Additive layer manufacturing (ALM) provides a method for flexible and economical manufacturing of almost arbitrary geometries...

Sep 1st, 2011

Researchers from iwb present latest material processing results

Editor's Note:Occasionally an opportunity to look deeper into emerging industrial material processing applications presents itself. At last May's Laser World of Photonics in Munich, where I video-taped activities by researchers from the Institut für Werkzeugmaschinen und Betriebswissenschaffen (iwb) in Garching, it occurred to me that ILS readers would appreciate an expansion on the taped comments by each of the presenting researchers. – David A. Belforte

Compensation of machine characteristics

Additive layer manufacturing (ALM) provides a method for flexible and economical manufacturing of almost arbitrary geometries, with reachable part properties sufficient to fulfill the customer requirements in terms of series and spare part production. As the name implies, parts are manufactured layer wise with a thin layer (30 to 100 µm) of powder coated on a building platform, after which a laser beam solidifies the material on the position in the respective height. These two steps are repeated periodically until the whole part has been manufactured.

This technique offers several advantages. First of all, almost any geometry is producible, due to accessibility to all regions of the parts. Another is that there is no need for a special tool; the only necessary tool is a laser beam, which is guided based on the CAD data of the process zone; and because of the direct link between CAD data and the machine, there is no need for a time-consuming preparation. Further, assembly operations can be reduced since joined components are producible directly within the process. The scope of materials that ALM can process is constantly expanding and includes metals, plastics, ceramics, and composites.

Laser beam melting of powder material can make almost any geometry

However, there are still some deficiencies, which are the subject for research projects. The iwb recognizes that each ALM machine acts slightly different and produces parts with a varying quality, and aims to compensate the so-called machine characteristic in a self-learning approach.

Until now, there was no possibility to visualize the local distribution of properties within the building chamber, with differences gathered by the operators in an unsystematic manner and formulated verbally. However, the experiential knowledge of the operators is not considered in the present process chain. Within the scope of the project, an extension of the process chain by a superimposed closed-loop control is investigated; information from completed building processes is analyzed, and fed back to the machine.

The results demonstrate clear characteristics of different machines. Operators are now able to visually capture the local distribution of the achievable part quality within the different building chambers. Based on that, they can decide whether the specific machine is suitable for production or not. In the future, the machine characteristic will be compensated. For this, the virtual model of a part can deliberately be deformed and produced on a machine. Due to the machine characteristic, which has a negative effect on the part quality, the shrinkage effects would be compensated.

(Interviewed: M.Sc. (TUM), Dipl.-Ing. (FH) Christian Eschey, email Christian.eschey@iwb.tum.de)

Robot guided laser welding and cutting

In today's globalized economy, product life cycles become increasingly dynamic, while markets become concurrently individual, seen as dominating trends for production in the year 2020. As a consequence, products as well as production facilities need to become more flexible. This can only be achieved by the use of innovative production processes and novel concepts for automation. Jan Musiol (jan.musiol@iwb.tum.de), Markus Schweier and Jens Hatwig explain the plan to accomplish this.

The goal of the project RoboLaSS is to develop new technologies and to optimize established methods for laser material processing that will lead to increased profitability and flexibility of remote laser beam welding and cutting for industrial production. By theoretical and experimental analysis of remote laser welding (RLW), remote laser ablation cutting (RAC) and remote laser fusion cutting (RFC), the processes' quality will be increased and qualification for industrial applications will be accomplished.

FIGURE 1. Heat exchanger cassette (Source: Castelnuovo).

For system technology, process-adapted optics are designed and optimized for the specific requirements of RLW, RAC, and RFC. An increase in system flexibility is achieved by an optical system which is designed to carry out RLW and RAC. Flexible handling systems and novel beam guidance solutions augment the range of prospective applications, whereas offline programming or online teaching of these material processing tasks become increasingly complex.

