Patent Publication Number: US-2010126877-A1

Title: Electrochemical grinding electrode, and apparatus and method using the same

Description:
BACKGROUND 
     This invention relates generally to electrochemical grinding electrodes, and electrochemical grinding apparatuses and methods. More particularly, this invention relates to components of the electrochemical grinding electrodes, and the electrochemical grinding apparatuses and methods using the electrochemical grinding electrodes. 
     Scientific and metallurgical developments have placed unusual demands on metalworking industries. Challenges faced by the metalworking industries are presented by not only modern materials with high strength-to-weight ratios, but also by fabrication requirements demanding greater precision and surface integrity. 
     Electrochemical grinding (ECG) is a machining process that provides a faster and more cost effective metal cutting and grinding solution for today&#39;s toughest materials. Unlike conventional grinding techniques, electrochemical grinding offers the ability to machine difficult materials independent of their hardness or strength. This is because electrochemical grinding is a unique machining process in which electrical energy combines with chemical energy and mechanical energy for metal removal. Since electrochemical grinding does not rely solely on an abrasive process, grinding results are precise cuts free of heat, stress, burrs and mechanical distortions. 
     Electrochemical grinding generally employs an electrode, such as a wheel electrode, to chemically grind a workpiece, thus, the electrode plays an important role in electrochemical grinding. As such, there has been significant effort to improve properties of the electrode. However, conventional electrodes for electrochemical grinding have their own limitations; for example, some may have lower arc resistance and/or inferior abrasive properties, which shortcomings may be disadvantageous for electrochemical grinding. 
     Therefore, there is a need for new and improved electrochemical grinding electrodes, and electrochemical grinding apparatuses and methods using such electrochemical grinding electrodes. 
     BRIEF DESCRIPTION 
     An electrochemical grinding electrode is provided in accordance with one embodiment of the invention. The electrochemical grinding electrode comprises an electrically conductive material; an arc resistance material; and an abrasive material different from the arc resistance material. 
     An electrochemical grinding apparatus is provided in accordance with another embodiment of the invention. The electrochemical grinding apparatus comprises an electrode configured to machine a workpiece; a power supply configured to energize the electrode and the workpiece to opposite electrical polarities; and an electrolyte supply configured to pass an electrolyte between the electrode and the workpiece. Further, the electrode comprises an electrically conductive material; an arc resistance material; and an abrasive material different from the arc resistance material. 
     An embodiment of the invention further provides an electrochemical grinding method. The electrochemical grinding method comprises driving an electrode to move relative to a workpiece, and passing an electric current between the electrode and the workpiece while passing an electrolyte therebetween to perform electrochemical grinding of the workpiece. Further, the electrode comprises an electrically conductive material; an arc resistance material; and an abrasive material different from the arc resistance material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of the present disclosure will become more apparent in light of the following detailed description when taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic diagram of an electrochemical grinding apparatus in accordance with one embodiment of the invention; 
         FIG. 2  is a schematic microgram of an example electrode in accordance with one embodiment of the invention; 
         FIGS. 3(   a )- 3 ( b ) are a schematic diagram of an example workpiece with a first set of heat-affected zones thereon and a table diagram of sizes of the first set of heat-affected zones respectively in accordance with one embodiment of the invention; and 
         FIGS. 4(   a )- 4 ( b ) are a schematic diagram example workpiece with a second set of heat affected zones thereon and a table diagram of sizes of the second set of heat-affected zones respectively. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     Embodiments of the present disclosure will be described hereinbelow with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the disclosure in unnecessary detail. 
       FIG. 1  illustrates a schematic diagram of an electrochemical grinding apparatus  10  in accordance with one embodiment of the invention. In embodiments of the invention, the electrochemical grinding apparatus  10  may be used to remove material from a workpiece  100  to form a desired configuration. As illustrated in  FIG. 1 , the electrochemical grinding apparatus  10  comprises an electrode  11 , a power supply  12 , an electrolyte supply  13 , a servomotor  14  and a controller  15 . In non-limiting examples, the electrode  11  may be in a rod, wheel or spindle shape. 
     In the illustrated example, the electrode  11  and the workpiece  100  are connected to negative and positive poles of the power supply  12 , respectively. Accordingly, the electrode  11  may function as a cathode and the workpiece  100  may act as an anode. Alternatively, the polarities of the electrode  11  and the workpiece  100  may be reversed. The electrolyte supply  13  is used for providing an electrolyte, such as a sodium nitrite solution between the electrode  11  and the workpiece  100  during electrochemical grinding. The servomotor  14  is connected to the electrode  11  and the workpiece  100  to drive the electrode  11  and the workpiece  100  to move linearly and/or rotate relative to each other. Alternatively, the servomotor  14  may drive only the electrode  11  or only the workpiece  100  to effect relative motion between the workpiece and the electrode. The controller  15  is connected to the power supply  12  and the servomotor  14  for controlling respective operations. Alternatively, the electrolyte supply  13  may be connected to the controller  15 . In some examples, the servomotor  14  and the controller  15  may not be employed. In embodiments of the invention, except the electrode  11 , other elements of the electrochemical grinding apparatus may be readily available and implemented by one skilled in the art. 
