Soluble sacrificial materials for use in generative manufacturing using ultrasound

Description

BACKGROUND OF THE INVENTION

[0001] The described invention relates in general to systems, devices, methods, and materials used in additive manufacturing, and more specifically to soluble sacrificial materials for use in ultrasonic additive manufacturing processes.

[0002] Ultrasonic additive manufacturing (UAM) is an additive manufacturing technique used to create to create solid objects, parts, or components. UAM involves building up a solid metal object through ultrasonically welding successive layers of thin metal foil (provided as tapes or sheets) into a three-dimensional shape, with periodic machining operations to create the detailed features of the resultant object. High-frequency ultrasonic vibrations are locally applied to the metal foils (to break oxide layers found thereon), which are held together under high pressure, to create a solid-state weld. UAM systems typically include a rolling ultrasonic welding system, consisting of an ultrasonic transducer, a primary booster, a welding sonotrode, and a secondary booster. The vibrations of the transducer are transmitted to the welding sonotrode (i.e., a horn), which is disc-shaped, rolling in the x-direction, and from there to a foil-metal base, which creates an ultrasonic solid-state weld between the thin metal foil and the base material. The continuous rolling and raster pattern of the sonotrode over the foil welds the entire foil to the substrate. By welding a succession of metal foils, first side by side, then one on top of the other (but staggered so that seams do not overlap), a solid metal part can be built. Through the course of the build, there are usually periodic machining operations, using an integrated computer numerically controlled (CNC) system, to add features to the part, to remove excess foil material, and to level the topmost surface of the part. This process is repeated until a solid component has been created or a feature is repaired or added to a component. Thus, the process typically involves subtractive as well as additive steps.

[0003] UAM is often used to create components or parts that include internal features such as chambers, cavities, and / or channels through which fluids or gases will flow when the component or part is in use. A portion of the component or part may be created and then the chambers, cavities, and / or channels may be machined into that portion. Applying the additional metal foils necessary to complete the component or part can result in the successively added foil layers bowing or deforming into the chambers, cavities, and / or channels, thereby changing the geometry of these structures and having potentially adverse effects on the mechanical properties thereof and / or the flow of fluids or gases through such openings. To prevent this undesirable outcome, the machined chambers, cavities, and / or channels can be filled with a supportive material prior to the application of additional foil layers. This material is "sacrificial" in the sense that it is removed after the build is complete. Powdered metals and low melting point metals have been used for this purpose, but such materials can be difficult and even dangerous to completely remove from the component or part once the UAM process is complete. Accordingly, there is an ongoing need for a completely soluble sacrificial material that can be easily and entirely removed from a completed component or part. MOHANTY SOUMYARANJAN ET AL: "Fabrication of scalable tissue engineering scaffolds with dual-pore microarchitecture by combining 3D printing and particle leaching", MATERIALS SCIENCE AND ENGINEERING C, ELSEVIER SCIENCE S.A, CH, vol. 61, 19 December 2015 (2015-12-19), pages 180-189, XP029403031, ISSN: 0928-4931, DOI: 10.1016 / J.MSEC.2015.12.032 discloses a new technique to fabricate dual-pore scaffolds for various tissue engineering applications where 3D printing of poly(viny alcohol) (PVA) mould is combined with salt leaching process. In this technique the sacrificial PVA mould, determining the structured pore architecture, was filled with salt crystals to define the random pore regions of the scaffold. After crosslinking the casted polymer the combined PVA-salt mould was dissolved in water. DATABASE WPI Week 201661 Thomson Scientific, London, GB; AN 2016-399643 & CN 105 670 189 A (HENAN INST ENG) (2016-06-15) disclose a rapidly dissolvable fused glass pellet polyvinyl alcohol silk material and a preparation method thereof. US 2017 / 304964 A1 discloses structures manufactured using ultrasonic additive manufacturing, and more particularly, forming structures with free spaces using ultrasonic additive manufacturing. US 2018 / 111337 A1 discloses additive manufacturing systems for printing three-dimensional (3D) parts and support structures. In particular, the present disclosure relates to a water soluble material for use in 3D printers, and methods of printing 3D parts.SUMMARY OF THE INVENTION

[0004] The invention is set out in the appended set of claims.

[0005] In accordance with one example, a first sacrificial material for use in ultrasonic additive manufacturing is provided. This sacrificial material includes at least one water-soluble solid (such as a salt); and at least one water-soluble binding agent, wherein the at least one water-soluble solid is mixed with the at least one water-soluble binding agent and cured at a predetermined temperature for a predetermined period of time prior to use in ultrasonic additive manufacturing.

[0006] In accordance with another example, a second sacrificial material for use in ultrasonic additive manufacturing is provided. This sacrificial material includes a water-soluble solid (such as a salt); and a water-soluble binding agent, wherein the water-soluble binding agent includes a synthetic polymer, wherein the synthetic polymer includes or is polyvinyl alcohol or polyvinyl acetate, and wherein the water-soluble solid is mixed with the water-soluble binding agent and cured at a predetermined temperature for a predetermined period of time prior to use in ultrasonic additive manufacturing.

