling direction during layout to reduce springback and deformation; At the same time, optimize the lap width (soft copper lap ≥1.5 times the thickness, hard copper ≥1.2 times the thickness) to avoid material waste and unstable feeding.

Mould selection and surface treatment

Selection of die materials: Wear-resistant alloy tool steels such as Cr12MoV and SKD11 are preferred, or hard alloy (tungsten steel) is used to make punch and die, so as to avoid the rapid wear of the die caused by the high ductility of copper.

Die surface treatment: The working surface of the die must be polished, nitrided or coated with TiN (surface roughness Ra≤0.2μm) to reduce the friction coefficient with copper and reduce the phenomenon of die sticking ("galling") from the root.

Adding an auxiliary structure: a discharging plate (made of polyurethane or hard rubber) is arranged at the outlet of the female die to prevent the workpiece from being stuck in the die; When punching a thin copper sheet (≤0.5mm), very thin MoS₂ (molybdenum disulfide) or special stamping oil can be coated on the die surface to enhance the lubrication effect.

Second, the core control of machining process (key link, ensuring accuracy and efficiency)

Accurate matching of stamping parameters

Punching speed: copper is fast in heat conduction and easy to deform, and the punching speed should be 20%~30% lower than that of steel parts (the punching speed of ordinary steel parts is 100~200 times/min, and that of copper parts can be controlled at 80~150 times/min), so as to avoid local overheating of materials, intensified die sticking or "secondary shearing" burr caused by high-speed stamping.

Pressure control: according to the hardness of copper, adjust the punching force (the tensile strength of soft copper is 200-300 MPa, and that of hard copper is 350-500 MPa), and the formula of punching force is F=K×L×t×σb(K is the safety factor of 1.3-1.5, l is the punching perimeter, t is the plate thickness, and σb is the tensile strength), so as to avoid die damage or workpiece deformation caused by excessive pressure.

Feeding accuracy: servo feeder is adopted, and the feeding accuracy is controlled within ±0.02mm, especially for thin copper sheets (≤0.3mm), so as to avoid workpiece size out of tolerance or material jam caused by feeding deviation; Before feeding, the copper strip should be leveled (using multi-roller leveler) to eliminate the internal stress after rolling.

Lubrication and cooling measures

Selection of special lubricant: special stamping oil for copper materials (including extreme pressure additives and anti-sticking agents, avoiding chlorine-containing additives to prevent corrosion of copper materials) must be used, and it is forbidden to dry flush or use ordinary engine oil (insufficient lubricity and easy to stick to the mold).

Lubrication method: the thin copper sheet (≤1mm) is lubricated by spraying, and the thick copper sheet (≥1mm) is lubricated by daubing or soaking, so as to ensure that the contact surface between the mold and the material is covered with oil film throughout; Replenish oil regularly during stamping to avoid die sticking caused by oil film rupture.

Cooling control: copper has good thermal conductivity, and the die temperature does not increase obviously during continuous stamping, but it is still necessary to avoid long-term high-temperature operation (die temperature ≤120℃), and natural cooling or air cooling can be used to assist in cooling to prevent the die hardness from decreasing.

Three, quality control and common problem solving (to ensure the product qualification rate)

Detection of key quality indicators

Burr control: copper parts are prone to burr after blanking, so the height of burr (thin copper sheet ≤0.03mm, thick copper sheet ≤0.05mm) should be strictly controlled. If the burr exceeds the standard, the blanking gap should be adjusted in time, the cutting edge of the die should be polished or the punching speed should be reduced.

Dimensional accuracy: copper parts are easy to rebound after stamping (especially in bending and drawing processes), so the springback amount (3 ~ 5 for bending angle and 0.1~0.3mm for diameter of drawing parts) should be reserved, or it should be corrected through subsequent shaping processes; In mass production, the key dimensions are sampled every 100 pieces to avoid precision drift caused by die wear.

Surface quality: the surface of copper material is easy to be scratched and oxidized, so gloves should be worn during processing to avoid hand sweat contact; When stacking workpieces, paper or plastic film shall be used to separate them. After stamping, antirust treatment shall be carried out in time (such as applying antirust oil and vacuum packaging), especially in humid environment (it is rainy in Kunshan area, so it is necessary to strengthen moistureproof).

Common problems and solutions

Sticking to the mold (the workpiece is stuck on the mold): the reason is that the surface of the mold is rough, the lubrication is insufficient and the gap is too small; Solution: re-polish the die, replace the special stamping oil, adjust the blanking gap to a reasonable range, and set a chip removal groove at the die edge if necessary.

Warp and deformation of workpiece: the reasons are too large blanking force, uneven feeding and insufficient lap width; Solution: Reduce the blanking force, optimize the feeding mechanism, increase the lap width, or add the leveling process after stamping (using leveling machine or manual leveling).

Cracking and tearing: The reason is that there are impurities in the material, the process is too concentrated and the fillet is too small; Solution: Choose high-quality oxygen-free copper (such as T2 and C1100) and avoid using recycled copper; Split the complex process and increase the radius of internal angle; Check the surface of the material before stamping, and remove the blank with scratches and inclusions.

IV. Equipment and Safety Specifications (to ensure production safety and efficiency)

Equipment maintenance: regularly check the accuracy of the slider, guide rail and feeding mechanism of the punch to ensure the stable operation of the equipment; Clean up the residual copper chips and oil stains on the surface in time after the mold is used to avoid the rust of the mold or the wear of the cutting edge; Regularly grind the cutting edge of the die (check after stamping every 10,000 ~ 20,000 pieces, and grind when the cutting edge wears more than 0.1mm).

Safe operation: When stamping copper parts, due to the good ductility of the material, there may be "blocking" (the material gets stuck in the mold and causes the equipment to stop). It is forbidden to clean the stuck material directly by hand, and special tools (such as copper bars and fixtures) are needed; Operators should wear protective gloves and goggles to avoid splashing copper chips and hurting people; The equipment shall be equipped with an emergency stop button to ensure quick stop in case of emergency.

Five, material selection supplement (reduce the processing difficulty from the source)

Soft copper (such as T2 and T3): excellent ductility, suitable for bending, stretching and deep drawing processes, but easy to stick and deform, so it is necessary to control lubrication and die accuracy;

Hard copper (such as H62 and H65 brass): with higher hardness, the punching performance is better than that of soft copper, but the ductility is slightly poor, so it is necessary to pay attention to springback when bending to avoid cracking;

Oxygen-free copper (C1100): It has high purity and few impurities, and is suitable for stamping parts with high precision and high surface quality, especially for copper stamping parts in the fields of electronics and electrical appliances.

To sum up, the core of copper stamping parts processing is "adapting material characteristics, optimizing process parameters, ensuring die accuracy, and strengthening lubrication and cooling". At the same time, combining with the needs of mass production, controlling quality and efficiency, and strengthening moisture-proof and rust-proof treatment according to the climate characteristics of Kunshan area can effectively reduce processing risks and improve product qualification rate.