机械双语试卷.

1、Manufacturing Engineering and TechnologyMachiningTest Paper(2004-06-17)1 Drawing and marking (Close Test. 10 marks)1.1 Fig 1a) shows a turning tool. Please mark the tool angles (rake angle, cutting edge angle, tool cutting edge inclination angle and minor cutting edge angle) in Fig 1b). (5 marks)1.2

2、 Pointing the process methods and marking the main motions in Fig 2. (5 marks)2 Judging. Marking for true and × for false. (Close Test. 30 marks, 2 marks for each)2.1 The built-up edge is one of the factors that most adversely affecting surface finish in cutting. ()2.2 When continuous chip are

3、formed, the machine tool is easier to vibrate and chatter than the case in which discontinous chips are formed. (×)2.3 In turning the highest temperature is usually found in the middle of crater wear area rather than the tool corner. ()2.4 When using carbide inserts to hard turning, we should c

4、ool the cutting zone with cutting fluid discontinously. (×)2.5 In surface grinding we should use oils as grinding fluids and in thread grinding we should use water-based emulsions. (×)2.6 Indexable carbide inserts are usually brazed to the tool shank. (×)2.7 Diamond tools are usually

5、used to finish-machining cast iron and steels. (×)2.8 the most important limitation of high-speed steel is the cutting speeds that can be employed, which are low relative to those of carbide tools. ()2.9 In a planer, the workpiece is mounted on a table that travels along a straight path; in a s

6、haper, the tool travels along a straight path, and the workpiece is stationary. ()2.10 Three-jaw chucks have jaws that can be moved and adjusted independently of each other; they can be used for square or odd-shaped workpieces. (×)2.11 For drilling, reaming and tapping, blind holes must be dril

7、led deeper than subsequent reaming or tapping operations that may be performed. ()2.12 In conventional milling (up milling), the feed direction is same as the cutting direction. (×)2.13 The broaching operation can be used to machine internal and external surfaces, such as holes of circular, squ

8、are, keyways, and flat surfaces. ()2.14 In gear hobing, the gear blank rotation is main cutting motion, while the hob rotation is feed motion. (×)2.15 A hard grinding wheel means its abrasive particles have very high hardness. (×)3 Qualitative problems (Close Test. 20 marks, 4 marks for ea

9、ch)3.1 Why is it not always advisable to increase cutting speed in order to increase production rate?Answer: Because cutting temperature will be obviously raised with the increase of cutting speed, which has a great and adverse influence on tool life so that we have to resharpen or replace tool ofte

10、n. Then the production rate may not be increased finally and a poor machined surface is generated. 3.2 Which tool materials would be suitable for interrupted cutting operations? Why?Answer: The tool materials having good toughness such as HSS, whisker-reinforced nanocrystalline tool materials, would

11、 be suitable for interrupted cutting operation. Because in interrupted cutting the tool will suffer impact coming from workpiece, if the tool has no enough impact toughness it will break, generally, chipping will occur in its edges or nose. 3.3 Describe the conditions under which broaching would be

12、the preferred method of machining.Answer: The conditions which broaching would be the preferred consideration include: a large numbers of workpiece will be broached; there are high requirements on dimension accuracy and machined surface finish for the workpiece; the the workpiece has a suitable stru

13、cture so that it can be clamped securely in broaching machine, and it should have sufficient strength and stiffness to withstand cutting forces during broaching. 3.4 Why is the stiffness of machine tool important in machining operations?Answer: Because low stiffness of machine tool will result in la

14、rger magnitudes of vibration and chatter in cutting tools and machines, and can have adverse effects on product quality. The possible troubles include poor machined surface finish, loss of dimension accuracy of the workpiece, premature wear, chipping and failure of the cutting tool, damage to the ma

15、chine components and objectionable noise, etc. 3.5 It is generally recommended that, when grinding hardened steels, the grinding wheel should be of a relatively soft grade. Explain the reason.Answer: The grade of a grinding wheel is a measure of the bonds strength. A softer wheel has a weaker bond a

