For: Bosch Rexroth – Rineer Hydraulics GRINDING BASICS Presented by Dale Savington For: Bosch Rexroth – Rineer Hydraulics

Cylindrical Grinding Processes Machine Requirements (Utilizing CBN) Abrasives Properties of Abrasives

Superabrasives Bonds Mechanics of Grinding Coolant Truing & Dressing

CYLINDRICAL PROCESSES (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

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 Traverse rate 10 – 25% of wheel width per rotation of part Wheel Velocity S.F.P.M. 8,500 + m/sec. 43 + Finish Grinding

Peel (“Quick Point”) Grinding Multiple grinding functions Wheel face configuration Wheel Velocity S.F.P.M. 17,000 + m/sec. 86 + Easier coolant delivery into grinding zone (narrow contact area)

Cylindrical Grinding Plunge Q Prime (Q’) = work piece diameter x 3.14 (π) x in-feed rate Example: Work piece diameter = 25.4mm (1”) In-feed rate = 4.039mm/min. (0.159”/minute) Q’ then equals: (25.4 x 3.14 x 4.039)/60 = 5.37 mm3/mm· sec. 1 x 3.14 x 0.159 = 0.5 in3/in· min. Therefore: (5.37/(3.14 x 25.4)) x 60 = 4.039mm/min. 0.5/(3.14 x 1”)= 0.159”/min. infeed rate Note: (mm3/mm· sec.) to (in3/in· min.) conversion of 10.75

Surface Grinding

Conventional Grinding Wheel Speed = S l o w Stock Removal = Light Fast

Creep Feed Wheel Speed = S l o w Stock Removal = Heavy S l o w

HEDG (High Efficient Deep Grinding) Wheel Speed = Fast Stock Removal = Heavy Fast

Surface Grinding Example: In-Feed per pass= 0.0508mm (0.002”) Q Prime (Q’) =In-feed rate/pass x Traverse rate/min. Example: In-Feed per pass= 0.0508mm (0.002”) Traverse rate per min.= 3,810mm (3.81m)/min. (150” (12.5’)/minute) Q’ then equals: (0.0508 x 3,810)/60 = 3.225 mm3/mm· sec. 0.002 x 150 = 0.3 in3/in· min. Therefore: (3.225/(0.0508) x 60 = 3,810mm/min. traverse rate 0.3/(0.002”)= 150”/min. traverse rate Note: (mm3/mm· sec.) to (in3/in· min.) conversion of 10.75

MACHINE REQUIREMENTS

Parts will Mirror Machines Rigidity Machine Rigidity Slides Spindle’s Centers Head Stock Tail Stock Base Parts will Mirror Machines Rigidity

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) Dynamic Balance – real time Static Balance Wheel Balance (Dynamic vs Static) 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. Wheel Balance (Dynamic vs Static)

Acoustic Sensors Dressing: Sound of dresser touching wheel through coolant. Complete contact = dressed wheel Other uses: Picture of grinding process Crash prevention Acoustic Sensors

Machine Requirements (Maximizing Grinding Process) Rigidity Coolant Flow Spindle power Smooth Transitional Plumbing Wheel Velocity Coolant Tank Capacity Rotary Dresser 1. In process gaging 2. Automatic loading 3. Chillers 4. Coolants should be Water soluable oil (.3%) or straight oil 5. Coolant flow meters, temperature monitors, (Discuss Searcy Project) Coolant with lubricity Acoustic Sensors Dynamic Balancing

ABRASIVES

What affects Abrasive Decision? Ferrous Materials Non-Ferrous Materials Fatigue Concerns (Potential thermal damage) Dimensional Tolerances Process Controls Production Numbers

Types of Abrasives Aluminum Oxide Silicon Carbide Cubic Boron Nitride (CBN) Diamond

Abrasive Selection Ferrous Materials Non-Ferrous Materials Cubic Boron Nitride (CBN) Diamond Silicon Carbide Aluminum Oxide

PROPERTIES OF ABRASIVES

Aluminum Oxide (Al2O3) For Grinding Ferrous Materials Thermal Conductivity (W/mOK) = 29 Hardness on Knoop Scale (kg/mm2) = 1400 - 2100

Non-Ferrous Materials Silicon Carbide (Si,C) For Grinding Non-Ferrous Materials Thermal Conductivity (W/mOK) = 400 Hardness on Knoop Scale (kg/mm2) = 2700

Cubic Boron Nitride (CBN) (B,N) For Grinding Ferrous Materials Hardness on Knoop Scale (kg/mm2) = 4500 Thermal Conductivity (W/mOK) = 1300

Non-Ferrous Materials Diamond (C) For Grinding Non-Ferrous Materials Thermal Conductivity (W/mOK) = 2000 Hardness on Knoop Scale (kg/mm2) = 8000

Review Knoop Thermal Hardness Conductivity Aluminum Oxide 1400-2100 29 Silicon Carbide 2700 400 Cubic Boron Nitride (CBN) 4500 1300 Diamond 8000 2000

The Puzzle Why Not Diamond? Diamond + Ferrous Material + Heat = REACTION Note: Silicon Carbide has similar reaction

SUPERABRASIVES

What are Superabrasives? Diamond Cubic Boron Nitride (CBN) Borazon Show overhead on make up of Diamond and CBN

