New Grain Development...29 3M Abrasive Systems Division 3Q max = mm /s Standard Ceramics: max of 350...

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3M Abrasive Systems Division

© 3M 2011. All Rights Reserved.

New Grain Development

Precision Shaped Grains (PSG)

High Performance Grinding

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Definition of Grinding

German DIN Standard 8580

Grinding = Machining with geometrically undefined

cutting edges

Milling / Turning = Machining with geometrically

defined cutting edges

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3M™ Cubitron™ II (made of Precision Shaped Grain) DIN definition of grinding is no longer valid! New = Grinding can be machining with geometrically defined cutting edges


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3M™ Cubitron™ II Wheel Structure (PSG Grain)


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3M™ Cubitron™ II Wheel Structure


Standard Ceramic Wheel Structure

(3M™ Ceramic Abrasive Grain 321)

3M™ CubitronTM II Wheel Structure with PSG

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Cutting Behavior of Conventional Abrasive Grains

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Chip Formation with 3M™ Precision Shaped Grain


Idealized image

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Flowing Chips

Grinding swarf that looks like the chips generated by turning or

milling operations.

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Chips generated with a 3M™ Cubitron™ II Wheel


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Grinding Parameters for Single Rib Gear Grinding with PSG


• Surface speed vc (m/s)

• Feed-rate vw (mm/min)

• Speed ratio (wheel – workpiece) qs

• Dressing: Overlap ratio ud

• Specific material removal rate (Q-prime) Q‘w

(mm3/mm/sec)

• Specific chip volume V‘w (mm3/mm)

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Surface speed vc


Hardened steel: 30 m/s

Quenched and tempered steel : 35 m/s

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High Feed-rates Vw Reduce Risk of Burning

Standard Machines: vw = 3,500 mm/min, new machines ≥12,000 mm/min

Source: Höfler Maschinenbau

Increase of performance by increasing feed-rate Vw

Burning

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Speed Ratio qs for Different Grinding Processes

- Creep-feed grinding

- Reciprocal grinding Cylindrical grinding

Single rib

gear grinding

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Range of Speed Ratios qs

Gear Grinding

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Feed-rate Vw and Speed Ratio qs

High speed ratio qs at feed-rate vw 3,500 mm/min = risk of burning!

Low speed ratio qs at feed-rate vw 12,000 mm/min = low risk of burning!

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Idealized image

Dressing Behavior: 3M™ Ceramic Abrasive Grain 321 versus 3M™ CubitronTM II

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Dressing Strategy

For roughing:

Overlap ratio ud = 1, synchronous 0.6

For finishing:

Overlap ratio ud = 4 to 6, asynchronous – 0.6 to – 0.8

Dressing interval compared to 3M Ceramic Abrasive Grain 321

Rule of thumb: 2 x fewer dressing cycles, at ½ dressing depth

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Specific Material Removal Rate (Q-Prime) Q‘w Q’w as a benchmark

Material removal in mm3 per mm

wheel width per second

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Q’w Values Single Rib Grinding with 3M™ CubitronTM II

PSG PSG

Hardened: 24 – 30 20 – 24

Tempered: 20 – 24 16 – 20

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V’w (Specific Chip Volume in mm3/mm)


This value refers to the volume of material removed

mm3 per mm wheel width until the wheel has to be

dressed again.

In other words: it is a factor of the process

economics.

The higher this factor, the more economic is the

grinding process.

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Formula for the Specific Chip Volume V’w

Spur Gear Helical Gear

ae = total radial infeed (mm)

v’w = material removal per mm wheel width (mm3/mm)

zb = face width of gear (mm)

z = Number of teeth until redress (number)

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V’w Values Single Rib Grinding with 3M™ CubitronTM II PSG Roughing 3,000 – 5,000 mm3/mm Finishing 300 – 700 mm3/mm PSG Roughing 2,000 – 4,000 mm3/mm Finishing 300 – 500 mm3/mm

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Advantages of High Chip Volume Values V’w


- Lower wheel wear (longer wheel life)

- Higher gearing quality

- Possible to grind all teeth

in one dressing cycle

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Economic and Quality Benefits of 3M™ Precision Shaped Grain


• No grinding burn if used properly

• More uniform surface finish

• Half of standard production time

• Half of dressing amounts

• Half the number of dressing cycles

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Case History: Grinding from Solid


Gear Data

Material: 30CrNiMo6, soft state

Module 14, number of teeth z 123

Face width zb 400 mm

Helix angle b 6.6642

PSG 3M™ Cubitron™ II wheel

Machine power 37 kW

Feed-rate vw: 600 mm/min

Infeed ae: 4.5 mm

Material removal rate Q’w: 45 mm³/mm/s

Chip volume V’w: 5,000 mm³/mm

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Case History: Internal Gear


Gear Data

Material: 30CrNiMo6, soft state

Modul 16, number of teeth z 89


Helix angle b 8.25


Machine power: 50 kW

Feed-rate vw: 4,000, 2,000, 1,000 mm/min

Infeed ae: 0.54, 0.12, 0.05 mm

Material removal rate Q’w: 30 mm³/mm/s (roughing)

Chip volume V’w: 4,000 (roughing), 1,600 mm³/mm

Surface finish Rz: 4 mm

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Case History: Planet Gear


Gear Data

Material: 18CrNiMo7-6 hardened 58 HRc

Modul 16, Number of teeth z 34


Helix angle b 7.5


Machine power: 24 kW, 95% spindle load


Infeed ae: 0.15, 0.06, 0.04 mm


Chip volume V’w: 2,000 (finishing), 400 mm³/mm

Surface finish Ra: < 0.4 mm

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Case History: Planet Gear


Gear Data

Material: 18CrNiMo7-6 hardened, 58 HRc

Module 3.5, Number of teeth z 35

Face width zb 72 mm

Helix angle b 0


Machine power: 24 kW, 40% spindle load


Infeed ae: 0.12, 0.06, 0.04 mm


Chip volume V’w: 1800 (roughing), 400 mm³/mm

Surface finish Ra: < 0.4 mm

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Q max = mm3/s

Standard Ceramics: max of 350 mm3/s

Q max = (ae max * hev*nss*g*fz max) / (cos b / 30)

ae max: max. depth of cut per flank and per stroke (mm)

hev: ground height of profile (mm)

nss: rpm of threaded wheel

g: Number of starts on threaded wheel

fz max: max. axial feed rate in mm/rev.

cos b: cosine of helix angle

Material Removal Rate Qmax

30

45 15

0Swiss made

30

45 15

0

min.

6

9 3

0

h

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Case History: Continous Generating Grinding


Gear Data

Material: 16MnCr5, 58 to 60HRc

Module 9.0, Number of teeth z 67

Pressure angle 20

Helix angle b 10

PSG 3M™ Cubitron™ II

99DA120/60 H15VPMF901W, 2-start

Machine: Liebherr LCS 700

RPM wheel: 3520, 3520, 3520 (3 passes)

Feed-rate vw: 1.2, 1.2, 0.45 mm/rev (3 passes)

Infeed x1: 1st 0.45, 2nd 0.36, 3rd 0.30 mm

MRR Qmax: 883 mm³/mm/s (roughing)

Grinding time: reduced from 0:45:00 to 0:09:47.

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New Grain Development...29 3M Abrasive Systems Division 3Q max = mm /s Standard Ceramics: max of 350...

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