CNC is an abbreviation of Computer Numerically Controlled. It is a feature widely available for machine tools like lathe, milling, drilling, etc. to enhance their working ability and efficiency with the aid of a computer. To date, some of these machines are manually operated, giving operators no chance to rest or concentrate on other tasks. CNC machines are considered as they offer high average precision and accuracy and also time efficiency.
In this reading, I’ll be discussing what a CNC machine is, its applications, parts, diagrams, types, elements, specifications, and how it works. We’ll also examine the advantages and disadvantages of a CNC machine, as well as its control code.
Let’s Get Started!
What is a CNC Machine?
CNC machines can be defined as machine tools that are automatically controlled using a computer. CNC machine processes a piece of material like metal, plastic, wood, ceramic, or composite to meet the spec of a coded programmed instruction without a manual operator.
The working program is written by a person or generated by graphical computer-aided design (CAD) software. As for 3D printers, the part to be printed is sliced before the program will be generated on the computer. The second operation of CNC machines is known as Computer-aided manufacturing (CAM), the topic is similar to CAD but discusses the production areas.
For some component that requires a number of different tools like drills, mills, saws, etc. modern machines comprise multiple tools into a single cell. However, a number of different machines use an external controller and the component is moved from machine to machine by human or robotic operators. In either case, the steps are applied to parts that require a very close match with the original CAD
Applications of CNC Machine
CNC machining is a versatile method used in various industries, including aerospace, electronics, defense, mining, industrial machinery, food and beverage, clothing, automotive, and product design. It uses 3-axis milling machines for basic geometric shapes, while multi-axis milling centers are available for complex parts.
5-axis CNC milling centers offer increased flexibility but also increase costs. Despite its speed, manual machining still holds a significant place in the industry, particularly for low-volume rapid prototyping.
CNC machining is a reliable and useful way of producing parts, but its costs may be slightly higher than other fabrication methods. Lastly, CNC machining has solidified its place in the manufacturing sector as a reliable and useful tool for producing parts.
These are some applications of CNC Machines:
- The main application of the CNC machine is to work with greater accuracy and automatically control the machine tool.
- This is also used in large fabrication industries.
- This machine is used for the automatic removal of metal from the workpiece.
Related: What Is A Lathe Machine? Its Diagram, Parts and How it Works
Components of a CNC Machine
In all CNC Machines there major parts include bed, headstock, tailstock, tailstock quill, footswitch or pedal, chuch, control panel, and tool turret.
Bed: These parts on CNC machines carry all the machine load, this is to say all other components are mounted on it. The bed component is made of hard material like cast iron because in CNC lathe machines the tool turret travels over them.
Headstock: The headstock is one of the main components of CNC lathe machines due to the fact that the workpiece is fixed to it. The CNC lathe features a motor to help drive the main spindle.
Tailstock: This lathe CNC machine part provides extra grip to the workpiece when performing operations like knurling, threading, and turning. The support is provided at the end surface of the workpiece.
Tailstock quill: The tailstock quill helps to centralize the workpiece between the headstock and tailstock.
Footswitch or Pedal: The pedal is used to open and close the chuck when trying to grip the component, just as the tailstock quill is taken forward and reversed position.
Chuck: The chuck is mounted on the main spindle which gives space for fixing the tool.
Control panel: The control panel is also one of the important parts of CNC machines which are used to set or feed the program for the operation to be performed on the workpiece. It is also called the brain of the CNC machine.
Tool turret: In this part, the tool is mounted on it and allows the operator to be carried out. Tool turrets vary in shape and a number of tools can be used on them.
Diagram of a CNC Machine
Elements of CNC Machines
The followings are the elements of CNC machines:
1. Program
This is the computer input that is done with a keyboard when trying to tell the machine to perform a functional control code. This control code is of two sets; G-codes and M-codes. M-codes are miscellaneous machine commands that do not command axis motion. Whilst G-cold is used to command specific movements of the machine, such as machine moves or drilling functions.
2. Tape Reader
The tape reader serves as a storage device where the program can be stored for a particular machining operation. Modification of the program can be easily done by editing the existing program to its requirement.
3. Mini-computer
This is the main control unit of CNC machines. The interprets the input to the language the computer understood in order to control the following function:
- Vary the spindle speed accordingly and also control the direction of rotation of the spindle.
- To start and stop the machine spindle.
- To start and stop the coolant supply.
- Change the required tools as per requirements.
- Control the feed rate, and
- To change the workpiece.
