What is CNC machining? A Comprehensive Guide

Today you will learn about CNC machining and its applications.

This comprehensive guide will cover the following topics;

1. What is CNC machining?
2. Types of CNC machining operation
3. Equipment and Components used
4. Materials used

Let’s dive right in.

 

What is CNC machining?

CNC machining is a term common in industrial manufacturing.

CNC stands for Computer numerical control. CNC machining is a subtractive manufacturing technique that utilizes computerized controls and tools.

Machine tools remove layers of material from a workpiece to make custom-designed parts.

A CNC machine is programmable and autonomous.

The process can use a wide range of materials including and not limited to;

• Metals
• Plastics
• Wood
• Foam
• Composites

Here are some of its applications.

• CNC machining for Automotive part production
• CNC machining for the Aerospace industries
• CNC machining for consumer goods and electronics
• CNC machining for the health sector among others.

Subtractive manufacturing has its counterpart- additive manufacturing. The process of additive manufacturing involves 3D printing.

We also have formative manufacturing processes like plastic injection molding.

While subtractive manufacturing removes layers, additive manufacturing assembles them. This is where the issue of wastage in CNC machining arises.

Each process has its pros and cons. Today, we will be focusing on the types of operations, equipment and materials used.

I know you want to know how the process works which brings me to the next topic.

The CNC machining process

Let’s take a quick recap;

• There is the use of computerized controls to manipulate machine tools to shape out a part
• The process involves removing layers from a workpiece hence the term subtractive manufacturing
• A CNC machine is programmable and autonomous

Digging deeper we find that the CNC machining process has the following stages;

1. Designing a Computer-aided design (CAD) model
2. Converting the CAD file to a CNC program
3. Preparing the CNC machine
4. Actual machining operations

CAD Model Design

You can design your CAD model in-house or hire a company providing the services.

It is a 2D vector or 3D solid part that is a replica of the desired product. With this type of software, manufacturers can tune their parts’ geometries.

Once the design is complete the designer exports it into a CNC-compatible file format. It can either be a STEP or IGES file format.

In the 21st century, you can design anything, your only limitation is the CNC machine. Most machine tools are cylindrical. This results in parts without sharp corners.

The nature of the materials used and machine workload capabilities further restrict designing.

Before we go to file conversion let’s take a quick peek at CNC machining tolerances.

Machines are accurate but they live small variations on each duplicate part of around

_/+ .005in

This is approximately twice the size of a human hair strand. Machine Tolerances are different but some parts need the dimensions not to be bigger. A machine in this case can go on the lower side. To save costs manufactures specify areas that need such tolerances.

 

CAD File Conversion

After formatting a CAD design, it is run through computer-aided manufacturing software. It extracts the part’s geometry and creates digital commands to guide machine tools.

The machines have several programming languages. The most common ones are G-code and M-code.

The general/geometric code (G-code) when, where, and how machine tools move eg- what path to take, and how fast to move.

The miscellaneous function code M-code controls auxiliary functions in a CNC machine.

When the program is complete, the manufacturer will feed it into a CNC machine.

Machine preparation

Machine setup is vital before running the CNC program. The operator makes sure machinery spindles and machine vises are in place.

The required tooling is also affixed to the machine. These can be drill bits or end mills. The operator also introduces the workpiece into the CNC machine.

Once the machine is ready, the operator can start the CNC program.

CNC machining Operation Execution

Once the CNC program is up and running, it prompts the CNC machine to start the process. The program dictates the tooling’s action on the workpiece. It guides it all through the process as it works on the workpiece to give a custom part.

Some firms invest in their CNC machines for in-house production. Others hire dedicated CNC machining service providers.

What types of CNC machining operations involved?

CNC Machining Operations

In this section, we will cover the common mechanical operations in a CNC machine. They include;

1. Drilling
2. Milling
3. Turning

CNC Drilling

The process of CNC drilling employs multipoint drill bits to create vertical holes. The machine drives the drill bit perpendicular to the surface of the workpiece.

The diameter of the holes produced is equal to the rotating drill bit.

Angular drilling is possible through the use of specialized operations and workholding devices.

Some of the operations under CNC drilling are;

• Counterboring
• Countersinking
• Reaming
• Tapping

CNC Milling

The process of drilling uses rotating multipoint cutting tools. The cutting tools remove materials from the workpiece to generate the desired part.

What is the difference between CNC milling and manual milling?

A CNC machine feeds the workpiece in the same direction as the rotating cutting tool. In manual milling, the workpiece’s direction is opposite to the rotating cutting tool.

