Laser materials processing
5 Absorbtion of Laser beams 6 Laser Beam Diagnostics and Monitoring 7 Target Beam-Properties for efficient Materials-Processing
5 Absorbtion of Laser beams 6 Laser Beam Diagnostics and Monitoring 7 Target Beam-Properties for efficient Materials-Processing
Set of flashcards Details
| Flashcards | 13 |
|---|---|
| Language | English |
| Category | Technology |
| Level | University |
| Created / Updated | 16.01.2015 / 11.06.2018 |
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Which 3 different kinds of interaction are possible, when laser radiation is incident o material?
- Transmission
- Absorption
- Reflection
Which effect is necessary for the thermal effect on the workpieces?
Absorption degrees (german: Absorptionsgrade) of the lasers used for materials processing on metals are ...?
Which efficent methods concerning the workpiece surfaces are feasible to improve absorption on metals?
- Coating of the workpiece surface with good-absorbing layers, e.g. graphite-sprays.
- Treat the workpiece with an etched surface (german: gebeizt)
- Allow it to build oxide-layers during heated-up (allow contact to air-oxygen during processing, if workpiece can sustain oxides).
How is the absorbtion on plastics with an CO2" Laser?
Which are the 2 measuring principles to measure the intensity-profiles of a beam?
With Explanation!
- Systems, which work with a hollow, insidemirrored copper-needle. The copper-needle guides entering laser beam power to a photoelectric detector located in the rotation-axis. Withsoftware then a 2-dim. pattern of the beampowers is calculated, showing the positions of the measures and the measured beam-powers there.
- Imaging-technology, using a CCD-Photo-Chip. For this purpose here, of course it is heavily necessary to add largely damping glasses set in the optical path before the chip in order not to overheat it.
Advantages of CCD-camera-type systems:
- pulsed-laser beams
- extreme narrow focus-diameters of down to ca. 10 µm
- more variety of wavelengths (using appropri. CCDs).
Definition of a beam-diameter:
The diameter enclosing 86% of all measured beam-power is defined as the focus-diameter.
Thus, the measuring of the intensity-distribution of a beam also delivers the diameter of the beam.
Definition of the focus-diameter df:
The smallest measured diameter in the whole measured caustic of the focussed beam is df.
Shape of the caustic and localization of the focus-plane:
The shape of the caustic (in german: Kaustik) of a focussed beam is developed through the correct vertically positioned of multiple diameter-measurements, see fig. right. The focus-plane is localized along the caustic there, where df had been detected.
All employed devices to measure the laser beam power are of the calorimetric type.
How do they work?
They have absorbing surfaces for the laser beam. Through the heating of the absorber the incident laser beam power can be calculated. Of course, these systems have to be calibrated by the manufacturer prior to the use.
If speed (= high feed-rate) is required in the process: Then important requirements for the laser-beam-properties could be:
- high laser-power PL
- high beam-intensity I (= high PL and narrow df)
If tolerance against mis-positionings of the beam is required in the process: Then important requirements for the laser-beam-properties could be:
For tolerances in the normal direction to the workpiece-surface:
- high ZRf
For tolerances in the lateral direction, perpendicular to the feed-direction:
- high df , or a scanned laser beam (scanned in lateral direction)
If low heat-input / low distortion is required in the process: Then important requirements for the laser-beam-properties could be:
- Narrow df (allowing a feast feed-rate and thus little time for heating up)
- Pulsed beam-operating-mode (allowing cooling time between two high power pulses)
- Wavelength-selective absorption (appropriate beam-wavelength, or appropriate absorption-behaviour of the treated material, or both)
