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engineering
mechanical engineering

Questions and Answers of Mechanical Engineering

Explain why hole preparation may be important in mechanical joining of components?
What precautions should be taken in mechanical joining of dissimilar metals? Why?
What difficulties are involved in joining plastics? What about in joining ceramics? Explain.
Comment on your observations concerning the numerous joints shown in various figures in Section 12.17?
How different is adhesive bonding from other joining methods? What limitations does it have? Explain.
It was noted that soldering is generally applied to thinner components. Why?
Explain why adhesively bonded joints tend to be weak in peeling?
Discuss the need for and role of fixtures in holding work pieces in proper positions for the welding operations described in this chapter?
Inspect various household products and describe how they are joined and assembled. Explain why those particular processes were used?
Name several products that have been assembled by (a) Seaming, (b) Stitching, and (c) Soldering?
Suggest methods of attaching a round bar (made of thermosetting plastic) perpendicularly to a flat metal plate?
Describe the tooling and equipment that are essential to perform the double-lock seaming operation shown in Fig. 12.53, starting with flat sheet. (See also Fig. 7.23.)?
What joining methods would be suitable in assembling a thermoplastic cover over a metal container? The cover has to be removed periodically?
Repeat Question 12.64, but for a cover made of (a) A thermosetting plastic, (b) Metal, and (c) Ceramic. Describe the factors involved in your selection of assembly methods?
Do you think the strength of an adhesively bonded structure is as high as that obtained by diffusion bonding? Explain.
Comment on workpiece size limitations, if any, for each of the processes described in this chapter?
Describe part shapes that would be difficult, or impossible, to join by the processes described in this chapter. Gives specific examples?
Give several applications of electrically conducting adhesives?
Describe the factors that influence the size of the two weld beads shown in Fig. 12.13?
Give several applications for fasteners used in various household products and explain why other joining methods have not been used instead?
Comment on workpiece shape limitations, if any, for each of the processes described in this chapter?
List and explain the guidelines that must be followed to avoid cracks in welded joints, such as hot tearing, hydrogen-induced cracking, and lamellar tearing?
Describe the reasons that fatigue failure generally occurs in the heat-affected zone of welds and not through the weld bead itself?
If the parts to be welded are preheated, is the likelihood that porosity will form increased or decreased? Explain.
What is the advantage of electron-beam and laser-beam welding processes as compared to arc welding? Explain.
Describe the common types of discontinuities in welds and explain the methods by which they can be avoided?
What are the sources of weld spatter? How can spatter be controlled? Explain.
Describe the functions and characteristics of electrodes. What functions do coatings have? How are electrodes classified? Explain.
Why is the quality of welds produced by submerged arc welding very good? Explain.
Describe the advantages and limitations of explosion welding?
Explain the difference between resistance seam welding and resistance spot welding?
Could any of the processes described in this chapter be used to make a large bolt by welding the head to the shank? (See Fig. 6.17.) Explain the advantages and limitations of this approach?
Describe wave soldering. What are the advantages and disadvantages of this process?
What are the similarities and differences between a bolt and a rivet? Explain.
It is common practice to tin plate electrical terminals to facilitate soldering. Why is tin a suitable material?
Review the contents of Table 12.3 and explain why some materials require more heat than others to melt a given volume?
Two flat copper sheets (each 1.5 mm thick) are being spot welded with a current of 7000 A and a current flow time of 0.3 s. The electrodes are 5 mm in diameter. Estimate the heat generated in the
Calculate the temperature rise in Problem 12.87 assuming that the heat generated is confined to the volume of material directly between the two round electrodes and that the temperature distribution
Explain the factors involved in electrode selection in arc welding processes?
In Fig. 12.24 assume that most of the top portion of the top piece is cut horizontally with a sharp saw. Thus, the residual stresses will be disturbed and, as described in Section 2.10, the part will
The accompanying figure shows a metal sheave that consists of two matching pieces of hot-rolled, low-carbon-steel sheets. These two pieces can be joined either by spot welding or by V-groove welding.
A shielded metal arc welding operation is taking place on carbon steel to produce a fillet weld (see Fig. 12.21b). The desired welding speed is about 25 mm/s. If the power supply is 10 V, what
The energy applied in friction welding is given by the formula E = IS2/C, where I is the moment of inertia of the flywheel, S is the spindle speed in rpm, and C is a constant of proportionality
A rivet can buckle if it is too long, as shown in Fig. 12.61. Using information from solid mechanics, determine the length-to-diameter ratio of a rivet that will not buckle during riveting?
A submerged arc welding operation takes place on 10 mm thick stainless steel plate, producing a butt weld as shown in Fig. 12.20c. The weld geometry can be approximated as a trapezoid with 15 mm and
Define the terms wafer, chip, device, integrated circuit, and surface mount?
