Milling is one of the most common processes in CNC machining, most likely because it is so versatile. Using a single tool, machine shops can create nearly limitless shapes on the surface of a workpiece. Milling can completely transform a piece of metal stock into a finished part of nearly any complexity.
The milling process in CNC machining consists of removing material with a rotating cutting tool. Unlike turning, the workpiece does not need to rotate in milling operations. In some cases, the workpiece will move linearly against a cutting tool; in other cases, the workpiece will remain stationary while the cutting tool moves.
CNC Milling can be divided into several subtypes, based on the characteristic being milled, the specific tool being used, and the motion of the cutting tool along the surface of the workpiece. Milling subtypes include:
The milling machine, often referred to simply as a "mill," is the most basic tool used for milling. Milling machines vary widely, however, and many are combined into machining centers. In milling machines or in machining centers, the shape of the product is determined by the motion of either the workpiece or the cutting tool, along three linear dimensions (X,Y,Z) and up to three rotational dimensions (pitch, yaw and roll).
In the past, machine shops manually moved workpieces between lathes, mills, saws and drills to form a completed part. Today, versatile equipment that can perform multiple processes on the same workpiece offers greater efficiency. Mill/turn centers, for example, combine milling capabilities with turning and boring. Many also include motorized turrets with live tooling, allowing the machine to combine rotary cutting with linear motion. CNC technology and 3D software help engineers choose the best strategy to produce precise, accurate machined products as efficiently as possible.
Whether milling takes place on a traditional milling machine or a 6-axis machining center, the process is the same: a rotating cutting tool is brought into contact with a workpiece to chip away material. The resulting form depends on the speed of rotation, the shape of the cutting tool, and the motion of the cutting tool along the surface of the workpiece.
Written by Nik Seyferth
Nik is Sales Manager at Eagle CNC Technologies in Muskegon, MI.
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