JP2002231417A - Method of manufacturing spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a spark plug for eliminating waste of energy consumption, preventing the outflow of molten metal in a process of welding a noble metal chip to an electrode, and obtaining a welding part having a uniform width. SOLUTION: When forming the whole peripheral laser welding part 10 straddling a noble metal chip 31' and a chip fixing object surface forming part to a superposed assembly 70 by superposing a chip fixing object surface 3s of a central electrode 3 and the noble metal chip 31', and successively superposing and continuing unit welding parts 101 to 112 corresponding to respective laser irradiating pulses P1 to P12, corrective irradiation energy Eh used when forming the welding parts resulting in increasing the ovelap number of the unit welding parts 101 to 112 among the whole peripheral laser welding part 10, is set lower than ordinary irradiation energy Et used when forming the other welding part to eliminate waste of the energy consumption. Here, at least one of the forefront welding part 10t and the tail end welding part 10e is selected as the welding parts resulting in increasing the overlap number.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for manufacturing a spark plug.

[0002]

2. Description of the Related Art In recent years, spark plugs used for ignition of an internal combustion engine have been developed to improve spark wear resistance.
A type in which a noble metal ignition portion is formed by welding a noble metal tip mainly composed of Pt, Ir, or the like to the tip of an electrode made of a heat-resistant alloy is used. For example, when a noble metal tip is joined to the tip surface of a center electrode that forms a spark discharge gap in opposition to a ground electrode, a method of manufacturing the disk-shaped noble metal tip is to attach the tip surface of the center electrode (tip fixation). A laser beam is irradiated along the outer periphery of the noble metal tip while rotating the center electrode, thereby forming a laser welded part all around (for example, JP-A-6-45050). , JP 10
Publication No. 112374).

[0003]

In the above-described method for manufacturing a spark plug, welding of a noble metal tip to an electrode is often performed using a pulsed laser beam from a YAG laser or the like. With respect to this pulsed laser beam, a laser welded portion can be formed along the outer periphery of the noble metal tip over the noble metal tip and the portion of the electrode to which the chip is to be formed, and a blow hole or the like is formed inside the welded portion. In order to prevent the formation of the laser beam, the conditions such as the irradiation energy per one pulse and the pulse width can be arbitrarily determined in relation to the material and outer diameter of the noble metal tip and the electrode.

Here, as shown in FIG. 10, a laser beam LB oscillating at 12 pulses per one rotation of the center electrode 3 is applied along the outer periphery of the superposed surface of the center electrode 3 and the noble metal tip 31 '. 12 unit welds 10
Consider a case in which A to 10L are successively overlapped and form a full-circumference laser welded portion 10 extending over the center electrode 3 and the noble metal tip 31 '. All around laser weld 10
In addition, in addition to the overlap with the immediately preceding welded portion, the welded portion 10e of the tail portion (hereinafter, referred to as a tail weld portion) 10e
Since it also overlaps with t, the number of overlaps of the unit welded portion is larger than other welded portions. On the other hand, in order to shorten the piece time and increase the production efficiency, the rotation speed (the number of rotations) of the center electrode 3 needs to be maintained at a predetermined value or more. The heat input at the time of formation may not be sufficiently extracted during the rotation of the center electrode 3 one round. In such a case, even when the laser beam LB for forming the tail welding portion 10e is irradiated, a part of the heat input when the head welding portion 10t is formed exists as residual heat.

[0005] Therefore, in the end welded portion 10e of the entire circumference laser welded portion 10, the overlapped portion with the leading welded portion 10t (in FIG. 10 (b), the eleventh unit welded portion 10K and the twelfth welded portion 10K). This residual heat is superimposed on predetermined irradiation energy (new heat input for the tail welded portion 10e) for forming the tail welded portion 10e in the unit welded portion 10L). As a result, the size of the welded portion that forms the tail welded portion 10e (unit welded portions 10K and 10L) becomes large, resulting in unevenness in the width of the welded portion 10 (see FIG. 10C), as well as the molten metal. May flow out of the weld (also referred to as sagging) (see FIG. 1).
0 (a)). Such an outflow portion F of the molten metal is generated not only on the center electrode side but also on the noble metal tip side, impairing the appearance and lowering the product yield. Further, when the outflow portion F of the molten metal reaches the discharge surface of the noble metal tip, the spark discharge gap may be narrowed, resulting in poor ignition.

Further, the outflow portion F of the molten metal formed in the tail welded portion 10e not only causes the width of the welded portion 10 to become non-uniform, but also causes the tail end welded portion 10e ( Is the discharge surface 3 of the noble metal ignition part 31
1a. Generally, the welded portion 10 is formed of an alloy of a noble metal tip material and an electrode material, and is inferior in spark abrasion resistance as compared with a noble metal tip alone.
In a relatively short time, the spark discharge gap is widened, causing a problem such as an ignition mistake.

