ME383_Test2_Metal forming

Production of pipes and tubes is associated with which of the following bulk deformation processes (more than one)? (a) extrusion, (b) hobbing, (c) ring rolling, (d) roll forging, (e) roll piercing, (f) tube sinking, or (g) upsetting.

(a) extrusion, (e) roll piercing, (f) tube sinking

Which of the following are advantages and characteristics of hot working relative to cold working (more than one)? (a) fracture of workpart less likely, (b) increased strength properties, (c) isotropic mechanical properties, (d) less overall energy required, (e) lower deformation forces required, and (f) more significant shape changes are possible.

(a) fracture of workpart less likely, (c) isotropic mechanical properties, (d) less overall energy required, (f) more significant shape changes are possible.

Holding force in drawing is most likely to be which of the following relative to maximum drawing force? (a) less than, (b) equal to, or (c) greater than.

(a) less than

What does the centerburst defect in extrusion have in common with the roll piercing process?

They are both examples of how compressive stresses applied to the outside surface of a solid cylindrical cross-section can create high tensile stresses in the interior of the cylinder.

Identify some of the ways in which force in flat rolling can be reduced.

Ways to reduce force in flat rolling include: (1) use hot rolling, (2) reduce draft in each pass, and (3) use smaller diameter rolls.

The production of tubing is possible in indirect extrusion but not in direct extrusion: (a) true or (b) false?

(b) false, Tube and pipe cross-sections can be produced by either direct or indirect extrusion.

Which of the following are variations of sheet metal bending operations (more than one)? (a) coining, (b) flanging, (c) hemming, (d) ironing, (e) notching, (f) shear spinning, (g) trimming, (h) tube bending, and (i) tube forming.

(b) flanging, (c) hemming, (i) tube forming.

Which of the following is typical of the work geometry in sheet metal processes? (a) high volume-to-area ratio, or (b) low volume-to-area ratio.

(b) low volume-to-area ratio.

The coefficient of friction between the part and the tool in cold working tends to be which of the following relative to its value in hot working? (a) higher, (b) lower, or (c) no effect.

(b) lower

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, and (e) straight-sided.

(b) open back inclinable

The flow curve expresses the behavior of a metal in which of the following regions of the stress-strain curve? (a) elastic region, or (b) plastic region.

(b) plastic region.

Which of the following are bulk deformation processes (more than one)? (a) bending, (b) deep drawing, (c) extrusion, (d) forging, and (e) rolling.

(c) extrusion, (d) forging, and (e) rolling.

Increasing strain rate tends to have which one of the following effects on flow stress during hot forming of metal? (a) decreases flow stress, (b) has no effect, or (c) increases flow stress.

(c) increases flow stress.

The cutting force in a blanking operation depends on which mechanical property of the sheet metal (one best answer)? (a) compressive strength, (b) modulus of elasticity, (c) shear strength, (d) tensile strength, or (e) yield strength.

(c) shear strength,

Hot working of metals refers to which one of the following temperature regions relative to the melting point of the given metal on an absolute temperature scale? (a) room temperature, (b) 0.2Tm, (c) 0.4Tm, or (d) 0.6Tm.

(d) 0.6Tm.

The average flow stress is the flow stress multiplied by which of the following factors? (a) n, (b) (1+n), (c) 1/n, or (d) 1/(1+n), where n is the strain hardening exponent.

(d) 1/(1+n), where n is the strain hardening exponent.

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 sheet metal section to be bent.

(d) length before bending of the straight sheet metal section to be bent.

Which one of the following stamping dies is the most complicated? (a) blanking die, (b) combination die, (c) compound die, (d) wiping die for edge bending, (e) progressive die, or (f) V-die.

(e) progressive die

In a wire drawing operation, why must the drawing stress never exceed the yield strength of the work metal?

Because if the drawing stress exceeded the yield strength, the metal on the exit side of the draw die would stretch rather than force metal to be drawn through the die opening.

Why is flash desirable in impression die forging?

Because its presence constrains the metal in the die to fill the details of the die cavity.

