阅读说明：本技术 利用局部超声波增强的材料流和熔合的增材制造系统和方法 (Additive manufacturing system and method utilizing localized ultrasonic enhanced material flow and fusion ) 是由 K·许 A·德什潘德 于 2016-08-26 设计创作，主要内容包括：可用于实现固体(>95％)金属材料的室温3D打印的超声波细丝建模系统和方法。将振动工具应用于金属细丝以形成体素,诱导机械变形以及层间和层内的物质传输。可在体素到体素的基础上建造所期望的结构。此外,通过改变所施加的超声波能量,可以控制所得结构的微结构。(Ultrasonic filament modeling systems and methods useful for achieving room temperature 3D printing of solid (> 95%) metal materials. A vibrating tool is applied to the metal filaments to form the voxels, inducing mechanical deformation and mass transport between and within the layers. The desired structure can be built on a voxel-to-voxel basis. Furthermore, by varying the applied ultrasonic energy, the microstructure of the resulting structure can be controlled.)

1. A method for 3D printing a metal object having a density of at least 95% of a pure metal density, the method comprising:

forming a series of layers comprising the metal object, each layer being formed from metal filaments, wherein forming each layer comprises:

forming a series of voxels from the wire filament by applying ultrasonic energy to a print tool in contact with the wire filament, wherein a portion of the print tool in contact with the wire filament vibrates at an amplitude of 0.9 microns to 1.1 microns in response to ultrasonic energy,

wherein each voxel in the series of voxels is connected by mass transport to neighboring voxels in the layer and neighboring voxels of a previous layer,

wherein the temperature of the metal filament increases by less than 6 degrees celsius during formation of voxels, wherein each voxel is formed by applying ultrasonic energy for a time between 200 milliseconds and 400 milliseconds, and wherein formation of a series of voxels occurs at room temperature and in ambient atmosphere.

2. The method of claim 1, wherein the metal filament comprises at least one of aluminum, titanium, gold, silver, copper, or a steel alloy.

3. The method of claim 1, further comprising varying the intensity of the applied ultrasonic energy between the formation of voxels to change the microstructure of the metal.

4. The method of claim 1, wherein the printing tool comprises a tungsten carbide rod, wherein the printing tool is coupled to a piezoelectric crystal operating between 40kHz and 200 kHz.

5. The method of claim 1, wherein the printing tool comprises a tungsten carbide rod.

6. A method for additive manufacturing, the method comprising:

contacting a first length of the metal line with the metal base;

bonding a portion of a first target area to the metal substrate by applying ultrasonic energy to induce material flow and solid state diffusion in a first length of the metal wire in the first target area; and

bonding a portion of a second target region to the metal substrate by applying ultrasonic energy to induce material flow and solid state diffusion in a first length of the metal wire in the second target region at least partially overlapping the first target region.

7. The method of claim 6, further comprising:

contacting a second length of metal wire with the first target area and the second target area; and

inducing material flow and solid state diffusion in a second length of the metal wire in a third target region by applying ultrasonic energy, bonding a portion of the third target region to one of the first target region or the second target region.

8. The method of claim 6, wherein ultrasonic energy is applied to the first length of wire by a printing tool comprising tungsten carbide.

9. The method of claim 6, wherein the ultrasonic energy source is a piezoelectric crystal operating at a frequency of about 60kHz, wherein the piezoelectric crystal and the printing tool are coupled by a stainless steel horn.

10. The method of claim 6, wherein a temperature increase in the wire is less than 6 degrees Celsius while generating a material flow and solid state diffusion in the first length of the wire in the first target region.

11. The method of claim 7, wherein a total density of the first target region, the second target region, and the third target region exceeds 95% of a density of a pure metal.

12. The method of claim 6, wherein the portion of the first target region that is bound to the substrate forms a voxel.

13. The method of claim 12, further comprising repeatedly forming a series of voxels to form a desired structure.

14. The method of claim 13, further comprising varying the amount of ultrasonic energy applied to a set of voxels in the series of voxels to control the microstructure of the metal particles in the desired structure.

15. The method of claim 6, wherein the metal comprises at least one of aluminum, titanium, gold, silver, copper, or a steel alloy.

16. The method of claim 6, wherein the method is performed at room temperature in an ambient atmosphere.

17. The method of claim 8, wherein in response to the ultrasonic energy, a free end of the print tool vibrates with an amplitude of 0.9 microns to 1.1 microns.

18. The method of claim 6, wherein the ultrasonic energy is applied for a time of 200 microseconds to 400 microseconds.

19. The method of claim 6, further comprising removing at least a portion of the first department area, the second target area, or the third area to form a desired structure.

Technical Field

The present disclosure relates to additive manufacturing, and in particular to additive manufacturing methods that utilize localized ultrasound to enhance material flow and fusion.

Background

Currently, additive manufacturing methods have various drawbacks. Accordingly, there remains a need for improved additive manufacturing systems and methods.

