JP4082881B2 - Manufacturing method of spark plug - Google Patents

Description

【００４１】
上記スパークプラグ試験品を、２０００ｃｃのエンジンに取り付けて、エンジン回転数６５００ｒｐｍ、スロットル全開状態にて実機耐久試験を行った。そして試験１００時間終了後において、発火部３１に剥離が認められなかったものを溶接強度良好（○）、そうでなかったものを溶接強度不良（×）として評価した。また、１００時間経過時点において失火が発生しなかったものを耐久性良好（○）、そうでなかったものを耐久性不良（×）として評価した。該結果を表１に示す。この結果からも明らかな通り、同軸度δが０．１５ｍｍ以下、傾き角度θが５゜以下の試験品において、溶接強度及び耐久性のいずれも良好であることがわかる。
【図面の簡単な説明】
【図１】本発明のスパークプラグの一実施例を示す縦断面図及びその要部拡大図。
【図２】図１のスパークプラグの、中心電極側発火部の製造工程説明図。
【図３】同軸度δと傾斜角度θの説明図。
【図４】発火部偏心の溶接部深さに及ぼす影響を示す説明図。
【図５】偏心により発火部に偏消耗が発生する様子を説明する図。
【図６】傾斜により発火部に生ずる不具合を総合的に説明する図。
【図７】貴金属チップの位置合わせ治具の一実施例をその使用方法とともに示す説明図。
【図８】貴金属チップの位置合わせ治具の別実施例をその使用方法とともに示す説明図。
【図９】同軸度と傾斜角度の測定方法の概念説明図。
【図１０】レーザー照射強度線図並びにスパークプラグの中心電極先端部の拡大斜視図、平面模式図及び縦断面図。
【図１１】貴金属チップ及び全周レーザー溶接部を円周方向に展開して示す説明図。
【図１２】レーザー溶接時に使用する貴金属チップの押さえ治具の実施例をいくつか示す斜視図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spark plug and a manufacturing method thereof.
[0002]
[Prior art]
In recent years, spark plugs used for ignition of internal combustion engines are mainly composed of Pt, Ir or the like at the tip of a center electrode made of a heat-resistant alloy of Ni base or Fe base in order to improve spark wear resistance. A type in which a noble metal ignition part is formed by welding a noble metal tip is used. For example, when a noble metal tip is joined to the tip surface of the center electrode that will form a spark discharge gap facing the ground electrode, a cylindrical noble metal tip is used as the manufacturing method for the tip surface of the center electrode (tip-fixed surface). ) And irradiating a laser beam along the outer periphery of the noble metal tip while rotating the center electrode, and a method for forming an all-around laser weld is proposed.
[0003]
[Problems to be solved by the invention]
In the spark plug having the all-around laser welded portion, it is necessary to pay particular attention to the form and accuracy of the laser welded portion. Conventionally, however, attention has been paid exclusively to laser irradiation conditions, etc., and sufficient results are not always obtained from the viewpoint of optimizing the welding strength, the convenience of adjusting the spark discharge gap, and the life of the ignition part. It was not done.
[0004]
The object of the present invention is to further improve the joint strength, ignition part life, etc. of the ignition part by focusing on the relative positional relationship between the precious metal tip to be welded and the center electrode, and the ignition part after welding and the center electrode. It is an object of the present invention to provide a spark plug structure and a method for manufacturing the same.
[0006]
[Means for solving the problems and actions / effects]
  In order to solve the above problems, the spark plug manufacturing method of the present invention includes a center electrode having a main body portion forming a cylindrical outer peripheral surface,
  A precious metal ignition part having an outer peripheral surface of a cylindrical surface, and is fixed to the tip in the axial direction of the center electrode through an all-around laser welded part,
  A ground electrode that is disposed in such a manner that the side surface faces the front end surface in the axial direction of the noble metal ignition part and forms a spark discharge gap with the noble metal ignition part.A spark plug manufacturing method comprising:
A tip positioning step of superposing a noble metal tip having a cylindrical outer peripheral surface on the tip end surface in the axial direction of the center electrode so that the coaxiality is 0.15 mm or less to form an overlay assembly;
By irradiating the overlapping assembly with a laser beam in the circumferential direction with respect to the central axis of the central electrode, the cylindrical outer periphery of the noble metal tip spans the formation portion of the tip surface of the central electrode and the noble metal tip. Including a welding process for forming an all-around laser weld in the form of leaving the front end portion of the surface,
In the chip positioning step, a mounting part that is detachably mounted on the outer peripheral surface of the main body part of the center electrode, and a precious metal chip that is held by the mounting part is mounted on the main body part by the mounting part. A chip positioning jig having a mounting part that is positioned concentrically with respect to the surface and a chip holding part that is integrated is used.
