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

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Presentation on theme: "GRINDING BASICS Presented by Dale Savington For: Bosch Rexroth – Rineer Hydraulics."— Presentation transcript:

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

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

3 Superabrasives Bonds Coolant Truing & Dressing Mechanics of Grinding

4 CYLINDRICAL PROCESSES (GRINDING BETWEEN CENTERS)

5 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 High volume of coolant to get into grinding zone

6 Conventional Traverse Grinding Cross –Feed (Traverse) only Stock Removal (in-feed depth) 0.0” to mm (0.0007”) ≥ 10% of abrasive Ø / pass Finish Grinding Wheel Velocity S.F.P.M. 8,500 + m/sec Traverse rate 10 – 25% of wheel width per rotation of part

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

8  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 mm 3 /mm· sec. 1 x 3.14 x = 0.5 in 3 /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: (mm 3 /mm· sec.) to (in 3 /in· min.) conversion of 10.75

9 Surface Grinding

10 CONVENTIONAL GRINDING Wheel Speed = S l o w Stock Removal = Light Fast

11 CREEP FEED Wheel Speed = S l o w S l o w Stock Removal = Heavy

12 HEDG (HIGH EFFICIENT DEEP GRINDING) Wheel Speed = Fast Stock Removal = Heavy Fast

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

14 MACHINE REQUIREMENTS

15 MACHINE RIGIDITY Spindle’s Slides Centers Head Stock Tail Stock Parts will Mirror Machines Rigidity Base

16 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) = Kw (25 H.P.) Peel – depends on contact area, material and stock removal

17 SPINDLE INTEGRITY Run-OutOut of Balance

18 WHEEL BALANCE (DYNAMIC VS STATIC) Static Balance Dynamic Balance – real time Portable Dynamic Balance

19 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.

20 ACOUSTIC SENSORS Dressing:  Sound of dresser touching wheel through coolant.  Complete contact = dressed wheel Other uses:  Picture of grinding process  Crash prevention

21 MACHINE REQUIREMENTS (MAXIMIZING GRINDING PROCESS) Rigidity Spindle power Wheel Velocity Rotary Dresser Dynamic Balancing Coolant Flow Smooth Transitional Plumbing Coolant Tank Capacity Acoustic Sensors Coolant with lubricity

22 ABRASIVES

23 WHAT AFFECTS ABRASIVE DECISION? Ferrous Materials Production Numbers Fatigue Concerns (Potential thermal damage) Non-Ferrous Materials Dimensional Tolerances Process Controls

24 TYPES OF ABRASIVES Aluminum Oxide Silicon Carbide Cubic Boron Nitride (CBN) Diamond

25 ABRASIVE SELECTION Aluminum Oxide Cubic Boron Nitride (CBN)Diamond Silicon Carbide Ferrous MaterialsNon-Ferrous Materials

26 PROPERTIES OF ABRASIVES

27 ALUMINUM OXIDE (AL 2 O 3 ) For Grinding Ferrous Materials Hardness on Knoop Scale (kg/mm 2 ) = Thermal Conductivity (W/m O K) = 29

28 SILICON CARBIDE (SI,C) For Grinding Non-Ferrous Materials Hardness on Knoop Scale (kg/mm 2 ) = 2700 Thermal Conductivity (W/m O K) = 400

29 CUBIC BORON NITRIDE (CBN) (B,N) For Grinding Ferrous Materials Thermal Conductivity (W/m O K) = 1300 Hardness on Knoop Scale (kg/mm 2 ) = 4500

30 DIAMOND (C) For Grinding Non-Ferrous Materials Hardness on Knoop Scale (kg/mm 2 ) = 8000 Thermal Conductivity (W/m O K) = 2000

31 REVIEW Knoop Thermal HardnessConductivity Aluminum Oxide Silicon Carbide Cubic Boron Nitride (CBN) Diamond

32 THE PUZZLE WHY NOT DIAMOND? REACTION Diamond + Ferrous Material + Heat = Note: Silicon Carbide has similar reaction

33 SUPERABRASIVES

34 WHAT ARE SUPERABRASIVES? Diamond Cubic Boron Nitride (CBN) Borazon

35 WHAT MAKES SUPERABRASIVES SUPER? Hardness - (Resistance to wear) Thermal Conductivity- (The ability to absorb heat) Flexibility- (one wheel for many applications) Wheel Life- (100 + times Conventional Abrasives)