Brief description of the drawings

With respect to the following description and drawings:

FIG. 1 illustrates an example additive manufacturing system of an example embodiment;

FIG. 2A illustrates operation of an exemplary additive manufacturing system of an exemplary embodiment;

FIG. 2B illustrates operation of an exemplary additive manufacturing system in a parallel and orthogonal layer approach of an exemplary embodiment;

FIG. 2C illustrates operation of an exemplary additive manufacturing system in a continuous stitching process according to an exemplary embodiment;

FIG. 3A illustrates operations of an exemplary additive manufacturing system to deposit a single voxel, according to an exemplary embodiment;

FIG. 3B illustrates the operation of an exemplary additive manufacturing system depositing a pair of adjacent voxels, according to an exemplary embodiment;

FIG. 3C illustrates operations of the example additive manufacturing system to deposit two layers of adjacent voxels, according to example embodiments;

FIG. 4 shows the results of operation of an exemplary additive manufacturing system in a continuous stitching mode of an exemplary embodiment;

FIG. 5 shows the results of operation of an exemplary additive manufacturing system in an orthogonal layer approach of an exemplary embodiment;

fig. 6A shows the results of operation of an example additive manufacturing system as a free-standing metal additive manufacturing method of an example embodiment;

fig. 6B shows the results of operation of an example additive manufacturing system as part of a hybrid additive-subtractive manufacturing method according to an example embodiment;

FIGS. 7A and 7B illustrate thermal characterization of the operation of an example additive manufacturing system of an example embodiment;

FIGS. 8A and 8B illustrate microstructural features of a material formed by operation of an exemplary additive manufacturing system of an exemplary embodiment;

Detailed Description

The following description is of various exemplary embodiments only, and is not intended to limit the scope, applicability, or configuration of the disclosure in any way. Rather, the following description is intended to provide suitable illustrations for implementing various embodiments, including the best mode. It will be apparent that various changes may be made in the function and arrangement of elements described in these embodiments without departing from the scope of the disclosure.

For the sake of brevity, conventional techniques for additive manufacturing, wire bonding, 3-D printing, and the like may not be described in detail herein. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent exemplary functional relationships and/or physical or communicative couplings (communicative couplings) between the various elements. It should be noted that many alternative or additional functional relationships may exist in an actual additive manufacturing system and associated method of use.

The idea of building three-dimensional objects "additively" layer by layer over the past few decades has changed from rapid prototyping tools for concept visualization to current production tools capable of producing end-user engineering parts, and has evolved not only towards innovating the manufacturing industry, but also towards fundamentally redefining how objects are manufactured. The significance of this transition is enormous: penetration into the various levels of human experience that are conceivable: aerospace, automotive, biomedical, military, electronic, consumer, food, and personal products. Currently, additive manufacturing of polymers with production quality is affordable and readily available. However, existing methods of additive manufacturing of fully dense metals are far from affordable and readily available.

The existing metal additive manufacturing process comprises the following steps: indirect methods such as adhesive spray processes, Ultrasonic Consolidation (UC), and Layered Object Manufacturing (LOM); and direct methods of Selective Laser Melting (SLM), Electron Beam Melting (EBM), and Laser Engineered Net Shape (LENS). Indirect processes require post-processing to produce fully dense parts. In some processes, the metal parts are partially melted or a low melting point adhesive is used to bond the metal parts together. Therefore, when high bulk density parts are required, post-processing operations such as binder removal, sintering or liquid metal infiltration are required. Ultrasonic consolidation is a composite additive-subtractive process in which sheets (or strips) of metal foil are first stacked by ultrasonic welding. The metal stack is then shaped into the desired layer shape using a cutting operation, typically end milling. By alternating between these welding and cutting processes, a three-dimensional object is built. LOM employs the same alternating additive and cutting process as US, but the welding step is replaced with applying adhesive between the sheets, and a post friction sintering process may be required.

Furthermore, the existing direct metal processes involve melting and bonding of materials using thermal energy by operating a melt pool, which is created by laser or electron beam thermal coupling into metal powder. The resulting structure, morphology and microstructure are highly dependent on the thermophysical and heat transfer processes in the micro-soldering process. Another unique feature of these direct metal additive manufacturing processes is the use of fine powders as starting materials, typically around 20 microns in average diameter, and the process is performed in a controlled environment of inert gas or vacuum to prevent oxidation, beam scattering when electron beam melting, and process hazards. Although high quality metal parts can be produced, these features are a major obstacle to the reduction of technical costs and the ease of availability.

In contrast to the drawbacks of prior methods, the exemplary embodiments disclosed herein allow for additive manufacturing of metal articles that are practically fully dense (e.g., greater than 95% of the solid metal density) at ambient conditions at room temperature. Various exemplary embodiments utilize an Ultrasonic Filament Modeling (UFM) process. The operating principle of UFM technology can be analogized to the combination of wire bonding and fused deposition modeling: three-dimensional objects are formed by metallurgical bonding between roads and layers using solid wires as starting materials.

Referring now to fig. 1, in an exemplary embodiment, an additive manufacturing system 100 includes a filament modeling assembly 110 and a control assembly 120. The filament modeling assembly 110 is configured to provide and additively pack filaments (e.g., filaments comprising one or more of aluminum, titanium, silver, gold, copper, steel alloys, metal-polymer mixtures, etc.) on a substrate. The control component 120 controls the operation of the filament modeling component 110 such that a composite 3D structure is formed.