[0007]
When joining a noble metal tip to be ignited to the center electrode by laser welding, place the noble metal tip on the tip surface of the center electrode and direct the laser beam in the circumferential direction near the boundary surface between the center electrode and the noble metal tip Are irradiated while being relatively moved to form an all-around weld that spans the center electrode base material and the noble metal tip. Various factors affecting the performance and life of the spark plug in which the center electrode and the noble metal tip were joined by the laser welded part were examined, and the main body forming the outer peripheral surface of the cylindrical surface-like noble metal tip and the main body of the center electrode, respectively. It was found that the joining state of the noble metal tip by the laser welded part greatly changes depending on the coaxiality with the outer peripheral surface of the part. As a result of further earnest studies, the welding strength and the life and durability of the precious metal ignition part are dramatically improved by keeping the coaxiality below a certain limit value, specifically, 0.15 mm or less. As a result, the inventors have completed the spark plug of the present invention.
[0008]
Further, in order to obtain a structure in which the main body portion of the center electrode and the noble metal tip are joined with the coaxiality as described above, the coaxiality is 0.15 mm or less at the stage before welding as in the method of the present invention. It is important to position the central electrode body and the noble metal tip so that the entire circumference laser weld is formed in this state.
[0009]
When the concentricity exceeds the above limit value, the center axis of the noble metal tip is decentered from the center axis of the center electrode, so the circumference of the stack assembly is near the boundary surface between the center electrode and the noble metal tip. The heat capacity distribution in the direction is also non-uniform. Therefore, even if the laser beam is irradiated under a certain condition, the depth and width of the formed laser welded part (the length of the welded part in the axial direction) are likely to be uneven due to the influence of the heat capacity distribution, and the welding strength Leading to a decline. In addition, since the center axis of the ignition part formed at the tip of the center electrode is decentered from the center axis of the body part of the center electrode, it is easy to cause eccentricity with respect to the ignition part on the ground electrode side. It tends to cause uneven wear. Furthermore, if an imbalance occurs in the depth or width of the laser weld with the central axis in between, the central axis of the ignition part may be inclined with respect to the central axis of the main body of the central electrode. Etc. are more likely to occur.
[0010]
However, the coaxiality between the noble metal firing portion and the center electrode main body obtained by positioning the center electrode main body portion and the noble metal tip so that the coaxiality is 0.15 mm or less and performing laser welding is also 0.15 mm. As a result, it is possible to solve all of the above-described problems.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
A spark plug 100 as an example of the present invention shown in FIG. 1 includes a cylindrical metal shell 1, an insulator 2 fitted inside the metal shell 1 so that the tip 21 protrudes, and a noble metal ignition formed at the tip. One end is joined to the central electrode 3 and the metal shell 1 provided inside the insulator 2 with a portion 31 (hereinafter also referred to simply as an ignition portion) protruding, and the other end side is laterally formed. A ground electrode 4 and the like are provided which are bent back and arranged so that the side faces the tip of the center electrode 3. Further, the ground electrode 4 is formed with a noble metal ignition part (hereinafter also simply referred to as an ignition part) 32 facing the ignition part 31, and there is a gap between the ignition part 31 and the opposing ignition part 32. The spark discharge gap g is used.
[0012]
As used herein, the term “ignition part” refers to a part of the joined noble metal tip that is not affected by the composition variation due to welding (for example, a part alloyed with the material of the ground electrode or the center electrode by welding). The remaining part). In addition, “main component” (also synonymous with “mainly composed” or “mainly composed”) means a component having the highest weight content in the material of interest. .
[0013]
The insulator 2 is made of a ceramic sintered body such as alumina or aluminum nitride, for example, and has a hole 6 for fitting the center electrode 3 and the terminal fitting 8 along its own axial direction. Yes. The metal shell 1 is formed in a cylindrical shape from a metal such as low carbon steel, and constitutes a housing of the spark plug 100, and a screw for attaching the plug 100 to an engine block (not shown) on its outer peripheral surface. Part 7 is formed.
[0014]
In addition, about the ignition part 32 which opposes, it is good also as a structure which abbreviate | omits this. In this case, a spark discharge gap g is formed between the ignition part 31 and the side surface of the ground electrode 4 having no ignition part. The part to be bonded to the tip of the center electrode 3 and the ground electrode 4, in this embodiment, at least the surface layer part is composed of a heat-resistant alloy containing Ni or Fe as a main component (for example, INCONEL 600 or INCONEL 601: trade names). Has been. On the other hand, the ignition part 31 and the opposing ignition part 32 are mainly composed of a noble metal mainly containing any one of Ir, Pt and Rh. Use of these noble metals can improve the wear resistance of the ignition part even in an environment where the temperature of the center electrode is likely to rise. Moreover, the weldability with respect to the center electrode 3 and the ground electrode 4 which use the above heat-resistant alloys as a base material is also good. For example, when a noble metal based on Pt is used, in addition to Pt alone, a Pt—Ni alloy (for example, Pt-1 to 30 mass% Ni alloy), a Pt—Ir alloy (for example, Pt-1 to 20 mass% Ir) Alloy), Pt—Ir—Ni alloy, and the like can be preferably used. In addition, as the main component of Ir, Ir—Ru alloy (for example, Ir-1 to 30% by mass Ru alloy), Ir—Pt alloy (for example, Ir-1 to 10% by mass Pt alloy), Ir—Rh alloy (For example, Ir-5 to 25 mass% Rh alloy), Ir-Rh-Ni alloy (for example, Ir-1 to 40 mass% Rh-0.5 to 8 mass% Ni alloy), etc. can be used. In the case where an Ir-based noble metal material is used, oxides (including complex oxides) of metal elements belonging to Group 3A (so-called rare earth elements) and Group 4A (Ti, Zr, Hf) of the periodic table of elements are used. Can be contained within a range of 0.1 to 15% by mass. Thereby, the oxidation and volatilization of the Ir component can be effectively suppressed, and as a result, the spark consumption of the ignition part can be improved. The oxide is Y₂O₃Is preferably used, but in addition to this, La₂O₃, ThO₂, ZrO₂Etc. can be preferably used. In this case, the metal component may be Ir alone or Ir.
