A milling machine is a machine tool that removes metal as work is fed against a rotating multipoint cutter. This machine is superior to other machines as regards accuracy and better surface finish and designed for machining variety of tool room work. This is why milling machine finds wide application in production work.
Miling machines operations:
Following are different operations performed on milling machine:
|1. Plain milling||9. End milling|
|2. Face milling||10. Saw milling|
|3. Side milling||11. Milling keyways, grooves and slots|
|4. Strandddle milling||12. Helical milling|
|5. Angular milling||13. Gear cutting|
|6. Gang milling||14. Cam milling|
|7. Profile milling||15. Thread milling|
|8. Form milling|
The plain milling is an operation of production of plain, flat and horizontal surface parallel to axis of rotation of plain milling cutters the operation is also called slab milling. To perform the operation, the work and the cutter are secured properly on machine. The depth of cut is adjusted by rotating the vertical feed screw of the table and the machine is started after selecting the proper speed and table feed
The face milling operation is performed by a face milling cutter rotated about an axis perpendicular to work surface. The operation is carried out in a plain milling machine, and the cutter is mounted on a stub arbor to produce a flat surface. The depth of cut is adjusted by rotating the cross feed screw of the table. It is used to produce flat surface.
The side milling is operation of production of a flat vertical surface on side of a work piece by using side milling cutter. The depth of cut is adjusted by rotating the vertical feed screw on the table.
The straddle milling is the operation of production of flat vertical surface on both sides of the workpiece by using two side milling cutters mounted on the same arbor. The distance between the two cutters is correctly adjusted by using suitable spacing collars. The straddle milling is very commonly used to produce square or hexagonal surfaces.
The angular milling is operation of production of an angular surface on a workpiece other than at right angles to axis of milling machine spindle. The angular grove may be single or double angle and may be varying included angle according to the type shape of angular cutter used. One simple example of angular milling is production of V blocks.
The gang milling is the operation of machining several surfaces of a workpiece simultaneously by feeding the table against number of cutters having same or different diameters mounted on arbor of the machine. The method saves much machining time and is widely used in repetitive work. The cutting speed of gang of cutters is calculated from cutter of largest diameter.
Milling Hexagonal Bolt Head:-
One of the common examples of side milling or the straddle millings he operation of milling of hexagonal bolt heads. The procedure adapted to mill a hexagonal bolt head is described below:
- Width across the flat bolt head is first determined.
- The half side milling cutters are mounted on arbor and distance between them is Correctly adjusted equal to the width across the flat of the bolt head by using Suitable spacing collars.
- A Universal dividing head is mounted on the table with its spindle swiveled to vertical position.
- The workpiece is mounted at nose of dividing head spindle by the help of suitable chuck.
- The workpiece is centered below the cutter and the first cut is taken.
- The workpiece is rotated through on sixth of the revolution by using indexing mechanism and then the second cut is taken.
- The workpiece is turned again for one sixth of revolution by using indexing mechanism and then second cut is taken. This finishes the work and the hexagonal bolt head is produced.
- Instead of using straddle milling, single side milling cuter is used, the work will have to be rotated through one sixth of the rotation for six numbers of times to finish six faces of work.
The milling is operation of production of various types of contours by using a form cutter. Irregular contour may be of any shape. After machining, the formed surface is checked by a template gauge. The cutting speed for form milling is 20% to 30% less than that of the plain milling.
The profile milling is an operation of reproduction of an outline of a template or complex shape of the master die on a workpiece. Different cutters may be used for profile milling. An end mill is one of the most widely used milling cutters in profile milling work.
The end milling is an operation of production of a flat surface which may be vertical, horizontal or at an angle in reference to the table surface. The cuter used is an end mill. The end milling cutters are also used for production of slots, grooves and keyways. A vertical milling machine is most suitable for end milling operation.
The saw milling is an operation of production of a narrow slots or grooves on workpiece by using a saw milling cutter. The saw milling can also be performed for complete parting-off operation. The cutter and the workpiece are set in a manner so that the cutter is directly set over one of the T slots of the table.
Milling Keyways, Grooves and Slots:-
The operation of production of keyways, grooves and slots of varying shapes and sizes can be performed in a milling machine by using a plain milling cutter, a metal slitting saw, an end mill or by a side milling cutter. The open slots can be cut by a plain milling cutter, or a metal saw, or by side milling cutter. The closed slots are produced by using end mills. A dovetail is manufactured by using special type of cutters designed to give required shape on the workpiece. The T slot is produced by first-milling a plain slot on a workpiece and then the shank of the T slot a milling cutter is introduced through the first machined slot. The second slot is cut at right angles to first slot by feeding the work past the cutter.
A woodruff key is produced by using a woodruff key slot cutter. Standard keyways are cut on the shafts by using side milling cutters on end mills. The cutter is exactly at the center line of the workpiece and then the cut is taken.
The gear cutting operation is performed in milling machine by using a form relived cutter. The cutter may be of cylindrical type or end mill type. The cutter profile corresponds exactly with tooth space of the gear. Equally spaced gear teeth are cut on the gear blank by holding the work on the universal dividing head and then indexing it.
The helical milling is the operation of production of helical flutes or grooves around the periphery of the cylindrical or conical workpiece. The operation is performed by swivelling the table to the required helix angle and then by rotating and feeding the work against rotary cutting edges of a milling cutter.
The thread milling is an operation of production of threads by millers. The operation is performed in special thread milling machines to produce accurate threads in different quantities. The operation requires three driving motions in machine: one for the cutter, one for the work and third for longitudinal movement of the operation is performed by a single thread milling cutter, the cutter head is swiveled to exact helix angle of thread. The cutter is rotated on the spindle and the work is revolved slowly about its axis. The thread is completed in one cut by setting the cutter to full depth of the thread and then feeding it along entire length of the workpiece.
When the thread is cut by multiple milling cutter, the cutter axis and the work spindle are set parallel to each other after adjusting depth of cut equal to full depth of thread. The thread is completed by simply feeding the revolving cutter longitudinally through distance equal to pitch length of the thread.
The cam milling is the operation of production of cams in milling machine by use of universal dividing head and vertical milling attachment. The cam blank is mounted at end of dividing head spindle and the end mill in held in vertical milling attachment. The axis of the cam blank and the end mill spindle should be always remaining parallel to each other when set for cam milling. The dividing head is geared to table feed screw so that the cam is rotated about its axis while it is fed against the end mill. The axis of the cam can be set to zero to ninety degrees in reference to surface of the table for obtaining different rise of cam.