A shaper is a versatile machine tool primarily designed to generate a flat surface by a single point cutting tool. But it may also be used to perform many other operation. The different operation which a shaper can perform are as follow :
1. Machining horizontal surface
2. Machining vertical surface
3. Machining angular surface
4. Cutting slots, grooves, and keyways
5. Machining irregular surface
6. Machining splines or cutting gears
Classification of the mechanical processes
Non-traditional machining processes can be classiffied into various groups according to the type of fundamental machining they employ, namely, mechanical, electrical, chemical, electro-chemical, thermo-electrical, etc. The classification of the machining processes based upon the type of energy used, the mechanism of metal removal in the process, the source of immediate energy required for material removal, and the medium for transfer of those energies, etc.
1. Mechanical
1. Abrasive jet machining
2. Ultrasonic machining
2. Chemical
1. Chemical machining
3. Electro-chemical
1. Electro-chemical machining
2. Electro-chemical grinding
4. Thermo-Electric
1. Ion-Beam machining
2. Plasma arc machining
3. Electrical discharge machining\
4. Electrical-Beam machining
5. Laser-Beam machining
MILLING MACHINE
The milling machine is a machine tool in which metal is removed by means of a revolving cutter with many teeth, each tooth having a cutting edge which removes metal from a workpiece.
The work is supported by various methods on the work table, and may be fed to the cutter, longitudinally, transversely or vertically.
A great variety of work may be done on a milling machine.
The machine is perhaps next to the late in importance.
Generally there are two type of milling machine
1. Upmilling process - In upmilling process the workpiece is fed opposite to the cutter's tangential velocity.
2. Downmilling process - In downmilling process the workpiece is fed in the same direction as that of the cutter's tangential velocity.
Specification of milling machine
The following are the specification of a column and knee type milling machine:
1. Width and length of the table.
2. Maximum distance the knee can travel.
3. Maximum longitudinal movement and cross feed of the table.
4. Number of spindle speeds.
5. Power of the main drive motor.
Type of milling machines
According to the general design of the milling machine, the usual classification of the milling machine are:
1. Column and knee type:
(a) Hand milling machine (b) Plain milling machine (c) Universal milling machine
(d) Omniversal milling machien (e) Vertical machine
2. Manufacturing of fixed bed type:
(a) Simplex milling (b) Duplex milling machine (c) Triplex milling machine
3. Planer type:
4. Special type:
(a) Rotary table milling machine (b) Drum milling machine (c) Planetary milling machine
(d) Pantograph, Profiling and tracer controlled milling machine
Types of milling cutter
Common types of milling cutters are enumerated below:
1. Plain milling cutter 2. Side milling cuttter
3. End milling cutter 4. Face milling cutter
5. Metal slitting cutter 6. Angle milling cutter
7. Formed milling cutter 8. Woodruff-key milling cutter
9. T-slot milling cutter 10. Fly cutter
Milling Operation
The milling operation are classified as follows:
1. Plain or slab milling 2. Face milling 3. Angular milling 4. Form millijng
5. Straddle milling 6. Gang milling 7. End milling 8. T-slot milling
9. Dove-tail milling 10. Saw milling 11. Involute gear cutting
1. Plain or slab milling - Plain milling is used to machine flat and horizontal surfaces .Here plain milling cutter is used, which is held in the arbor and rotated. The table is moved upwards to give the required depth of cut.
2. Face milling -This milling process is used for machining a flat surface which is at right angles to the axis of the rotating cutter. The cutter used in this operation in the face milling cutter.
3. Angular milling - In angular milling an angle milling cutter is used. The cutter used may be a single or double angle cutter, depending upon whether a single surface is to be machined or two mutually inclined surface simultaneously.
4. Form milling - This milling process is used for machining those surface which are of irregular shapes. The form milling cutter used has the shape of its cutting teeth conforming to the profile of the surface to be proved.
5. Straddle milling - Straddle milling is an operation is an which a pair of side milling cutters is used for machining two parallel vertical surfaces of a workpiece simultaneously. The distance between the cutters is adjusted by the spacers. This process is used to mill square and hexagonal surfaces.
6. Gang milling - Gang milling is the name given to a milling operation which involves the use of a combination of more then two cutters, mounted on a common arbor, for milling a number of flat horizontal and vertical surfaces of a workpiece simultaneously. This method saves much of machining time and is widely used in repetitive work. The cutting speed of a gang of cutters is calculated from the cutter of the largest diameter.
