Abstract:
A process is provided for forming a resistance welding electrode. The process includes the step of providing a billet formed from a high conductivity metal. The billet includes a first portion having a first inner cavity formed therein. The process further includes the steps of inserting an insert into the first inner cavity of the billet, and deforming the insert so as to mechanically lock the insert in place in the billet. The deformed billet comprises the resistance welding electrode.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. patent application Ser. No. 08/975,022, filed Nov. 20, 1997, now U.S. Pat. No. 6,047,741. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to welding electrodes, and to a process for forming same. 
     Resistance welding has long been used as a quick and effective method of joining metal members. The workpieces to be welded are placed in abutting relationship and a large electrical current is caused to flow through the workpieces by a pair of opposed electrodes that contact the workpieces on opposite sides of the weld point. The current causes the abutting surfaces of the workpieces to be heated sufficiently to effect the formation of a weld nugget. Typically, the electrodes apply significant pressure to the workpieces during welding. This facilitates the welding process by urging the material together and, also, reducing electrical resistance between each electrode tip and the adjacent workpiece material that it contacts. 
     Since welding is accomplished by resistance heating of the material being welded, it will be appreciated that the electrodes will also be heated substantially. It is important to have electrodes of high electrical conductivity in order to minimize the power loss in the electrode, and the resulting heating of the electrode. 
     Over time, the repeated heating and pressing operations involved in resistance welding cause breakdown, softening, mushrooming and other deformation of the electrodes. The current density of the current going through the workpieces drops. As this occurs, electrical current requirements for welding increase with the enlarged welding tip face contacting the workpiece material until ultimately, redressing or replacement of the electrode is required. Accordingly, it is also important to have an electrode which is capable of withstanding significant distorting force at the elevated temperatures which result from the welding process so as to minimize the number of times it becomes necessary to redress or replace the electrode within a given period of time. 
     It is known in the art to form resistance welding electrodes by combining a copper electrode body with an anneal resistant, high hardness insert. Typically, the insert performs much better than the copper material from which the electrode body is formed. However, the insert material is much more expensive than the copper used to form the electrode body. 
     The insert may be brazed onto the shank of the electrode. The brazing step is disadvantageous, however, as it adds an additional step to the electrode manufacturing process and, hence, increases the cost of the electrode. Furthermore, the brazing operation may anneal and soften the electrode body. 
     It is also known to force the insert into an electrode body via a press-fit operation. The steel being welded today is often galvanized or coated with a zinc or other, softer metal coating. As a result, resistance welding electrode may tend to stick to the coated metal. An electrode tip joined to an electrode body only by means of a press-fit may tend to pull out of the body as the electrode is retracted following resistance welding of coated materials, thus requiring replacement of the electrode. 
     Accordingly, there is a need for an improved resistance welding electrode which can be manufactured via an efficient and more cost effective process and, yet, is capable of performing in an acceptable manner. 
     SUMMARY OF THE INVENTION 
     This need is met by the present invention, whereby an improved resistance welding electrode, and a process for forming the same are provided. The process involves providing a billet having an inner cavity, inserting a dispersion strengthened copper insert into the billet and deforming the insert-containing billet via cold-working operations so as to lock the insert in place mechanically in the billet. The forming operations may be performed in a single step such that the electrode can be manufactured in an efficient and cost effective manner. Furthermore, because the insert is mechanically locked in place within the billet, it is unlikely that the normal amount of sticking that occurs during resistance welding of coated steel will pull the insert out of the billet. It is also noted that the billet is preferably formed from a CDA C10700 silver bearing copper which is a high conductivity material. Previously, it was generally thought that silver bearing copper should not be used in forming welding electrodes as it was believed that such material would anneal at the temperatures involved in resistance welding. However, by virtue of cooling water located in an inner cavity of the silver bearing copper main body portion and because the main body portion makes only limited, if any, contact with a workpiece, annealing of the main body portion is prevented. 
     According to a first aspect of the present invention, a process for forming a resistance welding electrode is presented. A billet formed from a high conductivity metal is provided. The billet includes a first portion having a first inner cavity being defined by a first wall and a first stop face. An insert is inserted into the first inner cavity of the billet with the insert having a first portion positioned substantially adjacent the first stop face. The insert is deformed such that an outer diameter of the first portion of the insert is increased, thereby mechanically locking the insert in place in the billet. 
