Modelling and Simulation. in Manufacturing Technology

Transcription

1 Modelling and Simulation in Manufacturing Technology Cutting ith Undefined Cutting Prof. Dr.-Ing. F. Klocke Structure Chip removal mechanisms From geometrically defined to geometrically undefined cutting Grinding paths Chip thickness for single-grain Chip thickness for grinding heels (multi-grain) Process factors - Correlations and influences Energy balances Grinding tools and grinding heel preparation Structure and characteristics of grinding tools Effects of grinding heel specifications on the process Wear mechanisms in grinding processes and their effects on the heel topography Preparation of grinding heels Overvie of grinding processes and application examples Definition of parameters Overvie of grinding processes / procedures variants Characteristics and application examples of some common grinding procedures Other active principles of cutting edge engagement ith geom. undef. edges

2 Process basics Milling is a chip removing process ith a geometrically defined cutting tool ith a rotatory cutting movement. cutting movement correlation: grinding - milling? feed movement From milling to grinding Milling Grinding Cutting edges :

3 Chip formation in grinding grinding heel grain trajectory F t,s F n,s bond v s accumulation grain (cutting edge) chip orkpiece T µ h cu eff h cu I elastic deformation II elastic and plastic deformation III elastic and plastic deformation and chip removal Survey of the process The grinding process and its parameters Coolant Process parameters Workpiece Grinding heel Process monitoring Machine Operator Process Product

4 Analysis of physical correlations necessary Input v c ae Q Process = Black-Box Many physical correlations are still not clear Output optimisation Analysis of physical correlations necessary Input Process = Black Box Output The Black-Box : Grinding process Wear mechanisms of the grain abrasion adhesion tribo-chemical reaction surface disorder Formation of machined surface formation of burrs peppering damage of the external zone microhardness Chip formation questions: Ho are these factors linked? Which kinematic boundary conditions exist?

5 Structure Chip removal mechanisms From geometrically defined to geometrically undefined cutting Grinding paths Chip thickness for single-grain Chip thickness for grinding heels (multi-grain) Process factors - Correlations and influences Energy balances Grinding tools and grinding heel preparation Structure and characteristics of grinding tools Effects of grinding heel specifications on the process Wear mechanisms in grinding processes and their effects on the heel topography Preparation of grinding heels Overvie of grinding processes and application examples Definition of parameters Overvie of grinding processes / procedures variants Characteristics and application examples of some common grinding procedures Other active principles of cutting edge engagement ith geom. undef. edges From milling to grinding A Vectoral description of grain path ith position vector A

6 Cycloid path of a grain Single-grain Multi-grain grain 1 grain 3 grain 2 Cycloid paths of grinding grains Cutting edges ith different heights grinding heel depth of cut a e

7 Static and kinematic cutting edges Kinematic roughness Korneingriffsbahnen cutting paths orkpiece Werkstück kinematic kinematische roughness Rauheit Werkstück orkpiece

8 Structure Chip removal mechanisms From geometrically defined to geometrically undefined cutting Grinding paths Chip thickness for single-grain Chip thickness for grinding heels (multi-grain) Process factors - Correlations and influences Energy balances Grinding tools and grinding heel preparation Structure and characteristics of grinding tools Effects of grinding heel specifications on the process Wear mechanisms in grinding processes and their effects on the heel topography Preparation of grinding heels Overvie of grinding processes and application examples Definition of parameters Overvie of grinding processes / procedures variants Characteristics and application examples of some common grinding procedures Other active principles of cutting edge engagement ith geom. undef. edges Chip formation in grinding f a Ψ R a e v c h cu max v h cu, max 2 π d s v v s a d e s... ~ F c,rz, r s

9 Chip roots (photos taken by scanning electron microscope) cutting direction 25 µm 10 µm orkpiece material: Ck15N orkpiece material: Ck45N Geometrical and kinematic contact length geometrical contact length: 1 kinematic = ± l g l 1 contact length: k q l g = ae d eq 2 ith: l g = ae + x 2 2 d d x 2 = eq eq ae q= vs v

