Manufacturing Processes – II - NPTEL
Module5Abrasive Processes(Grinding)Version 2 ME, IIT Kharagpur
Lesson29Classification of grindingmachines and their usesVersion 2 ME, IIT Kharagpur
Instructional ObjectivesAt the end of this lesson the students would be able to:(i)(ii)(iii)recognise various types of basic grinding machinesillustrate techniques of grinding in these machinesstate various applications of grinding machines29. Grinding MachinesGrinding Machines are also regarded as machine tools. A distinguishing featureof grinding machines is the rotating abrasive tool. Grinding machine is employed toobtain high accuracy along with very high class of surface finish on the workpiece.However, advent of new generation of grinding wheels and grinding machines,characterised by their rigidity, power and speed enables one to go for high efficiencydeep grinding (often called as abrasive milling) of not only hardened material butalso ductile materials.Conventional grinding machines can be broadly classified as:(a)Surface grinding machine(b)Cylindrical grinding machine(c)Internal grinding machine(d)Tool and cutter grinding machine29.1 Surface grinding machine:This machine may be similar to a milling machine used mainly to grind flat surface.However, some types of surface grinders are also capable of producing contoursurface with formed grinding wheel.Basically there are four different types of surface grinding machines characterised bythe movement of their tables and the orientation of grinding wheel spindles asfollows: Horizontal spindle and reciprocating table Vertical spindle and reciprocating table Horizontal spindle and rotary table Vertical spindle and rotary table29.1.1 Horizontal spindle reciprocating table grinderFigure 29.1 illustrates this machine with various motions required for grinding action.A disc type grinding wheel performs the grinding action with its peripheral surface.Both traverse and plunge grinding can be carried out in this machine as shown inFig. 29.2Version 2 ME, IIT Kharagpur
AA: rotation of grinding wheelB: reciprocation of worktableC: transverse feedD: down feedDCBFig.29.1: Horizontal spindle reciprocating table surface grinderAADB(a)D(b)CBA: rotation of grinding wheelC: transverse feedB: reciprocation of worktableD: down feedFig. 29.2 Surface grinding (a) traverse grinding(b) plunge grinding29.1.2 Vertical spindle reciprocating table grinderThis grinding machine with all working motions is shown in Fig. 29.3. The grindingoperation is similar to that of face milling on a vertical milling machine. In thismachine a cup shaped wheel grinds the workpiece over its full width using end faceof the wheel as shown in Fig. 29.4. This brings more grits in action at the same timeand consequently a higher material removal rate may be attained than for grindingwith a peripheral wheel.Version 2 ME, IIT Kharagpur
A: rotation of grinding wheel B: reciprocation of worktableC: down feed of grinding wheelCCABABBFig. 29.3 Vertical spindle reciprocatingtable surface grinderFig. 29.4 Surface grinding in Vertical spindlereciprocating table surface grinder29.1.3 Horizontal spindle rotary table grinderSurface grinding in this machine is shown in Fig.29.5. In principle the operation issame as that for facing on the lathe. This machine has a limitation in accommodationof workpiece and therefore does not have wide spread use. However, by swivellingthe worktable, concave or convex or tapered surface can be produced on individualpart as illustrated in Fig. 29.6DCAA: rotation of grinding wheelB: table rotationC: table reciprocationD: down feed of grinding wheelBFig. 29.5 Surface grinding in Horizontal spindle rotary table surface grinderVersion 2 ME, IIT Kharagpur
CDBAA: rotation of grinding wheelB: table rotationC: table reciprocationD: down feed of grinding wheelΘ: swivel angleΘFig. 29.6 Grinding of a tapered surface in horizontalspindle rotary table surface grinder29.1.4 Vertical spindle rotary table grinderThe principle of grinding in this machine is shown in Fig. 29.7. The machine is mostlysuitable for small workpieces in large quantities. This primarily production typemachine often uses two or more grinding heads thus enabling both roughing andfinishing in one rotation of the work table.ACA: rotation of grinding wheelB: work table rotationC: down feed of grinding wheelBFig. 29.7 Surface grinding in vertical spindle rotary table surface grinder29.1.5 Creep feed grinding machine:This machine enables single pass grinding of a surface with a larger downfeed butslower table speed than that adopted for multi-pass conventional surface grinding.This machine is characterised by high stiffness, high spindle power, recirculating ballscrew drive for table movement and adequate supply of grinding fluid. A furtherdevelopment in this field is the creep feed grinding centre which carries more thanone wheel with provision of automatic wheel changing. A number of operations canbe performed on the workpiece. It is implied that such machines, in the view of theirsize and complexity, are automated through CNC.Version 2 ME, IIT Kharagpur
29.1.6 High efficiency deep grinding machine:The concept of single pass deep grinding at a table speed much higher than what ispossible in a creep feed grinder has been technically realized in this machine. Thishas been made possible mainly through significant increase of wheel speed in thisnew generation grinding machine.29.2 Cylindrical grinding machineThis machine is used to produce external cylindrical surface. The surfaces may bestraight, tapered, steps or profiled. Broadly there are three different types ofcylindrical grinding machine as follows:1. Plain centre type cylindrical grinder2. Universal cylindrical surface grinder3. Centreless cylindrical surface grinder29.2.1 Plain centre type cylindrical grinderFigure 29.8 illustrates schematically this machine and various motions required forgrinding action. The machine is similar to a centre lathe in many respects. Theworkpiece is held between head stock and tailstock centres. A disc type grindingwheel performs the grinding action with its peripheral surface. Both traverse andplunge grinding can be carried out in this machine as shown in Fig.29.9.ABA: rotation of grinding wheelB: work table rotationC: reciprocation of worktableD: infeedDCFig. 29.8 Plain centre type cylindrical grinderDDAAABC(a)B(b)Fig. 29.9 cylindrical (a) traverse grinding and(b) plunge grindingA: rotation of grinding wheelB: workpiece rotationC: reciprocation of worktableD: infeedVersion 2 ME, IIT Kharagpur
29.2.2 Universal cylindrical surface grinderUniversal cylindrical grinder is similar to a plain cylindrical one except that it is moreversatile. In addition to small worktable swivel, this machine provides large swivel ofhead stock, wheel head slide and wheel head mount on the wheel head slide.A: swivelling wheel headB: swivelling wheel head slideC: swivelling head stockD: rotation of grinding wheelDFig. 29.10 important features of universal cylindrical grinding machineThis allows grinding of any taper on the workpiece. Universal grinder is alsoequipped with an additional head for internal grinding. Schematic illustration ofimportant features of this machine is shown in Fig.29.10.29.2.3 Special application of cylindrical grinderPrinciple of cylindrical grinding is being used for thread grinding with specially formedwheel that matches the thread profile. A single ribbed wheel or a multi ribbed wheelcan be used as shown in Fig. 29.11.DAACCB(a)A: rotation of grinding wheelB: rotation of workpieceC: DownfeedD: Longitudinal feed of wheelB(b)Fig. 29.11 Thread grinding with (a) single rib (b) multi-ribbed wheelRoll grinding is a specific case of cylindrical grinding wherein large workpieces suchas shafts, spindles and rolls are ground.Crankshaft or crank pin grinders also resemble cylindrical grinder but are engaged togrind crank pins which a
29. Grinding Machines Grinding Machines are also regarded as machine tools. A distinguishing feature of grinding machines is the rotating abrasive tool. Grinding machine is employed to obtain high accuracy along with very high class of surface finish on the workpiece. However, advent of new generation of grinding wheels and grinding machines,
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