Laser Polishing of Metals. Fraunhofer Institute for Laser Technology ILT Steinbachstraße Aachen (Germany)

Transcription

1 Laser Polishing of Metals Fraunhofer Institute for Laser Technology ILT Steinbachstraße Aachen (Germany)

2 Content Laser Polishing of Metals - Basics 3D Laser Polishing Examples of Laser Polished Parts Page 1

3 Process Principle Remelting of a thin surface layer and smoothing of surface due to surface tension Nearly no material removal cw laser radiation Laser radiation P L, f L β v S v S laser polished initial surface roughness l Scan dy γ b Track d Laser remelted layer melt pool heat affected zone solid Page 2

4 Process Variants Macro polishing Micro polishing Laser radiation continuous wave (cw) pulsed ( ns) Scheme cw laser radiation laser radiation v S v S laser polished remelted layer melt pool initial surface roughness laser polished remelted layer melt pool initial surface roughness heat affected zone solid heat affected zone solid Remelting depth µm < 5 µm Processing time 7-60 s/cm² 1-10 s/cm² Initial surface roughness milled, turned or EDM- processed Ra = µm ground and fine-milled Ra = µm Achievable surface roughness Depending on material, quality of material and initial roughness Ra = µm / Rz = µm Page 3

5 Main Influencing Variables of the Material z Initial roughness λ Wave length λ Amplitude z Material properties Heat conductivity / heat capacity Absorption Viscosity / surface tension Melting and evaporation temperature Homogeneity Grain size Segregations Inclusions Medium diameter Distribution Page 4

6 Overview of Surface Structures Macro Polishing Remains of initial roughness Ripples Undercuts Step structures Bulges Martensite needles Page 5

7 Overview of Surface Structures Micro Polishing Undercuts Border-Bulging Process-induced Micro-Waviness Holes Step-Structures Micro-Structures + Remains of initial roughness Material-induced Page 6

8 Analysis of Surfaces with Roughness Spectrum WLI measurements with different magnifications λ = 5-10 µm 1,000 Micro Roughness Meso Roughness Macro Roughness 20µm 100µm 400µm Phase-correct profile filter λ = µm λ = µm λ = µm Rauheit Ra [µm] Roughness Ra [µm] 0,100 0,010 0,001 0,6251,25 2, Ortswellenlänge Spatial wavelength λ [µm] Page 7

9 Content Laser Polishing of Metals - Basics 3D Laser Polishing Examples of Laser Polished Parts Page 8

10 CAM-NC-Data Chain for Laser Polishing of 3D Surfaces CAM-Software Technology Processor 3D Laser Polishing Machine NC CAD Model APT + Scanner Part Tool path calculation Adaption of tool paths Fully automated processing Application database Page 9

11 Machine Kinematics Base Machine + Laser Scanner 5-axis base machine Optics: 3-axis laser scanner Y H Collimator Converging Lens Y H XH Z H Optics A H Optical fiber Diverging lens A H C H Workpiece F-Theta-Lens ZS YS - v, a small + travel range large + v > 5 m/s, a > 1000 m/s² - travel range small XS --> v base-machine << v processing Page 10

12 Industrial Machine Tool for Laser Polishing Medium to Large Parts (Karl H. Arnold Maschinenfabrik GmbH & Co. KG) 3-axis laser scanner and 5-axis portal machine with XYZ-AC kinematics Designed for parts with up to 100 kg Ergonomic process chamber Solid-state laser beam source (continuous wave or pulsed) Optional: Tactile probe for determination of part orientation, Process gas system with more than one inert gas Page 11

13 Industrial Machine Tool for Laser Polishing Small Parts (Fraunhofer ILT) 3-axis laser scanner and 6-axis robot with pneumatic gripper Suitable for complexly shaped parts up to 1 kg Glovebox process gas chamber with automated airlock Solid-state laser beam source (continuous wave or pulsed) Optional: Triangulation sensor, Interior processing optics for bore or tube polishing Page 12

14 Content Laser Polishing of Metals - Basics 3D Laser Polishing Examples of Laser Polished Parts Page 13

15 Examples for laser polished parts (Fraunhofer ILT) Blow mold Stavax, Embossing tool plus (Bosch) manufactured product 10 mm 10 mm laser polished tool Impeller, Titanium (MediKomp) grinded Tool for glass making milled 10 mm laser polished 20 mm laser polished Page 14

16 Results on GGG40 Moulds for Glass Forming Polishing of freeform surfaces Material GGG40 Achievable roughness: Ra = 0.35 µm Processing time: 40 s/cm² Change in mechanical properties (e.g. increased hardness) in remelted layer 20 mm Laser polished Manufactured with laser polished mould Initial surface Page 15

17 Selective Laser Polishing Process Chain Digitalization of leather textured freeform surface Using selective median filter to eliminate errors of measurement Separation of work piece geometry and leather texture by Fourier analysis Separation of elevations and dips by histogram analysis Correction of laser beam dimension Selective laser polishing of work piece Dual gloss effect on workpiece Page 16

18 Tooling Industry Two-Gloss-Level Design by Selective Laser Polishing Selective laser polishig of matt surfaces Circle pattern Selective laser polishing of photo chemical etched surfaces Polishing only of the pits in the tool Initial surface 2 mm 2 mm Ridges not polished Laser polished pits Page 17

19 Tooling Industry Polishing of Micro-Lens Arrays Light scattering surfaces by 1. laser ablation (ps-laser) and 2. laser polishing (ns-laser) Tool steel (X38CrMoV5-1) Structure depth: 35 µm Structure width: 120 µm 1 mm Page 18

20 Medical Engineering Dental implants Polished area Material: Ti Grade 4 Initial state: turned Laser-on-workpiece time: 0.53 s 5 mm As-received (turned) Laser polished 50µm 50µm Page 19

21 Medical Engineering Ventricular Assist Device (VAD) Polishing of the entire surface except the exterior of the wings Manual polishing: 3 h Laser polishing: approx. 5 min Initial state (milled) Laser polished 1,000 Roughness Ra [µm] 0,100 0,010 Initial state Manual polishing Laser polishing 0, ,25 2, Spatial wavelength λ [µm] 10 mm 50µm 50µm Page 20

22 Conclusion - Laser Polishing of Metals Laser polishing is feasible for 3D geometries, automated and fast (almost independent of complexity). Offers new possibilities for functional and tribological surfaces, medical applications, design surfaces and many more Page 21