Table of Bend Allowance Parameters for Selected Metals
| Metal | Density (g/cm³) | Modulus of Elasticity (GPa) | Yield Strength (MPa) | Ultimate Tensile Strength (MPa) | Bend Allowance (mm per degree) | Bend Radius (min) (mm) | Springback (%) |
|---|---|---|---|---|---|---|---|
| Steel | 7.85 | 200-210 | 250-400 | 400-600 | 0.50-0.55 | 1.0 x Material Thickness | 5-15 |
| Aluminum | 2.70 | 69-79 | 80-300 | 120-450 | 0.60-0.65 | 1.5 x Material Thickness | 3-10 |
| Copper | 8.96 | 110-130 | 70-300 | 200-550 | 0.55-0.60 | 2.0 x Material Thickness | 10-20 |
| Brass | 8.50 | 100-125 | 200-550 | 400-700 | 0.50-0.55 | 1.5 x Material Thickness | 5-15 |
| Stainless Steel | 7.93 | 193-200 | 205-550 | 520-860 | 0.45-0.50 | 1.0 x Material Thickness | 2-10 |
| Titanium | 4.51 | 105-115 | 275-900 | 345-1035 | 0.70-0.75 | 2.5 x Material Thickness | 1-5 |
Introduction
In the realm of metal fabrication, particularly when dealing with sheet metal forming processes such as bending, understanding the bend allowance chart is paramount for achieving precise and accurate bends. This chart serves as a crucial reference guide, detailing the necessary allowances and adjustments required to account for material deformation during the bending process. The parameters outlined in the bend allowance chart are influenced by several factors, including the metal’s inherent properties like density, modulus of elasticity, yield strength, and ultimate tensile strength. This document aims to elucidate these concepts, focusing on specific metals commonly used in industry: steel, aluminum, copper, brass, stainless steel, and titanium.
Steel
Density: Steel, with a density of 7.85 g/cm³, is one of the most widely used metals in fabrication due to its high strength-to-weight ratio. This density affects the force required to bend the material and influences the bend allowance.
Modulus of Elasticity: Steel typically has a modulus of elasticity ranging from 200 to 210 GPa. This value is indicative of the material’s stiffness and its ability to resist deformation. A higher modulus signifies less deformation under load, impacting the bend allowance.
Yield Strength & Ultimate Tensile Strength: With yield strengths between 250 and 400 MPa and ultimate tensile strengths between 400 and 600 MPa, steel’s resistance to plastic deformation and breaking under tension play a significant role in determining the bend allowance. These properties dictate how much the material can be stressed before permanent deformation occurs.
Bend Allowance: For steel, the bend allowance typically ranges from 0.50 to 0.55 mm per degree. This allowance must be factored into the design to ensure the final bend meets the desired specifications.
Bend Radius: The minimum bend radius for steel is generally 1.0 times the material thickness. This radius is crucial to prevent excessive thinning or cracking of the material during bending.
Springback: Steel can exhibit springback in the range of 5 to 15%, which refers to the material’s tendency to return to its original shape after being bent. Proper compensation for springback is essential for achieving accurate bends.
Aluminum
Density: Aluminum, lighter than steel with a density of 2.70 g/cm³, is often chosen for applications where weight reduction is critical. Its lower density results in different bending dynamics compared to steel.
Modulus of Elasticity: Aluminum’s modulus of elasticity falls within the range of 69 to 79 GPa, indicating a lower stiffness compared to steel. This affects the material’s response to bending forces.
Yield Strength & Ultimate Tensile Strength: With yield strengths ranging from 80 to 300 MPa and ultimate tensile strengths from 120 to 450 MPa, aluminum’s bending behavior is influenced by its relatively lower strength properties.
Bend Allowance: Aluminum requires a bend allowance of approximately 0.60 to 0.65 mm per degree, reflecting its different material characteristics.
Bend Radius: The minimum bend radius for aluminum is typically 1.5 times the material thickness, accounting for its softer nature and greater ductility.
Springback: Aluminum can experience springback in the range of 3 to 10%, necessitating careful consideration during the bending process to achieve the desired final shape.
Copper
Density: Copper has a density of 8.96 g/cm³, placing it between steel and aluminum in terms of weight. This density influences the force and energy required for bending.
