When a serious motor vehicle accident happens, persons with severe injuries may be trapped inside damaged vehicles. In these cases, it is necessary to rescue the injured persons as fast as possible to increase their chance to survive. Nevertheless, secondary injuries due to the rescue procedures must be avoided. In this scenario, structural parts typically have to be cut to create rescue openings. Therefore, several high-tech rescue systems are available, most common hydraulic apparatus. Alternatively, reciprocating saws, angle grinders or plasma cutters are used, depending on the specific on-scene conditions.
Lately, there has been tremendous progress regarding the developments on vehicle safety. One example is the integration of super high-strength steels and carbon fiber reinforced plastics, concurrently meeting the requirements of weight reduction. As a result, mechanical rescue systems like hydraulic shears reach their performance limits.
The main goal of this work is the development of a mobile laser cutting device for rescue operations. The focus is put on high flexibility concerning the processing of high-strength materials and multilayer structures. Moreover, robustness, easy handling and system weight shall be optimized, as rescuers often work under harsh conditions concerning temperature, humidity, dirt and stress. Crucial aspect of laser rescuing is safety which must be guaranteed for all persons involved at any time. Here, results of laser cutting experiments, using materials and structures relevant for rescue situations, are presented.
Due to their outstanding mechanical properties, in particular their high specific strength parallel to the carbon fibers, carbon fiber reinforced plastics (CFRP) have a high potential regarding resource-efficient lightweight construction. Consequently, these composite materials are increasingly finding application in important industrial branches such as aircraft, automotive and wind energy industry. However, the processing of these materials is highly demanding. On the one hand, mechanical processing methods such as milling or drilling are sometimes rather slow, and they are connected with notable tool wear. On the other hand, thermal processing methods are critical as the two components matrix and reinforcement have widely differing thermophysical properties, possibly leading to damages of the composite structure in terms of pores or delamination. An emerging innovative method for processing of CFRP materials is the laser technology. As principally thermal method, laser processing is connected with the release of potentially hazardous, gaseous and particulate substances. Detailed knowledge of these process emissions is the basis to ensure the protection of man and the environment, according to the existing legal regulations. This knowledge will help to realize adequate protective measures and thus strengthen the development of CFRP laser processing. In this work, selected measurement methods and results of the analysis of the exhaust air and the air at the workplace during different laser processes with CFRP materials are presented. The investigations have been performed in the course of different cooperative projects, funded by the German Federal Ministry of Education and Research (BMBF) in the course of the funding initiative “Photonic Processes and Tools for Resource-Efficient Lightweight Structures”.
To process natural stone such as marble or granite, saw blades equipped with wear-resistant diamond grinding segments are used, typically joined to the blade by brazing. In case of damage or wear, they must be exchanged. Due to the large energy input during thermal loosening and subsequent brazing, the repair causes extended heat-affected zones with serious microstructure changes, resulting in shape distortions and disadvantageous stress distributions. Consequently, axial run-out deviations and cutting losses increase.
In this work, a new near-infrared laser-based process chain is presented to overcome the deficits of conventional brazing-based repair of diamond-tipped steel saw blades. Thus, additional tensioning and straightening steps can be avoided. The process chain starts with thermal debonding of the worn grinding segments, using a continuous-wave laser to heat the segments gently and to exceed the adhesive’s decomposition temperature. Afterwards, short-pulsed laser radiation removes remaining adhesive from the blade in order to achieve clean joining surfaces. The third step is roughening and activation of the joining surfaces, again using short-pulsed laser radiation. Finally, the grinding segments are glued onto the blade with a defined adhesive layer, using continuous-wave laser radiation. Here, the adhesive is heated to its curing temperature by irradiating the respective grinding segment, ensuring minimal thermal influence on the blade.
For demonstration, a prototype unit was constructed to perform the different steps of the process chain on-site at the saw-blade user’s facilities. This unit was used to re-equip a saw blade with a complete set of grinding segments. This saw blade was used successfully to cut different materials, amongst others granite.
In dental prosthodontics, miniaturized unit assembly systems are increasingly used in order to enable the optimized adaptation
of the prosthesis to the individual anatomic situation. To manufacture these miniaturized systems, there is the
need to cover the complete device, in the reported case made of polycarbonate, comprising among others springs that
apply pressure to fix and adjust the prosthesis. The laser is a suitable joining tool for applications in micro technology.
Therefore, laser transmission welding was investigated for joining the specific miniaturized components, so-called retention
modules. The housing was made of PC with carbon black. The cover consisted of transparent PC with a thickness of
400 μm along the joining contour. The wall thickness of the joining partners amounted to 400 μm.
The investigations presented in this paper include detailed examinations of the welding process with and without laser
mask. For both process variants, the influence of the main process parameters laser output power, welding speed and
focal position was studied. The process was qualified especially with regard to joining strength, swelling, process time,
reproducibility, accuracy and functionality of the complete assembly. It was examined how the positioning of the mask
determines the formation of the weld seam. The geometry of the retention module and the clamping were optimized. It
turned out that the clamping of the components is crucial for a reliable process. Optimized process conditions enable the
micro welding of plastic components for dental products considering the high requirements regarding functionality,
biocompatibility, lifetime, and esthetics. Laser transmission micro welding proved to be a suitable method to package the
final assembly without any refinishing operation.
Due to special material properties, among others their two-way memory effect (TWME), shape memory alloys (SMA) are finding increasing attention in micro system technology. However, only slow and quite complicated training methods are available to induce the TWME. At the Laser Zentrum Hannover e.V., investigations are being carried out to realize the induction of the TWME into SMA components using laser radiation. By precisely heating SMA components with laser radiation, local tensions remain near the component surface. Concerning the shape memory effect (SME), 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. Further, higher numbers of thermal cycling are expected because of the low dislocation density in the main part of the component. Results regarding the dependence of the laser induced TWME on material and machining parameters will be presented.
In the course of increasing miniaturization of components in minimal access surgery the superelastic properties of nickel titanium shape memory alloys (NiTi-SMA) find more and more attention. However, only a few processes are available for machining of miniaturized NiTi-components. Changes of the mechanical properties due to heat input or mechanical tensions have to be avoided. Especially for complex geometries with dimensions in the submillimeter-range, these requirements are hardly to meet. Finding new methods for manufacturing micro-instruments of NiTi wires with high geometrical resolution and superelastic mechanical properties for applications in endoscopic surgery are the main goals of the investigations presented here. Because of the precise focussing properties and the possibility of an excellent non-tactile energy coupling, material processing by lasers is a suitable alternative to conventional machining-processes. Comparing investigations with laser systems with different wavelengths and pulse duration show the suitability of ultra-short pulse Ti:Sapphire lasers for this machining process. Only by the use of ultra-short laser pulses it is possible to structure micro-components of NiTi almost without thermal influence. Results of mechanical and metallographic examinations show that the special properties of miniaturized SMA-components can be maintained. Experimental results as well as example geometries produced with ultra-short pulse lasers are presented in the paper.