The Effect of Grinding on Grinding Wheel Condition

Prasann B. Handigund, Melissa HasenbankMichele H. Miller

Michigan Technological UniversityHoughton, MI

Introduction

Grinding Wheel Grinding Process

Abrasive wear

Abrasive pull-out

Wheel diameter shrinksChip accumulation

Surface finish

Dimensional accuracyGrinding force

Temperature

Wheel Wear and Self-Dressing

Wear Modes:-Attritious wear-Grit fracture-Bond fracture and grit pullout

Self-Dressing:-Attritious wear leads to force increase-With sufficient force, grit fractures or pulls out-Grit cutting forces can be controlled by selection of grit type and binder

ZX

top view

cup grinding wheel

workpiece

piezoelectric actuator

air bearing spindle

3 axis force transducer

Self-Dressing Test Setup

Effect of Infeed(Experimental Data)

0

50

100

150

200

250

300

0 50 100 150 200 250

Volume of Material Removed (mm3)

Cut

ting

Forc

e (N

)

infeed=10 nm

infeed=20 nm

infeed=40 nm

wheel 1

workpiece: silicon carbide

Effect of Workpiece Material(Experimental Data)

0

50

100

150

200

250

300

0 50 100 150 200 250

Material Removed (mm3)

Cu

ttin

g F

orc

e (

N)

Silicon Carbide

Pyrex glass

wheel 1

infeed = 40 nm

Effect of Wheel Composition(Experimental Data)

0

50

100

150

200

250

300

0 50 100 150 200 250

Volume of Material Removed (mm3)

Cu

ttin

g F

orc

e (N

)

Wheel 1

Wheel 2

workpiece: silicon carbide

infeed = 40 nm

Matching Wheel to Workpiece

Time

Cut

ting

For

ce

wheel 1

wheel 2

wheel 3

Specific EnergyW

heel

Wea

r R

ate

1

2

3

Goal: Predict the these plots based on wheel properties and operating conditions

Purpose of Developing a Model

• Based on desired wear and energy, use model to select suitable wheel properties and operating conditions

• Exercise model to find ways to improve on the wear/energy tradeoff

Elements of Model

• Cutting force model– Dependence on work material, chip thickness, grit

shape, chip clearance, etc.– Focus on components that change as wheel

“wears”

• Wear model– Abrasive wear due to attrition and fracture– Binder wear– Abrasive pullout/binder fracture

First Steps

• Develop and validate technique for grit wear measurement

• Determine dependence of grit wear rate on normal force, cutting speed, abrasive material, …

• Determine dependence of grit cutting force on wear flat area, chip thickness, work material, …

• Determine grit force that causes grit fracture or pullout

Grit Wear Measurement Technique-Obtaining Imprint

Grit Wear Measurement Technique-Measuring Volume

Comparison to ProfilometryProfilometry-Nominal Feed:0.3 mm

0

10

20

30

40

50

60

0 500 1000 1500 2000

Scan Direction (µm)

Z (

µm)

SEM-Specimen-Nominal Feed:0.3mm

0

10

20

30

40

50

60

0 200 400 600 800 1000Scan Direction (µm )

Z (µ

m)

SEM-Mold-Nominal Feed:0.3 mm

0

10

20

30

40

50

60

0 200 400 600 800 1000 1200

Scan Direction ( µm)

Z (

µm)

Rmax (µm) f (mm)

Profilometry 32 0.448

SEM Specimen 37 0.462

SEM Mold 1 46 0.530

SEM Mold 2 39 0.500

Rmax (µm) f (mm)

Profilometry 105 0.639

SEM Specimen 118.8 0.638

SEM Mold 1 123 0.660

SEM Mold 2 122 0.650

Test Rod 1

Test Rod 2

Profilometry on Rod

Stereo SEM on Rod

Stereo SEM on Mold

Accuracy and Repeatability

Test 1: Mold anode of a battery (in which volume is known) and measure volume of mold cavity

Test 2: Make two molds of wheel and measure volume of same grit on each

Test 3: Measure volume of one molded grit repeatedly (5 times)

Object vol = 13.16 mm3

Mold vol = 13.65 mm3

% Variation = 3.7

Mold 1 = 129,400 µm3

Mold 2 = 138,800 µm3

% Variation = 7.3

min = 665.3 µm3

max = 682.9 µm3

% Variation = 2.6

Surface Grinding Experiment

Mobilmet 160 water-basedCoolant

2.5 umWheel depth of cut

75 mm/sTable speed

15.42 m/sWheel speed

Electroplated diamond (1A1), 100 mm dia. x 12.5 mm with 25 mm x 12.5 mm abrasive patch180 grit size (2)100 grit size (1)