SUMMARY OF THE INVENTION An object of the present invention is to manufacture a spark plug capable of preventing waste of energy consumption, preventing molten metal from flowing out in a step of welding a noble metal tip to an electrode, and obtaining a weld having a uniform width. It is to provide a method.

[0008]

In order to solve the above-mentioned problems, a method for manufacturing a spark plug according to the present invention is directed to a center electrode and a ground electrode arranged to face the center electrode. A method for manufacturing a spark plug in which a noble metal ignition portion forming a spark discharge gap is formed by welding a noble metal tip to at least one of the center electrode and the ground electrode, wherein the center electrode and / or By superimposing the noble metal tip on the chip-fixed surface of the ground electrode to form a superposition assembly, and irradiating the superposition assembly with pulsed laser light from the emission optical unit of the laser irradiation unit. In the circumferential direction of the noble metal tip, it straddles the noble metal tip and the portion where the chip is fixed, and responds to each laser irradiation pulse. The unit welds are sequentially overlapped to form an all-around laser weld, and among the all-around laser welds, a weld at a leading portion where the number of overlaps of the unit welds increases (hereinafter, a leading weld) The laser irradiation energy per pulse (hereinafter referred to as “corrected irradiation energy”) used to form at least one of a welded portion at the end and a welded portion at the end (hereinafter referred to as a tail welded portion) is used for other welded portions. It is characterized in that it is set lower than the laser irradiation energy per pulse (hereinafter, referred to as normal irradiation energy) used in the formation.

In other words, according to the manufacturing method of the present invention, a laser beam is applied to a superposed assembly in which the chip-fixed surface of the electrode and the noble metal tip are overlapped with each other over the noble metal chip and the chip-fixed surface forming portion, and In the case where the unit welds corresponding to the pulse form an all-around laser weld in which the unit welds corresponding to the pulse are sequentially overlapped, when forming a weld in which the number of overlaps of the unit welds increases among the all-around laser welds. The correction irradiation energy to be used is set lower than the normal irradiation energy used when forming other welded portions, so that waste of energy consumption is eliminated. Specifically, the welded portion where the number of overlaps increases is often formed at the leading welded portion or the trailing welded portion.

Therefore, even if the residual heat in the head weld is superimposed on the new heat input for the tail weld, the corrected irradiation energy used for forming at least one of the head weld and the tail weld is different. The total energy (remaining heat and new heat input) between the weld and the other welds, which is adjusted to be lower than the normal irradiation energy used when forming the welds, will increase the number of overlapping unit welds. And the total amount of heat). With this, when the tail weld is formed,
Since it is possible to avoid the molten metal becoming larger than the other welded parts and the molten metal flowing out of the welded part, a reduction in product yield due to poor appearance and poor ignition due to narrowing of the spark discharge gap Etc. can be prevented beforehand.

Also, by making the total energy (total heat) uniform, the width between the tail welded portion and the other welded portions can be made substantially uniform, and the noble metal firing accompanying the consumption of the noble metal firing portion. Exposure of the tail welding portion to the discharge surface of the portion is less likely to occur. Therefore, it is possible to prevent a failure such as an ignition error due to an increase in the spark discharge gap.

[0012] The head weld portion referred to here includes a case where there is only one unit weld portion located at the front end and a case where a unit weld portion including the front end and subsequent unit weld portion is added. The welded portion is divided into a case where there is only one unit weld located at the rear end and a case where a unit weld including the rear end and before the unit weld is added. That is, the number of unit welds constituting the first weld or the last weld varies depending on welding conditions such as the pulse generation frequency and the relative rotation speed between the superposition assembly and the output optical unit.

In the present specification, the laser irradiation energy per pulse can be measured by, for example, receiving a laser beam emitted from a laser oscillation unit with an energy detector such as a calorimeter or a power meter before performing laser welding. The irradiation energy per time (for example, one second) is measured, and a value calculated by dividing the irradiation energy by the number of pulses per second is used.

