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engineering
mechanical engineering
Questions and Answers of
Mechanical Engineering
Under what conditions would you discourage the use of cutting fluids? Explain.
In Fig. 8.18, it can be seen that the percentage of the energy carried away by the chip increases with cutting speed. Why?
How would you go about measuring the effectiveness of cutting fluids? Explain.
Describe the conditions that are critical in benefiting from the capabilities of diamond and cubic boron-nitride cutting tools.
The last two properties listed in Table 8.6 can be important to the life of the cutting tool. Explain why? Which of the properties listed are the least important in machining operations? Explain.
It will be noted in Fig. 8.30 that the tool materials, especially carbides, have a wide range of hardness at a particular temperature. Why?
Describe your thoughts on how would you about recycling used cutting tools. Comment on any difficulties involved, as well as on economic considerations.
As you can see, there is a wide range of tools materials available and used successfully today, yet much research and development continues to be carried out on these materials. Why?
Drilling, boring, and reaming of large holes is generally more accurate than just drilling and reaming Why?
A highly oxidized and uneven round bar is being turned on a lathe. Would you recommend a relatively small or large depth of cut? Explain your reasons.
Does the force or torque in drilling change as hole depth increases? Explain.
Give reasons that pure aluminum and copper are generally rated as easy to machine.
Can you offer an explanation as to why the maximum temperature in cutting is located at about the middle of the tool-chip interface?
State whether or not the following statements are true for orthogonal cutting, explaining your reasons: (a) For the same shear angle, there are two rake angles that give the same cutting ratio, (b)
If a drill bit is intended for woodworking applications, what material is it most likely to be made from? Are there any reasons why such a drill bit cannot be used to drill a few holes in a piece of
What are the consequences of a coating on a cutting tool that has a different coefficient of thermal expansion than does the substrate? Explain.
Discuss the relative advantages and limitations of near-dry machining. Consider all relevant technical and economic aspects.
In modern manufacturing with computer-controlled machine tools, which types of metal chips are undesirable and why?
Explain why hacksaws are not as productive as band saws.
Describe workpieces and conditions under which broaching would be the preferred method of machining.
With appropriate sketches, explain the differences between and similarities among the following processes (a) Shaving, (b) Broaching, (c) Turn broaching.
Why is it difficult to use friction sawing on non-ferrous metals? Explain.
Review Fig. 8.68 on modular machining cent and explain workpieces and operations that would be suitable on such machines.
Describe types of workpieces that would not be suitable for machining on a machining center. Give specific examples.
Why may grinding operations be necessary for parts that have been machined by other processes?
It was stated that the grinding ratio, G, depends on the following factors: (1) Type of grinding wheel, (2) Workpiece hardness, (3) Wheel depth of cut, (4) Wheel and workpiece speeds, and (5) Type of
List the processes described in this chapter that would be difficult to apply to a variety of nonmetallic or rubberlike materials. Explain your thoughts, commenting on such topics as part geometries
Make a list of the processes described in this chapter in which the following properties are relevant or significant: (a) Electrical, (b) Mechanical, (c) Thermal, and (d) Chemical, Are there
List and explain the precautions you should take when grinding with high precision. Comment on the role of the machine tool, processing parameters, the type of grinding wheel, and use of grinding
Describe the methods you would use to determine the number of active cutting points per unit surface area on the periphery of a straight (Type 1; see Fig. 9.2a) grinding wheel. What is the
Describe and explain the difficulties involved in grinding parts made of(a) Thermoplastics,(b) Thermosets,(c) Ceramics?
Explain why ultrasonic machining is not suitable for soft and ductile metals?
It is generally recommended that a soft grade wheel be used for grinding hardened steels? Explain why.
Explain the reasons that the processes described in this chapter may adversely affect the fatigue strength of materials?
Describe the factors that may cause chatter in grinding operations and give the reasons they cause chatter?
Outline the methods that are generally available for deburring manufactured parts. Discuss the advantages and limitations of each method?
In which of the processes described in this chapter are the physical properties of the workpiece material important? Explain.
Explain why there are so many different types and sizes of grinding wheels?
Give all possible technical and economic reasons that the material removal processes described in this chapter may be preferred, or even required, over those described in Chapter 8?
What processes would you recommend for die sinking in a die block, such as that used for forging? Explain.
The proper grinding surfaces for each type of wheel are shown in Fig. 9.2? Explain why grinding on other surfaces of the wheel is improper and/or unsafe.
Wheel (b) in Fig. 9.3 has serrations along its periphery? Explain the reason for such a design.
In Fig. 9.10, it will be noted that wheel speed and grinding fluids can have a major effect on the type and magnitude of residual stresses developed in grinding? Explain the possible reasons for
Explain the consequences of allowing the workpiece temperature to rise excessively in grinding operations?
Comment on any observations you have regarding the contents of Table 9.4?
Why has creep-feed grinding become an important manufacturing process? Explain.
There has been a trend in manufacturing industries to increase the spindle speed of grinding wheels? Explain the possible advantages and limitations of such an increase in speed.
Why is preshaping or premachining of parts generally desirable in the advanced machining processes described in this chapter? Explain.
Why are there large differences between the specific energies involved in grinding and in machining? Explain.
Why are finishing operations sometimes necessary? How could they be minimized to reduce product costs? Explain, with examples.
Why has the wire-EDM process become so widely used in industry, especially in tool and die manufacturing? Explain.
''Make a list of the material removal processes described in this chapter that may be suitable for the following workpiece materials: (1) Ceramics, (2) Cast iron, (3) Thermoplastics, (4)
Explain why producing sharp corners and profiles using some of the processes described in this chapter can be difficult?
How do you think specific energy, μ, varies with respect to wheel depth of cut and hardness of the work-piece material? Explain.
