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

The project aims to develop a production process where the fabrication of geometrically complex parts with full freedom in the placement of various materials. Parts can then be produced with the right materials at the correct part section, such as e.g. a knee implant. The knee implant comes into contact partly with bone and partly with tissue, where one metal is friendly with bone and another with tissue. It will then be natural to manufacture 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 heat conduction, electrical conductivity, wear resistance, corrosion resistance, etc. The idea is to further develop the additive (3D-print) technology so that it can produce geometrically accurate multi-metal products with any shape. 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 workpiece being built, and next to find a good way of solidifying the powder onto the workpiece. The project will investigate whether this can be done with the help of modern laser technology. The laser physics group at NTNU, the materials scientists at SINTEF Industri and the additive manufacturing group at SINTEF Manufacturing will jointly search for a solution to this challenge. The integration element: Powder is transferred from a powder bed to a conveying plate by applying an electrostatic field between them (powder attraction). First, the powder receives a charge from the reservoir and hence sticks to the plate. This is similar to a balloon that attaches to the ceiling after having rubbed it against someone's hair. The plate is made of an electrically conductive material with an electrically insulating coating, which means that the attached powder does not lose its charge. Hence, the powder can be transported without falling off. We call this plate an integration element because it is a machine element that connects the process steps of powder attraction and powder deposition. Powder attraction is easy to realize if you manage to establish an integration element that is electrically conductive, has a thin electrically insulated coating and is transparent to the applied laser. Finding a material combination and implementing it as an integration element that fulfills all these requirements is challenging and one of the main tasks in the project. The project has built a test rigg to measure and try how the different materials and combinations work as integration elements. Placing powder with laser: The deposition process is where the powder is transferred in a certain pattern from the integration element to the object. Depositing powder to build an object is an unsolved problem that is challenging. We are investigating whether modern laser technology can be used for this purpose. The idea is to draw a pattern on the integration element with a laser beam so that the illuminated powder falls onto the workpiece. In laser technology, this process is called Laser-Induced Forward Transfer (LIFT). LIFT has been demonstrated to work in other types of processes, but not for additive deposition of powder materials. Investigating LIFT for powder deposition is a main activity in the project. We also investigate selective manipulation of powder charge through electron emission (UV laser exposure) in combination with electrostatic transfer as a deposition method. The project has built two miniature prototypes to test combinations of different lasers and integration elements. Such a multi-material freeform production system will drastically expand the design freedom in the production of new products. It will also make it possible to limit the use of rare materials as they can be used only where they are needed in the part.

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.