Patent Publication Number: US-10312668-B2

Title: Spark plug having firing pad

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/681,289 filed on Aug. 9, 2012, U.S. Provisional Application Ser. No. 61/716,250 filed on Oct. 19, 2012, U.S. Provisional Application Ser. No. 61/759,088 filed on Jan. 31, 2013, and U.S. Non-Provisional application Ser. No. 13/962,496 filed on Aug. 8, 2013. The entire contents of these applications are incorporated herein. 
    
    
     TECHNICAL FIELD 
     This invention generally relates to spark plugs and other ignition devices for internal combustion engines and, in particular, to a firing pad that is welded to a center electrode, to a ground electrode, or to both. 
     BACKGROUND 
     Spark plugs can be used to initiate combustion in internal combustion engines. Spark plugs typically ignite a gas, such as an air/fuel mixture, in an engine cylinder or combustion chamber by producing a spark across a spark gap defined between two or more electrodes. Ignition of the gas by the spark causes a combustion reaction in the engine cylinder that is responsible for the power stroke of the engine. The high temperatures, high electrical voltages, rapid repetition of combustion reactions, and the presence of corrosive materials in the combustion gases can create a harsh environment in which the spark plug functions. This harsh environment can contribute to erosion and corrosion of the electrodes that can negatively affect the performance of the spark plug over time, potentially leading to a misfire or some other undesirable condition. 
     To reduce erosion and corrosion of the spark plug electrodes, various types of noble metals and their alloys—such as those made from platinum and iridium—have been used. These materials, however, can be costly. Thus, spark plug manufacturers sometimes attempt to minimize the amount of precious metals used with an electrode by using such materials only at a firing tip or spark portion of the electrodes where a spark jumps across a spark gap. 
     SUMMARY 
     According to one embodiment, there is provided a method of attaching a firing pad to an electrode for a spark plug. One step involves applying a laser beam to a sparking surface of the firing pad in order to produce a fused area and an unfused area. The fused area is subject to the application of the laser beam, while the unfused area does not have the laser beam applied to it. Another step in the method involves maintaining the laser beam at the sparking surface so that a weld is formed between the firing pad and the electrode. The laser beam creates one or more fused portion(s) that have an overall fused area that is located largely or entirely inboard of the peripheral edge. Another step in the method involves controlling the laser beam to leave at least one unfused portion at the sparking surface 
     According to another embodiment, there is provided a method of attaching a firing pad to an electrode for a spark plug. The method includes the steps of initially applying a laser beam to a sparking surface of the firing pad or the electrode outboard of a peripheral edge of the firing pad, and causing the laser beam to move from the sparking surface of the firing pad to the electrode outboard of the peripheral edge of the firing pad or causing the laser beam to move from the electrode outboard of the peripheral edge of the firing pad to the sparking surface of the firing pad, wherein the laser beam crosses the peripheral edge of the firing pad as the laser beam moves. The method further includes the steps of forming one or more fused portion(s) on the electrode while the laser beam moves, and forming one or more fused portion(s) on the sparking surface of the firing pad while the laser beam moves. 
     According to another embodiment, there is provided a method of attaching a firing pad to an electrode for a spark plug. The method includes the steps of striking a sparking surface of the firing pad with a laser beam, penetrating entirely through a thickness of the firing pad with the laser beam, and mixing a material of the firing pad with a material of the electrode to form a fused portion as thermal energy from the laser beam increases at a surface-to-surface interface between the firing pad and the electrode, wherein an unfused portion exists between the fused portion and a peripheral edge of the firing pad. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred exemplary embodiments of the invention will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements, and wherein: 
         FIG. 1  is a cross-sectional view of an exemplary spark plug; 
         FIG. 2  is an enlarged view of a firing end of the spark plug of  FIG. 1 , where the firing end includes an exemplary firing pad; 
         FIGS. 3A-3Q  are top views of various embodiments of potential weld configurations for a firing pad, such as the one shown in  FIG. 2 ; 
         FIG. 4  is an enlarged cross-sectional view of the firing pad of  FIG. 2 , showing a laser beam of a welding operation; 
         FIG. 5  is an enlarged view of a firing end of a spark plug, where the firing end includes an exemplary firing pad attached to a center electrode; and 
         FIG. 6  is an enlarged view of a firing end of a spark plug, where the firing end includes an exemplary firing pad attached to a distal end of a ground electrode. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The firing pads and weld configurations described herein can be used in spark plugs and other ignition devices including industrial plugs, aviation igniters, or any other device that is used to ignite an air/fuel mixture in an engine. This includes spark plugs used in automotive internal combustion engines, and particularly in engines equipped to provide gasoline direct injection (GDI), engines operating under lean burning strategies, engines operating under fuel efficient strategies, engines operating under reduced emission strategies, or a combination of these. The various firing pads and weld configurations may provide improved ignitability, effective pad retention, more lenient manufacturing tolerances, enlarged surface areas for exchanging sparks across a spark gap, and cost effective solutions for the use of noble metal, to cite some possibilities. As used herein, the terms axial, radial, and circumferential describe directions with respect to the generally cylindrical shape of the spark plug of  FIG. 1  and generally refer to a center axis A, unless otherwise specified. And, as an aside, the welds and weld configurations shown in the figures are merely illustrative and demonstrative in nature. Actual welds and weld configurations may look different than shown. For example, actual welds and weld configurations may have overlapping pools of weldment material, and may not appear so nicely geometrical as shown. 
