What is CNC Milling: Definition, Work Process & Technologies
CNC milling is one of the most impressive technological advances of this century.
Although most people are more familiar with 3D printing as a way to produce precise physical prints, CNC milling has been around for longer and is still widely used today.
From its wide range of applications in the electronics industry to its prevalent use by manufacturing companies, the technology is still rapidly growing and evolving as more and more companies are discovering its effectiveness.
So, with CNC machining expanding to new industries such as musical instrument manufacturing, it’s not surprising that the technology itself is estimated to become a 100 billion dollar industry by 2025.
Still, even though the process and uses of CNC milling are well-known to people operating in the industry, those on the outside might be much less familiar with how it can be applied or even how it works.
So, in this article, let’s dig deep into the subject of what CNC milling is, how it differs from 3D printing, who might benefit the most from the technology, and answer all of the essential questions that you might have.
What is CNC Milling?
To understand the CNC Milling process, let us break it down into its two components- ‘CNC’ and ‘Milling’. Milling is one of types of machining operations where a workpiece is rotated along rotational axes and cutting tools are used to chip away pieces of the workpiece.
This is done to shape the workpiece as per the requirement. An important thing to note is that this technology is different from other shaping methods like 3D printing.
This is because milling works by removing material from the workpiece while other alternatives work by adding material to the workpiece.
Now coming to ‘CNC’, it stands for Computer Numerical Control. CNC allows controlling the cutters and workpiece movement with computer software. With computerized controls, there is no need for manual labor to control the movement processes.
CNC milling is a type of CNC machining process that uses milling machines, equipped with rotary cutting tools and controlled by computer numerical control technology, to perform precise movements and tasks. CNC milling makes it possible to take a digital design of an object and produce it in a physical form from raw materials.
Who Invented CNC Milling?
The concept of milling dates back to the 18th century. However, the first CNC milling machines were first developed in the early 1950s.
The credit for inventing the CNC milling machines goes to Richard Kegg. He created this machine with assistance from MIT in 1952 and called it the Cincinnati Milacron Hydrotel.
How Does CNC Milling Work?
In principle, CNC milling is a basic process where you take an initial workpiece and keep on removing material from it at different locations with a cutting tool. To reach these different locations, the workpiece keeps on rotating.
In actuality, the whole CNC milling process goes through a number of steps.
What are the different stages of a typical CNC Milling process?
Creating CAD Model
First things first, you need to prepare a CAD model blueprint for your intended part shape. CAD stands for Computer Aided Design. As the name suggests, CAD software helps you in creating a 2-D or 3-D model for anything you have in mind.
Converting CAD to CNC
The CNC milling machine will not recognize a CAD model directly. However, you can convert the CAD model to a CNC program very easily. These features are already present in most CAD software.
Setup of CNC Milling Machines
Before starting the program, it is important to properly set up the machine and the workpiece. The particular steps of setting up the CNC machine can vary based on different manufacturers and different models.
Executing the Program
Once the machine is properly set up, the operator can execute the CNC machine program. The entire milling process that follows will be done automatically. Once the program execution is complete, the required part will be created by the machine.
What are the Different CNC Milling Methods?
Due to the vast application of the CNC milling process, it is now no longer a single process but, in fact, a big field in itself. There are many different forms of CNC milling operations available nowadays. These different CNC milling methods include:
Plain milling is the most popular milling process out there. In plain milling, the purpose is to create flat surfaces that are parallel to the rotational axes of the cutting tool.
In angular milling, the milling takes place by removing material from a flat surface with the cutter cutting the workpiece at an angle that is not a right angle. To understand it better, think of it as an angled cutter removing material from the workpiece.
In face milling, the workpiece that is milled is at a right angle to the rotational axes of the cutter. This milling process is usually applied for machining the face of bars and plates.
Form milling process applies to the machining of the workpiece to create irregular surfaces such as curves. In form milling, the shape of the cutter is the same as the required shape of the contours.
Other CNC Milling operations
Besides these common CNC milling processes, there are some other methods as well to create specialized parts. These methods include:
In Gang milling, two or more cutting tools are mounted on a single machine arbor. Every cutter works individually on the workpiece, increasing the production rate. The cutters can vary in terms of their shape and size.
Straddle milling is a specialized form of gang milling machine. In straddle milling, the two or more cutting tools are mounted parallel to each other. These cutters work on the face and sides of the workpiece at the same time.