[0015]
As shown in FIG. 1, the center electrode 3 has a main body 3M having a cylindrical outer peripheral surface (here, formed as two concentric cylindrical surfaces having different diameters connected by a step 3J). ing). As shown in FIG. 3 (a), the noble metal ignition part 31 is fixed to the tip of the noble metal ignition part 31 in the direction of the axis O <b> 2 of the center electrode 3 via the all-around laser welding part 10. And the coaxial degree of the outer peripheral surface 3p of the main-body part 3M of the center electrode 3 and the outer peripheral surface 31p of the noble metal ignition part 31 is 0.15 mm or less. The coaxiality is a parameter reflecting the distance δ between the central axis O2 of the outer peripheral surface 3p of the main body 3M and the central axis O1 of the outer peripheral surface 31p of the noble metal firing part 31, and the definition is 18 of JIS: B0021. Use the one specified in 13.2. The coaxiality is calculated from the shape profile measured by using a known shape profile measuring device at the cross-section perpendicular to the axis of the two outer peripheral surfaces set to a necessary and sufficient number to ensure accuracy. However, as a simple method, as shown in FIG. 9A, an image in the vicinity of the ignition part 31 is taken, and the position of the outline of the outer peripheral surface 31p of the ignition part 31 is determined by a known image analysis technique. A plurality of inspection lines ML orthogonal to the outer peripheral surface outline are set at predetermined intervals, and the coordinates of the intersection points EP1 and EP2 with the outer peripheral outline are obtained. On the other hand, the outer peripheral surface outline is similarly determined for the main body 3M of the center electrode 3, and linear regression is performed with respect to the center point of each inspection line ML2 located between the two outlines (for example, a linear equation based on the least square method) To obtain the position of the central axis O2 of the outer peripheral surface 3p. The average values of the distances from the central axis O2 to the EP1 and EP2 measured on the ignition part 31 side are W1 and W2, respectively, and the distance δ ′ between O1 and O2 is | W1-W2 | / 2. Asking. Then, this measurement is performed at various viewing angles around the axis of the central electrode 3, and the value of δ ′ at the viewing angle at which the measured value of δ ′ is maximum is calculated as the final coaxiality δ.
[0016]
The ignition part 31 on the center electrode 3 side is formed using laser welding. As shown in FIG. 2 (a), a tip assembly surface 170 of the center electrode 3 is used as a chip fixing surface, and a noble metal chip 31 ′ having a chip diameter D and a chip thickness H is overlapped thereon to form an overlap assembly 170. , (B) and (c), the laser beam LB is irradiated to the overlapping assembly 170 to straddle the noble metal tip 31 ′ and the chip fixing surface, and the thickness of the noble metal tip 31 ′. The all-around laser welded portion 10 that does not reach the discharge surface 31a (see FIG. 10) in the direction is formed along the circumferential direction of the tip outer peripheral surface. On the other hand, the ignition part 32 on the ground electrode 4 side can be similarly formed by laser welding of a noble metal tip. For the ignition part 32, for example, when using a relatively low melting point such as a Pt-based metal, resistance welding is performed. May be used.
[0017]
When making the overlapping assembly 170, the noble metal tip 31 having the cylindrical outer peripheral surface 31p ′ on the tip surface 3s in the axis O2 direction of the center electrode 3 having the main body 3M forming the cylindrical outer peripheral surface 3p. Are stacked while being positioned so that the coaxiality is 0.15 mm or less (chip positioning step). The overlapping assembly 170 is irradiated with a laser beam LB in the circumferential direction with respect to the central axis O2, thereby straddling the portion where the tip surface 3s of the center electrode 3 is formed and the noble metal tip 31 ′. The all-around laser welded portion 10 is formed so as to leave the tip end portion of the 31 ′ cylindrical outer peripheral surface 31p ′.
[0018]
The joining state of the ignition part 31 by the laser welded part 10 is greatly affected by the coaxiality δ between the outer peripheral surface 31p 'of the cylindrical noble metal tip 31' and the outer peripheral surface 3p of the main body 3M of the center electrode 3. Therefore, as described above, by keeping the coaxiality δ at 0.15 mm or less, the welding strength, life, and durability of the ignition part 31 can be greatly improved. However, when the coaxiality δ increases beyond 0.15 mm, the noble metal tip 31 ′ is positioned so as to be closer to one side with respect to the center axis O 2 of the center electrode 3. In the vicinity of the boundary surface with 31, the heat capacity of the laser beam irradiated portion of the overlapping assembly 170 becomes uneven in the circumferential direction. As a result, even if the laser beam LB is irradiated under a certain condition, due to the influence of the heat capacity distribution, as shown in FIG. 4B, the depth and width of the formed laser weld 10 (the weld in the direction of the axis O2). 10) is likely to be non-uniform, leading to a reduction in welding strength.