As shown in fig. 2A and 2B, in some embodiments, an exemplary mechanical and tooling configuration of a UFM is similar to an FDM process, wherein a heated thermoplastic extruder "writes" directly the roads and layers that make up a 3D assembly. In contrast, however, in UFMs, solid metal filaments are guided, shaped, and metallurgically bonded to a substrate (or previous layer) and adjacent filaments on a unit-by-unit basis using a guiding tool on a positioning system.

Those skilled in the art are aware that important aspects or features of UFM processes are: (1) the mechanical stress (and hence mechanical energy input) required to "shape" the filament into the desired path geometry in the presence of applied ultrasonic oscillations is greatly reduced (< 50%) compared to the yield strength of the material; (2) under the observed conditions, the observed mass transport forming metallurgical bonds across interfiber and interlaminar interfaces is more than 10000 times higher than that predicted by fick diffusion; and (3) the temperature rise of the UFM process is almost negligible, reflecting the high coupling efficiency from the acoustic energy input to the desired plastic and mass transport. These unique features enable the ultrasonic filament modeling process disclosed herein to be implemented within a desktop 3D printing environment as well as within a high precision, high fidelity industrial additive manufacturing environment. Furthermore, the unique properties of UFM full dense metal 3D printing at room temperature makes it possible to print both polymers and metals at the same time, a material combination that is not achievable in metal melting based metal additive manufacturing processes.

Referring now to fig. 2A and 2B, in an example embodiment, additive manufacturing system 100 (e.g., additive manufacturing system 200) includes an acoustic energy source 212, an X-axis motor 216, a y-axis motor 217, at least one z-axis motor 218, a printer control board 222, and a power source 224. Additive manufacturing system 200 may also include build plate 219 for depositing a 3D printed object thereon; the build plate 219 may be fixed in position or may be translatable and/or rotatable in the x, y, and z dimensions.

In an exemplary embodiment, additive manufacturing system 200 utilizes a source of ultrasonic vibrations in acoustic energy source 212. In addition, the acoustic energy source 212 may further include a printing tool 213 for guiding the filament and imparting acoustic energy thereto. The acoustic energy source 212 may further comprise a stainless steel horn connected to a piezoelectric crystal that oscillates at a frequency of 60 kHz. The acoustic energy source 212 can provide a desired amount of ultrasonic energy, such as 5 watts, 10 watts, 15 watts, and/or the like. The ultrasonic energy provided to the aluminum voxel is modulated, for example, by amplitude and time. At the end of the stainless steel horn is a printing tool 213 (e.g., formed of tungsten carbide or other suitable durable material) that guides and forms voxels (e.g., 99.99% Al of 300 μm diameter) from the filament. In addition to the modulation of the ultrasonic energy input, the force with which the metal filaments are pressed against the substrate/existing layer can also be controlled.

The printing tool 213 may comprise a blade, needle, cylinder, rectangle, plate, or other suitable shape. The print tool 213 may be configured with any suitable dimensions and/or materials, such as an aspect ratio configured to achieve an amplitude of about 1 micron vibration of the free end of the print tool 213 in response to ultrasonic vibrations of about 60kHz applied to the print tool 213. In one exemplary embodiment, the printing tool 213 is configured to have a width of about 3mm and a length of about 12mm to 25 mm. In another exemplary embodiment, the printing tool 213 is configured to have a width of about 2mm and a length of about 12 mm. Further, it should be understood that the dimensions of the printing tool 213 may be selected and/or adjusted as desired, for example, according to the dimensions of the metal filaments used in the additive manufacturing system 200, including the particular metal or alloy of the metal filaments, and/or others. To use different materials and/or achieve different characteristics of the deposited material, a particular printing tool 213 may be removed from the additive manufacturing system 213 and replaced with a different printing tool 213.

In an exemplary embodiment, operation of additive manufacturing system 200 begins with having printing tool 213 guide a filament to a desired voxel location and holding the filament in place with very little pressure (e.g., by operation of one or more motors 216, 217, or 218). Once positioned, the filaments are provided with ultrasonic energy by the printing tool 213. The combination of the force applied by the printing tool 213 and the ultrasonic energy illumination causes the filament portions defined by the printing tool/filament contacts to form and fuse on the substrate/existing layer, forming voxels. The above process is repeated as the printing tool 213 moves down the axis of the metal filament until the desired "way" is completed. Each voxel may overlap with preceding and following voxels, and may overlap with voxels in those neighboring roads. The above process is then repeated for each way and each layer until the desired structure is formed. In various exemplary embodiments, additive manufacturing system 200 may reach a target speed of build, e.g., 0.2mm³0.3 mm/sec³Per second, and/or otherwise, depending on input power, filament material, etc.

