The bending of stainless steels is performed with the same processes and equipment as for mild steels. However, for the austenitic grades, the power requirements are 50 to 60% higher than for the latter materials. Since the elastic springback is greater, the bending or contouring angles must be significantly modified.
The stainless steels lend themselves perfectly to roll-type contour forming operations. The tooling is either in hardened steel (58-60 HRC) or in aluminium bronze. To obtain a given profile, a greater number of roll pairs are generally used for stainless steel than for mild steels.
> Press blanking
For all grades of stainless steel in the annealed condition, the clearance between the punch and the die is:
- 5% for thicknesses <1,5 mm
- 7 to 8% for thicknesses > 1,5 mm
An optimum clearance produces a depth of cut equivalent to about a third of the sheet thickness. When cutting out shapes, sharp part angles must not be employed. The radius of the junction between two edge elements must not be less than one and a half times the sheet thickness. Lubrication with cutting oil is recommended to ensure a good quality of cut, together with long tool life.
> Straight-Blade shearing
The clearances are similar to those for press blanking. A sheet clamp is recommended to obtain a good quality of cut.
> Plasma-Arc cutting
Plasma is an ionized gas, which therefore conducts electricity. A plasma jet directed onto a metal surface can be strongly heated by passing an electric current through it (transferred arc). The cut ends obtained in stainless steels are only very slightly oxidized with a highly friable burr.
> Laser-Beam cutting
YAG or CO2 lasers are employed, 1500 to 2000 watts CO2 lasers are commonly widely used for cutting thin and medium sheets. A shielding gas is recommended in order to avoid oxidation of the edges. The quality of cut end is better than that obtained by plasma-arc process, but not as good as that produced by water jet cutting.
> Water jet cutting