Fundamentals of Grinding
Fundamentals of
Grinding
• Grinding is a process of material removal in the form of chips by the mechanical action of regularly shaped Abrasive Particles bonded together in the form of a wheel
• Grinding is required to achieve the following
– SIZE
– FORM
– FINISH
WHAT IS GRINDING & WHY IS IT REQUIRED?
• Grinding Wheel is a Multipoint cutting tool composed of Selectively Sized Abrasive Grains held together by a Bonding Material.
• A typical Grinding wheel consists of the following
>ABRASIVES - 40 - 45 %
>BONDING MATERIAL - 13 - 18 %
>VOIDS - 40 - 45 %
WHAT IS A GRINDING WHEEL ?
SLIDING , PLOWING, CHIP FORMATION
HOW GRINDING TAKES PLACE
WHEEL MARKING
SYSTEM
Abrasive
Type
Alu. Oxide
A, AA, RA
SA, DA
SiC
Black C
Green GC
Zirconia ZA
Abrasive
Type
Alu. Oxide
A, AA, RA
SA, DA
SiC
Black C
Green GC
Zirconia ZA
Grit Size
8, 10, 12, 14
16, 20, 24, 30
36, 46, 54, 60
80, 100, 120
150, 180, 220
240, 280, 320
400,600,800
Grit Size
8, 10, 12, 14
16, 20, 24, 30
36, 46, 54, 60
80, 100, 120
150, 180, 220
240, 280, 320
400,600,800
Grade
F G H I
J K L M
N O P Q
R S T U
V X Y Z
Grade
F G H I
J K L M
N O P Q
R S T U
V X Y Z
Grit
Combination
1
3
5
7
Grit
Combination
1
3
5
7
STRUCTURE
1 2 3 4 5
6
..............Upto
.....................3
5
STRUCTURE
1 2 3 4 5
6
..............Upto
.....................3
5
Bond System
V - Vitrified
B -
Resinoid
R - Rubber
Bond System
V - Vitrified
B -
Resinoid
R - Rubber
Cumi
Symbol
VG VVR V6
V7
V30 V10 VL
V8
V2018 VF8
VMPA VMSA
BN BR BFW
RT R RB
Cumi
Symbol
VG VVR V6
V7
V30 V10 VL
V8
V2018 VF8
VMPA VMSA
BN BR BFW
RT R RB
A 46 3 K 5 V 10
WHEELS MARKING SYMBOLS IN A CUMI GRINDING WHEEL
• A Mineral Crystal with Hardness much higher than that of work piece
WHAT IS AN ABRASIVE ?
TYPES OF ABRASIVES
• Natural
– Corundum, Emery, Diamond
• Synthetic
>Aluminium Oxide - Conventional Abrasive
>Silicon Carbide - Conventional Abrasive
>Cubic Boron Nitride - Super Abrasive
>Diamond - Super Abrasive
PROPERTIES OF ABRASIVES
• Friability - Ability to Fracture under load
• Thermal Conductivity - Ability to Conduct Heat
• Hardness - Resistance to Penetration
• Toughness - Ability to Withstand Load
Application of Conventional Abrasives
• Aluminium Oxide - For Ferrous Materials
• Silicon Carbide - For Non Ferrous Materials
TYPES OF ALUMINIUM OXIDE
Marking
• Brown Alumimium Oxide A
• While Aluminium Oxide AA
• Semifriable SA
• Combination of A & AA DA
• Pink Aluminium Oxide RA
• Sharp Crystalline Abrasive 80A
• Sintered Aluminium Oxide MSB
• Zirconia AZA
TYPES OF SILICON CARBIDE
Marking
• Black Silicon Carbide C
• Green Silicon Carbide GC
• Mixture of C & GC CGC
BROWN ALUMINIUM OXIDE(A)
• Brown in colour
• Discovered in 1899
• 95% pure
• Most commonly used abrasive
• Titanium di oxide imparts toughness
WHITE ALUMINIUM OXIDE(AA)
• White in colour
• 99% pure
• More friable than “A”
• Cooler cutting
• Better holding with the bond because of higher grain porosity
SEMIFRIABLE (SA)
• Brown in colour
• % Of titanium oxide is less than 2%
• Friability index falls between A & AA
PINK ALU. OXIDE (RA)
• Pink in Colour
• Alloyed Abrasive of Alu. Oxide and Chromic Oxide
• Retains the Sharpness for Longer time
ZIRCONIA ALU. OXIDE
• Produced by fusing zircon sand and alumina at about 1900 deg. C
• Alu. Oxide - 75% & zirconia - 23%
• Hard, very tough and sharp abrasives
SINTERED ALU. OXIDE(MSB)
• Micro crystalline abrasive
• Produced by sintering process
• Hard & tough
• Controlled fracture
BLACK SILICON CARBIDE(C)
• Black in colour
• Harder than alumina
• Chemically reactive with iron and steel alloys leading to poor attrition resistance
GREEN SILICON CARBIDE (GC)
• Green in colour
• Purer than black sic
• Cooler cutting
• More friable than black
GRAIN (GRIT) SIZE
• The size of screen opening thru which the grain pass
• Ex. 60 grit means there will be 60 openings per linear square inch of the screen
GRAIN COMBINATION
• Combination of different grit sizes in predetermined percentages
• Ex. A463 l5 V10 - combination of 46,54 & 60 grits. Primary grit 46 will be at higher percentage.