     The step of deforming the insert may comprise containing a first section of the first portion of the billet by a forming element and then applying pressure to the billet so as to displace at least the first portion of the billet not contained by the forming element and the first portion of the insert thereby increasing the outer diameter of the first portion of the insert and mechanically locking it in the billet. The step of providing a billet may comprise providing a generally cylindrical cut-off portion of high conductivity metal, upsetting and forward extruding the cut-off portion so as to form the billet having the first portion and a second portion, and forming the first inner cavity in the first portion of the billet. The process may further comprise the step of forming a second inner cavity in the second portion of the billet. The step of forming the first inner cavity in the first portion of the billet and the step of forming a second inner cavity in the second portion of the billet may be performed substantially simultaneously. Preferably, the insert is formed from an internally oxidized copper-aluminum alloy or dispersion strengthened copper. The billet may be formed from a high conductivity copper or a silver bearing copper. 
     According to another aspect of the present invention, a process for forming a resistance welding electrode comprises providing a generally cylindrical cut-off portion of high conductivity metal. A billet is formed from the generally cylindrical cut-off portion having a first portion with a first inner cavity therein and a second portion with a second inner cavity therein. The first inner cavity is defined by a first wall and a first stop face. An insert is inserted into the first inner cavity of the billet. The insert includes a first portion positioned substantially adjacent the first stop face. A first section of the first portion of the billet and a second portion of the insert are contained via a forming element. Pressure is applied to the billet thereby increasing an outer diameter of a second section of the first portion of the billet and an outer diameter of the first portion of the insert so as to lock the insert in place mechanically in the billet, thereby forming the resistance welding electrode. 
     The step of containing a first section of the first portion of the billet and a second portion of the insert via a forming element may comprise the steps of positioning the first section of the first portion of the billet and the second portion of the insert in an inner cavity of the forming element, the forming element being part of a punch assembly. The inner cavity of the forming element includes an inner diameter substantially equal to an outer diameter of the first portion of the billet. The second section of the first portion of the billet is positioned in an inner cavity of a forming die, the forming die being part of a die assembly. The inner cavity of the forming die having an inner diameter substantially equal to an outer diameter of a second section of a first portion of the electrode. The die assembly includes a forming pin located axially within the second inner cavity and extending into the second inner cavity. The forming pin has an outer diameter substantially equal to an inner diameter of the second inner cavity of the billet. The step of applying pressure to the billet may comprise the step of applying pressure to the billet via a forming punch of the punch assembly to cause the outer diameter of the second section of the first portion of the billet to increase, the outer diameter of the first portion of the insert to increase and a length of the insert to decrease. The forming punch has an outer diameter substantially equal to the outer diameter of the first portion of the billet. The step of applying pressure to the billet via a forming punch may cause forward extrusion of the first portion of the billet over the forming pin thereby increasing a length of the second inner cavity into the first portion of the billet. 
     According to yet another aspect of the present invention, a process for forming a resistance welding electrode comprises providing a generally cylindrical cut-off portion of high conductivity metal. The cut-off portion is upset and forward extruded so as to form a billet having a first portion and a second portion. A first inner cavity is back extruded in the first portion of the billet with the first inner cavity being defined by a first wall and a first stop face. A second inner cavity is back extruded in the second portion of the billet. An insert is inserted into the first inner cavity of the billet. The insert includes a first portion positioned substantially adjacent the first stop face. A first section of the first portion of the billet and a second portion of the insert are contained via a forming element. Pressure is applied to the billet thereby increasing an outer diameter of a second section of the first portion of the billet and an outer diameter of the first portion of the insert so as to lock the insert in place mechanically in the billet. The first portion of the billet is forward extruded thereby extending the second cavity into the first portion of the billet. The second portion of the billet is contoured such that second portion of the billet has a predetermined shape. The steps of back extruding the first inner cavity and back extruding the second inner cavity may be performed substantially simultaneously. The steps of applying pressure to the billet and forward extruding the first portion of the billet may be performed substantially simultaneously. 
     According to a further aspect of the present invention, a resistance welding electrode comprises a main body formed from a high conductivity metal. The main body includes a first portion having a first inner cavity being defined by a first wall and a first stop face. An insert is provided in the first inner cavity. The insert includes a first portion which is substantially adjacent the first stop face. The first portion of the insert has a diameter greater than a diameter of the first inner cavity such that the insert is mechanically locked in place in the main body. The main body includes a substantially planar surface composed of a substantially planar surface of the first portion of the main body and a substantially planar surface of the second portion of the insert. 
