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engineering
mechanical engineering
Manufacturing Processes for Engineering Materials 5th edition Serope Kalpakjian, Steven Schmid - Solutions
Explain why the maximum reduction per pass in drawing should increase as the strain-hardening exponent, n, increases.
If, in deriving Eq. (6.74), we include friction, will the maximum reduction per pass be the same (that is, 63%), higher, or lower? Explain.
Devise an experimental method whereby you can measure the force required for forging only the flash in impression-die forging.
Explain what effects back tension has on the die pressure in wire or rod drawing, and discuss why these effects occur.
Explain why the inhomogeneity factor, ϕ, in rod and wire drawing depends on the ratio h/L as plotted in Fig. 6.12
Describe the reasons for the development of swaging process.
Occasionally, wire drawing of steel will place within a sheath of a soft metal, such as copper lead. Why would this procedure be effective?
Recognizing that it is very difficult to manufacture a die with a sub millimeter diameter, how w~ you produce a 10-μm-diameter wire?
What changes would you expect in the strength hardness, ductility, and anisotrophy of annealed metal after they have been drawn through dies? Why?
With respect to the topics covered in this cha list and explain specifically two examples each w friction (a) Is desirable (b) Is not desirable.
List and explain the reasons that there are many different types of die materials used for processes described in this chapter.
A manufacturer is successfully hot forging a certain part, using material supplied by Company A. A new supply of material is obtained from Company B, with the same nominal composition of the major alloying elements as that of the material from Company, However, it is found that the new forgings are
Why should we be interested in residual stress developed in parts made by the forming process described in this chapter?
Make a summary of the types of de found in the processes described in this chapter, each type, specify methods of reducing or eliminate the defects.
In the free-body diagram in Fig. 6.4b, the incremental stress dσx on the element was shown pointing to the left. Yet it would appear that, because of the direction of frictional stresses, μp, the incremental stress should point to the right in order to balance the horizontal forces. Show that the
Plot the force vs. reduction in height curve in open-die forging of a solid cylindrical, annealed copper specimen 2 in. high and 1 in. in diameter, up to a reduction of 70%, for the cases of(a) No friction between the flat dies and the specimen,(b) μ = 0 .25(c) μ = 0.5. Ignore barreling and use
Calculate the work done for each case in Problem 6.63.In problem 6.63(a) No friction between the flat dies and the specimen,(b) μ = 0 .25(c) μ = 0.5. Ignore barreling and use average pressure formulas.
Determine the temperature rise in the spec for each case in Problem 6.63, assuming that process is adiabatic and the temperature is uniform throughout the specimen.
To determine its forgeability, a hot-twist test performed on a round bar 25 mm in diameter and 200 mm long. It is found that the bar underwent 200 before it fractured. Calculate the shear strain at outer surface of the bar at fracture.
What is the magnitude of μ when, for plane-compression, the forging load with sliding fric-is equal to the load with sticking friction? Use average-pressure formulas.
Explain why there might be a change in the density of a forged product as compared to that of the cast blank.
Note that in cylindrical upsetting, the frictional stress cannot be greater than the shear yield stress k, of the material. Thus, there may be a distance x in Fig. 6.8 where a transition occurs from sliding to sticking friction. Derive an expression for x in terms of r, h, and μ only.
Assume that the work piece shown in the accompanying figure is being pushed to the right by a lateral force F while being compressed between flat dies,(a) Make a sketch of the die-pressure distribution for the condition for which F is not large enough to slide the work piece to the right,(b) Make a
For the sticking example given in Fig. 6.10, drive an expression for the lateral force F required to slide the work piece to the right while the work piece is being compressed between flat dies.
Two solid cylindrical specimens, A and B, both de of a perfectly plastic material, are being forged with friction and isothermally at room temperature to a reduction in height of 25%. Originally, specimen A has a height of 2 in. and a cross-sectional area of 1 in.2, and specimen B has a height of
In Fig. 6.6, does the pressure distribution along the four edges of the work piece depend on the particular yield criterion used? Explain.
Under what conditions would you have a nor-pressure distribution in forging a solid cylindrical work piece as shown in the accompanying figure? Explain.
Take two solid cylindrical specimens of equal diameter but different heights, and compress them (frictionless) to the same percent reduction in height. Show that the final diameters will be the same.
A rectangular work piece has the following original dimensions: 2a = 100 mm, h = 30 mm, and width = 20 mm. The metal has a strength coefficient of 300 MPa and a strain-hardening exponent of 0.3. It is being forged in plane strain with μ = 0.2. Calculate the force required at a reduction of 20%. Do
Assume that in upsetting a solid cylindrical specimen between two flat dies with friction, the dies are rotated at opposite directions to each other. How, if at all, will the forging force change from that for non-rotating dies?
