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

The project aimed to develop a multi-material production process for creating geometrically complex parts. These parts could be built with the desired materials in the correct locations, such as a knee implant. The knee implant partially contacts bone and partially tissue, where one metal is compatible with bone and another with tissue. Naturally, the implant should be made with two different metals so that both bone and tissue thrive. This technology enables the production of parts with the right properties in the right place, such as thermal conductivity, electrical conductivity, wear resistance, corrosion resistance, etc. The idea was to further develop additive technology (3D printing) to produce geometrically accurate multi-metal products of arbitrary shape. The project was based on a method for producing multi-metal powder layers developed at NTNU and SINTEF. The challenge was both to transfer the powder layer to the part being built and to achieve good bonding with the part. The project aimed to investigate whether this could be done using modern laser technology in combination with electrophotography. The laser physics environment at NTNU, the materials environment at SINTEF Industry, and the production environment at SINTEF Manufacturing would jointly seek a solution to this challenge. Electrophotography is based on two natural phenomena: materials with opposite electrical polarity attract each other, and there are materials that become electrically conductive when exposed to light. Based on these phenomena, electrophotography can create and transfer toner images to paper in a six-step process: 1. The entire surface of a photoreceptor is charged in the dark. The photoreceptor has the property of providing electrical resistance in the dark and being electrically conductive when illuminated. 2. A pattern is then drawn on the photoreceptor with a light beam, creating an invisible image consisting of charges. 3. The charge image is then developed with toner of opposite polarity, creating a visible image on the photoreceptor. 4. The image is then transferred to the paper with an electrostatic field, and charges are deposited on the back of the sheet to hold the toner in place. 5. The paper and toner image then pass between two heated rollers that press and melt the toner in place. The paper then comes out of the copier ready for collection. 6. The photoreceptor is cleaned, and the next cycle can begin. In a color printer, a photoreceptor is used for each color (Cyan, Magenta, Yellow, and Key (black)), and the color image is created by sequentially transferring the respective colors. We have developed an element that replaces the paper so that the toner image (metal powder in our case) can be transferred to the element instead of the paper. The element is transported to the product that will receive the powder image, and then we use modern laser technology to transfer the powder image from the element to the product. The powder image is then melted onto the product using an additive manufacturing method known as Powder Bed Fusion. We have tried several concepts and succeeded with one of them. The method makes the electrophotography process no longer a method for transferring toner to paper, but it can now transfer powder images to any substrate. Powder Bed Fusion is a method that builds up a product layer by layer, and our newly developed solution is an addition to electrophotography that allows for the transfer of powder images layer by layer. We have thus laid the foundation for developing a new additive process that can process multi-material images layer by layer, and thus multi-material products can be created. Conclusion: The project has positively addressed a challenge that SINTEF and NTNU have been working on for 35 years. The development is based on Professor Bjørke's patent from 1993. Neither Karlsen and Bakkelund's patent from 2001 nor Karlsen and Åsebø's patent from 2007 have proven feasible. Major international stakeholders who helped develop the electrophotography process have approached us and asked if we can really do this, i.e., stack images on top of images. This shows us that IPR protection is urgent. A video has been posted on LinkedIn describing the first test to verify how one of the methods can work: https://www.linkedin.com/posts/vegard-br%C3%B8tan-886a0440_cirp-sintef-additivemanufacturing-activity-7082976317549215744-wfTF?utm_source=share&utm_medium=member_desktop

Vi mener at løsningen vi har utviklet ikke bare adresserer vår opprinnelige utfordring med å skape en prosess for å produsere multimateriale produkter med fri geometri, men også fungerer som et generelt tillegg til elektrofotografiprosessen. Dette gjør det mulig for hele print-industrien å bruke elektrofotografi i nye markeder. Vi er overbevist om at denne løsningen er den første i verden som kan stable bilder av metallpulver, og at mange bruksområder vil bli oppdaget når teknologien tas i bruk og blir kjent.

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.