In the past, complex machine parts or molds were often broken down into small, simple parts. Then, they are joined together into complete parts by welding and riveting methods. This machining does not guarantee high accuracy and is expensive. Later, thanks to copying technology, it is possible to process more complex details. However, this machining still has many disadvantages such as low productivity and difficulty in ensuring high accuracy. Therefore, the application of CNC to machine tools is a leap forward in machining technology. It ensures high precision, can process complex parts.

In the process of industrialization and modernization of the country, our country's mechanical industry is developing in the direction of automation, design and processing with the help of computers. That requires experiential learning, technology mastery and continuous development of mechanical production facilities. In order to achieve the above goal, domestic mechanical enterprises and training institutions have been investing more and more modern machine tools, completing the problem of exploitation and effective use of technical and economic efficiency. is an urgent requirement, especially the issue of training scientific and technological human resources capable of accessing, mastering and effectively exploiting modern CNC machines.

• CNC: stands for Computer Numerical Control and is a type of machine that is controlled automatically with the help of a computer. Parts are automatically programmed to operate according to the sequence of events set by the user to create a product of the required shape and size.

• Milling: is a type of machining that uses cutters to shape a workpiece, often on a moveable tabletop, although some milling machines also feature movable cutters. Milling started out as a manual task performed by humans, but most milling these days is done by a CNC mill, which utilizes a computer to oversee the milling process. 

• CNC milling, or computer numerical control milling, is a machining process which employs computerized controls and rotating multi-point cutting tools to progressively remove material from the workpiece and produce a custom-designed part or product. This process is suitable for machining a wide range of materials, such as metal, plastic, glass, and wood, and producing a variety of custom-designed parts and products.

Overview of CNC Milling Process.

Like most conventional mechanical CNC machining processes, the CNC milling process utilizes computerized controls to operate and manipulate machine tools which cut and shape stock material. In addition, the process follows the same basic production stages which all CNC machining processes do, including:

• Designing a CAD model

• Converting the CAD model into a CNC program

• Setting up the CNC milling machine

• Executing the milling operation

The CNC milling process begins with the creation of a 2D or 3D CAD, CAM part design. Then the completed design is exported to a CNC-compatible file format and converted by CAM software into a CNC machine program which dictates the actions of the machine and the movements of the tooling across the workpiece. Before the operator runs the CNC program, they prepare the CNC milling machine by affixing the workpiece to the machine’s work surface (i.e., worktable) or work holding device (e.g., vise), and attaching the milling tools to the machine spindle. The CNC milling process employs horizontal or vertical CNC-enabled milling machines—depending on the specifications and requirements of the milling application—and rotating multi-point (i.e., multi-toothed) cutting tools, such as mills and drills. When the machine is ready, the operator launches the program via the machine interface prompting the machine to execute the milling operation.

Once the CNC milling process is initiated, the machine begins rotating the cutting tool at speeds reaching up to thousands of RPM. Depending on the type of milling machine employed and the requirements of the milling application, as the tool cuts into the workpiece, the machine will perform one of the following actions to produce the necessary cuts on the workpiece:

• Slowly feed the workpiece into the stationary, rotating tool

• Move the tool across the stationary workpiece

• Move both the tool and workpiece in relation to each other

As opposed to manual milling processes, in CNC milling, typically the machine feeds moveable workpieces with the rotation of the cutting tool rather than against it. Milling operations which abide by this convention are known as climb milling processes, while contrary operations are known as conventional milling processes. Once the milling operation is completed, and the part is produced to the custom-designed specifications, the milled part passes to the finishing and post-processing stages of production.

CNC Milling Machine Operations

CNC Milling is a machining process suitable for producing high accuracy, high tolerance parts in prototype, one-off, and small to medium production runs.. The versatility of the milling process allows it to be used in a wide range of industries and for a variety of part features and designs, including slots, chamfers, threads, and pockets. The most common CNC milling operations include:

• Face milling refers to milling operations in which the cutting tool’s axis of rotation is perpendicular to the surface of the workpiece. The process employs face milling cutters which have teeth both on the periphery and tool face, with the peripheral teeth primarily being used for cutting and the face teeth being used for finishing applications.

• Plain milling, also known as surface or slab milling, refers to milling operations in which the cutting tool’s axis of rotation is parallel to the surface of the workpiece. The process employs plain milling cutters which have teeth on the periphery that perform the cutting operation. Depending on the specifications of the milling application, such as the depth of the cut and the size of the workpiece, both narrow and wide cutters are used. Narrow cutters allow for deeper cuts, while wider cutters are used for cutting larger surface areas.

• Angular milling, also known as angle milling, refers to milling operations in which the cutting tool’s axis of rotation is at an angle relative to the surface of the workpiece. The process employs single-angle milling cutters angled based on the particular design being machined to produce angular features, such as chamfers, serrations, and grooves.

• Form milling refers to milling operations involving irregular surfaces, contours, and outlines, such as parts with curved and flat surfaces, or completely curved surfaces. The process employs formed milling cutters or fly cutters specialized for the particular application, such as convex, concave, and corner rounding cutters.

The main types of CNC Milling Machines.

• Machine interface: The machine interface refers to the machine component the operator uses to the load, initiate, and execute the CNC machine program.

• Column: The column refers to the machine component which provides support and structure to all other machine components. This component includes an affixed base and can include additional internal components which aid the milling process, such as oil and coolant reservoirs.

• Knee: The knee refers to the adjustable machine component which is affixed to the column and provides support to the saddle and worktable. This component is adjustable along the Z-axis (i.e., able to be raised or lowered) depending on the specifications of the milling operation.

• Saddle: The saddle refers to the machine component located on top of the knee, supporting the worktable. This component is capable of moving parallel to the axis of the spindle, which allows the worktable, and by proxy the workpiece, to be horizontally adjusted.

• Worktable: The worktable refers to the machine component located on top of the saddle, which the workpiece or work holding device (e.g., chuck or vise) is fastened. Depending on the type of machine employed, this component is adjustable in the horizontal, vertical, both, or neither direction. 
  Spindle: The spindle refers to the machine component supported by the column which holds and runs the machine tool (or arbor) employed. Within the column, an electric motor drives the rotation of the spindle.

• Arbor: The arbor refers to the shaft component inserted into the spindle in horizontal milling machines in which multiple machine tools can be mounted. These components are available in various lengths and diameters depending on the specifications of the milling application. The types of arbors available include standard milling machine, screw, slitting saw milling cutter, end milling cutter, and shell end milling cutter arbors.

• Ram: The ram refers to the machine component, typically in vertical milling machines, located on top of and affixed to the column which supports the spindle. This component is adjustable to accommodate different positions during the milling operation.

• Machine tool: The machine tool represents the machine component held by the spindle which performs the material removal operation. The milling process can employ a wide range of milling machine tools (typically multi-point cutters) depending on the specifications of the milling application e.g., the material being milled, quality of the surface finish required, machine orientation, etc. Machine tools can vary based on the number, arrangement, and spacing of their teeth, as well as their material, length, diameter, and geometry.

Applications of CNC Milling Machines.

With increasingly affordable tooling costs and the ability to create a wide variety of complex parts, CNC milling is a popular solution for projects from prototypes to full fabrication of unique precision parts. CNC milling machines have been widely applied in life and production. CNC milling serves industries such as:

• Aircraft and aerospace

• Prototypes and custom designs

• Commerce

• Maintenance

• Electronic device

• Medical, disposable and non-implantable

• Entertainment

• Technology and security

• Telecommunication

• Transport and cars

• Industrial and O.E.M.