In one exemplary embodiment, additive manufacturing system 200 is operable to couple acoustic energy into a fully dense metal filament to guide the filament and induce voxel forming and material fusing required for 3D printing. The acoustic energy source 212 uses a piezoelectric crystal-based transducer that oscillates at a frequency of about 60kHz (more broadly, between about 40kHz and about 200 kHz). During the UFM process, the printing tool 213 delivers ultrasonic energy to the interface between a solid filament (e.g., solid aluminum 300 microns in diameter with a purity of 99.99%) and the existing surface, as shown in fig. 2A-2C. Since ultrasonic energy is used to shape the filament and allow for the formation of a metallurgical bond at the metal-metal interface, the print tool 213 gradually reduces the length of the filament to form a "road" of solid metal, for example, dimensions of about 600 microns in width and about 125 microns in height. These steps are then repeated to form adjacent roads that make up a layer, and then the steps in the road and layer directions are repeated to form the three-dimensional object. A scanning electron microscope image of a two-layer structure constructed according to an exemplary UFM method is shown in fig. 4. These images depict the formation of the filament path and the metallurgical bonding with the adjacent path. No appreciable voids were found between the roads and the layer.

Printer control board 222 may include any suitable electronic components, such as microprocessors, resistors, capacitors, inductors, transistors, diodes, light emitting diodes, switches, oscilloscopes (wires), jumpers, fuses, amplifiers, antennas, etc., to control the operation of additive manufacturing system 200. In some example embodiments, additive manufacturing system 200 may be controlled by a software program running on a connected personal computer.

In some exemplary embodiments, additive manufacturing system 200 uses an X-axis motor 216, a y-axis motor 217, and a z-axis motor 218. These motors may operate to position and/or reposition components of additive manufacturing system 200, e.g., to position and/or reposition printing tool 213 and/or build plate 219 as needed. However, any suitable assembly or system for translation, rotation, and/or other movement of the relevant portions of additive manufacturing system 200 is considered to be within the scope of the present disclosure.

Referring now to fig. 4, additive manufacturing system 200 may operate in a "continuous stitching" mode, thereby continuously forming discrete voxels. In this mode, build plate 219 and/or print tool 213 may be translated in the X, Y or Z dimension between voxels; however, it is most common that a single linear "way" of adjacent voxels will be formed, followed by adjacent ways, and so on. Figure 4 shows the resulting high quality interlaminar and interfilament bonding.

Referring now to fig. 5, additive manufacturing system 200 may operate in a mode in which a voxel "road" of a first layer is orthogonal to a voxel "road" of a second adjacent layer (e.g., by rotating build plate 219 between layers, repositioning print tool 213, and/or otherwise). Fig. 5 shows an exemplary 18-layer structure formed from a1100 (99.9%) aluminum in the manner described above with a layer thickness of 0.11mm and a 2mm x 2mm footprint. Furthermore, a high quality of the resulting material is evident.

Referring now to fig. 3A, 3B, and 3C, photomicrographs of one or more exemplary voxels formed by operation of the additive manufacturing system 200 are presented. Figure 3A shows the formation of voxels of 1.5mm length and 0.15mm thickness that are continuously bonded. Figure 3B shows the formation of two adjacent voxels of 1.5mm length and 0.15mm thickness that are continuously joined. Figure 3C shows the formation of a continuously bonded voxel of 0.15mm thickness of 1.5mm length of the adjacent first layer and a continuously bonded voxel of 0.15mm thickness of 1.5mm length of the adjacent second layer thereon.

To further illustrate the feasibility of the exemplary UFM method as a standalone 3D printing process, an L-shaped 3D object was successfully printed by operation of additive manufacturing system 200. As shown in fig. 6A, the object has a length of 5mm, a width of 4mm, a height of about 1.5mm, and a layer thickness of about 125 microns.

In addition, the UFM may be used as a composite additive-subtractive manufacturing process. Referring now to fig. 6B, a 16-layer aluminum structure was 3D printed and processed into the elongated bar object photographed and displayed in fig. 6B. X-ray microtomography results were obtained for the middle portion of the sample and a representative slice is shown in fig. 6B. In the micro-CT scan of the UFM-printed sample, the inter-layer interface was discernible, but no inter-filament interface was observed. Densities in excess of 95% were observed.

The exemplary UFM process of the present disclosure does not produce significant heating as compared to existing metal additive manufacturing processes that require significant heating. Referring now to fig. 7A and 7B, high resolution IR imaging and thermal coupling detection of surface temperature may be used to quantify the temperature rise associated with exemplary embodiments of UFMs. As shown in fig. 7A, high speed IR imaging shows a maximum temperature rise of less than 5 degrees for forming a voxel. In fig. 7A, one frame of thermal imaging captured during voxel formation shows the spatial temperature distribution near the voxel at the time the maximum temperature is reached.

An exemplary temperature evolution over time at the filament-substrate interface is also presented in fig. 7B. The time evolution of the temperature at the critical filament-substrate interface indicates that the fusion of voxels starts within 30 microseconds of the application of ultrasonic energy, while the shaping of voxels continues as the voxel processing time continues (in fig. 7B, the irradiation of ultrasonic vibrations starts at the 50 th microsecond). The relative motion between the two surfaces generates frictional heat, resulting in a sharp increase in temperature. Another 30 microseconds in the process, metallurgical bond formation began and the relative motion between the filament and the substrate ceased. This eliminates the source of frictional heat and causes the interface temperature to drop. A maximum temperature increase of about 5 degrees was observed. Another feature in the illustrated time-temperature curve is a sharp decrease at about 350 microseconds of cessation of ultrasonic vibration. This indicates that the second heat source in the process is eliminated: cyclic plastic strain heating due to high frequency cyclic shear deformation at voxel formation. In operation, additive manufacturing system 200 may apply ultrasonic energy to the voxels for a suitable length of time, such as 100 microseconds, 200 microseconds, 320 microseconds, 400 microseconds, 550 microseconds, and/or the like.

