Workshop Procesess - Grinding Process.pdf

WORKSHOPS

1. GRINDING
PROCESSES

2. Learning objectives
•Define grinding
•Explain various grinding processes
•Identify types of grinding wheels
•Carryout grinding processes

3. 1.1 Introduction
Grinding is an abrasive machining process in
which excess material is removed by action of
hard, abrasive particles usually in the form of
a bonded wheel
Cutting action of abrasive grains

4. 1.2 Importance of Grinding
Can be used on all types of materials
Can be used to produce extremely fine surface
finishes, to 0.025 µm.
For certain abrasive process, can hold
dimensions to extremely close tolerances

5. 1.3 Grinding Processes
Grinding involves a number of processes, but
the following are the common ones;
Cylindrical grinding
Internal grinding
Centerless grinding
Surface grinding

6. Two types of cylindrical grinding: (a) external, and (b) internal.
1.Cylindrical Grinding
Cylindrical grindingis used to grind the cylindrical
surfaces and shoulders of the workpiece

7. Internal grinding: used to grind the internal
diameter of the workpiece.
2.Internal Grinding

8. Centerless grindingis a grinding process in
which the workpieceis supported by a blade
instead of center.
The regulating wheel rotates at lower speed and is
inclined at a slight angle
3.Centreless Grinding

9. Surface grindingis used to produce flat accurate
surfaces and can be carried out on all materials,
hard or soft.
4.Surface Grinding

10. 4.1 Basic Elements of a surface grinding machine

11. Elements cont..
Wheelhead:
The wheelheadcarries the wheel spindle,
which is mounted in precision bearings.

12. Saddle:
The saddle is fitted on top of the base in the
two veesideways and provides the cross-
traverse movement.
Elements cont..

13. Table:
Thetableisguidedbythevee-and-flat
slidewayonthesaddleandcanbemanually
operatedwithahandwheelorautomatically
operated
Elements cont..

14. Controls:controlsofatypicalgrinderincludethe
1.Handwheels;
a)Columnhandwheel:usedtoraisingand
loweringthecolumnduringthecutting
action.
b)Saddlehandwheel:forcrossmovementof
thesaddle
c)Tablehandwheel:toreciprocatethetable
Elements cont..

15. 2.Tablespeedcontrolknob:canbeadjustedto
giveinfinitelyvariablespeeds0.6to30
m/min
3.Theswitchpanel:controlsmotorsforpumps,
wheelspindle,cuttingfluid.Itcarriesthe
mainisolatorandalargemushroom-headed
stopbutton.
Elements cont..

16. 1.4 The Grinding Wheel
•Thegrindingwheelisaprecisiontoolwithwhich
thegrindingactionisperformed.

17. Cont.….
•Consistsofabrasiveparticlesandbonding
material.
•Abrasiveparticlesaccomplishcutting
•Bondingmaterialholdsparticlesinplaceand
establishesshapeandstructureofwheel

18. 1.4.1 Characteristics of Grinding Wheel
i.Abrasive materials
ii.grain size
iii.wheel grade
iv.grain spacing/structure
v.bond type
•Characteristics of grinding wheel are
determined by the following five factors;
Grain Grain Size Grade Structure Bond
Nature of
abrasive grain
Size of abrasive
grain(F or #)
Retention
strength of
abrasive grains
Proportion of
grains to the
entire wheel
Nature of
bonding agent

19. •Abrasive materials or grains are hard and
sharp crystals used to wear away another
material when one or the other is moved in
pressurized contact.
1.4.1 Characteristics Cont.…
1.Abrasive Materials

20. 1.1 General Properties of Abrasive Materials
•Higher hardness
•Strong wear resistance
•Extremely tough
•Highly friable (ability to fracture when cutting
edge becomes dull so as to expose new edge)
1.4.1 Characteristics Cont.…

21. •Aluminumoxide(Al
2O
3)-mostcommonabrasive.
Usedtogrindsteelandotherferroushigh-strengthalloys.
•Siliconcarbide(SiC)-harderthanAl
2O
3butnotastough
Usedonaluminum,brass,stainlesssteel,somecastironsandcertain
ceramics
•Cubicboronnitride(CBN)–veryhard,veryexpensive
Suitableforsteels
Usedforhardmaterialssuchashardenedtoolsteelsand
aerospacealloys(e.g.,Ni-basedalloys).
•Diamond–Evenharder,veryexpensive
Occurnaturallyandalsomadesynthetically
Notsuitableforgrindingsteels
Usedonhard,abrasivematerialssuchasceramics,cemented
carbides,andglass
1.2 Types and Application of Abrasive Materials
1.4.1 Characteristics Cont.…

