Rapid Manufacturing Process by Using a Focused Ultrasound Beam

摘要

The invention refers to a process for rapid manufacturing that uses a focused ultrasound beam according to the invention. The process is based on the local ultrasound welding of the material (2) grains that is under a powder form, welding that takes place solely in the focal spot of the focused ultrasound beam, the focal spot being scanned across the X-Y-Z directions within the powder (2) bed so as to 3D build the entire object (7) that is desired. The processes taking place in the focal spot region are local melting, local melting due to friction followed by filling of the gaps existing between grains, removal of the grain asperities, local inter-diffusion between neighboring grains as well as other phenomena that take place at the interfaces between materials when these are subjected to an ultrasound field.

主权项

1. Rapid manufacturing process by using a focused ultrasound beam according to the invention, characterized by that it makes use of the local welding of the powder grains that are placed in the focal spot of the focused ultrasound beam, the focal spot of the ultrasound beam being scanned within the powder mass in such a way so as to create the object (7) in 3D, the processes taking place in the focal spot of the focused ultrasound beam being at least one of the following such as local melting, local melting because of friction followed by the filling of the gaps existing between grains, removal of the grains asperities, local inter-diffusion between neighboring grains as well as other phenomena that take place at the interface between materials that are exposed to an ultrasonic field, the rapid manufacturing process by using a focused ultrasound beam containing the following steps:
step 1: filling of a bin (1) with the powder of material (2) that will e used for making the object. The thickness of the powder bed (2) is determined by the attenuation distance of the ultrasound used for the building process in the respective powder (2) within the working conditions used for building the desired object and by the maximum vertical travel allowed for the focal spot. The powder is supplied to the bin (1) by current state-of-the-art feeding systems. step 2: degassing and eventual drying of the powder. This step can be achieved in a slight vacuum, the pressure being contained in the 10−12 Torr to 0.1 Torr range. Moreover, the bin (1) containing the powder material (2) can be vibrated a certain time interval in order to compactify the powder mass, the vibration frequency ranging in the 2 Hz and 2 MHz interval while the vibration amplitude ranges between 10 nm and 1 mm. step 3: application of a cap/sealing_(3) atop of powder (2) and pressing the powder (2) over the whole building duration with a large enough force, force magnitude that depends on the material used and on its properties. The bin (1) containing the powder (2) may also be vibrated a certain time interval during this step also, with the cap/sealing_(3) pressing powder (2), the vibration parameters being similar to those mentioned at step 2. step 4: atop the cap/sealing_(3) is put a liquid (4) that has the role of creating an acoustic impedance match between source (5), respectively ultrasound optics (6) for focusing of ultrasound, and cap/sealing_(3), so that an optimum ultrasound power transfer being ensured. In some other situation, this liquid may lack/may not exist, the source (5) formed by an array of individual sources (5) being sit directly on the cap/sealing_(3). step 5: if necessary, the powder (2) may be heated up to a certain temperature during the building process, but without evaporating or boiling the liquid (4), in case the liquid (4) is used. step 6: the source (5) of ultrasound is started and—if ultrasound focusing optics (6) is used, optics (6) is descended so as the focal spot lies at the base of bin (1) in the powder bed (2). step 7: that deepest layer of powder (2) mentioned in step 6 is scanned at constant height by the focal spot of the ultrasound, in this way the local/selective welding process taking place. The power of source (5) may be varied during the scan, being maximum only where the local welding of the powder grains is needed. step 8: the ultrasound focal spot is moved up in the vertical direction, from bottom to top, on a certain distance determined by the spatial resolution of the ultrasound focal spot—more precisely, determined by the size of the ultrasound focal spot and by the power of source (5)—with the help of optics (6). Step 7 is repeated until the whole 3D object (7) is realized. In the case when the source (5) is an array of individual sourced (5) sitting on the cap/sealing (3), the relative phase mismatch between the individual sources (5) is varied in such a way that the focal spot is scanned in all three spatial directions—making the object in a layer-by-layer from bottom to the top—with spatial resolution determined by the size of the ultrasound focal spot and by the power of the individual sources (5). Moreover, if the geometry of the object (7) allows, steps 7 and 8 can be merged together. If the object (7) is larger than the layer thickness deposited during step 1, then the cap/sealing_(3) is removed, then a new layer of powder (2) is put into the bin (1) with a thickness determined by the factors mentioned for step 1 and steps 2 to 8 are repeated. The whole ensemble of steps 1 to 8 is repeated until the whole object (7) is made. During same step 8 some non-destructive imaging techniques—as for example ultrasound imaging by using a frequency different than that used for 3D building the object (7)—may be used in order to monitor in real-time the building process and for determining the presence of any building errors. For example, the ultrasound imaging can be realized with an ecography system placed laterally with respect to the bin (1), the imaging ultrasound beam propagating at 90° with respect to the ultrasound beam used for the 3d building of the object (7). step 9: after the completion of the object (7) building, the ensemble is left to cool down if this ensemble was heated during step 5. step 10: if liquid (4) was used, then liquid (4) is taken-off from above the cap/sealing_(3). If the liquid (4) is solid under ambient conditions, then liquid (4) is left to cool down and eventually solidify, after which the resulting solid material is removed from atop of the cap/sealing (3) if necessary. step 11: the cap/sealing (3) is removed. step 12: the object (7) and the remaining powder (2) are taken off from the bin (1). Object (7) is cleaned as regards the eventual non-welded powder (2) grains remaining on it. This cleaning can be achieved in several ways as for example—but without restraining generality—gas blasting.