METHODS OF ULTRASOUND ASSISTED 3D PRINTING AND WELDING

Abstract

Methods of ultrasound assisted 3D printing and welding involve the use of an ultrasonic sonotrode placed in on top of the solidified layer in the vicinity of a melt pool. The sonotrode, pressed against the solidified materials at the edge of the melt pool, is synchronized with the heat source such that it travels side-by-side with the melt pool to transmit ultrasonic vibrations to the solidifying melt pool, reducing hot tearing and porosity formation, and to consolidate the solidified materials under the sonotrode. The methods of the present invention are capable of making a large variety of commercially important alloys 3D printable and weldable.

Claims

1. A method for forming high internal quality and high mechanical property 3D printing articles, comprising the step of: forming a melt pool by melting solid materials using a heat source conventionally used for 3D printing; placing the acoustic sonotrode of an ultrasonic vibration system in close vicinity of the melt pool for transmitting high-intensity ultrasonic vibration to the melt pool; applying a compressive thrust load on the sonotrode; synchronizing the sonotrode and the heat source such that the sonotrode and the melt pool travel side-by-side at a fixed distance between them; and applying ultrasonic vibrations through the sonotrode to transmit the vibrations to the materials under or nearby the sonotrode, including the solidifying material in the melt pool.

2. A method of claim 1, wherein the melt pool is formed by melting solid materials, consisting of metallic materials, polymers, or composite materials, using a laser or an electron beam and wherein the solid materials are provided in the form of a wire using a wire feeding mechanism, powders using a powder-feeding mechanism, or powders in a powder bed.

3. A method of claim 1, wherein the ultrasonic vibration is applied either on the just solidified material close to the edge of the melt pool or partially on the top of the melt pool so that ultrasonic vibration is transmitted to the melt pool as well as the just solidified materials near the weld pool.

4. A method of claim 1, wherein the sonotrode is either a rolling sonotrode vibrating substantially parallel to the plane of the contact surfaces or a sonotrode vibrating substantially perpendicular to the plane of the contact surfaces.

5. A method of claim 1, wherein the sonotrode is wide enough to cover at least one or more scans width of printed materials.

6. A method of claim 1, wherein the ultrasonic vibration is applied at a frequency between about 10 kHz and about 200 kHz, at a power level between about 1 watt and about 10,000 watts.

7. A method of claim 1, wherein the compressive thrust load is high enough to ensure effective transmission of ultrasonic vibration to the melt pool to form small equiaxed grains during the solidification of the melt pool.

8. A method of claim 1, wherein the sonotrode is made of titanium alloy, aluminum alloy, steel, or ceramic materials.

9. A method for forming high internal quality and high mechanical property welding of solid articles, comprising the step of: forming a melt pool by melting solid materials using a heat source conventionally used for welding; placing the acoustic sonotrode of an ultrasonic vibration system in close vicinity of the melt pool for transmitting high-intensity ultrasonic vibration to the melt pool; applying a compressive thrust load on the sonotrode; synchronizing sonotrode and the heat source such that the sonotrode and the melt pool travel side-by-side at a fixed distance between them; and applying ultrasonic vibration through the sonotrode to transmit the vibrations to the materials under or nearby the sonotrode, including the solidifying material in the melt pool.

10. A method of claim 9, wherein the melt pool is formed by melting solid metallic materials using a heat source including but not limited to flame, arc, laser, and electron beam and wherein the solid materials are provided in the form of a wire using a wire feeding mechanism or powders using a powder-feeding mechanism.

11. A method of claim 9, wherein the ultrasonic vibration is applied either on the just solidified material close to the edge of the melt pool or partially on the top of the melt pool so that ultrasonic vibration is transmitted to the melt pool as well as the just solidified materials near the weld pool.

12. A method of claim 9, wherein the sonotrode is either a rolling sonotrode vibrating substantially parallel to the plane of the contact surfaces or a sonotrode vibrating substantially perpendicular to the plane of the contact surfaces.

13. A method of claim 9, wherein the sonotrode is wide enough to cover the just solidified materials.

14. A method of claim 9, wherein the ultrasonic vibration is applied at a frequency between about 10 kHz and about 200 kHz, at a power level between about 1 watt and about 10,000 watts.

15. A method of 9, wherein the compressive thrust load is high enough to ensure effective transmission of ultrasonic vibration to the melt pool to form small equiaxed grains during the solidification of the melt pool.