10 Contact conditions in different grinding processes external cylindrical grinding flat grinding internal cylindrical grinding transformed contact conditions real contact conditions Up grinding don grinding up grinding grain (cutting edge) v s chip orkpiece l k v v kinematic contact length speed ratio 1 l = 1 ± q vs q = v k l g

11 Structure Chip removal mechanisms From geometrically defined to geometrically undefined cutting Grinding paths Chip thickness for single-grain Chip thickness for grinding heels (multi-grain) Process factors - Correlations and influences Energy balances Grinding tools and grinding heel preparation Structure and characteristics of grinding tools Effects of grinding heel specifications on the process Wear mechanisms in grinding processes and their effects on the heel topography Preparation of grinding heels Overvie of grinding processes and application examples Definition of parameters Overvie of grinding processes / procedures variants Characteristics and application examples of some common grinding procedures Other active principles of cutting edge engagement ith geom. undef. edges Chip thickness not deformed chip thickness for single-grain cutting h cu, max 2 π d s v v s a d e s not deformed chip thickness for multi-grain cutting h cu,max k 1 C stat α v v s β a d e eq γ ith α, β, γ positive parameters α, β and γ depend on the grinding heel specifications C stat is the static cutting edge density factor k = const. d eq = equivalent grinding heel diameter

12 Structure Chip removal mechanisms From geometrically defined to geometrically undefined cutting Grinding paths Chip thickness for single-grain Chip thickness for grinding heels (multi-grain) Process factors - Correlations and influences Energy balances Grinding tools and grinding heel preparation Structure and characteristics of grinding tools Effects of grinding heel specifications on the process Wear mechanisms in grinding processes and their effects on the heel topography Preparation of grinding heels Overvie of grinding processes and application examples Definition of parameters Overvie of grinding processes / procedures variants Characteristics and application examples of some common grinding procedures Other active principles of cutting edge engagement ith geom. undef. edges Effect of chip thickness on process parameters h cu,max max. chip thickness h cu,max k 1 C stat α v v s β a d e eq roughness R z grinding force F c γ h cu ~ R z h cu ~ F c grinding poer P c h cu ~ P c

13 depth of cut a e max. chip thickness h cu,max kinematic contact length l k Effect of depth of cut Source: Rappold Winterthur Schleiftechnik k l g q l ± = 1 1 eq e g d a l = γ eq e β s α stat cu,max d a v v C 1 k h Effect of cutting speed Source: Rappold Winterthur Schleiftechnik grinding heel circumferential speed v s max. chip thickness h cu,max γ eq e β s α stat cu,max d a v v C 1 k h

14 Effect of grinding heel diameter grinding heel diameter d s contact area A k h cu,max k 1 C stat α v v s β a d e eq γ kinematic contact length l k max. chip thickness h cu,max Source: Rappold Winterthur Schleiftechnik Static and kinematic cutting edges in grinding F' n l k = 0 k n ( N ) N ( l) mon ith N mom = number of momentary cutting edges kin dl

15 Cutting speed cutting speed v c chip thickness h cu number of kinematic cutting edges N kin number of chips increases higher damage of external zone by higher temperature due to friction grinding forces decrease because N kin and h cu decrease roughness decreases N kin ~ F c h cu ~ R z Structure Chip removal mechanisms From geometrically defined to geometrically undefined cutting Grinding paths Chip thickness for single-grain Chip thickness for grinding heels (multi-grain) Process factors - Correlations and influences Energy balances Grinding tools and grinding heel preparation Structure and characteristics of grinding tools Effects of grinding heel specifications on the process Wear mechanisms in grinding processes and their effects on the heel topography Preparation of grinding heels Overvie of grinding processes and application examples Definition of parameters Overvie of grinding processes / procedures variants Characteristics and application examples of some common grinding procedures Other active principles of cutting edge engagement ith geom. undef. edges

16 Energy distribution and heat flo during grinding process tool rake friction Effect of different contact lengths e.g. creep grinding ith lo table speeds l g = a e d eq h cu,max k 1 C stat α v v s β a d e eq γ F' l k = temperature rises n 0 k n ( N ) N ( l) mon l k ~ T kin dl kin. contact length l k high influence on external zone normal force rises roughness decreases l k l k ~ F n, S ~ 1 R z