36 SOME ADVANTAGES (FOR SUPERABRASIVES) Decreased Cycle Time Reduced Dressing Reduced Gaging Reduced Time for Wheel Changes Reduced Coolant Changes Reduced Filter Changes Less Swarf Contamination Reduced Coolant Disposal Costs More Consistent Parts (Less Scrap)

37 CONVENTIONAL ABRASIVES CONSTRUCTION Conventional Layer = full area of wheel Wheel Vitrified Bond Resin Bond Rubber Bond Shellac Bond

38 SUPERABRASIVE CONSTRUCTION Superabrasive Layer = 3mm (1/8”) to 12.7mm (1/2”) Wheel Core Resin Bond Metal Bond Vitrified Bond

39 BONDS

40 GRINDING MATRIX VITRIFIED WHEEL Grain Bond Pore Chip

41 GRINDING WHEEL BOND SYSTEMS, Resin, Metal & Bonds Sintered Vitrified Abrasive + Bond = Wheel

42 GRINDING WHEEL BOND SYSTEMS Open Structure (Low fired) Vitrified Bonds Abrasive + Bond + Pores = Wheel

43 GRINDING WHEEL BOND SYSTEMS Plated Wheels (Single Layer) Wheel body Cathode (-) Abrasive Anode (+) Electrolyte (Nickle Solution) Plated Wheel Cut-A-Way

44 Mechanics of Grinding

45 ABRASIVE WEAR Fracture wear Chip Bond Abrasive Cut a way of wheel

46 ABRASIVE WEAR Attritious wear (Rubbing) Work Piece Conventional Abrasive (one grain)

47 ABRASIVE WEAR Fracture wear Work Piece Conventional Abrasive (one grain)

48 ABRASIVE WEAR Fracture wear Work Piece Conventional Abrasive (one grain)

49 ABRASIVE WEAR Attritious wear Work Piece CBN Abrasive (one grain)

50 STANDARD MARKINGS CONVENTIONAL ABRASIVES Abrasive Type Abrasive Size Abrasive (combination) Hardness (Grade) Structure (Pore) Bond A C SG30 A JKLRJKLR VVVBVVVB

51 STANDARD MARKINGS SUPERABRASIVES Abrasive TypeAbrasive SizeHardness (Grade) Concentration Bond BN D BN JkLJkL BMVBMV 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

52 COOLANT Type, Flow, Pressure & Nozzle Design

53 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 = SG (Issues – Heat & Disposal) ( Specific Gravity (SG not a factor in calculations) )

54 COOLANT CONDITION Tank Size & Coolant Temp. Filtration & Particle Distribution Chemistry (Lubricity)

55 COOLANT PRESSURE Equal Wheel Velocity Bernoulli’s Equation for Pressure ΔP (Bar) = SG x Vj 2 / 200 Where:Vj 2 = (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 = 136 psi

56 Bernoulli’s Equations

57

58 Copyright © 2013 [Dale Savington]. All Rights Reserved

59

60 COOLANT FLOW Coolant Velocity = Wheel Velocity

61 “P” LINE /RIM SECTION

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63

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65 TRUING & DRESSING

66 THE DIFFERENCE BETWEEN TRUING & DRESSING

67 TRUING RESIN & METAL BONDS

68 DRESSING RESIN & METAL BONDS

69 TRUING & DRESSING PLATED WHEELS

70 TRUING & DRESSING VITRIFIED BONDED (CBN WHEELS)

71 EXAMPLES OF ROTARY DRESSERS

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

73 TRUING & DRESSING (DEPTH OR IN-FEED)  Conventional Abrasives – Aluminum Oxide  ≤ mm (0.0007”) per pass  Ceramic Abrasives – Seeded Gel (SG)  ≤ 0.005mm (0.0002”) per pass  CBN Abrasives  ≤ mm (0.0001”) per pass

74 TRUING & DRESSING (TRAVERSE RATE)  Starting Parameters  0.1mm (0.004”) per revolution of wheel Assuming 0.5mm (0.020”) radius dresser Faster traverse rate creates rougher finish Slower traverse rate creates finer finish

75 CBN VS CONVENTIONAL (SURFACE FINISH – PLUNGE GRINDING ONLY) CConventional Grinding Surface Finish = Grit Size CCBN Grinding: Surface Finish = Diamond Overlap

76 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 Nozzle increased production by 42% (762mm/min to >1,065mm/min.) + decrease dress amounts. “Automotive Valve Seats”

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

78 the end


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