CNC milling, a typical CNC machining type, produces custom designed part by removing materials under computerized controls and rotating multi-point cutting tools. It is an ideal machining process to creat custom parts in different shapes. The available CNC milling materials could be metal, plastic, glass and wood. The CNC milling process begins with a CAD model, and the CAM soltware converts it to correct instructions for the CNC machine, then CNC milling machine starts working and removes the material from the workpiece following the CNC programme. CNC milling is capable to make precision custom parts for various industries.
CFS Machine Shop is not only a machining workshop, we can also combine CNC machining with other processes, including casting, forging and stamping. We are one stop shop for all your machined source, and aim to offer high quality products with competitive prices. In this article, we will introduce everthing about CNC milling, including its definition, working process, machine types, design tips and more.
What is CNC Milling?
CNC milling, a short of Computer Numerical Control milling, is a manufacturing process to shape a part using computer numerical control machining systems and a multi-point cutting tool or milling cutter. CNC milling machines are normally installed with rotary cutting tools, which move along multiple axes (typically three or more), and cut out the required shape including holes in a variety of materials, including metals, plastics, and so on.
How does CNC Milling work?
Same as other cnc machining processes, CNC milling is a machining process that cut and remove material into a desired shape by computer control of CNC milling machines.
Here are the complete CNC Milling process showing how CNC milling works:
1). Creating a 3D Model for CNC Milling
The creation of a 3D computer-aided design (CAD) model is the first step to start CNC milling process of a custom part. This model includes all vital details like size, geometry, and overall shape. It’s important for designers to create CAD models that suit the capabilities of their CNC milling machines, particularly considering features like undercuts – these are recessed areas in the item that standard tools might struggle to reach. While undercuts are possible to machine, they often require special tools or advanced milling machines, which could add to the production costs.
2). Transforming CAD Designs for CNC Application
Once the 3D CAD model for a specific part is ready, the next step is to generate a CNC program, which guides its manufacturing in the CNC milling machine. CAM software allows designers to create instructions for CNC machines, allowing them to control the movement of tools and cutters throughout the process. These programs are typically written in G-code, which handles the operational aspects of the tools like spindle speed and cutting depth, and M-code, which deals with miscellaneous functions such as tool changes and machine power control. Most CAM software also includes a simulation tool to ensure the CNC program can successfully create the intended part.
3). Preparing the CNC Milling Machine
After both the CAD model and CNC program are ready, it’s time to set up the CNC milling machine for machining jpb. This involves uploading the CNC program into the machine and placing a prepared blank material into its holding setup. The machine is also equipped with the appropriate tools, spindles, and fixtures for the task.
4). Executing the Milling Process
With everything in place – the CAD model, CNC program, and machine setup – the milling operation can start. The CNC machine largely operates independently, meticulously following the program to execute all the planned machining tasks on the material. Human involvement is usually minimal at this stage. Once the program is fully executed, the part is ready to proceed to any subsequent manufacturing steps.
Types of CNC Milling Methods
Plain Milling (Slab Milling)
Plain milling, commonly referred to as slab milling, is a foundational CNC milling method used for creating even surfaces on workpieces. It employs a straight, flat cutting tool with multiple blades, rotating on its axis while the workpiece is fixed on the mill table. This process allows for meticulous material removal. Plain milling is adept at forming flat, parallel surfaces, grooves, and slots. Its simplicity is suitable for both basic and complex tasks, with the cutter’s depth and feed rate adjustable for desired finishes. In manufacturing, plain milling is crucial for precise finishes and tasks like squaring blocks or cutting keyways. The availability of vertical and horizontal mills expands its versatility, making it indispensable for creating flat surfaces with precision in numerous machining operations.
Face milling is a technique focused on machining flat surfaces with a special ‘face mill’ cutter. Known for its efficiency, this method is integral in various sectors for material removal and surface finishing. The face mill, featuring multiple blades, spins around its axis as it shaves off the workpiece surface, ensuring a smooth finish. This method is ideal for creating large flat surfaces swiftly and accurately. Face milling excels in rapid material removal, making it perfect for roughing tasks and achieving uniform, polished finishes. The method’s adjustability in speed and feed rate allows for precision in dimensions, widely used in automotive, aerospace, and construction for machining engine blocks, aircraft parts, and flat mounting surfaces.
