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Identify the three basic types of sheet metalworking operations.
The three basic types of sheet metalworking operations are (1) cutting, (2) bending, and (3) drawing.
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?
(a) The tooling is called a punch-and-die. (b) The machine tool is called a stamping press.
In blanking of a circular sheet-metal part, is the clearance applied to the punch diameter or the die diameter?
The die diameter equals the blank diameter, and the punch diameter is smaller by twice the clearance.
What is the difference between a cutoff operation and a parting operation?
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.
What is the difference between a notching operation and a seminotching operation?
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.
Describe each of the two types of sheet-metal-bending operations: V-bending and edge bending.
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.
For what is the bend allowance intended to compensate?
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.
What is springback in sheet-metal bending?
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.
Define drawing in the context of sheet metalworking.
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.
What are some of the simple measures used to assess the feasibility of a proposed cup-drawing operation?
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.
Distinguish between redrawing and reverse drawing.
In redrawing, the shape change is significant enough (e.g., drawing ratio greater than 2.0) that it must be carried out in two drawing steps, probably with an annealing operation between the steps. In reverse drawing, two draws are accomplished on the part, one in one direction, the second in the opposite direction.
What are some of the possible defects in drawn sheet-metal parts?
Drawing defects include (1) wrinkling, (2) tearing, (3) earing, and (4) surface scratches, as described in Section 20.3.4.
What is an embossing operation?
Embossing is a sheet metalworking operation used to create indentations in the sheet, such as raised lettering or strengthening ribs.
What is stretch forming?
Stretch forming of sheet metal consists of simultaneously stretching and bending the sheet-metal workpart to achieve shape change.
Identify the principal components of a stamping die that performs blanking.
The principal components are the punch and die, which perform the cutting operation. They are attached respectively to the punch holder (a.k.a. upper shoe) and die holder (a.k.a. lower shoe). Alignment of the punch and die during the stamping operation is achieved by means of guide pins and bushings in the punch holder and die holder.
What are the two basic categories of structural frames used in stamping presses?
Two basic categories of press frame are (1) gap frame, also called C-frame because its profile is the shape of the letter “C”, and (2) straight-sided frame, which has full sides for greater strength and stiffness of the frame.
What are the relative advantages and disadvantages of mechanical presses versus hydraulic presses in sheet metalworking?
The main advantage of mechanical presses is faster cycle rates. Advantages of hydraulic presses are longer ram strokes and uniform force throughout stroke.
What is the Guerin process?
The Guerin process is a sheet-metal forming process that uses a rubber die that flexes to force the sheet metal to take the shape of a form block (punch).
Identify a major technical problem in tube bending?
A major technical problem in tube bending is collapse of the tube walls during the bending process.
Distinguish between roll bending and roll forming.
Roll bending involves the forming of large sheet and plate metal sections into curved forms. Roll forming involves feeding a lone strip or coil through rotating rolls so that the shape of the rolls is imparted to the strip.
What is the blade rake angle?
The Blade Rake Angle or Shear Angle is the angle between the two surfaces that come together to shear the material. An angle of zero means that the shearing takes place at the same time along the entire surface. A larger value of angle means that less surface is in contact with the shearing blades at any moment during the operation.
The principal terms used to describe bending on a press brake are bend allowance, bend angle, bend radius, and bend springback.
What are the factors that affect the formability of a metal?
(1) part shape is the primary factor, (2) sheet metal’s ductility, (3) die design, (4) stamping press, (5) press speed, (6) lubrication, (7) sheet-metal feeding mechanism, and (8) monitoring/control systems.
Name the four forming processes
(1) drawing, (2) bending, (3) flanging, and (4) hemming.
List the factors that affect the hold down pressure in a drawing operation
Factors that affect the hold down pressure in a drawing operation include (1) draw reduction severity, (2) metal properties, (3) metal thickness, and (4) die lubrication.
Most sheet metalworking operations are performed as which one of the following: (a) cold working, (b) hot working, or (c) warm working?
In a sheet-metal-cutting operation used to produce a flat part with a hole in the center, the part itself
is called a blank, and the scrap piece that was cut out to make the hole is called a slug: (a) true or (b)
As sheet-metal stock hardness increases in a blanking operation, the clearance between punch and
die should be (a) decreased, (b) increased, or (c) remain the same?
A circular sheet-metal slug produced in a hole punching operation will have the same diameter as (a) the die opening or (b) the punch?
The cutting force in a sheet-metal blanking operation depends on which mechanical property of the metal (one correct answer): (a) compressive strength, (b) modulus of elasticity, (c) shear strength, (d) strain rate, (e) tensile strength, or (f) yield strength?
Which of the following descriptions applies to a V-bending operation as compared to an edgebending
operation (two best answers): (a) costly tooling, (b) inexpensive tooling, (c) limited to 90°
bends or less, (d) used for high production, (e) used for low production, and (f) uses a pressure pad
to hold down the sheet metal?
Sheet-metal bending involves which of the following stresses and strains (two correct answers): (a) compressive, (b) shear, and (c) tensile?
Which one of the following is the best definition of bend allowance: (a) amount by which the die is
larger than the punch, (b) amount of elastic recovery experienced by the metal after bending, (c)
safety factor used in calculating bending force, or (d) length before bending of the straight sheetmetal
section to be bent?
Springback in a sheet-metal-bending operation is the result of which one of the following: (a) elastic
modulus of the metal, (b) elastic recovery of the metal, (c) overbending, (d) overstraining, or (e)
yield strength of the metal?
Which of the following are variations of sheet-metal-bending operations (two best answers): (a)
coining, (b) flanging, (c) hemming, (d) ironing, (e) notching, (f) shear spinning, (g) trimming, and
(h) tube bending?
The following are measures of feasibility for several proposed cup-drawing operations; which of the operations are likely to be feasible (three best answers): (a) DR = 1.7, (b) DR = 2.7, (c) r = 0.35, (d) r = 0.65, and (e) t/D = 2%?
The holding force in drawing is most likely to be (a) greater than, (b) equal to, or (c) less than the
maximum drawing force?
Which one of the following stamping dies is the most complicated: (a) blanking die, (b)
combination die, (c) compound die, (d) edge-bending die, (e) progressive die, or (f) V-bending die?
Which one of the following press types is usually associated with the highest production rates in
sheet-metal-stamping operations: (a) adjustable bed, (b) open back inclinable, (c) press brake, (d)
solid gap, or (e) straight-sided?
Which of the following processes are classified as high-energy-rate forming processes (two best
answers): (a) electrochemical machining, (b) electromagnetic forming, (c) electron beam cutting,
(d) explosive forming, (e) Guerin process, (f) hydroforming, (g) redrawing, and (h) shear spinning?
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