CNC milling or computer numerical control milling is a machining process that uses computer control and rotating multi-point cutting tools to gradually remove material from the workpiece and produce custom-designed parts or products. This process is suitable for machining various materials, such as metal, plastic, wood, and producing various custom-designed parts and products.
Under the protection of precision CNC machining services, it can provide a variety of functions, including mechanical, chemical, electrical and thermal processing. CNC milling is a machining process, including drilling, turning and various other machining processes, which means that material is removed from the workpiece by mechanical means (such as the action of the cutting tool of a milling machine).
This article focuses on the CNC milling process and outlines the basics of the process, as well as the components and tools of the CNC milling machine. In addition, this article explores various milling operations and provides an alternative to the CNC milling process.
Cnc Milling Definition
What is milling? This is a machining method in which a tool is used to form a workpiece on a usually movable table, although some milling machines also have movable tools. Milling was originally a manual operation performed by workers, but today, most milling is done by CNC milling machines that use computers to supervise the milling process. CNC milling can provide higher precision, accuracy and productivity, but in some cases, manual milling is still very useful. Manual milling requires a lot of technical skills and experience, thus shortening the turnaround time. It also has the added benefit that manual milling machines are cheaper and users do not need to worry about programming the machine.
Overview Of CNC Milling
Like most traditional mechanical CNC machining processes, the CNC milling process utilizes computer control to operate and manipulate the machine tool that cuts and shapes the blank. In addition, the process follows the same basic production stages as all CNC machining processes, including:
- Design CAD model
- Convert CAD model to CNC program
- Setting up a CNC milling machine
- Perform milling operations
The CNC milling process begins with the creation of a 2D or 3D CAD part design. Then, export the complete design to a file format compatible with CNC, and convert it into a CNC machine program through the CAM software, which instructs the movement of the machine and the movement of the tool on the entire workpiece. Before the operator runs the CNC program, they prepare the CNC milling machine by fixing the workpiece to the working surface of the machine tool (ie, the worktable) or the workpiece fixture (such as a vise), and mounting the milling tool on the spindle of the machine tool. The CNC milling process uses horizontal or vertical CNC powerful milling machines-depending on the specifications and requirements of the milling application-and rotating multi-point (ie, multi-tooth) cutting tools such as milling cutters and drills. When the machine is ready, the operator starts the program through the machine interface, prompting the machine to perform the milling operation.
Once the CNC milling process is started, the machine tool begins to rotate the cutting tool at speeds of up to thousands of revolutions per minute. Depending on the type of milling machine used and the requirements of the milling application, when the tool cuts into the workpiece, the machine tool will perform one of the following operations to make the necessary cuts on the workpiece:
- Slowly feed the workpiece into a fixed rotating tool
- Move the tool on a fixed workpiece
- Move tool and workpiece relative to each other
In contrast to the manual milling process, in CNC milling, the machine tool usually conveys movable workpieces by the rotation of the cutting tool instead of the rotation of the cutting tool. The milling operation that follows this convention is called climb milling, and the opposite operation is called conventional milling.
Generally, milling is most suitable as an auxiliary or finishing process for a machined workpiece to provide the definition of part features (such as holes, grooves, and threads) or to produce part features. However, the process can also be used to form stock materials from start to finish. In both cases, the milling process will gradually remove material to form the desired shape and part form. First, the tool cuts small pieces (ie chips) from the workpiece to form an approximate shape. Then, the workpiece will be milled with higher progress and higher precision, so as to complete the finishing of the part with its precise features and specifications. Usually, the finished part needs to be processed several times to obtain the required accuracy and tolerances. For parts with more complex geometries, once the milling operation is completed and the parts are produced in accordance with the custom-designed specifications, the milled parts will enter the finishing and post-processing stage of production.
CNC Milling Machine Operation
CNC milling is a machining process, suitable for prototype, one-off and small and medium-sized production runs to produce high-precision, high-tolerance parts. Although the manufacturing tolerances of parts are usually between +/- 2 wires to +/- 10 wires, some milling machines can achieve tolerances as high as +/- 1 wire or even higher. The versatility of the milling process allows it to be used in a wide range of industries and for various part features and designs, including grooves, chamfers, threads and cavities. The most common CNC milling operations include:
- Face milling
- Plane milling
- Angle milling
- Form milling
Face milling, in which the axis of rotation of the cutting tool is perpendicular to the surface of the workpiece. This method uses a face milling cutter that has teeth on both the outer circumference and the tool surface, wherein the outer circumference teeth are mainly used for cutting, and the face teeth are used for finishing applications. Generally, face milling is used to form a flat surface and contour on the finished part, and can produce a higher quality finish than other milling processes. Both vertical and horizontal milling machines support this process.
The types of face milling include end mills and side mills, which use end mills and side mills, respectively.
