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