[0019]
Specifically, when the center electrode 3 is cut by a cutting plane that is parallel to the projection plane in which the distance between the projected center axes O1 and O2 is maximum and includes the center axis O2, it appears on both sides of the center axis O1. Of the two cross-sections S1 and S2 of the all-around laser welded portion 10, the central axis O2 of the noble metal firing portion 31 is located on the side that is eccentric (and / or inclined side: described later) with respect to the central axis O1. The first section S1 is the one located on the other side, the second section S2 is the one on the other side, the depth of the first section S1 in the direction orthogonal to the central axis O1 is T1, and the depth of the second section S2 is also T2. , T1> T2 in an unbalanced weld depth. In addition, in this specification, the welding part depth means the penetration | invasion distance to the ignition part 31 side of each cross section S1 and S2 measured from the outer peripheral surface of the ignition part 31 in the direction orthogonal to the central axis O1. Further, assuming that the welding width of the first cross section S1 in the direction of the central axis O2 is d1 and the welding width of the second cross section S2 is d2, d1> d2, and the welding width is also unbalanced.
[0020]
However, the noble metal ignition portion 31 and the main body portion 3M are coaxially positioned by positioning the main body portion 3M of the center electrode 3 and the noble metal tip 31 'so that the coaxiality is 0.15 mm or less and performing laser welding. The degree can also be set to 0.15 mm or less, which makes it possible to eliminate the above-described imbalance of the weld depth.
[0021]
Further, when the coaxiality between the noble metal firing portion 31 and the main body portion 3M exceeds 0.15 mm, as shown in FIG. 5B, the ground electrode 4 side that is coaxially aligned with the main body portion 3M is provided. Since the noble metal ignition part 31 is eccentrically positioned with respect to the central axis O3 of the noble metal ignition part 32, the occurrence position of the spark discharge is biased and the consumption of the ignition part, particularly the ignition part 32 on the ground electrode 4 side, is ignited. This is less likely to occur uniformly throughout (hereinafter referred to as “uneven consumption” in the present specification). As a result, the life of the ignition part is easily exhausted early due to the progress of local consumption. However, by making the coaxiality of the noble metal ignition part 31 and the main body part 3M 0.15 mm or less, such uneven consumption is less likely to occur.
[0022]
Note that the eccentricity between the central axis O2 of the main body 3M and the central axis O1 of the noble metal ignition part 31 is not limited to the element in which O1 / O2 is shifted in parallel as shown in FIG. In some cases, O1 / O2 includes an element that shifts to an inclined form. When such an inclination occurs, for example, as shown in FIG. 6B, the edge on one side of the ignition part 31 on the center electrode 3 side is directed toward the ignition part 32 on the ground electrode 4 side. As a result, the spark discharge gap g becomes narrow at this position, leading to uneven consumption.
[0023]
In addition, there are cases where the following problems in the process of forming the spark discharge gap g are caused. That is, as shown in FIG. 6C, the spark discharge gap g is formed by inserting and positioning a gap forming jig KF from the side with respect to the end face of the ignition part 31, and facing the jig KF. 4 is generally formed by bending. However, when the central axis O1 of the noble metal ignition part 31 is inclined, the jig KF is caught on the outer peripheral edge of the end face of the ignition part 31 raised due to the inclination, or is liable to be crushed during bending. Leads to.
[0024]
Therefore, as shown in FIG. 3B, the main body portion in orthographic projection onto an arbitrary virtual plane parallel to the central axis O2 of the main body portion 3M of the center electrode 3 as shown in FIG. When the angle θ formed by the central axis O2 of the 3M outer peripheral surface 3p and the central axis O1 of the outer peripheral surface 31p of the noble metal firing portion 31 appears as the projection plane OVP, the angle θ in the projection plane OVP is adopted. By reducing the angle so as to be 5 ° or less, as shown in FIG. 6 (a), the above-mentioned problems can be effectively solved.
[0025]
The inclination angle θ is measured as shown in FIG. 9B by taking an image of the vicinity of the ignition portion 31 and using the known image analysis method for the outer peripheral surface outline of the main body portion 3M of the center electrode 3. decide. Then, a plurality of inspection lines MP1 orthogonal to the outer peripheral surface outline are set at a predetermined interval, and a linear regression is performed on the center point of each inspection line MP1 located between the two outer contour lines, thereby the center of the outer peripheral surface 3p. An axis O2 is obtained. On the other hand, with respect to the ignition part 31, the intersection point F1 between the central axis O2 and the discharge surface 31s of the ignition part 31 is used as a reference point, and the lower side of the figure (on the side of the central electrode 3) by a predetermined dimension from the reference point. ), A plurality of inspection lines MP2 are set in parallel with the inspection line MP1 at predetermined intervals at a plurality of positions in the predetermined section Z, and each inspection line MP2 positioned between the outlines of the ignition unit 31 is set. By performing linear regression on the center point, the center axis O1 of the outer peripheral surface 31p is obtained, and the intersection angle with the center axis O2 is obtained. This measurement is performed at various viewing angles around the axis O2 in the center electrode 3, and the angle value at the viewing angle at which the measured value of the crossing angle is maximized is calculated as the final tilt angle θ.
