Traditional Milling Machine
The Milling Machine is a machine tool for machining complex metal parts or other material workpieces. It is often called Mill, but this word refers only to cutting tools to be used (whose shape remembers the French “fraise”). The original class of Milling Machines include the Boring-Milling Machine to process Boring thanks to a controlled movement and stability of the boring head.
Milling is a cutting process that uses a milling cutter to remove material from the surface of a workpiece. The milling cutter is a rotary cutting tool, often with multiple cutting points. As opposed to drilling, where the tool is advanced along its rotation axis, the cutter in milling is usually moved perpendicular to its axis so that cutting occurs on the circumference of the cutter.
Mill orientation is the primary classification for milling machines:
- The X-Y table is moved while the spindle itself moves parallel to its own Z-axis.
- The table is at a fixed elevation and the spindle moves to the three axis.
The first of these classifications according to method of control, size, purpose and power source is used for small dimensioned machines, the latter for 3 or more axis machines, known as Machining Centers.
“Numerical control” (NC) is the automation of machine tools that are operated by precisely programmed commands encoded on a storage medium, as opposed to controlled manually via hand wheels or levers, or mechanically automated via cams alone. Most NC today is “CNC” (computer numerical control) , in which computers play an integral part of the control.
Modern CNC Mills differ little in concept from the original model. Mills typically consist of a table that moves in the X and Y axes, and a tool spindle that moves in the Z (depth). The position of the tool is driven by motors through a series of step-down gears in order to provide highly accurate movements. On commercial metalworking machines closed loop controls are standard and required in order to provide the accuracy, speed, and repeatability demanded.
CNC-like systems are now used for any process that can be described as a series of movements and operations. These include laser cutting, welding, boring, drilling.
Milling Machines are solid structured machines due to the fact these are subject to vibrations of the spindle. In order to insure that the machine runs properly its high speed and maintains its accuracy, regular lubrication is required for the moving parts of the column, the knee and head, the spindle drive. Lubriifcation is used to capture chemical powders and chips in order to prevent the the cutting edge and tools’ consumption.
There are two types of Milling Machines:
- Vertical: In the Vertical Mill the spindle z-axis is vertically oriented. Milling cutters are held in the spindle and rotate on its axis (three-dimensional rotation). The spindle can generally be extended or the x-y table can be raised/lowered, giving the same effect, allowing plunge cuts and drilling.
- Horizontal: A Horizontal Mill has the same sort of x–y table, but the cutters are mounted on a horizontal arbor across the table. Many horizontal mills also feature a built-in rotary table that allows milling at various angles. Because the cutters have good support from the arbor and have a larger cross-sectional area than an end mill, quite heavy cuts can be taken enabling rapid material removal rates. These are used to mill grooves and slots. Plain mills are used to shape flat surfaces. Several expensive cutters may be ganged together on the arbor to mill a complex shape of slots and planes.
The most advanced CNC Milling-Machines, the 4 and Multiaxis Machines add to the class of Milling Machines.