     Preferably, the diameter of a first section of the first portion of the main body is less than the diameter of a second section of the first portion of the main body. The first section of the first portion of the main body terminates at the substantially planar surface. The main body may further include a second inner cavity provided in a second portion of the main body which is adapted to be supplied with a cooling fluid during a resistance welding process. Preferably, the insert is formed from an internally oxidized copper-aluminum alloy or dispersion strengthened copper. The main body may be formed from a high conductivity copper or a silver bearing copper. 
     Accordingly, it is an object of the present invention to provide an improved low cost resistance welding electrode and process for forming same. It is further an object of the present invention to provide a resistance welding electrode having a dispersion strengthened copper insert which is mechanically locked in position within a main body formed from a high conductivity metal. Other features and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A-6A illustrate various manufacturing steps for manufacturing a resistance welding electrode according to the present invention; 
     FIGS. 1B-6B are cross-sectional views of the electrode after each of the manufacturing steps illustrated in FIGS. 1A-6A; 
     FIG. 7 is a side view of the electrode manufactured according to the present invention; and 
     FIG. 8 is a top view of the electrode of FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIGS. 1A-6A, a press  10  is provided having a stationary bed portion  12  and a ram portion  14  which is caused to move back and forth relative to the bed portion  12  by a conventional drive apparatus (not shown). The bed and ram portions  12  and  14  include respectively first and second electrode forming tooling  16  and  18 , which are provided at first, second, third, fourth and fifth forming stations  20 ,  40 ,  60 ,  80  and  100 . Referring specifically to FIG. 1A, positioned adjacent to the first forming station  40  is a conventional cutting station  120 . A roll of substantially solid wire stock  122  having a predetermined diameter is fed to the cutting station  120  where it is cut into discrete, generally cylindrical cut-off portions  124 , one of which is shown in FIG.  1 B. The cut-off portions  124  are used in forming resistance welding electrodes  180 , one of which is shown in FIGS. 6B,  7  and  8 . The wire stock  122  is fed through a quill  126  and cut to a predetermined length by a cutter  128  thereby forming the cut-off portions  124 . Conventional work transfer fingers  130  (shown schematically in the drawings) move each of the discrete cut-off portions  124  from the cutting station  120  to the first forming station  20  and from the first forming station  20  through the remaining forming stations  40 ,  60 ,  80  and  100 . 
     Referring now to FIG. 2A, the cut-off portion  124  is then transferred to the first forming station  20  where the cut-off portion  124  is transformed into a billet  140  shown in FIG.  2 B. The billet  140  includes a nose or first portion  142  having a first outer diameter D B1 , a stem or second portion  144  having a second outer diameter D B2  and an intermediate tapered portion  146 . The first forming station  20  includes a first forming die assembly  22  and a first forming punch  24 . The first die assembly  22  includes a first forming die  26  and a second forming die  28  which are fixedly coupled to the bed portion  12  and, hence, are stationary. The first die  26  includes a first inner cavity  26 A having an inner diameter substantially equal to the first outer diameter D B1 . The second die  28  includes a second inner cavity  30  having a first section  30 A having an inner diameter substantially equal to the first outer diameter D B1 , a second section  30 B having a tapered diameter corresponding to the tapered portion  146 , and a third section  30 C having an inner diameter substantially equal to the second outer diameter D B2 . 
