OBJECTIVE :
1) To identify and understand the CNC Machine System compared to
conventional machine system.
2) To learn how to develop a CNC machine programming of a selected sample of
product for machining processes.
3) To learn how to do ‘zero set-up’ for machine and work piece before machining
process can be started.
4) To cut a selected sample of product using CNC machine ( CNC Turning/ CNC
Milling).
APPARATUS : MAHO CNC 432, CNC Milling Machining, Cutting Tools, etc.
Figure 1: MAHO CNC 432
Figure 2: Cutting Tool for CNC Milling Machine (MAHO CNC 432)
THEORY :
CNC is the most advanced NC system that has a computer to control the machine tool. To produce a component, numerical control program that can run on the CNC machine computer has to be prepared.
Initially the part programs (numerical control programs) are fed into the system. Generally, the punched tape readers can be used to feed the part programs into the system. In NC machines, the tape is passed through the reader for each and every workpiece and the program is executed block by block only. In CNC machines, the program is fed only once and stored in the memory of the computer and can be used for producing any number of parts. The flexibility and computational capability is improved by the use of CNC. New features or functions can be added into the CNC controller by reprogramming the unit.
NC is hardware based while CNC is software based. Generally, the CNC are referred by the term “soft wired” NC because of the reprogramming capability. In a machining centre with the complete automation of tool and work handling within the cell, many operations can be carried out at one work station, making batch production highly economically. The various machining operations that can be performed by a machining centre are turning, drilling, milling, boring, etc.
Using CNC the tool is made to follow any path for machining operation. The changeover from one machining operation to another is fully automatic with the use of auto-tool changer.
PROCEDURE :
1. The components of the CNC machine system was observed, identified and studied :
i. Type of tools, tool magazine
ii. Cooling system
iii. Possible way to program the machine
iv. Number of axis of rotation or movement of the machine
v. Jig and fixture of the system to hold the tool and workpiece
vi. Chip removal system
vii. Maintenance required
viii. The accuracy and quality produce
ix. Heart of the control system
x. Power control system: Hydraulic, Pneumatic, electro-pneumatic, electro- hydraulic
2. The zero set-ups for workpiece and machine was check and observe to determined why it is very important and how it can be done before the machining process is actually started.
3. The program that has been developed for the sample to be cut was been studied.
4. The developed program was test-run using available screen graphics simulation of CNC machine.
5. The machining process was started and the movement of the related component of the CNC machine (working table, tool, tool spindle, etc) was observed.
6. After the machining process, the dimension, shape and quality of the product produce was check.
RESULTS & DISCUSSION
1. By using a neat sketch illustrates and lists the main components of the CNC machine as mentioned in Procedure (1) above.
a. Type of tools and tool magazine
Figure1.1 The tool magazines.
The tool magazine that is being used in this CNC machine is the carousel type and can hold up to 24 cutting tools.
b. Cooling System
The method of cooling system used in this process is called as water flood and the type of coolant being used is vegetable oil. There are several nozzles being used, one is to cool the work piece together with the cutting tool while the rest is to flush away the chips. Used coolants will flow to the drain and pumped out to be re-used.
c. Possible way to program the machine.
Several considerations should be taken in order to program the machine. These steps involved the dimensions of every detail on the desired work piece together with the type of material of the work piece. It is noted that this CNC machine cannot machine wood as it will cause failure to the system itself.
d. Number of axis of rotation or movement of the machine.
Figure. 1.2 Axis vertical CNC machine consist of x, y and z axis.
e. Jig and fixture of the system to hold the tool and work piece.
Figure 1.3 The Jig and Fixture of the CNC machine.
f. Chip removal system.
While the machining process is executed, chips that is being produced is removed by the coolant due to the pressure of the sprayed coolants. These chips is flowed together with the coolants to the filter section and being moved through a conveyor towards the chips tank.
g. Maintenance required.
- make sure that there is an authorized personnel to observed the machine process
to avoid any error from happening
- the perimeter of the CNC layout must be clear in the sense that no object that
may cause obstacles for machine operators to move around the compound.
- while the cutting process take place, the CNC shutter door must be closed in
order to avoid the coolants and chips from spilling out which is dangerous.
h. The accuracy and quality produced.
Overall, when the cutting process has done, the work piece is taken out and being analyzed. It is determined that the accuracy and quality matched the desired dimension and require no further finishing.
i. Heart of the control system.
In CNC machine, the heart of it is the Machine Control Unit, or MCU. Here, all data is being input and the rest of the process is taken care by the MCU.
Figure 1.4. The monitor and keyboard representing the MCU.
j. Power control system.
The control system of this CNC machine comes from, Hydraulic, Pneumatic, electro-pneumatic and electro-hydraulic mechanism.
Figure.1.5 Some of the power control system mechanism.
