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Publication
Featured researches published by Heinz Haferkamp.
Optical Tools for Manufacturing and Advanced Automation | 1994
Heinz Haferkamp; Holger Schmidt; Dirk Seebaum
The focusing characteristics of divergent laser beams change with the distance between laser source and processing head. To keep the energy distribution on the workpiece surface on the same level while working with a flying lens, the use of deformable mirror systems has proven to be a suitable solution. In this case, a newly-developed system is brought into the beam guidance system to keep the focal spot diameter constant.
Proceedings of SPIE, the International Society for Optical Engineering | 2001
Heinz Haferkamp; Stefan Paschko; Martin Goede
Due to special material properties, shape memory alloys (SMA) are finding increasing attention in micro system technology. However, only a few processes are available for the machining of miniaturized SMA-components. In this connection, laser material processing offers completely new possibilities. This paper describes the actual status of two projects that are being carried out to qualify new methods to machine SMA components by means of laser radiation. Within one project, the laser material ablation process of miniaturized SMA- components using ultra-short laser pulses (pulse duration: approx. 200 fs) in comparison to conventional laser material ablation is being investigated. Especially for SMA micro- sensors and actuators, it is important to minimize the heat affected zone (HAZ) to maintain the special mechanical properties. Light-microscopic investigations of the grain texture of SMA devices processed with ultra-short laser pulses show that the HAZ can be neglected. Presently, the main goal of the project is to qualify this new processing technique for the micro-structuring of complex SMA micro devices with high precision. Within a second project, investigations are being carried out to realize the induction of the two-way memory effect (TWME) into SMA components using laser radiation. By precisely heating SMA components with laser radiation, local tensions remain near the component surface. In connection with the shape memory effect, these tensions can be used to make the components execute complicated movements. Compared to conventional training methods to induce the TWME, this procedure is faster and easier. Furthermore, higher numbers of thermal cycling are expected because of the low dislocation density in the main part of the component.
Smart Structures and Materials 1999: Smart Materials Technologies | 1999
Heinz Haferkamp; Martin Goede; M. Leester-Schaedel; Stefan Paschko
The mechanical properties of shape memory alloys (SMAs) are finding more and more attention in micro-system technology. However, only a few processes are available for machining of miniaturized SMA-components. During the machining process, changes of the shape memory properties due to the extension of the heat effected zone or mechanical tensions have to be avoided. Especially for complex geometries with dimensions in the submillimeter-range, these requirements are difficult to fulfill.
Laser Materials Processing: Industrial and Microelectronics Applications | 1994
Heinz Haferkamp; Dirk Seebaum
The use of high power CO2 lasers for various applications in material and production technologies has increasingly grown, and new applications are on their way to being used in industry. Due to varying beam path lengths, proper beam delivery is essential to obtain constant working conditions when using machines with moving beam guidance. The focussing characteristics of divergent laser beams change with the distance between laser source and processing head. To keep the energy distribution on the workpiece surface on the same level while working with flying optics, the use of deformable mirror systems has proven to be a suitable solution. In this case, a newly-developed system is brought into the beam guidance system to keep the focal spot diameter constant. As far as applications are concerned, where the distance of the focal spot to the surface of the workpiece is of major interest for the performance of the process, these optical devices are also used to tune the focal length. For example collision danger or dynamic limitations of the handling system may mean that the focal spot has to follow the surface outline without keeping the distance between processing head and material surface constant. Besides cutting and shaping by material removal applications, welding is a kind of application where a focus shift without moving the processing head may be advantageous, especially for 3D processes. Therefore, another deformable mirror is installed near to the focusing optics. Investigations have been carried out on the location of the deformable mirror close to the laser source (RS 3000 RF), and inside the processing head.
