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Laser-based manufacturing concepts for efficient production of tailor welded sheet metals
Marius Spottl
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1
Hardy Mohrbacher
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1
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H. Mohrbacher (&) NiobelCon bvba, Schilde,
Belgium
1
M. Spottl WISCO Lasertechnik GmbH, Ravensburg,
Germany
Laser welding is an established manufacturing technology for a large variety of automotive applications due to its attractive properties such as low heat input, high precision and fast welding speed. Especially when welding high strength steels, which are dominantly used in today's car body construction, the low heat input by laser welding bears significant advantages with regard to the properties of the weld seam. The exploitation of the full application potential of laser welding in mass production requires an appropriate manufacturing concept and corresponding auxiliary technologies. The present paper demonstrates the integration of laser welding into the surrounding manufacturing concepts by a modular setup with different levels of automation. This approach offers flexible solutions for individual needs thereby optimizing investment cost, labor cost and productivity. Recently available laser sources enable exceptionally high welding speed on thin gauged sheet metals but require efficient material handling concepts to utilize the full speed potential. Industrial concepts are presented offering efficient material handling and high process robustness for mass production welding.
1 Introduction
Laser welded steel blanks have made a remarkable
evolution from rather infrequent applications at the end of the
1980s to an indispensable semi-product in todays
automotive body design. Within a decade, the design of laser
welded blanks has evolved from very simple to rather
complex layouts in order to comply with the continuously
increasing challenges of weight reduction, engineering
properties and cost [1]. Over the same period of time,
companies active in this market and have developed
various laser welding production concepts and related
subtechnologies. Meanwhile, many of these have disappeared
again since only those allowing to manufacture a superior
product in terms of cost, quality and flexibility could
survive in this highly competitive market. Principally two
fundamental production concepts have been established.
One concept uses a fixed laser head and moving the
material along the head. The other concept moves the laser
head over the material being in fixed position. Besides,
hybrid concepts moving the head as well as the material in
a coordinated way have also been realized for particular
applications. Two key aspects control the optimization
towards higher productivity and accordingly lower
manufacturing cost: (i) material handling time and (ii) welding
speed. A further important aspect towards reducing cost is
to lower the part specific investment into tooling. For laser
welding this concerns cutting dies as well as material
handling and clamping devices. All these aspects have to
be considered in combination when designing a welding
machine for a particular application or market.
Furthermore it is necessary to enhance process robustness to
provide weld seams of consistently high quality. The
operating window of stable processing conditions becomes
smaller at higher welding speed. Therefore an innovative
welding technology has been developed increasing process
robustness without sacrificing welding speed or increasing
heat input.
2 Laser welded blank production concepts
For laser welded blank production various manufacturing
concepts are used in the industry [1, 2]. These production
concepts are the result of different production strategies
and also of rapid parallel technology development by
different players in the market. A production concept is
basically characterized by way of achieving a relative
displacement of laser beam and sheet material as well as by
the manner of managing the material flow through the
process. The driving forces behind any welding machine
concepts are maximization of the utilization of the laser
welding equipment, the optimization of production
flexibility and the reduction of cost.
Fixed-optics laser welding systems are characterized by
a stationary welding head while the sheet assembly to be
welded is passing underneath (see Fig. 1). This technology
allows producing straight weld seams (see Fig. 2). Moving
optics systems represent the opposite approach where the
sheets to be welded are at rest while the laser welding head
is executing a linear or free form trajectory (see Fig. 3). In
this way weld seams of arbitrary shape such as circular,
curved or angular ones can be made. The technology also
allows producing complex blank assemblies, as shown in
Fig. 4. Considering the part spectrum in todays
automotive market, the vast majority of blanks require straight
weld seams connecting two or three individual sheets. For
the production of single straight welded assemblies,
machines equipped with fixed optics are clearly the method
of choice. Each additional straight weld in a blank design
requires a corresponding additional pa (...truncated)