Report

Micro Machining Technology • Micro EDM • High speed precision grinding • Micro scratching tests •Modelling and simulation of machining processes Tahsin Tecelli Öpöz 2/25 Outline • Research environment • Micro EDM • High speed precision grinding • Micro scratching tests • Finite Element Modelling and Simulation • Impact of the research • Publications 3/25 Research environment Micro Electrical Discharge Machining Robotic polishing Precision grinding/diamond turning Surface metrology 4/25 Micro EDM Micro electrical discharge machining of micro holes 1 Micro Tool Manufacturing using WEDG (Dia.<10 µm) 3 Surface Damage in Micro EDMed Holes Etched with nitric acid Etched with nitric+chromic acid Hole shape formation 2 (Disclosure of technological features of micro EDM) Micro EDM Discharge pulse form and surface characteristics (a) Discharge energy 12.7 µj (b) Discharge energy 123 µj 5/25 6/25 Micro EDM Micro hole end-tip shape formation Concave tip shape E= 0.78 µJ, OGP=75 V Flat (rough) tip shape E= 223 µJ, OGP=75 V Bullet tip shape E= 33.4 µJ, OGP=80 V Micro EDM 7/25 Heat affected layer in Micro EDMed holes’ wall Micro EDM 8/25 Material removal response with machining time Micro EDM 9/25 Micro hole entrance diameter with machining time 10/25 Precision grinding High speed applications and micro scratching tests 1 High speed precision grinding (20k – 160k rpm) 2 Single grit grinding test to reveal micromechanics concept in grinding Rubbing Ploughing Cutting Super glue Steel wheel 3 A CBN grit from top view 4 A single grit glued onto the wheel Material removal mechanism stages at micro scale grinding 11/25 Micro Scratching tests Scratch form measurement and profile extraction Increasing depth of cut Traverse scratching Workpiece : Inconel 718 Grit : CBN (40/50) Speed = 3000 rpm (Vc = 327.6 m/min) Work table speed = 200 mm/min Scratches with increasing depth of cut: An example Talysurf CCI interferometer measurement Longitudinal section profile extracted using 1st line shown in previous figure Deepest point around 450 (a) (b) Cross section profile extracted at 450 using 2nd line shown in previous figure 12/25 Micro Scratching tests Abrasive grit cutting edge shape alteration during scratching: Single edge and multiple edges scratch formation Groove section area Depth of cut (ap) Total Pile-up area (a) Single scratch (a) Single scratch Depth of cut (ap) Groove section area Groove section area (b) Multiple scratches Depth of cut (ap) Total Pile-up area Total Pile-up area 13/25 Micro Scratching tests Pile-up ratio variation with depth of cut at different grit cutting edges 0.5 0.8 0.7 R² = 0.6748 1 0.6 Pile-up ratio Pile-up ratio 0.4 0.3 0.2 3 0.5 0.4 2 0.3 0.2 0.1 0.1 0 0 0.5 1 1.5 2 2.5 3 3.5 Depth of cut (µm) 4 4.5 5 R² = 0.3949 0 5.5 0 Traverse scratching; Workpiece: En24T; Grit: CBN (40/50 mesh); Vc= 546.6 m/min 1 1.5 2 2.5 Depth of cut (µm) 3 3.5 4 Traverse scratching; Workpiece: En24T; Grit: CBN (40/50 ); V c= 327.6 m/min 3.5 1 single edge scratch 3 multiple edges scratch 0.8 2.5 0.6 Pile-up ratio Pile-up ratio 0.5 R² = 0.7924 0.4 2 1.5 1 R² = 0.5083 0.2 R² = 0.5354 0.5 0 0 0 2 4 6 Depth of cut (um) 8 Traverse scratching; Workpiece: En24T; Grit: CBN (40/50 ); V c= 327.6 m/min 10 0 0.5 1 1.5 2 2.5 3 3.5 4 Depth of cut (µm) 4.5 5 5.5 6 6.5 Traverse scratching; Workpiece: Inconel 718; Grit: CBN (40/50) ; Vc= 327.6 m/min 14/25 Micro Scratching tests Material removal along scratch length: Pile-up ratio 35 30 2.5 2 Pile-up ratio Pile-up ratio 25 20 1.5 1 0.5 15 0 200 300 400 500 600 10 (a) Lateral cross sectional view of a scratch Scratching direction 5 0 0 Workpiece: En24T steel Grit: CBN (40/50) S=3000 rpm (Vc= 327.6 m/min) Hardness= 289.2 HV at 1 kg load (b) Longitudinal cross sectional view of a scratch 100 200 300 400 500 600 Dimensional length along scratch direction (µm) 700 800 Traverse scratching; S=3000 rpm (Vc= 327.6 m/min); Workpiece: En24T steel; Grit: CBN (40/50) 900 15/25 Micro Scratching tests Material removal along scratch length: Chip removal strength Chip removal strength (µm2) 70 scratch first part (grit entrance side) scratch second part (grit exit side) 60 60 50 50 40 40 30 30 20 20 10 10 0 0 0 1 2 3 4 4 3 2 1 -10 0 -10 Depth of cut (µm) -20 -30 -40 Traverse scratching; S=3000 rpm (Vc= 327.6 m/min); Workpiece: En24T steel; Grit: CBN (40/50) 16/25 Micro Scratching tests Cutting forces, force ratio, and specific energy Fn, Vc=54.6 m/min 9 Ft, Vc=54.6 m/min 8 Fn, Vc=327.6 m/min Cutting forces (N) R² = 0.4748 5 R² = 0.6721 4 3 6 5 4 7 R² = 0.332 R² = 0.6896 1 2 2.5 3 R² = 0.9674 3.5 4 4.5 Depth of cut (µm) 5 5.5 R² = 0.7598 S=3000 rpm R² = 0.7598 S=3000 rpmµm2 GA=236 GA=236 µm2 Depth of cut= 4.55 µm Depth of cut= 4.55 µm R² = R² 0.9289 = 0.9289 2 R²R²==0.7477 0.7477 1 0 0 50 0 6 Ft, Vc=327.6 m/min 5 0 2 Fn, Vc=327.6 m/min Ft, Vc=327.6 m/min R² = 0.9674 6 1 0 S=500 rpm Depth of cut=3.59 µm GA=154µm2 Depth of cut=3.59 µm Vc=54.6 m/min Fn,Ft,Vc=327.6 m/min S=3000 rpm 4 GA=236 µm2 Depth of3cut= 4.55 3 µm 2 S=500 rpm GA=154µm2 Fn,Vc=54.6 Vc=54.6 m/min m/min Ft, 8 7 Ft, Vc=327.6 m/min 6 50 100 100 150 150 200200 250 250 2 Groove area (µm 2 ) 300 300 350 350 400 400 Groove area (µm ) Traverse scratching; Workpiece: En24T; Grit: CBN (40/50 ); Traverse scratching; En24T; Grit: CBN (40/50 ); SignalWorkpiece: recorded with Labview software Traverse scratching; Workpiece: En24T; Grit: CBN (40/50); Signal recorded with Labview software Signal recorded with Labview software 4 20 3.5 Vc=54.6 m/min 18 Vc=54.6 m/min Vc=327.6 m/min 16 Vc=327.6 m/min Specific energy (J/mm3) 3 2.5 Fn/Ft Cutting forces (N) 7 Fn, Vc=54.6 m/min S=500 rpm 9 8 2 GA=154µm Depth of cut=3.59 µm Cutting forces (N) 9 2 1.5 1 14 12 10 8 6 4 0.5 2 0 0 0 50 100 150 200 250 Groove area (µm2) 300 Traverse scratching; Workpiece: En24T; Grit: CBN (40/50) Signal recorded with Labview software 350 400 0 1 2 3 Depth of cut (µm) 4 5 Traverse scratching; Workpiece: En24T; Grit: CBN (40/50) Signal recorded with Labview software 6 17/26 Micro Scratching tests Acoustic Emission (raw signal) during scratching AE characteristic of material deformation No visible scratch Visible scratch No visible scratch Depth of cut: 2 µm Sa: ~ 90 nm for all surfaces 0.015 0.5 0.015 0.4 0.01 0.01 0.3 0 -0.005 0.005 Raw AE signal (V) 0.2 Raw AE signal (V) Raw AE signal (V) 0.005 0.1 0 -0.1 0 -0.005 -0.2 -0.01 -0.01 -0.3 -0.015 6.614 6.615 6.616 6.617 Time (Micro seconds) (a) 1st signal rubbing 6.618 x 10 6 -0.4 6.694 6.696 6.698 Time (Micro seconds) (b) 4th signal cutting & ploughing 6.7 x 10 6 -0.015 7.29 7.291 7.292 7.293 7.294 Time (Micro seconds) (c) Last signal rubbing 7.295 x 10 6 Modelling