Post on 22-Feb-2015
GRINDING BASICSGRINDING BASICS
Presented By:
Dale Savington
Tooling & Accessories Group
PRESENTATION OUTLINE
• Cylindrical Grinding Processes
• Machine Requirements (Utilizing CBN)
• Abrasives
• Properties of Abrasives
PRESENTATION OUTLINE
• Superabrasives
• Bonds
• Coolant
• Truing & Dressing
• Mechanics of Grinding
CYLINDRICAL CYLINDRICAL PROCESSESPROCESSES
(GRINDING BETWEEN CENTERS)(GRINDING BETWEEN CENTERS)
Conventional Plunge / Face Grinding
• Down-Feed (face bump grind)
• Q’ (Prime) 2.14 (0.2) +
• Wheel Velocity
• S.F.P.M. 8,500 +
• m/sec. 43 +
• High volume of coolant to get into grinding zone
• Work Velocity
•75 to 125:1 of wheel velocity
Conventional Traverse Grinding
• Cross –Feed (Traverse) only
• Stock Removal (in-feed depth)
• 0.0” to 0.0178 mm (0.0007”)
• 10% of abrasive Ø / pass
• Finish Grinding
• Wheel Velocity• S.F.P.M. 8,500 +• m/sec. 43 +
• Traverse rate
•10 – 25% of wheel width per rotation of part
• Work Velocity• 75 to 125:1 Wheel Velocity
Peel Grinding
• Multiple grinding functions•Multiple diameters•Multiple shoulder / Faces
• Q’ (Prime) 53 (5) +
(Up to 100 mm3/mm/sec.)
•Traverse feed expressed as mm or inches per revolution of part.
• Work Velocity
• 10 to 30:1 wheel velocity
• Easier coolant delivery into grinding zone (narrow contact area)
• Wheel Velocity
• S.F.P.M. 20,000 +
• m/sec. 100 +
What is Q’ (Prime)?
• Cylindrical Grinding Plunge• Q’ = work piece diameter (dw) x 3.14 (π) x in-feed rate (vf)
Example:
Work piece diameter – 25.4mm (1”)
In-feed rate = 0.67mm/sec.(0.159”/minute)
Q’ = 5.37mm3/mmsec. (0.5 in3/inmin.)
What is Q’ (Prime)?
• Cylindrical Grinding Traverse• Q’ = work piece diameter (dw) x 3.14 (π) x depth/pass (a) x
work speed (nw)
Example:
Work piece diameter = 25.4mm (1”)
Depth per pass = 0.0127mm (0.0005”)
Work speed = 5.4 (rpm/60) (325rpm)
Q’ = 5.47 mm3/mmsec. (0.51 in3/inmin.)
MACHINE MACHINE REQUIREMENTSREQUIREMENTS
Machine Rigidity
Spindle’s Slides
CentersHead Stock
Tail Stock
Parts will Mirror Machines Rigidity
Base
Kilowatts!
Wheel Spindle POWER!
Wheel spindle power per 25.4mm (1”) of wheel to work contact
Conventional Abrasives = 3.75 Kw (5 H.P.)
CBN Abrasives = 7.5 Kw (10 H.P.)
(HEDG) = 18.75 Kw (25 H.P.)
Peel – depends on contact area, material and stock removal
Spindle Integrity
Run-Out Out of Balance
Wheel Balance(Dynamic vs Static)
Static Balance Dynamic Balance – real time
Portable Dynamic Balance
Wheel Balance(Dynamic vs Static)
• Static Balance allows balance in stationary position off the spindle.
• Dynamic Balance is continuous balance on the spindle at working rotating speeds.
Acoustic Sensors
Dressing:
• Sound of dresser touching wheel through coolant.
• Complete contact = dressed wheel
Other uses:
• Picture of grinding process
• Gap Sensor
Machine Requirements(Minimum for Utilizing CBN)
Rigidity
Spindle power
Wheel Velocity
Rotary Dresser
Dynamic Balancing
Coolant Flow
Smooth Transitional Plumbing
Coolant Tank Capacity
Acoustic Sensors
Coolant with lubricity
ABRASIVESABRASIVES
What affects Abrasive Decision?
Ferrous Materials
Production Numbers
Fatigue Concerns(Potential thermal damage)
Non-Ferrous Materials
Dimensional TolerancesProcess Controls
Types of Abrasives
Aluminum Oxide
Silicon Carbide
Cubic Boron Nitride (CBN)
Diamond
Abrasive Selection
Aluminum Oxide
Cubic Boron Nitride (CBN) Diamond
Silicon Carbide
Ferrous Materials Non-Ferrous Materials
PROPERTIES OF PROPERTIES OF ABRASIVESABRASIVES
Aluminum Oxide(Al2O3)
For GrindingFerrous Materials
Hardness on Knoop Scale (kg/mm2) = 1400 - 2100
Thermal Conductivity (W/mOK) = 29
Silicon Carbide(Si,C)
For GrindingNon-Ferrous Materials
Hardness on Knoop Scale (kg/mm2) = 2700
Thermal Conductivity (W/mOK) = 400
Cubic Boron Nitride (CBN)(B,N)
For GrindingFerrous Materials
Thermal Conductivity (W/mOK) = 1300
Hardness on Knoop Scale (kg/mm2) = 4500
Diamond(C)
For GrindingNon-Ferrous Materials
Hardness on Knoop Scale (kg/mm2) = 8000
Thermal Conductivity (W/mOK) = 2000
Review
Knoop Thermal Hardness Conductivity
Aluminum Oxide 1400-2100 29
Silicon Carbide 2700 400
Cubic Boron Nitride (CBN) 4500 1300
Diamond 8000 2000
The PuzzleWhy Not Diamond?