Since glass is a good lubricant for hot extrusion would you use glass for impression-die forging as well? Explain.
A mechanical press is powered by a 30-hp motor and operates at 40 strokes per minute. It uses a flywheel, so that the rotational speed of the crankshaft does not vary appreciably during the stroke. If the strike length is 6 in., what is the maximum contact force that can be exerted over the entire
Estimate the force required to upset a 0.125-in.-diameter C74500 brass rivet in order to form a 0.25-in.-diameter head. Assume that the coefficient of friction between the brass and the tool-steel die is 0.2 and that the rivet head is 0.125 in. in thickness
Using the slab method of analysis, derive Eq. (6.17).
In Example 6.4, calculate the velocity of the strip leaving the rolls.
With appropriate sketches, explain the changes that occur in the roll-pressure distribution if one of the rolls is idling, that is, power is shut off to that roll.
It can be shown that it is possible to determine /x in flat rolling without measuring torque or forces. By inspecting the equations for rolling, describe an experimental procedure to do so. Note that you are allowed to measure any quantity other than torque or forces.
Derive a relationship between back tension, σb and front tension, σf in rolling such that when both tensions are increased, the neutral point remains in the same position.
Take an element at the center of the deformation zone in flat rolling. Assuming that all the stresses acting on this element are principal stresses, indicate the stresses qualitatively, and state whether they are tensile or compressive. Explain your reasoning. Is it possible for all three principal
Describe and explain the factors that influence spread in cogging operations on square billets
It was stated that in flat rolling a strip, the roll force is reduced about twice as effectively by back tension as it is by front tension. Explain the reason for this difference, using appropriate sketches.
It can be seen that in rolling a strip, the rolls will begin to slip if the back tension, σb is too high. Derive an analytical expression for the magnitude of the back tension in order to make the powered rolls begin to slip. Use the same terminology as applied in the text.
In Steckel rolling, the rolls are idling, and thus there is no net torque, assuming frictionless bearings. Where, then, is the energy coming from to supply the necessary work of deformation in rolling? Explain with appropriate sketches, and state the conditions have to be satisfied.
(a) Make a neat sketch of the roll-pressure distribution in flat rolling with powered rolls,(b) Assume now that the power to both rolls is shut off and rolling is taking place by front tension only, i.e., Steckel rolling. Superimpose on your diagram the new roll pressure distribution, explaining
In Fig. 6.34, assume that L = 2L2. Is the roll force, F, for L now twice or more than twice the ro force for L2? Explain.
A flat-rolling operation is being carried out where h0 = 0.2 in., hf = 0.15 in., w0 = 10 in., R = 8 μ = 0.25, and the average flow stress of the material' 40,000 psi. Estimate the roll force and the torque. Include the effects of roll flattening.
A rolling operation takes place under the conditions shown in the accompanying figure. What is the position xn of the neutral point? Note that there are a front and back tension that have not been specified. Additional data are as follows: Material is 5052-O aluminum; hardened steel rolls; surface
Select any three topics from Chapter 2, and, with specific examples for each, show their relevance to the topics described in this chapter.
Explain why there are so many different types of tool and die materials used for the processes described in this chapter.
The box is to be made from a single piece of sheet metal. Repeat Problem Design a box that will contain a 4 in. × 6 in. × 3 in. volume. The box is to be produced from two pieces of sheet metal and will require no tools or fasteners for its assembly.
In opening a can using an electric can opener, you will note that the lid often develops a scalloped periphery, (a) Explain why scalloping occurs, (b) What design changes for the can opener would you recommend in order to minimize or, if possible, eliminate scalloping? (c) Since lids typically are
Lay out a roll-forming line to produce any three of the cross sections shown in Fig. 7.27b.
Obtain a few pieces of cardboard and carefully cut the profiles to produce the bends shown in Fig. 7.68. Demonstrate that the designs labeled as "best" are indeed the best designs. Comment on the difference in strain states among the designs.
Describe the differences between compound, progressive, and transfer dies.
It has been stated that the quality of the sheared edges can influence the formability of sheet metals. Explain why.
Explain why and how various factors influence springback in bending of sheet metals.
Does the hardness of a sheet metal have any effect on its springback in bending? Explain.
As noted in Fig. 7.16, the state of stress shifts from plane stress to plane strain as the ratio of length-of-bend to sheet thickness increases. Explain why.
Describe the material properties that have an effect on the relative position of the curves shown in Fig. 7.19.
In Table 7.2, we note that hard materials have higher R/t ratios than soft ones. Explain why.