Why is the term pressworking often used for sheet metal processes?

Because these operations are generally performed on presses.

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. See Article 20.3.4.

Extrusion is a fundamental shaping process. Describe it.

Extrusion is a compression process in which the work material is forced to flow through a die orifice, thereby forcing its cross-section to assume the profile of the orifice.

Besides flat rolling and shape rolling, identify some additional bulk forming processes that use rolls to effect the deformation.

Some other processes that use rolls are ring rolling, thread rolling, gear rolling, roll piercing, and roll forging.

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.

What is sticking friction in metalworking?

Sticking friction is when the work surface adheres to the surface of the tool rather than slides against it; it occurs when the friction stress is greater than the shear flow stress of the metal.

What are the relative advantages and disadvantages of mechanical versus hydraulic presses in sheet metalworking?

Advantage of mechanical presses: faster cycle rates. Advantages of hydraulic presses: longer ram strokes and uniform force throughout stroke.

Indicate some of the advantages of cold working relative to warm and hot working.

Advantages of cold working are: (1) better accuracy, (2) better surface finish, (3) increased strength due to work hardening, (4) possible directional properties due to grain flow, and (5) no heating of work required.

What is isothermal forming ?

An isothermal forming operation is performed in such a way as to eliminate surface cooling and thermal gradients in the workpart. This is accomplished by preheating the forming tools.

Which of the four basic bulk deformation processes use compression to effect shape change (more than one)? (a) bar and wire drawing, (b) extrusion, (c) forging, and (d) rolling.

(a) bar and wire drawing, (b) extrusion, (c) forging, and (d) rolling. Bar and wire drawing (a) is the only tricky answer; although tensile stresses are applied to the work, the work is squeezed through the die opening by compression - the term indirect compression is sometimes used.

Which of the following bulk deformation processes are involved in the production of nails for lumber construction (more than one)? (a) bar and wire drawing, (b) extrusion, (c) forging, and (d) rolling.

(a) bar and wire drawing, (c) forging, (d) rolling. Bar stock is rolled, drawn into wire stock, and upset forged to form the nail head.

Which of the following rolling mill types are associated with relatively small diameter rolls in contact with the work (more than one)? (a) cluster mill, (b) continuous rolling mill, (c) four-high mill, (d) reversing mill, or (e) three-high configuration.

(a) cluster mill, (c) four-high mill

The maximum possible draft in a rolling operation depends on which of the following parameters (more than one)? (a) coefficient of friction between roll and work, (b) roll diameter, (c) roll velocity, (d) stock thickness, (e) strain, and (f) strength coefficient of the work metal.

(a) coefficient of friction between roll and work, (b) roll diameter

Which of the following are classified as forging operations (more than one)? (a) coining, (b) fullering, (c) impact extrusion, (d) roll forging, (e) thread rolling, and (f) upsetting.

(a) coining, (b) fullering, (d) roll forging, (f) upsetting

Sheet metal bending involves which of the following stresses and strains (may be more than one)? (a) compressive, (b) shear, and (c) tensile.

(a) compressive, (c) tensile.

A round sheet metal slug produced in a hole punching operation will have the same diameter as which of the following? (a) die opening, or (b) punch.

(a) die opening

Theoretically, the maximum reduction possible in a wire drawing operation, under the assumptions of a perfectly plastic metal, no friction, and no redundant work, is which of the following (one answer)? (a) zero, (b) 0.63, (c) 1.0, or (d) 2.72.

(b) 0.63

As sheet metal stock hardness increases, the clearance between punch and die should: (a) be decreased, (b) be increased, or (c) be unaffected.

(b) be increased

Which of the following processes are classified as high- energy-rate forming processes (more than one)? (a) electrochemical machining, (b) electromagnetic forming, (c) electron beam cutting, (d) explosive forming, (e) Guerin process, (f) hydroforming, (g) redrawing, and (h) shear spinning.

(b) electromagnetic forming, (d) explosive forming

Johnson's formula is associated with which of the four bulk deformation processes (one answer)? (a) bar and wire drawing, (b) extrusion, (c) forging, and (d) rolling.