REACTIONDiamond + Ferrous Material + Heat =
Note: Silicon Carbide has similar reaction
SUPERABRASIVESSUPERABRASIVES
What are Superabrasives?What are Superabrasives?
Diamond
Cubic Boron Nitride (CBN) Borazon
What makes Superabrasives Super?
Hardness (Resistance to wear)
Thermal Conductivity (The ability to absorb heat)
Flexibility (one wheel for many applications)
Wheel Life (100 + times Conventional Abrasives)
Some Advantages(For Superabrasives)
Decreased Cycle TimeReduced Dressing
Reduced Gaging
Reduced Time for Wheel Changes
Reduced Coolant Changes
Reduced Filter Changes
Less Swarf ContaminationReduced Coolant Disposal Costs
More Consistent Parts (Less Scrap)
Conventional Abrasives Construction
Conventional Layer = full area of wheel
WheelVitrified Bond
Resin Bond
Rubber Bond
Shellac Bond
Superabrasive Construction
Superabrasive Layer = 3mm (1/8”) to 6mm (1/4”)
WheelCore Resin Bond
Metal Bond
Vitrified Bond
BONDSBONDS
Grinding MatrixVitrified Wheel
Grain
Bond
Pore
Chip
Grinding Wheel Bond Systems
Grinding Wheel Bond Systems
Resin , , Metal & BondsSintered Vitrified
Abrasive + Bond = Wheel
Grinding WheelBond Systems
Open Structure (Low fired) Vitrified Bonds
Abrasive + Bond + Pores = Wheel
Grinding Wheel Bond Systems
Plated Wheels (Single Layer)
Wheel bodyCathode (-)
AbrasiveAnode (+)
Electrolyte (Nickle Solution)
Plated Wheel Cut-A-Way
Mechanics of GrindingMechanics of Grinding
Abrasive wear
Fracture wear Chip
Bond
Abrasive
Cut a way of wheel
Abrasive wear
Attritious wear(Rubbing)
Work Piece
Conventional
Abrasive (one grain)
Abrasive wear
Fracture wear
Work Piece
Conventional Abrasive (one grain)
Abrasive wear
Fracture wear
Work Piece
Conventional Abrasive (one grain)
Abrasive wear
Attritious wear
Work Piece
CBN Abrasive (one grain)
Standard MarkingsConventional Abrasives
Abrasive Type
Abrasive Size
Abrasive (combination)
Hardness (Grade)
Structure (Pore)
Bond
A
C
SG30
A
60
120
80
24
1
2
J
K
L
R
6
12
10
V
V
V
B
Standard MarkingsSuperabrasives
Abrasive Type Abrasive Size Hardness (Grade)
Concentration Bond
BN
D
BN
140
240
120
J
k
L
100
75
150
B
M
V
Superabrasives are always combinations 120/140, 80/100 etc.
Calculating concentration take number and divide by 4
Example 100 ÷ 4 = 25% by volume of abrasive in wheel
COOLANTCOOLANT
Coolant Flow
Coolant Velocity
= Wheel V
elocity
Nozzle Designs
Surface grinding
Centerless
Cam grinding
Coolant Condition
Tank Size &Coolant Temp.
Filtration & Particle Distribution
Chemistry(Lubricity)
TRUING & DRESSINGTRUING & DRESSING
The Difference Between Truing & Dressing
TruingResin & Metal Bonds
DressingResin & Metal Bonds
Truing & Dressing Plated Wheels
Truing & Dressing Vitrified Bonded (CBN Wheels)
Examples of Rotary Dressers
Truing & Dressing (Depth or In-Feed)
• Conventional Abrasives – Aluminum Oxide• ≤ 0.0178mm (0.0007”) per pass
• Ceramic Abrasives – Seeded Gel (SG)• ≤ 0.005mm (0.0002”) per pass
• CBN Abrasives• ≤ 0.0025mm (0.0001”) per pass
Truing & Dressing (Traverse Rate)
• Starting Parameters • 0.1mm (0.004”) per revolution of wheel
Assuming 0.5mm (0.020”) radius dresser
Faster traverse rate creates rougher finish
Slower traverse rate creates finer finish
CBN vs Conventional (Surface Finish – plunge grinding only)
• Conventional Grinding Surface Finish = Grit Size
• CBN Grinding: Surface Finish = Diamond Overlap
the end