In the case where the entire circumference laser welding portion in the present invention is formed while the superposition assembly and the single emission optical portion are relatively rotated about the center axis of the superposition assembly, the head welding is performed. It is desirable that the correction irradiation energy used when forming the tail welding portion of the part and the tail welding part be set lower than the normal irradiation energy. There are many factors such as the material of the electrode, the ambient temperature, the outer diameter of the noble metal tip, and the like, which are varied in the amount of heat drawn at the head weld, and there is a possibility that setting and adjusting the correction irradiation energy to suppress the residual heat to a predetermined value or less may become complicated. is there. However, such a risk is small in the case of new heat input at the tail welding portion, and setting and adjustment of the correction irradiation energy can be easily performed. In general, it can be said that the welded portion has a lower reflectance of laser light due to surface irregularities and the like and is more likely to absorb laser irradiation energy than an unwelded lap assembly. Therefore, the correction irradiation energy used when forming the tail weld portion where the weld portion having a relatively low reflectance is already almost formed,
If the energy is set lower than the normal irradiation energy, the effect of suppressing new heat input for the tail welded portion will be remarkable.

Further, when the laser irradiation energy per pulse is set to be lower than the laser irradiation pulse of the irradiation order that arrives before the laser irradiation pulse for forming the tail welding portion, The laser irradiation energy per pulse can be adjusted so as to gradually decrease as the number of overlapped unit welds gradually increases, and the total energy of the tail weld and other welds can be uniform. Can be achieved more precisely.

When the correction irradiation energy used for forming the tail welding portion is set to be lower than the normal irradiation energy, the laser irradiation energy per pulse used for forming the head welding portion is reduced. The setting may be made substantially equal to the normal irradiation energy, and the adjustment operation can be simplified.

Next, the laser welding portion of the present invention, by rotating the superposition assembly and the plurality of emission optical portions relative to each other about the central axis of the superposition assembly, forms a pulse-like signal from the plurality of emission optical portions. By irradiating the laser light almost in synchronization, the unit welds are sequentially overlapped and connected, and when formed by a plurality of section welds corresponding to the number of output optical parts, the unit welds in the section welds. The correction irradiation energy used to form at least one of the leading weld and the trailing weld, which increases the number of overlaps of the welds, is set lower than the normal irradiation energy used to form other welds. Will do. The entire circumference laser weld is divided and formed by section welds corresponding to a plurality of emission optics that irradiate pulsed laser light almost in synchronization. The welding time is reduced.

In the case where the entire circumference laser weld is formed by a plurality of section welds as described above, for the same reason as the case where it is formed by a single weld, the first weld and the last weld are connected. It is desirable that the correction irradiation energy used when forming the tail welding portion is set lower than the normal irradiation energy.

By setting the average laser output required for forming the section welds to be approximately equal for each laser irradiation unit, the total energy of the tail weld and the other welds in each section weld is made uniform. In addition, the total energy of each section weld can be made uniform, and a weld having a uniform width over the entire circumference can be obtained.

Means for solving the problem relating to the present invention is as described above.
The following solution (hereinafter referred to as a related solution) is also conceived.

That is, as a related solution means, a center electrode and a ground electrode arranged to face the center electrode are provided, and a noble metal tip is welded to at least one of the center electrode and the ground electrode. A method for manufacturing a spark plug having a noble metal firing portion forming a spark discharge gap, wherein the noble metal tip is overlapped with a tip fixing surface of the center electrode and / or the ground electrode. By irradiating a pulsed laser beam from the emission optical unit of the laser irradiation unit to the superposition assembly, in the circumferential direction of the noble metal chip, straddling the noble metal chip and the chip fixing surface forming site, In addition to forming an all-around laser weld where the unit welds corresponding to each laser irradiation pulse are sequentially overlapped, The laser irradiation energy per pulse used when forming a close weld where the distance between the center points of adjacent unit welds becomes shorter is used for forming other welds. It is also possible to set it lower than the laser irradiation energy per pulse used for the above.

As a scene where the above-mentioned related solution is adopted,
For example, a case where the relative rotational speed between the superposition assembly and the output optical unit changes during laser welding can be cited.
In such a case, the change in the rotation speed appears as a change in the distance between the center points of the adjacent unit welds, and the number of overlaps of the unit welds increases accordingly. Therefore, the irradiation energy per pulse is adjusted in accordance with the fluctuation of the distance between the center points. In this way, when implementing the related solution, for example, when the relative rotation speed changes as described above, the rotation speed is monitored by the speed detector during laser welding, and these changes are detected by the laser irradiation unit. This can be realized by adjusting (controlling) the irradiation energy per pulse by feeding back to the above.
Therefore, when the close welded portion is formed, it is possible to avoid that the molten portion becomes larger than the other welded portions and the molten metal flows out of the welded portion, and in this case, the product yield is also reduced due to poor appearance. It is possible to prevent the occurrence of ignition failure due to the decrease or the spark discharge gap narrowing.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a spark plug manufactured by the method of the present invention. Spark plug 100
Is a cylindrical metal shell 1, an insulator 2 fitted inside the metal shell 1 so that the tip 21 protrudes, and a noble metal firing portion (hereinafter, also simply referred to as a firing portion) 3 formed at the tip.
One end is connected to the center electrode 3 provided inside the insulator 2 and the metal shell 1 by welding or the like while the other end is bent to the side while the other end is bent to the side, and the side surface is formed as the center electrode. 3 is provided with a ground electrode 4 and the like arranged so as to face the distal end portion. The ground electrode 4 has the above-mentioned firing part 3.
A noble metal firing portion (hereinafter, also simply referred to as a firing portion) 32 facing 1 is formed, and a gap between the firing portion 31 and the facing firing portion 32 is a spark discharge gap g.