What makes Superabrasives Super? Hardness - (Resistance to wear) Thermal Conductivity- (The ability to absorb heat) Flexibility- (one wheel for many applications) Be prepared to show overh ead of Properties of Superabrasives Hardness for CBN =4700Knoop Diamond =7000 Knoop Alumimum Oxide =1400 - 2100 Knoop Silicon Carbide =2700 Knoop Thermal Conductivity for CBN =1300 Diamond =2000 Aluminium Oxide =29 Silicon Carbide =400 Grinding Ratio for M2 Steel =229 Volume of Work / Volume of wheel T15 Steel =150 D2 Steel =217 Wheel Life- (100 + times Conventional Abrasives)

Some Advantages (For Superabrasives) Decreased Cycle Time Reduced Dressing Reduced Gaging More Consistent Parts (Less Scrap) Reduced Time for Wheel Changes Reduced Coolant Changes Reduced Filter Changes Reduced Coolant Disposal Costs Less Swarf Contamination

Conventional Abrasives Construction Conventional Layer = full area of wheel Vitrified Bond Resin Bond Rubber Bond Shellac Bond Wheel 1. If a grinding wheel is 24 inch in diameter with a 12 inch hole The entire wheel from O.D. to hole is conventional abrasive compared to the 1/8 to 1/4 inch section for Superabrasives. 2. This small section is going to last from 100 + time a conventional wheel

Superabrasive Construction Superabrasive Layer = 3mm (1/8”) to 12.7mm (1/2”) Wheel Core Resin Bond Metal Bond Vitrified Bond 1. If a grinding wheel is 24 inch in diameter with a 12 inch hole The entire wheel from O.D. to hole is conventional abrasive compared to the 1/8 to 1/4 inch section for Superabrasives. 2. This small section is going to last from 100 + time a conventional wheel

BONDS

Grinding Matrix Vitrified Wheel Grain Pore Bond Chip

Grinding Wheel Bond Systems Sintered Vitrified Resin , Metal & Bonds Abrasive + Bond = Wheel

Grinding Wheel Bond Systems Open Structure (Low fired) Vitrified Bonds Abrasive + Bond + Pores = Wheel

Grinding Wheel Bond Systems Plated Wheels (Single Layer) Wheel body Cathode (-) Electrolyte (Nickle Solution) Abrasive Anode (+) Plated Wheel Cut-A-Way

Mechanics of Grinding

Abrasive wear Bond Abrasive Fracture wear Chip Cut a way of wheel

Abrasive wear Conventional Abrasive (one grain) Attritious wear (Rubbing) Work Piece Abrasive wear

Abrasive wear Conventional Abrasive (one grain) Fracture wear Work Piece Abrasive wear

Abrasive wear Conventional Abrasive (one grain) Fracture wear Work Piece Abrasive wear

CBN Abrasive (one grain) Attritious wear Work Piece Abrasive wear

Standard Markings Conventional Abrasives Abrasive Type Abrasive Size Abrasive (combination) Hardness (Grade) Structure (Pore) Bond A C SG30 60 120 80 24 1 2 J K L R 6 12 10 V B

Standard Markings Superabrasives Abrasive Type Abrasive Size Hardness (Grade) Concentration Bond BN D 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

Type, Flow, Pressure & Nozzle Design Coolant Type, Flow, Pressure & Nozzle Design

Coolant Types Water, Water Soluble Oils, Straight Oils Specific Gravity of each & traits for grinding: Water = 1 SG (Issue – lack of Lubricity) Water Soluble Oil = 1 SG (Issues – Foaming & bacteria) Straight & Synthetic Oils = 0.87-0.95 SG (Issues – Heat & Disposal) ( Specific Gravity (SG not a factor in calculations) )

Particle Distribution Coolant Condition Filtration & Particle Distribution Tank Size & Coolant Temp. Chemistry (Lubricity)

Coolant Pressure Equal Wheel Velocity Bernoulli’s Equation for Pressure ΔP (Bar) = SG x Vj2 / 200 Where:Vj2 = (M/s)2 Example: Wheel velocity – 43.3M/s (8,500 S.F.P.M.) Then: 1 x (43.3)2 / 200 = 9.4 Bar Bar conversion Bar x 14.508 = 136 psi

Bernoulli’s Equations

Copyright © 2013 [Dale Savington]. All Rights Reserved

Copyright © 2013 [Dale Savington]. All Rights Reserved

Coolant Flow Coolant Velocity = Wheel Velocity

“P” Line /Rim Section

TRUING & DRESSING

The Difference Between Truing & Dressing

Truing Resin & Metal Bonds

Dressing Resin & Metal Bonds

Truing & Dressing Plated Wheels

Truing & Dressing Vitrified Bonded (CBN Wheels)

Examples of Rotary Dressers

Direction for Dressing with rotary Dressers Preferred (opens wheel) Closes Wheel

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 (Depth or In-Feed)

Truing & Dressing (Traverse Rate) Starting Parameters 0.1mm (0.004”) per revolution of wheel Assuming 0.5mm (0.020”) radius dresser Truing & Dressing (Traverse Rate) 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 CBN vs Conventional (Surface Finish – plunge grinding only)

“Automotive Valve Seats” Nozzle increased production by 42% (762mm/min to >1,065mm/min.) + decrease dress amounts. “Automotive Valve Seats” 508mm x 458mm x 304.8mm Vitrified CBN wheel Thru-Feed Grinding Metal bond rotary dresser Dr. Webster Nozzle Each orifice is an oval 4mm 19 total orifices

Hard Tuning Shafts to see if it was cost affective Cost was prohibitive because of tool life and change times

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