Plane milling, also called surface milling or flat milling, in which the axis of rotation of the cutting tool is parallel to the surface of the workpiece. This process uses ordinary milling cutter teeth to perform cutting operations on the periphery. Depending on the specifications of the milling application, such as the depth of cut and workpiece size, narrow and wide cutters can be used. Narrow knives can be used for deeper cuts, while wide knives can be used to cut larger surface areas. If the flat milling application requires the removal of a large amount of material from the workpiece, the operator first needs to use a coarse-tooth milling cutter, slow cutting speed and fast feed rate to produce the approximate geometry of the custom-designed part. Then, the operator introduces finer tooth-shaped tools, faster cutting speeds and slower feed speeds to produce the details of the finished part.
Angle milling refers to where the rotation axis of the cutting tool is at a certain angle with respect to the surface of the workpiece. This process uses a single-angle milling cutter (the angle is determined according to the specific design being machined) to produce angular features such as chamfers, serrations, and grooves. A common application of angle milling is the production of dovetail tenon, which uses 45°, 50°, 55° or 60° dovetail milling cutters according to the design of the dovetail.
Form milling refers to milling operations involving irregular surfaces, contours and contours, such as parts with curved and flat surfaces or fully curved surfaces. This process uses profile milling cutters or flying cutters that are specifically used for specific applications, such as convex, concave and corner fillet milling cutters. Some common applications of form milling include the production of hemispherical and semicircular cavities, beads and contours, as well as complex designs and complex parts through a stand-alone setup.
Other milling machine operations
In addition to the above operations, the milling machine can also be used to complete other specialized milling and machining operations. Examples of other types of milling machine operations available include:
Stride milling: Stride milling refers to a milling operation in which the machine tool processes two or more parallel workpiece surfaces through one cut. This process uses two tools on the same machine spindle, which are arranged so that the tools are on either side of the workpiece and can mill both sides at the same time.
Combined milling: what is combined milling? Combined milling refers to a milling operation that uses two or more tools (usually tools of different sizes, shapes or widths) on the same machine spindle. Each cutter can perform the same cutting operation at the same time, or it can perform different cutting operations at the same time, so that more complex parts can be produced in a shorter production time.
Contour milling: Contour milling refers to where the machine tool creates a cutting path on the workpiece along a vertical or inclined surface. This process uses contour milling equipment and cutting tools, which can be parallel or perpendicular to the surface of the workpiece.
Gear cutting: Gear cutting is a milling operation that uses involute gear cutters to produce gear teeth. These cutters are a type of forming milling cutter, which can be provided in various shapes and pitch sizes according to the number of teeth required for a specific gear design. In this process, special turning tool heads can also be used to produce gear teeth.
Other machining processes: Since milling machines support the use of other machine tools besides milling tools, they can be used for machining processes other than milling, such as drilling, boring, reaming and tapping.
Like most CNC machining processes, the CNC milling process uses CAD software to generate an initial part design and CAM software to generate a CNC program that provides machining instructions to produce parts. Then load the CNC program onto the selected CNC machine tool to start and execute the milling process.
Matters needing attention for milling machine
Generally, milling machines are divided into horizontal and vertical machine configurations, and they are distinguished according to the number of motion axes.
On a vertical milling machine, the spindle of the machine tool is vertical, while the spindle of the milling machine is placed horizontally in the horizontal direction. The horizontal machine tool also uses a spindle in the milling process to provide additional support and stability, and has the ability to support a variety of cutting tools, such as wheel milling and straddle milling. The control of vertical and horizontal milling machines depends on the type of machine used. For example, some machines can raise and lower the main shaft and move the table laterally, while other machines have fixed main shafts and tables that can move horizontally, vertically, and rotationally. When choosing vertical and horizontal milling machines, manufacturers and workshops must consider the requirements of the milling application, such as the number of surfaces that need to be milled and the size and shape of the part. For example, heavy workpieces are more suitable for horizontal milling operations, while sinking die applications are more suitable for vertical milling operations. Auxiliary equipment can also be used, which can be retrofitted to vertical or horizontal machines to support the reverse process.
Most CNC milling machines can use 3 to 5 axes-usually along the XYZ axis and (if applicable) around the axis of rotation to provide performance. X axis and Y axis represent horizontal movement (movement left and right and back and forth on the plane, respectively), while Z axis represents vertical movement (up and down movement), and W represents horizontal movement. The axis represents the diagonal movement on the vertical plane. In a basic CNC milling machine, you can move horizontally on two axes (XY), while newer models allow additional motion axes, such as 3-axis, 4-axis and 5-axis CNC machine tools. Some characteristics of milling machines classified by the number of motion axes are summarized below.
3-axis Cnc Milling
- Can meet most processing needs
- The machine is simple to set up.
