Milling
WHAT IS MILLING?
Milling is the process of cutting away material by feeding a workpiece past a rotating multiple tooth cutter. The cutting action of the many teeth around the milling cutter provides a fast method of machining. The machined surface may be flat,angular, or curved. The surface may also be milled to any combination of shapes. The machine for holding the workpiece, rotating the cutter, and feeding it is known as the Milling Machine.
Milling Machines
Milling machines are often classed in two basic forms, horizontal and vertical, which refers to the orientation of the main spindle. Both types range in size from small, bench-mounted devices to room-sized machines.
The main spindle is mounted horizontally near the top of the column. The machine capacity is determined by the maximum distance from the table to the spindle as well as working surface size and travel in all directions. The milling cutters have a hole in them in order to be mounted on an arbour. The cutters are usually large in diameter and are found in a range of types including slab, side and face, saw, angle and form cutters.
The spindle is mounted vertically in a head at the top of the column. The milling cutters are generally mounted in a chuck. There are a range of end mills, slot drills
and profiled cutters (angle, ball-nose, dovetail, tee-slot, corner-rounding, etc.)
CLASSIFICATION OF MILLING
Peripheral Milling
In peripheral (or slab) milling, the milled surface is generated by teeth located on the periphery of the cutter body. The axis of cutter rotation is generally in a plane parallel to the workpiece surface to be machined.
Face Milling
In face milling, the cutter is mounted on a spindle having an axis of rotation perpendicular to the workpiece surface. The milled surface results from the action of cutting edges located on the periphery and face of the cutter.
End Milling
The cutter in end milling generally rotates on an axis vertical to the workpiece. It can be tilted to machine tapered surfaces. Cutting teeth are located on both the end face of the cutter and the periphery of the cutter body.
Gang Milling
refers to the use of two or more milling cutters mounted on the same arbor and when cutting horizontal surfaces. All cutters may perform the same type of operation or each cutter may perform a different type of operation. For example, several workpieces need a slot, a flat surface, and an angular groove. The best method to cut these would be gang milling. All the completed workpieces would be the same
METHODS OF MILLING
Up Cut Milling
Up Cut Milling is also referred to as conventional milling. The direction of the cutter rotation opposes the feed motion. For example, if the cutter rotates clockwise , the workpiece is fed to the right in up milling.
Danger - Cutter may be inclined to lift work.
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Down Cut Milling
Down Cut milling is also referred to as climb milling. The direction of cutter rotation is same as the feed motion. For example, if the cutter rotates counterclockwise , the workpiece is fed to the right in down milling.
Danger - Milling cutter can be inclined to pull work under cutter
The chip formation in down milling is opposite to the chip formation in up milling. The figure for down milling shows that the cutter tooth is almost parallel to the top surface of the workpiece. The cutter tooth begins to mill the full chip thickness. Then the chip thickness gradually decreases.
Chip Formation
