Forming

Bending
Bending of stainless steels is performed using the same processes and equipment as with mild steels. However, for austenitic grades, the power requirements are 50 to 60% higher. Since the ‘elastic springback’ is greater, bending or contouring angles must be significantly modified.

Contour forming
Stainless steels lend themselves perfectly to roll-type contour forming operations. The tooling is either in hardened steel (58-60 HRC) or aluminium bronze. To obtain a given profile, a greater number of roll pairs are generally used for stainless steel than for mild steels.

Cutting
Press blanking

For all grades of stainless steel in annealed condition, the clearance between the punch and the die is:

– 5% for thicknesses <1.5 mm
– 7 – 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 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 that of the sheet thickness. Lubrication with cutting oil is recommended to ensure a good quality of cut and long tool life.

Straight-Blade shearing
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 conducts electricity. A plasma jet directed onto a metal surface can be 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 used, 1500 – 2000 watt CO2 lasers being widely used for cutting thin and medium sheets.. The quality of cut end is better than that obtained by plasma-arc cutting but not as effective as that produced by water jet cutting. A shielding gas is recommended to avoid oxidation of edges

Water jet cutting
In this technique a jet of water, generally containing an abrasive powder, is propelled through a fine nozzle at very high pressure (4000 – 5000 bar). It is fairly slow and the section large but the quality is very good. The main disadvantage is risk of contamination on the sheet.