Grinding wheels

Ceradyne Ceraloy 146-S5Workpiece material

Every 40 passesWear flat and grit pullout measurement frequency

Every 20 passesForce measurement frequency

Every 20 passesMold preparation frequency

3M Express light body fast setMold material

Estimating Number of Cutting Grits, Grit Pullouts, and Total Number of Grits

Total Number of Grits

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

0 100 200 300 400 500 600

Pass #

Nu

mb

er o

f Gri

ts

Wheel 1

Wheel 2

Wheel 3

Total number of grits = number of wear flats+number of non-cutting grits+number of pullouts

Total area = 25 mm x 12.5 mm

% Cutting Grits

0

2

4

6

8

10

12

14

16

0 100 200 300 400 500 600

Pass #

% C

utt

ing

Gri

ts

Wheel 1

Wheel 2Wheel 3

% cutting grits = (number of wear flats)/(number of grits on new wheel)

% of Grits Pulled Out

0

10

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600

Pass #

% G

rits

Los

t

Wheel 1

Wheel 2

Wheel 3

% grits lost = (number of pullouts)/(number of grits on new wheel)

Normal Force/Cutting Grit

0

0.5

1

1.5

2

2.5

3

0 100 200 300 400 500 600Pass #

Forc

e (N

)

Wheel 1

Wheel 2

Wheel 3

Steps to get this plot: a) measure normal force at regular intervals; b) remove wheel at regular intervals and count wear flats; c) divide the two

Tangential Force/Cutting Grit

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400 500 600Pass #

Forc

e (N

)

Wheel 1

Wheel 2

Wheel 3

Steps to get this plot: a) measure tangential force at regular intervals; b) remove wheel at regular intervals and count wear flats; c) divide the two

Exposed Grit Volumes

Wheel 2

0

100,000

200,000

300,000

400,000

500,000

600,000

700,000

800,000

0 100 200 300 400 500 600

Pass #

Vo

lum

e (

µm

3 )

Wheel 3

0

100,000

200,000

300,000

400,000

500,000

600,000

700,000

800,000

0 100 200 300 400 500 600

Pass #

Vol

ume

( µm

3 )

Wheel 1

0

100,000

200,000

300,000

400,000

500,000

600,000

700,000

800,000

0 100 200 300 400 500 600Pass #

Vo

lum

e (

m3 )

Observations

• For small grit wheels, the % cutting grits decreases with time due to large number of grit pullouts.

• For large grit wheel, the % cutting grits increases with time due to flattening of outermost grits.

• Forces for large grit wheel are larger than for small grit wheel—higher grit wear rates expected.

• Grit volume wear rates are higher for large grit wheels.

• Larger grits sustain more wear before falling out.

Review of Progress

Grit Wear Measurement: Mold/Stereo SEM technique is accurate and repeatable.

Normal Force/Grit Wear Rate Relationship: Can be found with force measurement, wear flat count and SEM volume measurement.

Wear Flat Area/Cutting Force Relationship: Need wear flat area measurement.

Pullout Force: Rough estimate is possible based on average grit forces, but need force distribution.

Wheel Loading Investigation

• Many factors: workpiece material, wheel, feeds/speeds, coolant usage, …

• Look at relationship between chip size and chip clearance

• Test potential solutions: vibration assistance, high pressure coolant

Geometrical View

Feed Speed

Chi

p th

ickn

ess(

or c

hip

leng

th?)

Depth of cut = …Wheel rpm = …Wheel dia. = …Grit size = …Grit concentration = …

Average space between grits L

oadi

ng r

ate

Does (chip size)/(chip clearance) predict rate of chip accumulation?

Test Setup

58% black

Image Analysis

Effect of Wheel Hardness

0

10

20

30

40

50

60

70

80

0 20 40 60 80 100 120 140

# of Passes

% B

lack

Wheel 4 (80/H)Wheel 2 (80/J)Wheel 5 (80/K)

Effect of Grit Size

0

10

20

30

40

50

60

70

80

0 20 40 60 80 100 120 140

# of Passes

% B

lack

Wheel 1 (60/J)Wheel 2 (80/J)Wheel 3 (100/J)

Alumina Wheels Grinding Steel

Surface grindingTable speed = 50 mm/secDepth of cut = 25 µm

Each data point represents the average of 3 pictures

Metal MEMS Mirror Arrays

El ectrostatical lyActuated Dia phragm

Attachment Post

Mirror Segment

CMOS Elec tronics

16 µm

0.93 µm

1.72 µm

9 µm

Planarization Process

Polishing pad

CMOS Die

Dummy pieces for balancing

Polishing pad Polished Silicon Nitride Over CMOS

-0.20.00.20.40.60.81.0

0 200 400 600 800

Scan Direction (µ m)

He

igh

t (

m)

CMOS Surface Before Planarization

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

0 200 400 600 800

Scan Direction (µm)

Hei

gh

t (

m)