     Referring to  FIG. 1 , a spark plug  10  includes a center electrode (CE) base or body  12 , an insulator  14 , a metallic shell  16 , and a ground electrode (GE) base or body  18 . Other components can include a terminal stud, an internal resistor, various gaskets, and internal seals, all of which are known to those skilled in the art. The CE body  12  is generally disposed within an axial bore  20  of the insulator  14 , and has an end portion exposed outside of the insulator at a firing end of the spark plug  10 . In one example, the CE body  12  is made of a nickel (Ni) alloy material that serves as an external or cladding portion of the body, and includes a copper (Cu) or Cu alloy material that serves as an internal core of the body; other materials and configurations are possible including a non-cored body of a single material. The insulator  14  is generally disposed within an axial bore  22  of the metallic shell  16 , and has an end nose portion exposed outside of the shell at the firing end of the spark plug  10 . The insulator  14  is made of a material, such as a ceramic material, that electrically insulates the CE body  12  from the metallic shell  16 . The metallic shell  16  provides an outer structure of the spark plug  10 , and has threads for installation in the associated engine. 
     Referring now to  FIGS. 1 and 2 , the GE body  18  is attached to a free end of the metallic shell  16  and, as a finished product, may have a generally and somewhat conventional L-shape. At an end portion nearest a spark gap G, the GE body  18  is axially spaced from the CE body  12  and from a CE firing tip  24  (if one is provided). Like the CE body, the GE body  18  may be made of a Ni alloy material that serves as an external or cladding portion of the body, and can include a Cu or Cu alloy material that serves as an internal core of the body; other examples are possible including non-cored bodies of a single material. Some non-limiting examples of Ni alloy materials that may be used with the CE body  12 , GE body  18 , or both, include Ni—Cr alloys such as Inconel® 600 or 601. In cross-sectional profile, the GE body  18  can have a generally rectangular shape or some other suitable configuration. The GE body  18  has an axially-facing working surface  26  that generally confronts and opposes the CE body  12  or the CE firing tip  24  (if one is provided) across the spark gap G. The working surface  26  can be generally planar and without a recess as shown, or it could have a recess or other surface features to accommodate seating of a firing pad, to cite several possibilities. 
     In the embodiment shown in the figures, the spark plug  10  includes an optional CE firing tip  24  that is attached to an axially-facing working surface  28  of the CE body  12  and exchanges sparks across the spark gap G. Referring to  FIG. 2 , the CE firing tip  24  shown here has a two-piece and generally rivet-like construction and includes a first piece  30  (rivet head) welded to a second piece  32  (rivet stem). The first piece  30  may be directly attached to the CE body  12 , and the second piece  32  may be directly attached to the first piece so that an axially-facing sparking surface  34  is provided for exchanging sparks across the spark gap G. The first piece  30  can be made of a Ni-alloy material, and the second piece  32  can be made of a noble metal-alloy material such those including iridium (Ir), platinum (Pt), or ruthenium (Ru); other materials for these pieces are certainly possible. In other embodiments not shown in the drawings, for example, a separate and discrete CE firing tip is omitted, in which case sparks are exchanged from the CE body itself  12 . The optional firing tip  24  could be attached to the GE instead of the CE, it could have a one-piece or single-material construction, and it could have different shapes including non-rivet-like shapes such as cylinders, bars, columns, wires, balls, mounds, cones, flat pads, rings, or sleeves, to cite several possibilities. The present spark plug is not limited to any particular firing end arrangement, as the firing pads and weld configurations described herein could be used with any number of firing end arrangements, including those with or without separate firing tips  24 . 
     With reference to  FIG. 4 , the spark plug  10  includes an exemplary firing pad  36  welded to the working surface  26  of the GE body  18  for exchanging sparks across the spark gap G. The exemplary firing pad  36  is thin in the sense that its greatest width dimension (W) across the sparking surface  38  is at least several times larger than its greatest thickness dimension (T) through the firing pad  36 ; in the embodiment of  FIG. 4 , dimension W is measured in the radial direction and dimension (T) is measured in the axial direction so that they are perpendicular, but this is not necessary and depends on the embodiment. This “thin pad” configuration is different than many previously-known firing tip configurations with so-called fine wire constructions in which the greatest width dimension across the sparking surface of the wire (i.e., the diameter) is less than the thickness dimension of the wire (i.e., the axial height). This “thin pad” configuration also gives firing pad  36  a relatively large sparking surface  38  relative to the total amount of precious metal used, particularly when compared to previously-known fine wire tips. Among other possible advantages, the firing pads and weld configurations described herein may provide improved ignitability, effective pad retention, more lenient manufacturing tolerances, enlarged surface areas for exchanging sparks across a spark gap, and cost effective solutions for the use of noble metal, to cite some possibilities. For instance, the large sparking surface  38  can limit material degradation at the working surface  26 . The sparking surface  38  directly confronts and opposes a complementary sparking surface on the CE (with or without separate firing tip  24 ), between which sparks are propagated, discharged, and/or exchanged across the spark gap G during operation of the spark plug  10 . It should be appreciated that the weldment illustrated in  FIG. 4  extends entirely through the firing pad  36  and penetrates into the ground electrode  18 ; the amount or distance of penetration may be dictated by the particular application, materials involved, etc. This type of completely penetrating weldment is usually not possible with the so-called fine wire tip constructions. 
