Piezo based beam shaping for high dynamic laser material ...€¦ · MOTION | POSITIONING STRICTLY...

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Physik Instrumente

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Piezo based beam shaping for high dynamic laser material processing in 3DEPIC Event on High Power Laser 2019, Almelo NL

Mr. Lukas Rau

PBPS| lde | © PI 2019


STRICTLY CONFIDENTIAL 2

Today’s laser material processing


Picture courtesy: Fraunhofer IWS

▪ Laser machining processes are more and more

relevant for various industrial applications

▪ Combination of operational speed, achievable

quality and workpiece thickness mainly determine

the outcome of laser machining processes

▪ There is still potential for process enhancement

aiming for…

▪ …faster process speed with improved quality

▪ …controlled energy distribution in the work piece

▪ …deeper penetration with high frequency oscillations

Example : How process speed slows

down with increasing thickness of

sample

Example for improvement of laser weld seam

using high-frequency oscillation

conventional

High freq. osc.500μm



“PISTOL³” project: development of high dynamic focus shifter module

▪ Sponsored by German Federal Ministry of Education and Research (BMBF)

▪ Project partners:

▪ Fraunhofer IOF - optic-mechanical design focus shifter

▪ Fraunhofer IWS - process integration of focus shifter

▪ PI Ceramic GmbH - Piezo technology, electronic control

▪ Optics Balzers - optical / dielectric coating

▪ Kjellberg - end user welding & cutting

▪ Heliatek - end user structuring

Abteilung | Kürzel | © PI 2017



Physic Instrumente GmbH & Co. KG


▪ PI’s in-house core technologies

▪ Drive technologies:

Piezo, magnetic direct drives and

voice-coil solutions

▪ Sensors:

Capacitive sensors, SGS and optical

incremental encoders

▪ Motion controllers:

Low-noise, dynamic with adjusted

control concepts



Process improvement by Piezo basedfocus shifter module

▪ Solution

▪ Piezo based deformation of mirror membrane

▪ Elliptic membrane due to 90° beam deflection

▪ Dielectric coating for high reflectivity

▪ Use of PICA Thru© actuators


Deformation

Mirror

membrane with

dielectric coating

PICA Power

Piezo actuator

Schematic of Piezo based focus shifter device

Clamping at

mirror housing

▪ PICA Thru© actuators

▪ Large choice of designs

▪ Microsecond response time

▪ Extreme reliability > 109 cycles

Laser beam

deflected

by 90°

PICA Thru© high-voltage ring actuators

(H x OD x ID = 40mm x 10mm x 5mm)



kHz

4min

4max

3

2

1

5

6

Specs of focus shifter module


▪ Operating conditions

▪ Drive frequency up to 2 kHz

▪ Future aim is a drive frequency up to 4 kHz

▪ Stroke of 28 µm realizes a mean shift of

the focus plane by 15 mm (prototype status)

▪ Electronic control

▪ Analog input of 10 V

▪ Strain gauge for monitoring

▪ For reliability, temp sensors at stack and

membrane

▪ Piezo high-power controller (E-481 or E-482,

amplifies 10 V signal to 1000 V )

1 = laser beam, 2 = high dynamic focus shifter

module, 3 = focus lens, 4 = beam focus,

5 = work pieceE-481 / E-482 PICA Piezo high-power amplifier/controller



Features of focus shifter module


Piezo based focus shifter module

▪ Major process features

▪ Faster cut due to high-speed focus oscillation

▪ Increased weld quality due to reduced stress

▪ Design features

▪ Compact 3” housing, reduction to 2” possible

▪ Easy to integrate into existing systems

▪ Cost effective solution

▪ Little investment costs

- compact size, high life time

▪ Reduction of process costs

- easy integration into existing system

▪ Long lifetime

▪ High durability of Piezo actuators

▪ Proper temperature management required



Constraints for temperature management

▪ Operating temperature limited to 150°C,

mostly due to vulnerability of solder spots

▪ Heat sources

▪ Self-heating of Piezo ceramic (predominant)

▪ Dielectric losses

▪ Proportional to voltage, frequency, dielectric loss factor etc.

▪ Absorbed laser power (beam with up to 4 kW)

▪ 99.2% beam energy directed to work object

▪ 0.8% undergo scattering (dominant) and absorption (less dominant)

▪ Consequence: limited drive frequency

without cooling of 350 Hz at 1000 V


Top left: absorption only at mirror surface

[Fraunhofer IOF]; right: temperature of stack at

350Hz, 1000V



Optimization of temperaturemanagement

▪ Design analysis

▪ Thermal simulation to predict stack heating

▪ Fluid simulation to predict stack heating with coolant

▪ Validation and calibration

▪ Execution of numerous experiments

for calibration of simulation models

▪ Calibration approach

▪ Thermal simulation: conductivity coefficient

▪ Flow simulation: flow velocity


Top: forecast of velocity vectors (coolant) and stack

temperature; bottom: measurement setup



Characteristics of focus shifter moduleand its operation

▪ Highly efficient air cooling

▪ Temperature well under control

▪ Pressurized air of 3 to 6 bars required

▪ Achievable drive frequency

▪ Assuming air pressure of 6 bars and

linear extrapolation of the curves

▪ 2 kHz → validated for current design

▪ 4 kHz → feasible, requires a redesign

of mechanics and electronics


20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

Tem

per

atu

re (

°C)