Here are some operations under CNC milling;

• Face milling- involves cutting shallow flat surfaces and flat cavities on the workpiece.
• Peripheral milling- involves cutting deep cavities on the workpiece. They can be slots or threads.

CNC Turning

This process employs a single-point cutting tool. Unlike the previous operations. the cutting tools in CNC turning are stationary.

A CNC Lathe feeds the cutting tool on a linear axis along the circumference of a

rotating workpiece.

The cutting tool removes material along the circumference to achieve your desired diameter.

It is ideal for creating cylindrical parts with internal and external features. Examples are slots grooves, tappers, and threads.

A CNC mill with rotating cutting tools is best for complex parts.

CNC lathes work best for the fast production of accurate rounded parts.

Common CNC machining operation characteristics.

CNC machining operation	Characteristics
CNC Drilling	Uses rotating multi-point drill bits Perpendicular or angular drilling Cylindrical holes
CNC Milling	Rotating multipoint cutting tools Cutting tool and workpiece move in the same direction Produces a wide range of products Removal of material from the workpiece
CNC Turning	Single point stationary cutting tools Rotating workpiece Removes material along the circumference

Other operations are;

1. Broaching
2. Sawing
3. Grinding
4. Honing
5. Lapping

CNC Machining Equipment and Components

We have seen the various types of machining operations. With it comes different software, equipment, and tools, or efficient machining.

We will now shift our focus to the various types of equipment and components of a CNC machine.

 

CNC Machining Software

To ensure accuracy and precision, engineers use the following software;

1. CAD
2. CAM
3. CAE

CAD: Computer-aided design (CAD) software generates a 2D vector or a 3D solid part model. It also documents all technical specifications of the part at hand. It is also used to simulate a product without prototyping.

CAM: Computer-aided manufacturing (CAM) software extracts the technical information from a CAD model. It then generates the necessary commands to guide the machine tooling. The machine tooling carves out the desired part following the program’s prompts.

CAE: Computer-aided engineering (CAE) software plays part in the following production phases;

• Pre-processing
• Analysis
• Post-processing

Engineers use it as an assistive support tool for analysis applications like;

• Design
• Simulation
• Planing
• Manufacturing
• Diagnosis
• Repair

Its main aim is to test and change the design.

Software used include;

• Fine element analysis (FEA) software
• Computational fluid dynamics (CFD) software
• Multibody dynamics software

There are instances where the three software can combine to run as a single unit. You can call this integrated program the CAD/CAM/CAE software.

 

Types of CNC machine tools

The process of machining utilizes several tools including;

CNC Drilling Equipment

The CNC drilling employs multipoint rotating drill bits. The nature of the drill bits allows chip to fall away from the workpiece. Types of drills include;

• Spotting drills- Used to drill shallow or pilot holes
• Peck drills- Used to reduce chip on the workpiece
• Screw machine drills- Used to make holes without using pilot holes
• Chucking reamer- Used to enlarge existing holes

CNC Milling Equipment

The CNC milling process uses rotating multipoint cutting tools. The tools can have a vertical or horizontal alignment. Types of milling tools include; end mills, helical mills, and chamfer mills.

CNC machines also have milling machinery called mill machines or mills. Mills have 3-axis movement with advanced mills having up to 5-axis rotation.

Types of mills include; hand, plain, universal, and omniversal milling machines.

CNC Turning Equipment

The CNC turning process used stationary single-point cutting tools and a rotating workpiece. The turning tools are available for; roughing, finishing, threading, and grooving.

CNC machines have lathes and turning machines. Examples of CNC lathes are; turret, engine, and special purpose lathes.

CNC Machining Materials

The process of CNC machining uses several materials.

They include;

Metal- Steel, titanium, aluminum

Plastics

Wood

Foam

Composites

Materials used in CNC machining ought to have;

Enough hardness, shear, and tensile strength, and chemical and temperature resistance

There are some essential questions you must ask yourself before choosing materials. These are;

1. What purpose will the part serve?
2. Indoor vs Outdoor environment
3. Stress load
4. Type of tolerance required
5. Dimensional tolerance
6. Type of fastening required
7. What is the operating temperature.

Useful tips on CNC machining materials

1. Never assume that metals are your only option
2. There is a wide variety of plastic materials
3. Rigid foam and carve foam have different purposes

Summary

We have gone through the basics of CNC machining operations. You now know what CNC machining is, how the process work, and the equipment used.

If you still have any burning questions, please drop us a line in the comment section below.