Analysis of sheet metal cutting Cutting Force : F = StL; where S = shear strength of metal, MPa t = sheet thickness, mm L = length of the cut edge, mm Note : In blanking & punching, L is the perimeter length of the blank or hole being cut.

Contd… If shear strength is unknown, an alternative way for estimating the cutting force is : F = 0.7 (TS) t L; where TS = ultimate tensile strength, MPa

Problem no.1 A round disc of 150 mm diameter is to be blanked from a strip of 3.2 mm, half hard cold rolled steel whose shear strength is 320 MPa. Determine : a) punch & die diameter, b) blanking force Solution : 150, 149.52 mm, 482.5 kN.

Slotting, Perforating & Notching Slotting : is a term sometimes used for a punching operation that cuts out an elongated or rectangular hole

Contd… Perforating : involves the simultaneous punching of a pattern of holes in a sheet metal.

Contd… Notching : involves cutting out a portion of metal from the side of the sheet. Semi Notching : removes a portion of metal from the interior of the sheet.

Trimming & Shaving Trimming : is a cutting operation performed on a formed part to remove unwanted (layer) metal & establish size. Typical example in sheet metal is trimming the upper portion of a deep drawn cup to leave the desired dimensions on the cup.

Contd… Shaving : shearing operation performed with very small clearance to obtain accurate dimensions & cut edges that are smooth & straight.

Contd… Shaving is a secondary or finishing operation performed on the parts that have been previously cut.