Shearing of Stainless Steel

Conventional press/guillotine equipment is used for shearing stainless steel, but should normally be down-rated by 40% compared with their carbon steel rating. Blades and cutters should be well adjusted with edges maintained sharp, thus avoiding the dragging of metal over the blade which would lead to work hardening. The same considerations should apply in working the nibbler to cut out shapes in sheet metal. Stainless steel have greater strengths than low carbon (mild) steels.

Further the tendency of the Austenitic grades to work harden has a significant effect on the shearing of these steels.

More power is therefore required, and it is necessary to derate the shear (guillotines) against their nominal capacity, which is usually given in terms of the thickness of low carbon steel which they are capable of shearing.

Indicative relative derated capacities are as follows:

Low carbon (mild) steel 10mm thick material
Corrosion Resisting Steel (3CR12) 7mm thick material
Ferritic Stainless Steel (eg 430) 7/8mm thick material
Austenitic material (eg 304) 5/6mm thick material

Corrosion resisting (3CR12) and Ferritic Stainless Steel tend to fracture after being cut through approximately half their thickness. In this respect they are similar to carbon steel and low alloy steels.

Austenitic Stainless Steel are typified by a high ductility, and hence a greater resistance to fracture. A greater degree of penetration therefore takes place before fracture occurs. The clearance setting of the blades is therefore important. For shearing thin gauge sheet a clearance of 0.025 to 0.050mm is suggested.

Closer clearance tends to induce blade wear, whereas larger clearances allow the material being sheared to drag over to an excessive degree, resulting in excessive wear of the blades and a poor cut.

As the material thickness increases the clearance should be increased accordingly and adjusted to best suit the specific piece of equipment being used, consistent with minimum roll over, burr height and distortion (camber, twist and bow).

The nominal suggested clearances for such thicker material are:

3CR12 Corrosion resisting steel 2.5% of material thickness

Ferritic/Austenitic Stainless Steel 3 - 5% of material thickness

To counteract the greater shearing force required, the hold down pressure on the clamps may have to be increased, particularly when shearing the Austenitic grades.

The higher power requirements can to some extent be countered by altering the rake/shear angle. A rake of 1 in 40 is a shear angle of approximately 1½ °. This is the suggested least rake which should be used. Small rake/shear angles necessitate higher power/force, but cause less distortion, whereas larger rakes/shear angles (eg 1 in 16 or 3½ °) reduce the power/force required, but need higher hold down pressure on the clamps and tend to increase distortion.

Blades MUST BE SHARP. Blunt blades increase the roll over, burr height and distortion (camber, twist and bow).

The moving blade should be provided with as large as possible back clearance/rake angle, without causing chipping of this blade.

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