What is a CNC Milling Machine? How Does It Work? How Does a CNC Milling Machine Compare to a CNC Lathe? When Do You Need Such a CNC Machine?
Focusing on milling—using rotating tools to gradually remove material from a workpiece—CNC milling machines are a mainstay in factories worldwide. These machines remove material mechanically from a workpiece using various cutting tools along one or more axes. CNC milling machines are used in various manufacturing industries: from aerospace, marine, automotive, oil drilling/pumping and refining, to medical, FMC manufacturing, and precision engineering industries. Milling machines, also known as CNC machining centers, can operate along multiple axes. They are equipped with automatic tool changers, advanced machine cooling systems, pallet changers, and advanced software to improve machining efficiency and precision.
What is a CNC Milling Machine/Machining Center?
Let's first look at what a CNC milling machine is.
CNC milling machines are machine-operated cutting tools programmed and managed by a computer numerical control (CNC) system to accurately remove material from a workpiece. The end result of the machining process is a specific part or product created using computer-aided design (CAD) software. These machines are typically equipped with a spindle and three linear axes to position or move the parts to be machined. More advanced versions may have a 4th or 5th rotary axis to allow for more precise shapes in different sizes and dimensions.
Milling Process: CNC milling/machining centers typically employ a material cutting process called milling or machining. The milling process involves securing a block of pre-shaped material (also known as the workpiece) to a fixture connected to the milling platform. Then,a rapidly rotating tool (or a series of interchangeable tools) is applied to the material to remove small fragments of material until the desired shape of the part is achieved. Different axes, cutting head speeds, and feed rates can be applied depending on the material and complexity of the part being machined.
Applications: Milling is often used to process asymmetrical parts from an axial perspective. These parts may have unique curvatures or surface profiles, which may require a combination of drilling and tapping, slots, grooves, and holes for machining. They can also constitute part of the tooling for other manufacturing processes, such as in the manufacture of 3D molds.
Features of Advanced CNC Milling Machines/Machining Centers
Manual to Automated: Historically, milling machines were manually operated. Operators had to use a combination of different tools on the machine to machine more complex parts or products. Alternatively, they had to use various setups on a single machine to complete the work. With advances in CNC control and automatic tool changers (ATC), higher efficiency, flexibility, and speed are achieved, even for more complex parts. The provision of digital readouts and measuring systems also improves the accuracy of the CNC machining process.
Flexibility for HMLV Manufacturing: To meet the needs of manufacturers requiring "high mix, low volume" (HMLV) or "small batch" production flexibility, CNC machining centers can be equipped with pallet changers or other automated solutions to form part of flexible manufacturing cells (FMC) or flexible manufacturing systems(FMS). This enables these machines to meet various processing needs and requirements.
How Does a CNC Milling Machine Work?
The general principle of CNC milling machines or CNC machining centers is to clamp the part to be machined on the top of the machine table. It can be clamped directly to the table or fixed in place with a vise or fixture.The spindle (moving part) including the cutting tool is then positioned vertically or horizontally. In this configuration, the tool can reach each XYZ position on the workpiece and begin cutting and shaping operations. In doing so, the workpiece or part can be fixed, mounted, or moved/positioned in a straight line by the worktable to the spindle with the cutting tool. This allows for material removal based on the required shape of the machined part.
CNC Milling Machines vs. CNC Lathes (Turning Centers)
With a CNC milling machine (aka CNC machining center),a vise or fixture is used to hold or mount the workpiece in place while a cutting tool is operated on top of or around the workpiece. Material is then gradually removed using a cutting tool or drill bit that rotates at high speeds along two or more axes at varying feed rates.
However, in the case of a CNC lathe (aka CNC turning center), the workpiece (usually cylindrical) is mounted on a rotating chuck or spindle. It is then turned or rotated along the spindle while the cutting tool located in a rotating or positioning turret will move in a direction parallel to the workpiece.
Thus, a CNC milling machine uses a rotating tool with a fixed workpiece, while a CNC lathe will use a fixed tool that rotates the material to be machined.
