機械制造過程

1、第十三章13.1explain why continuous chips are not necessarily desirable.Its easy to scratch the surface of the processing workpiece and chip easy to get involved in the tool13.8Is there any advantage to having a ?The advantage is not only increasing the rake angle and cutting depth, but also can enhance

2、the tool life when the built-up edge on a tool is stable.十四章14.18 Why does temperature have such an important effect on tool life?1.Materials become weaker and less hard as they become hotter; 2.Chemical reactivity typically increases with the increasing temperature, as does diffusion between the wo

3、rk piece and the cutting tool. 3.The effectiveness of cutting fluid is compromised at excessive temperatures, meaning there is higher friction to overcome, and therefore more tool wear is expected.4.In interrupted cutting, there are excessive thermal shock if the temperatures are high.14.25 Negative

4、 rake angles generally are preferred for ceramic, diamond, and cubicboron-nitride tools. Why? These materials are brittle and relatively weak in tension. Consequently, negative rake angles are preferred mainly because of the lower tendency to cause tensile stresses and chipping of the tools.14.26 Do

5、 you think that there is a relationship between the cost of a cutting tool and its hot hardness? Explain. Generally, as hot hardness increases, the cost of the tool material increases. For example, ceramics have high hot hardness and are generally made of inexpensive raw materials. However, their pr

6、oduction into elective and reliable tool materials involves major steps, and, hence, expenses. Likewise, carbides utilize expensive raw materials as well as involving a number of processing steps. Diamond and cubic boron nitride are expensive as well.14.28 In Table 22.1, the last two properties list

7、ed can be important to the life of a cutting tool. Why?Cutting-Tool Materials and Cutting Fluids 226(thermal conductivity and coefficient of thermal expansion)These properties are important in thermal cracking or shock of the tool material due to internal thermal stresses developed when subjected to

8、 thermal cycling, as in interrupted cutting operations. 14.32 Which of the properties listed in Table 22.1 is, in your opinion, the least important in cutting tools? Explain. By the student. It would appear that modulus of elasticity and density are not particularly important in cutting. However, as

9、 a very low order effect, elastic modulus may have some influence in very high precision machining operations because of the deflections involved. As for density, although the cutting tool itself has a rather small mass compared to other components, in high-speed operations where tool reversals may

10、be involved, inertia effects can be important.第十五章15.1 describe the types of machining operation that can be performed on a lathe.15.5why are turret lathes typically equipped with more than one turret ?15.15 List and explain the factors that contribute to poor surface finish in the processes describ

11、ed in this chapter. By the student. As an example, one factor is explained by Eq. (8.35) on p. 449, which gives the roughness in a process such as turning. Clearly, as the feed increases or as the tool nose radius decreases, roughness will increase. Other factors that aect surface nish are built-up

12、edge (see, for example, Figs. 8.4 and 8.6), dull tools or tool-edge chipping (see Fig. 8.28), or vibration and chatter (Section 8.11.1). Describe your observations concerning the contents of Tables 23.2 and 23.4, and explain why those particular recommendations are made. By the student. Some observa

13、tions are listed below:Machining Processes Used to Produce Round Shapes 234 Referring to Table 23.2 on p. 619, note that the side rake angle is high for aluminum but low for titanium. This can be explained by the benets of maintaining higher compression on the shear plane for titanium (to obtain hig

14、her ductility), a situation not needed for aluminum. Note from Table 23.4 on p. 622 that the cutting speeds for steels are much lower than those for copper alloys. This can be explained by power requirements associated with machining steels. Note that the tools used in Table 23.4 vary by workpiece m

15、aterial. For example, no diamond is listed for steel, explainable by the solubility of carbon in steel at elevated temperatures 15-20Does the force or torque in drilling change as the hole depth increases? Explain. The force and torque may increase as the hole depth increases, but not by a signicant

16、 amount. The factors which would increase the force and torque are contact area between the tool and cylindrical surface of the hole and diculties in removing chips from the bottom of deep holes and possible clogging. Unless the hole depth is very deep, these are usually considered unimportant and t

17、he force and torque can be taken as constant.15.25 Describe your observations concerning the contents of Tables 23.2 and 23.4, and explain why those particular recommendations are made. By the student. Some observations are listed below:Machining Processes Used to Produce Round Shapes 234 Referring

18、to Table 23.2 on p. 619, note that the side rake angle is high for aluminum but low for titanium. This can be explained by the benets of maintaining higher compression on the shear plane for titanium (to obtain higher ductility), a situation not needed for aluminum. Note from Table 23.4 on p. 622 th

19、at the cutting speeds for steels are much lower than those for copper alloys. This can be explained by power requirements associated with machining steels. Note that the tools used in Table 23.4 vary by workpiece material. For example, no diamond is listed for steel, explainable by the solubility of

20、 carbon in steel at elevated temperatures.第十六章16.13 Explain why broaching crankshaft bearings is an attractive alternative to other machining processes. Broaching (Section 24.4 on p. 675) has certain advantages such as capability to remove material at high volume rates in one setup and with good sur

21、face nish of the product. Turn broaching is the term used for broaching the bearing surfaces of crankshafts and similar parts (see bottom of p. 676) and is an ecient process because multiple broaches can be used and thus production rate is high. For example, the photograph below is Fig. 23.25 of the

22、 4th edition of this text, and shows a number of broaches acting simultaneously on the bearing surfaces of an automotive crankshaft.16.25 With appropriate sketches, explain the dierences between and similarities among shaving, broaching, and turn-broaching operations. By the student. Note, for examp

23、le, that the similarities are generally in the mechanics of cutting, involving a nite width chip and usually orthogonal cutting. The dierences include particulars of tooling design, the machinery used, and workpiece shapes.第十八章18.25 Describe the factors involved in a grinding wheel acting “soft” or

24、acting “hard.”An individual grinding wheel can act soft or hard depending on the particular grinding conditions. The greater the force on the grinding wheel grains, the softer the wheel acts; thus, a grinding wheel will act softer as the workpiece material strength, work speed, and depth of cut incr

25、ease. It will act harder as the wheel speed and wheel diameter increase. Equation (9.6) gives the relationship between grain force and the process parameters. See also Section 9.5.2.18.30 What diculties, if any, could you encounter in grinding thermoplastics? Thermosets? Ceramics? Refer to Section 26.3.4 on p. 734 on grindability of materials and wheel selection, and also compare with Section 21.7.3 on p. 586. Some of the diculties encountered are:Abrasive Machining and Finishing Op