(b) extrusion

Flash in impression die forging serves no useful purpose and is undesirable because it must be trimmed from the part after forming: (a) true or (b) false?

(b) false Flash causes build-up of pressure inside the die which causes the work metal to fill the cavity.

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 20.9.

The Guerin process is a sheet metal forming process that uses a rubber die which flexes to force the sheet metal to take the shape of a form block (punch).

A major technical problem in tube bending is collapse of the tube walls during the process.

What is a reversing mill in rolling?

A reversing mill is a two-high rolling mill in which the direction of rotation of the rolls can be reversed to allow the work to pass through from either side.

What is a two-high rolling mill?

A two-high rolling mill consists of two opposing rolls between which the work is compressed.

What is the difference between deep drawing and bar drawing?

Deep drawing is a sheet metal forming process used to fabricate cup-shaped parts; bar drawing is a bulk deformation process used to reduce the diameter of a cylindrical workpart.

In blanking of a round sheet metal part, indicate how the clearance should be applied to the punch and die diameters.

For a blanking operation, die size = blank size, and the punch is smaller by twice the clearance.

Describe V-bending and edge bending.

In V-bending, a simple punch and die which have the included angle are used to bend the part. In edge bending, the punch force a cantilevered sheet metal section over a die edge to obtain the desired bend angle. See Figure 20.14.

What are the characteristics that distinguish bulk deformation processes from sheet metal processes?

In bulk deformation, the shape changes are significant, and the workparts have a low area-to-volume ratio. In sheet metal processes, the area-to-volume ratio is high.

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 annealing between the steps. In reverse drawing, two draws are accomplished on the part, one in one direction, the second in the opposite direction.

Describe the effect of strain rate in metal forming.

Increasing strain rate tends to increase the resistance to deformation. The tendency is especially prominent in hot forming operations.

How does increasing temperature affect the parameters in the flow curve equation?

Increasing temperature decreases both K and n in the flow curve equation.

What is isothermal forging?

Isothermal forging is a hot forging operation in which the die surfaces are heated to reduce heat transfer from the work into the tooling.

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.

Name some products that are produced by extrusion.

Products produced by continuous extrusion include: structural shapes (window frames, shower stalls, channels), tubes and pipes, and rods of various cross-section. Products made by discrete extrusion include: toothpaste tubes, aluminum beverage cans, and battery cases.

Why is friction generally undesirable in metal forming operations?

Reasons why friction is undesirable in metal forming: (1) inhibits metal flow during deformation, causing residual stresses and product defects; (2) increases forces and power required; and (3) wearing of the tools.

What are the reasons why the bulk deformation processes are important commercially and technologically?

Reasons why the bulk deformation processes are important include: (1) they are capable of significant shape change when hot working is used, (2) they have a positive effect on part strength when cold working is used, and (3) most of the processes produce little material waste; some are net shape processes.

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. See Section 20.10.

List some of the products produced on a rolling mill.

Rolled products include flat sheet and plate stock, round bar and rod stock, rails, structural shapes such as I-beams and channels.

What is stretch forming ?

Stretch forming of sheet metal involves stretching and simultaneous bending of the workpart to achieve shape change.

What is the Guerin process?

The Guerin process is a sheet metal forming process that uses a rubber die which flexes to force the sheet metal to take the shape of a form block (punch).

Indicate the mathematical equation for the flow curve.

The flow curve is defined in Eq. (18.1) as Yf = Kεn.

One way to classify forging operations is by the degree to which the work is constrained in the die. By this classification, name the three basic types.

The three basic types are: (1) open die forging, (2) impression die forging, and (3) closed die forging.

Identify the three basic types of sheet metalworking operations.

The three operations are: (1) cutting, (2) bending, and (3) drawing.

What are the two basic types of forging equipment?

The two types of forging machines are hammers, which impact the workpart, and presses, which apply a gradual pressure to the work.

What are the two basic categories of structural frames used in stamping presses?

Two press frame types are: (1) gap frame, also called C-frame, and (2) straight-sided frame. See Article 20.6.1.