MILLING

MILLING

@ Milling :-

      it is defined as the machining process for removing excess material proicess for removing excess material from a work piece with a rotating cutter

@ milling m/c :-

      A m/c tool which is used for producing flat, counted or helical surfaces, grooves or slots cutting of gear etc with the help of rotating multiple teeth cutter

# Principle of working of a milling m/c :-   

           milling m/c carries out cutting operation on a work piece with revolving cutter as the work piece is fed against it a milling cutter as a cutter edge on its circumferance and cutting edge acts as a individual cutter during a cycle of rotation

# Type of milling m/c :-

     - According to the drive :-
* Come pulley belt drive
* individual motor drive
     - according to design
* kee And Column type
* Horizontal milling m/c
* Vertical Milling M/c
*  Omniversal milling m/c
       - Planner type milling m/c
* Production type Milling m/c
* simplase milling m/c
* Drum Type milling m/c
* Profile milling m/c

i) Knee an d column type :-

           these are low production m/c the knee and column type is the most commonly m/c in  view of its flexibilty and carries swtup . the table of these m/c is mounted on the vertical column. these knee can be moved up and down

ii) horizontal millimg m/c :-

       Horizontal milling m/c consist of a horizontally mounted milling spindle . the spindlethe main feed drive the knee and the milling table are supported by the column rotatry motion to the main spindle is provided the main drive  either through a steeped cone pully drive or a gear drive the knee can be move up a down

iii) Universal milling m/c :-

         a vertical m/c consist of a melling spindle mounted vertically in the milling head .the milling head consist of a scale provided in a degree and can be swivelled and set any oblique position

iv) universal milling m/c :-

        it is similar to the horizontal milling m/c the work table of this m/c is provided with another extra swivelled movement attachment with a index

@ milling method :-

      i) Convential milling ( Up Milling ) :-
              in convectionally milling the cutting tool roates in the opposite direction of the table movement in convectional milling the chip start zero thickness and gradually increase to the maximum sizes
     ii) Climb milling :-
              when the feed motion is in the same direction as that of the motion of the cutter is known as climb milling . in climb milling the chip start maximum thickness and goes to zero to zero thickness gradually . this is suitable for obtaining fine finished from the workppied
iii) Milling cutters :-
      a hardened steel disc or cylinder with the cutting teeth arranged either on its periphery or some one end face or on both is callewd milling cutters . usually the cutter in a fixed but rotating hour orspindle and thework piece moves across the cutter

@ Types of milling cutters :-

* plain milling cutters :-
         this are also called scale milling cutters and are basically cylindrical with the cutting teeth on the periphery . this are generally used for making flat surfaces
* side milling cutters ;-
       this cutter is similar to plain cutters except that is has has teeth of side
* angle  milling cutters :-
           anmy willing cutters which have cutting teeth cut an angle to the axis of rotation are known as angle milling cutters
* Form milling cutters :-
        any cutters  whose teeth have been gives a special shape is known as form milling cutters

@ milling operation :-

      - face milling :-
                the milling process is employed for machining a flat surface which is at right angle to the axis of rotating cutters
          - straddle milling :-
      the straddle milling is operation of producing flat vertical faces on both side of the work piece by using to side milling cutters mounted on the same arnors
          - angular milling :-
             these milling operation is used to m/c a flat surfaces at an angle to the to the cutter axis other than right to the axis of rotation of the cutter
- form milling :-
        this milling process is employed for machinery those surfaces . which are of irregular dsurfaces the cutter used is called form milling cutters will have the shape of its cutting teeth as of its cutting teeth forming to the profiole of the surfacews of the product

   @ cutting speed, feed and depth Of cut :-

     i) cutting Speed :-

             the curtting speed of milling cutter is its peripheral linear speed resulting from rotation. in simple words we con say that the cutting speed of one cutting tooth
   The cutting speed has to be selected carefully two high cutting speed causes the cutter teeth to become sharp prematuraly and to lovbe cutting speed cause low cutting effeciency

ii) feed 

     the feed in a milling m/c is defined as the rate at which the workpiece advance under the cutter . the feed is expressed in a milling m/c following three different methods
- Feed per  minute :-
the feed per minute is defined by the distance of the work advances in one minute. it is expressed in mm/minute
- feed per teetth ;-
      the feed per tooth is defined by the distance of the work advances in the time between engagement by the two successive teeth. it is expressed in mm/tooth of the cutter
- feed per resolution :-
      the feed per cutter resolution is the distance of the work advances in the time when the cutter terms through through one complete resolution . it is expressed in mm/resolution of the cutter
- depth of cut :-
     the depth of the penetration of milling vcutter tteth into the job during its one one passage that is cutted over the job is known as depth of cutter for a milling operation is mm/cutt-0.5mm

@ factor veffecting the cutting speed of milling cutter ;-

   * size of the cutt, style and size of the cutter, sharpness of the cutter teeth etc effects the cutting speeds
* High cutting speed can be used for cutters with better hardness of the cutter material
* high cutting speed cam also be used when heat is dissipated quickly by the use of coolent
* Surface finish and dimensional accuraccy condition of the milling m/c etc also effect the cutting speed

@ milling m/c accesoriees and attachments :-

1.) tool holding decices :-

         - Arbors :-
                     these are cutters holder devices an arbor is usually made with taper shank for proper alignment with spindle moving taper hole at its mose
- Collect :-
      a collect is an accurate time saving cutter holding device used on milling m/c . it is fitted on main  spindle of the milling m/c with a hand wheel driven sleeve and is operated by handle fitted on it
- adapters :-
     an adaptors is form of collect used on milling m/c having standard spindle end cutter having shank are usually mounted on adaptors
- spindle spring collects :-
      straight shank cutter are usually adaptors called spring collect or spring cluck

2. work holding devices ;-

     a work piece must be held security rigidly on the milling m/c table for accurate milling operation

i) vices:-

   vices are most common devices used for holding work on the milling m/c table due to its quick loading and unloading arrangement the work piece is held between two jaws which are specified their jaw lengths

ii) Tee-bolt and clamps :-

        tee bolts are used for holding work directly on milling m/c. the milling m/c table is provided with tee slots and work piece is held the help of the tee bolts

iii) circular table :-

      it is used for milling circular surfaces . a circuylar table mounted on the m/c base may be used for providing circular surfaces after centrillizatrion

iv) Firctures :-

      these are especially useful when large number of identical parts are to be produce . the use of fixture mimimizes loading, locating, clamping and unloading type depending upon  design requirements different types iof fixture are used on milling m/c

2 milling m/c attachments :-

       Many standard a special devices are used on a milling m/c for augmenting the range to i,prove, versatility, productivity and acuuracy of operation some milling atachments are used for positioning and driving the cutter by altering bthe axis of rotation . while other devices for positioning holding and feeding the work

i) vertical milling attachments :-

     is is an attachments used for comes converting a horizontal milling m/c into a vertical milling m/c by orienting the cutting spindle axis from the horizontal to vertical position

ii) slotting attachments :- 

     a horizontal milling m/c is converted into slotter whih is a small vertical shaped a slotting attachments . the attachments is mounted on the column and is sported by the over arm . it convert the rotatary motion of milling m/c spindle to reciprocating motion for the ram by means of an crank with the attachments

iii) Rack milling attachments :-

        the attachments consist of a gear train and enables the spindle axis tobe oriented at right angle to m/c spindle . it is used for cutting . rack teeth and cutting worms and other cellaneous parts
- Spiral milling attachments :-
       it is device usad for milling helical and spiral gear teeth . this attachments is used on a plain milling m/c by botting on the face of the collumns