     The firing pad  36  is preferably made from a noble metal material and can be formed into its thin shape before or after it is welded to the electrode body. The firing pad  36  can be made from a pure precious metal or a precious metal alloy, such as those containing platinum (Pt), iridium (Ir), ruthenium (Ru), or some combination thereof. According to some non-limiting examples, the firing pad  36  can be made from a platinum alloy containing between 10 wt % and 30 wt % Ni and the balance being Pt, or one containing between 1 wt % and 10 wt % tungsten (W) and the balance being Pt; in either of the preceding platinum-alloy examples, other materials like Ir, Ru, rhodium (Rh) and/or rhenium (Re) could also be included. Other materials are certainly possible for the firing pad  36 , including pure Pt, pure Ir, pure Ru, and any suitable alloy thereof, to name a few. Before being welded to the electrode, the firing pad  36  can be produced by way of various processes and steps including heating, melting, and metalworking. In one example, the firing pad  36  is stamped, cut, or otherwise formed from a thin sheet or tape of noble metal material; in another example, the firing pad is cut or sliced from a wire of noble metal material with a diamond saw or other severing tool, which can then be further flattened or metalworked to refine its shape. The present spark plug is not limited to any particular material or method of manufacturing, as the firing pads and weld configurations described herein could be used with any number of alloy or non-alloy materials or manufacturing methods. 
     As mentioned, the firing pads and weld configurations described herein and shown in  FIGS. 3A-3Q  may provide improved ignitability, effective pad retention, more lenient manufacturing tolerances, enlarged surface areas for exchanging sparks across a spark gap, and cost effective solutions for the use of noble metal. These provisions are attributable, at least in part, to a welded or overall fused area  42  that is located mostly, and in some cases entirely, inboard of a peripheral edge  40  of the firing pad  36 . This differs from previously-known laser seam welds where, instead of the weld being located mostly or entirely inboard of a peripheral edge, the weld is on top of the entire peripheral edge so that it completely covers the boundary between the firing tip and the electrode body. One potential challenge for forming a laser seam weld like this is that if there is even a slight misalignment or mispositioning of the firing tip or electrode body with respect to each other or with respect to the laser beam (sometimes the result of manufacturing tolerances), the laser can fail to adequately strike the intended junction between the two pieces and can cause retention and dilution problems. For example, the laser might be aimed more toward the electrode body and might only graze the firing tip at its side or might miss it altogether; this can cause a weakened or even ineffective retention between the firing tip and the electrode body. The mispositioning and misalignment can also create a solidified weld pool that is diluted with too much electrode body material and not enough noble metal material. This dilution can hinder sparking performance of the firing tip. The largely inboard weld configurations taught herein, in contrast, can provide consistent and effective welds even when the firing pad, the electrode, and/or the laser is somewhat misaligned or mispositioned, as will be explained. 
     In the embodiments shown in the figures, the ability to weld mostly and in some cases entirely inboard of the peripheral edge  40  can be attributed, at least in part, to the large surface area of the firing pad  36 , the thinness of the firing pad, the welding types and techniques used to attach the firing pad to the CE body  12  and/or GE body  18 , or a combination thereof. The inboard weld produces the overall fused area  42  and an unfused area  44  at the sparking surface  38 . The overall fused area  42  is generally subject to the intense thermal energy of the impinging laser beam and includes the resulting solidified weldment, while the unfused area  44  is not subject to the same thermal energy and does not include the solidified weldment. The overall fused area  42  may be produced via a non-pulsed or continuous wave (CW) laser, a pulsed laser, a fiber laser, or some other laser or electron beam. In some embodiments, the overall unfused area  44  includes one or more inner unfused portion(s)  50  and one or more outer unfused portion(s)  52 . The outer unfused portion  52  may be located between the overall fused area  42  and the peripheral edge  40  of the firing pad  36  (i.e., outer unfused portion  52  is located inboard of the peripheral edge  40  and outboard of fused area  42 ). The fused and unfused areas  42 ,  44  can be provided in different configurations, including the various weld configurations shown in  FIGS. 3A-3Q . 