     The first punch  24  is fixedly coupled to and moves with the ram portion  14 . The first punch  24  has an outer diameter substantially equal to the first outer diameter D B1 . As the ram portion  14  is driven towards the bed portion  12 , the first punch  24  engages the cut-off portion  124  held adjacent to the first die  26  via the pair of the work transfer fingers  130  and inserts the cut-off portion  124  into the first inner cavity  26 A of the first die  26  and into the first section  30 A of the second inner cavity  30  of the second die  28 . The first punch  24  then applies sufficient pressure to the cut-off portion  124  to effect forward extrusion and upsetting of the cut-off portion  124  such that the billet  140  is formed. The cut-off portion  124  is upset since the first diameter D B1  of the first portion of the billet  140  is greater than the diameter of the cut-off portion  124 . The cut-off portion  124  is forward extruded as the cutoff portion  124  is forced through the third section  30 A which has an inner diameter less than the diameter of the cut-off portion  124 . The first die assembly  22  includes an ejection pin  32  which ejects the billet  140  from the first and second dies  26 ,  28  and into the work transfer fingers  130  after the cut-off portion  124  has been forward extruded and upset 
     The billet  140  is then transferred to the second forming station  40  shown in FIG.  3 A. The second forming station  40  includes a second forming die assembly  42  and a second forming punch  44 . The second die assembly  42  includes a third forming die  46  and a fourth forming die  48  which are slidably coupled to the bed portion  12 . The third die  46  includes a third inner cavity  46 A having an inner diameter substantially equal to the first diameter D B1 . The fourth die  48  includes a fourth inner cavity  50  having a first section  50 A having an inner diameter substantially equal to the first diameter D B1  and a second section  50 B having an inner diameter substantially to the second diameter D B2 . The second die assembly  42  includes a forming pin  52  which is fixedly coupled to the bed portion  12  and extends into the fourth inner cavity  50 . The forming pin  52  has an outer diameter substantially equal to an inner diameter of a second inner cavity  148  in the second portion  144  of the billet  140 , see FIG.  3 B. The third and fourth dies  46 ,  48  slide about the forming pin  52  and are biased towards the ram portion  14  via a pair of springs  54 . 
     The second punch  44  is fixedly coupled to the ram portion  14  and moves with the same. The second punch  44  includes a first portion  44 A having an outer diameter substantially equal to the first diameter D B1  and a second portion  44 B having an outer diameter substantially equal to an inner diameter of a first inner cavity  150  in the first portion  142  of the billet  140 , see FIG.  3 B. The first inner cavity  150  is defined by a first wall  150 A and a first stop face  150 B. As the ram portion  14  is driven towards the bed portion  12 , the second punch  44  engages the billet  140  held adjacent to the third die  46  via the pair of the work transfer fingers  130  and inserts the billet  140  into the second die assembly  40 . The second portion  144  of the billet  140  is contained in the second section  50 B of the fourth inner cavity  50  of the fourth die  48  while the first portion of the billet  140  is contained in the third inner cavity  46 A of the third die  46 . The intermediate portion  146  of the billet  140  is positioned within the first section  50 A of the fourth inner cavity  50  of the fourth die  50 . The second punch  44  applies sufficient pressure to the first portion  142  of the billet  140  so as to form the first inner cavity  150  through back extrusion. The second punch  44  continues to apply sufficient pressure against the billet  140  thereby causing the third and fourth dies  46  to slide towards and around the forming pin  52 . The second inner cavity  148  is thus formed through back extrusion as the second portion  148  of the billet  140  is driven over the forming pin  52 . 
     In the illustrated embodiment, the first inner cavity  150  is smaller than the second inner cavity  148  such that the amount of force required to form the first inner cavity  150  is less than the amount of force required to form the second inner cavity  148 . Accordingly, the first inner cavity  150  may be formed prior to sliding the third and fourth dies  46 ,  48  for formation of the second inner cavity  148 . As the first and second inner cavities  150 ,  148  are formed, the lengths of the first and second portions  142 ,  144  increase as the extruded material is displayed around the second portion  46 A of the second punch  46  and the forming pin  52 . Further, the intermediate portion  146  is displaced into the first portion  142  of the billet  140 . The second die assembly  42  further includes an ejection sleeve  56  positioned about the forming pin  52  and is movable relative to the pin  52 . The ejection sleeve  56  ejects the billet  140  from the dies  46  and  48  and into the work transfer fingers  130  after the first and second cavities  150 ,  148  have been formed. 
     The billet  140  is then transferred to the third forming station  60  shown in FIG.  4 A. The third forming station  60  includes a third forming die assembly  62  and a third forming punch assembly  64 . The third die assembly  62  includes a fifth forming die  66  and a pressure pin  68  which are fixedly coupled to the bed  12  and, hence, are stationary. The fifth die  66  includes a fifth inner cavity  66 A having a inner diameter substantially equal to second outer diameter D B2  of the second portion  144  of the billet  140 . The pressure pin  68  has an outer diameter substantially equal to the inner diameter of the second inner cavity  148 . 
