Brass and copper are widely used in sheet metal fabrication due to their excellent electrical conductivity, thermal conductivity, corrosion resistance, and aesthetic appeal. They are commonly applied in electrical components, decorative parts, heat exchangers, and plumbing fittings. However, brass and copper have unique material properties—such as high ductility, low strength, and sensitivity to temperature—that make their bending process different from that of steel or aluminum. Mastering the key points of bending brass and copper sheet metal is essential to ensure product quality and production efficiency. In this blog, we will explore the material characteristics of brass and copper and the core considerations for their bending operations.

### 1. Understanding the Material Properties of Brass and Copper

Before bending brass and copper, it is crucial to grasp their inherent properties, as these directly determine the bending process parameters and tool selection:

#### (1) Copper

Copper is a pure metal with extremely high ductility and thermal conductivity. Its tensile strength is relatively low (approximately 220-300 MPa for annealed copper), and it has good plastic deformation ability, making it easy to bend. However, copper’s high thermal conductivity means that during bending, the heat generated by friction is quickly dissipated, which has little impact on the material’s properties. Additionally, copper has a distinct grain structure; bending parallel to the grain direction may cause slight surface roughness, while bending perpendicular to the grain direction results in a smoother surface finish.

#### (2) Brass

Brass is an alloy of copper and zinc, and its properties vary with the zinc content. Common brass grades include H62 (62% copper, 38% zinc) and H65 (65% copper, 35% zinc). Compared to pure copper, brass has higher tensile strength (300-400 MPa for annealed brass) and slightly lower ductility. The zinc content significantly affects bendability: higher zinc content (e.g., H68) improves strength but reduces ductility, making it more prone to cracking during bending; lower zinc content (e.g., H59) has better ductility but lower strength. Brass also has good corrosion resistance but is sensitive to stress corrosion, especially in humid or corrosive environments.

### 2. Key Considerations for Bending Brass and Copper

#### (1) Rational Selection of Inside Bend Radius

Due to the high ductility of brass and copper, their minimum allowable inside bend radius (R_min) is relatively small, but improper radius selection can still lead to surface defects or cracking. The recommended minimum bend radii are as follows:

- Annealed copper (O temper): R_min = 0.3t-0.5t (t is material thickness). For example, for 1.5mm thick copper sheet, the minimum inside bend radius can be 0.45mm-0.75mm.

- Annealed brass (H62/H65, O temper): R_min = 0.5t-1t. For 2mm thick H62 brass sheet, the minimum inside bend radius should be 1mm-2mm.

- Hardened brass (H62/H65, H temper): Due to reduced ductility, R_min needs to be increased to 1t-2t to avoid cracking.

It should be noted that if the bend radius is too small, the outer surface of the bend may appear "orange peel" (surface roughness caused by grain deformation), which affects the aesthetic quality. For parts requiring a high surface finish, the bend radius should be appropriately increased to 1.5t-2t.

#### (2) Correct Handling of Grain Direction

Like other sheet metals, brass and copper have a grain structure formed during the rolling process. Bending parallel to the grain direction is prone to surface defects (such as orange peel or slight cracking), while bending perpendicular to the grain direction can obtain a smoother surface and higher bendability.

In practical operations:① Check the grain direction mark on the material sheet (usually indicated by arrows); ② Prioritize bending perpendicular to the grain direction. If the part structure requires parallel bending, increase the inside bend radius by 50% and reduce the bending speed to minimize defects.

#### (3) Selection of Appropriate Tooling

Brass and copper are relatively soft, so tooling selection should focus on avoiding surface scratches and ensuring uniform force distribution:

- V-die width: The recommended V-die width for brass and copper is 6t-8t. A wider V-die (e.g., 8t) can distribute the bending force evenly, reducing the risk of surface indentations; a narrower V-die (e.g., 6t) is suitable for thin sheets (≤1mm) to ensure bending accuracy. For example, when bending 2mm thick copper sheet, a V12-V16 die (6t-8t) is appropriate.

- Punch radius: The punch radius should be consistent with the designed inside bend radius. To avoid scratching the material, the punch surface should be polished (Ra ≤ 0.4 μm), and low-friction coatings (such as PTFE or DLC) can be applied. For soft copper sheets, polyurethane or plastic punch sleeves can be used to isolate direct contact between the tool and the material.

- Tool material: Use hardened steel (HRC 58-62) tooling. Avoid using carbide tooling, as its high hardness can easily scratch the soft surface of brass and copper.

#### (4) Strict Control of Bending Speed and Force

Brass and copper have high ductility but low strength. Excessive bending speed or force can lead to material deformation, surface scratches, or even edge tearing:

- Bending speed: The optimal bending speed is 2-5 mm/s. A slow and stable speed allows the material to undergo plastic deformation gradually, reducing the risk of surface defects. Avoid high-speed bending, as it may cause the material to slide unevenly against the tooling, resulting in scratches.