     In the embodiment of  FIG. 3A , the overall fused area  42  is confined entirely inboard or radially inward of the peripheral edge  40 . The overall fused area  42  includes a fused portion that can be made up of multiple overlapping weld pools in an unbroken and continuous shape that generally follows the peripheral edge  40  without actually crossing the peripheral edge. In this embodiment, the shape of the overall fused area  42  is a square, but it could have a shape that is a circle, oval, rectangle, triangle, diamond, or another shape, which may or may not necessarily depend on the shape of the firing pad  36 . The welding process used to produce the overall fused area  42  has weld starting and stopping points somewhere along its unbroken extent and inboard of the peripheral edge  40 . The overall fused area  42  is delimited or bounded by an inner edge  46  and an outer edge  48 , while the unfused area  44 , on the other hand, includes the first or inner unfused portion  50  and the second or outer unfused portion  52 . The first unfused portion  50  is located inboard or radially inward of the inner edge  46  and, in this particular embodiment, is completely surrounded and circumscribed by the overall fused area  42 . The second unfused portion  52  is located outboard or radially outward of the outer edge  48  so as to form a thin apron or fringe of unfused material around the periphery of the firing pad  36 . It should be appreciated that the overall fused area  42  is inwardly spaced from the peripheral edge  40 , as opposed to being formed over top of it. Because the fused area  42  shown in  FIG. 3A  only includes a single fused portion, as opposed to other embodiments that include multiple fused portions, the fused area  42  and the fused portion  42  of  FIG. 3A  are the same. In examples where a fused area includes multiple fused portions, the overall fused area is the sum or total surface area of the fused portions involved. 
     The embodiments of  FIGS. 3B-3D  are similar to the embodiment of  FIG. 3A  in that they too include an unbroken fused portion  42  that generally follows the peripheral edge  40  of the sparking surface  38  without actually crossing it. Like the previous embodiments, the weld configurations in  FIGS. 3B-3D  include first and second unfused portions  50 ,  52 , but also include one or more additional fused portions located near the center of the sparking surface  38  to supplement and increase the retention strength of the weld. In  FIG. 3B , a second fused portion  54  is produced by a laser applied at the center of the sparking surface  38  for a relatively short amount of time sufficient to penetrate through the firing pad  36  at a single spot thereat. The second fused portion  54  could be located at an off-center position in other embodiments and could be a single shortened weld line produced by a briefly applied moving laser. In this embodiment, the second fused portion  54  is located inboard or radially inward of a first fused portion  56  and is completely surrounded at the sparking surface  38  by the first unfused portion  50 . Together, the first and second fused portions  56 ,  54  constitute the overall fused area  42 . In  FIG. 3C , the second fused portion  54  is produced by a laser applied near the center of the sparking surface  38  and moved to encircle a centerpoint and make multiple overlapping weld pools in a circular or ring pattern so that the second fused portion  54  is completely surrounded by unfused portion  50 . In  FIG. 3D , the second fused portion includes four individual fused portions  58 ,  60 ,  62 ,  64  that slightly overlap one another at an overlapping fused junction  66  near the center of the sparking surface  38 . The fused portions  58 ,  60 ,  62 ,  64  are shortened weld lines that can have weld starting and stopping points away from the center, at the center, or a combination thereof. In other embodiments, there could be more or less individual fused portions than those shown here, such as six or three fused portions. The fused portions  58 ,  60 ,  62 ,  64  join together to form an integral fused segment that is completely surrounded by the unfused portion  50 . 
     Like the embodiments of  FIGS. 3A-3D , the overall fused area  42  in  FIGS. 3E and 3F  includes a fused portion that generally follows the peripheral edge  40  of the sparking surface  38 , but also includes a fused portion that runs over and crosses the peripheral edge  40 . In  FIG. 3E , a second fused portion  68  extends from the first fused portion  56 , crosses over the peripheral edge  40  of the firing pad, and terminates on the underlying electrode body (CE or GE body, depending on the embodiment). The second fused portion  68  can be produced simply by a continuation of the welding process used to produce the first fused portion  56 , and need not be the result of a separate welding step, although it could. The welding process could either begin or end at a point  70  (either weld starting point or stopping point), which is located off of the firing pad  36  and on the underlying electrode body; that is, outboard of the peripheral edge  40 . Or the weld starting or stopping point could be at a point  72 , for example, which is located inboard of the peripheral edge  40  and on the sparking surface  38 , or could begin or end at another point. Similarly, in  FIG. 3F  the second fused portion  68  extends from the first fused portion  56 , crosses over the peripheral edge  40 , and terminates at a location located off of the firing pad  36 , but it also traverses the center of the sparking surface  38  in a diagonal manner. The welding operation of this embodiment could begin or end at the point  70  located off of the sparking surface  38 , it could begin or end at the point  72  which is located on the sparking surface, or could begin or end at another point. 
