机械专业英语卷试题

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Text 1

A body that is completely free in space has twelve degrees of freedom. It can rotate about or have linear movement along each of the three mutually perpendicular axes XX, YY or ZZ, so it has six freedoms of rotation and six freedoms of translation. When workpiece is located, it must be constrained from moving in any direction, so these freedoms are eliminated or restricted to ensure that the operation is performed with the required accuracy. This can be done by six locations in the case of the body shown in Fig.8.1, which is known as six-point locating principle. It is illustrated in Fig.8.2.

The base of the component is resting on three locating pins which is the minimum number of points upon which it will foxily seat. The three adjacent locating surfaces of the workpiece art resting against 3, 2 and 1 pint respectively, which prevent 9 degrees of freedom. The test three degrees of freedom are arrested by three external forces usually provided directly by clamping. Some of such forces may be attained by friction. If more than six points art used, the additional points will be surplus and unnecessary and would therefore be redundant constraints.

There are three general forms of location: plane, concentric, and radial. Plane locators locate a workpiece from any surface. The surface may be flat, curved, or have an irregular contour. In most applications, plane-locating devices locate a part by its external surfaces, Fig.8.3a.Concentric locators, for the most part, locate a workpiece from a central axis. This axis may or may not be in the center of the workpiece. The most-common type of concentric location is a locating pin placed in a bole. Some workpieces, however, might have a cylindrical projection that requires a locating hole in the fixture, as shown in Fig.8.3b. The third type of location is radial. Radial locators restrict the movement of a workpiece around a concentric locator, Fig.8.3c. In many cases, locating is performed by combination of the three locating methods.

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Question 1

Which sentence is not right? ( )

A. Radial locators restrict the movement of a workpiece around a concentric locator. B. In many cases, locating is performed by combination of three locating methods. C. Plane locators locate a workpiece from flat surface, but not curved surface.

D. The workpiece which has a cylindrical projection requires a locating hole in the fixture.

Question 2

What the word “perpendicular” means in the 1st sentence of the 1st paragraph? ( ) A. 平行的 B. 交叉的 C. 垂直的 D. 倾斜的

Question 3

How many rotation degrees of freedom have a body completely free in space? ( ) A. twelve. B. six. C. three. D. one.

Question 4

Which is not the one of three general forms of location? ( ) A. plane B. concentric C. radial D. point

Text 2

As with location, clamping will influence the accuracy and quality of the workpiece and will further influence substantially the speed and efficiency of the operation being carried out on the workpiece. The process of clamping induces a locking effect which, through frictional or some

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other forms of mechanism, provides a stability of location which cannot be change until and unless external loading is able to overcome the locking effect. Hence when a cutting force is producing a load or moment on the workpiece,格化it is necessary that a sufficient clamping force must be exerted to withstand such actions.Fixtures are used to restrict the freedoms of the workpiece to be machined and locate the workpiece. Clamping device, however, is used to ensure that the fixture, workpiece and location features will not be distorted or damaged under the action of cutting forces, gravity, inertial force and centrifugal force etc.[5]This means that clamping forces should not be excessive but sufficient to hold the workpiece rigidly and should be applied at the points where the workpiece has the support from the solid metal of the fixture body. Clamping forces should be directed towards supporting and locating elements on overhanging or thin sections of the workpiece. In addition, the force should be transmitted to the rigid sections of the fixture body frame.

Cylindrical workpieces located in V-blocks can be clamped using another V-block or clamped in a 3-jaw chuck. The latter is usually more common, especially in turning operations.

Question 5

What the phrase “V-blocks” means in the last sentence of the last paragraph? ( ) A. V型塞 B. V型码 C. V型块 D. V型规

Question 6

Which force could not damage workpiece and location features? ( ) A. cutting forces B. gravity

C. inertial force D. frictional force

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Question 7

On which kind of machine could the “3-jaw chuck” be used on? ( ) A. turning machine B. milling machine C. drilling machine D. Grinding machine

Question 8

Which sentence is not right? ( )

A. Locking effect provides a stability of location which cannot be change until external loading is able to overcome the locking effect.

B. Locking effect should be produced by mechanism when the frictional force is overcome the external loading.

C. Locking effect can be provided in frictional or some other forms of mechanism.

D. Clamping forces should be directed towards supporting and locating elements on overhanging or thin sections of the workpiece.

Text 3

The main components of a fixture include locators, clamping device, guiding and tool-setting elements, fixture body, connecting elements and other components and devices.

Locator. A locator is usually a fixed component of a fixture. It is used to establish and maintain the position of a part in the fixture by constraining the movement of the part through directly contacting or fitting with the locating surface on the workpiece. For workpieces of greater variability in shapes and surface conditions, a locator can also be adjustable.

Clamping device. A clamp is a force-actuating mechanism of a fixture. The forces exerted by the clamps hold a workpiece securely in the fixture against all other external forces to prevent the position of workpiece from changing during the machining operation.

Guiding and Tool-setting Elements. It is used to specify the position of cutting tool relative to the fixture, such as jig bush.

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Fixture Body. Fixture body, or tool body, is the major structural element of a fixture .It maintains the spatial relationship between the fixture elements mentioned above, viz, locators, clamps supports, and the machine tool on which the part is to be processed.

Connecting Elements. Connecting Elements are used to specify the position of a fixture relative to machine tool and to fix the machine tool, such as orienting keys, T-bolts.

Other Components or Devices. Other components or devices are used to load and unload workpiece or meet others needs during machining. Such as auxiliary support, loading/unloading device, and indexing device etc.

Question 9

Which sentence is right to T-bolts of the fixture? ( ) A. It is used to load and unload workpiece

B. It is used to specify the position of cutting tool relative to the fixture C. It is a force-actuating mechanism of a fixture. D. It can be used to fix fixture to the machine.

Question 10

Which component does jig bush belong to? ( ) A. locators

B. clamping device

C. guiding and tool-setting elements D. fixture body

Question 11

Which is used to to prevent the position of workpiece from changing during the machining operation ? ( ) A. locators

B. clamping device

C. guiding and tool-setting elements D. fixture body

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