16、nd /or a less amount of bonding material. It is recommended for harder workpiece such as hardened steel, because the dull grains are easily dislodged and other sharp grains can contact the workpiece to remove chips continually, so as to reduce residual stresses and thermal damage to the workpiece. 4

17、 Synthesis and design (Open Test. 30 marks, 15 marks for each)Observing Fig 3. The a) and b) show two cutting tools, and the c) and d) show two parts. Choose one from a), b) and one from c),d) to do your design.1) Which kind is the cutting tool? What operation can be done with the cutting tool? Acco

18、rding with the tool materials and geometries, analyze the applied performance of the tool.2) The part c) is made from normal medium carbon steel, 5 pieces are required; the part d) is made from wrought aluminum, 10,000 are required. Please choose suitable process methods to machine the part, and arr

19、ange the process routing for it. a) b) c) d)Fig. 31) a) It is a turning tool (left offset tool). The tool shank is made from medium carbon steel and there is a rhombic carbide insert clamped on the shank by a clamp screw. The insert is indexable and has four cutting edges, when one of its edge becom

20、es dull, another sharp edge can be indexed to use. The tool has a positive working rake angle and clearance angle, and a sharp corner, it can be used for external cylindrical or taper surface turning or facing. The tool has a 90°cutting edge angle, so it can be used to turn 90°stage surfac

21、e. The tool is suitable to cutting cast irons or steels at higher cutting speeds and larger back engagements of the cutting edges, but had better to avoid cutting discontinuously; it is suitable for dry cutting or turning with cutting fluids, but should avoid cooling discontinuously. Because carbide

22、 insert is hard and brittle, special attention should be given to proper mounting and using the tool in order to prevent from impact and vibrating as well heat stress.b) It is an end milling cutter and made from HSS. It has a solid structure and flat end, four helical cutting edges. It can be holden

23、 by a collet or special chuck, cut workpiece with its circumferential cutting edges. It can be used to mill plane, side surface and curved surface as well slot, but is not suitable to feed in axial direction. It is suitable to cutting nonferrous alloys, also ferrous alloys such as cast irons and mil

24、d or medium carbon steels. Because its hot hardness is low relatively, it is suitable to cut at lower cutting speeds and needs cooling continuously. However, it possesses good impact toughness, so, it can be used to cut discontinuously. 2) c) The part has a stepped cylindrical shape, so it can be pr

25、oduced by turning. Only 5 pieces are needed, we can choose an energy lathe to make it with P-type carbide insert or a HSS solid tool, and choose a rolled stock as the blank. Because the part has a severe shape and position tolerance, so the left end face and cylindrical surface should be completed i

26、n one setup of the part. The through hole has a higher finish requirement, after drilling a finish turning is needed. In addition, screw threading and chamfer are needed. Machining routing: Sawing the blank (longer than 5 times of the part)holding the blank with a three chuck in lathe, let the overh

27、ang be little longer than the final length of the partfacing one endrough-turning external surfacesmedium finish-turning the50 external cylindrical surface to the dimension for threading M50finish turning the 44 segment to dimension accuracy and the step face with a left offset toolcoringdrilling th

28、e through holeinternal turning the holechamferinggrooving in the50 external surfacescrew threadingpartingturning around the workpiece and chamfering another end.d) The part is made from wrought aluminum alloy, a quantity of 10,000 pieces and a roughness of Ra 1.6 is required, so some economic proces

29、ses such as extrusion should be used to produce the blank and a semi-finish-machining, finish-machining process should be applied. The through hole should be per-formed in the blank, then, the final dimension including the keyway may be broached optimally. There is no finish requirement for its exte