- Bending force: Calculate the required bending force accurately using the formula F = (K * σ_y * t² * L) / V (K=0.33 for V-die). Excessive force can cause indentations on the material surface, while insufficient force may lead to incomplete bending or excessive springback. For example, when bending 1.5mm thick H65 brass sheet with a bend length of 100mm and a V12 die, the bending force is approximately 12-15 kN.

#### (5) Proper Lubrication and Surface Protection

Brass and copper are prone to galling (material adhesion to tooling) and surface scratches during bending. Proper lubrication and surface protection are critical:

- Lubrication selection: Use low-friction, residue-free lubricants, such as synthetic lubricants or wax-based lubricants. Avoid oil-based lubricants, as they are difficult to clean and may affect subsequent processes (e.g., electroplating or welding). For parts with high surface finish requirements, dry lubricants (e.g., molybdenum disulfide powder) can be used.

- Surface protection: Before bending, clean the material surface with isopropyl alcohol to remove oil, dust, or debris. Use lint-free gloves when handling to avoid scratching the surface with fingerprints or nails. For thin brass/copper sheets (≤0.8mm), cover the surface with a protective film during bending and remove it after processing.

#### (6) Handling of Springback

Springback of brass and copper is relatively small (usually 1-3 degrees) due to their low yield strength, but it still needs to be compensated for to ensure bending accuracy:

- Overbending compensation: Based on test bends, determine the springback angle and overbend accordingly. For example, if the desired final angle is 90 degrees and the springback is 2 degrees, bend the material to 88 degrees.

- Bottoming bending: For parts with strict angle tolerances, use bottoming bending (coining). Apply a small amount of additional pressure (10-15% of the total bending force) after the material is bent to the desired angle to reduce elastic deformation and minimize springback. Note that the bottoming force should not be excessive, to avoid surface indentations.

#### (7) Annealing Treatment for Hardened Materials

Hardened brass (e.g., H62-H temper) or copper has low ductility and is prone to cracking during bending. Annealing treatment before bending can significantly improve ductility:

- Annealing parameters for copper: Heat to 450-500°C, hold for 1-2 hours, and cool slowly in air.

- Annealing parameters for brass: Heat to 400-450°C, hold for 1-1.5 hours, and cool slowly in air.

After annealing, the material returns to the O temper (soft state), which is easy to bend. If the part requires strength after bending, re-anneal or perform cold working to restore the hardness.

### 3. Common Problems and Solutions in Bending Brass and Copper

#### (1) Surface Orange Peel

Cause: Small bend radius, bending parallel to grain direction, or excessive bending speed. Solution: Increase the bend radius to 1.5t-2t, adjust the bend direction to be perpendicular to the grain, and reduce the bending speed to 2-3 mm/s.

#### (2) Surface Scratches

Cause: Contaminated tooling, sharp tool edges, or insufficient lubrication. Solution: Clean the tooling surface thoroughly, round the tool edges (radius 0.5-1mm), apply an appropriate amount of lubricant, and use protective film on the material surface.

#### (3) Edge Cracking

Cause: Hardened material, too small bend radius, or unremoved burrs on cut edges. Solution: Anneal the material before bending, increase the bend radius to R_min, and deburr the cut edges with sandpaper or a deburring tool.

#### (4) Excessive Springback

Cause: Insufficient bending force or inappropriate tooling. Solution: Increase the bending force moderately, use bottoming bending, or adjust the punch angle to compensate for springback.

### 4. Best Practices for Bending Brass and Copper

1. **Material Inspection**: Before production, check the material grade, temper, and surface condition. Reject materials with surface defects (e.g., scratches, oxidation) or incorrect temper.

2. **Test Bends**: Perform test bends with the same material, thickness, and tooling as the production part to determine the optimal bend radius, bending speed, and springback compensation value.

3. **Tooling Maintenance**: Regularly inspect and polish the tooling surface to ensure it is smooth and free of burrs. Apply anti-rust oil to tooling when not in use to prevent corrosion.

4. **Process Standardization**: Document the bending parameters (tooling model, bend radius, speed, force) for each part and train operators to follow the standard operating procedures.

5. **Post-Bending Inspection**: Inspect the bend angle, surface finish, and dimensional accuracy of the finished part. Clean the surface to remove lubricant residues and protective film.

### Conclusion

Bending brass and copper sheet metal requires full consideration of their material properties (high ductility, low strength, sensitivity to grain direction) and targeted control of key factors such as bend radius, tooling selection, bending speed, lubrication, and springback compensation. By following the above key points and best practices, fabricators can effectively avoid surface defects and edge cracking, ensure bending accuracy, and produce high-quality brass and copper parts. For parts with high surface finish or strict tolerances, it is necessary to combine specialized tooling, surface protection measures, and strict process control to meet the design requirements.

@taidinggroup