Turning
is a machining process used for the generation of external and conicalsurfaces on a rotating work piece by means of a single point traversing cutting tool. The process is performed on a lathe; where in the cutting tool is fed against a rotating work piece.
The forged axle has scales and excess material on its surface. In order to remove this excess material rough turning is carried out through out the surface of the axle. The exact shape of the axle is obtained in this process and the surface of the
machined axle after this operation is rough.
During operation the axle is fixed between the chucks and made to rotate at a very high speed. The carbide tool having 8 cutting edged is fed against this rotating axle which removes the excess material in the form of chips.
Copyright ® Salman Ali
Nitte Meenakshi Institute Of Technology
The material is removed from both the edged simultaneously i.e. the turning operation makes use of 2 tool at the same time in order to reduce the time of operation.
In Rail Wheel Factory (RWF) axle machining shop rough turning is done by both CNC lathes and conventional lathe.
In the CNC lathe the feed, the motion of the tool spindle/holder for each type of axle is programmed and fed into the computer which guides the cutting operation. Various parameters like length of the axle, feed, diameter of the axle, speed of rotation etc can be adjusted' altered by the operator as and when required.In the comentional lathe the tool holder is placed in the carriage and each lathe used for rough turning has 4 carriage's, two of which used for turning the body of axle while the other two for turning the wheel seat, dust guard and journal. The carriages are guided by the Templates which have the same shape as that of the axle to be machined.
As tracer placed in the carriage traces the template, tool carriage and hence the tool moves along the same shape; hence the required shape is obtained on the axle. Each parameter like feed, speed, carriage movement etc can be controlled by the operator. The process can also be automated and can be stopped and adjusted at any point of time.
NOTE:
A dimensional accuracy up to I micron can be obtained in CNC machine while accuracy up to 1 mm can be obtained in conventional lathe.
STATION 3: Drilling. Reaming and
Tapping
After rough turning of the axle, threaded holes are drilled at the two ends surfaces in order to fix the bearing to the axle.
Drilling
Drilling is a machining operation of producing a cylindrical hole in a solid work piece by means of a revolving tool called the Drill bit. Drill bit is also called as twist drill since it has sharp twisted edges formed around a cylindrical body. It is made up of HCS.
Copyright ® Salman Ali
Nitte Meenakshi Institute Of Technology
In operation, the drill bit is held in the chuck of the machine and rotated by a spindle at high speed , With the help of the hand wheel or ty automatic means, the drill bit is forced to move against the rigidly clamped work piece.
The hole is generated by the sharp cutting edges of the rotating drill bit while the excess material removed (chips) gets curled and escapes through the helical grooves provided in the drill bit
Since the cutting action takes place inside the work piece, lot of heat is generated: this may cause damage to the tool as well as the work piece.
Hence coolant is used to reduce the heat, Both the ends are drilled at the same time.
Reaming:
Reaming is the operation of finishing a previously drilled hole to bring it to an exact size and to improve the surface finish of the hole.
The operation is earned out using a multi tooth revolving tool caller Reamer, which consists of a set of parallel straight or helical cutting edges along the length of the cylindrical tool.
This operation is carried out at a speed lower than drilling in order to obtain a good surface finish.
Tapping :
Tapping is the operation of producing internal threads in a previously drilled hote by means of a tool called tap. The tap has threads cut on its periphery and is hardened to improve its properties,The threads cut on the tap form the replica of the threads to be produced in the work piece Taps are available in standard sizes.
To generate a specific size thread in the work piece, a hole with diameter smaller than the size of the tap is first drilled using twist drill. To perform the tapping operation, the tool is held rigidly in the spindle and is rotated at a speed less than drilling operation. The rotating tap is fed slowly in the hole of the work piece to cut the material and produce threads.
Copyright ® Salman Ali
Nitte Meenakshi Institute Of Technology
Note :
All the three drilling,reaming and tapping tools are held in same spindle but speed is varied for respective operations.
These tools are made up of HCS.
Operations are carried out simultaneously on both sides.A continuos supply of coolant is required in order to reduce the heat production and wash away the chips.