GRINDING

GRINDING 

     a process of material removal in form of small clips by mean of rotating abrassive particles bonded together in grinding wheel to produce flat, cylindrical or other surfaces is known as grinding
- sharpening of turning tool, sharpening of milling cutter
- cylindrical grinding of shaft
    a wheel used for grinding various type surfaces by its abrassive action is called grinding wheel
    the m/c tool design for finishing with inclose vtolerance the flat, cylindrical or other surfaces by the abrassive action of a rotating grinding wheel is called grinding m/c or grinder

@ purposes of grinding :-

      * it is used for sharpening of cutting tools, it is also used for bgrinding threads in order to have close tolerance and better finish
* to produce surfaces with higher degree of smoothness
* some time, it is also used for higher material removal rates
* To m/c material which are too hard for m/c by other method using cutting tools

@ Termonology used in grinding :-

   i) Abrassive :-

        any substance used for abrading, grinding and lapping of material

ii) Bond :-

      the material used for holding the abrassive grain together

iii) cutting rate :-

     the rate of material removal during grinding

iv) Grit or grain size :-

         the size of the cutting particle of grinding wheel

v) Grade or hardness :-

        it is strength by which grain are held together

vi) Loading :-

      the process of filling pores of grinding wheel by chips during grinding operation

@ Grinding action :-

     grinding wheel are composed of very hard abrassive particlesheld together by an adhesive substance called bonding material. the basic arrangement  of surfaces grinding which has similarity with up milling
       cutting point are operation except that irregularly shaped and randomly distributed the grain actually participating in grinding called  active grain
     under high speed of rotation pf grinding wheel active grain remove the metal in form of small clips from workpied portion that come in contact with wheel
   the sharp edges of active grain wear out and become blunt . thisresult in larger force on active grain during machining when cutting edges is too blunt and force is sufficiently high the grain get fractured
    when a fracture take place new sharp cutting edges are generated when whole grain is removed new grain become exposed and active

@ Grinding wheel  :-

      a wheel composed of hard and sharp edge abrassive grain held together by a bonding material and usually used for finishing with inclose tolerance
   the various surfaces by its abrassive action is known as grinding wheel
- six important elements consisder about const. of wheel

i) Abrassive :-

       a substance used removal of metal by abrastion is known as abrassive for making grinding wheels. abrassive used for making grinding wheel
* Natural abrassive 
- sand stone or quartz
- emery
- diamond
* Artificial abrassive :
 - silicon carbide
- aluminium oxide
- Boron carbide

ii) grit or grain size :-

the size of the grain is called grit or grain sizw
     the grain size influences the stoke removal rate and surfaces finish

iii) Bond :-

    a bond an adhesive material employed for holding abrassive grain together and giving the desired shapeto grinding wheel the bond commonlly used for the manufacture of grinding wheel are
- vetrified bond
- silicate bonds
- shellic bond
- rubber bond
- bakellite bond

iv) Grade :-

     the grade is  also called the hardness of the wheel two desigenates the forces holding the grain . the grade of a wheel dpend on the kind of bond , structure of wheel and amount of abrassive grains(A-F) (very soft ), G K (soft), L-O (medium), P-S (hard) , T-z (very hard)

v) Structure ;-

    the structure of a grinding wheel represent the grain wheel represents the grain spacing. it can be open or close O-7 (Close  Struccture) , 8-4 (open structure)

vi) common wheel shapes :-

     the shape and size of grinding wheel depends on the design of the m/c , power of m/c , the operation to be performed , the shape and size of the work piece and grinding condition according to  shape the wheel can be classified as
- Straight wheels used for cylindrical internal and surfaces grinding
- bevelled face straight wheel used for grinding threads, gear teeth
- straight recessed wheel used for cylindrical grinding and facing
- abrassive cutting types used for abrassive cutting of a slotting operations
- cylinder, straight up and flaring cup

@ Types of wheel :-

* Built up wheel :-

              they consist of a number of bonded abrassive means spaces are always provided between the blocks

* Cone and plug shape :-

    they are employed to grind implicate shapes to which their outer surface suit

* Mounted wheel :-

     it is also known as mounted points. yhey are small diameter wheel mounted permanently on mandrels by cementing or other other bonding proess

* Diamond :-

        these wheel are made in similar shape as of aluminium oxide or silicon carbide . these wheel are made with three different types of bond backellite , metallic vetrified. in order to concern diamonds wheel larger than 25mm in diameter are produced with a bonded diamond layer at the cutting surfaces
        specification of grinding wheels as per (BIS) bear of indian standardthe marking system omprises of seven standard

@ manufacture symbol ( optional)

- Types of abrassive
- Grain size of abrassive
_ Grade of abrassive
-  Structure (optional)
- Type Of Bond
- Identification Mark (Optional)

@ Types Of abrassive  :-

* Aluminiu oxide
* Sil
* White aluminium oxide
* green Grit

@ Grain size of abrasive :-

- Coarse Grain (8,10,12, 14,16,24)
- medium grain (30, 36,46,54, 60)
- Fine Grain (80, 100,120,150,180)
- Very Fin Grain (220, 240, 280,320,400, 500, 600)

# suffix :-

     it is manufactures on identification markor trade recret and depend upon the process and type of manufacturing

# Symbols :-

 A= Al2O3 (Abrassive0
 4 6 = Medium grain size
 K = soft Grade
 5 = Structure
 V = Vetrified bond
 BE= Suffix

@ Turning :-

         the process of removing the abrassive material from the cutting fac and side of wheel so that it will run true with repect to axis of rotstion is called turning
        as seen as fresh wheel is fitted it becomes necessary to true its face to obtain true its face to obtain true surface of grinding wheel in term of either the form or concentricity a diamond dressing tool can be used

