Important Questions and Answers: CNC Machines

CNC MACHINES

1. Define numeraical control machine

Numerical control machine cane be defined as a form of programmable machine in which the process are controlled by a program of numbers, letters, and symbols.

2. What is NC part programming?

NC part programming is the step by procedure of by which the sequence of processing steps to be performed on the NC machine is controlled by a program of numbers, letters, and symbols.

3. What is APT language?

APT [automated programming language]is a computer program, it automatically calculates the tool path, generates program and controls the machine by receiving general high level languages.

4. Mention any 4 post processor statement in APT.

COOLNT END FEDRAT/

MACHIN/

RAPID

5. What is CNC?

CNC is system consists of a computer, controller and a NC machine tool. Computer is used to store and edit the program. Controller controls the tool path based on the program.

6. What is meant by machining centre?

The machining centre is CNC system with automatic tool changing arrangement that is designed to perform a verity of machining operations, with large number of cutting tools.

7. What is part program?

Part program is a high level language containing the instructions for machining a part to various standard words, codes and symbols.

8. What is post processing?

Post processing is a computer program that takes a generalized part program output and adopts it to a particular machine control unit and machine tool combination. It is the basic intelligence required to change the program into computer language.

9. Write the order of instructions in a part program.

End of Preparatory function   Feed function       Tool function       block

10. What is manual part programming?

Manual part programming is a process of writing programs which consists of a set of instructions [contains codes, symbols and numbers] to carry out the machining of the work.

11. What is preparatory function?

It is word address format represented by the letter G, Followed by a numerical code for the operation of the control unit to instruct the machine tool.

12. What is canned cycle?

Canned cycle simplifies and shortens the programming in such way whenever any one of the operation is required.

13.What are the major areas to be considered in the design of NC machine tools?

i.Machine structure and frame ii.Location of transducer iii.Slideways

iv.Elements of transmission and positioning of sliders

v.Spindlesvi.Tool holding arrangements

14.How the heat effect on the machine bed, tool holder can be taken care?

i.Providing correctly designed mild steel structure with higher

stiffness ii.Use of ribs, braces, angle plates to increase stiffness

iii.Normal weight distribution over the entire frame

iv.The hollow cross section for beds, bases and columns with a number of ribs welded with the walls cater for the rigidity as well as opening for inspection, lubrication and collection of chip coolants.

v.Thermo symmetrical   design   of   all   parts.

vi.Providing large heat removing surfaces vii.Use

of excellent coolants

viii.Avoiding direct as well as local sources of heat such as sunlight and electrical motors.oil pumps respectively.

ix.Reduction of ambient temperature by using air conditioning units

x.Proper alignment of the machine elements relative to each other while in operation as well as in stationary conditions

15.Explain Slide and Slideways

In general machine tools are provided with tables, slides, carriages etc., to carry the work pieces or cutting tools etc., These parts are sliding in nature and mounted on the ways that are fixed on the other parts (column, housing, bed or knee) of the machines known as sliding ways.

16. Explain the term “stick-up”

Conventional sliders operating under sliding friction do not have a constant coefficient of friction and the highest value of co-efficient tends to be at the lowest rates of slide velocity.

This phenomenon given to the familiar “stricking” of oil lubricated slideing surfaces when

the fine adjustment is needed, a jerky action when movement takes place at low velocities.

The term “stick-slip” is used to describe these situations.