[0026]
Hereinafter, a specific example of a method for manufacturing the spark plug 100 will be described.
As shown in FIG. 2B, the assembly assembly 170 of the noble metal tip 31 and the center electrode 3 is placed on the tip 31 ′ (center electrode 3) with respect to the emission optical part of the laser irradiation unit 200 (see FIG. 10). , While rotating relatively around the central axis O1 (O2) of the chip, the chip-fixed surface (in this case, the front end surface of the central electrode 3) is placed in the spot of the pulsed laser beam LB toward the overlapping assembly 170. ) And the outer peripheral surface of the chip, and the irradiation angle φ with respect to the chip fixing surface is in the range of −5 ° to + 60 ° (the upper side from the horizontal is +; for example, + 45 °). To do. In this case, only one of the assembly 170 or the laser irradiation unit 200 may be rotated, or both may be rotated (for example, in directions opposite to each other).
[0027]
In this case, it is desirable to adjust the rotational speed as follows. First, the relative rotational speed between the overlay assembly 170 and the laser irradiation unit 200 is 10 rpm or more (preferably 60 rpm or more, more preferably 120 rpm) when only one laser irradiation unit 200 is used as shown in FIG. The above is preferable. In order to perform all-around laser welding, the overlap assembly 170 and the laser irradiation unit 200 must be rotated relative to each other for at least one turn. When the relative rotation speed is less than 10 rpm, welding for one turn is performed. There is a problem that the piece time for manufacturing one spark plug becomes long.
[0028]
Further, in laser welding, the metal melted portion is biased to the position where the laser irradiation is applied, and for example, such a melted portion is formed in an excessively large volume on one side with respect to the central axis O1 of the noble metal tip 31 ′. Then, the noble metal tip 31 ′ loses its support on the side, and for example, the melted portion is crushed by the centrifugal force due to rotation or the own weight of the noble metal tip 31 ′, and the central axis O1 tends to be inclined or biased. When the relative rotation speed between the overlap assembly 170 and the laser irradiation unit 200 is less than 10 rpm, the rotation speed is slow, and therefore, the unit welds formed in the circumferential direction of the overlap assembly 170 overlap each other. And the volume of the metal melted part that is biased near the laser irradiation position tends to be excessively increased. As a result, the inclination and the deviation of the central axis O1 become remarkable, and it becomes difficult to keep the coaxiality δ between the obtained ignition part 31 and the main body part 3M to 0.15 mm or less. On the other hand, the upper limit value of the relative rotational speed is preferably limited to about 150 rpm when the overlapping assembly 170 is rotated in order to prevent excessive deformation due to the centrifugal force of the metal melting portion generated during welding.
[0029]
Further, in order to set the coaxiality δ to 0.15 mm or less, it is desirable to use the following method. First, in the chip positioning step, as shown in FIG. 7A, a mounting portion 50e that is detachably mounted on the outer peripheral surface 3p of the main body portion 3M of the center electrode 3, and the main body portion 3M in the mounting portion 50e. A chip positioning jig 50 having a chip holding part 50h for concentrically positioning the noble metal chip 31 'held by itself with respect to the outer peripheral surface 3p of the main body part 3M is used. That is, by attaching the jig 50 to the main body 3M in the mounting portion 50e, the outer peripheral surface 3p of the main body 3M of the center electrode 3 can be used as a reference for axis alignment, and the chip holding portion 50h of the jig 50 can be used. The center axis O1 of the noble metal tip 31 ′ held in the center can be accurately and simply positioned within a tolerance of 0.15 mm in coaxiality with respect to the center axis O2 of the main body 3M.
[0030]
Specifically, the mounting portion 50e of the chip positioning jig 50 can be mounted on the main body 3M on a cylindrical mounting surface 50b that follows the outer peripheral surface 3p of the main body 3M. On the other hand, the chip holding part 50h can hold the outer peripheral surface 31p 'of the noble metal tip 31' on a cylindrical chip holding surface 50a formed concentrically with the mounting surface 50b. By using the cylindrical mounting surface 50b and the chip holding surface 50a, the coaxial alignment between the central axis O1 of the noble metal chip 31 'and the central axis O2 of the main body 3M can be performed with higher accuracy. In this case, it goes without saying that the mounting surface 50b and the chip holding surface 50a must be formed with an accuracy of coaxiality of 0.15 mm or less in the holding state of the noble metal tip 31 '. Further, the “cylindrical surface shape” here includes a concept that covers only a part of the noble metal tip 31 ′ or the outer peripheral surfaces 31 p and 3 p of the main body 3 </ b> M in the circumferential direction.
