Dirk Petring

Dynamics of ripple formation and melt flow in laser beam cutting

The dynamical behaviour of the laser beam fusion cutting process of metals is investigated. Integral methods such as the variational formulation are applied to the partial differential equations for the free boundary problem and a finite dimensional approximation of the dynamical system is obtained. The model describes the shape of the evolving cutting kerf and the melt flow. The analysis is aimed at revealing the characteristic features of the resultant cut, for example, ripple formation and adherent dross. The formation of the ripples in the upper part of the cut, where no resolidified material is detectable, is discussed in detail. A comparison with numerical simulations and experiments is made.

High speed laser cutting of thin metal sheets

Increasing productivity in splitting up of metal sheets by means of mechanical cutting processes is today limited by long change-over times as well as nonproductive times and insufficient quality caused by tool wear. In the case of high-quality materials even a slight quality reduction concerning development of dross attachment and induced stress leads to a lot of rejects. In order to increase the cutting speeds within a range economical for industrial use, i.e. about 100 m/min, a completely new type of laser cutting process had to be developed. As opposed to conventional laser cutting, during which a semicylindric cutting front is formed, a closed keyhole with subsequent melt film ejection is produced during the completely new laser cutting process. The incoupling of energy no longer only results from pure surface absorption but in addition from plasma formation and multiple reflection. With the help of the wear resisting tool `laser the cutting quality is constantly good and can even be significantly improved in comparison with the conventional cutting method with circular knifes. In the case of a sheet thickness of 0.2 mm grain oriented electrical steel can be cut e.g. with a cutting speed of 130 m/min, aluminum with 270 m/min, copper with 95 m/min and zinc with 280 m/min; the necessary laser power is 1300 W. Based on the results of basic research the prototype of a laser slitting line was constructed and went into operation in autumn 1991. Up to now various materials for different customers have been cut on this slitting line and used in industry. Especially when cutting grain oriented electrical steel, which is a material with very high requirements on the cutting process, it becomes evident that the laser cutting process compared with the conventional technique has considerable advantages concerning cutting quality and quality assurance.

Diode laser systems for cutting applications of thin materials

For cutting applications of sheet thicknesses up to 1u2005mm a compact diode laser system of high brilliance has been developed. By the combination of three different wavelengths as well as two polarization states six linear polarized diode laser bars are superimposed nearly without loss in beam quality. The maximum optical output power amounts to 155u2005W at a beam parameter product of about 22u2005mm mrad. The wavelength- and polarization-multiplexing is realized with one cemented optical component consisting of edge filters, a λ/4-retardation plate and a polarization beam splitter. The linear shaped beam of the six superimposed diode laser bars is symmetrized by micro step mirror beam shaping technology. Limited by manufacturing tolerances and particularly the mounting process of the diode laser bars, the system reaches the limits of incoherent beam multiplexing of six broad area diode laser bars. Combined with beam expanding and focussing optics, cutting experiments on different metallic and organic materials with sheet thicknesses ranging from 0.1 to 1u2005mm have been realized.For cutting applications of sheet thicknesses up to 1u2005mm a compact diode laser system of high brilliance has been developed. By the combination of three different wavelengths as well as two polarization states six linear polarized diode laser bars are superimposed nearly without loss in beam quality. The maximum optical output power amounts to 155u2005W at a beam parameter product of about 22u2005mm mrad. The wavelength- and polarization-multiplexing is realized with one cemented optical component consisting of edge filters, a λ/4-retardation plate and a polarization beam splitter. The linear shaped beam of the six superimposed diode laser bars is symmetrized by micro step mirror beam shaping technology. Limited by manufacturing tolerances and particularly the mounting process of the diode laser bars, the system reaches the limits of incoherent beam multiplexing of six broad area diode laser bars. Combined with beam expanding and focussing optics, cutting experiments on different metallic and organic materials wi...

Quality improvement of polymer parts by laser welding

The growing significance of laser technology in industrial manufacturing is also observed in case of plastic industry. Laser cutting and marking are established processes. Laser beam welding is successfully practiced in processes like joining foils or winding reinforced prepregs. Laser radiation and its significant advantages of contactless and local heating could even be an alternative to conventional welding processes using heating elements, vibration or ultrasonic waves as energy sources. Developments in the field of laser diodes increase the interest in laser technology for material processing because in the near future they will represent an inexpensive energy source.