The term "ignited portion" as used herein refers to a portion of the joined noble metal tip that is not affected by a change in composition due to welding (for example, alloyed with the material of the ground electrode or center electrode by welding). The remaining part excluding the part that did)
Shall be referred to.

The insulator 2 is made of a ceramic sintered body such as alumina or aluminum nitride, and has a hole 6 for fitting the center electrode 3 and the terminal fitting 8 along its own axial direction. Have. The metal shell 1 is formed of a metal such as low-carbon steel in a cylindrical shape, forms a housing of the spark plug 100, and has a screw on its outer peripheral surface for attaching the plug 100 to an engine block (not shown). The part 7 is formed.

The firing portion 31 and the facing firing portion 32
It is good also as composition which omits one of either. In this case, a spark is generated between the ignition portion 31 and the side surface of the ground electrode 4 having no ignition portion, or between the opposing ignition portion 32 and the front end surface of the center electrode 3 having no ignition portion. The discharge gap g is formed.

In this embodiment, at least the surface layer portion of the center electrode 3 and the ground electrode 4 on which the chip is fixed is formed of a heat-resistant alloy containing Ni or Fe as a main component. In the above, "main component" means a component having the highest weight content, and is not necessarily "50% by weight".
It does not mean a component that occupies the above.)

On the other hand, the ignition portion 31 and the opposing ignition portion 32 are made of a noble metal or a noble metal alloy containing Ir, Rh or Pt as a main component. By using these noble metals, even in an environment where the temperature of the center electrode 3 and / or the ground electrode 4 tends to increase, the ignition portions 31 and 3 can be used.
2 can have good wear resistance. Also,
The weldability to the above heat-resistant alloys is also good. For example, when using a precious metal based on Pt, P
t alone, a Pt-Ni alloy (for example, Pt-1 to 30% by weight Ni alloy), a Pt-Ir alloy (for example, Pt-1 to 2)
0% by weight of an Ir alloy), a Pt-Ir-Ni alloy, or the like. Further, as a material containing Ir as a main component,
Ir-Ru alloy (for example, Ir-1 to 30 wt% Ru alloy), Ir-Pt alloy (for example, Ir-1 to 10 wt% P
t alloy), an Ir-Rh alloy, an Ir-Rh-Ni alloy, or the like. Further, as a material containing Rh as a main component, an Rh-Ir alloy (for example, Rh-3 to 38% by weight
r alloy) can be used.

When an Ir-based noble metal material is used, an oxide (composite oxide) of a metal element belonging to Group 3A (so-called rare earth element) and Group 4A (Ti, Zr, Hf) of the periodic table of elements is used. ) In the range of 0.1 to 15% by weight. Thereby, the oxidation and volatilization of the Ir component can be effectively suppressed, and the spark erosion resistance of the ignition portion can be improved. As the oxide but is _Y 2 _{O 3} is preferably used, _La 2 also Other O
₃ , ThO ₂ , ZrO _{2 and the} like can be preferably used. In this case, as the metal component, Ir alone may be used in addition to the Ir alloy.

As shown in FIG. 2, the diameter of the center electrode 3 is reduced by a frusto-conical tapered surface 3t at the tip end.
A disk-shaped noble metal tip 31 ′ made of an alloy composition constituting the ignition portion 31 is superimposed on the tip surface 3 s. Further, the entire circumference laser welded portion 10 is formed by laser welding along the outer edge of the joining surface, and the noble metal tip 31 'is fixed to form the ignition portion 31. 9, the noble metal tip 32 'is aligned with the ground electrode 4 at the position corresponding to the firing portion 31, and the entire circumference is similarly laser-welded along the outer edge thereof, as shown in FIG. It is formed by forming a welded portion 11 and fixing it. These chips 31 ′ and 32 ′ are formed into a plate by hot rolling a molten alloy obtained by blending and melting each alloy component so as to have a predetermined composition.
After the plate material is formed by punching into a predetermined chip shape by hot punching, or after the molten alloy is processed into a linear or rod-shaped material by hot rolling or hot forging, this is processed in the longitudinal direction. It can be used by cutting to a predetermined length. Further, those formed into a sphere by an atomizing method or the like can also be used. The tips 31 ′ and 32 ′ have, for example, a diameter D of 0.4 to 1.2 mm and a thickness H of 0.5 to 1.
Use a 5mm one.

