Cnc machining nm09/2


Review questions — Section 4



Download 0.53 Mb.
Page13/27
Date28.01.2017
Size0.53 Mb.
#9464
1   ...   9   10   11   12   13   14   15   16   ...   27

Review questions — Section 4


Note: Show all workings

Question 1

Given that the circle diameter is 60 mm and the width across the flats is 40 mm. Calculate the length of ’W’.





Question 2

Calculate the chordal distance between points ‘A’ and ‘B’.





Question 3

From the information given, calculate the value of radius.





Question 4

Calculate the diameter of the largest circle which can be drawn inside the triangle shown.




Practical exercises — section 4

Calculations


Calculations Student instructions

  1. The exercises which follow represent the type of geometry associated with the plotting of tool path co-ordinate for CNC machining.

  2. To make the calculations easier always attempt to develop right angled triangle at point where lines are tangent to curves or where line from a common link between circle or arc centres.

  3. Make your calculations accurate to two decimal places as most Machine Control Units require each tool path plot to be within an accuracy of 0.02 mm.

  4. Calculators should be used.

  5. Do not be tempted to look to the solution sheets before you have completed your own effort. This may cause you some difficulty come the time you will be required to apply your skills under assessment conditions.

Linear programming — exercise sheets 1 -3


Work out the values for ‘x’ and ‘y’ for the points shown on exercise sheets 1 -3. Fill in your answers in the coordinates box on each sheet.






Circular interpolation — exercise sheet 4


Work out the values for ‘x’ and ‘y’ for points 1 -7 in exercise 4 and write your answers in the coordinate box on the sheet.



Exercise 5

An NC controlled boring machine is to be programmed to drill a number of gear boxes as shown below. In the co-ordinate tables provided, complete the drilling tool path values starting and finishing at point ‘A’ in both Incremental and Absolute terms.





Absolute values

Incremental values

X values

Y values

X values

Y values






























































4.6 Preparing NC programs

4.6.1 Manual systems


In any manual programming system, the programmer is required to write a complete manuscript which must include all tool co-ordinates as well all the appropriate machining codes.

Earlier systems used a Buffer Teletype which was like a large typewriter with a chip set and buffer memory that could encode man readable data into a numeric code. With the evolution of micro computers, Buffer Teletypes are rarely used simply because computers now perform the encoding process much faster as well as offering many other advantages. Once encoded, data is normally down loaded to a tape punch which stores the program in the form of a punched tape.


4.6.2 Direct input


CNC machines have a Machine Control Unit (MCU) which can accept part programs keyed directly into the control unit via an alpha-numeric keyboard.

This direct input can be via:



  1. Edit function —By selecting the edit function an MCU program data can be entered, edited and stored.

  2. MDI facility —MDI (Manual data input) is another facility most modem machine control units have, generally this facility is not used to insert long part programs instead it is used to write short statements such as the command to start spindle rotating when using an edge finder to set a program zero.

  3. IGF facility — As an accessory many MCU's have available a computer assisted chip set known as an Interactive Graphical Function. This feature allows a conversational type input resembling APT programming language. The computer asks the programmer to respond to prompts (conversion) and once all the data is entered the computer will complete all of the calculations and assign the appropriate machining codes to machine the part. The computer will also provide a program output in the word address format.

4.6.3 Computer aided programming


This aspect of NC part programming uses a stand alone computer which has been loaded with a Computer Aided Manufacturing (CAM) software package. Depending on the nature of the industry the computer can be a mainframe, a mini or a micro computer such as is found in personal computers. Like in any computer, the heart of the system is the software.

Software such as SmartCAM, MasterCAM and GeoPath are all examples of CAM software. These brand names like many others have the facilities to:


    1. Draw the part

    2. Automatically calculate and define all tool path coordinates.

    3. Define appropriate post processing functions such as M Codes etc.

    4. Validate the program by an animated graphical display of Tool Path.

    5. Edit the program as required.

    6. Output the program data to the MCU.

4.6.4 Voice numerical control


Voice programming of NC machines (abbreviate VNC) involves vocal communication of the machine procedure to a voice-input NC tape preparation system. VNC allows the programmer to avoid steps such as writing the program by hand, key punching or typing, and manual verification. One of the principal companies specialising in voice input systems is Threshold Technology, Inc., of Delran, New Jersey.

To perform the part programming with VNC, the operator speaks into a headband microphone designed to reduce background acoustical noise. Communication of the programming instructions is in shop language with such terms as ‘tum’, ‘thread’, and ‘mill line’, together with numbers to provide dimensional and coordinate data. Before the voice input system can be used, it must be ‘trained’ to recognise and accept the individual programmers voice pattern. This is accomplished by repeating each word of the vocabulary about five times to provide a reference set which can subsequently be compared to voice commands given actual programming. The entire vocabulary for the Threshold system contains about 100 words. Most NC programming jobs can be completed by using about 30 of these vocabulary words.



The advantages of VNC lie principally in the savings in programming time and resulting improvements in manufacturing lead time. Savings in programming time up to 50% are claimed. Improvements in accuracy and lower computer skill requirements for the programmer are also given as benefits of VNC.


Download 0.53 Mb.

Share with your friends:
1   ...   9   10   11   12   13   14   15   16   ...   27




The database is protected by copyright ©ininet.org 2024
send message

    Main page