What is CNC machining?
CNC machining is a manufacturing process in which pre-programmed computer software dictates the movement of factory tools and machinery. The process can be used to control a range of complex machinery, from grinders and lathes to mills and routers. With CNC machining, three-dimensional cutting tasks can be accomplished in a single set of prompts.
The term CNC stands for ‘computer numerical control’, and the CNC machining definition is that it is a subtractive manufacturing process that typically employs computerized controls and machine tools to remove layers of material from a stock piece known as the blank or workpiece and produces a custom-designed part.
This process works on a wide range of materials including metals, glass, foam, plastics, wood, and composites. It also finds application in a variety of industries, such as large-scale CNC machining, telecommunications parts and prototyping machining, and CNC machining aerospace parts, which require tighter tolerances than other industries.
Note there is a difference between the CNC machining definition and the CNC machine definition- one is a process and the other is a machine. A CNC machine is a programmable machine that is capable of autonomously performing the operations of CNC machining.
How does a CNC machine work?
CNC “Computer Numerical Control” Taking digitized data, a computer and CAM program is used to control, automate, and monitor the movements of a machine. The CNC controller works together with a series of motors and drive components to move and control the machine axes, executing the programmed motions.
Modern CNC machines are fully automatic. All you need is digital files with instructions on how to cut trajectories and tools. Design or machining processes require many tools to make a particular part. Machinists can create digital tool libraries that are connected to the physical machine. Such machines can automatically change tools based on digital instructions, thereby making workhorses.
The CNC machining process begins with the design of the parts in CAD software. The 3D model determines the required dimensions and properties of the final part. Some of these programs are supplied in CAD-CAM packages so that the process can continue in the same programs.
Otherwise, CAD models are fed into the CAM software provided for this purpose. If both CAD and CAM are from the same family of products, no file translation is required. Otherwise, the CAD files have to be imported.
The CAM (Computer Aided Manufacturing) software prepares the model for the entire manufacturing process. First, the model is checked for errors. A CNC program is then created to manufacture the physical part. The program essentially consists of a series of coordinates that guide the cutting head during the manufacturing process.
The third step is choosing the right parameters. This includes cutting speed, voltage, speed, etc. The configuration depends on the geometry of the part and the machines and tools available. Finally, the software determines the nesting. Nesting means the orientation and placement of parts relative to the raw material. The aim is to maximize material consumption.
All of this information is then translated into codes that the machine can understand – M-Code and G-Code. A common misconception is that all you need to do any editing operation is G-code. However, this is not the case as the code can be broken down into the two codes above.
G-code refers to a language used to tell a machine how to move. Basically it’s the geometric code. The G-code determines the movement and speed of the cutting heads. The instructions are fed to a machine control system, which is just an industrial computer. This in turn determines how the motors should move. And of course the engines determine the path they have to follow.
The M code, on the other hand, provides all information that the G code overlooks. For this reason, it is called either machine code or other code. The instructions of the M code contain information on the use of coolant, tool changes, program stops, etc.
So both are equally important but not the same.
Types of CNC Machining Operations
In short, CNC machining is a metal fabrication method where written code controls the machinery in the manufacturing process. The code determines everything from the movement of the cutting head and the part to spindle speed, RPMs, etc. CNC machining services use a subtractive fabrication method.
So, we now know how CNC machines work. But not all these machines are used for CNC machining.
We will take a closer look at all the different types of CNC machines that are available a little later. But in a traditional sense, CNC machining refers to only a few of these automated processes. Namely milling, turning, grinding, routing, drilling, etc.
1. CNC Milling
It is an operation where the cutting tool rotates. When the milling tool comes into contact with the workpiece, it removes chips from it.
Milling operations include:
- End milling
- Chamfer milling
- Face milling
- Drilling, boring, tapping, etc.
It is a very universal manufacturing method with great accuracy and tolerances. Milling works on a wide variety of materials and is also very quick. The ability to make a wide range of complex parts is a huge asset.
The disadvantages include a large amount of waste, the need for a variety of tools, and high equipment costs.
2. CNC Drilling
Drilling is a machining process that uses multipoint drill bits to create cylindrical holes in the workpiece.
In CNC drilling, the CNC machine normally feeds the rotating drill bit perpendicular to the plane of the workpiece surface, creating vertically oriented holes with diameters that match the diameter of the drill bit used for the drilling process.
However, angular drilling operations can also be performed using special machine configurations and workpiece holding fixtures. The operational capabilities of the drilling process include counter drilling, countersinking, reaming, and tapping.
3. CNC Turning
While the two are often just referred to as CNC machining, turning and milling have significant differences. Turning is pretty much the opposite of milling. This means that the workpiece rotates instead of the cutting tool.
CNC turning is commonly used to manufacture shafts, for example. The tool is brought against the rotating workpiece in order to cut off metal parts, known as chips or swarf. It is possible to achieve high accuracy for a suitable kind of limit values and adjustment systems.
Turning is possible on the outside of a cylinder or on the inside. The latter operation is called boring.
|Drilling||Employs rotating multi-point drill bits Drill bit fed perpendicular or angularly to workpiece Produces cylindrical holes in workpiece|
|Milling||Employs rotating multi-point cutting tools Workpiece fed in same direction as cutting tool rotation Removes material from workpiece Produces broader range of shapes|
|Turning||Employs single-point cutting tools Rotates workpiece Cutting tool fed along the surface of the workpiece Removes material from the workpiece Produces round or cylindrical parts|
4. CNC Grinding
CNC grinders use a rotating grinding wheel to remove material. The aim is to give a metal part a high-precision finish.
