Abstract
(Englisch)
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a) Original research objectives :
Up-to-now the usual method to reduce product contamination from micro-welding is the capture and removal of the particles that might impact on the product by advanced nozzle systems, e.g. by applying gas jets for the transport and removal of the particles. In any conventional welding process debris will be left on the product as a result of condensation of particles generated during the process originating from a turbulent, fiercely boiling melt where a keyhole is present in the molten material. This melting process is not in good equilibrium and not well-controlled. In order to prevent the product contamination one should strive for a quiet, small volume of molten metal. This can be realised by introducing the heat input from the laser beam in a better controlled way .The subject of the CLAW program is to prevent as much as possible any particle generation at the source by putting just the exact amount of energy in the metal part so as to obtain a quiet melt. Research at Philips indicates that new equipment and new process parameters are needed for this. Based on this approach a novel well-controlled micro-welding technique will be developed, which gives virtually no contamination, and at the same time little thermal-mechanical distortion. The energy input needed to create the quiet melt will be realised by two different methods: 1) via a laser beam, and 2) via a laser guided micro-arc. The reasoning behind this is, that micro-laser welding is often used for welding of fine-mechanical parts, and laser guided micro-arc welding could be more appropriate for micro-electronics. The latter technique will be based on a hybrid process, whereby a (small) laser is used to control an arc. These new technologies will both offer opportunities for the clean micro-assembly of miniaturised key-components and low distortion welding. The industrial objective of the CLAW project is to develop these technologies into novel, industrial scale micro-welding processes with low distortions in the range of 0.5 µm and 1 mrad in angle, respectively, and low pollution/residual contamination such that subsequent cleaning steps are not necessary. This objective has been quantified in the industrial issues: · to prevent product contamination during micro-welding, such that subsequent cleaning is not necessary. This is achieved when the contamination levels are sufficiently low and the particle sizes are in the sub-micron or nano-meter range.· to handle and manipulate micro-parts with sub-micron accuracy in an industrial production line. This is achieved when the (delicate!) parts can be gripped and positioned with sub-micron accuracy within a cycle time of 2 seconds, without leaving a permanent deformation of the parts. · to join micro-parts by laser micro-welding or micro-arc welding processes with sub-micron final accuracy. This is achieved when a novel, industrial scale micro-welding process is available with low distortions in the range of 0.5 µm and 1 mrad in angle, respectively and when a total assembly time of 2 seconds is realised (including handling and manipulation). b) Expected deliverables :The project will result in low-distortion and clean micro-welding processes for micro-parts. The industrial targets are first to apply the developed technology within their own companies. The knowledge will be written down and disseminated via reports and publications, containing design rules (software) with respect to laser parameters, weld geometry, material (composition) and shielding gas. Whenever possible patents will be applied for to secure the leading edge of Europe. A second target is to develop the project results into new production equipment. c) Project's actual outcome ( in terms of technical achievements or if appropriate task per task)Process:Basic description of micro welding process.Collation and measurement of sufficient material data.Set up of processing chart for demonstrator welding.Products:Specification of demonstrators.Successful welding of demonstratorsEquipment:Set up of laser diode for heat conduction welding.Specifications and design of welding systemsSpecifications and design of positioning systems for grippers, components and weld headsSet up of 3 different grippersSet up of first prototypic process control equipmentSpecifications and design for total system integration and automationLaser-arc-hybrid welding head built and testedSimulation:Establishment of simulation boundary condition.Set up of appropriate physical boundary condition to enable development of the numerical algorithm.Detailed specification of software tools.Determination of the scope of processes requiring simulation.Alpha version of non-coupled solvers completed.Alpha version of a time dependent axis-symmetrical 2D surface tension model established.Preliminary physical handling model established.Agreement of framework of design rules software tools.d) Broad dissemination and use intentions for the expected outputs (such as industrial development, standards, regulations and norms, improvement of environment, health, working conditions, employment, net economic benefits, etc)The whole economic benefit of the project can be estimated to more than 500 MECU within 5 years after completion of the project, counting direct savings as well as the turnover of new products, which are manufactured by the new technologies, not counting the decrease of product development time and the resulting saving of costs. Compared to the project costs of some 5 MECU the impact of the results is enormous.The major objective of the project is the development of a low pollution welding technology. The novel welding techniques are very clean. As a result environmentally unfriendly metal vapours causing harm to man and nature are strongly reduced. Moreover as a result of the reduction of debris formation on the parts, cleaning of the products can be drastically decreased. In this way the use of chemical solvents, like acids and cleaning lubricants can be avoided. This reduces health hazards for the people on the manufacturing line and spares environmentally unfriendly waste. Another advantage of this fast and accurate joining process is the reduced consumption of energy and the reduction of scrap. Energy will be saved because the welding time is short and the melt pool intended to be very small. With the novel welding technologies the required accuracies of the products can be achieved without further adjustment and scrap due to exceeding distortion can be drastically reduced. The introduction of this important new clean and low-distortion accurate micro-welding technology in old production processes implies transfer of knowledge, training, and new opportunities for employment in very advanced production processes. The technology will replace tedious manual labour and potential dangerous cleaning steps, and will offer new opportunities, unknown so far, for the design of new, advanced products. An example is the improved miniaturised hearing aid which has a thin metallic membrane welded to the microphone. It will be easier to clean and will have a better acoustic performance. Thus the new hearing aid will increase the customer's satisfaction and the well being of the hearing impaired.
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