CNC Milling
Vacuum chamber machined by CNC milling
Aluminum box machined by CNC milling
CNC Milling Job in Progress
CNC milling is a cutting process in which material is removed from a block by a rotating tool.
In CNC milling the cutting tool is moved in all three dimensions to achieve the desired part shape. In CNC milling the cutting tool usually rotates about an axis that is perpendicular to the table that holds the material to be cut. A
milling machine looks somewhat like a drill press at first glance. A
cutting tool protrudes down from a rotating spindle. A block of
material is placed on a moving table below the cutter. While the
cutting tool turns, a computer controls the vertical (Z axis) motion of
the cutter and the horizontal (X and Y axis) motion of the block of
material. The cutter is guided to move through the material, removing
portions to create shapes.
Additionally, the material can be turned to
various orientations in the middle of the process and cutting tools of
various shapes can be used. Material is usually removed by both the end and the side of the cutting tool. Some common cutter shapes include:
Referring to the above images from left to right:
- Plain endmill - used for most milling - creates walls with straight 90 deg edges and sharp corners at the bottom of recesses.
- Chamfer endmill - creates 45 deg bevels on the top edge of a wall or recess
- Grooving endmill - creates rectangular grooves in side walls
- Ball mill - creates rounded edges at the bottom edge of a recess
- Rounding endmill - creates rounded edges at the top edge
- Angle endmill - creates walls at angles other than 90 deg
- and, not shown, a conventional drill
CNC Milling has several advantages over other manufacturing processes. It is cost effective for short runs. Complex shapes and high dimensional tolerances are possible. Smooth finishes can be achieved. CNC milling can produce almost any 2D or 3D shape provided that the rotating cutting tools can reach the material to be removed. Examples of CNC milled parts include engine components, mold tooling, complex mechanisms, enclosures, etc.
CNC Milling can process most rigid materials including most metals: Aluminum, Stainless Steel, Copper, Steel, Brass, Titanium, Sterling Silver, Bronze, etc.
And hard plastics and other materials: Nylon, Acetal, Polycarbonate, Polystyrene, Acrylic, Fiberglass, Carbon fiber, Teflon, ABS, PVC, etc.
Although tooling is mainly software, custom jig tooling is often required for workholding.
Cost reduction options include reducing the amount of material removed, limiting complexity, avoiding intricate features and making shapes that are easy to hold.
CNC Milling Design Considerations
- Providing corner radius of 10% or more of wall height is ideal.
- Avoid flimsy shapes.
- Provide shapes that are practical to hold during machining, such as straight edges.
- As the milling process applies pressure to the material, weak shapes are difficult to machine, such as long thin shapes and thin walls.
- Generates a cut surface with a visible pattern resulting from the rotation and movement of the cutter.