What do the terms linewidth and registration refer to?
Compare diffusion and ion implantation?
What is the difference between evaporation and sputtering?
What is the definition of yield? How important is yield? Comment on its economic significance?
What is accelerated life testing? Why is it practiced?
Explain the basic processes of (a) Surface micromachining and (b) Bulk micromachining?
What is LIGA? What are its advantages over other processes?
What is the difference between isotropic and anisotropic etching?
What is a mask? What is its composition?
Why is silicon the most commonly used semiconductor in IC technology? Explain.
What is the difference between chemically assisted ion etching and dry plasma etching?
Which process(es) in this chapter allow(s) fabrication of products from polymers? (See also Chapter 10.)?
With an appropriate sketch, describe the thermosonic stitching process?
Explain the difference between a die, a chip, and a wafer?
Why are flats or notches machined onto silicon wafers? Explain.
What is a via? What is its function?
What is a flip chip? Describe its advantages over a surface-mount device?
Explain how IC packages are attached to a printed circuit board if both sides will contain ICs?
In a horizontal epitaxial reactor (see the accompanying figure), the wafers are placed on a stage (susceptor) that is tilted by a small amount, usually l°-3°. Why is this procedure done?
What do the terms VLSI, IC, CVD, CMP, and DIP stand for?
The accompanying table describes three changes in the manufacture of a wafer: increase of the wafer diameter, reduction of the chip size, and increase of the process complexity. Complete the table by
The speed of a transistor is directly proportional to the width of its polysilicon gate, with a narrower gate resulting in a faster transistor and a wider gate resulting in a slower transistor.
A common problem in ion implantation is channeling, in which the high-velocity ions travel deep into the material through channels along the crystallography planes before finally being stopped. What
The MEMS devices discussed in this chapter apply macroscale machine elements, such as spur gears, hinges, and beams. Which of the following machine elements can and cannot be applied to MEMS, and
Figure 13.7b shows the Miller indices on a wafer of (100) silicon. Referring to Fig. 13.5, identify the important planes for the other wafer types illustrated in Fig. 13.7a?
Explain how you would produce a spur gear if its thickness were one-tenth its diameter and its diameter were(a) 10 (m,(b) 100 (m,(c) 1 mm,(d) 10 mm, and(e) 100 mm.
Which clean room is cleaner, a Class 10 or a Class 1?
Describe the difference between a microelectronic device, a micromechanical device and MEMS?
Why is silicon often used with MEMS and MEMS devices?
How do n-type and n-type dopants differ? Explain.
Explain the purpose of a spacer layer in surface micromachining?
What do the terms SIMPLE and SCREAM stand for?
Which process(es) in this chapter allow the fabrication of products from ceramics? (See also Chapter 11.)?
What is HEXSIL?
Describe the differences between stereolithography and microstereolithography?
Lithography produces projected shapes; consequently, true three-dimensional shapes are more difficult to produce. Which of the processes described in this chapter are best able to produce
List and explain the advantages and limitations of surface micromachining as compared to bulk micromachining?
What are the main limitations to the LIGA process?
Describe the process(es) that can be used to make the microtweezers shown in Fig. 13.49 other than HEXSIL?
A certain wafer manufacturer produces two equal-sized wafers, one containing 500 chips and the other containing 300 chips. After testing, it is observed that 50 chips on each type of wafer are
How is epitaxy different than other forms of film deposition?
A chlorine-based polysilicon etch process displays a polysilicomresist selectivity of 4:1 and a polysil-icomoxide selectivity of 50:1. How much resist and exposed oxide will be consumed in etching
During a processing sequence, four silicon-dioxide layers are grown by oxidation: 400 nm, 150 nm, 40 nm, and 15 nm. How much of the silicon substrate is consumed?
A certain design rule calls for metal lines to be no less than 2 (m wide. If a 1 (m-thick metal layer is to be wet etched, what is the minimum photoresist width allowed? (Assume that the wet etch is
Using Fig. 13.18, obtain mathematical expressions for the etch rate as a function of temperature?
If a square mask of side length 100 (m is placed on a {100} plane and oriented with a side in the (110) direction, how long will it take to etch a hole 4 (um deep at 80°C using thylene-diamine /
Obtain an expression for the width of the trench bottom as a function of time for the mask shown in Fig. 13.17b?
Calculate the undercut in etching a 10-(m-deep trench if the anisotropy ratio is(a) 200,(b) 2, and(c) 0.5. Calculate the sidewall slope for these three cases?
Estimate the time required to etch a spur-gear blank from a 75-mm-thick slug of silicon?
Comment on the differences between wet and dry etching?
A resist is applied in a resist spinner spun operating at 2000 rpm, using a polymer resist with viscosity of 0.05 N-s/m. The measured resist thickness is 1.5 (m. What is the expected resist thickness
Examine the hole profiles in the accompanying figure and explain how they might be produced?
A polyimide photoresist requires 100 mJ / cm2 per (m of thickness in order to develop properly. How long does a 150 (m film need to develop when exposed by a 1000 W/m2 light source?
How many levels are required to produce the micromotor shown in Fig. 13.22d?

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