Exemplary UFM systems and methods can be used to affect the microstructure of a metal. In conjunction with the operation of additive manufacturing system 200, metallurgical sample preparation and atomic force microscopy can be used to characterize cross-sections of voxels (perpendicular to the filament axis) in three states: (i) raw aluminum filament untreated, and (ii) and (iii) aluminum voxels formed with two different levels of ultrasonic energy input corresponding to 0.96 and 0.98 micron amplitudes for the print tool 213. It should be appreciated that additive manufacturing system 200 may be configured to utilize any suitable amplitude of printing tool 213 (e.g., an amplitude of about 0.9 microns to about 1.1 microns). The results summarized in fig. 8A and 8B indicate that as the UFM process occurs, a significant evolution of the microstructure occurs. Fig. 8A shows the microstructure of the aluminum voxel formed at a lower ultrasonic power (corresponding to an amplitude of 0.96 μm), and fig. 8B shows the microstructure of the aluminum voxel formed at a higher ultrasonic power (corresponding to an amplitude of 0.98 μm), with the ultrasonic irradiation time being set to 300 microseconds, respectively.

The original filaments showed an average particle size of about 10 microns, whereas the formed voxels illustrated in fig. 8A and 8B all showed the formation of secondary grains within the primary grains. Grain size analysis showed that the primary grains remained approximately the same size; they deform due to plastic strain in the voxels. Furthermore, at lower ultrasonic energy input, the average secondary grain size was 1.4 microns, whereas at increased ultrasonic energy input the average secondary grain size decreased to 0.9 microns. Thus, additive manufacturing system 200 facilitates design and/or control of the sub-grain structure based on the power applied to printing tool 213, enabling better control of the properties of the resulting structure.

The operation of additive manufacturing system 200 takes advantage of the physical phenomena identified herein for the first time. First, the UFM process utilizes the well observed ultrasonic softening of crystalline metals. The acoustic softening effect was first found in the fifties of the twentieth century and is considered to be a reduction in activation energy due to dislocation slip caused by concentration of acoustic energy at lattice defects such as dislocations and grain boundaries. An empirical relationship has been derived that relates the observed softening to residual hardening effects in qualitative terms related to the acoustic energy input. In addition, improved plastic models have been developed and used to interpret acoustic softening observations. The material softening observed in the UFM process is consistent with that described in the literature.

More importantly, additive manufacturing system 200 utilizes a second novel mechanism disclosed herein for the first time that involves dramatically increasing mass transport (4-6 orders of magnitude) at the lattice level over a large spatial domain (hundreds of nanometers) in a short time (less than 1 second). This second phenomenon utilized by UFM process and/or additive manufacturing system 200 involves a large mass transport across material interfaces in the presence of ultrasonic vibrations in the kHz frequency range, but with a very limited temperature rise. The former phenomenon has been observed in wire bonding and more recently Ultrasonic Consolidation (UC), but with a greater degree of temperature increase. In contrast, additive manufacturing system 200 provides a large mass transfer of material without a significant temperature increase.

In various exemplary embodimentsWherein the power density of the ultrasonic waves irradiated into the aluminum voxels used in the UFM reaches 160W/cm based on the measured and/or calculated amplitudes, voxel geometries and process parameters²The above. The principles of the present disclosure contemplate that the theory of quantum diffusion of vacancies is a possible explanation for the enhanced mass transport achieved by additive manufacturing system 200.

The process temperature increases. The temperature increase in the UFM process can be attributed to three heat sources captured in the time temperature evolution shown in fig. 7B: (1) the bulk heat generated by the large amount of plastic deformation associated with high variations in the filament during voxel formation, (2) the frictional heat generated due to the cyclical relative motion between the filament and the substrate (or existing filament surface), and (3) the voxel cyclic shear deformation in the axial direction of the filament. The volumetric heat due to plastic deformation associated with voxel height variation can be first evaluated by calculating the mechanical work done during linear deformation:

(formula 1)

Wherein sigma_y＝ξKε_ρ ⁿIs the flow stress, xi is the softening factor due to ultrasonic energy, ε_ρIs the plastic strain, K and n are the material constants (for example, for aluminum, they are considered to be K-155.65 MPa, n-0.2123). Assuming ξ is 1, the total mechanical work for voxel formation is W_P0.01J. For aluminum, it has been shown that about 30% of the plastic strain energy will be dissipated as heat, while the remainder of the plastic strain energy is stored in defects in the crystal lattice. This means that the compressive strain in voxel formation is equivalent to 0.01W less than the volumetric heat generated during aluminum voxel formation, considering that in the exemplary embodiment under consideration, the voxel formation process occurs at about 300 milliseconds.

