Sheet Metal Forming

CHAPTeR 1
Blanking
Soumya Subramonian, The Ohio State University 
BLANKING AND PIERCING are metal-
shearing processes in which the incoming sheet 
material is sheared to a desired shape. In blank-
ing, the removed piece of material is the prod-
uct, whereas in piercing, the material that is 
removed is scrap, while the remaining part of 
the strip is the product (Fig. 1.1). Blanking or 
piercing is used in almost all sheet-forming op-
erations. The size of holes punched can vary 
from less than 1 to 100 mm (0.05 to 4.0 in.) or 
more.
This chapter gives an overview of the phases 
in blanking, forces and stresses involved, fac-
tors affecting part quality and tool life, as well 
as tooling and press requirements. Fine blank-
ing is also briefly explained.
1.1 Blanking Process
The blanking process can be considered to 
include a series of phases in which the sheet 
metal undergoes deformation and separation, as 
seen in Fig. 1.2.
Contact of the Punch.
The punch first 
touches the fixed sheet. At impact, a compres
-
sive stress rapidly builds on the punch and sends 
a shock wave through it.
elastic and Plastic Deformation.
The punch 
penetrates into the sheet, first causing an elastic 
and then plastic deformation.
Shearing and Crack Formation.
When the 
stresses increase, shearing occurs followed by 
fracture. Fracture begins from both the punch 
end and die end of the sheet. They usually meet, 
and complete fracture of the material takes 
place.
Fig. 1.1
 
Schematic of blanking and piercing
Fig. 1.2
 
Phases of the blanking process. Source: Ref 1.1

---

2 / Sheet Metal Forming—Processes and Applications
Breakthrough.
If the sheet material has a 
high strength or is thick, a large force is required 
for the blanking process. During fracture, com-
pressive forces are stored in the tool. When 
complete fracture occurs, there is an instant re-
lease of these compressive forces. These gener-
ate shock, which can lead to breakage of the 
punch in some cases.
Stripping.
The punch moves down to the 
bottom dead center and ejects the part. At the 
bottom dead center, the direction of punch mo-
tion is reversed. Due to the friction between the 
stock and the surface of the punch, the surface 
pressure intensifies. A stripper or blank holder 
strips the blank from the punch.