Abstract:
A method of electrolytic additive manufacturing provides 3-D parts. The method can be used to form parts from particulate material in an electrolytic bath. Metal is electrolytically deposited, binding the particles. Layers of the particles are built up to form the parts. The same process can be used to form parts without the particulate material. Layers of metal are electrolytically deposited in the electrolyte bath to form the parts.

Description:
RELATED APPLICATIONS 
       [0001]    This application is based on provisional patent application U.S. Ser. No. 62/205,229, filed on Aug. 14, 2015, the disclosure of which is hereby incorporated by reference in its entirety as if fully set forth herein. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates generally to additive manufacturing and, more specifically, to additive manufacturing by localized electrochemical deposition. 
       BACKGROUND 
       [0003]    Porous structures are increasingly preferred in energy, biomedical, aerospace, chemical and other industries for various applications such as filtration and separation, distribution and control of fluid, electromagnetic shielding, heat exchanger, energy absorption, electrode matrices, and reaction matrices, due to their outstanding properties such as low specific weight, controlled permeability, large specific surface area, high energy absorption, and good absorption of electromagnetic waves. Specific examples of micro size porous parts include applications, such as wearable electronics and micro fuel cells. 
         [0004]    Existing powder metallurgy and additive manufacturing (AM) based processes, such as micro metal injection molding and laser micro sintering, are capable of producing porous metal micro parts. However, these existing processes have several inherent drawbacks, such as the need for complex micro molds and the difficulty of filling feedstock completely into narrow cavities in micro injection molding. Further, laser and other thermal processes often have inevitable thermal effects such as thermal residual stress, cracking, and burr formation. More particularly, some AM processes such as Selective Laser Melting (SLM) and Electron Beam Melting (EBM) suffer from very high residual stresses due to the complete melting of the material during manufacturing. For example, the residual stresses caused by the thermal gradient associated with sintering processes are very high (&gt;200 MPa). Another major roadblock that limits the application of the AM parts is that the part generally tends to have anisotropic properties due to the layered nature of the manufacturing. 
         [0005]    Other complexities associated with traditional AM processes include the need for complex machining systems such as vacuum chambers, as in the case of Selective Micro Laser Sintering, to avoid humidity and resulting oxidation. One of the problems of inkjet process is that the viscous dissipation of binder fluid results in orifice clogging, which impedes ejection of the binder fluid through the nozzle. Also, the jetting process must be performed in a low oxygen environment to prevent the formation of a surface oxide layer, thus, resulting in changes to the physical properties of the jet surface. In summary, existing additive manufacturing techniques have several limitations ranging from a restricted choice of work material, to anisotropy, strength, scalability, internal stresses, and poor layer binding, resolution, and surface finish. Therefore, there is a clear need for alternate manufacturing approaches to produce porous micro parts without aforementioned constraints. 
       SUMMARY 
       [0006]    Embodiments of the present invention are directed to methods of micro-fabricating metallic components layer by layer or voxel by voxel using localized electrochemical reactions. More specifically, embodiments of the present invention include electrochemically depositing metal binder to bind particles at specified locations. In other words, metallic micro-components are formed atom-by-atom, or layer-by-layer (i.e., additive manufacturing), via localized electrochemical deposition. An aspect of the present invention is that such additive manufacturing allows for the fabrication of powder and powder-less metal parts by additive manufacturing without thermal damage, as further described below. 
         [0007]    The electrochemical deposition process is capable of depositing most conductive material including metals, metal alloys, conducting polymers and even some semiconductors. The properties of the deposited materials can be modified according to the experimental conditions leading to the manufacturing of functional parts with varying properties. The residual stresses associated with the pulsed electrochemical deposition/electroforming processes are negligible compared to the sintering/melting processes. Electrochemical deposition techniques offer the technical and economic advantages characteristic to the electroplating technology, combined with being a mask less procedure achieving shorter development times. 
         [0008]    The objects and advantages of present will be appreciated in light of the following detailed descriptions and drawings in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic diagram of a system for producing a component by electrochemical deposition according to an embodiment of the present invention. 
           [0010]      FIG. 2  is a schematic diagram of the system of  FIG. 1  showing the electrochemical deposition in more detail. 
           [0011]      FIGS. 3A-3C  are schematic diagrams showing a component being produced by electrochemical deposition using a method according to an embodiment of the present invention. 
           [0012]      FIG. 3D  is a cross-sectional view of a component produced according to the method shown in  FIGS. 3A-3C . 
           [0013]      FIG. 4  is a schematic diagram of electrochemical deposition according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    With reference to  FIGS. 1 and 2 , in one embodiment, a system  10  for producing a component  11  by electrochemical deposition includes a spindle  12  coupled to a tool electrode  14 . The tool electrode  14  may be, for example, a platinum micro-electrode coated with insulating material  16  on the sides with an exposed disc-like end  18 . The system  10  further includes an electrochemical tank  20  containing an electroplating solution  22  and a substrate  24 . The substrate  24  may be, for example, a highly polished metal plate. A first layer  26  of a particulate material such as metal particles or an inert material such as diamond particles is deposited on the substrate  24  (shown in  FIG. 3A ). Exemplary particulate material is shown in Table 1. 
         [0000]    
       