Modulus of Elasticity: Copper’s modulus of elasticity spans from 110 to 130 GPa, indicating a moderate stiffness. This value is crucial for predicting the material’s deformation under bending loads.
Yield Strength & Ultimate Tensile Strength: With yield strengths ranging from 70 to 300 MPa and ultimate tensile strengths from 200 to 550 MPa, copper’s strength properties significantly impact its bending behavior.
Bend Allowance: The bend allowance for copper is typically between 0.55 and 0.60 mm per degree, reflecting its unique material properties.
Bend Radius: The minimum bend radius for copper is generally 2.0 times the material thickness, accounting for its ductility and tendency to deform plastically.
Springback: Copper can exhibit springback in the range of 10 to 20%, highlighting the importance of proper compensation during bending to achieve accurate results.
Brass
Density: Brass has a density of 8.50 g/cm³, similar to copper but with distinct mechanical properties that influence its bending behavior.
Modulus of Elasticity: Brass’ modulus of elasticity ranges from 100 to 125 GPa, indicating a stiffness comparable to copper but with different deformation characteristics.
Yield Strength & Ultimate Tensile Strength: Brass exhibits yield strengths between 200 and 550 MPa and ultimate tensile strengths between 400 and 700 MPa. These properties affect the material’s response to bending forces.
Bend Allowance: The bend allowance for brass is typically between 0.50 and 0.55 mm per degree, reflecting its specific material characteristics.
Bend Radius: The minimum bend radius for brass is generally 1.5 times the material thickness, accounting for its ductility and plasticity.
Springback: Brass can experience springback in the range of 5 to 15%, necessitating careful attention to detail during the bending process to ensure accuracy.
Stainless Steel
Density: Stainless steel has a density of 7.93 g/cm³, similar to regular steel but with enhanced corrosion resistance. This density affects the bending dynamics and force requirements.
Modulus of Elasticity: Stainless steel’s modulus of elasticity ranges from 193 to 200 GPa, indicating a stiffness comparable to regular steel but with different mechanical properties.
Yield Strength & Ultimate Tensile Strength: With yield strengths ranging from 205 to 550 MPa and ultimate tensile strengths from 520 to 860 MPa, stainless steel’s strength properties significantly influence its bending behavior.
Bend Allowance: The bend allowance for stainless steel is typically between 0.45 and 0.50 mm per degree, reflecting its unique material characteristics and higher resistance to deformation.
Bend Radius: The minimum bend radius for stainless steel is generally 1.0 times the material thickness, accounting for its high strength and tendency to work harden.
Springback: Stainless steel can exhibit springback in bending operations due to its high elastic properties. This phenomenon, where the material partially returns to its original shape after the bending force is removed, must be carefully considered in the design and manufacturing processes to ensure the desired final shape and dimensions are achieved.
Corrosion Resistance: One of the primary advantages of stainless steel is its excellent corrosion resistance, which is achieved through the addition of chromium and, in some cases, nickel. This resistance is crucial in applications where the material will be exposed to harsh environments, such as chemicals, saltwater, or extreme temperatures.
Heat Treatment: Stainless steel can be heat-treated to further enhance its mechanical properties, although the specific response to heat treatment varies depending on the grade. Austenitic stainless steels, for instance, are not hardenable by heat treatment, while ferritic and martensitic grades can be hardened to increase their strength and hardness.
Weldability: Stainless steel is generally weldable, but the welding process must be carefully controlled to avoid issues such as cracking, distortion, and loss of corrosion resistance. Proper selection of welding materials, techniques, and post-weld heat treatment can help mitigate these challenges.
Surface Finish: The surface finish of stainless steel is critical for maintaining its corrosion resistance and aesthetic appeal. Various finishes, such as polished, brushed, or matte, can be achieved through processes like grinding, polishing, or chemical treatment.
In conclusion, stainless steel’s unique combination of mechanical properties, corrosion resistance, and aesthetic appeal make it a versatile and valuable material in numerous applications. However, its processing and handling require careful consideration of factors such as bend allowance, bend radius, springback, heat treatment, weldability, and surface finish to ensure optimal performance and longevity.
