Stainless steel has a wide range of uses and is a common material in our lives, such as security windows, bus shelters, shelves, etc. Due to the high yield point, high hardness, and significant cold work hardening effect of stainless steel, stainless steel has some obvious bending characteristics.
When working with stainless steel, there are many finish options available. Starting with the standard 2B mill finish and ranging all the way to a pristine mirrored finish. All in all, there are over 50 varieties of stainless steel grades available for use. All stainless steel grades contain a minimum of 10.5% chromium. Additional chromium and other elements may be added to improve corrosion and/or heat resistance, or to enhance or improve mechanical properties and fabricating characteristics.
As a principal factor, takes into consideration(bending or rolling) the composition of the alloy, material thickness, required bend radius, and bend angle when calculating the bending force necessary to avoid a “spring back” of the bent stainless steel to its original shape.
The process of bending stainless steel sheets
As a principal factor, considering the composition of the alloy, material thickness, required bend radius, and bend angle when calculating the bending force necessary to avoid a “spring back” of the bent stainless steel to its original shape.
On the other hand, stainless steel contains at least 10.5% of chromium, less than 1.2% of carbon, and other alloying elements – such as nickel and manganese – that enhance its resistance to corrosion and hardness.
Compared to bending sheets of steel, the process of bending stainless steel sheets is made a little more complicated by the fact that they have a strong tendency to rebound. For this reason, the bending angle for stainless steel sheets needs to be greater than that of steel; otherwise, there may be cracks.
Stainless steel combines ductility, elasticity, and hardness. For this reason, it can be used in difficult bending operations, while offering resistance to heavy wear. Furthermore, it offers good mechanical behavior at both low and high temperatures.
Three Considerations for Bending Stainless Steel Sheet
Plate Thickness and Bending Tonnage Before bending stainless steel, it is essential to determine the thickness of the plate. Thicker plates require a larger bending machine. A machine like a press brake, plate rolling machine, or profile bending machine can be used for bending processing.
- You can refer to here for the types of bending machines: Beginner’s Guide To 10 Types Of Bending Machine
- About the metal bending process, you can refer to here: Bending basics: 12 types of metal bending processes
Ductility
A measure of a material’s ductility is its elongation at fracture. Austenitic stainless steels such as standard grades 1.4301 (304) or 1.4401 (316) have outstanding ductility. This value indicates by how many percent a standardized sample of a material can be stretched before it breaks. These values are:
- For stainless steel grade 1.4301 (304): typically more than 45%
- For carbon steel: typically 25%
Work-hardening
Besides its ductility, austenitic stainless steel also has a pronounced work-hardening tendency, whereby when the material is formed its mechanical strength goes up. This work-hardening effect increases with both the extent and the speed of the forming process. In the case of bending this means that greater power is needed for stainless steel than for carbon steel. Austenitic stainless steel requires about 50% more power than a carbon steel part of the same geometry. When changing from carbon steel to stainless steel bending, it is, therefore, necessary to check that the bending machine is strong enough for the geometry concerned.
Bending Angle and Bending Radius
Stainless steel has high resilience, and the bending angle and radius cannot be too small.
The bending angle and radius are crucial to consider. A larger bending radius may result in excessive spring-back, while a smaller radius may cause cracking. Generally, the bending radius is around 0.2. For materials like high-carbon steel, a larger inner radius is necessary to prevent cracking.
stainless steel sheet metal bend radius chart
| MATERIAL | .012 | .016 | .020 | .025 | .032 | .036 | .040 | .045 | .050 | .063 | .080 | .090 | .112 | .125 | .160 | .190 |
| 302 Annealed | .06 | .06 | .06 | .06 | .06 | .06 | .09 | .09 | .09 | .09 | .12 | .12 | .16 | .19 | .22 | .25 |
| 347-1A | .06 | .06 | .06 | .09 | .09 | .06 | .06 | .09 | .09 | .09 | .12 | .12 | .16 | .19 | .22 | .25 |
| 1/4 Hard Cres | .06 | .06 | .06 | .06 | .06 | .09 | .09 | .09 | .12 | .12 | .16 | .19 | .22 | .25 | .31 | .38 |
| 1/2 Hard Cres | .06 | .06 | .06 | .09 | .09 | .12 | .12 | .12 | .16 | .16 | .25 | .25 | .31 | .38 | .50 | .62 |
| Full Hard Cres | .06 | .06 | .09 | .12 | .12 | .16 | .16 | .19 | .22 | .25 | .31 | .38 | .44 | .50 | .62 | .87 |
Read More: Minimum Recommended Bend Radius Chart
Bending Springback
Stainless steels have higher spring back than carbon steels. Low-carbon steel has less spring back and is ideal for high-precision workpieces, while high-carbon steel and stainless steel have significant spring back.
The spring back of a metal plate is proportional to the material’s yield strength and inversely proportional to its elastic modulus. The larger the bending radius, the greater the spring back. Smaller bending radii result in higher accuracy.