Since the welding method for forming the above-mentioned ignition portions 31 and 32 is substantially the same, an embodiment of the manufacturing method according to the present invention will be described below, focusing on the ignition portion 31 on the center electrode 3 side. This will be described in detail below. As shown in FIG.
The tip surface 3 s of the center electrode 3 is used as a chip fixing surface, and a noble metal tip 31 ′ having a tip diameter D and a tip thickness H is overlapped therewith to form a lap assembly 70. As shown in FIG. 2B, the entire circumference laser welded portion 10 that straddles the noble metal tip 31 ′ and the surface to which the chip is fixed and does not reach the discharge surface 31a in the thickness direction of the noble metal tip 31 ′ is removed. It is formed along the direction.

At this time, when the noble metal tip 31 'is formed in a disk shape as in this embodiment, as shown in FIG. 2B, the noble metal tip 31' and the center electrode 3 are superposed. The assembly 70 is connected to the laser irradiation unit 150 (FIG. 3).
(See FIG. 2) relative to the output optical unit 50 around the central axis O of the chip 31 ′ (center electrode 3), and directed toward the superposition assembly 70 in the spot of the pulsed laser beam LB. The crossing edge Q between the surface to be fixed (in this case, the end surface of the center electrode 3) and the outer peripheral surface of the chip is included, and the irradiation angle θ with respect to the surface to be fixed is -5 ° to +60.
範 囲 range (+ above the horizontal is +; for example, +45
The method of irradiating the pulsed laser beam LB so as to satisfy ゜) is reasonable as a method of uniformly forming the entire circumference laser welded portion 10 as described above. In this case, the assembly 70
Alternatively, only one of the emission optical units 50 may be rotated, or both may be rotated (for example, in directions opposite to each other).

In this case, it is desirable to adjust the rotation speed as follows. First, the relative rotation speed between the superposition assembly 70 and the output optical unit 50 is 10 rpm or more (preferably 60 rpm or more, more preferably 120 rpm) when only one output optical unit 50 is used as shown in FIG.
pm or more). In order to form the laser welding portion 10 around the entire circumference, the superposition assembly 70 and the output optical portion 5 are required.
0 must be rotated relative to at least one lap,
If the relative rotation speed is less than 10 rpm, the welding time for one rotation, and thus the piece time for manufacturing one spark plug, may be long. When the overlapping assembly 70 is rotated, the upper limit of the relative rotation speed is preferably set to about 150 rpm in order to prevent deformation and scattering of the molten metal due to centrifugal force generated during welding.

Next, the configuration of the laser irradiation unit 150 will be described with reference to FIG. The laser irradiation unit 150 includes a laser oscillating unit 40 that irradiates the pulsed laser beam LB, and an emission optical unit 5 that irradiates the pulsed laser beam LB toward the outer peripheral surface of the superposition assembly 70.
0, and an optical transmission path 60 for transmitting the pulsed laser light LB from the laser oscillation unit 40 to the emission optical unit 50. In the laser oscillating section 40, when light such as xenon or the like is applied from the excitation lamp 42 at a predetermined pulse interval to the YAG rod 41 made of yttrium aluminum garnet single crystal, this light is reflected by the total reflection mirror 43 and the exit side translucent mirror. The laser light is amplified by reciprocating between the mirror 44 and the laser light, and is emitted from the exit side translucent mirror 44 as laser light. Then, the pulsed laser light LB that has been pulse-oscillated is changed in direction by the reflecting mirror 45 on the exit side of the laser oscillation section 40, and then enters the optical transmission path 60 formed by the optical fiber cable 61. Then, the pulsed laser light LB transmitted through the optical fiber cable 61 and emitted is converted into a spherical aberration correction lens group 51 of the emission optical unit 50 (note that the spherical aberration correction lens group 51 is used here, but even a single lens is used). And the light is focused toward the outer peripheral surface of the superposition assembly 70.

The laser irradiation unit 150 shown in FIG.
A laser controller 81, a charge controller 82, a high-voltage circuit 83, a capacitor C, and a discharge circuit 84 are additionally provided to obtain a pulsed laser beam LB necessary for implementing the present invention. In FIG. 3, these controllers and circuits are shown in a block diagram. The high-voltage circuit 83 used in the present embodiment is driven based on a charge command signal D1 from a charge controller 82 for controlling the voltage VC across the capacitor C.
It includes a step-up transformer, one or a plurality of rectifier circuits and the like (all not shown), and is connected to the discharge circuit 84.
The discharge circuit 84 includes at least a switching element (not shown) including a GTO, a thyristor, and the like. This switching element is connected to a laser controller 81, and is turned on / off (energization / non-energization control) based on a discharge signal Tg from the laser controller 81.
Is done.