     Thus, during operation of electrochemical grinding, the power supply  12  may pass a direct electric current between the rotating electrode  11  and the workpiece  100  while the electrolyte passes therebetween to cooperatively remove material from the workpiece. In embodiments of the invention, material removal from the workpiece  100  may be produced by a combination of electrolytic solubilization caused through the electrolyte and mechanical abrading performed by the electrode  11  on the workpiece  100 . Additionally, in certain embodiments, the electrode  11  may also be used for electro discharge machining (EDM) or electrochemical discharging machining (ECDM). 
     In some embodiments, the electrode  11  may comprise an electrically conductive material, an arc resistance material, and an abrasive material. In embodiments of the invention, the term “an” may mean “at least one”. The electrically conductive material may be used to conduct the electrical current passing through the electrode  11 , and thus may typically comprise a material such as a metal. Additionally, the electrically conductive material may also serve as electrically conductive bonding material to hold the abrasive material together. The arc resistance material may be used to bear electrical arc during operation, and thus such material generally has a sufficiently high melting points to support this function. The abrasive material may be nonconductive and have desired hardness. During electrochemical machining, the abrasive material is used, for instance, to wipe away oxide films formed on the working surface of the workpiece, or remove the material from workpiece directly. During the removal of the material from the workpiece, a lot of chips of the material may be produced. In order to eject the chips of the material out from a gap between the electrode  11  and the workpiece  100 , the electrode  11  therefore may further comprise an ejection promoting material. In some embodiments, the ejection promoting material may comprise an organic resin and may also bond the abrasive and conducting materials together. During grinding, the ejection promoting material may change surface energy of the chips so that the chips may be less likely to reattach on the workpiece. 
     In non-limiting examples, the conductive material may comprise copper (Cu), iron (Fe), or aluminum (Al); the arc resistance material may comprise zirconium diboride (ZrB 2 ), titanium diboride (TiB 2 ), titanium nitride (TiN), tungsten (W) or molybdenum (Mo); the abrasive material may comprise silicon carbide (SiC), boron nitride (BN), tungsten carbide (WC), zirconium oxide (ZrO 2 ), aluminum oxide (Al 2 O 3 ), boron carbide (B 4 C), silicon nitride (Si 3 N 4 ), or diamond; and the ejection promoting material may comprise epoxies, amines, silicon (Si), alcohols, or hydroxides. Additionally, large particles of the arc resistance materials, such as ZrB 2 , TiN or TiB 2  may also serve as the abrasive material. 
     Accordingly, in particular examples, the electrode  11  may comprise different combinations of components, such as TiB 2 /Cu/SiC, W/Cu/SiC, W/Cu/WC, TiB 2 /W/Cu/Al 2 O 3  or TiB 2 /Mo/Cu/Al 2 O 3 . In certain separate and respective embodiments, a weight percentage of the electrically conductive material may be in a range of about 10-20%; a weight percentage of the arc resistance material(s) may be in a range of about 50-80%; and a weight percentage of the abrasive material(s) may be in a range of about 10-30%. In one non-limiting example, assuming the electrode comprises TiB 2 /Cu/SiC, the weight percentage of Cu is in the range of 10%-20%, the weight percentage of TiB 2  is in the range of about 50%-80%, and the weight percentage of SiC is in the range of about 10%-30%. In certain embodiments, when the electrode  11  comprises the ejection promoting material, a weight percent of the ejection promoting material may be in a range of about 10-30%. 
     In some non-limiting examples, when the electrode  11  comprises more than one arc resistance material or abrasive material, the total weight percentage of the arc resistance materials may be in the range of about 50%-80%, and the total weight percentage of the abrasive materials may be in a range of about 10%-30%. In a particular example, the weight percentage of one of the arc resistance materials or abrasive materials may be larger than other arc resistance material(s) or abrasive material(s). In one non-limiting example, where the electrode comprises TiB 2 /W/Cu/Al 2 O 3 , the total weight percent of TiB 2  and W is in the range of about 50%-80%, and the weight percent of W may be in a range of about 1%-7% relative to a total weight of the electrode  11 . 
     In particular examples of the invention, the weight percentage of Cu may be about 20%, the weight percentage of the arc resistance material(s) may be about 65%, and the weight percentage of the abrasive material(s) may be about 15%. 