30、rnal cylindrical surface and side surfaces, so these surfaces do not need to be machined. The three end faces marked Ra3.2 can be are produced with end milling cuter (the left end face and right cylindrical end face also can be produced with face milling). In order to obtain a high machining efficie

31、ncy, a special fixture should be designed for fixing the workpiece on milling machine.Machining routing: fixing the workpiece on a vertical milling machine, milling the left end faceturning around the workpiece, milling the right plane and cylindrical end facemounting the workpiece on a broaching ma

32、chine, broaching the through hole and the keyway.5 Comprehension and discussion (10 marks)As you can appreciate, the cost of machining centers is considerably higher than more traditional machine tools. In view of the fact that many operations performed by these centers can also be done on conventio

33、nal machines, how would you go about justifying the high cost of these centers? Do you think under what condition we should purchase a precise and expensive machining center, and when we should use an economic machining center, even traditional machine tools only?Answer outline: Machinine efficiency

34、Machining accuracy and roughnessAutomationMultiple functionsMachining time, labor, workshop areaManufacturing Engineering and TechnologyMachiningTest Paper(2005-06-14)Name: Student No: Score:1. Drawing and marking (Close Test. 15 markings)1.1 Fig 1a) shows a turning tool. Please mark its major cutti

35、ng edge and minor cutting edge, rake face and major flank, cutting edge angle, rake angle and clearance angle. ( 3.5 markings)1.2 Give the process method name, mark the main motion and feed motion(s) for each illustration in Fig 2. (6.5 markings)1.3 There is a poor design consideration for each of t

36、he following workpieces, mark it and give your correction (5 markings).(a) to be threaded (b) to be shaped (c) gear to be generated (d) to be drilled (e) cavity to be milled (by end milling cutter)2. Judging. Mark for true and × for false. (Close Test. 30 markings, 2 markings for each)2.1 It is

37、 always advisable to increase cutting speed in order to increase production rate. (×)2.2 Long, continuous chips are undesirable because they tend to become entangled and interfere with cutting operations. ()2.3 Tool with high brittleness and hardness, or large positive rake angle is easy to chi

38、pping. ()2.4 When using carbide inserts to hard turning, we should cool the cutting zone with cutting fluid discontinously. (×)2.5 In surface grinding we should use oils as grinding fluids and in thread grinding we should use water-based emulsions. (×)2.6 Coated tools have unique propertie

39、s, such as lower friction and higher resistance to cracks and wear, they can be used at high cutting speeds, reducing required machining time and costs. ()2.7 Diamond tools are usually used to finish-machining cast iron and steels. (×)2.8 In machining, workpieces made from aluminum and magnesiu

40、m alloys have less tendency to chatter than do workpieces made from high carbon steel and cast iron. ()2.9 In a planer, the workpiece is mounted on a table that travels along a straight path; in a shaper, the tool travels along a straight path, and the workpiece is stationary. ()2.10 Collet is a lon

41、gitudinally-spit tapered bushing, it usually used for holding round tools or workpieces having a small diameter. ()2.11 If an existing hole has centerline deflection, we can correct it by reaming, while boring can only make an existing hole dimensionally more accurate. (×)2.12 In conventional m

42、illing (up milling), the feed direction is same as the cutting direction. (×)2.13 End milling is a versatile process, the production of cavities in forging or casting dies is usually done using ballnose end milling at high speed. ()2.14 Hobbing is one of gear generating methods, which produces

43、a variety of gears rapidly and with good dimensional accuracy. ()2.15 A hard grinding wheel means its abrasive particles have very high hardness. (×)3. Qualitative problems (Open Test. 20 markings, 4 markings for each)3.1 List the factors that contribute to poor surface finish in cutting.Answer

44、: a) geometric factors such as a large feed and back engagement of tool edge, too small radius of tool nose or too large cutting edge angle, dull tool edge or tool chipping, built-up edge; b) physical factors such as too hard or too soft workpiece material, improperly using cutting fluid; c) vibrati

