CNC Machine | Advantages, Disadvantages, Applications, History

Before discussing CNC machines let us first discuss what are machines and why the need of a CNC machine arrived. In our day to day life we see many machines around us. It could be a sewing machine, drilling machine or a very complex automotive engine.

Functions of all the machines is to reduce human effort and make our life easy.

Most of the machines around us depend on the human mind for crucial decisions. For example, in case of conventional drilling machine we have to stop the machine when drilling is completed. This machine cannot determine by itself that whether the hole is drilled or not. Similar is the case of other machines.

There is a basic problem with these machines, which is errors caused due to manual operation. Manual operation has chances of human errors because exhaustion, boredom etc.

All of the above factors forced engineers to develop machines which can perform desired operations without human intervention. It is also desired that these machines should have high accuracy and should avoid any accident. This is where the need of CNC machine arrived.

What is a CNC machine?

The word CNC stands for computer numerical control. In this practice the tool and workpiece both are controlled with the help of a numerical program.

The complete process of CNC machining depends on CAD and CAM.

The word CAD stands for Computer Aided Design whereas the word CAM stands for Computer Aided Manufacturing. With the help of CAD we make 3-D design of the object which we have to make and with the help of CAM that design is converted into reality.

Modern day CNC machines are highly precise and can reduce the time to perform a job drastically.

Advantages of CNC machines

1. Machining is accurate and have very high precision
2. Time taken to perform a job is very less
3. Safe to operate
4. Number of operators required to operate a machine are reduced
5. No possibility of human error
6. Reliable
7. Even very complex designs can also be made
8. Low maintenance required
9. They are versatile
10. Uniformity in designs
11. They could run for all 24 hours a day
12. Wastage generated by CNC machining is low as compared to conventional machining
13. It reduces the number of defective products produced to almost zero
14. It is more efficient and faster compared to conventional machining
15. It is energy efficient
16. It reduces overall production cost
17. Products manufactured by CNC machines are highly consistent in nature
18. Prototyping of the product is not required
19. By updating the software machine can be updated to some extent
20. One operator can supervise more than one machine at a time
21. It can work on a wide range of materials

Disadvantages of CNC machines

1. They are costly
2. Trained operator is required to operate the machine
3. In case of breakdown a highly skilled professional is required to solve the problem
4. Reduction in manual labour can lead to unemployment
5. Its installation cost is high

Applications of CNC machines

1. Metal removal industries
2. Material fabrication industries
3. For non-conventional machining industries where the machining task is difficult to perform manually

History of CNC machines

The advent of CNC machines generally takes us back to the cold war period when US Navy hired Parsons Corporation to increase productivity of its production line for helicopter blades. John T. Parsons (1913-2007) used punch-card computer to control the axes of the machines, used in manufacturing these blades. It is believed that he studied the possibility of operating a machine with a computer while working at IBM. It is considered as the beginning for CNC machines.

Due to his contribution towards the numerical control (NC) technology John T. Parsons is also known as father of the second industrial revolution.

In 1952, first CNC milling machine was developed by Richard Kegg, in collaboration with MIT. It is considered as the commercial beginning of the CNC technology.

In May, 1952 Parsons filed a patent for “Motor Controlled Apparatus for Positioning Machine Tool”. He was granted the patent in 1958. In response MIT filed a patent for “Numerical Control Servo-System.”

Types of CNC machines

1. CNC Laser Cutter
2. CNC Electric Discharge Machine
3. CNC Plasma Cutter
4. CNC Router Machine
5. CNC Lathe Machine
6. CNC Milling Machine
7. CNC Water Jet Cutter
8. CNC Grinder
9. CNC Drilling Machine

CNC Coding

G-Codes and M-Codes are used for CNC machine programming. They are based on three dimensional cartesian coordinate system.

G-Codes

G-Codes are used for specific machine movements. Following are some widely used G-Codes.

• G00: Rapid Motion Positioning
• G01: Linear Interpolation Motion
• G02: Circular Interpolation Motion-Clockwise
• G03: Circular Interpolation Motion-Counter Clockwise
• G04: Dwell
• G10: Set offsets
• G12: Circular Pocketing-Clockwise
• G13: Circular Pocketing-Counter Clockwise

M-Codes

M-Codes are for miscellaneous command they do not control the axial movement of the machine.

• M02: End of Program
• M03: Start Spindle – Clockwise
• M04: Start Spindle – Counter Clockwise
• M05: Stop Spindle
• M06: Tool Change
• M07: Coolant on mist coolant
• M08: Flood coolant on
• M09: Coolant off
• M10: Chuck open
• M11: Chuck close
• M13: BOTH M03 & M08, Spindle clockwise rotation & flood coolant
• M14: BOTH M04 & M08, Spindle counter clockwise rotation & flood coolant
• M16: Special tool call
• M19: Spindle orientation
• M29: DNC mode
• M30: Program reset & rewind
• M38: Door open
• M39: Door close
• M40: Spindle gear at middle
• M41: Low gear select
• M42: High gear select
• M53: Retract Spindle
• M68: Hydraulic chuck close
• M69: Hydraulic chuck open
• M78: Tailstock advancing
• M79: Tailstock reversing

Example of CNC Coding

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O0001

G20 G40 G80 G90 G94 G54(Inch, Cutter Comp. Cancel, deactivate all canned cycles, moves axes to machine coordinate, feed per min., origin coordinate system)

M06 T01 (Tool change to tool 1)

G43 H01 (Tool length comp. in a positive direction, length compensation for the tool)

M03 S1200 (Spindle turns CW at 1200RPM)

G00 X0. Y0. (Rapid Traverse to X=0. Y=0.)

G00 Z.5 (Rapid Traverse to z=.5)

G00 X1. Y-.75 (Rapid traverse to X1. Y-.75)

G01 Z-.1 F10 (Plunge into part at Z-.25 at 10in per min.)

G03 X.875 Y-.5 I.1875 J-.75 (CCW arc cut to X.875 Y-.5 with radius origin at I.625 J-.75)

G03 X.5 Y-.75 I0.0 J0.0 (CCW arc cut to X.5 Y-.75 with radius origin at I0.0 J0.0)

G03 X.75 Y-.9375 I0.0 J0.0(CCW arc cut to X.75 Y-.9375 with radius origin at I0.0 J0.0)

G02 X1. Y-1.25 I.75 J-1.25 (CW arc cut to X1. Y-1.25 with radius origin at I.75 J-1.25)

G02 X.75 Y-1.5625 I0.0 J0.0 (CW arc cut to X.75 Y-1.5625 with same radius origin as the previous arc)

G02 X.5 Y-1.25 I0.0 J0.0 (CW arc cut to X.5 Y-1.25 with same radius origin as the previous arc)

G00 Z.5 (Rapid traverse to z.5)

M05 (spindle stops)

G00 X0.0 Y0.0 (Mill returns to origin)

M30 (Program End)

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References:

https://cncmachines.com/what-is-a-cnc-machine

https://prototechasia.com/en/plastic-cnc-machining/history-cnc

https://en.wikipedia.org/wiki/Numerical_control

Image source:

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