Even though thick plate cutting has a subsidiary mar- ket share in laser material processing, it is still a necessary feature for state-of-the-art machines.
In recent years, research has concentrated on various
quality issues, especially dross attachment and surface
appearance, that compromise productivity. This has resulted in notable improvements.
About $1.1 billion was allotted to research and development of macro laser metal cutting in 20161. Roughly
20 percent of this research addressed sheet thicknesses
above 4 mm. Ongoing market monitoring points to a
persistent industrial interest in this sector, because thick
plate performance is a benchmark of laser cutting machines. CO2-laser cutting remains the established method
for industry; every laser cut is compared with CO2 quality.
However, in recent years the market share of solid-state
laser cutting devices has increased by a compounded annual growth rate of more than 10 percent2. Solid-state
lasers offer various advantages, such as higher efficiency,
easier handling and faster feed rate for thin sheets. However, in the case of thick plates, they have not achieved
acceptable cut quality, nor even a higher feed rate in comparison to CO2 cutting.
A basic approach to achieve optimal results for solid-state laser cutting is to adjust the cut kerf dimensions for
each application. (Of course, these must take into account
influencing factors such as energy deposition and heat
conduction.) In the case of thick plates, an appropriate
kerf width is required to maintain melt ejection.
Static beam shaping is one common method for adjusting cut kerf dimensions, but the result is not always sufficient. With this technique, various optical elements can
be utilized to modify the laser beam for spot size, beam
geometry, amount of foci, polarization state and other
factors. The result is an optical setup that suits a specific
cutting task. This is advantageous for specialized tasks
such as serial production. But static beam shaping cannot
adequately accomplish the frequently varying operations
that constitute the daily business of industry.
In addition, with solid-state laser cutting of thick
plates, mechanical post-treatment typically is needed
to remove dross. Thus, an additional production step is
necessary that requires manpower and machinery. Static
beam shaping can overcome this challenge by using
laser sources with higher output power. Although this
increases productivity, it also increases investment and
Innovative laser cutting
Fraunhofer IWS is pursuing dynamic beam shaping
(DBS) as a solution to the challenge of laser beam cutting
of thick metal plates. It addresses high productivity, improved quality and efficiency in combination with standard equipment. The technology is considered an add-on
to the conventional process.
The concept is based on two superimposed movements
of the laser beam (Figure 1). The first is the movement of
the cutting machine, defined by the feed rate and the part
geometry. The second is an additional, high-frequency
oscillation of the laser beam inside the cut kerf. As a consequence, energy deposition is distributed more homogeneously within the material, resulting in an optimized
In contrast to static beam shaping, DBS is a spatiotem-
poral method during the cutting process and is variable
at any time. Implementation requires a high-dynamic
2D-scanner unit in addition to standard components. The
scanner consists of two oscillating mirrors to achieve a
defined deflection of the laser beam in the focal plane. All
hardware for DBS is off the shelf and ready for integra-
tion into cutting machines. Optical properties are not af-
fected by the setup, since the scanner is installed between
collimation and the cutting head (Figure 2). Fraunhofer
IWS is currently working on further optimization of
hardware components in order to decrease the integration
space and develop a smaller drive mechanism.
Such a scanner supplies an additional five adjustments
to the laser beam cutting process. Each mirror has a time-dependent position, defined by a certain frequency and
amplitude. The phase shift between both mirrors provides the fifth parameter for controlling the cut kerf generation. As a result, an infinite amount of arbitrary beam
movements is possible (Figure 3). In addition, depending
on the chosen parameters, oscillation speeds of the laser
beam in the cut kerf can go as high as 500 m/min.
The artificial laser beam geometry created by DBS
Dynamic Beam Shaping Improves
Laser Cutting of Thick Steel Plates
BY CINDY GOPPOLD, THOMAS PINDER AND
PATRICK HERWIG, FRAUNHOFER IWS
Images courtesy of Fraunhofer Institute for Material and Beam Technology IWS.
➤ A technique for creating optimal performance
in a system by producing a specific beam irradiance distribution, usually through the use of
geometric optics. A common design involves
the use of ray mapping, a process that has
been under study for years.
See EDU.Photonics.com for this and other
definitions in the Photonics Dictionary and more
information in the Photonics Handbook.
Static Beam Shaping
Figure 1. Dynamic beam shaping (DBS) superimposes two movements of the laser beam: the movement of the
cutting machine and a high-frequency oscillation of the laser beam inside the cut kerf. To see an animated version of
this drawing, go to https://youtu.be/cUm231Ya6is.
IP July 2017
Keep in order