Ultrakurzpulslaser auf dem Weg in den industriellen Alltag Systemtechnische Herausforderungen und technologische Lösungen

Transcription

1 Ultrakurzpulslaser auf dem Weg in den industriellen Alltag Systemtechnische Herausforderungen und technologische Lösungen Arnold Gillner, Fraunhofer Institut für Lasertechnik Aachen

2 Motivation Advantages of ultrashort-pulsed Laser Machining Flexible tool with no material dependance Wide bandgap materials (Glass, Sapphire, Diamond) Semiconductors (Silicon, GaAs, SiC) Metals (WC, Steel, Copper) Polymers Biological materials High Accuracy Sub 100 nm precision in ablation depth Material selective processing In volume processing Tool independent processing Tool-free, wear-free and resource-efficient Almost no lead-time (Digital Photonic Production) Universal application (due to high variety of parameters)

3 Motivation Areas of application Tooling Safety Display Biotechnology Medicine Telecom Printing Aerospace Automotive Energy Electronics Consumer Goods

4 System development Lasers for ultra short pulse ablation Average Power: Pulse duration: Repetition Rate: Pulse Energy: Pulse Power: up to 1 kw 200 fs 600 ps khz Multi-MHz µj mj (typ. < 10 µj) 100 MW Intensity: 100 TW/cm 2 = W/cm (10 µm) 2 Ablation Rate: Wavelength up to 20 mm 3 /min (typ. < 5 mm 3 /min) 266 nm nm

5 Number of Lasers per Year Future Developments Market Size of Ultrafast Lasers Estimated market growth for the next years: ca. 30 % UKP wird das Anwendungsspektrum extrem verbreitern (Schmitz, Fa.Trumpf) 800 UKP wird zukünftig in der Mikromaterialbearbeitung ihren großen Auftritt haben, auch wenn sie derzeit noch nicht die ganz große Rolle spielt 600 (Frauenpreiß, Fa.Rofin) We have just seen the tip of the ice berg when it comes to ps-laser micromachining (Nebel, 400 Fa.Lumera) Ultra short pulsed lasers are gaining 50 % every year and will drive MICRO in 200 the future (Ullmann, Fa. Laserline) Year market estimation by Fraunhofer ILT

6 Requirements for industrialisation of ultrafast laser processing Process analysis Process model and process understanding Understanding Process simulation Adapted optics for improved use of ultrashort pulsed laser properties Adapted system technology for optimized energy deposition and increase of processing speed High speed trepanning in laser drilling System Development Process Transfer Ultrafast laser scanning Multiple beam processing approach

7 Ultrafast Laser Motivation and Basics Pulse interaction with metals Time Ranges of Energy Transfer Photon Electron: <10 fs Electron Electron: <100 fs Electron Lattice: 1-10 ps No interaction of radiation with vapour and melt Ablation mainly by vapourisation Minimal thermal influence

8 Overlap 70 % Groove depth / width [µm] Laser Cutting Experimental low laser fluence Saturation level Depth@70 % Width@70 % Depth@99 % Width@99 % Number of passes Pulse overlap : 70 % / 99 % Rep.-Rate : 2.5 MHz Scan speed : 9 / 3 m/s Spot diameter: 11 µm Pulse energy : 1 µj Fluence : 1,1 J/cm² Focal plane on the surface

9 Limit angle (measured) =73 Explanation for ablation-stop /-contour (asymptotic) Ablation region Limit angle (computed) =74,74 Projected (and so absorbed) intensity decreases with angle of incidence below a specific critical angle (limit angle), i.e. below ablation threshold. This is the explanation for the observed ablation stop and the triangular shape of the ablation contour. Page 9

10 Analytic Ablation Contour Intensity Distribution Asymptotic ablation contours TopHat I r) I 1 r ( 0 Gauss ODE determining the contour: Erfc-Function is the physically correct contour. Ablation mechanism leading to this contour is identified! I0 z( r) 1 I thres r 1 r Page 10

11 Groove depth [µm] Groove width [µm] Comparison to experimental results =Erf-Fit ,5 µj 5 µj 7,5 µj Repeats E p = 2,5 µj E p = 5 µj E p = 7,5 µj ,5 µj 5 µj 7,5 µj Repeats Pulse overlap: 50 % Rep.-Rate: 400 khz Scan speed: 2 m/s Spot diameter 11 µm Pulse Energy: 2,5 / 5 / 7,5 µj Fluence: 1,6 / 3,2 / 4,8 J/cm² Focus on the surface Page 11

12 Ultrafast Laser Motivation and Basics Laser Ablation with (Ultra-)short pulse Laser Time for manufacturing 10 hours Ablated volume 100 mm 3 Quality of ablation comparable to EDM No tools needed ns-laser ps-laser Eroded

13 Functional Surfaces Micro injection moulding of lens arrays with ps-laser Surface quality After Laser ablation: R a = 300nm After Laser polishing: R a = 100nm