Proceedings of SPIE, the International Society for Optical Engineering | 1999
Heinz Haferkamp; Martin Goede; Alexander von Busse
This paper presents an optical method of process control based on the thermographic detection of signals from the process zone. At the Laser Zentrum Hannover e.V., a monitoring system based on a high-temperature camera has been developed to enable on-line monitoring of the cut quality. During the cutting process, the temperature field was observed on-line using a thermocamera. The camera images were analyzed afterwards using specific digital image analysis. The crucial task of the work is the adequate application of analyzing and visualization techniques to extract significant information from the measured signals, and to find correlations to the cutting quality. Investigations have been carried out on cutting metal sheet materials such as steels and titanium. For the investigations, different process parameters such as laser power or process gas pressure were varied. Influences of the optical set-up on the signal were studied. Results show that the temperature distribution in the process zone is strongly connected to the cut quality, e.g. dross attachment, surface roughness of the cut kerf, width of the kerf. Observation of the temperature and temperature gradients at the cutting front allow a determination of the resulting cut quality.
Opto-Contact: Workshop on Technology Transfers, Start-Up Opportunities,and Strategic Alliances | 1998
Heinz Haferkamp; Ferdinand von Alvensleben; Oliver Thuerk
Rapid solidification of aluminum alloys during the remelting process using high power laser radiation results in refined effects of the solidified grain texture and improved wear resistance and material hardness. High temperature gradients can be achieved, and energy coupling into the aluminum alloy is locally restricted and can be precisely controlled. For the adjustment of defined grain textures, the dynamic behavior of the melted material on the irradiated material surface is of high interest. Current activities at the Laser Zentrum Hannover eV are focused on a new visualization system for locally and temporally highly-resolved visualization of the aluminum alloy surface during short pulse laser interaction. Experimental measurements have been performed to determine the heating and cooling velocities. The main aim of the work is the correlation of image information and the resulting grain structures dependent on material properties and actual laser beam and processing parameters. The aluminum samples are remelted using an Nd:YAG solid-state slab laser system providing short pulse durations and high pulse power. Frequency selective irradiation of the melting zone is realized by using a frequency-doubled Q-switched Nd:YAG laser system. Image information from the processing zone is obtained using a CCD-camera, coaxially mounted to the processing zone. By using pulse durations in the ns-range and high beam intensities of the illuminating laser source, time resolutions for process visualization can be realized, with orders of magnitudes higher than existing visualization techniques. Image data related to the temporal development of the solid and liquid isotherms are compared to the results of numerical calculations using the finite difference method.
Lasers as Tools for Manufacturing of Durable Goods and Microelectronics | 1996
Heinz Haferkamp; Friedrich W. Bach; Ferdinand von Alvensleben; K. Kreutzburg
The use of engineering ceramics is becoming more and more important. Reasons for this are the specific properties of these materials, such as high strength, corrosion resistance and wear resistance. To apply the advantages of ceramics, joining techniques of metal ceramic parts are required. In this paper, joining of metal ceramic joints by laser beam brazing is presented. This joining technique is characterized by local heat input, and the minimal thermal stress of the brazed components. During the investigations, an Nd:YAG laser and a vacuum chamber were applied. The advantages of Nd:YAG lasers are the simple mechanical construction, and laser beam guidance via quartz glass fibers, which leads to high handling flexibility. In addition, most of the materials show a high absorption rate for this kind of radiation. As materials, ceramic Al2O3 with a purity of 99.4% and metals such as X5CrNi189 and Fe54Ni29Co17 were used. As a filler material, commercially available silver and silver- copper brazes with chemically active elements like titanium were employed. During this study, the brazing wetting behavior and the formation of diffusion layers in dependence on processing parameters were investigated. The results have shown that high brazing qualities can be achieved by means of the laser beam brazing process. Crack-free joining of metal ceramic parts is currently only possible by the use of metals such as Fe54Ni29Co17 because of its low thermal expansion coefficient, which reduces thermal stresses within the joining zone.