17 Structure Chip removal mechanisms From geometrically defined to geometrically undefined cutting Grinding paths Chip thickness for single-grain Chip thickness for grinding heels (multi-grain) Process factors - Correlations and influences Energy balances Grinding tools and grinding heel preparation Structure and characteristics of grinding tools Effects of grinding heel specifications on the process Wear mechanisms in grinding processes and their effects on the heel topography Preparation of grinding heels Overvie of grinding processes and application examples Definition of parameters Overvie of grinding processes / procedures variants Characteristics and application examples of some common grinding procedures Other active principles of cutting edge engagement ith geom. undef. edges Tools for cutting ith geometrical undefined cutting edge

18 Chip formation ith undefined cutting edges grinding heel rake angle ork-piece bonding grain in-feed source: Fachkunde Metall, Europa Lehrmittel chips pore Composition of grinding heels

19 Structure of grinding heels Specification of conventional grinding heels abrasive grain size hardness texture bonding type special characteristics example A 60 L 5 B P corundum A V vitrified bonding silicon carbide C S silicate bonding R rubber bonding coarse medium fine very fine B resin bonding E shellac bonding Mg magnesit bonding closed texture open texture A B C D extremely soft E F G - very soft H I Jot K soft L M N O medium P O R S hard T U V W very hard X Y Z - extremely hard

20 Specification of high-hardness grinding heels abrasive grain size example D 126 bonding K hardness J body material A concentration C 50 diamond D carat/cm 3 term CBN B 1,1 C25 1,7 C ,2 C ,3 C ,4 C ,5 C ,0 C ,6 C J soft vol.% term N medium 12,0 V R hard 18 V T very hard 24 V240 K resin bonding alu-resin Bz A aluminum M metal bonding B phenolic resin G S KSS GSS MSS VSS resin bonding galvanic bonding sinter metal bonding vitrified bonding Tasks and characteristics of grinding tools Task While cutting ith geometrical undefined cutting edges the effect of material removal is caused by grains penetrating the orkpiece material Required properties hardness and toughness thermal stability chemical stability material removal from the orkpiece maintaining the sharpness ithstanding high machining temperatures ithstanding rapid temperature changes avoiding chemical reactions at high temperatures and high pressures

21 Grouping of conventional grinding heels symbol abrasive Knoop - hardness [N/mm 2 ] thermal stability [ C] thermal conductivity [W/(m C)] fields of application A corundum 1950 to medium-tough to hard materials belo 60 HRC (R m < 500 N/mm 2 ) such as: steel malleable cast iron Sol-Gelcorundum > corundum - 6 tough-hard steels over 60HRC, such as tool-steel grinding and polishing of glas C silican carbide surface grinding of HM, GG, ceramics, non- ferrous metals dressing manual grinding Grouping of high-hardness tools symbol abrasive Knoop - hardness [N/mm 2 ] thermal stability [ C] thermal conductivity [W/(m C)] fields of application B cubic boron nitride (CBN) hardened steel lo alloy steel HSS D diamond carbon saturated steel glas, stone, ceramics tungsten carbide, cermets glass-fibre re-inforced plastics (GRP)

22 Tasks and characteristics of bonds Task The purpose of the bond is to retain the grinding grit in place until it is blunted by the cutting operation. The bond should then release the grain so that the next sharp grain can be used. Required properties the bonding material must be firm enough formation of bond bridges ith sufficiently large cross-sections a durable joint must be formed beteen bond and grit Grouping of bonds symbol bonding type characteristics V vitrified bond brittle and thus sensitive to impact load high modulus of elasticity high thermal stability, lo resistance to thermal shock chemical resistance against oil and ater D resin bond high impact and shock resistance as ell as side pressure application in parting-off and roughing heels high elasticity in fine-grinding heels enables high surface qualities M G metal bond galvanic bond high ear resistance difficult to dress high thermal conductivity

