1. 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.

2. 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

3. 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, mm, kN.

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

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

6. 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.

7. 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.

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

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