机械制造技术基础(试题1-3)复习资料

机械制造技术基础（试题1）

班级姓名学号成绩

一、填空选择题（30分）

1．刀具后角是指。

2．衡量切削变形的方法有两种，当切削速度提高时，切削变形（增加、减少）。

3．精车铸铁时应选用（YG3、YT10、YG8）；粗车钢时，应选用（YT5、YG6、YT30）。

4．当进给量增加时，切削力（增加、减少），切削温度（增加、减少）。

5．粗磨时，应选择（软、硬）砂轮，精磨时应选择（紧密、疏松）组织砂轮。

6．合理的刀具耐用度包括与两种。

7．转位车刀的切削性能比焊接车刀（好，差），粗加工孔时，应选择（拉刀、麻花钻）刀具。

8．机床型号由与按一定规律排列组成，其中符号C代表（车床、钻床）。

9．滚斜齿与滚直齿的区别在于多了一条（范成运动、附加运动）传动链。滚齿时，刀具与工件之间的相对运动称（成形运动、辅助运动）。

10．进行精加工时，应选择（水溶液，切削油），为改善切削加工性，对高碳钢材料应进行（退火，淬火）处理。

11．定位基准与工序基准不一致引起的定位误差称（基准不重合、基准位置）误差，工件以平面定位时，可以不考虑（基准不重合、基准位置）误差。

12．机床制造误差是属于（系统、随机）误差，一般工艺能力系数C p应不低于（二级、三级）。

13．在常用三种夹紧机构中，增力特性最好的是机构，动作最快的是

机构。

14．一个浮动支承可以消除（0、1、2）个自由度，一个长的v型块可消除（3，4，5）个自由度。

15．工艺过程是指

。

1

二、外圆车刀切削部分结构由哪些部分组成？绘图表示外圆车刀的六个基本角度。（8分）

三、简述切削变形的变化规律，积屑瘤对变形有什么影响？（8分）

四、CA6140车床主传动系统如下所示，试列出正向转动时主传动路线及计算出最高转速与

最低转速。（8分）

五、什么叫刚度？机床刚度曲线有什么特点？（8分）

六、加工下述零件，以B面定位，加工表面A，保证尺寸10＋0.2mm，试画出尺寸链并求出工序尺寸L及公差。（8分）

2

3

七、在一圆环形工件上铣键槽，用心轴定位，要求保证尺寸34.8-0.16mm ，试计算定位误差并分析这种定位是否可行。（8分）

°

八、试制定图示零件（单件小批生产）的工艺路线。（12分）

°

九、在六角自动车床上加工一批1803.008

.0φ+-mm 滚子，用抽样检验并计算得到全部工件的平

均尺寸为Φ17.979mm ，均方根偏差为0.04mm ，求尺寸分散范围与废品率。

试题1参考答案

一．

1．后刀面与切削平面间的夹角。 2. 变形系数与滑移系数，减少 3.YG3，YT5 4．增加，增加 5. 软，紧密 6.Tc，Tp 7. 好，麻花钻8．字母，数字，车床9.附加运动，成型运动10. 切削油，退火

11．基准不重合，基准位置12. 系统，二级13. 螺旋，圆偏心

14．1，4 15. 用机械加工方法直接改变原材料或毛坯的形状、尺寸和性能，使之成为合格零件的过程。

二．

外圆车刀的切削部分结构由前刀面、后刀面、付后刀面、主切削刃、付切削刃与刀尖组成。六个基本角度是：r o、αo、kr、kr’、λs、αo’

三．

变形规律：r o↑，Λh↓；Vc↑，Λh↓；f↑, Λh↓; HB↑, Λh↓

积屑瘤高度Hb↑,引起刀具前角增加，使Λh↓

四．

最高转速约1400r/min，最低转速约10r/min

五．

刚度是指切削力在加工表面法向分力，Fr与法向的变形Y的比值。

机床刚度曲线特点：刚度曲线不是直线；加载与卸载曲线不重合；载荷去除后，变形恢复不到起点。

六．

2201.0

L＝mm

七．

Δ定＝0.022mm，定位装置可行。

八．

工序1：粗车各外圆、端面、Φ60圆孔；精车Φ200外圆与端面，精镗Φ60孔；精车Φ96外圆、端面B与端面C（车床）

工序2：插槽（插床）

工序3：钻6－Φ20孔（钻床）

工序4：去毛刺（钳工台）

九．

尺寸分散范围：17.859－18.099mm

废品率： 17.3%

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机械制造技术基础（试题2）

班级姓名学号成绩

一、填空选择题（30分）

1．工序是指

。

2．剪切角增大，表明切削变形（增大，减少）；当切削速度提高时，切削变形（增大，减少）。

3．当高速切削时，宜选用（高速钢，硬质合金）刀具；粗车钢时，应选用（YT5、YG6、YT30）。

4．CA6140车床可加工、、、等四种螺纹。

5．不经修配与调整即能达到装配精度的方法称为（互换法、选配法）。

6．当主偏角增大时，刀具耐用度（增加，减少），当切削温度提高时，耐用度（增加、减少）。7．在四种车刀中，转位车刀的切削性能（最好，最差）；粗磨时应选择（硬，软）砂轮。8．机床的基本参数包括、、。

