Define milling process?

  1. Milling is a machining operation that is performed with a rotary cutter with several cutting edges arranged on the circumference of the cutter.
  2. The milling process creates flat surfaces or curved profiles and many other complex shapes with great accuracy and also has a very good surface finish.

What is a milling machine?

  1. A milling machine is a machine tool that removes metal as the workpiece is fed against a rotating multipoint cutter.
  2. The arbor can accommodate one or more cutters simultaneously in the milling machine.
  3. In many applications, due to its higher production rate and accuracy, the milling machine has even replaced shapers and slotters.

Fig. 1 Multi-Point Cutter

What is the principle of milling process?

  1. In the milling machine, the metal is cut using a rotating cutter having multiple cutting edges.
  2. For cutting operations, the workpiece is fed against the rotary cutter.
  3. As the workpiece moves against the cutting edges of the milling cutter, metal is removed in the form of chips.
  4. The machined surface is formed in one or more passes of the work.
  5. The work to be machined is held in a vice, a rotary table, a three- jaw chuck, an index head, between centers, in a special fixture, or bolted to a machine table.

What are the basic types of a milling process?

There are 2 basic types of the milling process.

  • Up milling / Conventional milling process.

  • Down milling / Climb milling process.

Fig.2 Up & Down Milling Process

  • Up milling / Conventional milling process.

  1. In this type of milling process, the metal is removed in the form of small chips by a cutter rotating against the direction of the travel of the workpiece.
  2. The chip thickness is minimum at the start of the cut and maximum at the end of the cut.

  • Down milling / Climb milling process.

  1. Cutter moves in same direction as that of the workpiece and removes the material. 
  2. In this type of milling process, it is claimed that there is less friction involved and consequently less heat is generated on the contact surface of the cutter and workpiece.
  3. Power consumption is reduced by this process.

What are the types of milling process?

The milling process is broadly classified as:

  • Peripheral milling
  • Face milling
  • End milling

Fig.3 Peripheral & Face Milling Process

  • Peripheral milling:

  1. In the Peripheral milling, the cutting edges are on the circumference of the milling cutter and the milled surface is generally parallel to the cutter axis.
  2. The peripheral milling cutters are supported on a long arbor.
  3. The deflections of arbor lead to changes in dimensional and form accuracy of this process.
  4. Horizontal milling machine normally uses peripheral milling cutters. 
  5. Peripheral milling is adopted for the following machining operations:

        a. Slab milling to produce flat surfaces. 

        b. Slot milling to produce precision slots.

        c. Slide and face milling to machine adjacent horizontal and vertical surfaces.

        d. Form milling to produce the prismatic shape of any form.

        e. Straddle milling to machine 2 parallel vertical surfaces.

        f. Gang milling to machine a number of surfaces simultaneously with a set of cutters.

Fig. 4 Different Peripheral Milling Process

  • Face milling:

  1. In face milling, the cutting edges are provided on the face as well as on the periphery of the cutter, the surfaces generated is parallel to the face of the cutter and is perpendicular to the cutter axis.
  2. This process is widely used for milling operations involving a high metal removal rate.
  3. The operation of face milling is usually done with a face milling cutter having coated tungsten carbide inserts.
  4. Face milling cutters are used in conjunction with vertical milling machine.

Fig. 5 Face Milling Process

  • End milling:

  1. End mills are capable of performing peripheral as well as face milling operations simultaneously.
  2. It has got cutting edges on the bottom face as well as on its periphery.
  3. They are used for machining edges, shoulders, grooves, slots, and keyway pockets.
  4. End mills have a tapered shank that fits into a tapered sleeve provided in the spindle of a vertical milling machine.

Today, end mills are available in many tool materials.

  1. Cobalt High-Speed Steel (Super H.S.S).
  2. Coated High-Speed Steel.
  3. Solid Carbides.
  4. Micrograin solid carbides.
  5. Indexable inserts of cemented carbide or coated carbide.

What are the types of milling machines?

The classification of 5 types of milling machines are as follows:

1. Column and knee type milling machines.

a. Hand milling machines.

b. Horizontal milling machines.

c. Universal milling machines.

d. Vertical milling machines.

2. Planer milling machines.

3. Fixed bed type milling machines.

a. Simplex milling machines.

b. Duplex milling machines.

c. Triplex milling machines.

4. Machining center machines.

5. Special type of milling machines.

a. Rotary table milling machines.

b. Planetary milling machines.

c. Profiling machines.

d. Duplicating machines.

e. Pantograph milling machines.

f. Continuous milling machines.

g. Drum milling machines.

h. Profiling and tracer controlled milling machines.

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