Then, the charge permission signal D2,
When a charge voltage value signal Vg corresponding to the set charge voltage value set by the laser controller 81 is input, the charge controller 82 issues a charge command so that the voltage VC across the capacitor C becomes the set charge voltage value. Signal D
1 is output to the high voltage circuit 83 to control the high voltage circuit 83 side. Then, the capacitor C is charged through the high voltage circuit 83 during the output of the charge command signal D1. Next, when both ends of the capacitor C are charged with the voltage VC between both ends, the laser controller 81
When the discharge signal Tg having a predetermined constant pulse interval is input to the switching element of the discharge circuit 84, the switching element is turned on (in other words,
The discharge circuit 84 is driven). Then, the capacitor C is discharged, and pulse discharge occurs between the discharge electrodes of the excitation lamp 42 (in other words, the excitation lamp 42 emits light), and the pulsed laser LB oscillates.

That is, in the laser irradiation unit 150 of the present embodiment, the value of the voltage VC across the capacitor C can be controlled (variable) in accordance with the change of the set charging voltage value appropriately set by the laser controller 81. While the pulse interval for discharging the capacitor C is preset to be constant, and as a result, the pulsed laser light LB
Is controlled based on the value of the voltage VC across the capacitor C.

Next, with reference to FIGS. 3 and 4, a description will be given of a process in which the unit welds are sequentially formed in the entire circumference laser weld 10 so as to correspond to the laser irradiation pulse. When the charging permission signal D2 and the set charging voltage signal Vg from the laser controller 81 are input to the charge controller 82 after the overlapping assembly 70 is set at a predetermined welding position, the high voltage circuit 83 is driven, and the set charging voltage is set. Both ends of the capacitor C are charged with the voltage VC at both ends corresponding to the value. Then, when the discharge circuit 84 is driven based on the discharge signal Tg from the laser controller 81, the excitation lamp 42 emits light, and the pulsed laser light LB oscillates. The light LB is applied to the superposition assembly 70. At this time, the laser intensity S of the pulsed laser beam LB is determined according to the value of the voltage VC between both ends of the capacitor C.
(See FIG. 4A). When the peak value of the laser intensity S is St (hereinafter, referred to as normal laser intensity) and the pulse width is t, the laser irradiation energy Et per pulse (hereinafter, referred to as normal irradiation energy) is Et = St × t. Given by

Then, while rotating the superposition assembly 70 about its central axis O, the pulsed laser beam LB is emitted from the single emission optical unit 50 whose position is fixed. As a result, in the circumferential direction of the noble metal tip 31 ′, the unit welding portions 101, 102... Astride the noble metal tip 31 ′ and the chip fixing surface forming site and correspond to each laser irradiation pulse P 1, P 2. ... Are sequentially overlapped to form the entire circumference laser welded portion 10 (FIG. 4A).
(D)).

The pulse generation frequency f of the pulsed laser beam LB (that is, the frequency at which the switching element of the discharge circuit 84 output from the laser controller 81 is turned on / off) is 12 pulses / second (also referred to as pps). At this time, the period τ = 1000/12 milliseconds), and the rotational speed of the superposition assembly 70 is 60 rpm (1 rpm).
Then, exactly 12 pulses of pulsed laser light LB are emitted for one rotation of the superposition assembly 70, and the corresponding twelve unit welds 101 to 112 are sequentially superposed in the circumferential direction of the noble metal tip 31 '. It is formed in a continuous form. FIG. 5 generally shows an overlapping state of these twelve unit welded portions 101 to 112 in the circumferential direction. In the other welds except the first weld 10t (101 to 103 in FIG. 5) and the last weld 10e (110 to 112 in FIG. 5), the unit weld already formed when the unit weld is formed. (Hereinafter, referred to as the number of overlaps with the existing unit weld) is three formed immediately before itself (for example, in the fourth unit weld 104, 101 to 101).
103).

On the other hand, the number of overlaps with the existing unit welded portion increases to four or more in the last welded portion 10e. For example, in the case of the twelfth mere welded portion 112 at the rear end, in addition to three pieces 109 to 111 formed immediately before itself, three pieces of the top welded part 10t originally formed (also overlapped with 101 to 103) Therefore, the number of overlaps with the existing unit welds is 6. In the same manner, the eleventh unit weld 11
In Example 1, the number of overlaps with the existing unit welds was 5,
The number of overlaps with the existing unit weld in the unit weld 110 is four. Note that the top welded portion 10t (101
In the case of to 103), the number of overlaps with the existing unit weld is 0
Although there are two, when the tail welding portion 10e is formed as described above, it overlaps with this.