[0031]
In the present embodiment, the chip positioning jig 50 is configured to function as follows. That is, as shown in FIG. 7B, a plurality of chip positioning jigs 50 arranged along the circumferential direction of the outer peripheral surface 31p ′ of the noble metal tip 31 ′ approach each other in the radial direction with respect to the outer peripheral surface 31p ′. A plurality of separable chip gripping members 49 are provided. The gripping surfaces 50a of the chip gripping members 49 each constitute a chip holding surface 50a, and the noble metal tip 31 'is positioned on the distal end surface 3s of the center electrode 3 to release the grip, thereby overlapping the assembly. 170 is formed. At this time, on the rear side of each chip gripping member 49 in the direction of the axis O2, a cylindrical guide surface 50b is formed as a mounting surface 50b on the side facing the outer peripheral surface 3p of the main body 3M of the center electrode 3. ing. First, the main body 3M of the center electrode 3 is held so as to be freely movable in a direction orthogonal to the center axis O1 by a holder (not shown). The tip positioning jig 50 brings the tip of the center electrode 3 relatively closer to the gripped noble metal tip 31 ′ from the rear side in the direction of the axis O1 (here, the noble metal tip 31 is lowered. The tip 31 ′ is placed on the front end surface 3 s by moving “'toward the front end of the center electrode 3). At this time, the main body 3M of the center electrode 3 enters the cylindrical guide surface 50b. The guide surface 50b serves to guide the main body 3M while concentrically positioning the noble metal tip 31 ′. Fulfill. That is, when the main body portion 3M is eccentrically positioned with respect to the noble metal tip 31 ', the main body portion 3M is moved in a direction perpendicular to the axis as it enters the guide surface 50b, thereby performing eccentricity correction. Can do.
[0032]
As shown in FIG. 8, a chip positioning jig 55 that does not particularly have a mounting portion for coaxial positioning between the main body 3M and the chip 31 ′ may be used. In this case, the chip positioning jig 55 is used. And a mechanism (for example, an XY table for moving the main body 3M in a direction orthogonal to the axis O2) for relative movement of the main body 3M and the main body 3M so as to be positioned at an arbitrary position in the axis alignment direction are required. It becomes. In this respect, the axis alignment mechanism of FIG. 7 can be said to be much simpler.
[0033]
Further, when performing laser welding, it is more effective to adopt the following method in order to suppress the disadvantage that leads to tip eccentricity due to the temporary excessive increase in the volume of the metal melting portion. . That is, as shown in FIG. 2B, by irradiating the overlapping assembly 170 with the laser beam pulse LB, the entire circumference welded portion 10 and the unit welded portions 10u corresponding to the laser beam pulses LB are sequentially formed. It is formed so as to be in a stacked form. At this time, as shown in FIG. 11, in order to complete the all-around welded portion 10 that is continuous in the circumferential direction, a weld overlap portion LPW for connecting the ends of the unit welded portion array is formed. In this weld overlap portion LPW for connection of arrays, the number of overlap formation of the unit weld portions 10u is greater than that of other portions, so that at least one of the unit weld portions 101 to 103 and 110 to 112 formed in an overlapping manner. The laser irradiation energy per pulse used when forming this is set lower than the laser irradiation energy per pulse used when forming other unit welds. If it does in this way, it will be suppressed that the total heat input by a laser beam will become excessive in the welding overlap part LPW for arrangement | sequence connection, and the eccentricity of the ignition part 31 formed by extension of the volume of a metal fusion | melting part will be suppressed effectively. can do.
[0034]
For example, as shown in FIG. 10, when the overlapping assembly 170 is rotated around the central axis O2 of the center electrode 3 and irradiated with pulsed laser light LB from a single laser irradiation unit 200 fixed in position, In the circumferential direction of the noble metal tip 31 ′, the unit welds 101, 102,... Span the noble metal tip 31 ′ and the chip fixing surface forming portion and correspond to the laser irradiation pulses P 1, P 2,. .. Are formed in such a manner that the circumferential laser welds 10 are successively stacked (see FIGS. 10B to 10D).
[0035]
For example, when the pulse generation frequency f of the pulsed laser beam LB is 12 pulses / second (if the rotation speed of the overlapping assembly 170 is 60 rpm, the pulsed laser beam for exactly 12 pulses per rotation of the overlapping assembly 170 LB is irradiated, and twelve unit welds 101 to 112 corresponding to the LB are formed so as to be successively stacked in the circumferential direction of the noble metal tip 31 ′ in the circumferential direction of the twelve unit welds 101 to 112. The overlapping state is generally as shown in Fig. 11. In other welds except for the leading weld 10t (101 to 103 in Fig. 10) and the tail weld 10e (110 to 112 in Fig. 10), unit welding is performed. When the part is formed, the number of overlaps with the unit welds that have already been formed (hereinafter referred to as the number of overlaps with the existing unit welds) is three that are formed immediately before That (for example, in the fourth unit weld 104, three 101 to 103).
[0036]
On the other hand, in the tail welded part 10e, the number of overlaps with the existing unit welded part increases to four or more. For example, in the case of the twelfth unit welded portion 112 at the tail, in addition to the three 109-111 formed immediately before itself, the three first welded portions 10t (101-103) formed initially Since they overlap, the total number of overlaps with the existing unit welds is six. Similarly, the number of overlaps with the existing unit welds in the eleventh unit weld 111 is five, and the number of overlaps with the ready unit welds in the tenth unit weld 110 is four. In the case of the leading weld 10t (101 to 103), the number of overlaps with the existing unit welds is 0 to 2, but when the tail weld 10e is formed as described above, it overlaps with this. .