GRADE & STRUCTURE
• Grade
– Grade is the measure of the bonding strength of the wheel, usually referred to as hardness
• Structure
– Spacing of abrasive grains, measured in terms of volume of abrasives in grinding wheels
BOND
BINDING MATERIAL WHICH HOLDS THE ABRASIVE GRAINS TOGETHER IN A WHEEL.
BOND TYPES
• Vitrified bond (V)
• Resinoid bond (B)
• Rubber bond (R)
• Shellac bond (S)
• Oxychloride bond (Oxy)
• Magnesite bond
VITRIFIED BOND
Vitrification
• Bond mix melts /partly wets the abrasive
• Abrasive grain pulled together by surface tension
• Titanium rich phase from ‘A’ disbursed in to the surrounding matrix - it turns blue
VITRIFIED BOND
• More strength
• Water resistance
• Chemical resistance
• No shelf life
• Bond fractures induced by mechanical forces during grinding
• Very brittle
• Decreased bending strength
• Better form holding stability
VITRIFIED BONDS IN CUMIPrecision
V10/V10C/V45
V15/V1092/V2016
V8/VF8/V206/VMSA
V2018/VMTA/VMPA/
V60/V80/VL/VU869/
VMC/V204
VG/VMKRS/VB
VMKRP/VMKRC/V91
VMKRT
Non Precision
V6/V30/V7/V1734
VR/VVR
RESINOID BONDS
• Grains mixed with phenolic thermo-setting resins and plasticizers
• Baking at 150 to 200 deg. C
• High strength
• Ability to withstand shock loads
• Shelf life 1 - 2 years
• Low chemical & thermal resistance
RESINOID BONDS IN CUMI
PRECISION
BRT/TD924/TD1020/TD1071/B14/B14X/B8/BHK/BYZ/ BHP/RBG
NON PRECISION
BR/BM4/BM6/B754/BC4/BFW/BSN821/ TD995/TD722/BN/TD1035B/RS500/TDR014/ TDR015/BYZ
PROPERTIES OF RUBBER BONDS
• Better resiliency
• Absorbs shocks
• Produces good finish
RUBBER BONDS IN CUMI
RT1
R
RB
R188M
RCS
A) Grain Fracture
B) Bond Fracture
C) Attritious Wear
WHEEL WEAR
TYPES OF WHEEL WEAR
• GRAIN FRACTURE
TYPES OF WHEEL WEAR
• BOND FRACTURE
ATTRITIOUS WEAR
• Dulling of Abrasive Grains and Growth of Wear Flats by Rubbing against the Work Piece
TYPES OF WHEEL WEAR
WHEEL SELECTION
WHEEL SELECTION
FACTORS AFFECTING WHEEL SELECTION
�MATERIAL TO BE GROUND
�STOCK TO BE REMOVED
�WHEEL SPEED
�AREA OF GRINDING
�TYPE OF OPERATION - WET (OR) DRY
�GRINDING MACHINE
�SURFACE FINISH
GRIT SIZE SELECTION
• SURFACE FINISH
• STOCK REMOVAL
• FORM ACCRACY
GRIT SIZE SELECTION
GRIT SIZE Vs SURFACE FINISH
CLA Ra 60 80 120 180 240 320 400
24.0 0.6
20.0 0.5
16.0 0.4
12.0 0.35
10.0 0.25
8.0 0.2
6.3 0.16
4.0 0.1
3.2 0.08
2.0 0.05
1.2 0.03 osc osc
0.8 0.02 osc
GRIT SIZE SELECTION
GRIT SIZE Vs FORM
GRIT SIZE 60 80 120 180 240 320 400
CORNER RADIUS 0.5 0.4 0.2 0.13 0.1 0.08 0.05
�MATERIAL HARDNESS
�ARC / AREA OF CONTACT
�TYPE OF OPERATION
�FORM HOLDING
�WHEEL SPEED
�WHEEL WIDTH
�TYPE OF DRESSER
�TYPE OF COOLANT
GRADE SELECTION
GRADE SELECTION
MATERIAL HARDNESS
Wheel Grade
M
L
K
J
I
Soft Medium Hard50 Rc 50 - 57 Rc 58 - 63 Rc
STRUCTURE SELECTION
• STOCK REMOVAL
• THERMAL CONDUCTIVITY OF WORK MATERIAL
• MATERIAL REMOVAL RATE
STRUCTURE SELECTION
• STOCK REMOVAL
STRUCTURE SELECTION
• MATERIAL REMOVAL RATE
BOND SELECTION
• SEVERITY OF OPERATION
• WHEEL SPEED
• FORM HOLDING
• SURFACE FINISH
• MATERIAL REMOVAL RATE