If the heat input at the time of forming the leading welded portion 10t is not sufficiently removed during the rotation of the lap assembly 70, the pulsed laser beam for forming the trailing welded portion 10e is used. Even at the time of LB irradiation, part of the heat input when the leading welded portion 10t is formed exists as residual heat. Therefore, in this embodiment, the tail welding portion 10
The tail welding part 10e is formed so that even if this residual heat is superimposed on the laser irradiation energy for forming the e (new heat input for the tail welding part 10e), the molten metal does not flow out of the welding part. The laser irradiation energy per pulse (hereinafter referred to as “correction irradiation energy”) Eh is set lower than the normal irradiation energy Et (see FIG. 4A). Thereby, the total heat quantity (total energy) including the new heat input and the residual heat when forming each unit weld is made uniform.

In FIG. 3, the setting of the laser irradiation energy is changed and adjusted in such a manner that the voltage VC across the capacitor C corresponds to the normal irradiation energy Et and the correction irradiation energy Eh, respectively. That is, the laser controller 81 shown in FIG.
By changing and adjusting the set charging voltage value of the capacitor C so as to correspond to t and the corrected irradiation energy Eh,
That is, the voltage VC between both ends of the capacitor C is changed. The switching timing from the normal irradiation energy Et to the correction irradiation energy Eh is determined as follows. The number of pulses for turning on / off the switching element of the discharge circuit 84 by the laser controller 81 is counted by a pulse counter circuit (not shown) and fed back to the laser controller 81. When a predetermined number of pulses are counted from the start of the laser welding and the irradiation order of the laser irradiation pulse to be switched from the normal irradiation energy Et to the correction irradiation energy Eh is reached, the setting initially set by the laser controller 81. The charge voltage value (that is, the first set charge voltage value) is changed and adjusted to a second set charge voltage value lower than the first set charge voltage value. As a result, the value of the voltage VC across the capacitor C is changed and adjusted, and as a result, switching from the normal irradiation energy Et to the correction irradiation energy Eh is performed.

More specifically, in the embodiment shown in FIG. 4A, the eleventh laser irradiation pulse P11 corresponding to the eleventh unit welding part 111 and the twelfth unit welding part 112 at the rear end are used. With the twelfth laser irradiation pulse P12 corresponding to the above, the adjustment of the laser irradiation energy for one pulse, that is, the adjustment of the peak value of the laser intensity S (the adjustment from the normal laser intensity St to the correction laser intensity Sh) is performed. Will be For example, the normal irradiation energy Et is 1.25 J
In this case, the corrected irradiation energy Eh11 corresponding to the eleventh laser irradiation pulse is 1 J, and the corrected irradiation energy Eh12 corresponding to the last twelfth laser irradiation pulse P12 is 0.75 J.

Actually, during the formation of the entire circumference laser welded portion 10 in which the unit welded portions 10 are successively overlapped,
In changing and adjusting the laser irradiation energy for one pulse, a time lag occurs in lowering the laser irradiation energy for one pulse. In this embodiment, the laser controller 81 uses the first set charging voltage value corresponding to the normal irradiation energy Et and the corrected irradiation energy E
The second set charging voltage value corresponding to h is set, and the setting change timing from the first set charging voltage value to the second set charging voltage value is controlled as follows. That is, the laser irradiation pulse (for example, the eighth) of the irradiation order (for example, the eighth) that arrives before the twelfth laser irradiation pulse P12 for forming the last unit welded portion.
P8) is controlled to change the setting to the second set charging voltage value. That is, even if a set charging voltage signal for changing to the second set charging voltage value is issued for the eighth laser irradiation pulse P8, the laser irradiation energy for one pulse actually decreases due to the time lag because, for example, It is the eleventh laser irradiation pulse P11 and thereafter. Then, from the eleventh laser irradiation pulse P11 to the twelfth
It gradually decreases until the second laser irradiation pulse P12,
The twelfth laser irradiation pulse P12 finally takes a form corresponding to the second set charging voltage value set by the laser controller 81.