Gear milling is also known as gear cutting. It is a very niche form of milling applied for the creation of gears. It utilizes curved cutters to remove the materials from the intended gear teeth spacing.
Profile milling is used for completing the finishing process of shaping, including working on the vertical or slanted surfaces. This CNC milling process is also used for finishing the convex and concave surface of the workpiece.
Equipment and Components of CNC Milling Process
Here are the different components that you will go through during the entire process of CNC milling:
As we mentioned in the previous sections, designing a CNC model requires using a Computer Aided Design (CAD) software and a Computer Aided Manufacturing (CAM) software. CAD will do the job of designing the part and CAM does the job of making the CNC machine understand the design.
CNC Milling Machine Components
Obviously, CNC milling cannot be completed without a CNC milling machine. There are many different types of milling machines out there. The components of the machine can vary based on the model you use.
In general, you will find the following components in all CNC milling machines:
- Worktable: The worktable holds the workpiece that requires CNC milling. In general, the workpiece is fastened to the worktable with a withholding device.
- Saddle: The saddle is present under the worktable for support. The saddle also provides movement to the worktable in parallel to the spindle axis.
- Spindle: The spindle holds the cutting tool (also known as the cutting tool) and is responsible for the movement of the cutting tool.
- Arbor: Arbor is the shaft that passes through the spindle. In the case of gang milling and saddle milling, multiple cutting tools can be mounted on the same arbors. Arbors come in many different shapes and sizes, their use depending on the requirement and type of milling machine.
- Ram: Ram is not present in all milling machines. It is usually seen in vertical milling machines and angular milling machines. It provides support to the spindle. Ram can be adjusted in different positions for different cutting requirements.
- Machine Tools: A machine tool or cutting tool is the component to remove material from the workpiece. There are many different types of cutting tools available, which we will go through shortly.
- Interface: The Machine Interface is the digital console present on the CNC milling machine. The operator makes use of the interface to load and execute the programs and perform basic CNC milling operations.
- Knee: The knee is present under the saddle for support. The knee can be adjusted in position vertically. Raised or lowered knee can provide the option for adjusting the workpiece height for different milling requirements.
- Column: The column can be seen as the skeleton of the entire CNC milling machine. It provides mechanical strength to the machine by holding together the entire assembly. The column can have additional sections inside to hold the cooling oil and other assemblies.
What are the Different Types of Cutting Tools for CNC Milling Machines?
CNC milling has such wide applications that there are many different types of cutting tools available for different jobs. Some of these CNC cutting tools are:
- End Mills
- Face Mills
- Slab Milling
- Fly Cutter
- Ball Cutter
- Multi-Point Cutting Tools
- Hollow Mill Cutter
- Involute Gear Cutter
- Threads Cutting Tool
- Slide and Face Cutters
- Hobbling Cutter Tool
- Dovetails Cutter Tools
- Roughing End Mills
What are the Different Types of CNC Milling Machines?
Here is a short overview of the different types of CNC milling operations in use.
In horizontal machines, the spindle is present in parallel to the surface of the workpiece. It can create flat surfaces, planes, inclined planes, and grooves on the workpiece.
You can think of vertical milling operations as a drilling operation since the spindle is present perpendicular to the stationary workpiece or the flat moving surface of the workpiece.
For more information on the process, you can check our comparison of horizontal vs vertical milling machines.
In multi-axis milling, the cutting tool can move in four or more directions.
In case of 5 directions, the machine is called a 5-axis machine. The higher the axis, the more intricate parts can be created.
Column and Knee Milling
Column and knee milling machines are also called variable speed milling machines. In these machines, there is a very accurate vertical movement of the column and knee assembly, used for precise vertical milling operation.
Ram Milling Machine
In a ram milling machine, the cutting tool can be moved on the horizontal axis in the forward or rear direction. This is accomplished by a movable ram attached to the spindle.
Fixed Bed Manufacturing Milling Machine
In these machines, there is no movement of the column, the knee, or the saddle. The stationary workpiece is on the worktable directly mounted on the bed of the machine. Due to a simple design, these machines are generally cheaper than the others.
Planer Milling Operations
In planer milling, the cutting action occurs in a single plane by the linear relative motion of the workpiece and the cutting tool. These milling machines are used for creating flat surfaces.
To make a decision about which milling machine you require, you can read our detailed guide about the same.