23 Structure Chip removal mechanisms From geometrically defined to geometrically undefined cutting Grinding paths Chip thickness for single-grain Chip thickness for grinding heels (multi-grain) Process factors - Correlations and influences Energy balances Grinding tools and grinding heel preparation Structure and characteristics of grinding tools Effects of grinding heel specifications on the process Wear mechanisms in grinding processes and their effects on the heel topography Preparation of grinding heels Overvie of grinding processes and application examples Definition of parameters Overvie of grinding processes / procedures variants Characteristics and application examples of some common grinding procedures Other active principles of cutting edge engagement ith geom. undef. edges Effect of the specification on h cu - grain size grain size grain concentration bonding hardness texture const const const number of kinematic cutting edges N kin number of current cutting edges N mom distance beteen kinematic cutting edges l kin chip thickness h cu

24 Effect of the specification on h cu - grain concentration grain size const grain concentration bonding hardness texture const const number of kinematic cutting edges N kin number of current cutting edges N mom distance beteen kinematic cutting edges l kin chip thickness h cu Effect of the specification on h cu - bonding hardness grain size const grain concentration bonding hardness texture const const number of kinematic cutting edges N kin number of current cutting edges N mom distance beteen kinematic cutting edges l kin chip thickness h cu

25 Effect of the specification on h cu - texture grain size const grain concentration bonding hardness texture const const number of kinematic cutting edges N kin number of current cutting edges N mom distance beteen kinematic cutting edges l kin chip thickness h cu Structure Chip removal mechanisms From geometrically defined to geometrically undefined cutting Grinding paths Chip thickness for single-grain Chip thickness for grinding heels (multi-grain) Process factors - Correlations and influences Energy balances Grinding tools and grinding heel preparation Structure and characteristics of grinding tools Effects of grinding heel specifications on the process Wear mechanisms in grinding processes and their effects on the heel topography Preparation of grinding heels Overvie of grinding processes and application examples Definition of parameters Overvie of grinding processes / procedures variants Characteristics and application examples of some common grinding procedures Other active principles of cutting edge engagement ith geom. undef. edges

26 Variation of grinding heel topography ith material removal rate Variation of grinding heel topography ith material removal rate Before process start Wear types at grain and bonding chemical and thermal ear of bond micro cracks bond breakage grain breakage pressure softaning chemical ear abrasive ear scanning - electrons - microscope - pictures of single grains grain breakage mechanical abrasion a b a b a: before engagement b: after engagement time t

27 Examples of grain ear abrasion and small grain breakage crack initiation adhesion adherence of chips examples of grain ear grain breakage micro breakage The chip thickness h cu determines ear behaviour and ear speed

28 Motivation for grinding heel dressing Macroscopic ear Microscopic ear radial ear edge ear Consequence Profile lost Off-size condition Blunted grit-cutting-edges Increase of grinding forces Damage of the orkpiece structure in the external zone Tool conditioning Structure Chip removal mechanisms From geometrically defined to geometrically undefined cutting Grinding paths Chip thickness for single-grain Chip thickness for grinding heels (multi-grain) Process factors - Correlations and influences Energy balances Grinding tools and grinding heel preparation Structure and characteristics of grinding tools Effects of grinding heel specifications on the process Wear mechanisms in grinding processes and their effects on the heel topography Preparation of grinding heels Overvie of grinding processes and application examples Definition of parameters Overvie of grinding processes / procedures variants Characteristics and application examples of some common grinding procedures Other active principles of cutting edge engagement ith geom. undef. edges

29 Kinematics of common dressing processes standing dressing tools single-grit dressing tool dressing tile multi-grit dressing tool v fad v fad v fad v sd v sd v sd rotating dressing tools profile dressing roll form dressing roll pot dressing heel v rd v sd v sd v fad v rd v rd v fad v sd v frd Dressing tools standing dressing tools single-grit dressing tool dressing tile multi-grit dressing tool rotating dressing tools profile dressing roll form dressing roll pot dressing heel

