How Milling Machine Works? Full explained
Introduction:
Milling is the cutting operation that removes metal by feeding the work against a rotating, cutter having single or multiple cutting edges. Flat or curved surfaces of many shapes can be machined by milling with good finish and accuracy. A milling machine may also be used for drilling, making a circular profile and gear cutting by having suitable attachments.
Working Principle:
The work piece is holding on the worktable of the machine. The table movement controls the feed of work piece against the rotating cutter. The cutter is mounted on a spindle or arbor and revolves at high speed. Except for rotation the cutter has no other motion. As the work piece advances, the cutter teeth remove the metal from the surface of work piece and the desired shape is produced.
Horizontal Milling Machine Construction:
The main part of machine is base, Column, Knee, Saddle, Table, Over arm, Arbor Support and Elevating Screw.
1. Base: It gives support and rigidity to the machine
2. Column: The column is the main supporting frame mounted vertically on the base
3. Knee: The knee is a rigid casting mounted on the front face of the column. The knee moves vertically and this movement enables to adjust the distance between the cutter and the job mounted on the table. The adjustment is obtained manually or automatically by operating the elevating screw provided below the knee.
4. Saddle: The saddle rests on the knee and constitutes the intermediate part between the knee and the table. The saddle moves transversely.
5. Table: The table provides support to the work. The table is made of cast iron, its top surface is accurately machined and carriers slots which accommodate the clamping bolt for fixing the work. The worktable and hence the job fitted on it is given motions in three directions:
a). Vertical (up and down) movement provided by raising or lowering the knee.
b). Cross (in or out) or transverse motion provided by moving the saddle in relation to knee.
c). Longitudinal (back and forth) motion provided by hand wheel fitted on the side of feed screw.
6. Overarm: The Overarm is mounted at the top of the column and is guided in perfect alignment by the machined surfaces. The Overarm is the support for the arbor.
7. Arbor support: The arbor support is fitted to the Overarm and can be clamped at any location on the Overarm. The arbor is a machined shaft that holds and drives the cutters.
8. Elevating screw: The upward and downward movement to the knee and the table is given by the elevating screw that is operated by hand or an automatic feed.
CLASSIFICATION OF MILLING
Ø 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 work piece surface to be machined.
Ø Face Milling
In face milling, the cutter is mounted on a spindle having an axis of rotation perpendicular to the work piece surface. The milled surface results from the action of cutting edges located on the periphery and face of the cutter.
Ø End Milling
The cutter in end milling generally rotates on an axis vertical to the work piece. 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.
METHODS OF MILLING
Ø Up Milling
Up 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 work piece is fed to the right in up milling.
Ø Down Milling
Down 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 work piece is fed to the right in down milling.
The chip formation in down milling is opposite to the chip formation in up milling
Types of Milling Machines
Milling machines are among the most versatile and useful machine tools due to their capabilities to perform a variety of operations. They can be broadly classified into the following types:
Ø Column and knee type of milling machines
Ø Bed type
Ø Rotary table
Ø Tracer controlled
Horizontal Milling Machine Vertical Milling Machine
Column & Knee type Milling Machines Used for general purpose milling operations, column and knee type milling machines are the most common milling machines. The spindle to which the milling cutter is may be horizontal (slab milling) or vertical (face and end milling).
The basic components are:
Ø Work table, on which the work piece is clamped.
Ø Saddle, which supports the table and can move transversely.
Ø Knee, which supports the saddle and gives the table vertical movements for adjusting the depth of cut.
Ø Over arm in horizontal machines, which is adjustable to accommodate different arbor lengths.
Bed type Machines
In bed type machines, the work table is mounted directly on the bed, which replaces the knee, and can move only longitudinally. These machines have high stiffness and are used for high production work.
Rotary Table Machines
Rotary table machines are similar to vertical milling machines and are equipped with one or more heads to do face milling operations.
Tracer Controlled Machines
Tracer controlled machines reproduce parts from a master model. They are used in the automotive and aerospace industries for machining complex parts and dies.
Advantages
1. The metal is removed at a faster rate as the cutter has got multiple cutting edges and rotates at a higher speed.
2. It is possible to perform machining by mounting more than one cutter at a time.
3. The table of the machine can be moved to an accuracy of 0.02mm.
4. It is very useful since various cutters and precise tools can be machined.
5. Special attachments can be mounted on the machine to perform operations that are performed in other machine tools.
6. The quality of the shop is enhanced with the presence of this machine
Disadvantages
1. The cost of the milling machine is high.
2. As milling cutters cost high, the investment for procuring tools is more.
3. The production cost will increase if we carry out the operations performed in a shaper or a drilling machine with a milling machine.
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