         
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Material 
                 Particle Size 
               
               
                   
               
             
             
               
                 Copper 
                 500 mesh (&lt;25 μm), 400 mesh (&lt;37 μm), 325 mesh (&lt;44 μm) 
               
               
                 Diamond 
                 &lt;4 μm 
               
               
                   
               
             
          
         
       
     
         [0015]    The concentration of the particulate material is generally _500_g/l to _1250_g/l. The electroplating solution  22  includes a metal binder to be deposited on the substrate  24  The deposited metal binder interacts with the particulate material in the first layer  26  to bind the particles to create a first layer  28  of the component  11  on the substrate  24 . In an embodiment, the electroplating solution  22  is a Watts bath and contains nickel sulfate (240 g/L distilled water), nickel chloride (45 g/L distilled water) and boric acid (30 g/L distilled water). Exemplary electrolyte solutions are shown in Table 2. Basically, any electrolyte which deposits a metal can be used. 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Deposited 
                   
                   
               
               
                 Species 
                 Electrolyte 
                 Concentration Ranges 
               
               
                   
               
             
             
               
                 Nickel 
                 Nickel Sulfate, Nickel Chloride, 
                 700 m-5000 mol/m 3   
               
               
                   
                 Boric Acid 
               
               
                   
                 Nickel Sulfamate 
               
               
                 Copper 
                 Copper Sulfate 
               
               
                 Silver 
                 Silver Chloride 
               
               
                   
               
             
          
         
       
     
