Jakob Skov Nielsen

Multibeam fiber laser cutting

The appearance of the high power high brilliance fiber laser has opened for new possibilities in laser materials processing. In laser cutting this laser has demonstrated high cutting performance compared to the dominating cutting laser, the CO2 laser. However, quality problems in fiber-laser cutting have until now limited its application to metal cutting. In this paper the first results of proof-of-principle studies applying a new approach (patent pending) for laser cutting with high brightness and short wavelength lasers will be presented. In the approach, multibeam patterns are applied to control the melt flow out of the cut kerf resulting in improved cut quality in metal cutting. The beam patterns in this study are created by splitting up beams from two single mode fiber lasers and combining these beams into a pattern in the cut kerf. The results are obtained with a total of 550 W of single mode fiber laser power. Burr free cuts in 1 mm steel and aluminum and in 1 and 2 mm AISI 304 stainless steel is d...

A self-calibrating robot based upon a virtual machine model of parallel kinematics

ABSTRACT A delta-type parallel kinematics system for Additive Manufacturing has been created, which through a probing system can recognise its geometrical deviations from nominal and compensate for these in the driving inverse kinematic model of the machine. Novelty is that this model is derived from a virtual machine of the kinematics system, built on principles from geometrical metrology. Relevant mathematically non-trivial deviations to the ideal machine are identified and decomposed into elemental deviations. From these deviations, a routine is added to a physical machine tool, which allows it to recognise its own geometry by probing the vertical offset from tool point to the machine table, at positions in the horizontal plane. After automatic calibration the positioning error of the machine tool was reduced from an initial error after its assembly of ±170 µm to a calibrated error of ±3 µm. Excelling by speed, the calibration was executed in less than 3 min.

Calibration of a numerical model for heat transfer and fluid flow in an extruder

This paper discusses experiments performed in order to validate simulations on a fused deposition modelling (FDM) extruder. The nozzle has been simulated in terms of heat transfer and fluid flow. In order to calibrate and validate these simulations, experiments were performed giving a significant look into the physical behaviour of the nozzle, heating and cooling systems. Experiments on the model were performed at different sub-mm diameters of the extruder. Physical parameters of the model - especially temperature-dependent parameters - were set into analytical relationships in order to receive dynamical parameters. This research sets the foundation for further research within melted extrusion based additive manufacturing. The heating process of the extruder will be described and a note on the material feeding will be given.

Laser cutting - From 200 watt to 12 kilowatt

Laser cutting is the most widespread industrial application of high power lasers. The development of this process was initiated around 1970, when scientists at TWI first demonstrated laser cutting with coaxial gas assistance. 10 years later, the polarisation problem was solved and the technology got its breakthrough. Since then some 30,000 laser cutting systems have been installed worldwide, making the laser an important cutting tool in modern industry.In this paper some major development of the laser cutting process is described. The paper is focussing on some of the major cutting head developments, and includes examples from recent mirror based laser cutting development at high power.

Recent Results in High Power CO2-Laser Cutting for Shipbuilding Industry

In 1997 a high power laser cutting and welding test facility was established at the Danish shipyard Odense Steel Shipyard (OSS).This laser cell was equipped with state-of-the-art lens based cutting optics and optics for laser welding and shop primer removal. The laser was a 12 kW CO2-laser with motorized internal mode aperture, which could improve the beam quality at reduced laser power (approximately 6 kW).Initially laser cutting was performed with the lower order mode and lower power level.However, some research and development projects were initiated in order to establish the basis for applying the full power of the laser for laser cutting, by developing mirror based cutting systems.In this paper the results of these projects will be presented.Both off-axis and coaxial laser beam/gas jet configurations have been tested and results from both types are presented.The off axis nozzle arrangement demonstrates high cutting performance. However, such systems are very sensitive to the proper beam/nozzle alignment and though difficult to apply for contour cutting production.A novel cutting head, delivering coaxial laser beam and gas jet, has demonstrated more than a doubling of laser cutting speed, compared to state-of-the-art lens based laser cutting. This has been achieved by increasing the laser power at the workpiece from 4 kW to above 10 kW.The off-axis nozzle arrangement is showing higher performance at the same power level as the coaxial cutting heads. However, the coaxial cutting heads are much easier to operate in contour cutting.In 1997 a high power laser cutting and welding test facility was established at the Danish shipyard Odense Steel Shipyard (OSS).This laser cell was equipped with state-of-the-art lens based cutting optics and optics for laser welding and shop primer removal. The laser was a 12 kW CO2-laser with motorized internal mode aperture, which could improve the beam quality at reduced laser power (approximately 6 kW).Initially laser cutting was performed with the lower order mode and lower power level.However, some research and development projects were initiated in order to establish the basis for applying the full power of the laser for laser cutting, by developing mirror based cutting systems.In this paper the results of these projects will be presented.Both off-axis and coaxial laser beam/gas jet configurations have been tested and results from both types are presented.The off axis nozzle arrangement demonstrates high cutting performance. However, such systems are very sensitive to the proper beam/nozzle alignm...