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What is CNC Machining?

You might have seen our recent articles about CNC Milling or CNC Routing, within which we mention CNC Machining. If you’ve asked yourself ‘What on Earth is CNC Machining?’, then you’ve come to the right place.

CNC Machining is the overarching activity, with Milling and Routing (among others) being activities that fall within its borders. To explain CNC Machining, it can be said that it is a metal fabrication method controlled by code, which tells the manufacturing machinery what to do. Engineers use the code to control cutting speeds, directions, and RPM.

How Does CNC Machining Work?

CNC Machining is a ‘subtractive fabrication method’, meaning that it removes material as it does its work. This type of engineering is used for cutting and shaping materials such as metal, plastic, and even fabric. The automation process requires a digital file containing the code that instructs the machine about what tools and trajectories are needed. This file should be designed by an Engineer or Machinist who has experience with CAD (Computer-Aided Design) software.

CAD software is used by Machinists to define a number of considerations about the cutting process, and it often takes a fair bit of skill and experience to get to grips with. The CAD software is used to create a 3D model that defines the dimensions and needs of the part being made. Within the software, Machinists can build a digital tool library for different projects and if the CNC machine is advanced enough, it should be able to automatically change the tool mid-program. What this means is that if the code is good enough, the digital file should allow the part to be made from start to finish without human interaction.

This coding or programming process doesn’t come without its own challenges. One of those challenges is for the different coding languages to correlate. There are CAD programmes and CAM (Computer-Aided Manufacturing) programmes, and the CNC machining process requires both, but if they use different coding languages, the translation of files can cause minor issues.

In some cases, it’s possible to use a CAD-CAM package that combines both processes into one software. Where CAD is used to design the part, CAM is used to create the fabrication code that can be understood by the CNC Machine. This code contains the speed, RPMs, voltage, cutting heads, orientation, nesting and more.

The resulting code from all of this work is called a G Code or an M Code.

G Code vs M Code in CNC Machining

G Code

This is the code or language that tells the CNC machine how to move and at what speed. The code is uploaded to an industrial computer that relays information to the machine and instructs the motors.

M Code

The M Code fills in the gaps that the G Code misses, like how much coolant needs to be used, where a tool should be changed, and if the machine needs to pause for some reason.

Both are necessary to the process.

What are some well-known types of CNC machines?

Here are some CNC machines that you might not realise are CNC machines:

  • Plasma and Laser Cutters
  • Turning machines and Lathes
  • Milling Machines
  • Press Brakes
  • Flame Cutters
  • Waterjet Cutters
  • Routers
  • Electrical Discharge Machines

CNC Machining: Milling, turning, drilling, grinding, routing,

When you start looking into the more technical side of CNC Machining, the same words are going to pop up over and over again: milling, turning, drilling, grinding, and routing. Let’s spend a moment explaining what each of these refers to.

CNC Milling

A milling tool is used to remove chips from a part or workpiece, making it a subtractive fabrication method. The cutting tool rotates incredibly fast and is programmed to push against the workpiece to remove pieces, which generates a lot of heat and a lot of waste. There are different types of milling that offer different levels of complexity and finish, which makes it incredibly versatile and useful for a wide number of applications. On top of this, milling can be used for different material types, providing greater flexibility. The machines come in different sizes and can be very costly because of the precision they offer and the cooling requirements needed.

CNC Turning

If milling occurs when a spinning tool contacts the workpiece, then you can see turning as the complete opposite. In a turning process, the workpiece rotates towards the cutting tool to accurately cut off chips from the metal (or other material). Turning is most typically used to bore holes in materials.

CNC Drilling

Whilst turning can create holes (boring), and milling can too, typically we look to CNC drills as the optimal machine for placing precise holes in workpieces. A drill uses different tip types and applies pressure to create holes in a variety of materials.

CNC Grinding

A circular grinding part or grinding wheel is rotated at high speeds to remove material from a workpiece and create a high precision finish, especially for metals that need a quality visual appearance. CNC grinding often comes as the last, or one of the last processes in CNC machining, as it is most commonly used to give a good finish.

CNC Routing

We’ve written at length about CNC routing in our recent guide, explaining that CNC routing is similar to CNC milling, although it’s much faster and allows for a quicker output. Routing is typically being applied to softer materials that don’t need the level of precision that milling offers.

Which industries make use of CNC machining?

CNC machining, at the end of the day, is an automated process that reduces the chances of human error and allows machines to work faster and harder than humans can. For a number of industries, this precision and attention to detail, where every millimetre counts, is an absolute necessity. For example, consider the needs of:

  • Aerospace
  • Defence
  • Mining
  • Industrial Machinery
  • Automotive
  • Products
  • Electronics


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