@ Glazing :-

         with continuous use of grinding wheel become dull with the sharp abrassive grain becoming round. this condition of dull grinding wheel with worm out grains termed as glazing

@ Dressing :-

   a loaded grinding wheel can be not cut properly such as grinding wheel can be cleaned and sharpened by mean of a process called dressing
    thus dressing can be defined a operation of sharpening dull abrassive grain or emposing fresh sharp grain of the face by cutting a portion of wheel

@ Balancing of grid wheel :-

          if the centre of gravity of grinding and its axis of  rotation concide the grinding wheel in balance , the preocess of ensuring uniform distribution of the mass of grinding wheel around its axis
   so thatno resmblance force act on it during its rotation is called balancing of grinding wheel. a balance grinding wheel operate reliability at high peripheral speedand in balanced  grinding wheel produce chatter ans leaves in due strain on the m/c . the problem become series in wheel of large diameter

@ mounting of wheels :-

       the process of holding grinding whel properly on the m/c  spindle for statisfactoery running is called mounting of wheels
    grinding wheel should be mounted on spindle with great core because improper dressing and true wheel can be cause accident

@ Methods of grinding :-

    - Surfaces grinding :-
            it is operation for grinding flat surfaces in horizontal position. the work may be ground either by phephery or by end face of grinding wheel. the work piece is reciprocated at a constant speed below or on the end face of the grinding wheel
- cylindrical grinding :-
   it isthe process of grinding curved surfaces of cylindrical piece. these services may be straight, tapered or contoured. the work piece is mounted on two centres one is tale stoke centre and other is head stoke centre . when high accuracy is required the two spot supporting centre mustre main stationary when work piece revolves
- Centre less Grinding :-
           it is operation for grinding the dia. of work without holding the work at its centre betweeen two grinding wheel centre between  two grinding wheel is also employed for grinding curved surfaces for grinding curved surfaces of long cylinder rods which cannot be ground by cylindrical grinding due to lateral thrust of grinding wheel on the w/p
- From grinding :-
          it is done with specially shaped grinding wheel that grind the formed surfaces the wheel face may be formed with diamond tool , grinding gear teeth threads and spined shaft

@ Grinding Machines :-

      Metal working m/c in which the cutting of metal is performed by abrassive action are known as grinding m/c

i) cylindrical grinder or m/c :-

           thye cylindrical grinding m/c is generally is used for producing surfaces . the m/c is very similar to a centre lathe

@ principle part of cylindrical grinder :-

   i) Base :-

           the base of a plain grinder is a bone like structure with heavy ribs. it contain a storage comp[artment for cutting fluid. it also houses the driving mechanism and hydraulic drives

ii) m/c tool :-

    it effect the longitudinal moment . it consist of two tables upper and lower
- Lower table :-
       it is also known as sloding or reversing table . it is ,ounted at the top and front of the base sliding table is movedd to and fro by gear or hydraulic drive . lateral moment can be set in in accordance with desired grinding quality the upper table is mounted on it
- upper table :-
         it also known as survived or work table . hed stock and tail stock for work piece . which are both adjustable in grrind ways are mounted

iii)  Head stock :-

        it is mounted on the upper table on its left and it serves two mount the work piece between centre or chucks. the head stock centre does not revolve with the work piece and remain fixed and rigidity held

iv) Foot stock :-

       it is mounted on right end of work table . it supports the rear end of the work piece mounted between centres

v) Wheel head and slide :-

              it imparts the main rotatary motion and the down feed to grinding wheel . it is mounted on grinding spindle which is driven by a motor in upper part of wheel head

@ principle of Working :-

               the cylindrical grinding operation involves for moments
* rotation of work piece
*  Rotation Of grinding wheel about its axis
* Transversing of work piece past the griding wheel
* Feed of the wheel into work piece

@ Surface grinder or m/c :-

              it is process of producing flat surfaces by maen of a revolving abrassive wheel
two general types of m/c are
- Reciporating table type or planner type
- rotatary table type

@ tool and cutter grinder :-

           cutter grinding can be done on a universal grinder or an lathe by using suitable attachments but it is prefferable to use specially design m/c callled tool and cutter grinder. these m/c are used for sharpening plain cylindrical cutters angular cutters, formed cutters and other varities of other tool

# the main part of m/c are ;-

- Base and column :-
          these are made of heavy rigid casting to damper the vibratiion ensures accuracy of job. a saddle is mounted on the  bed . column is mounted on the saddle
- tilting wheel head :-
             the wheel head is rigidity mounted on an elevating column and consist of housing carrying a wheel spindle which reams in two bearing . the wheel head can be swivelled and tilting at 360 degree in all planes
- Work table :-
         the work table fitted on the table slide can be swivelled upto 45 degree on either side of column and fine adjustment of work table enable accurate sitting of small angles on either side of column
- Universal work head :-
           it can be swivelled all around on two plains and can work upto 250mm dia
- Electrical panal control board :-
                  it is mounted in side the base which is sealed against dust and moisture . the panal control can be position at any place around the m/c for easy accessibility

@ Centre less grinding m/c :-

           the centre less grinder basically consist of a hjeavy base . grinding wheel and regulating wheel head, work rest blades and upper and lower slides. the wheel head is regidity is fired to the bed . the upper slide consist of a regulating wheel of its turning unit. the upper slide is mounted on lower slide . the lower slide is mounted on lower slide. the work piece rest on the blade of the work rest between two wheel by moving lower slide. the work piece can be brought towards or away from the grinding wheel