Grinding gears from solid is a cost effective alternative to hobbing and shaping. When all the right aspects from coolant to power are considered in application, removal rates of 7in³/min/in. Learn who should consider grinding gears from solid and under what situations this methodology is most appropriate from Norton Application Engineers David Graham and Phil Plainte.

1. Grinding Gears Faster than
Machining
David Graham & Phil Plainte
Applications Engineers
Norton/Saint-Gobain Abrasives
September 2014

2. Outline
• Machine to Grind (MTG)
• MTG — Gears from Solid Test Results
• MTG — Gear Case Studies

3. Machine To Grind — Gear
• Why Grind Gears from Solid?
• Quick response to Customer needs
• Elimination of tooling lead time
• Reduced tooling cost
• Reduced tooling inventory
• Competitive cycle time
• Design freedom
 Root Radius modification to improve strength
• Capital Equipment Cost Avoidance

4. Machine to Grind — Gear
• Who Should grind Gears from Solid?
• Job Shops
• Producers of Large Gears
• Maintenance and Repair Facilities
• Gear Box Rebuilders
• Producers of Specialty Gears

5. Machine to Grind — Gear
• When Should they Grind Gears From Solid?
• Short Lead Time
• Special Form
• Small to Medium Lot Size

6. Machine to Grind — Gear
• When Should they Grind Gears From Solid?

7. Machine Grind — Gear
 Test Material: 8620
• Prior to Heat Treatment
 3 Diametral Pitch
• Form Depth 0.750”
 Involute Approximation
 Thickness 3”
• Two 1.5” parts Stacked

8. Machine to Grind — Gear
 Test Process
• Creep Feed Form Grind
 Up and Down Grind
• Non Continuous Dress
• Castrol Variocut B27 (straight oil)
• Coolant Velocity Matches Wheel Velocity
• High Pressure Cleaning Nozzles
• Coolant Flow Guide

9. What is A Grinding Wheel Made Of?
Grain Bond Porosity Wheel

10.  NQ Grain
 Shape Sharp Edges
aspect ratio ~ 1:1
• Average Loose Pack
Density
• Low Force Necessary
to Initiate Cutting
 Good Hardness and wear
resistance
 Micro Fractures to Keep
Grain Sharp
Grain
 TGII Extruded Grain
 Shape Long Thin Grain
8:1 Aspect ratio
• Very low Loose Pack
Density
• High Force Necessary
to Initiate Cutting
 Good Hardness and wear
resistance
 Micro Fractures to Keep
Grain Sharp

11.  Low Loose Pack Density
With TGII Grain
 Low Loose Pack Density
With Agglomerated NQ
Grain
 Vitrium Bond
• Low Bond % Volume
 Vitrium Bond
 High Strength
 Low Volume %
Bond Porosity

12. 5NQ Vitrium Bond Wheel
5NQ Agglomerated
Grain With High Porosity
High Strength Vitrium
Bond Leaves More
Space for Chips &
Coolant

13. TGII Vitrium Bond Wheel
When TGII High Aspect
Ratio Grains Are Used they
Create Very High Porosity
without Pore Inducers
Less of the High Strength Vitrium
Bond is Needed Leaving Even More
Space for Chips & Coolant

14. Machine to Grind — Gear
 Machine Tool
 40 HP Spindle
 4 + 1 Axis
 45 gpm Coolant
 Straight Oil

15. Machine to Grind — Gear
 Results — Productivity @ 7.0 Q’
• Time per Gap ~ 52 Seconds
• Grind Time ~ 30 minutes
~ 35 Minutes @ 6.0 Q’
(15 & 17.5 Min per 1.5” thick Gear)
 Gear
• 12” OD
• 34 teeth
• 0.75” Whole depth
7Q’ video

16. Machine to Grind — Gear
 Results — Wheel Life
• 575 Gears per Wheel — TG2 @ Q’ = 6.0
• 445 Gears per Wheel — NQ @ Q’ = 6.0
• 394 Gears per Wheel — TG2 @ Q’ = 7.0
 Gear
• 12” OD
• 34 teeth
• 0.75” Whole depth
• 1.5” Thick

17.  Specific Chip Volume
• V’w — A minimum of 14,500mm² was set for all
testing
• Sometimes used in place of G-ratio to
characterize wheel durability
 Higher value = a more economical process
• Equals the Total depth ground multiplied by the
tooth length ground between wheel dresses
 DOC X Face Width X Number of teeth
Machine to Grind — Gear

18. Machine to Grind — Gear
 Results — Specific Power

19. Machine to Grind — Gear
 Results — Energy

20. Case Study #1 — Hobbing Vs Grinding
 Material: 8620
 Hardness: 28-32 Rc
 Tooth Depth: 0.470”
 Tooth Length: 7”
 Number of Teeth: 175

21. Case Study #1 — Hobbing Vs Grinding
 Hobbing Parameters
•Coated HSS 2 start Hob
•Rough Axial advance Per Part Rev:
0.032”
•Number of Rough Passes: 5
•Finish Axial advance Per Part Rev:
0.020”
•Time per Rough Pass: 230 min
•Time for Finish Pass: 323 min
•Total cutting time: 24.5 hours
 Grinding Parameters
• Wheel — 5NQX Vitrium Bond
• Wheel Speed 6,000 sfpm
• Roughing Passes at 2.5 in³/min/in
• Finish Passes at 1.0 in³/min/in
• Time per Tooth Rough Passes: 1.6
min
• Time per Tooth Finish Passes: 1.1
min
• Total Dress Amount per Gear: 0.58
in
• Total Dress Time per Gear: 175
min
• Total Grind & Dress Time per
Gear: 10.9 hours

22. Case Study #1 — Hobbing Vs Grinding

23. Case Study #2 — Hobbing Vs Grinding
 Material: 4140
 Hardness: 28-32 Rc
 Tooth Depth: 0.438”
 Tooth Length: 7.25”
 Number of Teeth: 80

24. Case Study #2 — Hobbing Vs Grinding
 Hobbing Parameters
• Carbide 2 start Hob
• Rough Axial advance Per Part
Rev: 0.030
• Number of Rough Passes: 5
• Finish Axial advance Per Part
Rev: 0.020
• Time per Rough Pass: 74 min
• Time for Finish Pass: 110min
• Total cutting time: 8.0 hours
 Grinding Parameters
• Wheel — TG
• Wheel Speed 6,000 sfpm
• Roughing Passes at 1.1 & 2.2
in³/min/in
• Finish Passes at 0.25 in³/min/in
• Time per Tooth Rough Passes:
1.8 min
• Time per Tooth Finish Passes:
0.3 min
• Total Dress Time per Gear:
41.6 min
• Total Grind & Dress Time per
Gear: 4.0 hours

25. Case Study #2 — Hobbing Vs Grinding

26. Conclusions — Machine to Grind — Gear
• Why Grind Gears from Solid
• Reduce lead time
• Reduce tooling Cost
• Design Flexibility
• Who Should grind Gears from Solid
• Job Shops
• Maintenance & Repair Operations
• Custom Gear producers

27. Conclusions — Machine to Grind — Gear
• Grinding is a Cost Effective alternative to Hobbing and
Shaping
• Removal Rates of 7 in³/min/in Can be Achieved
• It is important to pay Attention to all aspects of the
Grinding system including
• Coolant application
• Keeping the wheel face clean with scrubber
nozzles
• Use a Good Quality Oil Coolant
• Machine with Sufficient Power and Stiffness
• Use an Appropriately Designed Grinding Wheel