9．滚齿时，刀具与工件之间的相对运动称（成形运动、辅助运动）。滚斜齿与滚直齿的区别在于多了一条（范成运动、附加运动）传动链。

10．衡量已加工表面质量的指标有

。

11．定位基准面和定位元件制造误差引起的定位误差称（基准不重合、基准位置）误差，工件以平面定位时，可以不考虑（基准不重合、基准位置）误差。

12．测量误差是属于（系统、随机）误差，对误差影响最大的方向称方向。

13．夹紧力的方向应与切削力方向（相同，相反），夹紧力的作用点应该（靠近，远离）工件加工表面。

14．辅助支承可以消除（0、1、2）个自由度，限制同一自由度的定位称（完全定位、过定位）。

15．磨削加工时，应选择（乳化液，切削油），为改善切削加工性，对不锈钢进行（退火，淬火）处理。

5

6 二、端面车刀的切削部分的结构由哪些部分组成？绘图表示表示端面车刀的六个基本角度。

（8分）

三、金属切削过程的本质是什么？如何减少金属切削变形？（8分）

四、列出切削英制螺纹的运动方程式，并写出CA6140车床进给箱中增倍变速组的四种传动

比。（8分）

五、加工下述零件，要求保证孔的尺寸B ＝30＋0.2，试画出尺寸链，并求工序尺寸L 。（8分）

六、磨一批d ＝12016

.0043.0φ--mm 销轴，工件尺寸呈正态分布，工件的平均尺寸X ＝11.974，均

方根偏差σ＝0.005，请分析改工序的加工质量。如何加以改进。（8分）

七、滚斜齿时需要多少种运动？列出每条运动链的首末端元件及计算位移。（8分）

八、制订下述零件的机械加工工艺过程，具体条件：45钢，圆料ф70，单件生产。（12分）

九．在一杆状形工件铣键槽，要求保证尺寸50-0.2mm与34.8-0.16mm，设计该工件的定位方案，并进行定位误差分析。（10分）

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试题2参考答案

一．

1．一个工人在一台机床上对一个（或多个）零件所连续完成的那部分工艺过程。

2．减少，减少 3.硬质合金，YT5 4.公制，英制，模数和径节

5．互换性 6.减少，减少7.最好，软

8．尺寸，运动，动力9.成型运动，附加运动10.表面层几何形状特征，表面层物理机械性能11.基准位置，基准位置12.随机，误差敏感

13.相同，靠近14.0，过定位15.乳化液，调质

二．

端面车刀切削部分结构由前刀面、后刀面、付后刀面、主切削刃，付切削刃与刀尖构成。端面车刀的六个基本角度：r o、αo、kr、kr’、λs、αo’

三．

被切金属在刀刃的挤压作用下，产生剪切滑移变形，并转变为切屑的过程。要减少切削变形，可增大前角，提高速度，增大进给量，适当提高工件材料硬度。

四．

u1 ＝18/45×15/48, u2 ＝28/35×15/48 u3 = 18/45×35/28

u4 ＝28/35×35/28

五．

6004.008.0--

L ＝mm

六．

废品率等于2.28％，改进措施：将算术平均值移至公差带中心，即使砂轮向前移动Δ，

Δ＝0.0035mm。

七．

滚齿时需要四种运动：

1．主运动电动机（n电）－滚刀（n刀）

2．范成运动滚刀（1/k r）－工件（1/Z k）

3．进给运动工件（1 r）－刀架（f）

4．差动运动刀架（L）－工件（1 r）

八．

工序1：粗测各外圆、端面、钻Φ14孔，精车Φ40外圆及端面；以Φ40为基准面，精镗Φ30孔，精车Φ60及端面（车床）。

工序2：铣键槽（铣床）

工序3：钻4－Φ6孔（钻床）

工序4：去毛刺（钳工台）

九．

用V型块及支承钉定位，定位误差等于0.0034mm，符合要求，定位方案可行。

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机械制造技术基础（试题3）

班级姓名学号成绩

一、填空选择题（30分）

1．刀具前角是指，用符号表示。

2．当工件材料硬度提高时，切削力（增加，减少）；

当切削速度提高时，切削变形（增加、减少）。

3．制造复杂刀具宜选用（高速钢、硬质合金）；粗车钢时，应选用（YT5、YG6、YT30）。4．为改善切削加工性，对高碳钢采取（淬火，退火）处理；对不锈钢（淬火，调质）处理。5．粗加工时应选择（水溶液、切削油），粗磨时，应选择（软、硬）砂轮。