30 Creation of tool-topography ith dressing processes Standing dressing tool Profile-roll Rotating dressing tool Form-roll Similar to: turning Similar to external cylindrical grinding Plunge grinding Traverse grinding Creation of a thread Overlapping of grit engagement paths thread + Overlapping of grit engagement paths Process preparation of CBN-grinding heels Dressing of CBN grinding heels Profiling Wheel topography after profiling Generating the grinding heel shape Sharpening Wheel topographie after sharpening Generation of the cutting edge space structure

31 By sharpening the grinding heel layer becomes ready for use Vie 1 2 Grinding heel : Dressing tool : Sharpening block height : Cutting speed : Grinding heel B 252 KSS 10JA V240 Diamond roller h Sb = 25 mm v c = 90 m/s q d : Dressing speed ratio a d : Dressing feed Q' Sb : spec. sharpening mat. removal a Sb : Sharpening block feed P R O F I L I N G S H A R P E N I N G S H A R P E N I N G q d = -0,375 a d = 50 µm Q' Sb = 400 mm³/mms a Sb = 70 mm Q' Sb = 710 mm³/mms a Sb = 240 mm Structure Chip removal mechanisms From geometrically defined to geometrically undefined cutting Grinding paths Chip thickness for single-grain Chip thickness for grinding heels (multi-grain) Process factors - Correlations and influences Energy balances Grinding tools and grinding heel preparation Structure and characteristics of grinding tools Effects of grinding heel specifications on the process Wear mechanisms in grinding processes and their effects on the heel topography Preparation of grinding heels Overvie of grinding processes and application examples Definition of parameters Overvie of grinding processes / procedures variants Characteristics and application examples of some common grinding procedures Other active principles of cutting edge engagement ith geom. undef. edges

32 Definition of parameters - e.g. surface grinding Parameters for the characterisation of the grinding process V a e v Legend: V : removed orkpiece volume mm 3 a e : engagement ( infeed) mm v : orkpiece speed m/s Workpiece Definition of parameters - e.g. face grinding a p V a e v v s Workpiece Legend: b s a p : contact idth mm b s : grinding heel idth mm v s : grinding heel speed m/s

33 Parameters for the grinding process V a p v a e l V = a e a l v = t Q Q = b p seff l b s v s Legend: Workpiece V : removed orkpiece volume mm 3 Q : material removal rate mm 3 /s Q : specific material removal rate mm³/mms Q = = dv = const = dt ae ap l = ae a t p v Structure Chip removal mechanisms From geometrically defined to geometrically undefined cutting Grinding paths Chip thickness for single-grain Chip thickness for grinding heels (multi-grain) Process factors - Correlations and influences Energy balances Grinding tools and grinding heel preparation Structure and characteristics of grinding tools Effects of grinding heel specifications on the process Wear mechanisms in grinding processes and their effects on the heel topography Preparation of grinding heels Overvie of grinding processes and application examples Definition of parameters Overvie of grinding processes / procedures variants Characteristics and application examples of some common grinding procedures Other active principles of cutting edge engagement ith geom. undef. edges

34 Overvie of different grinding processes external cylindrical Cylindrical internal cylindrical surface Surface turn Side grinding Peripheral grinding peripheralplungegrinding peripheraltraversegrinding sideplungegrinding sidetraversegrinding v v ft v fa r Surface grinding Surface - peripheral - grinding Q = a e a p v a = b = p s b seff Q a = e a b p seff v = a e v b s v s v a e a p

35 External - cylindrical - grinding Q = π d a v p b s = π d v = a v fr p v fr v fr mit d a d d e v s v fr = a e n a = b = b p s seff v a e Q = π d = π d a a e p a n e n a p Structure Chip removal mechanisms From geometrically defined to geometrically undefined cutting Grinding paths Chip thickness for single-grain Chip thickness for grinding heels (multi-grain) Process factors - Correlations and influences Energy balances Grinding tools and grinding heel preparation Structure and characteristics of grinding tools Effects of grinding heel specifications on the process Wear mechanisms in grinding processes and their effects on the heel topography Preparation of grinding heels Overvie of grinding processes and application examples Definition of parameters Overvie of grinding processes / procedures variants Characteristics and application examples of some common grinding procedures Other active principles of cutting edge engagement ith geom. undef. edges

