At Datum, we specialise in precision thin metal supply and understand how critical thickness is in Stainless Steel & Nickel forming. Even fractions of a millimetre can change how the sheet behaves when bent, folded, or crimped.
Bend Radius and Fold Quality
In addition to thickness, other properties influence the bend radius and fold quality:
- Material Strength: Stainless steel’s high tensile strength makes it more resistant to deformation than softer metals like aluminium or Nickel. This necessitates a larger bend radius, particularly in harder grades, to avoid stress fractures. Attempting a bend radius that is too small for a given thickness can cause the metal to fracture.
- Grain Direction: The rolling process at the mill elongates the metal’s grain structure. Bending across the grain (perpendicular) allows for a smaller radius because stress is distributed more evenly. Bending with the grain (parallel) increases the risk of cracking and requires a larger bend radius.
- Spring back: Stainless steel, especially grades like 304 and 316, has a high yield strength, which leads to significant spring back. This is the material’s tendency to return to its original flat shape after being bent. Thicker sheets exhibit more springback, so manufacturers must often overbend the material to achieve the desired final angle.
- Cold Work and Ductility: Bending is a form of cold working that increases the strength and hardness of metals but decreases its ductility. This can make the material brittle and prone to cracking, particularly at tight radii.
Tooling Adjustments for Different Gauges
To achieve a high-quality bend, the tooling must be carefully matched to the material thickness. This is crucial for avoiding surface defects and ensuring dimensional accuracy.
- Die Opening: For thin sheet (0.2-1 mm), a V-die opening of 6-8 times the material thickness is typically recommended. As the thickness increases, so must the die opening.
- Punch Radius: The punch radius should be close to the recommended bend radius to avoid excessive marking. A polished or coated punch is often used to minimise surface damage, especially on aesthetically critical parts.
- Press Force: The force required to bend the material increases sharply with thickness. While thin stainless steel requires less force, it demands greater precision, as small deviations in pressure can lead to distortion or over-bending.
Crimping and Marking Considerations
Crimping thin-gauge metals requires a balance of force and precision. Thin sheets (0.2–0.6 mm) are easy to crimp but are also prone to tearing if too much force is applied.
The risk of surface marking is also a significant consideration, as thinner sheets are more susceptible to scratches and die marks. For industries where aesthetics and hygiene are critical (e.g. medical and food processing equipment), protective films, non-marring dies, or polished tooling are often used to safeguard the surface finish.
Best Practices for High-Quality Fabrication
Ultimately, thickness is a defining factor in every bending, folding, and crimping operation. At Datum, we emphasise integrating this variable into the planning stage to achieve reliable, high-quality results.
- For thinner sheets, greater care must be taken to prevent marking and distortion while leveraging the ability to achieve tighter bends and finer detail.
- For thicker sheets, it is essential to plan for greater spring back, higher bend radii, and increased tooling loads.
- When crimping, the force and precision must be carefully balanced, with surface protection measures tailored to the sheet thickness.
By integrating thickness into the planning stage, selecting appropriate tooling, calculating bend radii, and protecting surfaces, we can achieve reliable, high-quality results. With thin-gauge metals in particular, attention to detail makes the difference between rework and precision parts.