[0037]
Then, when the heat input when the leading weld 10t is formed is not sufficiently drawn while rotating the overlapping assembly 170 once, irradiation with the pulsed laser beam LB for forming the tail welding 10e Even at the time, a part of heat input when the leading weld 10t is formed exists as residual heat. Therefore, for example, the end of the molten metal is not excessive even if this residual heat is superimposed on the laser irradiation energy for forming the tail weld 10e (new heat input for the tail weld 10e). Laser irradiation energy per pulse (hereinafter referred to as correction irradiation energy) Eh used when forming the weld 10e is set lower than the normal irradiation energy Et (see FIG. 10A). Thereby, it is possible to make uniform the total amount of heat (total energy) that combines the new heat input and the residual heat when forming each unit weld.
[0038]
Next, in the overlap assembly 170, forming the all-around laser welded portion 10 while pressing the noble metal tip 31 ′ against the tip surface 3s of the center electrode 3 in the direction of the axis O1 is to form the noble metal tip 31 ′ during formation of the welded portion. This is effective in preventing misalignment and thus eccentricity. In this case, for example, as shown in FIG. 12 (a), it is possible to press using the jig JG1 in a point contact form at the tip TP1, but as shown in FIG. 12 (b), The pressing jig JG2 that contacts the surface 31s ′ of the noble metal tip 31 ′ on the side opposite to the overlapping side with respect to the center electrode 3 in a surface contact form (here, the front end surface of the cylindrical jig JG2) It is more desirable to improve the effect of preventing displacement of the noble metal tip 31 ′.
[0039]
【Example】
In order to confirm the effect of the present invention, the following tests were conducted. First, the center electrode 3 having the shape shown in FIG. However, in FIG. 2A, the outer diameter D1 of the main body 3M is 2.5 mm, the diameter D2 of the tip surface 3s is 1.3 mm, and the taper angle of the taper surface 3t is 45 °. On the other hand, a noble metal tip having a tip thickness H of 0.6 mm and a tip diameter D of 0.8 mm was produced by punching from an Ir-5 wt% Pt alloy plate produced by alloy melting / rolling. Next, in the laser irradiation intensity diagram of FIG. 10A, the pulse width t is set to 6 milliseconds, and the irradiation energy per pulse becomes the penetration depth for each test No. shown in Table 1 to be described later. The pulsed YAG laser beam LB adjusted as appropriate is irradiated along the outer peripheral surface of the noble metal tip 31 ′ assembled on the center electrode 3 at a pulse frequency f of 12 pps (period τ = 1000/12 milliseconds), The all-around laser weld 10 was formed in the circumferential direction of the noble metal tip 31 ′, and other necessary parts were assembled to prepare a spark plug test product shown in FIG. It should be noted that the intensity of the laser pulse LB at the end is gradually reduced at a predetermined ratio as shown in FIG. Further, the noble metal tip 31 ′ is aligned with the main body 3M using the jig 50 of FIG. 7, and the forming coaxiality of the gripping surface 50a and the guide surface 50b of the chip 31 ′ is variously changed. , The coaxiality between the central axis O1 of the noble metal tip 31 ′ and the central axis O2 of the main body 3M was changed at various values of 0.05 to 0.25 mm shown in Table 1. Further, after the welding, the coaxiality between the ignition part 31 and the main body part 3M was measured by the method described above, and it was found that the coaxiality at the time of positioning was substantially the same. Further, the measurement of the inclination angle θ is performed in the same manner, and the measurement results are shown in Table 1 (note that the number n of test samples is 3 for each condition).
[0040]
[Table 1]

[0041]
The spark plug test product was attached to a 2000 cc engine, and an actual machine durability test was performed at an engine speed of 6500 rpm and a throttle fully opened. Then, after the test was completed for 100 hours, the case where peeling was not recognized in the ignition part 31 was evaluated as good welding strength (◯), and the case where it was not evaluated as poor welding strength (×). In addition, the case where no misfire occurred at the time of 100 hours was evaluated as good durability (◯), and the case where it was not so was evaluated as poor durability (×). The results are shown in Table 1. As is apparent from these results, it can be seen that both the welding strength and the durability are good in the test product having the coaxiality δ of 0.15 mm or less and the inclination angle θ of 5 ° or less.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing an embodiment of a spark plug of the present invention and an enlarged view of a main part thereof.
2 is a manufacturing process explanatory diagram of a center electrode side ignition part of the spark plug of FIG. 1; FIG.
FIG. 3 is an explanatory diagram of coaxiality δ and inclination angle θ.
FIG. 4 is an explanatory diagram showing the effect of ignition part eccentricity on the welded part depth.
FIG. 5 is a diagram illustrating a state in which uneven consumption occurs in a firing portion due to eccentricity.
FIG. 6 is a diagram for comprehensively explaining problems that occur in an ignition part due to inclination.
FIG. 7 is an explanatory view showing an embodiment of a noble metal tip positioning jig together with its usage.
FIG. 8 is an explanatory view showing another embodiment of a noble metal tip alignment jig together with its usage.
FIG. 9 is a conceptual explanatory diagram of a method for measuring coaxiality and tilt angle.
