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engineering
mechanical engineering
Questions and Answers of
Mechanical Engineering
Explain what is meant by surface integrity. Why should we be interested in it?
Give two examples each in which waviness of a surface would be (1) Desirable (2) Undesirable.
Explain why surface temperature increases when two bodies are rubbed against each other. What is the significance of temperature rise due to friction?
In Section 4.4.1, we note that the values of the coefficient of friction can be much higher than unity. Explain why.
Describe the tribological differences between ordinary machine elements (such as meshing gears, cams in contact with followers, and ball bearings with inner and outer races) and elements of metal
Give the reasons that an originally round specimen in a ring-compression test may become oval after deformation.
Can the temperature rise at a sliding interface exceed the melting point of the metals? Explain.
List and briefly describe the types of wear encountered in engineering practice.
Explain why each of the terms in the Archard formula for adhesive wear, Eq. (4.6), should affect the wear volume.
How can adhesive wear be reduced? How can fatigue wear be reduced?
Why are surface-roughness design requirements in engineering so broad? Give appropriate examples.
It has been stated that as the normal load decreases, abrasive wear is reduced. Explain why this is so.
Explain how you would estimate the magnitude of the wear coefficient for a pencil writing on paper.
Why is the abrasive wear resistance of a material a function of its hardness?
We have seen that wear can have detrimental effects on engineering components, tools, dies, etc. Can you visualize situations in which wear could be beneficial? Give some examples.
On the basis of the topics discussed in this chapter, do you think there is a direct correlation between friction and wear of materials? Explain.
You have undoubtedly replaced parts in various appliances and automobiles because they were worn. Describe the methodology you would follow in determining the type(s) of wear these components have
Why is the study of lubrication regimes important?
We have seen that a surface has various layers. Describe the factors that influence the thickness of each of these layers.
Differentiate among (a) Coolants and lubricants, (b) Liquid and solid lubricants, (c) Direct and indirect emulsions, (d) Plain and compounded oils.
Explain the role of conversion coatings. Based on Fig. 4.13, what lubrication regime is most suitable for application of conversion coatings?
Explain why surface treatment of manufactured products may be necessary. Give several examples.
Which surface treatments are functional, and which are decorative? Give several examples.
Give examples of several typical applications of mechanical surface treatment.
Explain the difference between case hardening and hard facing.
List several applications for coated sheet metal, including galvanized steel
Explain how roller-burnishing processes induce residual stresses on the surface of work pieces.
List several products or components that could not be made properly, or function effectively in service, without implementation of the knowledge involved in Sections 4.2 through 4.5.
What is the consequence of oxides of metals being generally much harder than the base metal? Explain.
Why have coordinate-measuring machines become important instruments in modern manufacturing? Give some examples of applications.
Give reasons why the control of dimensional tolerances in manufacturing is important.
Give examples where it may be preferable to specify unilateral tolerances as opposed to bilateral tolerances in design.
Explain why a measuring instrument may not have sufficient precision.
Comment on the differences, if any, among 1. Roundness and circularity, 2. Roundness and eccentricity, 3. Roundness and cylindricity.
It has been stated that dimensional tolerances for nonmetallic stock, such as plastics, are usually wider than for metals. Explain why. Consider physical and mechanical properties of the materials
Describe the basic features of nondestructive testing techniques that use electrical energy.
Identify the nondestructive techniques that are capable of detecting internal flaws and those that only detect external flaws.
Which of the nondestructive inspection techniques are suitable for nonmetallic materials? Why?
Why is automated inspection becoming an important aspect of manufacturing engineering?
What factors would you consider in specifying the lay of a surface?
Describe situations in which the use of destructive testing techniques is unavoidable.
Should products be designed and built for a certain expected life? Explain.
What are the consequences of setting lower and upper specifications closer to the peak of the curve in Fig. 4.23?
Identify factors that can cause a process to become out of control. Give several examples of such factors.
In reading this chapter, you will have noted that the specific term dimensional tolerance is often used, rather than just the word tolerance. Do you think this distinction is important? Explain.
Give an example of an assignable variation and a chance variation.
Referring to the surface profile in Fig. 4.3, give some numerical values for the vertical distances from the center line. Calculate the Ra and Rq values. Then give another set of values for the same
Calculate the ratio of Ra / Rq for (a) A sine wave, (b) A saw-tooth profile, (c) A square wave.
Refer to Fig. 4.7b and make measurements of the external and internal diameters (in the horizontal direction in the photograph) of the four specimens shown. Remembering that in plastic deformation
Using Fig. 4.8a, make a plot of the coefficient of friction versus the change in internal diameter for a reduction in height of(1) 25%,(2) 50%,(3) 60%.