     The third punch assembly  64  includes a first support element  69 , a second support element  70 , a third punch  72  and an insert supply mechanism  74 . The first support element  69  includes an inner cavity  69 A having a inner diameter substantially equal to the first outer diameter D B1  of the first portion  142  of the billet  140 . The second support element  70  includes an inner cavity  70 A having a inner diameter substantially equal to the inner diameter of the first inner cavity  150 . The first and second support elements  69 ,  70  are slidably coupled to the ram portion  104  through a support block  75 . The third punch  72  has an outer diameter substantially equal to the inner diameter of the first inner cavity  150 . The third punch  72  is slidably coupled to the ram portion  14 . The third punch  72  slides through an inner cavity  75 A of the support block  75  as the support block  75  engages the third die assembly  62 . The third punch  72  is biased towards the bed portion  12  via a spring  76 . The insert supply mechanism  74  supplies dispersion strengthened copper inserts  160  one at a time into the path of movement of the third punch  72  such that the third punch  72  inserts a copper insert  160  into the first inner cavity  150  of the billet  140  as shown in FIG.  4 B. The insert supply mechanism  74  comprises a supply conduit  162  having a plurality of inserts  160  therein. The inserts  160  are fed to the conduit  162  via a feed device (not shown). The conduit  162  extends through a bore  75 B in the support block  75  and is fixedly connected to the support block  75  so as to move with the same. A distal end  162 A of the conduit  162  terminates at an insert receiving channel  164  in the support block  75  such that the conduit  162  supplies inserts  160  to the channel  164 . 
     The supply mechanism  74  further includes a reciprocating pin  166  which extends into the channel  164 . A spring  168  biases the pin  166  toward an outer surface  164 A of the channel  164  away from the conduit  162 . The supply mechanism  74  includes a plunger  170  positioned in a plunger channel  172  within the support block  75  and connected to the channel  164 . The plunger  170  includes a beveled surface  170 A which engages a corresponding beveled surface  166 A on the pin  166 . The spring  168  biases the pin  166  toward the plunger  170  such that the beveled surface  166 A engages the beveled surface  170 A on the plunger  170  forcing the plunger  170  up from the plunger channel  172 . The plunger  170  includes a surface  170 B which extends above an upper surface  75 C of the support block  75  when the punch assembly  64  is in a first position separated from the die assembly  62 . Upon upward movement of the punch assembly  64 , the plunger  170  moves downward, engaging the pin  166  through the interaction of the beveled surfaces  166 A,  170 A such that the pin  166  is moved inward against the force of the spring  168 . As the pin  166  moves inward, it pushes an insert  160  located in the channel  164  in a direction toward the path of movement of the pin  72 . FIG. 4A shows the punch assembly  64  in a second position with the pin  166  extending through the channel  164  covering the conduit  162 . Upon separation of the punch assembly  64  from the die assembly  62 , the plunger  172  is pushed upwards from the plunger channel  172  as the spring  168  pushes against the pin  166 . Once the pin  166  extends away from the conduit  162 , another insert  160  is forced into the channel  164 . 
     As the ram portion  14  moves toward the bed portion  12 , the punch assembly  64  engages the billet  140  held adjacent to the fifth die  66  via the pair of the work transfer fingers  130 . The second portion  144  is pushed into fifth die  66  with the second inner cavity  148  being supported by the pressure pin  68 . The billet  140  is pushed into the inner cavity  69 A of the first support element  69 . The surface  170 B of the plunger  170  engages die assembly  62  pushing the pin  166  inward such that an insert  160  is pushed into the inner cavity  75 A of the support block  75 . With the insert  160  in the inner cavity  75 A, the support block  75  slides about the pin  72  with the insert  160  being pushed into the first inner cavity  150  of the first portion  142  of the billet  140 . The spring  76  provides sufficient force so as to press fit the insert  160  into the first inner cavity  150 . The insert  160  includes a first portion  160 A which is positioned substantially adjacent to the first stop face  150 B of the first cavity  150 . The billet  140  includes a substantially planar surface  140 A comprised of a substantially planar surface  142 A of the first portion  142  of the billet  140  and a substantially planar surface  160 C of a second portion  160 B of the insert  160 . The first portion  142  of the billet  140  includes a first section  142 B extending from the planar surface  142 A to a first end of the first portion  160 A of the insert  160  and a second section  142 C extending from the first end of the first portion  160 A of the insert  160  to the second portion  144  of the billet  140 . 
