Peripheral (cylindrical) and face milling are two of the machining operations by metal cutting that can be performed on a milling machine. The type of milling operation is determined by the movement of the machine's cutting tool, the milling cutter.
What is milling?
Milling means cutting or removing material from a workpiece using a rotating tool called a milling cutter. The cutter has multiple cutting edges, known as teeth or inserts, which perform feed movements along any of the machine tool's axes. Milling operations are carried out on a milling machine, which machines by removing chips.
A milling machine can machine a range of materials such as metals, steel, cast iron, non-ferrous metals, wood and synthetic materials; it can also machine parts with flat or curved surfaces, toothed surfaces and so on. The parts being machined can also be roughed or finished.
On a traditional universal milling machine, the cutting tool travels over the table until it reaches the surface of the workpiece in a rotary motion. This makes it possible to produce a wide variety of complex shapes.
Types of milling machine
Not all milling machines can perform peripheral and face milling. The type of machining depends on the milling machine used. There are many types of milling machine today, which can be classified by tool orientation and by the number of machine axes. There are also special milling machines.
By tool orientation, a milling machine can be:
- Horizontal. This type of machine uses cylindrical cutters mounted on a horizontal arbor driven by the machine headstock. It has a sliding overarm known as the ram.
- Vertical. The spindle axis is vertical and perpendicular to the worktable. The cutters on this machine are mounted in the spindle and rotate about their own axis. Vertical milling machines can be bed-type or turret/knee-type.
- Universal. It has a sliding overarm known as the ram that moves backwards and forwards on guideways.
Special milling machines:
- Circular
- Copy milling machines
- Gantry
- Moving-bridge milling machines
- Woodworking
By number of axes:
- Three axes. These milling machines control the relative movement between workpiece and tool in a Cartesian X, Y and Z system.
- Four axes. In addition to the X, Y and Z axes, they move about an A axis, which controls the rotation of the workpiece about one axis. They perform cylindrical milling.
- Five axes. In addition to the movement between workpiece and tool along the X, Y and Z axes, they control the rotation of the workpiece about two axes (perpendicular and parallel), as well as the rotation of the workpiece about a horizontal axis and the tilt of the tool. This fifth axis is the B axis.
What are peripheral and face milling?
Not all milling machines are capable of peripheral and face milling. Do you know what these types of milling involve?
Peripheral (cylindrical) milling
In this operation, the cutter's axis of rotation is parallel to the surface being machined. The cutter has a series of teeth around its circumference, which act as the tool's cutting points. For cylindrical milling, cutters can have straight or helical flutes, which makes the cutting section orthogonal or oblique respectively.
Cylindrical milling is also known as peripheral or tangential milling. It is called tangential because the teeth on the periphery of the cutting tool do the machining. If the axis is not correctly aligned, waviness appears on the workpiece surface.
Peripheral milling can in turn be of two types:
- Up milling or conventional milling. In this operation the workpiece is fed against the direction of rotation of the cutter. As the workpiece advances, the chips removed become larger and the workpiece is lifted by the action of the cutter, which causes vibration. Because large amounts of material are removed, the cutting tool wears quickly, more power is consumed and the surface shows waviness.
- Down milling (climb milling). The cutter and the workpiece move in the same direction. The cutting edges enter at maximum chip thickness and no vibration occurs. The tool feed rate is higher, yet power consumption is lower. The surface finish is better.
In peripheral milling the chips removed are comma-shaped, so helical cutters are recommended.
Face milling
In face milling the cutter is mounted in the machine spindle or in a tool holder. The cutting tool has an axis of rotation perpendicular to the workpiece surface. Face milling cutters have cutting edges distributed on the face of the tool and around its periphery.
The peripheral teeth remove chips of even thickness and the workload is uniform, making better use of the milling machine's capacity and power. The teeth on the face of the tool deliver a much better machining quality. Face milling can be carried out on universal milling machines.