What Are The Applications and Uses of a CNC Milling Machine?
To have an accurate idea about the applications of CNC milling, let us divide our discussion into two parts- the materials it supports and the industries that make use of the process directly or indirectly.
You already are familiar with what is CNC milling. It is used for shaping the parts and molding them as per requirements. Here are the materials on which you can apply the process of CNC milling:
Materials Compatible With CNC Milling
Metals are one of the most common materials that undergo the milling process. Metals melt at very high temperatures, rendering them useless for processes like 3d printing. Therefore, CNC milling is the best way to shape metals.
Plastics and Elastomers also work well with CNC milling due to their physical and chemical properties. Using high-temperature methods for plastics often changes their chemical composition.
Additionally, they also release toxic fumes on heating. Therefore, a process like CNC milling where there is no heat is ideal for these materials.
Ceramics and Composites often have temperature resistance properties, making them unusable for 3D printing and molding processes. CNC milling works best for these materials as it can work without harming the materials in any way.
Many people aren’t aware of this, but you can also shape glass using the CNC milling process. Glass is brittle and can break easily with other shaping processes. Therefore, using CNC milling with an appropriate cutting tool is a good choice for such materials.
For more specific materials and use cases, check our guide on CNC milling material and how to choose one for your application.
Industries That Use CNC Milling Machines
You will be surprised at the number of industries that use the CNC milling process.
Of course, this surprise will settle when you read about the advantages of CNC milling over other alternatives in the next section.
One of the most popular ways to use CNC technology is for rapid prototyping, providing designers and engineers with a fast and reliable way of seeing how the product or part looks at various stages of development.
Some of the industries that use CNC milling are:
Automotive industries require a lot of custom manufacturing services for parts that go into the vehicle. These parts are created using CNC milling machines for the manufacturing processes as well as repairs.
Because of the extremely high precision of CNC milling services, it’s understandable why they have become widely used in the aerospace industry, where the technology plays a crucial role in producing a wide range of parts used to ensure the safety and proper function of aircraft.
Aerospace industry works with a lot of specialized materials that have very high hardness as well as resistance to high temperatures. For the shaping of these materials, the industry heavily relies on CNC milling machines.
Some of the parts that are produced using CNC technology include engine components, landing gear components, and fuel panels.
A CNC milling machine is the backbone of any metal fabrication industry. A CNC machine is fast, automatic, as well as efficient. Additionally, it can work on the entire range of metals. Therefore, you will find a milling machine in every metal fabrication workshop.
Agricultural equipment requires a lot of large size custom-made tools and components. These are created using custom manufacturing services of a CNC milling machine.
The high versatility and preciseness of the CNC milling machine make it ideal for the electronics industry. CNC milling machine not only shapes the conductors and metals required for transmission, but also the polymer boards that house these conductors.
In the medical sector, specialized parts are required not just for diagnosis but also for applications such as prostheses. These are created using CNC milling by using the appropriate designs.
CNC milling allows manufacturing parts and tools from many grades of titanium and stainless steel, which are often used in making scalpels, medical devices, as well as implants.
CNC milling is also used for creating military components. In fact, the earliest application of the milling process was used for the manufacturing of weapons. Even prototypes of defense parts are made using a CNC milling machine.
Besides these industries, CNC milling is also applied in sectors such as mining, oil, and gas, automation, energy, etc.
Main Advantages of CNC Milling
There are countless reasons why CNC milling technology is widely regarded as one of the most reliable ways to produce parts from various materials.
Let’s look at some of the most significant advantages of CNC milling and machining below:
- High Production Rate – CNC milling is an automated process, and there are no human limitations on the speed at which the cutting tool can move. This creates a high production rate that is unmatchable by other manufacturing processes.
- Unmatched Precision – The accuracy and precision with which CNC milling can operate are second to none in the entire world, which is why it is used in fields like aerospace and medicine that need each detail to be executed without even the slightest error. Using a digital template and autonomous machining that CNC milling is based on, human error is eliminated from the manufacturing process, and the accuracy that is produced is as near perfection as is possible today.
- Longevity – Because the CNC milling machines can run practically on autopilot and don’t require much human involvement in the process, they can run without stopping for days, producing parts consistently and with the same precision. The only time that CNC machines need to be stopped is when they require regular maintenance or if there is an accident.