2. Highlight the final program developed for the selected sample of product that has been cut. Briefly explain the codes used in the program.
| Code | Application | Code | Application |
| G00 | positioning (rapid traverse) (M,T) | G48 | scaling off |
| G01 | linear interpolation (feed) (M,T) | G50.1 | cancel mirror image (M,T) |
| G02 | circular Interpolation CW (M,T) | G51.1 | program mirror image (M,T) |
| G03 | circular Interpolation CCW (M,T) | G55 | work coordinate system 2 select |
| G04 | dwell, a programmed time delay (M,T) | G56 | work coordinate system 3 select |
| G05 | unassigned | G57 | work coordinate system 4 select |
| G06 | parabolic interpretation (M,T) | G58 | work coordinate system 5 select |
| G07 | cylindrical diameter values (T) | G59 | work coordinate system 6 select |
| G08 | programmed acceleration (M,T) | G68 | coordinate system rotation ON (M) |
| G09 | exact stop check (M,T) | G69 | coordinate system rotation OFF (M) |
| G10 - G12 | unassigned or lock and unlock devices | G70 | inch programming (M,T) |
| G13 | computing line and circle intersect (M,T) | G71 | metric programming (M,T) |
| G14 - G14.1 | used for scaling (M,T) | G72 | circular interpolation CW (M) |
| G15 - G16 | polar coordinate programming (M) | G72 | finished cut along z-axis (T) |
| G15 - G16.1 | cylindrical interpolation - c axis (T) | G73 | peck drilling cycle (T) |
| G16.2 | end face milling - c axis (T) | G74 | counter tapping cycle (M) |
| G17 | XY plane selection (M,T) | G74 | rough facing cycle (T) |
| G18 | ZX plane selection (M,T) | G74 | cancel circular interpolation (M,T) |
| G19 | YZ plane selection (M,T) | G75 | circular interpolation (M,T) |
| G20 | input in inch | G76 | fine boring |
| G21 | input in mm | G80 | canned cycle cancel |
| G22 - G23 | machine axis off limit area (M,T) | G81 | drilling cycle, no dwell (M,T) |
| G22.1 G23.1 | cutting tool off limit area (M,T) | G82 | drilling cycle, dwell (M,T) |
| G24 | single-pass rough facing cycle (T) | G83 | deep hole, peck drilling cycle (M,T) |
| G28 | return to reference point (M,T) | G84 | right hand tapping cycle (M,T) |
| G29 | return from reference point (M,T) | G84.1 | left hand tapping cycle (M,T) |
| G30 | return to alternate home position (M,T) | G85 | boring, no dwell, feed out (M,T) |
| G31.1 - G31.4 | external skip function (M,T) | G86 | boring, spindle stop, rapid out (M,T) |
| G33 | thread cutting, constant lead (T) | G87 | boring, manual retraction (M,T) |
| G34 | thread cutting, increasing lead (T) | G88 | boring, spindle stop, manual ret. (M,T) |
| G35 | thread cutting, decreasing lead (T) | G89 | boring, dwell and feed out (M,T) |
| G36 | Automatic accel. And deccel. (M,T) | G90 | absolute dimension input (M,T) |
| G37 | used for tool gagging (M,T) | G91 | incremental dimension input (M,T) |
| G38 | measure diameter and center of hole (M) | G92 | set absolute zero point (M,T) |
| G40 | cutter compensation cancel (M) | G93 | inverse time feed rate (M,T) |
| G41 | cutter compensation left (M) | G94 | per minute feed (M,T) |
| G42 | cutter compensation right (M) | G95 | per revolution feed (M,T) |
| G43 | cutter offset, inside corner (M,T) | G96 | constant surface speed control (T) |
| G44 | cutter offset, outside corner (M,T) | G97 | stop constant surface speed control (T) |
| G45 | tool offset decrease | G98 | return to initial point in canned cycle |
| G46 | tool offset double increase | G99 | return to R point in canned cycle |
| G47 | tool offset double decrease |
| |
Table 1.1 The above are the code and application for G codes.
| Code | Application | Code | Application |
| M00 | Program stops | M05 | Stop spindle |
| M01 | Option stop - if machine is set to detected it | M07 | Coolant on #1 |
| M02 | End of program | M08 | Coolant on #2 |
| M03 | Start spindle - clockwise rotation | M09 | Coolant off |
| M04 | Start spindle - counter-clockwise rotation |
| |
Table 1.2 The above are the code and application for M codes.
G-codes
It is termed as the preparatory functions and commonly associated with the movement of the machine axis together with the associated geometry. The characteristic of G-code is that, it consists of two digits after the word ’G’. Furthermore, there are some G codes acts as a modal and functions as settings to the control. There are also G codes which act as default or turn on code which functioned when the controller is started.