     The weld configuration embodiments of  FIGS. 3G-3I  include multiple discrete fused portions that are generally located near the peripheral edge  40  and that generally follow the peripheral edge as a broken line without overlapping it. As is described below, some of the embodiments include additional fused portions located towards the center of the firing pad  36 . The individual fused portions are spaced from the peripheral edge  40  and are spaced from one another by sections or parts of the unfused area  44 . In  FIG. 3G , the overall fused area  42  is made up of eight fused portions  74 ,  76 ,  78 ,  80 ,  82 ,  84 ,  86 , and  88 ; more or less individual fused portions could be provided in other embodiments. Here, a pair of fused portions is located at each of the four sides of the peripheral edge  40  (e.g., portions  74  and  76 , portions  78  and  80 , and so on). Each of the fused portions  74 ,  76 ,  78 ,  80 ,  82 ,  84 ,  86 , and  88  is a shortened weld line produced by a briefly applied moving laser. Although the unfused area  44  is somewhat broken up by the eight fused portions, the unfused area is still mostly intact or integral without isolated or separated unfused portions. In this embodiment, a center section of the sparking surface  38  remains unwelded. In  FIG. 3H , the overall fused area  42  is made up of nine fused portions  90 ,  92 ,  94 ,  96 ,  98 ,  100 ,  102 ,  104 , and  106 . Here, a single fused portion is located at each of the four sides of the sparking surface  38 , a single fused portion is located at each of the four corners of the sparking surface, and a single fused portion  106  is located at the center of the sparking surface  38  and serves as a center stitch. The embodiment of  FIG. 3I  includes a similar weld configuration as that shown in  FIG. 3G , but it also includes a fused portion  108  produced by a laser beam applied at the center of the sparking surface  38  and moved to encircle a centerpoint and make multiple overlapping weld pools in a circular or ring shape. 
     The embodiment of  FIG. 3J  has five fused portions  110 ,  112 ,  114 ,  116 , and  118  that make up the overall fused area  42 , all of which are produced by a laser beam moved to encircle a centerpoint and make a series of overlapping weld pools in a circular or ring shape. Again in this embodiment, the individual fused portions are inboard or spaced radially inward from the peripheral edge  40  via segments of the unfused area  44  and are likewise spaced from one another via the same. The fused portions  110 ,  112 ,  114 , and  116  are each located at one of the four corners of the sparking surface  38 , and the fused portion  118  is located at an approximate center of the sparking surface. 
     The weld configurations illustrated in  FIGS. 3K and 3L  share first and second individual fused portions  120 ,  122  that are generally V-, X-, or U-shaped with a point or apex that may or may not abut or overlap each other near a center of the sparking surface  38 . In this particular example, each of the first and second fused portions  120 ,  122  laps over the peripheral edge  40  at the corners of the sparking surface  38 ; but this is not necessary. Apart from this corner lap, the first and second fused portions  120 ,  122  otherwise do not cross the peripheral edge  40  and are largely located inboard of it. Further, each of the first and second fused portions  120 ,  122  can have weld starting and stopping points that are located off of the sparking surface  38  and on the underlying electrode body. For example, the weld starting or stopping point of the first fused portion  120  can begin or end at a point  124  or at a point  126 , and likewise the weld starting or stopping point of the second fused portion  122  can begin or end at a point  128  or at a point  130 ; of course, other weld starting and stopping points are possible. In both of the embodiments shown, the first and second fused portions  120 ,  122  divide or partition the unfused area  44  into discrete unfused portions  132 ,  134 ,  136 , and  138 . In the particular embodiment of  FIG. 3L , four additional fused portions  140 ,  142 ,  144 , and  146  are located at one of the four sides of the peripheral edge  40 , but each is surrounded by unfused area  44 . 
     Each of the weld configuration embodiments of  FIGS. 3M and 3N  has four individual and unbroken fused portions  148 ,  150 ,  152 , and  154  that are linear and overlap two of the other fused portions in a tic-tac-toe or grid-like arrangement. Each of the fused portions  148 ,  150 ,  152 , and  154  crosses or laps the peripheral edge  40  twice at opposite sides of the firing pad  36 . Apart from these lapped sides, the fused portions  148 ,  150 ,  152 , and  154  do not cross the peripheral edge  40  and are hence located largely inboard of the peripheral edge. Further, each of the fused portions  148 ,  150 ,  152 , and  154  can have a weld starting and stopping point that is located off of the sparking surface  38  and on the underlying electrode body. For example, the weld starting or stopping point of any one or all of the fused portions  148 ,  150 ,  152 , and  154  can begin or end at a point  156  or a point  158 . In both of the embodiments shown, the fused portions  148 ,  150 ,  152 , and  154  divide the unfused area  44  into separate unfused portions  160 ,  162 ,  164 ,  166 ,  168 ,  170 ,  172 ,  174 , and  176 . In the embodiment of  FIG. 3M , the center section of the sparking surface  38  remains unwelded; while in the embodiment of  FIG. 3N , a single fused portion  178  is located at the center of the sparking surface  38  and is surrounded by the unfused portion  50 . 
     The weld configuration embodiments of  FIGS. 3O and 3P  share multiple individual fused portions  180 - 210  that are located near the peripheral edge  40  and that generally follow the peripheral edge without overlapping it. The fused portions  180 - 210  are spaced from the peripheral edge  40  via unfused portions, and each fused portion overlaps its two neighboring fused portions (i.e., leading and following fused portions) at an overlapping fused junction  212  so that the whole resembles a chain of linked fused portions. Further, each of the fused portions  180 - 210  can have a weld starting and stopping point at the respective fused junction. The chain of fused portions  180 - 210  partition the unfused area  44  into a first or inner unfused portion  214  and a second or outer unfused portion  216 . In the embodiment of  FIG. 3O , the center section of the sparking surface  38  remains unwelded; while in the embodiment of  FIG. 3P , a single fused portion  218  is located at a center of the sparking surface  38  and serves as a center stitch that is surrounded by unfused portion  214 . 