- Only need a workstation
- Higher requirements for operator knowledge
- Low efficiency and quality
4 axis Cnc Milling
- Better functions than 3-axis machine tools
- Higher precision and accuracy than three-axis machine tools
- Machine settings are more complicated than 3-axis machine tools
- More expensive than three-axis machine tools
5-axis Cnc Milling
Multiple axis configurations can be used (eg 4 + 1, 3 + 2 or 5)
- According to the configuration, it is more convenient to operate than three-axis and four-axis machine tools.
- Higher level of quality and precision
- Depending on the configuration, its running speed is slower than that of 3-axis and 4-axis machining
- More expensive than 3-axis and 4-axis machine tools
Depending on the type of milling machine used, the machine tool, machine tool table or both components can be dynamic. Usually, dynamic tables move along the XY axis, but they can also move up and down to adjust the cutting depth, and rotate along the vertical or horizontal axis to expand the cutting range. For milling applications that require dynamic tools, in addition to its inherent rotational motion, the machine tool also moves vertically along multiple axes, so that the circumference of the tool (not just its tip) cuts into the workpiece. CNC milling machines with greater degrees of freedom allow the milled parts produced to have greater versatility and complexity.
Milling Machine Type
There are several different types of milling machines to choose from, suitable for various machining applications. In addition to classifying only based on machine configuration or the number of motion axes, milling machines can also be classified according to their specific characteristics. Some of the most common types of milling machines include:
- Knee type
- Ram type
- Bed type (or manufacturing type)
Knee type: The knee type milling machine uses a fixed spindle and a vertically adjustable worktable, which is placed on a saddle supported by the knee. Depending on the position of the machine tool, the knee can be lowered and raised on the column. Some examples of knee milling machines include floor-standing and bench-top horizontal milling machines.Ram type:
Ram type milling machine uses a movable housing (ie, RAM) spindle that is fixed to a column, which allows the machine tool to move along the XY axis. The two most common types of vertical milling machines include floor-standing general-purpose horizontal and rotary cutter head milling machines.
Bed type: The bed type milling machine adopts a worktable directly fixed on the machine tool to prevent the workpiece from moving along the Y axis and Z axis. The workpiece is located below the cutting tool. Depending on the machine tool, the cutting tool can move along the XYZ axis. Some bed-type milling machines available include single-sided, double-sided and three-sided milling machines. Single-sided machine tools use one spindle that moves along the X-axis or Y-axis, while double-sided machine tools use two spindles, and three-cylinder machine tools use three spindles (two horizontal and one vertical) for machining along the XY and XYZ axes.
Planer milling machines: Planer milling machines are similar to bed milling machines because they have a fixed table along the Y and Z axes and a spindle that can move along the XYZ axis. However, the planer can support multiple machine tools (usually up to four) at the same time, thereby reducing the lead time for complex parts.
Some special types of milling machines available include turntables, rotating drums and planetary milling machines. The rotary table milling machine has a circular worktable that can rotate around a vertical axis and uses machine tools located at different heights for roughing and finishing. Drum milling machines are similar to turntable machines, except that the worktable is called a “drum” and it rotates around a horizontal axis. In a planetary machine, the table is fixed, and the workpiece is cylindrical. The rotating machine tool moves on the surface of the workpiece, cutting internal and external features (such as threads).
Cnc Milling Material
The CNC milling process is best used as a secondary machining process to provide finishing functions for custom-designed parts, but it can also be used to produce custom-designed and special parts from start to finish. CNC milling technology allows the process to process parts in a variety of materials, including:
- Metals (including alloys, special metals, heavy metals, etc.)
- Plastics (including thermosetting plastics and thermoplastics)
- Composite material
As with all machining processes, when selecting materials for milling applications, several factors must be considered, such as the properties of the material (ie hardness, tensile and shear strength, and chemical and high temperature resistance) and the cost-effectiveness of the material . Processing materials. These standards respectively determine whether the material is suitable for the milling process and the budget constraints of the milling application. The selected material determines the type of machine used and its design, as well as the best machine settings, including cutting speed, feed speed and depth of cut.
CNC milling is a machining process that is suitable for processing various materials and producing various custom-designed parts. Although this process may show advantages over other machining processes, it may not be suitable for every manufacturing application, and other processes may prove more appropriate and cost-effective.
Some other more conventional machining processes include drilling and turning. Like milling, multi-point tools (ie drills) are usually used for drilling, while single-point tools are used for turning. However, when rotating, the workpiece can be moved and rotated like some milling applications, while in the drilling process, the workpiece is stationary during the entire drilling process.
Some unconventional machining processes (that is, do not use machine tools, but still use mechanical material removal processes) include ultrasonic machining, water jet cutting, and abrasive jet machining. Unconventional, non-mechanical machining processes (ie, chemical, electrical and thermal machining processes) provide other alternative methods of removing material from the workpiece. These methods do not use machine tools or mechanical material removal processes, including chemical milling, electrochemical deburring, and laser Cutting and plasma arc cutting. These unconventional processing methods support the production of more complex processing, more demanding and more specialized parts that cannot usually be accomplished by conventional processing.