Opto-contact : workshop on technology transfers, start-up opportunities, and strategic alliances | 1998
Heinz Haferkamp; Martin Goede; Ulrich Schroeder
The principle of the presented visualization system is based on the backscatter absorption gas imaging technique. Applying this technique, developed by Lawrence Livermore National Laboratory and Laser Imaging Systems in the USA, it is possible to visualize a large amount of environmental relevant gases normally invisible to the human eye. An image of the spreading of gases is created from infrared (IR) laser radiation that is backscattered from the scenery background in the field of view of a special designed IR- camera. Gaseous components within this field of view absorb a portion of the emitted laser radiation at their specific absorption wavelength and cause an attenuation of a portion of the radiation, backscattered by the scenery background. This leads to a dark gas image on the video screen. Analyzing the wavelength of maximum attenuation then allows the identification of the observed gas. The applied method is based on commercially available IR technology consisting of a thermal imaging device and a tunable CO2-laser. Main advantages of this approach in comparison to conventional laser-based remote gas-sensing methods (i.e. Differential Absorption Lidar DIAL or Raman Lidar) are reachable speed of localization, high sensitivity as well as the detection of multileakages. Main aim of a project carried out at the Laser Zentrum Hannover is the computer based processing of spectroscopic and IR-image information provided by the visualization system described above. For this the dependence between the wavelength and the power output of the laser has to be known and so investigations have been carried out to determine this dependence.
ATZ - Automobiltechnische Zeitschrift | 1999
Heinz Haferkamp; Ingo Burmester; Johannes Stein
In Zusammenarbeit mit der Horotron GmbH, Elmshorn, entwickelt das Laser-Zentrum Hannover e.V. (LZH) zur Zeit ein neuartiges Verfahren zur Markierung der Fahrzeugkarosserie und anderer hochwertiger Kfz-Bauteile. Hintergrund ist die Bekampfung der Diebstahlkriminalitat bei Kraftfahrzeugen durch die Moglichkeit, gestohlene Fahrzeuge und Ersatzteile von gestohlenen Fahrzeugen durch Detektion der Markierungen schnell und zuverlassig zu identifizieren. Schwerpunkt der Untersuchungen stellen die lackierten Bleche der Fahrzeugkarosserie dar, in die unsichtbare Lasermarkierungen eingebracht werden sollen, die mit Hilfe der Infrarottechnik sichtbar werden.
Opto-Contact: Workshop on Technology Transfers, Start-Up Opportunities,and Strategic Alliances | 1998
Heinz Haferkamp; Martin Goede; Alexander von Busse; Oliver Thuerk
Compared to other technological relevant laser machining processes, up to now laser cutting is the application most frequently used. With respect to the large amount of possible fields of application and the variety of different materials that can be machined, this technology has reached a stable position within the world market of material processing. Reachable machining quality for laser beam cutting is influenced by various laser and process parameters. Process integrated quality techniques have to be applied to ensure high-quality products and a cost effective use of the laser manufacturing plant. Therefore, rugged and versatile online process monitoring techniques at an affordable price would be desirable. Methods for the characterization of single plant components (e.g. laser source and optical path) have to be substituted by an omnivalent control system, capable of process data acquisition and analysis as well as the automatic adaptation of machining and laser parameters to changes in process and ambient conditions. At the Laser Zentrum Hannover eV, locally highly resolved thermographic measurements of the temperature distribution within the processing zone using cost effective measuring devices are performed. Characteristic values for cutting quality and plunge control as well as for the optimization of the surface roughness at the cutting edges can be deducted from the spatial distribution of the temperature field and the measured temperature gradients. Main influencing parameters on the temperature characteristic within the cutting zone are the laser beam intensity and pulse duration in pulse operation mode. For continuous operation mode, the temperature distribution is mainly determined by the laser output power related to the cutting velocity. With higher cutting velocities temperatures at the cutting front increase, reaching their maximum at the optimum cutting velocity. Here absorption of the incident laser radiation is drastically increased due to the angle between the normal of the cutting front and the laser beam axis. Beneath process optimization and control further work is focused on the characterization of particulate and gaseous laser generated air contaminants and adequate safety precautions like exhaust and filter systems.