Grinding process

types of Grinding, grain size

2. Grinding is a material removal process in the form of
microchips accomplished by hard abrasive grits that
are contained in a bonded grinding wheel rotating at
very high surface speeds.
The rotating grinding wheel consists of many cutting
teeth ( abrasive particles ) and the work is fed relative
to the rotating grinding wheel to accomplish material
removal.

3. INTRODUCTION TO GRINDING PROCESS
Advantages:
it is the only economical method of cutting hard material
like hardened steel (applicable to both hardened and
unhardened material).
it produces very smooth surface with dimensional
accuracy.
good form and positioning accuracy.
Applications:
surface finishing .
slitting and parting.
descaling, deburring.
stock removal (abrasive milling) finishing of flat as well as
cylindrical surface •
grinding of tools and cutters and resharpening of the same.


5. Surface grinding: flat and slight contour surfaces.
Cylindrical grinding: straight, taper and contour
surfaces.
Internal grinding: straight, taper and contour surfaces.
Tool and cutter grinding: for giving shape and
sharpening.
Centreless grinding: external and internal surfaces.

6. Grinding with horizontal spindle and reciprocating
table.
Grinding with vertical spindle and reciprocating table.
Grinding with horizontal spindle and rotary table.
Grinding with vertical spindle and rotary table.

8. Surface Grinding

14. Plain cylindrical grinding.
Universal cylindrical grinding.
Form cylindrical grinding.

18. Chucking type internal grinding.
Planetary internal grinding.
Internal form grinding.

21. External centreless grinding
Internal centreless grinding

22. CENTERLESS GRINDING

26. Tool manufacturing
Tool re-sharpening

27. Grinding machines:
◦Enough powerful, rigid and stable.
◦Should possess high spindle speeds (rpm).
◦Precession control of depth of cut and feed.
◦Adequate safety measure.
Grinding wheels:
◦Need appropriate composition, structure and hardness.
◦Should be proper shape and size
◦Need regular truing and dressing
◦Should be free from eccentricity.
Environment:
◦Must be employed properly after its proper selection.
◦Dust and temperature in the grinding zone should be controlled.

28. Type, shape and size of the abrasive grains.
The bond material (matrix).
Structure and porosity of the wheel after firing.
Final bond strength.

29. Alumina (Al2O3):
◦Hard and chemically stable.
◦Used for Fe-based metal and alloy
Silicon Carbide (SiC):
◦Hardest but not chemically stable.
◦Used for non-ferrous metals and alloys.
Diamond (D):
◦Extremely hardest and sharp.
◦Used for plastics, ceramics, composites, glass, stones etc
◦High heat and wear resistance.
◦Very expensive.
Cubic Boron Nitride (cBN)
◦Very hard, tough and sharp
◦Highly chemically stable even against Fe
◦Very high wear resistance.
◦Very high cost.
◦Suitable for hard and strong metals like steels.

30. Vitrified
◦Hard, easy manufacture and cheap
◦Most common
◦Affected by damp and alkaline base solution.
Resin bond
◦Used for roughing, fettling and cutting off.
◦Affected by damp and water base solution
Rubber
◦High strength and elasticity
◦Used for parting, roll and tool grinding.
◦Affected by damp and alkaline solution and solution.
Shellac
◦Easy manufacturer under low temperature.
◦Used for fine finish, rolls, ceramics
Oxychloride
◦Less brittle and low temperature
◦Affected by shocks, damp, acid and alkaline solution
Metal bond
◦D and cBN in bronze, Ni, Al alloy and Fe
◦Suitable electro chemical grinding (ECG)

31. Abrasives: (Al2O3 - A, SiC - C, cBN – BN, diamond - D)
The size of the abrasive grains is generally denoted by a mesh number (S)
from which the average diameter of the grains, dg (mm) can be evaluated:
S * dg = 15.2
Course: 8, 10, 12…..24
Med: 30, 36, 54, 60
Fine: 70, 80, …180
Very fine: 220, 240…600
•The number indicating the size of the grit represents the number of
openings in the sieve used to size the grain. The larger the grit size
number, the finer the grit.

32. Bond material:
◦Vitrified: V
◦Silicate: S
◦Resinoid: B
◦Reinforced resinoid: BF
◦Shellac: E
◦Oxychloride: O
◦Rubber: R
◦Reinforced rubber: RF

33. Grade (hardness):
Vk+Vb+Vp =100
Very soft: C to G
Soft: H to K
Medium: L to O
Hard: P to S
Very hard: T to Z

34. Size of the wheel:
Vc = Π Dg Ng (m/s)

35. A typical grinding wheel specified by:
51-A-60-K-5-V-1985-6
51- manufacturer own code
A – the abrasive grit material is aluminium oxide
60 – average abrasive grit size
K – hardness of the wheel
5 – inter grit space [1-12] [min-max]
V – bond material
1985-6 – manufacturer identifier

36. Wheel balancing
Truing
Dressing

37. Shearing
Ploughing
Rubbing
Fracturing
Spherical chip formation

39. CONSTRUCTION OF A GRINDING WHEEL
•In order make the grinding wheel suitable for
different work situations, the features such as
abrasive, grain size, grade, structure and bonding
materials can be varied.
•A grinding wheel consists of an abrasive that does the
cutting, and a bond that holds the abrasive particles
together

40. GRAIN SIZE
•The number indicating the size of the grit represents
the number of openings in the sieve used to size the
grain. The larger the grit size number , the finer the
grit.

41. •Grade indicates the strength of the bond and,
therefore, the `hardness` of the wheel.
•In a hard wheel the bond is strong and it securely
anchor the grit in place, and therefore, reduces the
rate of wear.
•In a soft wheel, the bond is weak and the grit is easily
detached resulting in a high rate of wear.

42. STRUCTURE
•This indicates the amount of bond present between
the individual abrasive grains, and the closeness of the
individual grain to each other. An open structured
wheel will cut more freely. That is, it will remove
more metal. In a given time and produce less heat.

43. G = Volume of material removed / Volume of wheel
wear
G = 2 to 200