and Simulation FEM simulation of cutting (Abaqus/Explicit, ALE adaptive meshing, JC flow stress and Damage model, Fracture energy based damage evolution) (a) γ= 22º (b) γ= 0º (c) γ = - 30º (d) γ = - 45º 18/25 Modelling and Simulation FEM simulation of scratching Grit tool path Grit (end of simulation) Step-5 Grit (simulation start point) Step-1 Workpiece surface Clearance 3D view during scratching Max. Depth (ap) Y Step-3 100 µm 100 µm 100 µm X 3D FEM model Multi-pass grit simulation with 10 µm apart Total number of elements is 184085 Element size in grit= ~4 µm Element size in the contact area of the workpiece is lower than 1 µm Computational time is approximately 48 hours Stress and deformation during scratching Material accumulation (front pile-up) ahead of the grit 1st pass Residual plastic deformation (a) Plastic + Elastic deformation at the grit-workpiece contact location 2nd pass 3rd pass 19/25 Modelling and Simulation 20/25 FEM simulation of scratching Material deformation with friction: Longitudinal section Cross section at the end of step-2 (a) Frictionless µ=0 (b) Friction coefficient µ=0.1 (c) Friction coefficient µ=0.3 (d) Friction coefficient µ=0.5 Material deformation with friction: Lateral cross section Cross section at the end of step-3 (a) Frictionless µ=0 (b) Friction coefficient µ=0.1 (c) Friction coefficient µ=0.3 (d) Friction coefficient µ=0.5 Modelling and Simulation 21/25 FEM simulation of scratching FEM scratch simulation 4 Frictionless, max.depth=0.5 micron 3.5 Friction=0.2, max.depth=0.5 micron 0.75 2.5 2 Frictionless, max.depth=1 micron 0.7 0.65 Friction=0.2, max.depth=1 micron 0.6 Frictionless, max.depth=2 micron 0.55 Friction=0.2, max.depth=2 micron 0.5 Frictionless, max.depth=5 micron Similar trend obtained along the scratch length 0.45 Friction=0.2, max.depth=5 micron 0.4 0.35 1.5 0.3 50 55 60 65 70 75 80 85 1 300 step-5 200 100 step-4 0 0 0 step-1 step-2 step-3 50 100 150 200 250 Aproximate horizontal distance along grit trajectory (micrometer) Experimental scratch test 300 35 30 2.5 2 25 Pile-up ratio 0.5 Pile-up ratio Pile-up ratio 3 20 1.5 1 0.5 15 0 200 300 400 500 600 10 Scratching direction 5 0 0 100 200 300 400 500 600 Dimensional length along scratch direction (µm) 700 800 900 Modelling and Simulation FEM simulation of scratching Cutting forces along scratch length at different cutting speeds Horizontal distance along grit trajectory (micrometer) 0 0 50 100 150 200 250 300 -0.1 Forces (N) -0.2 -0.3 -0.4 Fx, Speed= 3 m/min Fy, speed= 3 m/min -0.5 Fx, speed= 6 m/min Fy, speed= 6 m/min Fx, speed= 12 m/min -0.6 Fy, speed= 12 m/min Fx, speed= 300 m/min Fy, speed= 300 m/min -0.7 22/25 23/25 Impact of the research Micro EDM; Emerging technology for micro mould manufacturing (medical devices, surgical equipments, biomedical implants etc.) Contacted by Rolls-Royce Plc. to be consulted on blind micro holes and micro slots Micro EDMing (used in sound reflector) Applications of Micro EDM Nozzle for diesel injectors Grinding; • Optimization of machining process • Designing grinding wheel • Prediction of machining quality • Optics, medical, aerospace, mould industry Plastic gear for watches Micro holes on turbine blades (http://www.sarix.com) Publications 19 publications including peer reviewed journals and conferences 24/25 25/25 Thank You...