45、on and chatter in cutting. 3.2 Which tool materials would be suitable for interrupted cutting operations? Why?Answer: The tool materials having good toughness such as HSS, whisker-reinforced nanocrystalline tool materials, would be suitable for interrupted cutting operation. Because in interrupted c

46、utting the tool will suffer impact coming from workpiece, if the tool has no enough impact toughness it will break, generally, chipping will occur in its edges or nose.3.3 Describe the conditions under which broaching would be the preferred method of machining.Answer: The conditions which broaching

47、would be the preferred consideration include: a large numbers of workpiece will be broached; there are high requirements on dimension accuracy and machined surface finish for the workpiece; the the workpiece has a suitable structure so that it can be clamped securely in broaching machine, and it sho

48、uld have sufficient strength and stiffness to withstand cutting forces during broaching. 3.4 We know that we may be able to decrease machining costs by increasing cutting speed. Explain which costs are likely to change, and how, as the cutting speed increases.Answer: Machining cost may be decreased

49、by increasing cutting speed, because the machining time for per piece decreases due to the high production rate. However, also other variables may change with cutting speed. As cutting speed increases, the tool life generally decreases, then the tool cost will increase, as does the tool-changing cos

50、t. So, machining cost does not always decrease as the cutting speed increases.3.5 It is generally recommended that, when grinding hardened steels, the grinding wheel should be of a relatively soft grade. Explain the reason.Answer: The grade of a grinding wheel is a measure of the bonds strength. A s

51、ofter wheel has a weaker bond and /or a less amount of bonding material. It is recommended for harder workpiece such as hardened steel, because the dull grains are easily dislodged and other sharp grains can contact the workpiece to remove chips continually, so as to reduce residual stresses and the

52、rmal damage to the workpiece.4. Synthesis and design (Open Test. 25 markings)1) There are four kinds of tool used to produce round shapes in Fig.3. Please give their names and analyze their applied performances. (12 markings, 3 markings for each) a) b) c) d)Fig 3Answer: a) is a twist drill. It can b

53、e used to make hole in solid workpiece, the hole has a same dimension as the drill nominally but its accuracy and finish are not good. b) is a boring bar with a carbide insert. It can be used to produce circular internal profiles in hollow workpieces or on a hole made by drilling, good machining acc

54、uracy and finish may be obtained with the tool. c) is a helical reamer. It can be used to make an existing hole dimensionally more accurate than can be obtained by drilling alone and improve its surface finish. d) is a tap. It is a chip-producing threading tool with multiple cutting teeth and can be

55、 used to produce internal thread in workpiece. 2) The part illustrated in Fig.4 is made from normal medium carbon steel, 2 pieces are required. Please choose suitable process method, tools and fixtures to machine the part, and arrange the process routing for it. (13 markings).Fig. 4Answer: Processes

56、: the part is a solid and round shaft and made from normal medium carbon steel, only 2 pieces are required, therefore, its main machining processes are cylindrical surface turning and grinding. Machine: the part is not large, we can utilize a horizontal engine lathe and a cylindrical grinder to turn

57、 and grind it.Cutting tools: facing tool, 45°bent tool, carbide insert type P10 (YT15) , or HSS; center drill, HSS;rough-turning tool for cylindrical surface, 90°offset tool, carbide insert type P30 (YT5);semi-finish turning tool for cylindrical surface, 90°offset tool, carbide insert

58、 type P10 (YT15); grooving and cut-off tool, carbide insert type P10 (YT15) or high-speed steel;thread cutter, P10 (YT15) carbide or HSS;rough-grinding wheel, A36G10V（aluminum-oxide, coarser abrasive grain size, softer grade, smaller dense, vitrified bond）;finish-grinding wheel, straight cylindrical grinding face, A80Q5V（aluminum-oxide, finer abrasive grain size, harder grade, denser structure, vitrified bond）.Fixtures: The part is not large has no shape and position tolerance,