What is CNC Machining?- Definition, Types, Working

What is CNC machining?

Computer Numerical Control (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 CNC 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 is suitable for a wide range of materials, including metals, plastics, wood, glass, foam, and composites, and finds application in a variety of industries, such as large CNC machining, machining of parts and prototypes for telecommunications, 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 (sometimes incorrectly referred to as a C and C machine) is a programmable machine that is capable of autonomously performing the operations of CNC machining.

Subtractive manufacturing processes, such as CNC machining, are often presented in contrast to additive manufacturing processes, such as 3D printing, or formative manufacturing processes, such as liquid injection molding.

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How does a CNC machine work?

CNC machines usually feature a version of a CAD software program. A CAD program, or computer-aided design, is software which allows you to draw what you want to cut. The drawing is either 2D or 3D and when completed it creates a code for the CNC machine to read.

CNC machines work by following co-ordinates along axis. Basic machines move along one or two axis, but advanced machines, and those creating 3D items, will move along three axis. The machine’s tools follow thousands of co-ordinates, cutting and shaping as they move.

Before a CNC machine begins its first task, a trial run is conducted. This trial run is referred to as cutting air and is incredibly important as any mistakes could result in a damaged machine or part.

Types of CNC Machines

According to the functions or types of machined parts, CNC machines can be classified into five types: CNC milling machines, CNC lathes, CNC drilling machines, CNC plasma cutters, and CNC grinders.

It’s important to know that these are not your average machines. They require the skills of a trained professional to be able to produce high-quality commercial products. All of the following machines use G-code, which is the language that a CNC machine understands. Each type of CNC machine caters to a specific purpose.

1. CNC Lathes and Turning Machines

CNC lathes and turning machines are characterized by their ability to rotate (turn) materials during the machining operation. The cutting tools for these machines are fed in a linear motion along with the rotating bar stock; removing material around the circumference until the desired diameter (and feature) is achieved.

A subset of CNC lathes is CNC Swiss lathes (which are the type of machines Pioneer Service operates). With CNC Swiss lathes, the bar of material rotates and slides axially through a guide bushing (a holding mechanism) into the machine. This provides much better support for the material as the tooling machines the part features (resulting in better/tighter tolerances).

CNC lathes and turning machines can create internal and external features on the component: drilled holes, bores, broaches, reamed holes, slots, tapping, tapers and threads. Components made on CNC lathes and turning centers include screws, bolts, shafts, poppets, etc.

2. CNC Milling Machines

CNC milling machines are characterized by their ability to rotate cutting tools while holding the material workpiece/block stationary. They can produce a wide range of shapes including face-milled features (shallow, flat surfaces and cavities in the workpiece) and peripheral milled features (deep cavities such as slots and threads).

Components produced on CNC milling machines are typically square or rectangular shapes with a variety of features.

3. CNC Laser Machines

CNC laser machines have a pointed router with a highly focused laser beam that is used to precisely cut, slice, or engrave materials. The laser heats the material and causes it to melt or vaporize, creating a cut in the material. Typically, the material is in a sheet format and the laser beam moves back and forth over the material to create a precise cut.

This process can produce a wider range of designs than conventional cutting machines (lathes, turning centers, mills), and often produce cuts and/or edges that do not require additional finishing processes.

CNC laser engravers are often used for part marking (and decoration) of machined components. For example, it can be difficult to machine a logo and company name into a CNC turned or CNC milled component.  However, laser engraving can be used to add this to the component even after the machining operations are complete.

4. CNC Electrical Discharge Machines (EDM)

A CNC electric discharge machine (EDM) uses highly controlled electrical sparks to manipulate materials into the desired shape. It can also be called spark eroding, die sinking, spark machining, or wire burning.

A component is placed under the electrode wire, and the machine is programmed to emit an electrical discharge from the wire which produces intense heat (up to 21,000 degrees Fahrenheit). The material is melted or flushed away with liquid to create the desired shape or feature.

EDM is most often used for creating precise micro holes, slots, tapered or angled features, and a variety of other more-complicated features in a component or workpiece. It is typically used for very hard metals that would be difficult to machine to the desired shape or feature.  A great example of this is the typical gear.

5. CNC Plasma Cutting Machines

CNC plasma cutting machines are also used to cut materials. However, they perform this operation using a high-powered plasma (electronically-ionized gas) torch that is controlled by a computer.

Similar in function to a handheld, gas-powered torch used for welding (up to 10,000 degrees Fahrenheit), plasma torches achieve up to 50,000 degrees Fahrenheit. The plasma torch melts through the workpiece to create a cut in the material.

As a requirement, anytime CNC plasma cutting is employed, the material being cut must be electrically conductive. Typical materials are steel, stainless steel, aluminum, brass, and copper.

Precision CNC machining provides a wide range of production capabilities for components and finishing in the manufacturing environment. Depending on the environment of use, material needed, lead time, volume, budget, and features required, there is usually an optimum method for delivering the desired result.

6. 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.

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.

Machining OperationCharacteristics
DrillingEmploys rotating multi-point drill bits Drill bit fed perpendicular or angularly to workpiece Produces cylindrical holes in a workpiece
MillingEmploys rotating multipoint cutting tools Workpiece fed in the same direction as cutting tool rotation Removes material from workpiece Produces a broader range of shapes
TurningEmploys 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.

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 centers are available.

For example, a 5-axis CNC milling center 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:

  • Aerospace
  • Electrical
  • Defence
  • Mining
  • Industrial machinery
  • Food & beverage
  • Clothing
  • Automotive
  • 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.