[0007] In yet another example, a third sacrificial material for use in ultrasonic additive manufacturing is provided. This sacrificial material includes a solid, wherein the solid is a sodium salt such as sodium chloride; and a binder, wherein the binder includes or is polyvinyl alcohol or polyvinyl acetate, and wherein the solid is mixed with the binder and cured at a predetermined temperature for a predetermined period of time prior to use in ultrasonic additive manufacturing.DETAILED DESCRIPTION OF THE INVENTION

[0008] As previously stated herein, the described invention relates in general to systems, devices, methods, and materials used in additive manufacturing and related processes, and more specifically to various soluble supportive sacrificial materials for use in ultrasonic additive manufacturing systems and processes. A supportive sacrificial material used in 3D printing processes or additive manufacturing processes enables building material on over-hangs (e.g., ledges) or when printing internal features (e.g., channels or conduits) within a part. In such cases, a sacrificial support material acts as an artificial substrate on which material may be printed or deposited. For such applications, an effective sacrificial support material should also be completely removable from a finished component or part so as not to interfere with the proper functioning of the component or part. While the actual sacrificial support material may vary based on the specific application for which it is being used, such material must typically (i) be easy to add to a feature of any size without disrupting printing for any significant period of time; (ii) be able to withstand processing conditions without affect to the additive process; and (iii) be able to be removed from the features associated with its use without affecting any surrounding material. UAM requires a very stiff substrate for printing, accordingly, any sacrificial support material must also be stiff or otherwise very supportive. While prior art approaches have utilized powdered metals or low melting point metals, as discussed above, these materials suffer from significant limitations which are effectively overcome by this invention.

[0009] The present invention overcomes the deficiencies of previously known sacrificial materials used for UAM by providing a suitably stiff and stable artificial substrate on which material may be printed or deposited. Exemplary embodiments of this artificial substrate include at least one water-soluble solid and at least one water-soluble binding agent or binder. The at least one water-soluble solid that is partially dissolved in, suspended in, or mixed with the at least one water-soluble binding agent and cured at a predetermined temperature for a predetermined period of time prior to use in ultrasonic additive manufacturing. The at least one solid may be a salt such as a sodium salt (e.g., sodium chloride), a potassium salt, an ammonium salt, or various combinations thereof; and the at least one binding agent may include polyvinyl alcohol (PVA), polyvinyl acetate, or similar materials. A suitable PVA is commercially available from Fibre Glast Developments Corporation (Brookville, Ohio) (see https: / / s3.amazonaws.com / cdn.fibreglast.com / downloads / PDCT-SDS-00002.pdf). This product is a mixture of ethanol (CAS No. 64-17-5; concentration ≥30 - ≤35) and n-Butanol (CAS No. 71-36-3; concentration ≥1 - ≤2). In an exemplary embodiment of this invention, the ratio of salt to PVA is five parts salt to one part PVA by volume, although a wide range of ratios is possible. In most instances, the addition of more PVA results in a mixture having a thinner consistency, thereby requiring additional time for curing.

[0010] Both primary components of the present invention (i.e., the solid and the binding agent) are 100% soluble in water and are therefore very easy to remove from various internal geometries, as desired. In certain embodiments, the PVA acts as a binder that holds together a fully soluble powder that does not dissolve or does not dissolve entirely in the PVA. The use of salt, such as sodium chloride provides a suitable level of stiffness (as compared to less suitable materials such as sugars) while still being very easy to dissolve when the sacrificial material is ultimately removed. In addition to salt(s), other embodiments of this invention include one or more additional stiffening components such as, for example, fiber glass, at least one metal powder (e.g., aluminum or tin), sand, or combinations thereof.

[0011] An exemplary embodiment of the sacrificial material of the present invention is prepared by mixing salt with PVA to form a mixture. The mixture is then poured or otherwise deposited into a cavity, channel, conduit, or other void that has been formed in a partially completed UAM part or component. The mixture is then cured at a predetermined temperature (e.g., 23°C to 200°C) for a predetermined period of time (e.g., fifteen minutes to twenty-four hours). Curing may occur at room temperature or at an elevated temperature by placing the part on a resistive heater, hot plate, or the like. The period of time required for curing is dependent on the size of the cavity and the temperature at which the mixture is heated. After the material has cured, channels or other features may be machined into the sacrificial material for the purpose of facilitating extraction of the material from the completed part or component. UAM is then utilized to complete the part or component and a solution containing water is introduced into the part or component to dissolve the sacrificial material so that it can be flushed out of the part or component or otherwise completely removed such that no residual material remains.

Claims

1. A sacrificial material for use in ultrasonic additive manufacturing, comprising: (a) a water-soluble solid, wherein the water-soluble solid is a sodium salt, a potassium salt, an ammonium salt, or combinations thereof; and (b) a water-soluble binding agent, wherein the water-soluble binding agent includes a synthetic polymer, wherein the synthetic polymer is polyvinyl alcohol or polyvinyl acetate, (c) wherein the water-soluble solid is mixed with the water-soluble binding agent and cured at a predetermined temperature for a predetermined period of time prior to use in ultrasonic additive manufacturing; and (d) a stiffening component, wherein the stiffening component includes fiber glass, at least one powdered metal, sand, or combinations thereof.

2. The sacrificial material of claim 1, wherein ratio of the water-soluble solid to the water-soluble binding agent is five parts water-soluble solid to one-part water-soluble binding agent, by volume.

3. The sacrificial material of claim 1, wherein the predetermined temperature is in the range of 23°C to 200°C, and wherein the predetermined period of time is within the range of fifteen minutes to twenty-four hours.

4. A sacrificial material for use in ultrasonic additive manufacturing, comprising: (a) a solid, wherein the solid is sodium chloride; and (b) a binder, wherein the binder is polyvinyl alcohol, and (c) wherein the solid is mixed with the binder and cured at a predetermined temperature for a predetermined period of time prior to use in ultrasonic additive manufacturing; and (d) a stiffening component, wherein the stiffening component includes fiber glass, at least one metal powder, sand, or combinations thereof.

5. The sacrificial material of claim 4, wherein ratio of the solid to the binder is five parts solid to one-part binder, by volume; wherein both the solid and the binder are water soluble, or wherein the predetermined temperature is in the range of 23°C to 200°C, and wherein the predetermined period of time is within the range of fifteen minutes to twenty-four hours.