     The weld configuration embodiment of  FIG. 3Q  is similar in some respects to the configurations of  FIGS. 3M and 3N . In  FIG. 3Q  there are four individual and unbroken fused portions  148 ,  150 ,  152 , and  154  that are linear and overlap and cross over one another in a tic-tac-toe sort of arrangement. The fused portions  148 ,  152  can be parallel to each other and do not cross each other, and the fused portions  150 ,  154  can likewise be parallel and not cross each other. In other embodiments—and depending on the size and shape of the firing pad  36 —there can be more or less than the four individual and unbroken fused portions shown in  FIGS. 3M, 3N, and 3Q ; for example, there could be only two fused portions parallel to each other or crossing each other, there could be three with two parallel fuse portions and one crossing the parallel fused portions, there could be five with three parallel and two parallel with the two crossing the three, or there could be another number of fused portions. Each of the fused portions  148 ,  150 ,  152 , and  154  crosses or laps the peripheral edge  40  twice at opposite sides of the firing pad  36 . Apart from these lapped sides, the fused portions  148 ,  150 ,  152 , and  154  do not cross the peripheral edge  40  and are hence located largely inboard of the peripheral edge. Further, each of the fused portions  148 ,  150 ,  152 , and  154  can have a weld starting and stopping point that is located off of the sparking surface  38  and on the underlying electrode body. For example, the weld starting or stopping point of any one or all of the fused portions  148 ,  150 ,  152 , and  154  can begin or end at a point  156  or a point  158 . The fused portions  148 ,  150 ,  152 , and  154  divide the unfused area  44  into separate unfused portions  160 ,  162 ,  164 ,  166 ,  168 ,  170 ,  172 ,  174 , and  176 . Different than the embodiment of  FIGS. 3M and 3N , the unfused portions shown in  FIG. 3Q  can be of substantially the same size and area with respect to one another. This is in part because the fused portions  148 ,  150 ,  152 , and  154  are spaced to more equally divide the sparking surface  38 . In an embodiment somewhat similar to  FIG. 3Q , instead of having any unfused portions, the entire sparking surface  38  could be welded (e.g., back and forth laser welder movement) to produce one or more fused portion(s) covering the entire sparking surface. 
     In the embodiments of  FIGS. 3A-3Q  above, a majority of the overall fused area  42  is located inboard or radially inward of the peripheral edge  40  of the firing pad  36 . Even though in some of the embodiments, a fused portion may cross or lap over the peripheral edge  40 , the majority (e.g., greater than 50%) of the overall fused area  42  is still located inboard. This is what is meant by being located “entirely or largely inboard of the peripheral edge.” Indeed, in the embodiments where no fused portion extends over the peripheral edge  40  (e.g.,  FIGS. 3A-D ,  3 G-J and  3 O-P), all of the overall fused area  42  is located inboard of the peripheral edge or boundary (i.e., “entirely inboard”). In those embodiments where one or more fused portions cross over the peripheral edge  40  (e.g.,  FIGS. 3E-F ,  3 K-N, and  3 Q), the majority of the overall fused area  42  resides inboard of the peripheral edge  40  (e.g., more than 50%, more than 75%, or even more than 90% of the overall fused area), but not all of it. Furthermore, it should be appreciated that in each of the embodiments of  FIGS. 3A-3Q , the overall fused area  42  is made up by adding together and combining all of the fused portions in the particular embodiment. And, as described above in some of the embodiments of  FIGS. 3A-3Q , the discrete individual fused portions are portions of the overall fused area  42  that are separated and spaced from each other via unfused area so that they do not share the same weld starting and stopping points. 
     It has been found that in some cases temperature fluctuations and the attendant thermal expansion and contraction may cause separation between the attached firing pad  36  and underlying electrode body. For instance, an edge portion of the firing pad  36  including the peripheral edge  40  may lift off of, and away from, the underlying electrode body, and/or a central portion of the firing pad may lift off of, and bow away from, the underlying electrode body. Although not wishing to be confined to a particular theory of causation, it is currently believed that when separation occurs—if it does indeed occur—it is the result of different rates of thermal expansion and contraction of different metals of the firing pad  36 . That is, the mixed material of the overall fused area  42  may have a different rate of thermal expansion and contraction than the material of the unfused area  44 . Separation can cause retention problems and can hinder sparking performance. 