14 High speed trepanning optics for Laser drilling Animation of the Helical drilling optics

15 Laser Drilling Drilling with Helical Drilling optics Laser parameter: 515nm, 5ps 3 (30 µj) Spot diameter: 15 µm Stainless steel: d=0.5 mm Drilling time: 5 sec Diameter: 60 µm Shape: Cylindrical Entrance Exit

16 Laser Drilling Cylindrical holes with high aspect ratio of 1:20 10 µm 100 µm Stainless steel: 1,1 mm; Drilling time 10 sec. Diameter: 60 µm, Shape: cylindrical 10 µm

17 Laser Drilling Drilling with Helical Drilling optics 25 µm 25 µm R a <2 µm 100 µm Stainless steel: 1,1 mm Drilling time: 45 seconds Diameter 60 µm / 220 µm

18 Hole diameter [µm] Variation of drilling taper Laser parameters Repitition rate f = 10 khz Pulse energy E p = 0.7 mj Process parameters Focal plane on the surface Process gas 2.5 bar O 2 Material X5CrNi18-10 Material thickness d = 1 mm Drilling time t = sec Rotation speed n = 3000 rpm Raw beam shift = -2-2 mm Raw beam tilt α = 0 Entrance Exit Entrance Exit 50 µm 50 µm 50 µm 50 µm Page Ø Entrance Ø Exit -2-1,5-1 -0,5 0 0,5 1 1,5 2 Beam parallel shift[mm]

19 System strategies for productivity increase Increase of average laser power high pulse energy / low reprate t Insufficient engraving result t high reprate / low pulse energy? Overheating due to low scanning speed

20 High Speed Scanning Technologies Akusto-optic Deflector Galvo Scanner Polygon Scanner Laser Quelle: Nikon MicroscopyU, Distribution of Energie by fast beam scanning Different approaches : AOD, Polygon Mirror, EOD, Piezo Mirror, Challenges: High Power, large scanning angle, high efficiency

21 High speed processing by high speed scanning using a Polygonic Mirror Max. Scan velocity: 340 m/s (max. rpm: ) Focal distance: 163 mm Focal diameter: µm Scan-field: 100x100 mm 2 Data import: Bitmap, PNG, 2D Array (Gray-scale value corresponds to number of Layers) Additional linear motor Number of mirrors: 11 Max. Output Frequency: modulated 20 MHz; digital 40 MHz

22 Multi parallel processing using Interference Technique 22

23 Multi parallel processing using Interference Technique Parameter Laser: 355nm, 400kHz, 10 ps Material: Brass Spot size: µm Feed rate: 4500 mm/min Periodicty: 780 nm line structure hole structure Spot by spot pulse overlap

24 Enhancing productivity: Massive parallel processing using beam splitting by diffractive optical elements (DOE) USP-Laser source DOE 2x2 Ultrafast-Laser with high pulse energy Mask mxn Diffractive Optical Element

25 Massive parallel processing using beam splitting by diffractive optical elements (DOE) Periodic pattern with n x m spots Movement of spot pattern with the scanner system Typical period of pattern: 0,3-2 mm Optical efficiency >70 % Spot uniformity > 93 % Semi-automated alignment Exchangeable beam splitter Masking of unwanted higher orders Masking of main orders to reduce number of spots (x and y direction)

26 Massive parallel processing using beam splitting Laser Structuring of Motor Components Aim: reduction of friction and wear Structures act as oil reservoir and a hydrodynamic bearing Compromise between efficiency and oil comsumption 27

27 Machining technology: Development of scanning systems & processing heads for cylinder liner processing Fixed scanning system for fast beam movement Relay optics Rotating processing head Laser focus

28 Wear depth[µm] Multi parallel Laser processing of piston rings Coating & micro structures 2,0 1,5 flat 1,3 F N F R Parallel structuring of piston rings with multiple beams Laser: ultrafast laser 6 ps Pulse energy: up to 300 µj 1,0 0,5 0,0 1 structured 0,5

29 Multibeam Scanner Drilling of foils Drilling speeds > holes /sec possible High reproducibility High circularity Use of different drilling technologies Single Pulse Percussion Helical drilling Possible Applications Filter Via holes masks

30 Werkzeugsystem für die UKP Materialbearbeitung Produktivität Multistrahl-Optik Integrierte Software 5 mm Sensorik zur Prozessüberwachung und Bauteilvermessung Einfaches Einrichten

31 Zustimmung in % der Beteiligten Marktanalyse UKP Umfrageergebnisse UKP-Workshop % 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Hemmnisse bei der industriellen Umsetzung von UKP Prozessen!!! alle Anwender n=81

32 Volle Zustimmung in % der Beteiligten Marktanalyse UKP Umfrageergebnisse UKP-Workshop % 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Zukünftiger Bedarf bei Laser und Systemtechnik im UKP-Bereich! alle Anwender n=81

33 Photonics production: Ultrafast Manufacturing using Ultrafast Lasers Today: Typical ablation rates of e.g. Aluminum ca. 1 mm 3 /min Limited by max. Laser power and Scanning speed Future potential: Ablation rates of >5 mm 3 /sec Use of fast deflection systems and >1 kw average Power Direct manufacturing of small components e.g. with specific surface features