The second heat generating source is frictional heat from relative motion between the voxels and the substrate or between the voxels and the printing tool 213. If it is assumed that there is no slip between the print tool 213 and the voxel, it can be modeled as:

Q_fmu FU (formula 2)

Where μ is the coefficient of friction at the voxel-substrate contact and U is the speed of their relative motion, which is approximated as: u-4 Af (equation 3) where a is the amplitude, F is the vibration frequency, and F is the contact force.

In an exemplary operation of the additive manufacturing system 200 using aluminum, the metallurgical bond forms at 30 microseconds with a contact force of about 10N, an amplitude of about 0.98 microns, and a frequency of about 60 kHz. For the aluminum filament-aluminum substrate interface under irradiation of ultrasonic vibrations, a friction coefficient of 0.3 was assumed during voxel formation. Based on these values, the total frictional heat generated at the filament-substrate contact was calculated to be about 0.7W.

The third heat-generating portion occurs upon plastic strain, which is caused by cyclic deformation in the voxel and dissipated as bulk heat. In one exemplary embodiment, the amplitude at the print tool 213/voxel contact is 0.98 microns; this is also the maximum displacement on the surface of the element for a given period of oscillation. The total shear strain produced during voxel formation is in the range of 0.33% to 0.83%. For the aluminum used in this exemplary embodiment, voxels enter plastic deformation when the strain is above 0.13%. Therefore, the amount of strain contributing to plastic strain heating in each vibration cycle is in the range of 0.2% to 0.7%. Considering the 30% heat sink partition and operating frequency of this exemplary UFM process, the average total heat generation due to cyclic plastic deformation during voxel formation is about 0.75W.

And (4) microstructure evolution. The microstructure of the aluminum voxels formed by the additive manufacturing system 200 exhibit a microstructure similar to that typically observed in the dynamic recovery of aluminum. The dynamic recovery may be under thermal operating conditions (T)>50％T_m) And occurs at a strain less than 40 ∈. This behavior is often present in materials with high stacking faults, such as aluminum and titanium. One distinct feature is the formation of small angle grain boundaries due to dislocation accumulation within the primary grains, resulting in the formation of secondary grains within the primary grains.

In UFMs, similar microstructural evolution is observed, for example, when implemented in additive manufacturing system 200. However, the operation of additive manufacturing system 200 is performed at room temperature (T < 5% Tm), and the amount of strain experienced in the voxels is approximately ∈ 1. Furthermore, the principles of the present disclosure contemplate that as the ultrasonic energy input into the voxel increases, the microstructure evolution process occurs to an increasing extent. Thus, while the driving mechanism observed behind the microstructural evolution in UFMs differs from that in dynamic recovery, the trend showing the dependency of the microstructure on the ultrasonic energy input is similar to that in dynamic recovery, where a decrease in the secondary crystallites is observed as the operating temperature increases. Thus, with respect to the operation of additive manufacturing system 200, from an energetics perspective, this trend indicates that the irradiation of ultrasonic energy brings the material lattice to a higher energy state where dynamic recovery due to dislocation hopping and merging can easily occur (as if the temperature of the material were significantly increased, but in practice the temperature of the material was not significantly increased).

Additive manufacturing system 200 is configured to take advantage of this behavior's dependence on ultrasonic energy input in order to manipulate the microstructure of the formed object. Additive manufacturing system 200 is believed to be the first system to utilize and/or disclose such capabilities. In the context of UFM as a metal 3D printing process, this dependence of material microstructure on process inputs means that the mechanical properties of the 3D printed components can be controlled and adjusted in real time by additive manufacturing system 200 under understanding and controlling process physics principles and during the build process.

Referring again to fig. 7A, to characterize the operation of additive manufacturing system 200, a FLIR a6751 camera may be used for IR imaging of voxel formation in UFM. The imaging frequency may be a suitable speed, for example 125.6 Hz. A black polymer film may be used on a portion of the tungsten carbide printing tool 213 to reduce the reflectivity of the surface. Thermocouples can be used to measure the substrate surface temperature, for example at 0.9mm and 4.3mm from the center of the voxel.

Referring again to fig. 8A and 8B, aluminum voxels of two different ultrasonic powers (corresponding to amplitudes of 0.96 microns and 0.98 microns, respectively) were formed on an aluminum 1100 substrate by operation of additive manufacturing system 200, and the microstructures of the formed voxels were examined. After forming the voxels on the substrate, their cross-sections were prepared according to the following standard metallography procedure. The samples were polished with a 320 grit silicon carbide abrasive disk and then polished with a 600 grit silicon carbide abrasive disk. Further polishing was performed using 6 μm polycrystalline diamond particles followed by 0.05 μm alumina slurry. Between each polishing step, the above samples were rinsed in an ultrasonic DI water bath. After the polishing process, the sample was etched in an etchant containing 25ml methanol, 25ml hcl, 25ml nitric acid and 1 drop HF. The etched samples were examined on a Bruker (Bruker) multimode Atomic Force Microscope (AFM) to show the microstructure of the aluminum voxels as shown in fig. 8A and 8B.