     In embodiments of the invention, the electrode  11  may be fabricated using known methods. In one non-limiting example, as known to one skilled in the art, first, certain quantities of the arc resistance materials, the abrasive materials and the electrically conductive material are determined according to respective weight percentages in the electrode  11  having a desired quantity. Then, the arc resistance material powders and the abrasive material powders are mixed together, and a polymer coating is coated on the mixed powders. In certain embodiments of the invention, the polymer coating may be appropriate for use in a selective sintering machine or other shaping step, which is known to one skilled in the art. 
     Subsequently, the polymer-coated mixed powders are processed using the sintering machine to tack the mixed powders together by sintering the polymer coating so as to build the mixed powders in a desired shape. Then, a high-temperature furnace is used to vaporize the polymer coating and sinter the mixed powders. Finally, the conductive material, such as the metal Cu is infiltrated in a liquid state into the mixed powders to get the desired electrode. Additionally, other known methods may also be used for fabricating the electrode. 
     In some embodiments of the invention, in order to provide improved infiltration of Cu in the mixed powders, some quantities of nickel (Ni) may be mixed with Cu to perform the infiltration. In one non-limiting example, the total weight percentage of Ni and Cu in the electrode may be in the range of about 10%-20%, and the weight percentage of Ni may be in a range of about 1%-3% relative to the total weight of the electrode  11 . 
       FIG. 2  illustrates a schematic micrograph of an example electrode in accordance with one embodiment of the invention. As illustrated in  FIG. 2 , taking the electrode comprising 65 wt % TiB 2 , 20 wt % Cu, and 15 wt % SiC as one non-limiting example, numeral  20  indicates the components Cu (white), numeral  21  indicates the components TiB 2  (gray color), and numeral  22  indicates the components SiC (black color). As can be seen, in the illustrated embodiment, the components Cu and TiB 2  in the electrode are distributed homogeneously and continuously, which is advantageous for electrochemical grinding of the electrode. 
     Generally, parameters, such as heat-affected zones (HAZ), material removal rate (MRR) of the workpiece, and/or electrode wear ratio (Grinding Ratio) may be used to evaluate properties of the electrode in machining of the workpiece. The electrode wear ratio can be expressed as the ratio of workpiece removal volumes to electrode wear volumes. 
       FIGS. 3(   a ) and  4 ( a ) illustrate one non-limiting exemplary embodiment with a rod electrode comprising 65 wt % TiB 2 , 20 wt % Cu, and 15 wt % SiC for electrochemical grinding of an example workpiece  30 . Operation conditions comprise a voltage of about 20 volts, an electrode feedrate of about 20 mm/min, a spindle velocity of about 2000 revolutions per minute, an electrolyte solution comprising about 6 wt % sodium nitrite solution, an electrolyte pressure of about 0.7 Mpa, and an electrolyte conductivity of about 50 ms/cm. 
     As illustrated in  FIGS. 3(   a ) and  4 ( a ), the workpiece  30  is in a V-shape and comprises a first surface  31  and a second surface  32  for electrochemical grinding by the rod electrode. In non-limiting examples, after electrochemically grinding the two surfaces  31  and  32 , six heat-affected zones (C 1 -C 6  and D 1 -D 6 ) can be selected on certain areas of the surfaces  31  and  32  respectively to evaluate the properties of the rod electrode. As illustrated in  FIG. 3(   b ), the sizes of the heat-affected zones C 1 -C 6  are between 40 microns and 60 microns. As illustrated in  FIG. 4(   b ), the sizes of the heat-affected zones D 1 -D 6  are between 10 microns and 50 microns. The sizes of the heat-affected zones C 1 -C 6  and D 1 -D 6  are acceptable for many machining specifications, and are relatively small compared to some conventional electrochemical grinding electrodes. Thus, during electrochemical grinding, influence of the electrode to the workpiece  30  may be little and acceptable, and grinding quality of the workpiece  30  may be improved. 
     Additionally, in the illustrated example, MRR of the workpiece is about 500-700 mm 3 /min, and the G ratio of the electrode wear is about 25 or more; these values relatively high compared to some conventional electrochemical grinding rod electrodes, suggesting that use of the electrodes described herein may allow for improved grinding efficiency and reduced electrode wear. In other examples, a wheel electrode comprising 65 wt % TiB 2 , 20 wt % Cu, and 15 wt % SiC may also be used for electrochemical grinding under similar operation conditions to those in the above example, and the electrode wear ratio may be up to about 80 or more, which shows even higher grinding efficiency. 
     While the disclosure has been illustrated and described in typical embodiments, it is not intended to be limited to the details shown, since various modifications and substitutions can be made without departing in any way from the spirit of the present disclosure. As such, further modifications and equivalents of the disclosure herein disclosed may occur to persons skilled in the art using no more than routine experimentation, and all such modifications and equivalents are believed to be within the spirit and scope of the disclosure as defined by the following claims.