4. Servo system
The servo system receives and controls signals from the feedback devices and set output according to the machine parts. The servo system consists of the following parts:
- Servo motors
- Feedback devices and
- Ball screw
5. CNC machine
The CNC machine is the complete equipment where the actual finished product is made. It houses the headstock, tailstock, foot-switch, tool turret, and chuck.
How Does a CNC Machines Works?
The working of a CNC machine is quite interesting due to the fact that it is a computer base. The machine works based on CAD and CAM programs as well as computer control. just as earlier mentioned, the CAD (Computer-Aided Diagram) is a drawing software of the item to be produced, which serves as a carbon copy of the product.
That is, the computer automatically produces what the CAD displays. It is also used to improve the productivity of the designer, improve communication through documentation, improve the quality of design, and create a backup file for the next production.
Whereas, CAM (Computer-Aided Manufacturing) features two different codes such as G-codes and M-codes on which all programs are written and fed to the machine to perform various operations i.e. the turning and grooving operation on a lathe.
The first to do when working on a CNC machine is to write and insert the part program which is G-code and M-code. This will be done in the Machine control unit of the CNC machine, which allows all data processes to take place. It will then send it to the driving system, which helps to control the motion and velocity of the machine tool.
There is a feedback system that records the position and velocity measurement of the machine tool and sends a feedback signal to the MCU. This MCU then compares the feedback signals with the reference signal to check for errors and if there is, it corrects it and sends a new signal to the machine tool. CNC machines also feature a display unit that is used to see commands, programs, and other important data.
Types of CNC Machines
The various types of CNC mahcines are CNC laser cutting machine, CNC lathe machine, CNC milling machine, CNC router machine, CNC plasma cutting mahcine, 5 Axis machine, 3D printer, and pick and place machine.
1. CNC Laser Cutting Machine
Laser cutting is a cutting tool that carries out its operations with the aid laser. The modern ones designed with CNC allow the operation to be atomically done by the program fed to the computer and It allows the operation to be perfectly cut. The issue with CNC laser cutting machines is that the cost is high and it takes time to fix any damage because it is not widely available in the market.
2. CNC Lathe Machine
A lathe is a popular machine tool among engineers due to the fact that almost all operations can be performed on it. The CNC lathe machine version allows perfect, fast, and accurate working as the computer controls the machine tool and other parts of the machine. Once the program is loaded to the computer, the operation starts making it suitable for mass production.
3. CNC Milling Machine
The CNC milling machine can perform operations that manual milling can perform with ease and perfection. Milling is known as the process of removing metal by feeding the workpiece to pass through a rotating multipoint cutter. It is ideal for gear making, boring and slots making.
A semi-skilled worker can perform the operation on CNC milling as it is done by inserting the program CAD into the system. The CNC milling machine is used for mass production like capstan and turret offering them dimensional tolerances and accuracy.
4. CNC Router Machine
This machine is mostly used by woodworkers, but all carpentry work such as door carvings, interior and exterior decorations, wood panels, signboards, wooden frames, moldings, etc. The CNC aspect works as other machine tools and allows the program to design and execute it. CNC router machine offers a better surface finish to the workpiece.
5. CNC Plasma Cutting Machine
Plasma cutting is used for cutting electrically conductive material using an accelerated jet of hot plasma. CNC version of the machines performs the operation in a computerized way. The only difference between the CNC plasma and laser is that laser is very expensive whereas hot plasma is less costly and portable.
6. 5-axis machine
The 5-axis means the direction of cutting. Literally, the direction cutting was three-axis X, Y, and Z but two additional axes were added which are A, B which makes it 5 axes making works to be cut from five different directions. It is mostly used for making sculptures. The CNC type also offers the same advantages as the others.
7. 3-D printer
A 3-D printer is a CNC machine that is used to print metals layer by layer, making it suitable for printing buildings and complexes. The work is done by CAD and CAM and the 3D printer visualized the design.
8. Pick and place machine
The pick and place machine is used in a warehouse that stores a lot of items, the machine is automatically controlled to pick and place-specific amounts of items with ease.
Related: What is Milling Machine? its Diagram & How it Works
Specifications of CNC Machines
Specification of a CNC machine can be categorized into the following points:
1. Machine specifications:
- Centers height.
- Distance between centers.
- Swing diameter over the bed.
- Swing diameter over the cross slide.
- Transverse movement of the cross slide.
2. Headstock specifications:
- Hole in the headstock spindle.
- Spindle end-use taper.
3. Tailstock specifications:
- Spindle diameter.
- Spindle end taper.
- Sleeve travel.