6．精基准的选择原则是。7．进给量越大，表面粗糙度（愈高，愈低）；精加工孔时，应选择（拉刀、麻花钻）刀具。8．机床的运动按其功用可分为与两大类。

9．滚斜齿与滚直齿的区别在于多了一条（范成运动、附加运动）传动链。滚齿时，刀具与工件之间的相对运动称（成形运动、辅助运动）。

10．在CA6140车床上加工公制螺纹时，所用挂轮是（63/100×100/75, 100/100×100/100）。

11．夹紧力作用点应（靠近，远离）工件的加工表面；工件以平面定位时，可以不考虑（基准不重合、基准位置）误差。

12．完全互换法适用于（大量，单件）生产，所有零件公差之和应（大于，小于）装配公差。13．工艺系统刚度等于（Fy/y，Fz/y），工艺系统刚度大，误差复映（大，小）。

14．一个支承钉可以消除（0、1、2）个自由度，消除六个自由度的定位称（完全定位、过定位）。

15．生产类型通常分为、、三种。

9

二、切断车刀切削部分结构由哪些部分组成？绘图表示切断车刀的六个基本角度。（8分）

三、量度切削变形的方法有几种？各有什么特点？能否全面衡量金属切削过程的物理本质？（8分）

四、列出切削公制螺纹的运动方程式，并写出CA6140车床进给箱中基本变速

组的八种传动比。（8分）

五、在热平衡条件下，磨一批Φ18-0.035的光轴，工件尺寸呈正态分布，现测得

平均尺寸X＝17.975，标准偏差σ＝0.01，试计算工件的分散尺寸范围与废

六、加工下述零件，以B面定位，加工表面A，保证尺寸10＋0.2mm，试画出尺寸链并求出工序尺寸L及公差。（8分）

10

七、指出下列定位方案所消除的自由度。（8分）

八、根据所学知识，列出提高零件加工质量的措施。（10分）

九、图示拨叉零件，材料HT300，单件小批生产（12分）

1．对零件进行工艺分析。

2．制订该零件的加工工艺过程。

其余

11

试题3参考答案

一．

1．前刀面与基面的夹角（ro） 2.增加，减少 3.高速钢，YT5

4. 退火，调质

5.水溶液，软

6.基准重合、统一、自为、互为、可靠原则

7.愈高，拉刀

8.成型运动，辅助运动

9. 附加运动，成型运动10.63/100×100/75 11.靠近，基准位置

12.大量，小于13.Fy/y, 小14.1，完全定位

15.单件，成批，大量生产

二．

切断车刀切削部分由前刀面、后刀面、付后刀面、主切削刃、付切削刃与刀尖组成。

切断车刀的六个基本角度：r o、αo、kr、kr’、λs、αo’

三．

量度方法有两种：1.变形系数（简单，直观但结果近似，从塑性压缩方面分析）。

2.滑移系数（复杂，结果较精确，从剪切变形考虑）。

两种方法都有片面性，不能全面反映金属切削过程的物理本质。

四．

u1 = 26/28 u2 = 28/28 u3 = 32/28 u4 = 36/28

u5 = 19/14 u6 = 20/14 u7 = 33/21 u8 = 36/21

五．

分散范围：Φ17.945－Φ18.005mm，废品率为6.2％

六．

301.005.0++

L＝mm

七．

x，y，z，y ，z ；y，z

x，y，z ；x，y，z，x ，y ，z

八．

提高加工精度的措施：减少误差，误差补偿，误差分组，误差转移，就地加工，误差平均，误差控制。

提高表面质量措施：采用合理的切削用量与刀具参数，采用冷压强化与光整工艺，采用良好的切削液，减少积屑瘤、鳞刺和震动。

九．

工序1：粗精铣尺寸40左右端面（铣床）

工序2：钻绞Φ24孔（车床）

工序3：粗精铣尺寸12左右端面、R25圆弧面（铣床）

工序4：钻攻M8螺纹孔（钻床）

工序5：去毛刺（钳工台）

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《Manufacturing Engineering and Technology—Machining》Test Paper

(2004-06-17)

Name: Student No: Score:

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 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 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 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 Indexable carbide inserts are usually brazed to the tool shank. (×)

2.7 Diamond tools are usually 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 shaper, 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 drilled 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. (×)

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2.13 The broaching operation can be used to machine internal and external surfaces, such as holes of circular, square, 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 each)

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 often. 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 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 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 structure 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 larger 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 machine 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 bond’s strength. A softer 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 thermal damage to the workpiece.