It is stated is Example 9.2 that the thrust force in grinding is about 30% higher than the cutting force. Why is it higher?
Why should we be interested in the magnitude of the thrust force in grinding? Explain.
Why is the material removal rate in electrical-discharge machining a function of the melting point of the workpiece material? Explain.
Inspect Table 9.4 and, for each process, list and describe the role of various mechanical, physical, and chemical properties of the workpiece material on performance?
Which of the processes listed in Table 9.4 would not be applicable to nonmetallic materials? Explain.
Describe the advantages of superabrasives over conventional abrasives. Are there any limitations? Explain.
Why does the machining cost increase rapidly as surface finish requirements become finer?
Which of the processes described in this chapter are particularly suitable for workpieces made of (a) Ceramics, (b) Thermoplastics, and (c) Thermosets? Explain.
Other than cost, is there a reason that a grinding wheel intended for a hard workpiece cannot be used for a softer workpiece? Explain.
How would you grind the facets on a diamond, such as for a ring, since diamond is the hardest material known?
Define dressing and truing, and describe the difference between them?
What is heat checking in grinding? What is its significance? Does heat checking occur in other manufacturing processes? Explain.
Explain why parts with irregular shapes, sharp corners, deep recesses, and sharp projections can be difficult to polish?
Explain the reasons why so many different de-burring operations have been developed over the years?
From Equation (9.8) that the grinding temperature decreases with increasing work speed. Does this mean that for a work speed of zero, the temperature is infinite? Explain.
Describe the similarities and differences in the action of metalworking fluids in machining vs. grinding operations?
Give examples of applications for the grinding wheels shown in Fig. 9.2?
Are there any similarities among grinding, honing, polishing, and buffing? Explain.
Is the grinding ratio an important factor in evaluating the economics of a grinding operation? Explain.
Although grinding can produce a very fine surface finish on a workpiece, is this necessarily an indication of the quality of a part? Explain.
If not performed properly, honing can produce holes that are bellmouthed, wavy, barrel shaped, or tapered. Explain how this is possible?
Which of the advanced machining processes described in this chapter causes thermal damage to work-pieces? List and explain the possible consequences of such damage.
Describe your thoughts regarding laser-beam machining of nonmetallic materials. Give several possible applications and include their advantages as compared to other processes?
It was stated that graphite is the generally preferred material for EDM tooling. Would graphite also be appropriate for wire EDM? Explain.
What is the purpose of the abrasives in electrochemical grinding? Explain.
In a surface-grinding operation, calculate the chip dimensions for the following process variables: D = 8 in., d = 0.001 in., v = 30 ft/min, V = 5000 ft/min, C = 500 per in2, and r = 20?
If the workpiece strength in grinding is increased by 50%, what should be the percentage decreases in the wheel depth of cut, d, in order to maintain the same grain force, all other variables being
Explain why the same grinding wheel may act soft or act hard?
Taking a thin, Type 1 grinding wheel as an example, and referring to texts on stresses in rotating bodies, plot the tangential stress, (t, and radial stress, (r, as a function of radial distance
Derive a formula for the material removal rate in surface grinding in terms of process parameters. Use the same terminology as in the text?
Assume that a surface-grinding operation is being carried out under the following conditions: D = 250 mm, d = 0.1 mm, v = 0.5 m/s, and V = 50 m/s. These conditions are then changed to the following D
For a surface-grinding operation, derive an expression for the power dissipated in imparting kinetic energy to the chips. Comment on the magnitude of this energy. Use the same terminology as in the
The shaft of a Type 1 grinding wheel is attached to a flywheel only, which is rotating at a certain rpm. With this setup, a surface-grinding operation is being carried out on a long workpiece and at
Calculate the average impact force on a steel late by a 1-mm spherical aluminum-oxide abrasive irain, dropped from heights of(a) 1 m,(b) 2 m, and(c) 10 m. Plot the results and comment on your
A 50-mm-deep hole, 25 mm in diameter, is being produced by electrochemical machining. Assuming that a high production rate is more important than the quality of the machined surface, estimate the
If the operation in Problem 9.66 were per-formed on an electrical-discharge machine, what would be the estimated machining time?
A cutting-off operation is being performed with a laser beam. The workpiece being cut is 1/4 in. thick and 4 in. long. If the kerf is 1/6 in. wide, estimate the time required to perform this
Referring to Table 3.3, identify two metals or metal alloys that, when used as workpiece and electrode, respectively, in EDM would give the (a) Lowest and (b) Highest wear ratios, R. Calculate these
Describe your understanding of the role of friability of abrasive grains on the performance of grinding wheels?
It was stated in Section 9.5.2 that, in practice, grinding ratios typically range from 2 to 200. Based on the information given in Section 9.13, estimate the range of wear ratios in
It is known that heat checking occurs when grinding under the following conditions: spindle speed of 4000 rpm, wheel diameter of 10 in., and depth of cut of 0.0015 in., and a feed rate of 50 ft/min.
A hard aerospace aluminum alloy is to be ground. A depth of 0.003 in. is to be removed from a cylindrical section 8 in. long and with a 3-in. diameter. If each part is to be ground in not more than
A grinding operation is taking place with a 10-in. grinding wheel at a spindle rotational speed of 4000 rpm. The workpiece feed rate is 50 ft/min and the depth of cut is 0.002 in. Contact
The regulating wheel of a centerless grinder is rotating at a surface speed of 25 ft/min and is inclined at an angle of 5°. What is the feed rate of material past the grinding wheel?
Using some typical values, explain what changes, if any, take place in the magnitude of the impact force of a particle in ultrasonic machining of a hardened-steel workpiece as its temperature is
Estimate the percent increase in the cost of the grinding operation if the specification for the surface finish of a part is changed from 63 μin. to 16 /μin?
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