22. Abrasive
materials
Marking Application
Aluminum Oxide
(Al
2O
3)
A Steel, other ferrous materials and
high strength alloys.
Silicon carbide
(SiC)
S Ductile metals (AL, brass, and
stainless steel), and brittle materials
(CI, and certain ceramics).
Cubic born
nitride (CBN)
B Hard materials (hardened tool
steels and aero space alloys).
Diamond D Hard abrasive materials (ceramics,
cemented carbides and glass).
Summary of Abrasive Materials and Their Application

23. •Thegrainsizeofabrasivematerialsisimportantparameter
indeterminingthesurfacefinishandmetalremovingrate.
•Large,coarsegrainsremovematerialfaster,whilesmaller
grainsproduceafinersurfacefinish
•Harderworkmaterialsrequiresmallergrainsizeandsofter
workmaterialrequirelargergrainsize
1.4.1 Characteristics Cont.…
2.Grain Size

24. •Thebondingmaterialholdstheabrasivegrainsand
establishesshapeandstructuralofthegrinding
wheel.
•Thebondingagentholdsabrasivegrainstogether
sothattheabrasivegrainscanshowthesufficient
grindingefficiency.
1.4.1 Characteristics Cont.…
3.Bonding Material

25. Porosityallows excellent coolant flow and
chip clearance. Densewheels are best for
harder materials, while open ones are better
for softer materials
1.4.1 Characteristics Cont.…

26. •Highstrength
•Hightoughness(resistshatteringinshock)
•Withstandhightemperature
•Holdabrasivematerialsrigidlytoaccomplish
cuttingforces
1.1 Properties of Bonding Materials
1.4.1 Characteristics Cont.…

27. Bonding
materials
Marking Application
Vitrified
bond
V Strong,rigid,resisttemp.,relatively
unaffectedbywaterandoilthatisusedas
grindingfluids.
Silicate bondS Limitedtosituationsinwhichheat
generatedmustbeminimized.
Rubber bond R mostfixable,usedincut-offwheels.
Resinoid
bond
B Veryhighstrength,usedforrough
grindingandcut-offoperations.
Shellac bondE Strongbutnotrigid,forgoodfinish.
Metallic
bond
M Commonfordiamondandcubicborn
nitride,usuallybronze.
1.2 Types and Application of Abrasive Bonding Materials

28. •Wheel structure refers to the relative spacing of abrasive
grains in the wheel.
•It contains abrasive grains, bond material & air gaps.
Typical structure of a grinding wheel
1.4.1 Characteristics Cont.…
4.Wheel Structure

29. •Open structure: Wheels whose grain spacing is
wide, and large air spaces exist. Ideal for chip
clearing.
•Dense structure: Wheels having grain spacing's
that are closer and smaller air spaces. Ideal for
surface finish.
4.Wheel Structure
1. Types and Application of Abrasive Bonding Materials

30. •Indicatesthegrindingwheel’sbondstrengthin
retainingtheabrasivegritsduringcutting.
•Softwheels–loosegrainreadily,lowremovalrate
andoftenusedforgrindingofhardmaterials
•Hardwheels–retainabrasivegrain,highstock
removalrates&oftenusedforgrindingsoftmaterial.
1.4.1 Characteristics Cont.…
5.Wheel Grade

31. •Grinding wheel markings specify all the important
wheel characteristics
•All abrasive wheels are marked with the following
characteristics;
i.Type
ii.Size
iii.Specification
iv.Maximum operating speed
v.Restrictions for use
vi.Other, non-safety related information
1.4.2 Grinding wheel Markings

32. 1.Reading Markings on a Grinding wheel
1.4.2 Grinding wheel Markings

33. 1.4.3 Grinding wheel Designation

34. 1.4.3 Grinding wheel Designation

35. 1.4.3 Grinding wheel Designation

36. Dressing the wheel refers to removing the current
layer of abrasive, so that a fresh and sharp surface is
exposed to the work surface.
Dressing with diamonds should always be carried out
using a copious supply of coolant which should be
turned on before the diamond touches the wheel.
1.4.4 Dressing a Grinding wheel

37. 1.4.4 Dressing Cont.…

38. 1.4.4 Dressing Cont.…

39. •Damaged wheels or even wheels suspected of
being damaged should not be used
•Always have machine guards in place before
turning on a grinding wheel
1.4.5 Safety when using Grinding wheels

40. •Run wheel for at least one minute before
actual work begins
•Always use eye protection
•Properly balance and dress wheels before use
1.4.5 Safety when using Grinding wheels

41. Summary of cutting characteristics

42. THE
End