Angular milling, a specialized CNC milling approach, involves machining at specific angles for creating angular features, slots, and grooves. It’s essential in precision engineering and toolmaking. The workpiece is angled on the mill table, allowing the cutter to engage at the required inclination, perfect for components with dovetails, V-grooves, or other angled designs. This method is crucial in aerospace and specialized tool manufacturing, requiring precise angular cuts. Accurate setup of the workpiece’s angle and selecting the right tools are key for successful angular milling.
Form milling stands out in CNC milling for producing complex shapes and contours with high accuracy. It uses customized cutting tools, shaped to match the desired profile, methodically removing material to create detailed features. This technique is tailored for components with non-linear or irregular shapes, like gears, camshafts, and decorative elements. Common in automotive, aerospace, and toolmaking, form milling requires selecting the right tool and programming the CNC machine to trace the exact contour. Considerations include material choice, tool speed, and feed rates for optimal results. Form milling is instrumental in producing intricate, custom components in modern manufacturing.
Common CNC Milling Machines
An important reason why CNC milling is popular in today’s manufacturing is that it move on different axes. This feature allows for achieving more complex designs with faster machining speeds and fewer operations. CNC milling machines are mainly divided into three types, including vertical CNC milling machines, horizontal CNC milling machines and multi-axis CNC milling machines.
Vertical CNC Milling Machines
Vertical CNC milling machines are cost-effective and widely used. The vertical CNC milling machine makes the tool run up and down. In this case, the machine moves on three axes – X, Y, and Z. Usually, it’s the workbench that moves, not necessarily the head. This type of CNC milling machine is generally easier to program while still offering a variety of functions.
Horizontal CNC Milling Machines
The milling head of the horizontal CNC milling machine is not facing up and down, but is placed horizontally. Like vertical CNC milling machines, horizontal CNC milling machines move on at least three main axes. However, horizontal CNC milling machines can also be rotated for more complex designs. Because horizontal CNC milling machines can move on up to five axes, they are more expensive. However, they are more suitable for production workshops that produce large numbers of identical parts. Programming these machines requires more work because they require more sophisticated software.
Typically, horizontal CNC milling machines are used to cut grooves and slots on the product. However, specialty tools are also available for cutting bevels and radii, but these specialty tools tend to be more expensive. Horizontal CNC milling machines are ideal for cutting gear workpieces.
Multi-axis CNC Milling Machines
Multi-axis CNC milling machines: Multi-axis CNC milling machines are exponentially controlled milling machines that can operate on more than four axes, which provides greater flexibility and complexity. Adding more shafts also increases the cost of the device, but it can produce better parts. One of the main benefits of adding an extra shaft is that it allows the milling head to do more in the same space. Multi-axis CNC milling machines can handle everything themselves without the need for workers to move and rearrange them.
3-Axis CNC milling machines are simple and efficient machines in which the workpiece is fixed in one position. 4-Axis CNC milling machines require high-end software, but they offer greater flexibility and production capacity. 5-Axis CNC milling machines can move cutting tools or parts along five axes simultaneously, providing the manufacturing capability to produce a variety of more complex and precise parts.
Understanding 3-, 4- and 5-Axis Milling Machines
3-Axis CNC Milling Machine
3-axis CNC milling machine generally refers to the machine with 3-axis, which move in straight lines in different directions, such as up and down, front and back, and left and right.
Three axes can only be processed one face at a time, which is suitable for machining some disk parts, which is a limitation for many parts that need to process holes or grooves on multiple faces.
4-Axis CNC Milling Machine
4-axis CNC milling machine adds a rotating axis on the 3 axis, generally 360° horizontal rotation. But can not be rotated at high speed, suitable for machining some box parts.
Most 4-axis CNC milling machines also allow the workpiece to rotate, which is called the B-axis, so that the machine can act as both a milling machine and a lathe.
If you need to drill into the side of a part or the curved surface of a cylinder, 4-axis CNC machining is the way to go. It greatly speeds up the machining process and has high machining accuracy.
5-Axis CNC Milling Machine
5-axis CNC milling machine has one more rotating shaft above the 4-axis, generally 360° rotation of the upright surface, and the 5-axis can be fully processed, and a clamping can be achieved, which can reduce the clamping cost and reduce product scratches.
Due to the high versatility of 5-axis CNC milling machine, it can be used to manufacture complex precision parts. For example, medical parts for artificial limbs or bones, aerospace parts, titanium parts, oil and gas machinery parts, military products, etc.
CNC Milling Materials
CNC milling machine has a very good machining adaptability to metal materials, and can be used to process a variety of metal materials, including steel, aluminum, copper, iron and so on. Different materials of metal have different characteristics and difficulties in the machining of CNC milling machines. For example, the copper material has good thermal and electrical conductivity, but the hardness is low, and the tool is easy to jam. Stainless steel materials have higher hardness, but are not easy to machine, requiring the use of high-speed cutting tools. In general, CNC milling machines have high accuracy and efficiency for the machining of various metal materials.
CNC milling machine is also very suitable for the machining of plastic materials, including ABS, PC, POM, PVC and other common plastic materials. Plastic materials have the characteristics of light weight and corrosion resistance, but compared with metal materials, its hardness is low, and the machining difficulty is relatively small. The CNC milling machine can control the speed, depth and angle of the machining, making the machining process more precise and efficient.
In recent years, the application of composite materials in industrial production has been more and more extensive, and the machining of composite materials by CNC milling machine has been paid more and more attention. The machining of composite materials is more difficult because different materials cannot be processed by traditional processing methods. CNC milling machine can complete the machining of composite materials by controlling the speed and feed speed of the saw blade. The composite material has the characteristics of thin and light, pressure resistance, etc., and is widely used in the manufacture of high-tech fields such as aviation, aerospace and automobile.
Tips: When selecting materials for CNC milling, several factors should be considered. These include the machinability of the material, the properties required for the final product (such as strength, weight and corrosion resistance), the yield and the cost of the material.
For example, if high volume is required, the material that is easy to machine and relatively inexpensive would be ideal. On the other hand, if the final product needs to have high strength and corrosion resistance, hard metals or composite materials may be the best choice.
Advantages and Disadvantages of CNC Milling
Advantages of CNC Milling:
- High Dimensional Accuracy
One of the biggest advantages of using CNC milling machines is that they can manufacture parts exactly to specifications. Because CNC milling machines rely on computer instructions to make parts, the possibility of human error common in manually operated machines is eliminated. This means that you can precisely create complex parts while achieving tolerances as low as 0.004 mm.
- Fast and Efficient
Conventional milling machines usually require the operator to manually change the cutting tool according to the cutting operation to be performed. This is not only time consuming, but also inefficient, as the final result depends on the operator’s judgment.
The CNC milling machine is equipped with a rotating turntable and can accommodate up to 30 different tools. These tools are automatically changed on the spindle during machining operations, allowing for quick and efficient cutting operations. With a CNC milling machine, you can have parts ready in a few hours, while traditional methods can take days (or weeks) to complete.
- A Variety of Material Selection
CNC milling machines are compatible with a wide range of materials, including plastics, metals and composites. As long as you have the material block, the CNC milling machine will have no problem machining it.
Disadvantages of CNC Milling
- High machine cost
The initial investment cost of CNC milling machines is higher than that of traditional manual equipments. That could push up overall manufacturing costs.
- Intensive operator training is required
Not just anyone can operate a CNC milling machine. From designers to programmers and machine operators, all need adequate training to get the best out of the process.
- High level of maintenance
Milling machines must be maintained frequently to ensure their proper operation and extend tool life. This increases downtime using the milling machine.
How to Design parts for CNC Milling?
Designing parts for CNC (Computer Numerical Control) milling involves careful consideration of various factors to ensure the manufacturability, quality, and cost-effectiveness of the final product. Here are six key principles and guidelines for designing parts for CNC milling:
Understand CNC Milling Capabilities
Before designing a part for CNC milling, it’s crucial to have a good understanding of the capabilities and limitations of CNC machines. Familiarize yourself with the types of CNC milling machines, tooling options, and the range of materials that can be used. This knowledge will help you make informed decisions during the design process and optimize your design for efficient machining.
Design for Machinability
Design parts with manufacturability in mind. Consider factors such as tool access, toolpath optimization, and material selection. Avoid intricate or sharp internal corners that may be difficult to machine or require specialized tooling. Use standard tool sizes and toolpaths whenever possible to minimize machining time and tool wear. Additionally, consider the order of machining operations to ensure stability and accuracy throughout the process.