         [0016]    Still referring to  FIG. 1 , the system  10  further includes a power supply  30  configured to apply an electric field between the tool electrode  14  and the substrate  24 . The power supply  30  may be a pulsed power supply, which is believed to have a higher current density and to intensify the asymmetrical distribution of current to produce a fine grained, smoother finished structure. In an embodiment, the tool electrode  14  acts as a micro-anode and is coupled to a negative terminal  34  of the power supply  30 , and the substrate  24  acts as the cathode and is coupled to a positive terminal  36  of the power supply  30 . Because the exposed part of the tool electrode  14  has a very small surface area, the electric field is highly confined and, hence, localized electrodeposition is possible. The tool shape and size determines exposed surface area. For a cylindrical tool, the length of the exposed cylinder may be 0-20 μm and the diameter, for example, may be 50-250 μm. The tool can be a rectangular plate, a ring or a disk, depending on the desired application. Thus, the localized electric field allows for the metal binder present in the electroplating solution  22  to be deposited at specific locations on first layer  26 . Consequently, where the metal binder is deposited, the metal binder binds the particles in the first layer  26 . 
         [0017]    With further reference to  FIGS. 1 and 2 , the inter-electrode gap between the anode (e.g., the tool electrode  14 ) and the cathode (e.g., the substrate  24 ) should be maintained to avoid short-circuiting the system  10  during electrodeposition. In that regard, the system  10  includes a three-axis stage  38 , which carries the substrate  24  and may be used to adjust the position of the substrate  24 . Clamping features may be used to hold the substrate  24  in place on the stage  38  (not shown). A controller  40  is configured to control the movement of the stage  38  along the three axes via stepper motors  42  and low-current stepper motor controllers  44 . In an embodiment, the stepper motors  42  may be NEMA 08 stepper motors. The low-current stepper motor controllers  44  may be connected to a parallel port breakout board  46 , which in turn is connected to the controller  40 . The stage  38  may be able to move along each of the axes by a distance ranging from 1 micron to 10 mm. The rate of movement (i.e., the feed rate) may be user defined and can range from about 32 mm/min to about 1 micron/sec. The controller  40  may further be configured to control the spindle  12 . More specifically, spindle  12  may be rotatable, and the controller  40  may be configured to control the rotation of the spindle  12  and, consequently, the tool electrode  14 . The rotation enhances electrolyte circulation and disperses oxygen bubbles, which can interfere with the process. 
         [0018]    Still referring to  FIG. 1 , the controller  40  includes a closed loop feed-back system that uses a current sensor  48 , a position sensor  50 , and a CCD camera  52 . The current sensor  48  measures the current between the tool electrode  14  and the substrate  24 , and the position sensor  50  senses the position of the stage  38 . The CCD camera  52  monitors the process. The images are used to give tool-substrate position, deposition progress, bubbling behavior, and collision prevention on a coarse level. As the inter-electrode distance between the tool electrode  14  and the substrate  24  decreases, the current increases. When the current reaches a pre-set threshold value, the controller  40  causes the stage  38  and, consequently, the substrate  24  to move away from the tool electrode  14 , thus increasing the inter-electrode gap. The controller  40  may be configured to move the stage  38  until the detected current reaches a pre-determined value, which corresponds to a pre-determined inter-electrode gap. This ensures that there is a constant gap between the anode and the cathode during electrodeposition. 
         [0019]    With reference to  FIGS. 1 and 3A-3D , a method according to an embodiment is shown. The electrolyte includes a suspension of particles in the electrolyte solution. First, the first layer  26  of particles is deposited on the substrate  24  as shown in  FIG. 3A . The tool electrode  14  is placed in the electroplating solution  22  with the disc-like end  18  near the substrate  24  on which electrodeposition is to occur. The power supply  30  applies the electric field between the tool electrode  14  and the substrate  24 . The localized electric field causes the metal ions present in the electroplating solution  22  (e.g., nickel in a Watts bath) to be deposited on the substrate  24 . Thus, the deposited metal binder binds the particles in the first layer  26  creating the first component layer  28  of metal, as shown in  FIG. 2 . The controller  40  controls the movement (e.g., the rotation) of the spindle  12  during electrodeposition. Due to the first component layer  28  of metal, the inter-electrode distance between the tool electrode  14  and the substrate  24  decreases causing the current therebetween to increase. The current sensor  48  senses the increased current, and the controller  40  moves the stage  38  via the stepper motors  42  until the current reaches the pre-determined value (alternately, the tool can be moved relative to the stage). Now, the pre-determined inter-electrode gap exists between the tool electrode  14  and the substrate  24 , and a second layer  54  of particles may be deposited on the substrate  24 . As shown in  FIGS. 3B and 3C , the electrodeposition steps may be repeated, thus locally depositing metal binder and forming a second layer  56  of bonded particles. Accordingly, as the controller  40  moves the stage  38  and the electrodeposition steps are repeated, the layer-by-layer interaction between the particles and the metal binder result in layers of the particulate material (such as copper or diamond) formed on the substrate  24  by which the desired micro-component  58  is fabricated, as shown in  FIG. 3D . 
         [0020]    In an embodiment, the controller  40  uses computer numeric control (“CNC”) software such as Mach3. Further, the power supply  30  is controlled by a program, such as LabVIEW, which in turn interacts with Mach3 to move the stage  38  along an axis as desired. A 3D CAD model of the desired micro-component may be loaded onto software, such as SKIENFORGE, which converts 3D models by slicing them into G codes that provide a path for the tool electrode  14  required for the layer-by-layer manufacturing. The G-codes generated through this software are then loaded into Mach3 program, which then sends out step/direction pulses based on the G-codes to control the movement of the stage  38 . 
         [0021]    With reference to  FIG. 4 , a component  60  may be produced by powder-less electrochemical deposition. In an embodiment where the tool  14  is formed from a generally inert material such as platinum, nickel or titanium, metal ions (M+) in the electroplating solution  22  may deposit as a solid layer in predetermined locations by the localized deposition. This is repeated layer by layer until the desired part is formed. In another embodiment where the tool  14  has a reduction potential less than the hydrolysis potential, metal ions (M+) originating from the tool  14  (i.e., the anode) are locally deposited as a solid in predetermined locations on the substrate  24 . 
         [0022]    Either the powder method or the powderless method can be used to form articles with varying porosity. By controlling parameters including voltage, pulse period, electrolyte concentration tool electrode speed, electrolyte circulation, as well as electrolyte additives, one can control porosity. For example, high voltage increases porosity by depleting ions and bubble formation. Lower electrolyte concentrations increase porosity. 
         [0023]    Thus, the present invention can be used to produce a wide variety of different porous articles, including multilayered aerospace components, biomedical component filters and the like. Due to the method of manufacture, thermal stresses are avoided. 
         [0024]    While specific embodiments have been described in considerable detail to illustrate the present invention, the description is not intended to restrict or in any way limit the scope of the appended claims to such detail. The various features discussed herein may be used alone or in any combination. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope of the general inventive concept.