     Some of the weld configurations of  FIGS. 3A-3Q  have overall fused areas and portions that may minimize or altogether preclude separation between the attached firing pad  36  and underlying electrode body. For example, the centrally-located or centrally-traversing fused portions of  FIGS. 3B-3D, 3F, 3H-3L, 3N, 3P, and 3Q  can minimize or altogether preclude bowing at the central portion. Similarly, the fused portions that cross the peripheral edge  40  of  FIGS. 3E, 3F, 3K, 3L, 3M, 3N, and 3Q  can minimize or altogether preclude lifting at the edge portions of the firing pad  36  where the crossing takes place. At least some of the weld configurations of  FIGS. 3A-3Q  have been found to preclude separation, both lifting edge portions and bowing central portions. For example, the weld configuration of  FIG. 3Q  has been shown to preclude both lifting edge portions and a bowing central portion. In this particular configuration, it is currently believed that the preclusion is due in part to the spacing of the fused portions  148 ,  150 ,  152 , and  154  on the sparking surface  38  and relative to one another, and the resulting substantially equal size of the unfused portions  160 ,  162 ,  164 ,  166 ,  168 ,  170 ,  172 ,  174 , and  176 . Of course, other factors may contribute to or solely provide the preclusion. And it should be appreciated that weld configurations that lack the centrally-located or centrally-traversing fused portions and that lack fused portions crossing the peripheral edge  40  may still minimize or altogether preclude separation, and it should further be appreciated that separation may not occur in all cases. 
     Furthermore, in some cases, having weld starting and weld stopping points located off of the sparking surface  38  and on the underlying electrode body may improve or ensure sparking performance, and may minimize or altogether preclude uneven and undesirable spark gap growth. It has been found that initiation of a laser welding process (i.e., weld starting) and cessation of the laser welding process (i.e., weld stopping) may cause relatively forceful movement and stirring of the material struck by the laser beam at that point. And the movement and stirring may thereby form one or more cavities or craters below the immediately surrounding surface level, may form one or more protrusions jutting out above the surrounding surface level, may produce porosity at the welding starting/stopping point, or may result in a combination of these consequences. If formed to a great enough extent on the sparking surface  38 , these consequences can sometimes hinder sparking performance and bring about uneven and undesirable spark gap growth. Accordingly, initiating and ending the laser welding process off of the sparking surface  38  and instead on the underlying electrode body may improve or ensure desired sparking performance and may minimize or altogether preclude uneven and undesirable spark gap growth. Nonetheless, it should be appreciated that weld configurations with weld starting and stopping points on the sparking surface  38  may still improve or ensure desired sparking performance and may still minimize or altogether preclude uneven and undesirable spark gap growth. 
     The firing pad  36  can be attached to the GE body  18  or the CE body  12  by a number of welding types, techniques, processes, steps, etc. The exact attachment method employed can depend upon, among other considerations, the materials used for the firing pad  36  and for the underlying electrode body, and the exact shape and size of the firing pad. In one example, the firing pad  36  is preliminarily resistance welded or tack welded to the electrode body for a non-primary or temporary retention against the electrode body. In the resistance welding example, a pair of protrusions or rails can be provided on and can project from a bottom surface of the firing pad  36 . The rails can be linear and can span completely across the extent of the bottom surface, though need not. During the resistance welding process, electrical current flow is focused and concentrated through the rails, and hence heat generated at the rails is increased. In this way, resistance welding is facilitated at the rails and a stronger weld is focused between the firing pad  36  and the GE body  18 . This may also help inhibit or altogether eliminate separation between the firing pad  36  and the GE body  18  during use in application. Furthermore, the firing pad  36  can be subjected to a cleaning process in which oil, dirt, and other contaminants are removed from the pad&#39;s outer surface. This too may facilitate welding and the formation of a stronger weld. Of course, the rails need not be provided, and cleaning need not be performed. 
     After the resistance weld, if indeed performed, the firing pad  36  is laser welded to the electrode body for a primary and more permanent retention that forms the various welding configurations shown herein. In other examples, resistance welding need not be performed, in which case a mechanical clamp or other temporary holding technique could be used to keep the firing pad in place during laser welding. A fiber laser welding type and technique can be performed for the weld configuration embodiments herein, as well as other laser welding types and techniques such as Nd:YAG, CO 2 , diode, disk, and hybrid laser techniques, with or without shielding gas. In the fiber laser example, the fiber laser emits a relatively concentrated beam that can create a keyhole opening weld; other laser beams can also produce a suitably concentrated beam and keyhole opening weld. 
     Referring now to  FIG. 4 , the laser weld is shown extending entirely through the firing pad  36  so that the overall fused area  42  and unfused area  44  are formed. A laser beam F impinges or strikes the sparking surface  38  at a point of entry, penetrates entirely through the thickness T of the firing pad  36 , and extends into the electrode body. The materials of the firing pad  36  and the electrode body can melt and mix together as the thermal energy from the laser beam F increases at a surface-to-surface interface S between the firing pad and the electrode body. The laser beam F can be aimed at an orthogonal angle relative to the sparking surface  38  as shown, or at another non-orthogonal angle. The precise composition of the resulting fused portions or weldments can vary within the interior of the weld so that there is a greater ratio of pad material to electrode material near the sparking surface  38 , which can aid sparking performance. When there are greater proportions of pad material at the sparking surface  38 , the firing pad  36  and weld configurations described herein can provide a greater effective sparking surface area capable of exchanging sparks, compared to some previously-known firing tips. Another potential advantage of the firing pad and welding configurations shown herein is that they allow for more lenient manufacturing tolerances. For instance, if the laser beam F in  FIG. 4  is slightly misaligned so that it strikes the firing pad  36  slightly to the right or slightly to the left of that shown, it is likely that a suitable weld will still be formed through the firing pad. In those spark plugs where a laser beam is being directed precisely at the boundary or junction between a firing tip and electrode, the tolerances are typically not so generous. Moreover, the firing pad  36  provides a large sparking surface  38 , particularly when compared to the amount of noble or precious metal used in the firing pad. 