16. A method of 9, wherein the sonotrode is made of titanium alloy, aluminum alloy, steel, or ceramic materials.

17. A method for forming high internal quality and high mechanical property solid articles with layered structure, comprising the step of: placing the acoustic sonotrode of an ultrasonic vibration system in close vicinity of where the liquid material is to be deposited on a solid substrate; applying a compressive thrust load on the sonotrode; synchronizing sonotrode and the liquid deposition system such that the sonotrode and the deposited liquid material travel side-by-side at a fixed distance between them; depositing liquid material, and applying ultrasonic through the sonotrode to the deposited liquid material during its solidification process.

18. A method of claim 17, wherein the deposition process includes but not limited to potting, coating, painting, filling, and spray.

19. A method of claim 17, wherein the liquid material, similar or dissimilar to the solid substrate, includes metallic, polymer, and ceramic material at its liquid state or semi-solid state.

20. A method of claim 17, wherein the sonotrode is either a rolling sonotrode vibrating substantially parallel to the plane of the contact surfaces or a sonotrode vibrating substantially perpendicular to the plane of the contact surfaces.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIGS. 1A and 1B are schematic representations of an ultrasound assisted 3D printing method using a rolling sonotrode in accordance with this invention.

[0017] FIGS. 2A and 2B are schematic representations of an ultrasound assisted 3D printing method using a sonotrode vibrating in the direction perpendicular to the top surface of the melt pool in accordance with this invention.

[0018] FIG. 3 is a schematic representation an ultrasound assisted welding method using a rolling sonotrode in accordance with this invention.

[0019] FIG. 4 is a schematic representation of an ultrasound assisted welding method using a sonotrode vibrating in the direction perpendicular to the top surface of the melt pool in accordance with this invention.

[0020] FIG. 5 is the Pb—Sn phase diagram showing the large solidification interval of the Pb-20% Sn alloy described in the example of this invention.

[0021] FIGS. 6A and 6B disclose comparable micrographs of grain structure in samples that have or have not been subjected to ultrasonic vibration, respectively.

[0022] FIGS. 7A and 7B disclose comparable micrographs of hot tearing in samples that have or have not been subjected to ultrasonic vibration, respectively.

[0023] FIGS. 8A and 8B disclose comparable micrographs of porosity formation in samples that have or have not been subjected to ultrasonic vibration, respectively.

DETAILED DESCRIPTION OF THE INVENTION

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety.

[0025] The present invention teaches to synchronize a high-intensity ultrasonic vibration system and a heat source so that the sonotrode and the melt pool travel side-by-side, to focus very high power density (VHPD) ultrasonic vibrations on the solidified material in close vicinity of the melt pool, and to apply a compressive thrust load on the ultrasonic vibrators. The combination of VHPD ultrasonic vibrations and compressive force allows 1) to vibrate the small melt pool to achieve grain refining and eliminating hot tearing and porosity, 2) to hot work on the material just solidified while it is still near the solidus temperature or even semi-solid temperatures, 3) to bond the just solidified material to the layer previously deposited, and 4) to hot work and cold work material previously deposited. Here the heat sources include but are not limited to laser, electron beams, flames, and arcs. Power density is defined as the energy of power per unit area at the end surface of a sonotrode, and the melt pool is fed either by a powder nozzle, a wire feeder, or by consuming powder bed.

[0026] The melt pool to be treated is only within millimeters in diameter during 3D printing or welding. Thus, a very small sonotrode tip is needed for processing such a small melt pool. Ultrasonic energy can be focused on such a small tip to achieve VHPD. Assuming the tip diameter is 3 mm, ultrasonic vibrations at the power level of 10 W would generate power densities over 140 W/cm.sup.2 at the end surface of the sonotrode, which is high enough to induce cavitations in molten aluminum. By placing the sonotrode on the just solidified material in close vicinity to the melt pool, attenuation of ultrasonic energy from the sonotrode to the melt pool is minimized, and the majority of the acoustic energy can be transferred to the melt pool to produce equiaxed grains and to eliminate hot tearing and porosity. In the mean time, the just solidified hot material under the sonotrode is hot pressed under the influence of VHPD ultrasonic vibration which promotes further consolidation and grain deformation. Ultrasonic consolidation of materials at high temperatures under compression is extremely effective in closing cracks, porosity, and delamination between layers. Furthermore, the cold material previously solidified is also subject to VHPD ultrasonic vibration. High-intensity ultrasonic vibrations are capable of increasing dislocation density and nano-sized grains in the solid material during cold working [3, 9].