In addition, the principles of the present disclosure develop a knowledge base for an innovative approach to metal-polymer digital material fabrication, where the material and spatial composition of the metal and polymer components can be designed, implemented, and characterized on a voxel-by-voxel basis. The core of the method lies in the parallel additive manufacturing process of ultrasonic metal bonding and thermal polymer fusion. Driven by acoustic softening and vibro-acoustic enhanced solid state diffusion, the metal component of the metal-polymer heterogeneous material can be spatially formed on a voxel-by-voxel basis as described above, while the hot melt driven process fills the locations of the polymer component. Alternating between the two, spatial and compositional heterogeneity can be achieved on different scales. In these example methods, the additive manufacturing system may be configured with a first tool (e.g., printing tool 213) for metal deposition and a second tool (e.g., nozzle) for polymer deposition.

The innovative thermoacoustic additive manufacturing method for polymer-metal heterogeneous materials disclosed herein addresses the challenges of process inefficiencies and material uncertainties faced in the digital materials and manufacturing arts. For example, new metal-polymer composite arrays with fine-tuned mechanical, physical, and electromechanical properties can reduce the overall weight and cost of the system and improve the performance of the composite by allowing it to have specific positioning, application, and demand characteristics; second, the real-time material property monitoring and control elements of the disclosed method can improve system reliability by allowing monitoring of the manufacturing process as well as product quality and real-time adjustments during its build process; third, the disclosed method uses sonic energy on the metal and thermal energy on the polymer to effect deformation and bonding of the materials. Such a unique combination of energy sources can make efficient use of energy. The "on-demand material" nature of the combined additive process reduces the manufacturing costs of the assembly and system and provides on-board design and manufacturing capability for spare or replacement parts, such as for space flight missions.

Heterogeneous materials based on polymers are better than traditional single phase materials in a wide range of important applications in aerospace engineering where performance requirements such as strength-to-weight ratio, space limitations and overall system energy efficiency are very important. In these ideal applications, the development of ionic polymer-metal composites (IPMC) as an active material system in the robotic and human support fields of space applications not only represents an important area of current development, but also plays a key role with the development of future space exploration. However, in addition to the need for new breakthroughs in the field of polymer chemistry, the obstacle to building practical devices with theoretically predicted properties and required reliability is preceded by the lack of a manufacturing process in which the material and spatial composition of the final product can be precisely designed, executed and controlled: a closed-loop composite metal-polymer direct digital fabrication process.

Current polymer and metal Direct Digital Manufacturing (DDM) systems can be roughly classified into three types, namely liquid, solid filament or film, and powder, depending on the form of the starting material used. When only liquid photo-curable polymers are used in polymer DDM, the metal AM system uses thermal energy to selectively melt and fuse the material of the layer-by-layer three-dimensional part. Methods such as Selective Laser Melting (SLM) or Laser Engineered Net Shape (LENS), while common, suffer from high equipment and operating costs, low energy efficiency and powder recovery, and health risks associated with the use of metal powders. Electron Beam free form fabrication (EBF3), originally developed by NASA, operates on the same principle as electron beam welding. By operating the 3D path of the molten metal pool, solid modeling can be achieved in a high vacuum environment. The key problem facing this process is the resolution of the process and the difficulty in scaling up. These approaches represent a fundamental problem why the composite metal-polymer additive manufacturing process has not been previously achievable: the molten metal based AM process is not compatible with the polymer process due to the large process temperature difference of the molten metal based AM process and the polymer process.

Ultrasonic additive manufacturing is a process that alternates between ultrasonic welding and digitally controlled milling of a metal foil layer to produce near net shape and net shape parts. The process utilizes acoustic softening of the metal and reinforcement in solid state diffusion to create a stress-free metallurgical bond between the metal foil layers, followed by mechanical grinding of each layer to form the component layer by layer. While this is an excellent example of combining traditional and advanced manufacturing processes, this approach generates a large amount of scrap and the use of aluminum foil stock material can result in the simultaneous use of metal and polymer becoming impractical. Additive modeling and droplet printing processes based on micro-extrusion (e.g., electrojetting) are processes being developed by the nano/micro manufacturing community. These processes enable the production of composite metal-polymer heterogeneous materials and printing with metal particles mixed in a polymer matrix to achieve the desired electrical properties of the final product. However, the mechanical properties of the final product are far inferior to those of the constituent metal components. Furthermore, the printed metal particle traces in the final product typically need to be subjected to a heat treatment to obtain the desired electrical properties.

One of the most important problems with current DDM methods is the "open-loop" nature of their operation. Typically, the DDM process, whether SLA, FDM, or other process, does not receive information about build characteristics (e.g., material characteristics of the components) and relies only on passive system-level signal detection (e.g., force and impact) to terminate the build process to prevent damage to the system (e.g., "wiper" in SLA and SLS systems). Such mechanisms are ineffective because defects in the product must accumulate to the point where the moving components in the system experience a threshold resistance in order to complete their intended function before the system shuts down the process. At this point, manual intervention is required to restart the build process, and the material in the failed build cannot be recovered. More importantly, such mechanisms do not provide information on product size, defects, or material characteristics. Quality control can only be achieved after manufacture.

