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
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New Grain Development
Precision Shaped Grains (PSG)
High Performance Grinding
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3M Abrasive Systems Division
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 Abrasive Systems Division
3M™ Cubitron™ II (made of Precision Shaped Grain) DIN definition of grinding is no longer valid!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 Abrasive Systems Division
3M™ Cubitron™ II Wheel Structure (PSG Grain)
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3M Abrasive Systems Division
3M™ Cubitron™ II Wheel Structure
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Standard Ceramic Wheel Structure
(3M™ Ceramic Abrasive Grain 321)
3M™ CubitronTM II Wheel Structure with PSG
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3M Abrasive Systems Division
Cutting Behavior of Conventional Abrasive Grains
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3M Abrasive Systems Division
Chip Formation with 3M™ Precision Shaped Grain
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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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3M Abrasive Systems Division
Chips generated with a 3M™ Cubitron™ II Wheel
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Grinding Parameters for Single Rib Gear Grinding with PSG
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• 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
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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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3M Abrasive Systems Division
Speed Ratio qs for Different Grinding Processes
- Creep-feed grinding
- Reciprocal grinding Cylindrical grinding
Single rib
gear grinding
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3M Abrasive Systems Division
Range of Speed Ratios qs
Gear Grinding
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3M Abrasive Systems Division
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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3M Abrasive Systems Division
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Idealized image
Dressing Behavior: 3M™ Ceramic Abrasive Grain 321 versus 3M™ CubitronTM II
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3M Abrasive Systems Division
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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3M Abrasive Systems Division
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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3M Abrasive Systems Division
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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3M Abrasive Systems Division
V’w (Specific Chip Volume in mm3/mm)
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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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3M Abrasive Systems Division
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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3M Abrasive Systems Division
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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3M Abrasive Systems Division
Advantages of High Chip Volume Values V’w
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- Lower wheel wear (longer wheel life)
- Higher gearing quality
- Possible to grind all teeth
in one dressing cycle
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3M Abrasive Systems Division
Economic and Quality Benefits of 3M™ Precision Shaped Grain
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• 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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3M Abrasive Systems Division
Case History: Grinding from Solid
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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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3M Abrasive Systems Division
Case History: Internal Gear
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Gear Data
Material: 30CrNiMo6, soft state
Modul 16, number of teeth z 89
Face width zb 293 mm
Helix angle b 8.25
PSG 3M™ Cubitron™ II wheel
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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3M Abrasive Systems Division
Case History: Planet Gear
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Gear Data
Material: 18CrNiMo7-6 hardened 58 HRc
Modul 16, Number of teeth z 34
Face width zb 380 mm
Helix angle b 7.5
PSG 3M™ Cubitron™ II wheel
Machine power: 24 kW, 95% spindle load
Feed-rate vw: 12,000, 2,500, 2,000 mm/min
Infeed ae: 0.15, 0.06, 0.04 mm
Material removal rate Q’w: 30 mm³/mm/s (roughing)
Chip volume V’w: 2,000 (finishing), 400 mm³/mm
Surface finish Ra: < 0.4 mm
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3M Abrasive Systems Division
Case History: Planet Gear
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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
PSG 3M™ Cubitron™ II wheel
Machine power: 24 kW, 40% spindle load
Feed-rate vw: 12,000, 3,000, 2,500 mm/min
Infeed ae: 0.12, 0.06, 0.04 mm
Material removal rate Q’w: 28 mm³/mm/s (roughing)
Chip volume V’w: 1800 (roughing), 400 mm³/mm
Surface finish Ra: < 0.4 mm
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3M Abrasive Systems Division
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
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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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3M Abrasive Systems Division
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