[0027] FIG. 1 illustrates a preferred ultrasound assisted 3D printing process using a rolling sonotrode 14 vibrating in the direction 32 parallel to the top surface of the powder bed 22 or the solidified materials of the currently scan layer 28. In this method, shown in FIG. 1A and FIG. 1B, the heat source 20 melts the materials in the powder bed 22 and forms the melt pool 10. The rolling sonotrode 14 is placed either on top of the solidified materials 26 close to the edge of the melt pool 10, partially on top of the melt 10, or on top of the solidified material 28 close to the melt pool 10. The rolling sonotrode 14 is synchronized with the heat source 20 so that it travels in the same direction as illustrated by arrow 30 at that same speed as that of the melt pool 10. As the heat source 20 travels over the powder bed 22, the melt pool 10 consumes the powder bed 22 and solidifies on the previously deposited layer 24 and the just solidified materials 26 in the current scan and the solidified materials on the currently scanned layer 28. The solid-liquid interface 12 is a boundary separating the melt 10 from the solids 22, 24, 26, and 28. VHPD acoustic vibrations vibrating in the direction as illustrated by arrow 32 are transmitted from the rolling sonotrode 14 to the melt pool 10, causing cavitations in the melt 10 and interface 12 related convections that break up columnar dendrites into fragments of equiaxed dendrites. VHPD acoustic vibrations are also applied on the just solidified materials 26 in the current scan for further consolidation of the hot material and on the previous solidified materials 24 and 28 for cold working of the cold material. The compressive load 18 applied on the rolling sonotrode 14 ensures improved transmission of the VHPD vibrations to the materials nearby and enhances the deformation and consolidation of materials under the rolling sonotrode 14.

[0028] FIG. 2 illustrates a preferred ultrasound assisted 3D printing process using a sonotrode 16 vibrating in the direction 32 perpendicular to the top surface of the powder bed 22 or the solidified materials of the currently scan layer 28. In this method, shown in FIG. 2A and FIG. 2B, the heat source 20 melts the materials in the powder bed 22 and forms the melt pool 10. The sonotrode 16 is placed either on top of the solidified materials 26 close to the edge of the melt pool 10, partially on top of the melt 10, or on top of the solidified material 28 close to the melt pool 10. The sonotrode 16 is synchronized with the heat source 20 so that it travels in the same direction as illustrated by arrow 30 at that same speed as that of the melt pool 10. As the heat source 20 travels over the powder bed 22, the melt pool 10 consumes the powder bed 22 and solidifies on the previously deposited layer 24 and the just solidified materials 26 in the current scan and the solidified materials of the currently scan layer 28. The solid-liquid interface 12 is a boundary separating the melt 10 from the solids 22, 24, 26, and 28. VHPD acoustic vibrations vibrating in the direction as illustrated by arrow 32 are transmitted from the rolling sonotrode 16 to the melt pool 10, causing cavitations in the melt 10 and interface 12 related convections that break up columnar dendrites into fragments of equiaxed dendrites. VHPD acoustic vibration is also applied on the just solidified materials 26 in the current scan for further consolidation of the hot material and on the previous solidified materials 24 and 28 for cold working of the cold material. The compressive load 18 applied on the sonotrode 16 ensures improved transmission of the VHPD vibrations to the materials nearby and enhances the deformation and consolidation of materials under the sonotrode 16.

[0029] The present invention related to ultrasound assisted 3D printing can be applied to printing materials including polymers, metallic materials, and composite materials containing ceramic particles to produce 3D solid components of high internal quality and high mechanical properties.