Another part of the project is the development of an automated path planning tool for the coupling of scanner optics and handling kinematics. The findings of RoboLaSS are directly implemented by means of industrial demonstrators from various production domains. A consortium of innovative and experienced associates was formed in order to attain the objectives and intentions of the project. The project association consists of research institutes, Fraunhofer Institute for Material and Beam Technology (IWS) and iwb who are working on the development and the optimization of remote laser material processes. technology manufacturers IPG Laser GmbH, Precitec KG, Precitec Optronik GmbH, and Arges GmbH are dealing with beam generation, shaping and guidance as well as with process monitoring for quality control and four industrial users of laser technology. The iwb, Reis GmbH & Co. KG Maschinenfabrik, and Blackbird Robotersysteme GmbH are responsible for optics handling and automated path planning. To demonstrate the achievements of the project, the companies Mars Lasertechnik GmbH, Benteler Automobiltechnik GmbH, Reinz-Dichtungs-GmbH, and EADS Innovation Works are transferring the results into industrial applications.

Figure 2. Remote ablation cutting of shaped heat exchanger plates.

One of the demonstrations is a heat exchanger used in chemical process engineering or in power plants. It consists of curl-stamped plates, which are shown in FIGURE 1. In order to form a hollow space for Fluid 1, two symmetric plates are joined together by remote laser welding. By using the scanner-optics combined with industrial robots (on the fly), this task is carried out at minimal cycle-times.

Several of these cassettes stacked together form a heat exchanger, while Fluid 2 flows between the single cassettes. In order to supply the cavities with the fluids through pipes, circular cuts are needed. These cut-outs are manufactured by the wear-less, high-speed process remote ablation cutting, as shown in FIGURE 2. The aim of RoboLaSS is to carry out the cutting and the welding process in one production unit with one laser source and one scanner-optics. Thus non-productive process times for transport are reduced. This project is sponsored by the German Federal Ministry of Education and Research (BMBF).

(Interviewed: Dipl.-Ing. Jan Musiol)

Laser-assisted milling of titanium alloys

Conventional steel materials are being substituted for advanced materials, e.g. composites, aluminum, or titanium alloys, for lightweight construction and high-performance components. This trend is very visible, especially in aerospace applications where aluminum alloys are the most commonly used materials and the demand for fiber-reinforced composites is stronger than ever.

A high galvanic corrosion between carbon fibers and aluminum encourages the use of titanium alloys in combination with composites because of their minor potential difference and the similar heat expansion of these two materials. Machining titanium alloys usually results in a short tool life, high production times, and costs. However, it is also a well-established processing technique, which has been investigated in detail for years. A capable and robust process ensures the desired material properties after machining and thus a high quality of the machined part. In the future, there will be no alternative to machining of such hard-to-machine materials.

Laser milling process

Laser-assisted milling represents an innovative method to enhance machinability with less tool wear and an increased material removal rate. The material is heated locally and thereby softened before machining. In spite of the high potential of the process, laser-assisted milling is not yet deployed widely in industrial applications. The main reasons are the lack of understanding of the physical process and the necessary high effort in systems engineering. Under a research project, funded by the German Federal Ministry of Education and Research (BMBF), the Institute for Machine Tools and Industrial Management (iwb) of the Technischen Universitaet Muenchen cooperates with the companies Pokolm Fraestechnik GmbH & Co. KG, Tebis AG, and IPG Laser GmbH to develop a prototype of a machine for laser-assisted milling.

This prototype was presented at the Laser World of Photonics in Munich for the first time and is characterized by application-related and cost-effective engineering using a modular design for laser beam integration. A conventional milling machine was upgraded with necessary laser safety measures and a fourth NC-axis to control the laser integration. Also a CAD/CAM process control unit, which is essential for an industrial application, was developed in cooperation with the industrial partners. Fundamental investigations proved that the process forces can be reduced by up to 20% and the material removal can be increased by up to 35% by the chosen strategy of laser-assistance in comparison to a conventional milling process. The long-term aim of the research cooperation is the commercial launch of a cost-effective system for laser-assisted milling of advanced materials.

(Interviewed: Dipl.-Ing. Robert Wiedenmann; email Robert.Wiedenmann@iwb.tum.de)

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