Describe the effects of various surface defects on the performance of engineering components in service. How would you go about determining whether or not each of these defects is important for a
In Example 4.1, assume that the coefficient of friction is 0.20. If all other initial parameters remain the same, what is the new internal diameter of the ring j specimen?
How would you go about estimating forces required for roller burnishing?
Estimate the plating thickness in electroplating a 50-mm solid metal ball using a current of 1 A and a plating time of two hours. Assume that c = 0.08.
Assume that a steel rule expands by 1 % because of an increase in environmental temperature. What will be the indicated diameter of a shaft whose actual diameter is 50.00 mm?
Examine Eqs. (4.2) and (4.10) what is the relationship between Rq and σ? What would be the equation for the standard deviation of a continuous curve?
Calculate the control limits for averages and ranges for the following: number of samples = 7; x = 50; R = 7.
Determine the control limits for the data shown in the following table:
Explain why the same surface roughness values do not necessarily represent the same type of surface.
In using a surface-roughness measuring instrument, how would you go about determining the cutoff value? Give appropriate examples.
What is the significance of the fact that the stylus path and the actual surface profile generally are not the same?
Describe the characteristics of (a) An alloy, (b) Pearlite, (c) Austenite, (d) Martensite, (e) Cementite.
Explain why gray iron undergoes expansion, rather than contraction, during solidification.
How can you tell whether a cavity in a casting is due to porosity or to shrinkage?
Explain the reasons for hot tearing in castings.
Would you be concerned about the fact that a portion of an internal chill is left within the casting? What materials do you think chills should be made of, and why?
Are external chills as effective as internal chills? Explain.
Is there any difference in the tendency for shrinkage-void formation for metals with short freezing and long freezing ranges, respectively? Explain.
It has long been observed by foundrymen that low pouring temperatures (that is, low superheat) promote equiaxed grains over columnar grains. Also, equiaxed grains become finer as the pouring
What are the reasons for the large variety of casting processes that have been developed over the years?
Why can blind risers be smaller than open-to risers?
What are the effects of mold materials on fluid flow and heat transfer in casting operations?
Would you recommend preheating the molds in permanent-mold casting? Also, would you remove the casting soon after it has solidified? Explain.
In a sand-casting operation, what factors determine the time at which you would remove the casting from the mold?
Explain why the strength-to-weight ratio of die-t parts increases with decreasing wall thickness.
We note that the ductility of some cast alloys is low (see Fig. 5.13). Do you think this should be a significant concern in engineering applications of stings? Explain.
The modulus of elasticity of gray iron varies significantly with its type, such as the ASTM class, Explain why.
List and explain the considerations involved in ting pattern materials.
Why is the investment-casting process capable producing fine surface detail on castings?
Explain why a casting may have a slightly differ-shape than the pattern used to make the mold
Explain why squeeze casting produces parts with better mechanical properties, dimensional accuracy, and surface finish than expendable-mold processes.
Why are steels more difficult to cast than cast irons?
How does the shape of graphite in cast iron affect its properties?
What would you recommend to improve the surface finish in expendable-mold casting processes?
You have seen that even though die casting produces thin parts, there is a limit to the minimum thickness. Why can't even thinner parts be made by this process?
What differences, if any, would you expect in the properties of castings made by permanent-mold vs sand-casting methods?
Which of the casting processes would be suitable for making small toys in large numbers? Explain.
Why are allowances provided for in making pat-s? What do they depend on?
Explain the difference in the importance of drafts green-sand casting vs. permanent-mold casting.
Make a list of the mold and die materials used in casting processes described in this chapter. Under type of material, list the casting processes that are used, and explain why these processes are
Explain why carbon is so effective in imparting strength to iron in the form of steel.
Describe the engineering significance of the existence of a eutectic point in phase diagrams.
Explain the difference between short and long freezing ranges. How are they determined? Why are they important?
Explain why it may be desirable or necessary for tings to be subjected to various heat treatments.
Describe the differences between case hardening and through hardening insofar as engineering applications are concerned.
Type metal is a bismuth alloy used to cast type for printing. Explain why bismuth is ideal for this process.
Do you expect to see larger solidification shrinkage for a material with a bcc crystal structure or fee? Explain.
If you were to incorporate lettering on a sand casting, would you make the letters protrude from the surface or recess into the surface? What if the part were to be made by investment casting?
List and briefly explain the three mechanisms by which metals shrink during casting.
Sketch the microstructure you would expect for a slab cast through (a) Continuous casting, (b) Strip casting, (c) Melt spinning.
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