[0030] FIG. 3 illustrates a preferred ultrasound assisted welding process using a rolling sonotrode 14 vibrating in the direction 32 parallel to the top surface of the sheet materials, 42 and 44, to be welded. In this method, the heat source melts the materials of the welding wire and sheet materials 42 and 44, and forms the melt pool 10. The rolling sonotrode 14 is placed either on top of the solidified seam 40 close to the edge of the melt pool 10, partially on top of the melt 10, or on top of the sheet material 42 or 44 close to the melt pool 10. The rolling sonotrode 14 is synchronized with the heat source so that it travels in the same direction as illustrated by arrow 30 at that same speed as that of the melt pool 10. VHPD acoustic vibrations vibrating in the direction as illustrated by arrow 32 are transmitted from the rolling sonotrode 14 to the melt pool 10, causing cavitations in the melt 10 that break up columnar dendrites into fragments of equiaxed dendrites. VHPD acoustic vibration is also applied on the just solidified materials 40 for further consolidation of the hot material. The compressive load 18 applied on the rolling sonotrode 14 ensures improved transmission of the VHPD vibrations to the nearby materials and enhances the deformation and consolidation of materials under the rolling sonotrode 14.

[0031] FIG. 4 illustrates a preferred ultrasound assisted welding process using a sonotrode 16 vibrating in the direction 32 perpendicular to the top surface of the sheet materials, 42 and 44, to be welded. In this method, the heat source melts the materials of the welding wire and sheet materials 42 and 44 and forms the melt pool 10. The sonotrode 16 is placed either on top of the solidified seam 40 close to the edge of the melt pool 10, partially on top of the melt 10, or on top of the sheet material 42 or 44 close to the melt pool 10. The sonotrode 16 is synchronized with the heat source so that it travels in the same direction as illustrated by arrow 30 at that same speed as that of the melt pool 10. VHPD acoustic vibrations vibrating in the direction as illustrated by arrow 32 are transmitted from the sonotrode 16 to the melt pool 10, causing cavitations in the melt 10 that break up columnar dendrites into fragments of equiaxed dendrites. VHPD acoustic vibrations are also applied on the just solidified materials 40 for further consolidation of the hot material. The compressive load 18 applied on the sonotrode 16 ensures improved transmission of the VHPD vibration to the nearby materials and enhances the deformation and consolidation of materials under the sonotrode 16.

[0032] The present invention related to an ultrasound assisted welding process can be applied to weld materials including metallic materials and composite materials containing ceramic particles to produce solid weldment of high internal quality and high mechanical properties.

[0033] The invention further provides examples of ultrasound assisted welding of metallic materials. The examples provided below are meant merely to exemplify several embodiments, and should not be interpreted as limiting the scope of the claims, which are delimited only by the specification.

Example

[0034] The inventor of the present invention and Dr. S. Bagherzadeh have validated the approach shown in FIG. 4 for eliminating hot tearing, porosity, and delamination on a Pb-20% Sn alloy using a sonotrode with a hemispherical tip. The sonotrode was bolt connected to an ultrasonic horn made of Ti-6A1-4V. The horn was driven by a 1.5 kW acoustic generator and an air-cooled 20 kHz transducer made of piezoelectric lead zirconate titanate (PZT) crystals. A Ronson Tech torch was used as the heat source. Ultrasonic systems employing higher frequencies of 40 kHz to 60 kHz with lower amplitude vibrations are preferably used for materials less ductile.

[0035] FIG. 5 shows the Pb—Sn phase diagram. Pb-20% Sn alloy has the largest solidification interval on the phase diagram. It is well known that alloys that have large solidification interval are difficult to weld and print due to hot tearing and porosity formation.

[0036] FIG. 6A shows the columnar grains formed in the melt pool in the sample without ultrasonic vibration. Long and large columnar grains prevail throughout the solidified melt pool. With ultrasonic vibrations, small equiaxed grains, shown in FIG. 6B, are obtained. The vibrating sonotrode is effective in eliminating large columnar grains and producing small equiaxed grains during the solidification of the melt pool.

[0037] FIG. 7A shows large hot tearing in a sample without ultrasonic vibration and FIG. 7B shows the solidified microstructure containing no hot tearing in a sample with ultrasonic vibration. Ultrasonic vibration is effective in producing small equiaxed grains in the melt pool, thus eliminating hot tearing defect.

[0038] FIG. 8A shows porosity in a sample without ultrasonic vibration and FIG. 8B shows the solidified microstructure containing limited porosity in a sample with ultrasonic vibration. Ultrasonic vibration is effective in driving pores out of the melt pool and results in much less porosity formation.

[0039] While the invention has been described in connection with specific embodiments thereof, it will be understood that the inventive methodology is capable of further modifications. This patent application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features herein before set forth and as follows in scope of the appended claims.

REFERENCES

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