- Fewer Personnel – The automated process that CNC milling is based on also means that fewer people are required to monitor and run it, which results in not only increased efficiency but in reduced production costs as well. A few skilled specialists are all that’s needed to oversee the entire process, which means better cost-effectiveness for the end client.
- Advanced Possibilities – Because of the advanced automation software and design software, CNC milling machines can outperform the most skilled technicians operating manual machines, even if the manufacturing process itself is similar. This means not only better consistency and the elimination of human error but also the ability to produce designs that are much more complex, with varying sizes, shapes, and even textures.
- Consistency – Since the process behind CNC milling is mostly automated, it produces remarkable consistency, even if personnel managing the tools changes. Once a master file of the design is created, it can be used to create an unlimited number of copies that will all be of the same quality and without any deviations. Each part will be a perfect match to the previous version, which is very hard to achieve even for the most skilled manual operators.
- Scalable – CNC milling is a very scalable solution. The method can be adopted by industries of every size. If you are using it for your workshop, the process can grow as the size of your workshop grows. Additionally, a CNC milling machine can be applied to parts of all shapes and sizes.
How Much Does a CNC Milling Machine Cost?
There are many parameters that affect the cost of CNC milling machines. Due to this, the bracket of the price range for these machines is very high.
For instance, you can find a small horizontal milling machine for as low as $10,000. At the same time, there are large CNC machines with advanced features where prices can go upward of $300,000.
Check our dedicated guide to better understand the various factors that determine how much does CNC milling cost.
CNC Milling vs 3D Printing
To understand how well CNC milling fares against other alternatives, let us have a detailed comparison of CNC milling vs its closes competitor- 3D Printing.
First things first, the basic principle of CNC milling and 3D printing is entirely opposite. 3D printing is an Additive Manufacturing process. This means that it works to create a piece by adding material layer by layer, usually by melting the material wire.
On the other hand, the CNC milling process is a subtractive manufacturing process. This means that it starts with a block of material and creates the required part by removing material from this block.
Since 3D printing works by melting the material wire and using it to make the parts, it works for only special types of polymer materials that are able to withstand the process. On the other hand, CNC milling is a very versatile process and can be applied to a wide range of materials.
Ease of Use
Both CNC machine and 3D printing requires a software to create the initial design for the machine. However, CNC manufacturing requires choosing between different tools and setup of these tools, and different position settings.
3D printing has no extensive setup requirements. Therefore, 3D printing is considered a simpler process while milling requires a skilled operator.
The relative accuracy of milling vs 3D printing can vary based on which model of each you choose. Most CNC milling machines generally have superior accuracy over 3D printing. However, there are many shapes and geometry that can only be created with 3D printing.
Whether milling or 3D printing is cheaper will depend on what you require of the machine. For large-scale requirements, milling is the cheaper option. However, for prototypes and small-scale requirements, 3D printing tends to be more effective cost-wise.
How to Choose CNC Milling Services?
CNC milling can be incredibly useful for a wide variety of projects. Still, to take advantage of the benefits listed above, you must take the time to find a reliable company to work with.
There’s actually a wide range of CNC milling operations offered by companies from all over the world, so you need to have at least a basic understanding of what you need before reaching out to potential candidates.
For one thing, you should have at least some ideas about what types of parts you want to be manufactured or what kinds of tools you would need. If you don’t, you’ll have a harder time narrowing down the list of companies that would be able to provide you with the necessary CNC milling services.
Alternatively, you could reach out to a reputable company that has extensive experience and offers a range of services, as they could help consult you to determine the best course of action in your situation.
Since the technology and expertise required in CNC milling projects are high, it’s imperative to seek out companies with the necessary experience, as well as a solid reputation.
Go through the testimonials and reviews from previous clients and look at what types of experiences they had with the company, as well as what problems they were able to solve.
Once you have narrowed down the list of choices to around five companies, reach out to them and ask questions about their approach, their suggestions for your project, the price for executing it, and anything else that you think could be relevant.
Quite a few companies offer Computer Numerical Control milling services, but while finding a reasonable price is important, it must not come at the cost of inferior quality.
Computer Numerical Control milling is one of the best gifts that modern technology has given us. It provides us with unprecedented production rates, higher accuracy, higher quality finishes, and the ability to work with all materials.
If you require any type of CNC machining operations for your next project, you can get in touch with 3ERP. It provides reliable machining and manufacturing services with fast delivery rates and the lowest costs.