As a practical guide, the amount of spring back is normally proportional to (0.2 Rp0.2 + Rm)/2, where Rp0.2 is yield strength and Rm is tensile strength. Springback can be controlled by overbending. For overbending, it is sometimes only necessary to make the punch angle smaller than the desired final angle of the workpiece
Springback of three austenitic stainless sheets of steel bent 90° to various radii
| Steel grade and condition (sheet) | Springback | for bend | radius of |
|---|---|---|---|
| 1t | 6t | 20t | |
| (302), annealed | 2° | 4° | 15° |
| 1.4301 (304), annealed | 2° | 4° | 15° |
| 1.4310 (301), half-hard | 4° | 13° | 43° |
| t = thickness |
Calculating the Bending Allowance
The formula for calculating the bending allowance is: BA=(π/180) x B x (IR+K x MT), or use a bending allowance gauge.
The bending allowance, which is the expansion of the outer side of the sheet, can be calculated with the knowledge of the sheet thickness, bending angle, and inner radius. This calculation determines the required length of the sheet for bending.
Four difficulties in bending stainless steel
- The thermal conductivity of stainless steel is worse than that of ordinary low-carbon steel, and the elongation is low, resulting in a large deformation force;
- Compared with carbon steel, stainless steel sheet has a strong spring-back tendency when bending;
- Due to the low elongation of the stainless steel plate, the bending angle R of the workpiece should be larger than that of the carbon steel during bending, otherwise, there may be cracks;
- Due to the high hardness of the SUS304 stainless steel plate, the cold work hardening effect is significant. Therefore, when selecting a bending tool, tool steel with a heat treatment hardness of 60HRC or more should be selected, and its surface roughness is an order of magnitude higher than that of a carbon steel bending tool.
Four tips for bending stainless steel
In view of the above characteristics of stainless steel, generally speaking for its bending:
- Under the unit size, the thicker the plate, the greater the required bending force, and as the plate thickness increases, the margin of the bending force should be larger when selecting the bending equipment;
- Under the unit size, the greater the tensile strength, the smaller the elongation, the greater the required bending force, and the larger the bending angle;
- When the thickness of the plate in the design corresponds to the bending radius, according to experience, the expansion size of a bending workpiece is the addition of the right-angled sides minus the two plate thicknesses, which can fully meet the design accuracy requirements, and the expansion amount can be calculated according to the empirical formula. Simplify the calculation process and greatly improve production efficiency;
- The greater the yield strength of the material, the greater the elasticity and recovery. In order to obtain a 90-degree angle of the bending part, the angle of the required pressing knife should be designed to be smaller. Compared with carbon steel, stainless steel with the same thickness has a larger bending angle. Special attention should be paid to this point, otherwise, there will be bending cracks, which will affect the strength of the workpiece.
Properties of Stainless Steel Sheet Metal
Anti-corrosion and Anti-staining
Stainless steel is a steel alloy that contains at least 10.5% chromium. The chromium content is what gives the metal its anti-corrosion and anti-staining properties. The actual chromium content, along with the carbon content and the content of other metals, varies based on the application in which the steel will be used.
It should be noted that stainless steel is not completely corrosion or stain-proof. The resistance of the metal will depend on its content, and certain chemicals can damage the metal regardless of its content. However, stainless offers some of the best corrosion and stain resistance available, especially when you consider the other qualities it offers (aesthetics, durability, etc.).
Range in thickness up to ¼ inch.
Stainless steel sheet metal can be quite thin, but for it to qualify as “sheet metal” it only reaches a ¼ inch in thickness — after that, the metal is referred to as “plate.” The thickness of stainless sheet metal is measured by gauge. The higher the gauge number, the thinner the sheet.
Variety of configurations
Stainless steel sheet metal comes in a variety of configurations, each with advantages and disadvantages. Manufacturers may offer different grades, finishes, and sizes, but the types tend to be standard across manufacturers. These types include:
- 200 Series Austenitic – This series is made of chromium, carbon, manganese, and/or nickel. It’s possible to harden this series, but one drawback is its lack of resistance to corrosion.
- 300 Series Austenitic – Between the 200 series and 300 series, austenitic stainless steel makes up around 70% of all stainless steel produced. The 300 series is the most ductile, weldable, and corrosion-resistant of all stainless steel types. The most popular grade is 304, often named A2 stainless. The 18% chromium content and 8% nickel content also lead to 304 being referred to as 18/8.
- Martensitic – This type is very strong and easy to machine, but it is less resistant to corrosion.
- Ferritic – Preferred for its ease of engineering, ferritic stainless is less corrosion-resistant than austenitic.
- Duplex – This up-and-comer is approximately 50/50 between austenitic and ferritic. It’s about 2x as strong as austenitic.
PDF: Guide To Bending Stainless Steel Sheet Metal
Works Cited: