Today, computer numerical control (CNC) milling machines have evolved over the years to produce precision parts that meet the stringent requirements of today’s demanding industries. The applications for CNC milling machines are nearly endless and span many industries, such as aerospace, automotive, robotics, and the medical industry. Countless products, from smartphones to supersonic jets, benefit from the reliability and versatility of CNC milling. It is an ideal method for rapid prototyping and mass production of plastics and metals.
What is CNC Milling?
CNC milling is a manufacturing process that uses a cutting tool mounted on a rotating spindle to selectively remove material from a piece of raw substrate. The workpiece is rigidly mounted on a table that moves or rotates in different planes so the tool can work at multiple angles. Advanced CNC milling machines can have 5 or more axes of independent motion to make more complex shapes or avoid moving the workpiece to a separate machine.
How does CNC milling work?
The CNC milling process begins with the creation of a 2D or 3D CAD part design. The complete design is then exported to a CNC-compatible file format and converted by CAM software into a CNC machine program that dictates the machine’s actions and the movement of the tool across the workpiece. Before operators run the CNC program, they prepare the CNC milling machine by securing the workpiece to the machine’s work surface (i.e., table) or workholding fixture (e.g., vise) and mounting the milling tool to the machine’s spindle. The CNC milling process employs a horizontal or vertical CNC-capable milling machine – depending on the specifications and requirements of the milling application – and rotating multi-point (i.e., multi-tooth) cutting tools such as milling cutters and drill bits. When the machine is ready, the operator initiates the program through the machine interface, prompting the machine to perform the milling operation. Once the CNC milling process is initiated, the machine begins spinning the cutting tool at speeds of up to thousands of revolutions per minute.
CNC milling is a subtractive machining technology that can produce both large and small quantities of highly complex and precision parts. To remove material from a blank workpiece, a milling machine uses a rotating cylindrical tool called a milling cutter. Depending on the milling machine used, the machine can cut at different angles and move along different axes. The final part will first be designed through CAD, or computer-aided design, and then fed into the milling machine for final production.
What does a CNC milling machine do?
CNC milling machines use subtractive machining techniques to create complex parts for a variety of industries. The milling machine cuts the workpiece and machines the final part through 3, 4, or 5 axes. Depending on the number of axes the CNC mill has, the more complex the final part can be. CNC milling machines are used by a variety of industries, including aerospace and medical, to create complex parts.
Differences between 3, 4, and 5-axis CNC milling machines
The complexity of the CNC milling process depends on the design of the final part. The more important and high-end the structure of the part or product, the more complex the design may need to be. For complex designs that require high precision, such as medical or aerospace components, more complex machines such as 5-axis CNC milling machines may need to be used. This is to achieve the final design, surface finish, and aesthetics.
Milling machines usually have 3, 4, or 5 axes. For simpler parts, fewer axes are required to achieve the final design. Simple geometries can usually use 3-axis milling machines. They are easy to program and operate, and achieve excellent accuracy at a low cost. The cutting tool is attached to a spindle that works on three linear axes. They rotate at thousands of RPM, which means that even the strongest materials can be cut easily and accurately.
3-axis machines are the most common type of milling machine and can cut vertically (Z axis) and in the X and Y directions. However, undercuts cannot usually be machined using a 3-axis milling machine. These are features that cannot be accessed by standard end mills. This means that more complex designs may require a more complex milling machine.
4-axis milling machines are more complex and have the additional ability to rotate in the X-axis (similar to a lathe).
5-axis milling machines include rotation in both the X-axis and the Y-axis. They are the most complete milling machines on the market and are suitable for highly complex designs such as medical devices and implants, impellers and aerospace structures for the medical industry.
Types of CNC Milling Processes
- Vertical Milling: In vertical milling, the 3-axis milling table is the work surface, located under the arm, and the spindle is mounted on the table. If a vertical turret milling machine is used, the spindle can be fixed. In this case, the table moves along the X and Y axes. Meanwhile, if a bed-type vertical milling machine is used, the table only moves along the X axis. The spindle moves along the length of the arm in the Y direction.
- Horizontal Milling: The spindle of horizontal milling runs horizontally instead of vertically, and all other parts are similar to vertical milling. Generally speaking, horizontal milling machines are best suited for heavier projects or longer projects. They are also suitable for parts that require a lot of material to be removed because the chips will fall away from the part and the tool.
- Face Milling: The axis of rotation of the cutting tool is perpendicular to the surface of the workpiece. It uses a face milling cutter with teeth on both the edge and the face, the latter of which is used for finishing. Face milling is also used to create flat surfaces and control the finished product. Face milling can produce higher quality surfaces than other milling processes and is compatible with both vertical and horizontal milling machines.
- Face milling: The axis of rotation of the cutting tool is parallel to the surface of the workpiece. Face milling cutters have teeth on the perimeter to perform the cutting operation. Both narrow and wide tooth cutters are available. This allows for deeper cuts and a larger surface area to be machined. Both coarse and fine tooth cutters are available. Coarse tooth cutters use slower cutting speeds and faster feed rates, while fine tooth cutters do the opposite. This results in a finer final part.
- Angled milling: This is a milling operation where the axis of rotation of the cutting tool is at an angle relative to the workpiece surface. Therefore, a single angle cutter can produce more angular features such as grooves, serrations, or chamfers.
- Form milling: Form milling is best used for milling operations involving more irregular surfaces. Contours, outlines, edges, or parts with curved, flat surfaces. It uses cutters or fly cutters that are specialized for specific applications, such as concave or radius cutters. Hemispherical or semicircular designs or other similarly complex designs and intricate parts will benefit from form milling technology.
Types of Milling Machines
Since there are many types of milling machines, there are also many unique milling machines with different features and functions. Some of the different types of milling machines are:
- Ram type: This type of machine allows the machine to move in the XY axis via a spindle fixed to a movable arm on a column. Horizontal milling machines are usually ram type.
- Knee type: Knee machines will adjust the table vertically instead of the spindle. The knee will lower and raise the table along the column to reach the machine. General milling is usually done on knee type machines.
- Planer type: This type of milling machine has a fixed table along the YZ axis and the spindle can move along the XYZ axis. They can also support up to four machines at once.
- Bed type: These milling machines have the workpiece fixed below the cutting tool. The machine can move along the XYZ axis.
Advantages of CNC milling process
Advanced CNC milling machines are equipped with integrated touch screen software control, chip management and swing arm automatic tool change (ATC) and other functions. Here are the advantages of these automatic CNC milling machines for plastics and metals:
- High precision: Milling machines generally use advanced CNC technology and precision machine tool equipment to achieve high-precision processing of workpieces. Computer control of the tool’s motion trajectory and cutting parameters can ensure that the processing accuracy reaches the micron level and meets the manufacturing needs of high-precision parts.
- High efficiency: CNC milling machines are highly automated and integrated, which can significantly improve production efficiency. Once the processing program is set, the machine can automatically complete the entire processing process without human intervention, greatly shortening the production cycle and reducing labor costs.
- Flexibility: CNC milling machines are suitable for processing a variety of materials and complex shapes. By changing different tools and adjusting the processing program, it is easy to cope with the processing needs of different materials and shapes. This flexibility makes CNC milling machines widely used in many fields such as aerospace, automobile manufacturing, and medical devices.
- Stability: The CNC milling process is stable and reliable, which can ensure the consistency and stability of product quality. Due to the use of computer control, the influence of human factors on processing quality can be eliminated, ensuring that each workpiece meets the predetermined processing accuracy and quality requirements.
- Repeatability: Once the CNC milling machine program is written and verified, it can be reused many times without rewriting the program for each processing. This repeatability gives CNC milling machines a significant advantage in mass production, which can greatly improve production efficiency and reduce production costs.
- Complex shape processing capability: CNC milling machines are able to handle complex geometric shapes and curves, including the processing of three-dimensional surfaces and internal structures. This is an important advantage for parts processing that is difficult to achieve with traditional processing methods.
- Reduce material waste: Through precise tool path planning and cutting parameter setting, CNC milling machines can minimize material waste and improve material utilization. This is of great significance for resource conservation and environmental protection.
- Easy to integrate into automated production lines: CNC milling machines can be easily integrated into automated production lines and work in collaboration with other automated equipment. This integration capability makes CNC milling machines occupy an important position in the modern production system and promotes the intelligent and automated development of the manufacturing industry.
About Elimold
Founded in 2012, Elimold is a pioneer in the new era of on-demand manufacturing, leading advancements in rapid prototyping and CNC machining. We know how to deliver high-quality products on time and on budget. We have a team of CNC machining experts and take a best-of-breed approach to everything we do. Tens of thousands of product developers and engineers around the world trust Elimold to bring their products to life.