     The third die assembly  62  further includes an ejection sleeve  78  positioned about the pressure pin  68  and is movable relative to the pin  68 . The ejection sleeve  78  in conjunction with the pin  72  ejects the billet  140  from the die  66  and support element  69 , respectively, and into the work transfer fingers  130  after the insert  160  is positioned in the billet  140 . As the punch assembly  64  is removed from the die assembly  62 , the pin  72  is extended further in a direction toward the die assembly  62  so as to eject the billet  140  from the punch assembly  64 . 
     From the third forming station  60 , the billet  140  is moved to the fourth forming station  80  where it is deformed so as to lock the insert  160  in place mechanically and form a resistance welding electrode  180 , one of which is shown in FIG.  5 B. The electrode  180  includes a nose or first portion  182  and a stem or second portion  184  which correspond to the first and second portions  142 ,  144  of the billet  140 , respectively. Further, the first portion  182  of the electrode  180  includes a first section  182 B and a second section  182 C which correspond to the first and second sections  142 B,  142 C of the first portion  142  of the billet  140 . The first portion  182  of the electrode  180  also includes a substantially planar surface  182 A which corresponds to the substantially planar surface  142 A of the first portion  142  of the billet  140 . The electrode  180  includes a substantially planar surface  180 A corresponding to the substantially planar surface  140 A of the billet  140 . The billet  140  is also referred to herein as the main body of the electrode  180 . 
     The fourth forming station  80  comprises a fourth forming die assembly  82  and a fourth forming punch assembly  84 . The fourth die assembly  82  includes a sixth die  86 , a seventh die  88  and an extrusion pin  90 . The sixth die  86  includes a seventh inner cavity  86 A having an inner diameter substantially equal to an outer diameter D E1  of the second section  182 B of the first portion  182  of the electrode  180 . The seventh die  88  includes a seventh inner cavity  88 A having an inner diameter substantially equal to the outer diameter of the second portion  144  of the billet  140 . The extrusion pin  90  has an outer diameter substantially equal to the inner diameter of the second inner cavity  148 . The extrusion pin  90  is fixedly coupled to the bed portion  12  and extends through the inner cavity  88 A. The sixth and seventh dies  86 ,  88  are slidably coupled to the bed portion  12  and slide about the extrusion pin  90 . 
     The fourth punch assembly  84  includes a forming element  92  and a forming punch  94  which are fixedly coupled to the ram portion  14  and move with the same. The forming element  92  includes an inner cavity  92 A having an inner diameter substantially equal to the outer diameter of the first portion  142  of the billet  140 , and specifically, substantially equal to the outer diameter of the first section  142 B of the first portion  142  of the billet  140 . The punch  94  has an outer diameter substantially equal to the outer diameter of the first section  142 B of the first portion  142  of the billet  140 . As the ram portion  14  moves toward the bed portion  12 , the punch assembly  84  engages the billet  140  held adjacent to the sixth die  86  via the pair of the work transfer fingers  130 . The second portion  144  of the billet  140  is pushed through the sixth die  86  until it engages the seventh die  88 . The first section  142 B of the first portion  142  of the billet  140  is contained within the forming element  92 . 
     The ram portion  14  continues to move towards the bed portion  12  with the second portion  144  of the billet supported by the seventh die  88  and the extrusion punch  90 . The first section  142 B of the first portion  142  of the billet  140  as well as the second portion  160 B of the insert  160  are contained and supported by the forming element  92  and the punch  94 . The punch  94  is driven with an appropriate amount of force to cause the sixth and seventh dies  86 ,  88  to slide about the extrusion pin  90 , thereby displacing material from the second section  142 C of the first portion  142  of the billet  140  and the first portion  162 A of the insert  162  outwards. The outer diameter of the second section  142 C and the outer diameter of the first portion  162 A of the insert  162  increase, thereby mechanically locking the insert  162  into the billet  140 . The length of the insert  160  also decreases in the process. In other words, the displacement of material causes the first portion  160 A of the insert  160  to swell outward and to compress longitudinally, thereby locking it into place as the outer diameter of the first portion  160 A is greater than the outer diameter of the second portion  160 B. Further, the second cavity  144  is forward extruded into the first portion  142  of the billet  140 . With the billet  140  deformed and the insert  160  locked in place, the billet  140  becomes the electrode  180 . 
