What is CNC Machining: Definition, Process, Purpose & More

How Does CNC Machining Work?

CNC machining relies on computer programs to create the layout of the process in which the machine tool should function. Since users cannot directly communicate with the machine tools, Computer-Aided Design (CAD) software is used.

CAD software creates the 2-dimensional and 3-dimensional models for the required CNC machined parts. With this design, the machine knows what the final part looks like.

The computerized controls do the calculation required for removing material, so the workpiece looks like the final part created in the CAD software.

Let us go through the breakdown of various processes that occur during CNC machining.

The Four Stages of CNC Machining

CNC machining occurs in four stages:

Stage 1: Creating the CAD Model

Before CNC machining begins, the 2D or 3D model of the final design is required. This model is created in CAD software. There are many CAD software programs available online, free and paid.

Creating CAD models is not difficult and can easily be learned. However, some complex parts might require more experience with CAD, for which expert designers can be hired.

Stage 2: Converting CAD Model to CNC File

No CNC machine understands CAD language directly. CNC machines only recognize movement based on coordinates. Therefore, the CAD model must be converted to a CNC understandable file called G code.

Many CAD software programs can write the output file directly in G code by using the particular setting before saving the file.

In other cases, converting the CAD design to G code will require dedicated software called Computer Aided Manufacturing (CAM). CAM software is a very functional tool when it comes to the automation of machine processes.

Besides using CAM software, many simple free tools can convert simple CAD designs to G code with the click of a button. However, they don’t have the vast suite of features that CAM software offers.

Stage 3: Configuring the CNC Machine

Before starting manufacturing processes, the CNC machine must be set up the right way.

Think of this as configuring the printer before you print something. You need to feed the printer with pages and check specific settings. CNC machines operate similarly.

Before machining begins, there are many setup processes to complete. For instance, you must ensure the workpiece is properly positioned on the machine. The dies must also be set correctly, and other position settings.

Stage 4: machining operation execution

Once the configuration stage is complete, the machine operation can begin. For this, you can execute the program on the display panel of the CNC machine.

Depending on what you design, you might have to go through various program prompts to choose different types of settings and options.

Once the CNC program is executed, the machine keeps going till the end of the program. It only stops if switched off by the operator or in the case of an unexpected error or power disruption.

What are the Different Types of CNC Machining Processes?

A CNC machine is not one specific machine, as it is a group of different types of CNC machines working on various machining processes. Some of the most popular CNC machining operations include:

CNC Milling

CNC milling is one of the most popular types of CNC machining processes. In fact, many professional machine shops often use a CNC machining and CNC milling process interchangeably. Face milling and peripheral milling are two of the most frequently used CNC mill applications.

In a CNC milling machine, rotating cutting tools move relative to the workpiece to remove material.

The cutting tool (also called a milling tool) is fixed on a spindle that can rotate. The rotation and movement of the spindle give CNC milling machines the ability to perform three or more axes milling operations.

CNC Drilling

The CNC drilling process is a lot simpler than using milling tools or the turning process. In CNC drilling, the workpiece is held stationary while a drill bit moves over the workpiece and creates holes.

The purpose of drilling holes might be to add screw bolts, aesthetic requirements, or any other use.

CNC Grinding

CNC grinding machines use a rotating flat abrasive wheel for removing material from rough workpiece surfaces. This machine process is usually applied to create a smooth-finished part. The grinding wheel rotates at a very high speed.

CNC Routing

CNC routers are very similar to CNC milling machines. The main difference is that in a CNC router, the workpiece is always stationary, and the cutting tool moves in X, Y, and Z dimensions. CNC routers create faster cuts than milling machines without compromising accuracy and design complexity.

Other Types of CNC Machines and CNC Operations

Besides the various types mentioned above, there are other CNC processes too. Some independent fabrication machines are integrated with a CNC for automatic movement. Some of these additional CNC machines are:

Broaching

Broaching utilizes a toothed cutting head to create niche shapes on a workpiece. Broaching cuts are very consistent and highly accurate. These machines can be linear or rotary (with a rotating toothed cutting tool).

Sawing

Sawing utilizes a toothed blade for creating straight, linear cuts. The cuts are created by the removal of material due to friction with the saw blade. When operated with a CNC, this process is usually applied for the automated cutting of materials.

Honing

Honing is similar to grinding in that it is generally used for the secondary finishing of a material. In the honing process, an abrasive stone or wheel is used for controlled grinding of the workpiece, creating the desired shape, size, or finishing.

Lapping

Lapping is also similar to grinding. But, lapping uses an abrasive paste, powder, or mixture instead of a grinding wheel to create a smooth surface finish. The abrasive mixture is inserted between two materials (one of which is the workpiece) and then rubbed against each other.

CNC lathes

CNC lathes are primary shaping tools used for machining metal or wood. In a lathe machine, the workpiece is rotated around a central axis, and the machining head moves linearly along the surface. CNC lathes can perform various functions, such as cutting, drilling, sanding, knurling, facing, and more. CNC lathes perform much better than manual lathes.

Plasma Cutters

Plasma cutters are an evolved form of cutting technology, using a high-temperature plasma jet to cut material. The plasma is created by an electrical arc, so this method applies to conductive materials only.

Laser Cutters

Laser cutters use a laser beam to cut through a material. Unlike plasma cutting, laser cutting is not limited to the cutting of electrically conductive materials. Laser beams can cut through anything by adjusting the laser parameters.

Flame Cutters

Flame cutting uses an Oxy-acetylene (also known as Oxy-fuel) gaseous mixture to cut through metals. When the Oxy-fuel stream is narrowed and ignited, it creates an ultra-high temperature flame that can easily cut through metal.

Press Brakes

The purpose of Press Brakes is to bend metal plates and sheets. The material is placed between a V-shape or a U-shape die. Then the die is pressed, resulting in the bend as required.

Electric Discharge Machines (EDM)

Electrical Discharge Machines (EDMs) are used for cutting conductive materials. In EDM, electrical pulses are emitted by a cutting head near the material, which creates an electrical arc. This arc melts and removes the material at the required position resulting in a cut.

Water Jet Cutters

Waterjet cutters utilize ultra high-pressure water for the cutting action. These cutters can cut through anything: metal, alloy, wood, stone, or glass. The water jet stream is controlled by CNC and moved according to the software.

Selecting the right CNC machine for the job

When making CNC machined parts, it is important to figure out which type of machine is most suitable for the parts in question.

Every machine has its pros and cons, but it is difficult to find every kind of CNC machine in one place — except maybe at a machine trade show, or in a CNC shop willing to invest lots of money.

If the most suitable machine is not available, you need to find a way to make the parts with the machines that are available. Here are some explanations of vertical vs horizontal milling and turning machines.

Figuring out the best way to load the workpieces

When you have chosen the CNC machine to make your parts, the next step — before programing — is to find the best way to load your workpieces in order to gain the best machined result. I believe this stage is more important than making the tool paths, but in my experience, most machinists have a difficult time with it, and it prevents them from moving forward smoothly.

As a prototype machining company, we try to hire people who have an open mind and are able to find solutions in this area, since we come across different CNC parts every day. (Of course, some people quit the job within two weeks!) Check out the different CNC workholding methods.

Knowing what type of cutting tool to use

After choosing the machines and deciding on the best way to make the parts, selecting the right cutting tools will help to achieve a tighter tolerance and better surface finish. In short, suitable cutting tools result in better components.

Here’s an example: milling ribs with draft might take hours using normal sphere cutting tools, but would require just a few minutes with a taper cutter.

So imagine how much time you could save when milling 10 pieces or more. Find out the differences between types of CNC cutting and machining tools.