20.1 Identify the three basic types of sheet metalworking operations.
Answer. The three basic types of sheet metalworking operations are (1) cutting, (2) bending, and
(3) drawing.
20.2 In conventional sheet metalworking operations, (a) what is the name of the tooling and (b) what is
the name of the machine tool used in the operations?
Answer. (a) The tooling is called a punch-and-die. (b) The machine tool is called a stamping press.
20.3 In blanking of a circular sheet-metal part, is the clearance applied to the punch diameter or the die
diameter?
Answer. The die diameter equals the blank diameter, and the punch diameter is smaller by twice the
clearance.
20.4 What is the difference between a cutoff operation and a parting operation?
Answer. A cutoff operation separates parts from a strip by shearing one edge of each part in
sequence. A parting operation cuts a slug between adjacent parts in the strip. See Figure 20.8.
20.5 What is the difference between a notching operation and a seminotching operation?
Answer. A notching operation cuts out a portion of the sheet metal from the interior of the sheet or
strip, while a seminotching operation removes a portion of the sheet metal from the interior of the
sheet or strip.
20.6 Describe each of the two types of sheet-metal-bending operations: V-bending and edge bending.
Answer. In V-bending, a simple punch and die that each have the included angle are used to bend
the part. In edge bending, the punch forces a cantilevered sheet-metal section over a die edge to
obtain the desired bend angle. See Figure 20.12.
20.7 For what is the bend allowance intended to compensate?
Answer. The bend allowance is intended to compensate for stretching of the sheet metal that occurs
in a bending operation when the bend radius is small relative to the stock thickness. In principle the
bend allowance equals the length of the bent metal along its neutral axis.
20.8 What is springback in sheet-metal bending?
Answer. Springback is the elastic recovery of the sheet metal after bending; it is usually measured
as the difference between the final included angle of the bent part and the angle of the tooling used
to make the bend, divided by the angle of the tooling.
20.9 Define drawing in the context of sheet metalworking.
Answer. Drawing is a sheet metalworking operation used to produce cup-shaped or box-shaped, or
other complex-curved, hollow parts. Drawing is accomplished by placing a piece of sheet metal
over a die cavity and then using a punch to push the metal into the cavity.
20.10 What are some of the simple measures used to assess the feasibility of a proposed cup-drawing
operation?
Answer. Measures of drawing feasibility include (1) drawing ratio DR = D/Dp; (2) reduction r = (D
- Dp)/D; and (3) thickness-to-diameter ratio, t/D; where t = stock thickness, D = blank diameter, and
Dp = punch diameter.