     The fourth die assembly  82  further includes an ejection sleeve  96  positioned about the extrusion pin  90  and is movable relative to the pin  90 . The ejection sleeve  96  in conjunction with the punch  94  ejects the electrode  180  from the die  86  and the forming element  92 , respectively, and into the work transfer fingers  130  after the insert  160  is mechanically locked in the billet  140 . As the punch assembly  84  is removed from the die assembly  82 , the punch  94  is extended further in a direction toward the die assembly  82  so as to eject the electrode  180  from the punch assembly  84 . 
     The electrode  180  is then transferred to the fifth forming station  100  shown in FIG.  6 A. The fifth forming station  100  includes a fifth forming die assembly  102  and a fifth forming punch assembly  104 . The fifth forming die assembly  102  includes a eighth die  106 , a ninth die  108  and a pressure pin  110 . The eighth die  106  and the ninth die  108  are slidably coupled to the bed portion  12  and slide about the pressure pin  110  which is fixedly coupled to the bed portion  12 . The eighth die  106  includes an eighth inner cavity  106 A having an inner diameter substantially equal to the outer diameter D E1 , of the electrode  180 . The ninth die  108  includes a ninth inner cavity  108 A having a tapered cross-section. The pin  110  has an outer diameter substantially equal to the inner diameter of the second portion  184  of the electrode  180 . 
     The fifth punch assembly  104  includes a forming element  112  and a forming punch  114 . The forming element  112  is slidably coupled to the ram portion  14 . The forming element  112  slides about the forming punch  114  and is biased towards the bed portion  12  via springs  115 . The forming element  112  includes an inner cavity  112 A having an inner diameter substantially equal to the outer diameter of the first section  184 B of the first portion  182  of the electrode  180 . The punch  114  has an outer diameter substantially equal to the outer diameter of the first section  182 B of the first portion  182  of the electrode  180 . As the ram portion  14  moves toward the bed portion  12 , the punch assembly  114  engages the electrode  180  held adjacent to the eighth die  106  via the pair of work transfer fingers  130 . The second portion  184  of the electrode  180  is pushed through the eighth die  106  until it engages the ninth die  108 . The first section  182 B of the first portion  182  of the electrode  180  is contained within the forming element  112 . The ram portion  14  and the punch  114  continue to drive the electrode  180  using an appropriate amount of force into the ninth die  108  to contour or coin the second portion  184  of the electrode  180  into the desired shape as defined by the tapered cross-section of the ninth die  108  and as shown in FIGS. 6B and 7. The sliding action of the fifth die and punch assemblies  102 ,  104  ensure that the electrode  180  is properly coined. 
     The fifth die assembly  102  further includes an ejection sleeve  116  positioned about the pin  110  and is movable relative to the pin  110 . The ejection sleeve  116  in conjunction with the punch  114  ejects the electrode  180  from the die  106  and the forming element  112 , respectively, and into the work transfer fingers  130  after the second portion  184  is coined. As the punch assembly  104  is removed from the die assembly  102 , the punch  114  is extended further in a direction toward the die assembly  102  so as to eject the electrode  180  from the punch assembly  104 . Once the second portion  184  is coined, the electrode  180  has the desired configuration as shown in FIGS. 7 and 8. 
     Preferably, the copper wire  122  comprises a CDA C10700 silver bearing copper or a CDA C10500 silver bearing copper. Alternatively, another metal which is highly electrically conductive and which is substantially resistant to annealing below approximately 900° F. may be used. The inserts  160  are preferably formed from a dispersion strengthened copper such as GlidCop® Al-25 or GlidCop® Al-60, which are commercially available from OMG America&#39;s, Inc. Dispersion strengthened copper is resistant to heading or “mushrooming” during welding cycles and, further, is resists sticking to galvanized and coated steels. In the illustrated embodiment, the insert  160  is formed of an internally oxidized copper-aluminum alloy. Of course, insert  160  may be formed from other appropriate materials or resistance welding alloys which are resistant to sticking and mushrooming. 
     The tapered second portion  184  is adapted to fit onto the arm of a conventional robotic welder. The electrode  180  is adapted to be water cooled through the second cavity  148 . The first or nose portion  182  of the electrode  180  is adapted to engage a workpiece during a resistance welding operation. 
     During the cold-working operations performed in stations  60 ,  80  and  100 , the insert  160  is maintained in a compressive state. This is important since dispersion strengthened copper is relatively brittle and may break if it is placed in tension. 
     It is further contemplated that the electrode  180  may be machined after it has been formed in the press  10 . 
     Having described the invention in detail and by reference to preferred embodiments thereof, It will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.