4. Feed rate:
- Rapid transverse.
- Programmable feed rate.
5. Main Spindle specifications:
- Speed range.
- Output power.
CNC Operations
Various CNC machining operations use written code to control the machinery in the manufacturing process. It involves a subtractive fabrication method, which includes milling, turning, grinding, routing, and drilling. Milling operations involve rotating the cutting tool, removing chips from the workpiece, and include end milling, chip milling, face milling, drilling, boring, tapping, etc.
Drilling is a machining operation that uses multipoint drill bits to create cylindrical holes in the workpiece. The machine feeds the rotating drill bit perpendicular to the plane of the workpiece surface, creating vertically oriented holes with diameters that match the drill bit used for the drilling process. Angular drilling operations can also be performed using special machine configurations and workpiece holding fixtures.
CNC turning is the opposite of milling, as the workpiece rotates instead of the cutting tool. It is commonly used to manufacture shafts, where the tool is brought against the rotating workpiece to cut off metal parts, known as chips or swarf. Turning can be done on the outside of a cylinder or inside, called boring.
CNC Machining operation characteristics include drilling using rotating multi-point drill bits, milling using rotating multipoint cutting tools, turning using single-point cutting tools, and CNC grinding using a rotating grinding wheel to remove material for a high-precision finish.
CNC routers are similar to CNC milling machines but are perfect for cutting softer materials with lower output power and faster manufacturing times. Overall, CNC machining offers a versatile and efficient method for producing complex parts with high accuracy and tolerances.
Control Code For CNC Machines
M-codes are miscellaneous machine commands that do not command axis motion. The format for an M-code is the letter M followed by two to three digits; for example:
- [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 orientate]
- [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] (raises tool spindle above current position to allow the operator to do whatever they would need to do)
- [M68 Hydraulic chuck close]
- [M69 Hydraulic chuck open]
- [M78 Tailstock advancing]
- [M79 Tailstock reversing]
G-cold is used to command specific movements of the machine, such as machine moves or drilling functions. The format for a G-code is the letter G followed by two to three digits; for example, G01. G-codes differ slightly between a mill and lathe application, for example:
- [G00 Rapid Motion Positioning]
- [G01 Linear Interpolation Motion]
- [G02 Circular Interpolation Motion-Clockwise]
- [G03 Circular Interpolation Motion-Counter Clockwise]
- [G04 Dwell (Group 00) Mill]
- [G10 Set offsets (Group 00) Mill]
- [G12 Circular Pocketing-Clockwise]
- [G13 Circular Pocketing-Counter Clockwise]
Codes used in CNC programming
The M-codes represent the miscellaneous machine commands which do not command axis motion. The format is the latter ma followed by two to three digits. Below are five functions:
- [M02 End of Program]
- [M03 Start Spindle – Clockwise]
- [M04 Start Spindle – Counter Clockwise]
- [M05 Stop Spindle]
- [M06 Tool Change]
G-codes are used for commanding specific movements of the machine, such as machine moves or milling functions. G-codes differ between lathe and mill applications. The format is later G followed by two to three digits. Below are some functions of G-codes:
- [G00 Rapid Motion Positioning]
- [G01 Linear Interpolation Motion]
- [G02 Circular Interpolation Motion-Clockwise]
- [G03 Circular Interpolation Motion-Counter Clockwise]
Related: What is Drilling? its Diagram, Operations, & How it Works
Advantages of CNC Machines
Below are the benefits of CNC machines in their various applications:
- mistakes in cutting conditions or in dimension can easily be edited Providing better precision and accuracy to the workpiece.
- Fewer workers are required which helps to save labor costs.
- A highly skilled operator is not required.
- Complex designs with high accuracy in the minimum possible time can be produced on CNC machines.
- It features an online editing program, which means any changes and modifications by the part data stored in the computer without sending the tape for re-processing.
- The conversion of the unit can easily be done by this machine (SI to British or from British to SI).
- It can diagnose its own fault easily, there is special software that enables easy troubleshooting if the CNC system fails to operate, and also have the capability to assist in maintaining and repairing the system automatically.
- It also helps with safety reasons.
- Low Maintenance required
- Reduce setup change over time.
- The CNC Machine has Higher Production and capability.
- It can run for 24 hours a day.
- It is Reliable.
Disadvantages of CNC Machines
Below are the limitations of CNC machines in their various applications:
- The installation cost is high.
- Even the parts of the CNC machine are high.
- It requires highly skilled professionals to solve issues when a failure occurs.
- Computer knowledge is required.
- Program knowledge is required