Multi-remote system for efficient pre-processing of large surfaces

The global situation in terms of lightweight design strategies using various materials is characterized by an increasing demand for flexible manufacturing technologies for sheet-like materials and semi-finished parts that enable efficient solutions, predominantly in the automotive and aircraft industries. This, in turn, requires the development and testing of flexible equipment concepts for different manufacturing technologies, such as welding, cutting, material removal and structuring. These technologies should be applicable to processes and technologies for metal, plastics and textiles. To fulfill these conditions, laser-remote processes with radiation sources adapted to material and absorption properties offer a promising approach. The availability of highly-brillant cw laser sources of different wavelengths opens up new opportunities for remote applications.

Despite the very high quality of the lasers, the scanner working areas remain limited. Enlargements of the working field can be implemented by combining scanners with Cartesian kinematic systems. Current solutions using two-dimensional on-the-fly coupling of the scanner and the axis system can indicate the potential of an optimized axes overlap. The combination of large field scanners with highly dynamic spindle drives promises high-precision, high-speed manufacturing. For this reason, the aim was to open the system and technological possibilities for potential commercial users by means of a laser system for high-speed manufacturing of planar, moderately shaped, sheet metal and textile prepregs made of composite materials, metals and plastics using remote technology, with cw high-performance lasers of different wavelengths.

Solution

© Fraunhofer IWS
Flexibilität eines Laser-Remote-Systems für verschiedene Anwendungen: 1: Schneiden von Metallfolien, 2: Schweißen von Wärmetauschern, 3: Zuschnitt von Textilien

The conceptual design of the proposed mechanical system, as well as the dimensioning of the required driving components and optical devices, were carried out in cooperation with project partners. The equipment structure is based on a single column design with a travelling z-axis carrier, holding a platform for the optical devices. The basic process setup consists of a fixed positioned scanner system and an on-the-fly coupling of a highly dynamic XY travelling unit for material feeding. Different laser beam sources and atmospheric pressure plasma equipment were added to the set-up. The details of the functional components are summarized in the following figure.

To guarantee the reliable processing of fiber-reinforced composite materials, such as CFRP, both the laser and the electrical components of the machine axes system are encapsulated to make them dustproof. A suction chamber that can be adapted to the work distance efficiently removes the by-products from the workspace; the by-products are subsequently filtered by means of special equipment and are separated.

A flexible control structure enables an user-friendly programming of all components and an embedding of sensor units, was designed for highly dynamic synchronizing of the driving unit and the connection with the scanner systems.

Results

The cw remote laser processes, which can be implemented by means of the prototype system, are profitably used in multi-material lightweight constructions for direct thermal joining of metal with thermoplastic fiber-reinforced compounds. Thus, laser macro-structuring by means of a fiber laser allows flexible pre-processing of the metallic joining partner. In the joining step itself, the parts, which are overlapped over one another, are adhesively bonded by laser induced heating of the metallic partner on the rear side, from which heat is conducted into the metal-thermoplastic interface.

When producing hybrid laminates using metals and thermoplastics or organosheets in a continuous process, then heating by the laser directly occurs in the joining gap between the prepregs. The surface of the locally molten thermoplastic is bonded to the metal between a pair of pressing rolls. Using the remote technology with integrated laser power control, depending on the scanner position, sheets up to 0,5 m width can be joined.

Atmospheric pressure plasma sources are suitable for surface activation and precision cleaning of surfaces made of polymers. These plasma sources are integrated into the setup of the system’s optical devices and can rotate in an overlapping mode, so that processing rates of typically 100 cm²/min become feasible, assuming a twin double head turbo nozzle, 10 cm processing width, 10 m/min traverse rate (conventional approach, air upward).

Projects