The surface quality that can be achieved is very high. Hence, it is used as a finishing operation rather than making the final piece from raw materials.
5. CNC Routing
CNC routers are seemingly similar to CNC milling machines. Again, the rotating piece is the cutting head. The main difference lies in the materials suitable for cutting.
Routers are perfect for cutting softer materials (not metals) that do not require very high accuracy. The reason for this is the lower output power.
At the same time, routers are faster. This allows you to manufacture the parts in less time.
Types of CNC Machines
The Different Types of CNC Machines:
- CNC laser cutting machine.
- CNC Lathe Machine.
- CNC Milling Machine.
- CNC Router Machine.
- CNC Plasma Cutting Machine.
- 3-D Printer.
- Pick and Place Machine.
1. CNC Milling Machine
One of the most common types of CNC machines, a CNC mill, uses computer controls to cut various materials. Mills can translate certain programs from numbers and letters to move the spindle in different ways.
Many mills use what is known as G-code, which, as mentioned, is a standardized programming language recognized by most CNC machines. A CNC mill can have a wide array of functions, such as face milling, shoulder milling, tapping, drilling and turning. Most CNC mills come in three to six-axis configurations.
A CNC mill is very large compared to other tools and can be quite costly. Some CNC milling machine manufacturers include Okuma, HAAS and DMG Mori.
2. CNC Lathe
A lathe is a CNC machine that functions to cut workpieces as they are rotated. CNC lathes can make precise cuts quickly by using various tools.
These CNC machines are quite effective in the precision they offer compared to manual lathes. They often have fewer axes than CNC milling machines, and are therefore smaller in size and more compact.
CNC lathes come with similar controls to those of CNC mills and can read both G-code and other proprietary programming languages. Some of the most common CNC lathe machine manufacturers include HAAS, Mori Seiki and Okuma. The framework of CNC lathes is similar to manual lathes.
3. CNC Router
A CNC router is a machine that is very similar to the commonly used handheld router utilized for cutting various materials. This type of CNC machine can aid in the cutting of steel, wood, aluminum, composites, plastic, and foam.
A CNC router is similar to a CNC mill. It comes with the ability to use computer numerical control to route tool paths that enable the machine to function. CNC routers reduce waste and increase productivity by producing various items in a much shorter amount of time than other machines.
Most routers can operate on a particular material in all three dimensions, and are great for smaller projects and the creation of prototype models and complex designs. You can also find three axis, four axis, five axis and six axis routers.
4. CNC Plasma Cutter
The process of plasma cutting involves the cutting of a material using a plasma torch. This method is most commonly used to cut heavy materials, such as steel and other forms of metal.
With a CNC plasma cutter, gas is blown at a very high speed from a nozzle. While this is being done, an electrical arc forms through the gas coming out of the nozzle to the surface that is being cut.
This converts some of the gas into plasma, and these plasma temperatures range from 10,000-50,000 degrees. The plasma is hot enough to melt whatever material is being cut, and it blows away any molten metal from the site of the cut.
In terms of shape and size, CNC plasma cutters are very similar to CNC routers. These machines only work with two-dimensional shapes.
5. CNC Electric Discharge Machine
Electric discharge machining, or EDM for short, involves creating a specific shape within a certain material by using electrical discharges, or sparks.
In this process, the material is removed from a specific work piece by a series of recurring electrical discharges between two electrodes. These electrodes are separated by a dielectric fluid, which often receives an electric voltage. In this machine, the material is placed in between two electrodes and the machine then calculates to see the amount of electrical discharge each electrode needs to produce.
6. 5- axis machine
5-axis machining refers to a machines ability to move a tool or a part in five different axes simultaneously. Basic machining operates on three primary axes, X,Y and Z; however, a 5-axis CNC machining tool can rotate two additional axes, A and B, which give the cutting tool a multidirectional approach.
7. CNC Laser Cutter
Last but certainly not least, there are CNC laser cutters.
These types of machines are similar to CNC plasma machines—the only difference is that lasers are mostly used for cutting and are great when it comes to cutting metals, plastic or hardwood. Depending on the density and strength of the material, the intensity of the laser can be adjusted.
What Can CNC Machining Make?
Seemingly, CNC machining has no limitations. It is suitable for a wide range of materials, including different types of metal, plastics, foam, composites and wood. 3-axis milling machines are able to produce most of the more basic geometric shapes. For more complex parts, multi-axis milling centres are available.
For example, a 5-axis CNC milling centre can help out. While the more common 3-axis one has 3 linear axes of movement, 5-axis machines can also rotate the cutting head and the machine bed. This significantly improves the flexibility but also increases the cost.
Even though CNC is a lot quicker, manual machining still has its place in the industry. Especially for low-volume rapid prototyping. But CNC machining still prevails in the sector when high accuracy is necessary. This is the reason why so many industries take advantage of it, including:
- Industrial machinery
- Food & beverage
- Product design, etc.
All in all, CNC machining has cemented its place in the manufacturing sector as a reliable and useful way of producing parts. At the same time, CNC machining cost may often be a little bit higher compared to other fabrication methods.