7. End milling - It is an operation of producing narrow slots, grooves and key ways using an end mill cutter. The mill tool may be attached to the vertical spindle for milling the slot. Depth of cut is given by raising the machine table.
8. T-slot milling - In the milling machine operation, first a plain slot is cut on the workpiece by a side and face milling cutter. Then the T-slot cutter is fed from the end of the workpiece.
9. Dove-tail milling - In this milling operation, the end of the cutter is shaped to the required dove-tail angle. The cutter is passed from one end of the workpiece to the other end.
10. Saw milling - It is an operation of production narrow grooves and slots on the workpiece. A slitting saw is used for saw milling.
11. Involute gear cutting - Gear milling operation, often referred as gear cutting, in-volves cutting of different types of gear on a milling machine. For this, either an end mill cutter or a form relieved cutter is used, which carries the profiles on its cutting teeth corresponding to the required profile of the gap between gear teeth.
The drilling machine is one of the most important machine tools in a workshop. As regards its importance it is second only to the lathe, Althrough it was primarily designed to originate a hole, it can perform a number of similar operations. In a drilling machine holes may be drilled quickly and at a low cost. The hole is generated by the rotating edge of a cutting tool known as the drill which exerts large force on the work clamped on the table. As the machine tool exerts vertical pressure to originate a hole it is loosely called a "drill press".
Electrical discharge machine also known as spark
erosion, electro-erosion or spark machining is a process of metal removal based
on the principle of erosion of metal by an interrupted electric spark discharge
between the electrode tool (usually
cathode) and the work (anode)
Fundamentally, the electric erosion effect is understood
by the breakdown. Of electrode material accompanying any from of electric
discharge. The discharge is usually through a gas, liquid of in some cases
through solids. A necessary condition for producing a discharge is ionization of
the dielectric, splitting up of as molecules into ions and electrons.
Illustrates the schematic layout of the electric
discharge machining system, The main components are the electric power supply,
the electric medium, the work piece and the tool, and a servocontrol.
The workpiece and the tool are electrically
connected to a dc electric power. The workpiece is connected to the positive
terminal of the electric source, so that it becomes the anode. The tool is the
cathode. A gap, known as the “spark gap” in the ranges of 0.05 to 0.05 mm is
maintained between the work-piece and the tool, and suitable dielectric slurry,
which is non-conductor of electricity is forced through this gap at a pressure
of 2 Kgf/cm² or less. When a suitable voltage in the range of 50 to 450 V is applied,
the dielectric breaks down and electrons are emitted form the cathode and the gap is ionized. In
fact, a small ionized fluid column is formed owing to formation of an avalanche
of electrons in the spark gap where the process of ionizational collision takes
place. When more electrons collect in the gap the resistance drops causing
electric spark to jump between the workpiece surface and the tool. Each
electric discharge or spark causes a focused stream of electrons to move with a
very high velocity acceleration from the cathode towards the anode, and
ultimately creates compression shock waves on both the electrode surface,
particularly at high spots on the workpiece surface, which are closest to the
tool. The generation of compression shock waves develops a local rise in
temperature. The whole sequence of operation occurs within a few microseconds.
However the temperature of spot hit by the electrons is of the order of 10,000
°C. This temperature is sufficient to melt a part of the metals. The forces of
electric and magnetic fields caused by the spark produce a tensile force and tear
off particles of molten and softened metal from this spot on the workpiece. A
port of the metal may vaporize and fill up the gap. The metal is thus removed
in this way from the workpiece. The electric and magnetic fields on the heated
metal cause a compression force to act on the cathodic tool so that metal removal from the tool is at a slower rate than
that from the workpiece. Hence, the workpiece is connected to the positive
terminal and tool to the negative terminal.
Advantage of EDM
Extremely high popularity of the EDM process is due to the following advantage.
1. The process can be applied to all electrically conducting metals and alloys irrespective of their melting points, hardness, roughness or brittleness.
2. Any complicated shape that can be made on the tool can be reproduced on the workpiece.
3. Highly complicated shapes can be made by fabricating the tool with split sectioned shapes, by welding, brazing or by applying quick setting conductive epoxy adhesives.
4. Time of machining is less than conventional machining processes.
5. EDM can be employed for extremely hardened work-piece. Hence the distortion of the work-piece arising out of the heat treatment process can be eliminated.
Disadvantage
1. Profile machining of complex contours is not possible at required tolerances.
2. Machining times are too long.
3. Machining heats the work-piece considerably and causes change in surface and metallurgical properties.
4. Excessive tool wear.
5. High specific power consumption.
