Question

solve these Qa please

8. What are the main sections of the machine tools? 9. What are the advantages of using the numerical controlled machine tools? 10. Classify the types of stresses which produced during machining to deform the machine tools or a WP?

Answer 1

     9.The various sections that are used in machine tools are:
1. Work holding device:
Work holding devices are used to hold the work-piece in the correct orientation to achieve the required accuracy in manufacturing.
Example: chuck

2. Tool holding device
Tool holding devices are used to hold the cutting tool in the correct position with respect to the workpiece and to provide enough holding force to contract the cutting forces acting on the tool.
Example: Tool post

3. Work motion mechanism
Work motion mechanism is generally used to provide the necessary speed to the workpiece for generating the required surface.
Example: headstock

4. Tool motion mechanism
Tool motion mechanism is generally used to support all the mechanisms and to maintain the relative position with respect to each other and to allow for relative movement between the various parts.

5. Support structures
Support structures are used to support all the mechanisms and to maintain the relative position with respect to each other and to allow for relative movement between the various parts.
Example: Bed.

10.The advantages of NC machines are;

1. Greater operator safety:

The numerical control system is operated from a remote station which in itself is a built-in safety factor. The operator's attention to the various functions of the machine tool are drastically reduced or eliminated. The operator is exposed less frequently to moving machine elements or to the cutting tools.

2. Greater operator efficiency:

Since a numerically controlled machine requires less attention, the operator can perform other tasks while the machine is operating. In some cases, the operator may be in charge of two or more machines.

3. Reduction of scrap:

It has been shown that through the consistent high accuracy of numerically controlled machines and the elimination of most of the human errors, scrap can be reduced to a minimum. Some companies have reduced the number of scrap parts produced on numerically controlled machines, as compared to conventional machines, by as much as 50 to 60 percent.

4. Reduced lead time for production:

The set up and tape preparation time for numerically controlled machines is usually short. Frequently very few jigs or fixtures are required. The jigs and fixtures which may be needed are usually standard and are readily available from the tool room. The tape may be filed for future production runs and requires very little storage space in the tool room.

5. Fewer chances for human error:

The numerical control machine operator is not asked to take trial cuts, make trial measurements, or make positioning movements. All of these are included in the programmed tape which controls the machine. The N/C system also relieves the operator of tool indexing, selecting the sequence of operations and other routine functions.

6. Maximal accuracy and interchangeability of parts:

The improvement of the accuracy of the parts produced by numerical control is almost automatic. More uniform quality is achieved because all parts are produced from the same tape, under the same conditions, and accuracy is maintained within the limits of the tooling and the machine tool. Consequently, interchanging of parts is possible.

7. Lower tooling costs:

Only simplified holding fixtures are usually required with numerically controlled machines. Tool fixture design may be reduced by as much as 70 percent, thereby reducing the work load on the drafting and tool departments, which would design and build any needed jigs and fixtures.

8. Increased productivity:

Precise tape control of all machine functions enables parts to be produced faster, with less setup and lead time than is possible with a hand operated machine.

9. Minimal spare parts inventory:

A large spare parts inventory is unnecessary. Additional quantities of spare parts may be produced by withdrawing from storage. tapes used for the original quantity produced.

10. Greater machine tool safety:

The possibility of an operator error which could result in damage to the machine is reduced in proportion to the greatly lowered need for human intervention.

11. Fewer man hours for inspection functions:

The production of uniform quality parts leads to reduced inspection time. Field experience has shown that once the programmed numerical control tape has been tested, little other checking is necessary within the expected tool life. Fewer parts in each job lot will need to be inspected. Many parts will require inspection of critical hole size and dowel hole positions only. In general, inspection time may be reduced by about one-half.

12. Greater machine utilization:

Numerical control requires less setup time for tooling, and production time may go as high as 75 to 80 percent up time. Some companies have found it possible to use fewer machines to complete the same amount of production.

11 The stresses acting on the worpieces are

a) compressive stresses during holding due to chuck or any other work holding devices.

b)shear stresses due to which removal of material takes place .This is due to shear action of tool on workpiece

Hope you understand the topic.Please do vote .Thank You.