Frequency (Hz)

at 1000v 3 bar

at 1000v 6 bar

Linear (at 1000v 3 bar)

Linear (at 1000v 6 bar)

Process limit



Currently running validation of cutting process (Fraunhofer IWS, Dresden)


▪ Example for process validation: Cutting of 10 mm

stainless steel with 3 kW laser power

▪ Cutting speed increased by 60% (optimum process

parameters at 100 Hz, 13 mm focus shift )

▪ Unchanged or even better cut edge quality

▪ High potential for further improvement, e.g.

operating frequency will be increased to > 1 kHz

w/o focus shifter: 0.5 m/min w focus shifter: 0.8 m /min

1. Beam deflection, 2. HiDyn module,

3. collimation, 4. focusing, 5. work piece

2

1

3

4





Currently running validation of welding process (Fraunhofer IWS, Dresden)


▪ Test and validation goals

▪ Processing of hard-to-weld Al die-cast and coated steel plates

▪ Achievement of significant process stability for

improvement of weld seam shape and quality

▪ Replacement of conventional galvo scanners for

high-frequency oscillation and higher welding speed

▪ Thus more simple optical setup and process control

2

13

4

5

Influence of the operating frequencies on the weld seam shape 1. Beam deflection, 2. HiDyn module,

3. collimation, 4. focusing, 5. work piece



Summary

▪ Topic:

Development of focus shifter module for improvement of laser cutting (faster

cutting speed) and welding (increased weld seam quality) processes

▪ Validation:

▪ Already accomplished steps:

▪ Validated control of temperature management also at higher operating conditions

(≤ 1 kV, ≤ 1 kHz) through simulation and test

▪ Improvement of cutting speed by 60% (specimen: 10 mm stainless steel, 3 kW laser power;

operating conditions: 100Hz, 13 mm focus shift)

▪ Steps still to come:

▪ Determination of process limits (max. frequency with full stroke) for welding and cutting process

▪ Analysis of cutting process by variation of material, work piece thickness, optical setup etc.

▪ Analysis of welding process regarding weld seam quality

▪ Next Goal: Market launch of focus shifter module in 2020




Physik Instrumente

© 2019 Physik Instrumente (PI) GmbH & Co. KG

Using these texts, images and drawings is only allowed with

consent of PI and by indicating the source.

Physik Instrumente (PI) GmbH & Co. KG

Auf der Roemerstrasse 1

76228 Karlsruhe

Germany

Phone +49 721 4846-0

E-Mail [email protected]

Visit us: www.pi.ws




Power as a function of frequency and voltage

16

0

10

20

30

40

50

60

70

80

90

100

600 650 700 750 800 850 900 950 1000 1050

Po

we

r (W

)

Voltage (V)

Power at 300 Hz

Power at 2 kHz

Power at 3 kHz

Power at 4 kHz

High Power High Temperature

𝑃 =𝜋

4. 𝑓. 𝑐. 𝑡𝑎𝑛𝛿. 𝑉𝑝𝑝

2

P = power dissipated [W]

f = operating frequency [Hz]

c = capacitance [F]

tan δ = dielectric loss factor

Vpp = peak to peak voltage [V]


Calculated using:

Backup

For Q&A



Radius of Curvature: 1 DoF vs. 2 DoF(Fraunhofer IOF, Jena)

▪ Spot for a mirror with one degree of freedom 1 DOF

▪ Correction of elliptical distortion with a mirror of 2 DOF


Spot

Deflection α = 0° Deflection angle α = 90°

0

2

4

6

8

10

0 15 30 45 60 75 90 105 120 135 150

Rx/

Ry

Deflection angle [°]

𝑅𝑥 = 2𝑅𝑦𝑅𝑥 = 𝑅𝑦

w/o correction (1 DoF)

y [µm]

0

2000

-2000

x [µm]02000 -2000

y [µm]

0

80

-80

x [µm]0 80-80

w correction (2 DoF)

Backup

For Q&A



Max. temperature simulated- without cooling

18

0

100

200

300

400

500

0 500 1000 1500 2000 2500 3000

Tem

pe

ratu

re (

°C)

Frequency (Hz)

Temp Measured at 700 V

Temp Simulated at 700 V


Boundary conditions:

• Uniform power distribution

• 700 V is considered to ensure safe

working condition for the actuator

in the absence of cooling

Backup

For Q&A



This presentation was presented at

EPIC Meeting on High Power Laser Systems 2019

HOSTED BY

SILVER SPONSORS

BRONZE SPONSORS

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