To address the various issues that prevent current additive manufacturing processes from being applied in designing and manufacturing multi-scale polymer-metal heterogeneous materials, the principles of the present disclosure contemplate an innovative metal-polymer composite additive manufacturing method in which the material and spatial composition of the metal and polymer component materials can be designed, implemented, and characterized on a voxel-to-voxel basis.

This new method can create paradigm shifts in the design, test, fabrication, and characterization cycles of new metal-polymer heterogeneous materials. It simplifies the development process of space technology such as ultra-high strength-to-weight ratio composites for soft machines and robots and adaptive materials based on ionic polymer-metal composites. The space-compatible and energy-efficient nature of the existing systems and methods means that on-board design and manufacture of new or replacement parts becomes possible during space travel and exploration, adding to the affordability and sustainability of such tasks. Furthermore, the present disclosure contemplates the combination of polymer-metal composite digital fabrication methods with the development of computational design and analysis tools to accelerate the development of the prototypes and concepts necessary to implement innovative methods of integrating design into products. The multi-scale metal-polymer heterogeneous digital fabrication methods developed herein allow unprecedented full composition range metal-polymer composites with length scales between 100 microns and possibly meters. This product composition adjustability enables new methods of structural design and assembly of sub-scale systems to be quickly prototyped and validated by combining the inherent flexibility of component and assembly design provided by the additive manufacturing nature of the proposed process.

The nature of the true 3D manufacturing and flexibility in material composition and performance tuning provided by the disclosed DDM method not only means speeding up the design, prototyping and new EVIPC-based soft actuator and sensor characterization methods, but also enables soft actuator designs with 3, 4 or 5 degrees of freedom in motion that previously could not be implemented due to the complex 3D metal electrode layers. The effect of this shortcut provides a synergy between the present disclosure and the soft machine technology subject area.

The principles of the present disclosure capture the physics and mechanics of process acoustic softening in a continuous spatiotemporal region. In a small material area, high frequency ultrasonic bonding environment similar to the process disclosed in this disclosure, a large amount of plastic deformation occurs in the entire material area between the ultrasonic capillary and the substrate. The process is driven almost entirely by the acoustic softening of the material. In this volume, the stress-strain relationship of the material differs due to the acoustic softening effect.

The exemplary system is implemented in an environment having a variety of components: metal and polymer wire material handling, acoustic and thermal energy sources and transfer, mechanical motion, and process control and feedback systems.

Metal and polymer wire material treatment: this part of the environment is responsible for the storage, feeding and removal of metal and polymer wire materials as a material source for the process. The acoustic and mechanical components are highly coordinated to provide the controlled movement of the wire required for the process. Metallic and polymeric constituent materials are processed separately in their respective capillaries and nozzles, with the material delivered to the desired voxel alternating between the two to reduce environmental complexity and achieve compositional heterogeneity.

Acoustic and thermal energy and transfer: the assembly converts energy from an electrical energy form to an acoustic and thermal form and transfers them into a metal capillary and a polymer nozzle. One exemplary system utilizes a single mode ultrasonic vibration system with an adjustable frequency range of 40kHz to 200kHz in the long axis vibration mode. A thermal energy system is used to provide heat to the polymer nozzle to reach above the glass transition temperature of the target polymer material and to heat the build area to an appropriate temperature (-50C) to prevent defects associated with thermal shock during extrusion and deposition.

Mechanical motion and process control and feedback systems: this component of the environment supports (1) 3-axis linear motion, (2) receives mechanical, thermal, acoustic signals from all other components, and observes system characteristics such as real-time status of the build process, component defect conditions, and material properties. The exemplary system illustrates real-time acoustic signal excitation, detection, and visualization for combined defect detection and material property assessment.

The principles of the present disclosure contemplate the application of this method to the design, prototyping and characterization of an ionic polymer-metal complex-based artificial muscle. For example, these principles consider an assembly ranging from a simple 1-axis motion actuator to an IPMC-based 4-axis active material that is capable of translating on 3 axes and rotating about 1 of these axes.

The principles of the present disclosure may be used in conjunction with the principles of additive manufacturing disclosed in U.S. provisional patent application No. 62/210041 filed on 26/8/2015, the contents of which are incorporated herein by reference in their entirety for all purposes.

While the principles of the disclosure have been illustrated in various embodiments, structures, arrangements, proportions, elements, materials, and components used in practice, which are particularly adapted to specific environments and operative requirements, may be employed without departing from the principles and scope of the present disclosure. These and other variations and modifications are intended to be included herein within the scope of this disclosure and the possible expression in the following claims.

The present disclosure has been described in connection with various embodiments.

However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present disclosure. Accordingly, the specification is to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present disclosure. Benefits, other advantages, and solutions to problems have been described with regard to various embodiments. However, the benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential element of any or all the claims.

As used herein, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. When language like "A, B or at least one of C" or "A, B and at least one of C" is used in the claims or specification, the phrase is intended to mean any of the following: (1) at least one of A; (2) at least one of B; (3) at least one of C; (4) at least one of A and at least one of B; (5) at least one of B and at least one of C; (6) at least one of A and at least one of C; or (7) at least one of A, at least one of B, and at least one of C.