Tolerances and Surface Finish
Specify the required tolerances and surface finish for your part. CNC milling can achieve tight tolerances and excellent surface finishes, but these factors affect machining time and cost. Clearly communicate your tolerance requirements on the design drawings, and consider the trade-offs between tighter tolerances and increased machining complexity. Be aware that achieving high surface finishes may require additional tooling or post-machining processes.
Choose the appropriate material for your part based on its mechanical properties, environmental conditions, and application requirements. Different materials have varying machinability characteristics, so consider how your material choice will affect the machining process. Discuss material options with your CNC machining provider to ensure you select the most suitable material for your project.
Design for Tool Access
Pay attention to tool access when designing your part. CNC milling machines have limitations in terms of tool reach and clearance, especially for complex geometries. Avoid deep pockets or features that may require long tool extensions, as these can lead to tool deflection and reduced accuracy. Consider breaking down complex parts into multiple simpler components, which can be machined more easily and assembled later.
Minimize Wasted Material
Design parts to minimize material waste. This not only reduces material costs but also benefits the environment. Use efficient nesting and placement of parts within the raw material stock to optimize material utilization. Consider designing parts with features that allow for efficient scrap removal during machining. Additionally, explore the possibility of using pre-cut or pre-sized material stock to minimize waste and reduce machining time.
To further assist in designing parts for CNC milling, consider using CAD (Computer-Aided Design) software that integrates with CAM (Computer-Aided Manufacturing) capabilities. This allows you to generate toolpaths directly from your design, ensuring seamless communication between design and manufacturing processes.
Collaboration between designers and CNC machining experts like CFS Machine Shop is essential to optimize part designs for CNC milling. Engaging with your machining provider early in the design process can lead to more efficient and cost-effective solutions while ensuring that your final product meets your quality and performance requirements.
CNC Milling Applications
CNC milling is a precision machining method, through CNC machine tools and computer control system independent of manual operation, it can achieve high precision machining of workpiece shape and surface accuracy. CNC milling has the advantages of high efficiency, accuracy and flexibility, and is widely used in machinery manufacturing, aerospace, mold manufacturing, automobile manufacturing and other fields.
First of all, CNC milling has a wide range of applications in the field of mechanical manufacturing. CNC milling can be used to produce various mechanical parts, such as bearing seats, flanges, gears, keyways, etc. By setting the appropriate machining parameters, high precision size and shape requirements can be achieved, and the precision and quality of parts can be improved.
Secondly, the application of CNC milling in the aerospace field is also very important. The aerospace field has very high machining requirements for parts, and needs to achieve high-precision and complex shape. CNC milling can precisely control the motion path of the milling cutter on the workpiece through the computer control system, and realize the machining of complex surfaces, thin-walled structures and other shapes, and improve the performance and safety of parts.
Thirdly, mold manufacturing is another important application area of CNC milling. Molds usually require highly accurate machining, and CNC milling has a wide range of applications in mold manufacturing. For example, in plastic injection mold manufacturing, CNC milling can achieve complex cavity structure and mold manufacturing with high surface quality requirements; In the machining of multi-axis compound stamping die, CNC milling can realize the machining requirements of complex curves and high precision.
CNC milling can also be used in automobile manufacturing. Modern cars are often lightweight in design, requiring complex curved parts to be machined. CNC milling can realize the machining of complex surfaces and lightweight designs by processing lightweight materials such as aluminum alloy and titanium alloy, and improve the performance and reliability of auto parts.
In addition, CNC milling is also widely used in electronic products, optical instruments, medical equipment and other fields. In the manufacture of electronic products, such as the shell processing of mobile phones, tablet computers, etc., high precision CNC milling is often required. The precision and surface quality requirements of optical instruments and medical equipment are also high, and CNC milling can meet these requirements.
Contact CFS Machine Shop for CNC Machining Services
As a professional CNC machining manufacturer, CFS Machine Shop offers precision CNC milling solutions for a wide range of custom metal parts. Our in house CNC milling machines and experienced team ensure high-quality results with tight tolerances and efficient production.
Whether you need aerospace components, automotive parts, medical device prototypes, or custom machining solutions, we have the expertise and capabilities to meet your needs.
Contact us today if you are looking for CNC machining services in China, and let us be your reliable partner in precision machining.