4 Synthesis and design (Open Test. 30 marks, 1

5 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? According 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

14

15

machine the part, and arrange the process routing for it.

a) b) c) d)

Fig. 3

1) 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 becomes 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 surface. 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 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 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 mild 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 produced 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 in 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 overhang be little longer than the final length of the part ——facing one end ——rough-turning external surfaces ——medium finish-turning the Ф50 external cylindrical surface to the dimension for threading M50——finish turning the Ф44 segment to dimension accuracy and the step face with a left offset tool ——coring ——drilling the through hole ——internal turning the hole ——chamfering ——grooving in the Ф50 external surface ——screw threading ——parting ——turning 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 processes 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 external 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 efficiency, 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 face——turning around the workpiece, milling the right plane and cylindrical end face——mounting the workpiece on a broaching machine, 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 conventional 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

Machining accuracy and roughness

Automation

Multiple functions

Machining time, labor, workshop area

16

《Manufacturing Engineering and Technology—Machining》Test 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 cutting 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 the 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 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 chipping. (√) 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 properties, 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. (×)

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2.8 In machining, workpieces made from aluminum and magnesium 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 longitudinally-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 milling (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 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: 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) vibration 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 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 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 structure 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 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 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 cost. 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 bond’s strength. A softer wheel has a weaker bond and /or a less amount of bonding material. It is recommended for harder workpiece

18

19 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. 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 3

Answer: a) is a twist drill. It can be 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 accuracy 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 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. 4

Answer:

Processes: 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 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 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, A—36—G—10—V（aluminum-oxide, coarser abrasive grain size, softer grade, smaller dense, vitrified bond）;

finish-grinding wheel, straight cylindrical grinding face, A—80—Q—5—V（aluminum-oxide, finer abrasive grain size, harder grade, denser structure, vitrified bond）.

Fixtures: The part is not large has no shape and position tolerance, it can be holden by a three-jaw chuck.

Machining routing: fixing the blank in lathe and hanging over a length little more than the final dimension of the part→facing→rough-turning cylindrical and taper surfaces→semi-finish-turning and finish-turning partly→grooving→chamfering→ cutting screw thread→turnin g around→chamfering →grinding Ф20 segment to finial dimension accuracy→inspection.

5. Comprehension and discussion (open test, 10 markings)

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 conventional 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

Machining accuracy and roughness

Automation

Multiple functions

Machining time, labor, workshop area

20

21 Final Examination Paper for

“Fundamentals of Machine Manufacturing Technology”

Name Class Serial No points

Close Part (2 Hours, 65 points)

1 Explain the following concepts(10 points)

Rake angle

Tool Reference plane

Down milling

Operation

Insufficient location

2 Answer the following questions(20 points)

(1) What are the functions of cutting fluid?(2points)

(2) What is the hardness of the abrasive wheel?(2points)

(3) What causes the error coping?(2points)

(4) What are the main aspects of machined surface quality? Enumerate and explain the forms of grinding burn.(4poins)

(5) What is up milling and down milling? What are their advantages and disadvantages?(2points)

(6) How does the buildup form? Explain the main factors to affect the formation of buildup.(4points)

(7) What are the main factors influencing the tool life? How do they influence the tool life?(4points)

3 Analysis and calculation(35points)

(1) Draw a schematic Figure to show and explain the external and internal transmission chain when hobbing a straight gear.(10points)

(2) Fig.1 is the schematic figure to show the cutting layer and chip formation. Please impose the forces on the chip and cutting layer to maintain the balance, and explain the influence of the cutting tool geometry(rake angle, relief angle, etc) and cutting parameters( speed, feed, and back engagement) on the cutting forces.(15points)

(3) The material for one part is 2Cr13，and its machining sequence is,（10points ） （a ） boring the inner hole to mm 14.008.31+φ；

（b ） cyaniding （氰化处理），ensure the depth t t δ+0 ；

（c ） grinding the inner hole to dimension mm 035.0010.032+

+φ，and ensure the depth of

cyaniding 0.1~0.3mm ；Draw the dimensional chain and calculate the dimension t t δ0for the

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