Application and performance of kw-class singlemode fibre lasers in the cutting of non-oriented electrical steel

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Mitchell Norman
5 years ago
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1 Application and performance of kw-class singlemode fibre lasers in the cutting of non-oriented electrical steel Authors: Steve Norman, René Siebert, Andy Appleyard, Harry Thonig, Andreas Wetzig, Eckhard Beyer

2 Content 1. Introduction: Rationale and scope of study 2. Application Overview / Technical challenges 3. Singlemode kw OEM Laser Beam Source & Characterisation 4. Cutting Trials and Results Analysis 5. Conclusions

3 Rationale & Scope 1. Rationale E-mobility projects focused on energy efficient drive trains - Battery technology / electric motors / drive electronics Typical process for stator / rotor involves mechanical punching Previous studies with CO 2 & Disc lasers have demonstrated impact of HAZ on laser-cut laminations Future trend towards thinner laminations / higher Si-content (more brittle) for lower losses / higher speeds 2. Scope Investigation & Optimisation of cutting process for prototyping / batch manufacturing non-oriented electrical steels using SINGLEMODE kw-class fibre lasers Comparison of magnetic performance against conventional guillotined parts

Application introduction electrical machine application core manufacturing cut rotor & stator laminations stack production: cut electrical steel laminations are assembled into magnetic cores by

4 Application introduction electrical machine application core manufacturing cut rotor & stator laminations stack production: cut electrical steel laminations are assembled into magnetic cores by automated stacking, riveting, welding or sticking copper/aluminium wire inserting Reference Sample geometry, parallel / perpendicular to rolling direction (RD) Chosen to represent stator equivalent geometry Reference sample geometry and cutting direction Figure: example core design

Integrated driver boards and local control unit provide status

5 SPI s kw OEM Laser Platform Pumped laser cavity with single mode/ multimode delivery fibre. Integrated driver boards and local control unit provide status and integrity monitoring and self protection capability. Customer supplied PSU and laser control system.

6 kw Single-Mode Power scaling: 2-Stage GTWave Architecture Seed Laser Power Amplifier HR OC PD PD QBH / LLK-D BDO RAL HB Pump Module HB Pump Module HB Pump Module HB Pump Module HB Pump Module All-fibre, integrated monolithic design:- High-brightness beam-combined pump modules (~400W / module) Power Scaled to 500W Oscillator and 1kW 2-stage MOPA

7 kw OEM Laser: Power Linearity Instantaneous output power vs set current 1200 Output Power vs Pump Current (%) Output Power, Watts % 20% 40% 60% 80% 100% Percentage Drive Current

8 kw OEM Laser: Open-Loop Power Stability (1000hr soak rated power) Open-loop operation for 1000hrs+ at rated current / power Output Power vs Pump Current (%) 1000 Power(W) Output Power, Watts % 20% 40% 60% 80% 100% Percentage Drive Current Time (hrs)

9 kw OEM Laser: Modulation response (for PSO-controlled cutting) Digital Modulation: 1000W modulation 10kHz Power (arb units) Time (usec) Analogue Modulation: 1000W SineWave 5kHz Power (arb units) Signal Trigger Signal Set Point Time (usec) Voltage (V) Voltage (V)

10 Laser Cutting Test Cell & Cutting Heads Precitec Laser Mechanisms Inc (LMI)

11 Process Investigations > 40 different process conditions were tested, always on M330 steel, 0.35mm thick Preferred conditions chosen on the basis of cut quality / process stability / speed For the selected processes, full range of samples at varying angles to the material s rolling direction were produced for subsequent characterisation by Fraunhofer IWS Configuration / Parameter Defined value / range Process Rationale Spot Size, 1/e 2, µm Nominal 25µm Optimised kerf width, low HAZ Process Assist gas Beam Source Power Range, Watts Nitrogen, pressure controllable over range 0 bar to 14 bar 200W 1000W Inert gas to avoid additional thermal input / oxidisation Key variable for process optimisation Cutting Speed, m/min 20m/min 35m/min Key variable, targeting maximum Cut sample dimensions, mm x mm x mm 250 x 30 x 0.35 and 60 x 60 x 0.35 Standard sample size for subsequent magnetic characterisation Cut quality assessment Visual (Cut edge / HAZ / dross) Subjective based on criteria for cutting non-electrical steels

12 Beam Characterisation: Focused Spot Measurement using PRIMES MicroSpot Monitor Cutting Head Optical Configuration Collimator: 100mm FL Focus lens: 125mm FL Nominal Spot Size: 25μm

13 Fine Kerf Precision Cutting of Magnetic steels: Advantages of Single-Mode Beam Quality Advantage of Singlemode for Fine Kerf Cutting 25um Spot, BPP = 5, M2 ~15 25um spot, BPP = 1, M2 ~ 3 25um spot, BPP = 0.35, M2 ~ um Spot, Rayleigh Diameter (35.0um) 0.11mm 25.0µm beam waist 0.03mm Rayleigh Range Beam Diameter 0.31mm Distance above Focus, mm

14 Focused Beam Source Characterisation: Thermal Lensing & Rayleigh Range 30 Thermal Lensing Characterisation (100/125 Lens configuration) 0.5 1/e 2 spot size, µm /e2 Spot Size, um Rayleigh Range, mm Rayleigh Range, mm Power, Watts

15 Cut-Sample Characterisation: Experimental strategy Hysteresis loops of various samples 1. fibre laser cut 2. conventionally cut by guillotine Measuring strategy 1. specific core loss index for efficiency 2. required magnetic field strength to reach certain polarisation index for maximum torque & power increase Cross section investigation Edge quality / HAZ / metallurgical tests Hysteresis loop measured with Brockhaus SST

16 Cutting Results Lateral Cross-Section M330 Steel sheet Fibre laser cut Conventionally cut by guillotine

17 Magnetic Parameter Determination acquired from Hysteresis Loops

18 Discussion of results Magnetic Performance 1. The variation of specific core losses with magnetic polarisation was not influenced by the choice of the cutting technique employed 2. SM FL processed samples might require a lower magnetic field to achieve certain polarisation ( torque ) consequently less electrical current in the copper windings; this potential benefit would be achieved without any further significant core losses in the corresponding range of polarisation

19 Conclusions 1. Singlemode fibre-laser-cut parts can match or exceed the magnetic performance of conventionally processed guillotine-cut parts. 2. Cut-edge quality of the FL-cut parts was dross-free and burr-free, and the corner edge of the laser-cut parts showed less deformation than mechanically stamped material. Further work is required to assess downstream wire-winding process / cut-through risks etc 3. The assembly of multi-layer laminations should be significantly improved using laser-cut parts ( stacking factor ).

Dr Jack Gabzdyl Product Line Manager Pulsed Lasers

AILU PHOTONEX 08 16 th October 2008 Fiber Lasers for Medical Applications Dr Jack Gabzdyl Product Line Manager Pulsed Lasers General Advantages of Fibre Lasers Beam Quality & Stability Diffraction-limited