36 Overvie of processes - Examples cylindrical surface External cylindrical Internal cylindrical surface Peripheral grinding peripheralplungegrinding peripheraltraversegrinding Characteristics of external - cylindrical - grinding generation of rotationally symmetric orkpiece geometries frontal centering processing at up-grinding (usually) use of back-rests, to avoid high orkpiece deflection Difficulties: orkpiece fitting: centering has to guarantee a true running deflection because of high stress resultants at long and thin orkpieces chattering

37 Application area of external cylindrical grinding Machining of: bearing carriers, shaft-steps, notches Printing rolls, rolls of paper producers steel rolling mills source: Effesis Characteristics of internal cylindrical grinding kinematically identic to centreless external cylindrical grinding bigger contact arc in comparison to external cylindrical grinding disadvantages problems ith chip transport and supply of coolant deformation of the orkpiece hen the orkpiece is long conicity, upvaluation of end of hole high ear

38 Application area of internal cylindrical grinding Machining of: gear-heels bearing rings retainer of spindles Source: Daimler Chrysler Characteristics of surface grinding Many procedure variants Machining of notches and profiles, big flat surfaces Machining by deep- and pendular grinding Disadvantages high heat insertion in deep grinding according to geometry bad chip transport

39 Application area of surface grinding Machining of: guidelines sealing-surfaces of motors profile of turbineblades for aircraft engines Characteristics of centreless grinding Creation of rotationally symmetrical orkpieces supported on the periphery (linear support of the orkpiece) restricted on cylindrical, conic or convex machining surfaces no sources of error in clamping / centering easy orkpiece change problems: dynamically instable compensation of deviation of circle form

40 Application area of centreless grinding Main application area: line production bolts, shafts, bearing elements Quelle: Schumag bearing carrier of camshafts, cam folloers pin of a nozzle, rotor axes, ball pivot Quelle: Schumag rods, pipes, platens, billiard balls Structure Chip removal mechanisms From geometrically defined to geometrically undefined cutting Grinding paths Chip thickness for single-grain Chip thickness for grinding heels (multi-grain) Process factors - Correlations and influences Energy balances Grinding tools and grinding heel preparation Structure and characteristics of grinding tools Effects of grinding heel specifications on the process Wear mechanisms in grinding processes and their effects on the heel topography Preparation of grinding heels Overvie of grinding processes and application examples Definition of parameters Overvie of grinding processes / procedures variants Characteristics and application examples of some common grinding procedures Other active principles of cutting edge engagement ith geom. undef. edges

41 Other active principles Basic principles of cutting edge engagement Bound by energy Bound by virtue Bound by path Bound by range ω Blast chipping Free abrasive gr. Grinding Honing Lapping Cutting edge Workpiece Active principle - bound by energy balst chipping cutting edge

42 Active principle - bound by virtue Gleitschleifen cutting edge Active principle - bound by path Grinding Honing cutting edge grinding / honing ω

43 Active principle - bound by range lapping cutting edge Questions I 1. Of hich components a grinding heel is built of? 2. Which tasks have the components of a grinding heel? 3. Which grain types and bonding types do exist? 4. Name diverse ear types that could occur on grinding heels. 5. Why must grinding heels get sharpened? 6. What is the material removal-rate a quantum for? 7. Ho do you assign the material romoval volume? 8. What is the difference beteen don-grinding / up-grinding? 9. Name four common grinding procedures! 10. What are the advantages and disadvantages in deep- and pendulum-grinding?

44 Questions I 1) What is the material removal-rate a quantum for? 2) Ho do you assign the material romoval volume? 3) In hich procedures for generating a rationally symmetric geometry is the tool feed a) radial b) axial? 4) What is the difference beteen don-grinding / up-grinding? 5) Name four common grinding procedures! 6) Ho can you avoid orkpiece deflection in the process of external cylindrical grinding? 7) What problems can occur in the internal cylindrical grinding process and ho are they caused? 8) What are the advantages and disadvantages in deep- and pendulum-grinding? 9) What are the typical devices, hich are machined in centreless grinding? 10) What are the four active principles of the cutting edge engagement in machining ith geometrically undefined cutting edges?