FIGS. 10A and 10B are a laser irradiation intensity diagram, an enlarged perspective view, a schematic plan view, and a longitudinal sectional view of a tip portion of a center electrode of a spark plug.
FIG. 11 is an explanatory view showing a noble metal tip and an all-around laser weld in a circumferential direction.
FIGS. 12A and 12B are perspective views showing some examples of a holding jig for a noble metal tip used during laser welding. FIGS.

Claims (5)

A central electrode (3) having a main body (3M) forming a cylindrical outer peripheral surface (3p);
A noble metal having a cylindrical outer peripheral surface (31p) fixed to the tip of the main body portion (3M) in the axis (O2) direction of the central electrode (3) via an all-around laser welded portion (10). Ignition part (31),
A ground electrode (4) which is disposed in such a manner that the side surface faces the front end surface in the axis (O1) direction of the noble metal ignition part (31) and forms a spark discharge gap (g) with the noble metal ignition part (31). A spark plug (100) comprising:
A noble metal tip (31 ′) having a cylindrical outer peripheral surface (31p ′) on the front end surface (3s) in the direction of the central axis (O2) of the central electrode (3) is connected to the outer peripheral surface of the main body (3M) ( 3p) and a chip positioning step of superimposing the noble metal tip (31 ′) and the outer peripheral surface (31p ′) of the noble metal tip (31 ′) so that the coaxiality is 0.15 mm or less to form an overlapping assembly (170);
By irradiating the overlapping assembly (170) with a laser beam (LB) in the circumferential direction with respect to the central axis (O2) of the central electrode (3), the front end surface (3s) of the central electrode (3) The entire circumference laser welded portion (10) is formed in such a manner as to span the formation site of the noble metal tip (31 ′) and leave the tip side portion of the cylindrical outer peripheral surface (31p ′) of the noble metal tip (31 ′). Forming a welding process,
In the chip positioning step, a mounting portion (50e) detachably mounted on the outer peripheral surface (3p) of the main body portion (3M) of the center electrode (3), and the main body portion (50e) 3M) is integrated with the mounting portion (50e) for concentrically positioning the noble metal tip (31 ') held by itself relative to the outer peripheral surface (3p) of the main body portion (3M). A method of manufacturing a spark plug (100), comprising using a chip positioning jig (50) having a chip holding portion (50h). The mounting portion (50e) of the chip positioning jig (50) is mounted on the main body portion (3M) on a cylindrical mounting surface (50b) that follows the outer peripheral surface (3p) of the main body portion (3M). On the other hand, the tip holding part (50h) has an outer peripheral surface (31p ') of the noble metal tip (31') in a cylindrical tip holding surface (50a) formed concentrically with the mounting surface (50b). The method for manufacturing a spark plug (100) according to claim 1, wherein the spark plug (100) is retained. A plurality of the chip positioning jigs (50) are arranged along the circumferential direction of the outer peripheral surface (31p ') of the noble metal tip (31'), and approach and separate from each of the outer peripheral surfaces (31p ') in the radial direction. A plurality of possible chip gripping members (49) are provided, and the gripping surfaces (50a) of the chip gripping members (49) each constitute the chip holding surface (50a), and the direction orthogonal to the central axis (O2) The noble metal tip (31 ′) is positioned and disposed on the tip surface (3s) of the center electrode (3) held so as to be freely movable, thereby forming the overlapping assembly (170). And the outer peripheral surface of the main body (3M) of the center electrode (3) on the rear side of each chip gripping member (49) in the axis (O1) direction of the noble metal tip (31 ') (3p) When the tip (3s) of the center electrode (3) is relatively approached from the rear side in the axis (O1) direction with respect to the gripped noble metal tip (31 '), the center electrode (3 A cylindrical guide surface (50b) for guiding the main body portion (3M) of the metal plate (3M) concentrically with respect to the noble metal tip (31 ') is formed as the mounting surface (50b). The method for manufacturing a spark plug (100) according to claim 2, characterized in that : By irradiating the overlap assembly (170) with a laser beam pulse (LB), the all-around welded portion (10) is sequentially turned into unit welded portions (10u) corresponding to the laser beam pulses (LB). While forming to form a series,
An array connection weld overlap portion (LPW) for connecting the end portions of the unit weld array is formed to complete the circumferential weld portion (10) continuous in the circumferential direction. At least one of the unit welds (101 to 103, 110 to 112) formed overlappingly in LPW), the laser irradiation energy per pulse used for forming the unit weld is used for other unit welds. The method for manufacturing a spark plug (100) according to any one of claims 1 to 3, wherein the spark plug (100) is set to be lower than the laser irradiation energy per pulse used when forming the . In the overlapping assembly (170), the all-around laser weld (10) is pressed while pressing the noble metal tip (31 ') against the tip surface (3s) of the center electrode (3) in the direction of the axis (O1). A pressing jig that forms and contacts the surface of the noble metal tip (31 ′) on the opposite side (31s ′) of the noble metal tip (31 ′) to the center electrode (3s) in the form of surface contact. The method for manufacturing a spark plug (100) according to any one of claims 1 to 4, wherein the method is performed using JG2) .

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