M-codes
This type of code related to miscellaneous function. M codes must be given in a single block and stand for commands such as spindle on/off, coolant on/off, program stop/automatic tool change, program end and so on.
T-codes
Designates the number of the tool to be used and also the function of the tool
F-codes
This refers to the feed rates, designates the relative speed of the cutting tools with respect to the work. In the English system, the feed rate is expressed in inches per minute and in the metric system in millimeters per minute.
S-codes
S codes stand for spindle function, designates the spindle speed in revolutions per minute (rpm) and also control the speed at which the spindle rotates.
N-codes
N codes representing the sequence number, indicates the sequence number of the block.
It is an optional tag that can be coded at the beginning of a block if needed. The process will start from the first N code to the next one, starting from N1 to N9999.
X, Y, Z-codes
These type of codes representing the designated the amounts of axis movement and are referred by the right-hand rule.
| Address | Information Stored |
| X, Y, Z | Linear axes |
| A, B, C | Rotary axes |
| U, V, W | Axes parallel to X, Y, Z axes |
| I, J, K | Axes used as auxiliary of X, Y, Z axes |
| R, Q | Axes used as auxiliary of Z axis. |
H, D-codes
H code is used to specify where the values of the tool length offset and the tool position offset are located. The D code indicates where the value of the cutter radius compensation for a tool is to be found if needed. Numbers associated with H and D codes range between 01 to 99. in all cases, it is recommended that H and T codes must have the same number values.
3. What are the important key parameters in developing the CNC programming?
Firstly, to write a program, we need word address format which described the machine motion and also the dimensions. A block is composed using words to represent complete to the CNC machine. The length of the blocks is different from one desired product to another. G codes and M codes made CNC programming much easier.
4. What basic procedures can be practice in developing the CNC programming?
There are a few basic procedures that can be practiced in developing CNC programming such as, draw the desired or ordered product to define its dimension for simpler programming. The selection of cutting tool must be suitable in order to get the desired shape or dimension. Another factor that must be taken into consideration is the tolerance which will resulted better accuracy in work piece.
5. Draw and portray the final shape, size and dimension of the final product being cut. What is the material of the product? How you can explain the final quality of the final product and why?
As for the result, the obtained product follows according to the dimension as desired. The material is called Perspex. The machining time was considered
6. Briefly discuss the movement of the main components of the CNC during machining process: tool changes, movement and rotation of the cutting tool spindle, work piece table, etc.
An important aspect that needs to be focused is the clamping device or fixture. The clamp used is the T-slots which able the work piece to be hold firmly. The tooling system that is being used is known as carousal, taken from the name of the rotating platform game play found in theme parks. A number of 24 cutting tools can be hold at the carousal and each of them is selected and fixed to the spindle for executing machining processes.
7. How can zero set-ups for work piece and machine tool is carried out?
Zero set-ups is carried out by moving the center of the drill bit to the one of the edge of the work piece to be set as the initial reference point. The other accurate method is to use the center finder. It gives an accurate position of the zero axes for all co-ordinates.
- Why zero set ups for work piece and machine tool are very important before the machining is started?
Zero set-up is important and must be done before executing the machining process. The reason for this matter is that by doing zero set-up, the dimensions that is entered, will be more accurate as all of the dimensions are referred to the zero point as the origin. Other than that, if the cutting tool is subjected to change, the following process can be proceed directly, again by referring to the zero set up point as the origin.
- What do you have seen on the run-test graphic screen?
In the run test graphic screen, it showed the virtual cutting process from the first data input in terms of block until the final block code. Through this run test, it is able to detect any errors or mistakes in order to determine the desired shape. From test graphic screen also allow us to observed the movement of the tool bit throughout the cutting process.
- The differences between CNC machine and conventional machine.
Several major differences present between CNC machine and conventional machine. One of them is in terms of commands input. CNC machine is executed using inputs such as preset codes to run the machine while conventional machine relies on human operation. Using CNC machine will results better products with high accuracy, constant dimension and able to be produced in mass rate. In the other hand, these factors cannot be achieved in conventional machine. Other than that, the capital cost of CNC machine is much higher than the conventional machine, that is why higher production is necessary in CNC machining.
CONCLUSION :
It can be concluded that;
1. CNC machines benefits human more than traditional machines. The reason is, the advantages that CNC machines can offer is greater than traditional machining. These advantages are in terms of, accuracy, consistency, production rate and time consuming. All these aspects are most likely to be achieved in the process of CNC machining.
2. CNC machine is a method of controlling the functions and motion of a machine tool by means of a prepared program containing instructions in the form of numerical data.
3. CNC machine offers greater flexibility, greater in quality of product, greater in safety of workers and the machine tool, and greater in minimize the cost and time of machining in manufacturing industry than the conventional machine type.
4. CNC machine are widely applied in the manufacturing industry like in aerospace industry and industrial robots because of it
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