     The firing pad and weld configurations described herein may possess certain geometric properties and can satisfy certain relationships that help provide improved ignitability, effective pad retention, lenient manufacturing tolerances, enlarged sparking surface areas, and cost effective solutions. For example, in any of the embodiments shown in  FIGS. 3A-Q , the overall fused area  42  may include a fused portion having a width dimension between approximately 0.14 mm and 0.30 mm, inclusive of the lower and upper limits (see width W 1  in  FIG. 3A  as an example). In another example, the unfused area  44  can include an outer unfused portion that is located between a fused portion and the peripheral edge  40  and has a width dimension between approximately 0.03 mm and 0.08 mm, or between approximately 0.03 mm and 0.13 mm, inclusive of the lower and upper limit values (see width W 2  in  FIG. 3A  as an example). In an example relationship, the unfused portion described immediately above can have a width value W 2  that is greater than or equal to approximately 10% of the average thickness of the firing pad  36  (e.g., approximately 40% of the average thickness T of the firing pad). In another exemplary relationship, the unfused portion can have a width value W 2  that is less than or equal to approximately 50% of the width of the laser beam or laser spot that is used to attach the firing pad to the electrode body (e.g., approximately 30% of the width of the laser weld beam). Other dimensions, relationships, etc., are certainly possible, as the preceding examples only represent some of the possibilities. 
     In other embodiments, the firing pad  36  could be provided and attached to the underlying electrode in a variety of ways. For example, in the embodiment of  FIG. 5 , a firing pad  236  could be welded directly or indirectly (e.g., via an intermediate piece) to the CE body  12  instead of being welded to the GE body  18 . Or, according to the embodiment of  FIG. 6 , a firing pad  336  could be welded directly or indirectly to a distal end surface of the GE body  18 , in which case a radially-directed spark gap would be located between the firing pad and CE body or CE firing tip. In yet another embodiment, which is not shown in the drawings, the firing pad could be joined directly or indirectly to both the GE body and the CE body. These are only some of the possibilities, as the firing pad  36  could have different shapes, configurations, and arrangements. For example, the firing pad  36  could have a rectangular shape, a circular shape, an oval shape, or an irregular shape, and with these different shapes the firing pad could have any of the weld configurations of  FIGS. 3A-3Q . The firing pad  36  could be arranged in an angular offset or diamond orientation (e.g., 45°) with respect to the lengthwise extent of the GE body  18 , and the end portion of the GE body could be trimmed or narrowed on its sides to form what-is-sometimes-referred-to as a V-trim. 
     Some thermal testing was performed in order to observe retention performance between the firing pad  36  and an electrode body. In the testing, the firing pad  36  and electrode body were attached to each other via the weld configuration embodiment of  FIG. 3Q . In general, the thermal testing subjected the firing pad  36 , electrode body, and overall fused area  42  to an increased temperature for a relatively abbreviated period of time, and then allowed them to cool to ambient temperature. The testing was meant to simulate expansion and contraction thermal stresses that are more extreme than those experienced in application in a typical internal combustion engine. In the example testing conducted, a sample spark plug was mounted in a collar-like structure made of brass material. The collar structure was secured to the shell of the sample spark plug and did not make direct abutment with the electrode body; the mount structure acted as a heat sink and facilitated cooling. An induction heater was then used to heat the attached firing pad  36  and electrode body up to 1,700° F. for about 20 seconds. After that, the firing pad  36  and electrode body were allowed to cool at rest down to about room temperature or slightly above room temperature. This rise and fall in temperature constituted a single test cycle, and the thermal testing was conducted on numerous sample spark plugs. On average, the sample spark plugs were capable of enduring over one-hundred-and-seventy-five cycles without exhibiting significant cracking, separation, or other conditions that could negatively impact retention between the firing pad  36  and the electrode body. One-hundred-and-seventy-five cycles is considerably greater than the one-hundred-and-twenty-five cycles oftentimes for such products deemed acceptable, and was unexpected in view of how thin the firing pads were. The cycles endured in the testing here is also comparable to pads with much greater thicknesses than the thin firing pads tested—this too was unexpected. It should be appreciated that not all testing will yield these exact results, as different testing parameters, samples, equipment, as well as other factors, can alter the outcome of testing performance. 
     It is to be understood that the foregoing is a description of one or more preferred exemplary embodiments of the invention. The invention is not limited to the particular embodiment(s) disclosed herein, but rather is defined solely by the claims below. Furthermore, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the invention or on the definition of terms used in the claims, except where a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will become apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to come within the scope of the appended claims. 
     As used in this specification and claims, the terms “for example,” “e.g.,” “for instance,” “such as,” and “like,” and the verbs “comprising,” “having,” “including,” and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open-ended, meaning that the listing is not to be considered as excluding other, additional components or items. Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that requires a different interpretation.