Milling Operations

 Milling Operations

CNC Machine Milling is one of the common high-production machining processes in which metal is removed by a rotating multiple-tooth cutter. The primary cutting motion in milling is a rotation of milling cutter, while feed motion of workpiece (machine tool table) is considered to be the secondary motion.

Milling is used for machining plane, contoured surfaces, slots, grooves, for making threads and cutting gears. A large number of different shapes can be machined. Grinding is often preferred to milling when the amount of metal to be removed is small and surface finish are critical. Milling grinding is frequently employed in combination such that the parts requiring high surface quality (i.e., sideways) are finished by grinding after the milling is performed. Some of the parts manufactured by milling is illustrated

The most outstanding properties of milling operations are as follows;

  1. chips removed are relatively small,
  2. chip thickness varies during the cutting,
  3. each cutting edge of the milling cutter takes part in cutting a part of the complete revolution during operation.

Milling Cutter

Cutters can be machined from solid or have inserted cutting edges that are held in place by mechanical fasteners. Milling cutters are broadly classified as;

  1. peripheral mills
  2. face mills
  3. end mills
  4. special mills

Peripheral Mills

Peripheral milling is a method of generating a machined surface by cutting with the teeth on the periphery of a cutter whose axis is parallel to the milled surface. The operation is usually performed on horizontal milling machines in which one or more cutter is mounted by means of keys on arbors with outboard support. Peripheral milling can be used for removing metal from flat surfaces, for cutting keyways and deep slots and for milling contoured surfaces. They may be classified as slab mills, slotting cutters, angle cutters and form cutters

There is not a unique coding scheme for tool holding of milling operations developed by any organization. One of the reason for this is that the tooling in milling is more complex, requires much more detail than the tooling In turning. Cutting tool manufacturers develop their tool holding systems while keeping the specific standards given for each type of adaptation into view. b u t They all specify DIN standards for the adopters, holders they produce.

Cutting Conditions

The efficiency of a machining operation, the life of a cutting tool depends strictly upon some cutting parameters. The cutting parameters that should also be specified in a part program to cut a workpiece on a CNC machine tool are;

• Depth of cut

  • Feed (or Feed-rate)
  • Cutting Speed
  • Spindle Speed (rpm)

The cutting speed is considered as the circumferential speed of a tool (or a workpiece). In milling operations, the cutting speed refers to the edge speed of rotating cutter, whereas in milling operations II refers to the edge speed of the rotating workpiece. Cutting speed (V) is expressed in millimeter per second (mm/s) and it can be calculated by the following formula;

v.™
60

Proper cutting speed varies from material to material. The softer the content, the higher the cutting speed. Recommended cutting rates for various materials can be found from machinability handbooks or catalogs of tooling manufacturers. The controller unit of Boxford CNC machines enables to program with cutting speed (surface speed) instead of programming with the feed-rates using the preparatory code of G97.