Metal milling is a subtractive manufacturing process where a rotating cutting tool removes material from a metal workpiece. Unlike a lathe (where the part spins), in milling, the tool rotates at high speeds while the workpiece is secured to a table.

Key Types of Metal Milling

• Vertical Milling: The spindle axis is vertical (perpendicular to the table). This is the most common setup for cutting slots, holes, and complex 3D shapes.
• Horizontal Milling: The cutter is mounted on a horizontal arbor. This setup is sturdier and better for heavy material removal or cutting deep grooves.
• CNC Milling (Computer Numerical Control): Modern machines use computer software (CAD/CAM) to automate the movements, allowing for extreme precision and 5-axis complexity.

Common Cutting Tools

• End Mills: The “drill bits” of milling. They can cut both axially (down) and laterally (sideways).
• Face Mills: Large-diameter tools used to flatten the top surface of a metal block quickly.
• Ball Nose Mills: Tools with a hemispherical end, used for carving smooth, curved surfaces or 3D contours.

Materials and Challenges

• Aluminum: Easy to mill, fast speeds, but can “gum up” the tool if not lubricated.
• Steel/Stainless Steel: Much harder; requires slower speeds, high torque, and often coolant to manage heat.
• Titanium: Very difficult to mill because it is tough and holds onto heat, which can destroy cutting tools quickly.

Essential Concepts

• Feeds and Speeds: The “Speed” is how fast the tool spins (RPM), and the “Feed” is how fast the table moves the metal into the tool. Getting this balance right prevents tool breakage.
• Chip Load: The thickness of the metal flake (chip) removed by each tooth of the cutter.
• Coolant/Lubricant: Essential in metal milling to wash away chips and prevent the tool from overheating.