Why do tubes have a tendency to buckle when bent? Experiment with a straight soda straw, and describe your observations.
Based on Fig. 7.22, sketch and explain the shape of a U-die used to produce channel-shaped bent parts.
Same as for Question 7.1, but for Chapter 3. Select any three topics from Chapter 2, and, with specific examples for each, show their relevance to the topics described in this chapter.
Explain why negative springback does not occur in air bending of sheet metals.
Give examples of products in which the presence of beads is beneficial or even necessary.
Assume that you are carrying out a sheet-forming operation and you find that the material is not sufficiently ductile. Make suggestions to improve its ductility.
In deep drawing of a cylindrical cup, is it always necessary that there be tensile circumferential stresses on the element in the cup wall, as shown in Fig. 7.50b? Explain.
When comparing hydroforming with the deep drawing process, it has been stated that deeper draws are possible in the former method. With appropriate sketches, explain why.
It will be noted in Fig. 7.50a that element A in the flange is subjected to compressive circumferential (hoop) stresses. Using a simple free-body diagram, explain why.
From the topics described in this chapter, list and explain specifically several examples where friction is (a) Desirable (b) Not desirable.
Explain why increasing the normal anisotropy, R, of a sheet metal improves its deep drawability.
Explain the reason for the negative sign in the numerator of Eq. (7.21).
If you could control the state of strain in a sheet-metal forming operation, would you rather work on the left or on the right side of the forming-limit diagram? Explain.
Describe (a) the similarities and (b) the differences between the bulk deformation processes described in Chapter 6 and the sheet-metal forming processes described in this chapter.
Comment on any effect that lubrication of the j punch surfaces may have on the limiting drawing ratio in deep drawing.
Comment on the role of the size of the circles on the surfaces of sheet metals in determining their formability. Are square grid patterns, as shown in Fig. 7.65, useful? Explain.
Make a list of the independent variables that influence the punch force in deep drawing of a cylindrical cup, and explain why and how these variables influence the force.
Explain why the simple-tension line in the forming-limit diagram in Fig. 7.63a states that it is for R = 1, where R is the normal anisotropy of the sheet metal.
What are the reasons for the development of forming-limit diagrams? Do you have any specific criticisms of such diagrams? Explain.
Explain the reasoning behind Eq. (7.20) for normal anisotropy, and Eq. (7.21) for planar anisotropy, respectively.
Describe why earing occurs. How would you avoid it? Would ears serve any useful purposes? Explain.
It was stated in Section 7.7.1 that the thicker the sheet metal, the higher is its curve in the forming-limit diagram. Explain why.
Inspect the earing shown in Fig. 7.57 and esti-1 mate the direction in which the blank was cut.
Describe the factors that should be considered in selecting the size and length of beads in sheet-metal I forming operations.
Discuss the material and process variables that influence the shape of the curve for punch force vs. stroke for shearing (see Fig. 7.7), including its height and width.
It is known that the strength of metals depends on their grain size (see Section 3.4.1). Would you then expect strength to influence the magnitude of R of sheet metals? Explain.
Explain why the three broken lines (simple tension, I plane strain, and equal biaxial stretching) in Fig. 7.63a I have those particular slopes.
Select several specific parts in a typical automobile, I and identify the processes described in this chapter that can be used to make those parts. Explain your reasoning.
Explain the reasons that such a wide variety of sheet-forming processes has been developed and used over the years.
Prepare a summary of the types of defects found in sheet-metal forming processes and include brief comments on the reason(s) for each defect.
Which of the processes described in this chapter use only one die? What are the advantages of using only one die?
It has been suggested that deep drawability can be increased by (a) Heating the flange and/or (b) Chilling the punch by some suitable means. Comment on how these methods could improve drawability.
Propose designs whereby the two suggestions given in Question 7.48 can be implemented in actual production. Would production rate affect your designs? Explain.
Describe your observations concerning Figs. 7.5 and 7.6.
In the manufacture of automotive-body panels from carbon-steel sheet, stretcher strains (Lueder's bands) are observed, which detrimentally affect surface finish. How can stretcher strains be eliminated? Explain.
In order to improve its ductility, a coil of sheet metal is placed in a furnace and is annealed. However, it is observed that the sheet has a lower limiting drawing ratio than it had before being annealed. Explain the reasons for this behavior.
What effects does friction have on a forming-limit diagram? Explain.
Why are lubricants generally used in sheet-metal forming? Explain, giving examples.
Through changes in clamping designs, a sheet-metal forming operation can allow the material to undergo a negative minor strain in the forming-limit diagram. Explain how this effect can be advantageous.
Give three examples each of sheet-metal parts that (a) can and (b) cannot be produced by incremental forming methods.
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