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FRINATEK-Fri prosj.st. mat.,naturv.,tek

New principle for production of layered three-dimensional multi-material products

Alternative title: Nytt prinsipp for lagvis produksjon av tredimensjonale multimateriale produkter.

Awarded: NOK 8.0 mill.

The project aims to develop a multimaterial production process for the production of geometrically complex parts. The parts can then be built with the desired materials in the right place in the part, such as a knee implant. The knee implant comes into partial contact with bone and partially with tissue, where one metal is friendly to bone and another to tissue. It is natural to produce the implant with two different metals so that both bone and tissue thrive. The technology therefore makes it possible to use materials with the right properties on the right section of the part. Such properties can be thermal conductivity, electrical conductivity, wear resistance, corrosion resistance, etc. The idea is to further develop additive (3D-print) technology so that it can produce geometrically accurate multi-metal products with arbitrary shapes. The project is based on a method for producing multi-metal powder layers developed at NTNU and SINTEF. The challenge is both to transfer the powder layer to the part being built and to achieve good bonding with the part. The project will investigate whether this can be done using modern laser technology. The laser physics environment at NTNU, the material environment at SINTEF Industry, and the production environment at SINTEF Manufacturing will jointly seek a solution to this challenge. Integration element (IE): The powder is transferred from a reservoir to a conveyor by applying an electrostatic field between them. In this process, the powder takes on a charge from the reservoir and lifts to the conveyor. This is the same physical phenomenon we experience at children’s birthday parties when balloons are rubbed in hair and stuck to the ceiling. The conveyor is made of an electrically conductive material with an electrically insulating coating that prevents the powder hanging on it from losing its charge. The powder can then be transported without falling off. We call the conveyor an integration element (IE) because this machine element connects the process steps; powder attraction and powder deposition. We have investigated a variety of IE materials and material combinations to find out how they function in the process. To our surprise, we have found three good principles for the construction of IE for the deposition of multimaterial powder layers: 1. Experiments have been done with the attraction of entire powder layers to the conveyors consisting of electrically charged backsides and insulating coatings on the front. The advantage of this type of IE is that the powder retains its charge for a long time, even after the external electric field is turned off. Deposition tests have been carried out showing that the powder pattern is transferred from the conveyor to the workpiece. The general idea is to draw a pattern on the integration element with a laser beam so that the powder that is illuminated falls or is pushed down onto the workpiece. Within laser technology, this process is called Laser-Induced Forward Transfer (LIFT). We have not yet built parts with this technology, but we are approaching results where it will be possible. 2. Powder attraction to ions deposited on the surface of glass/sapphire. Using the corona effect (dielectric breakdown of air molecules), we have deposited ions on the surface of electrically insulating materials. The powder has then been attracted to the ions and attached to the surface. The deposition process remains the same, where a laser is used to achieve LIFT. The advantage of such a setup is that the IE becomes a monomaterial, which makes the conveyor more laser transparent and mechanically stronger. The disadvantage is that the IE loose its charge quicker than the powder, so that the powder detaches earlier. 3. IE with a loose electrically conductive backside: Charged powder on the electrically insulating surface induces an opposite charge in the ground plane on the backside, and since opposite charges attract each other, the powder is held in place. If the insulating coating has low dielectricity, much of the holding force will disappear if the ground plane is removed, and the powder can fall off. Thus, if you remove the backside, the powder falls off. It has previously been shown by SINTEF that we can use electrophotography to create multimaterial powder images. The challenge then, was how we could deposit this powder image onto the product. Hence, we have started experimenting with lifting the ground plane of the IE to get the powder to release, which causes the powder to fall onto the workpiece. It is still uncertain how well this will work in practice, but the first tests look promising. The project is currently looking into IP protection and patenting. The project has developed good relations with the Multi-material solutions group at Fraunhofer ICGV. During the start of this year, a Horizon Europe application for 6MEUR was submitted together with them and several industrial partners focusing on battery production.

Additive manufacturing (AM) is a standardized term that includes a group of production processes of joining material successively, often layer upon layer. Since the market launch of the first AM machine in 1987, the field of AM has grown rapidly in both process variations and applications, and has become a multi-billion-dollar industry. Many AM-processes produce engineering materials that are being applied for critical parts in highly demanding user cases. With AM came new ideas about functionally graded materials and building sensors directly integrated into parts. Functionally graded materials with respect to material composition allows designs with a transition in physical properties through a component. This has been a topic of research for many years. The primary objective of the project is to develop a process for consolidation of multi-material powder layers with full three-dimensional freedom. Electrophotographic powder layer production is used together with laser consolidation to build an object layer by layer. The electrophotographic principle can transfer several materials simultaneously, thus producing an object with fully three-dimensional freedom in material and form. There are two main challenges: 1. Integration of the electrophotographic production and the laser fusing requires a laser transparent machine element that contains these attributes; dielectric layer, electrically conductive layer and mechanically stable. 2. We aim to develop a mathematical model of laser light interaction with the powder layer and the machine element. Based on the modelling results, identify and decide for the required laser operation regime (cw, ns, fs), power, wavelengths, focus geometry, focus depth and pulse repetition rate to achieve the desired fusion. The project will apply special laser expertise and equipment that is connected to the research partners in the project. Finally, we will demonstrate the principle through producing multi-material samples.

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FRINATEK-Fri prosj.st. mat.,naturv.,tek