This is because the laser controller 81
When the pulse counter circuit recognizes the laser irradiation pulse (for example, P7) of the irradiation order (for example, the seventh order) that arrives before the laser irradiation pulse P12 for forming the last unit welding portion 112, the next By simply switching the first set charging voltage value set by the laser controller 81 from the laser irradiation pulse (for example, P8) to the second setting charging voltage value, a laser irradiation pulse (for example, P11) of a predetermined order (for example, P11) In this case, the same operation and effect can be obtained as when the laser irradiation energy per pulse is set to decrease gradually. However, the entire circumference laser welded part 10 in which the unit welded parts 10 are sequentially overlapped and connected.
When the laser irradiation energy for one pulse is changed and adjusted during formation of the laser beam, if the laser irradiation unit 150 is configured so that a time lag does not occur in the reduction of the laser irradiation energy for one pulse, one pulse Since the laser irradiation energy can be changed and adjusted for each pulse, the laser irradiation energy may be adjusted as appropriate for each pulse corresponding to the laser irradiation pulse to be used as the correction irradiation energy Eh.
And by performing laser welding incorporating the above-mentioned laser irradiation energy control, it is effective to equalize the total heat (total energy) that combines the new heat input and the residual heat when forming each unit weld. Thus, the welded portion 10 having a substantially uniform width is formed.
(B), (d)).

FIG. 6A shows the adjustment of the normal laser intensity St and the correction laser intensity Sh (the adjustment of the normal irradiation energy Et and the correction irradiation energy Eh).
Here is an example of a change that replaces. Of these, FIG.
The correction laser intensity Sh is set so as to gradually increase from the first laser irradiation pulse P1 to the second laser irradiation pulse P2, and the third laser irradiation pulse P2 is set.
The normal laser intensity St is set from 3 to the last twelfth laser irradiation pulse P12. In this case, in anticipation of an increase in the total amount of heat at the tail welding portion 10e, the irradiation energy is adjusted to be low in the head welding portion 10t in advance so that the molten metal does not flow out of the welding portion.

FIG. 6 (b) is the same as FIG. 4 (a) and FIG.
(A) is an example of a combination. That is, the first welding portion 10t (the first unit welding portion 101 and the second unit welding portion 102 in FIG. 6B) and the last welding portion 1
In FIG. 6B, the corrected laser intensity Sh (corrected irradiation energy Eh) is set for both the eleventh unit weld 111 and the twelfth unit weld 112 in FIG. 6B. In this case, the adjustment for lowering the irradiation energy is distributed to the first welding portion 10t and the last welding portion 10e, so that the change adjustment between the normal irradiation energy Et and the corrected irradiation energy Eh becomes gentle.

Next, FIG. 7 is a schematic plan view of the tip of the center electrode when a manufacturing method according to another embodiment is applied.
This corresponds to a modification example of FIG. As described above, while rotating the superposition assembly 70 around its central axis O, the pulsed laser light LB from the plurality of emission optical units arranged and fixed at predetermined intervals in the circumferential direction of the noble metal tip 31 ′.
If the welding is performed by irradiating almost in synchronism, welding time may be shortened in some cases. For example, FIG.
As described above, if welding is performed by using two emission optical units 50a and 50b arranged at an interval of approximately 180 °, the laser beam sources 50a and 50b can be welded to a section welding portion 20 corresponding to approximately a half circumference.
0 and 220 may be shared respectively. In addition, as shown in FIG. 7B, three output optical units 5 arranged at approximately 120 ° intervals.
0a to 50c, the output optical parts 50a
50c may share the section welds 300, 310, 320 corresponding to approximately one third of the circumference. In addition, even if the timing of the laser irradiation pulse is slightly shifted for each section welding part, the welding time can be shortened as long as the timing is synchronized.

7 (a) or 7 (b), the entire laser welding portion 10 is overlapped with the existing unit welding portion by the section welding portions 200 and 220 or 300, 310 and 320.
If FIG. 5 is replaced with FIG. Therefore, the description so far of the adjustment of the normal laser intensity St and the correction laser intensity Sh (the adjustment of the normal irradiation energy Et and the correction irradiation energy Eh) can be applied to these embodiments as they are. However, FIG.
In the embodiment of (a), 24 pulses (ie, each laser light source 50a, 50
A pulsed laser beam LB (for 12 pulses from 0b) is irradiated, and the 24 unit welds corresponding thereto are sequentially superimposed in the circumferential direction of the noble metal tip 31 'to form the entire laser weld 20. I have. In the embodiment shown in FIG. 7B, the pulsed laser light LB of 24 pulses (ie, 8 pulses from each of the laser light sources 50a to 50c) is emitted for each 1/3 rotation of the superposition assembly 70. Is formed in such a manner that 24 unit welds corresponding to the above are sequentially overlapped in the circumferential direction of the noble metal tip 31 ′. Therefore, in FIG. 7A, the unit welds 201 to 2 correspond to the two section welds 200 and 220.
12, 221 to 232 are formed, and in FIG. 7B, the unit welds 301 to 308, 311 to 318, 321 to 328 correspond to the three section welds 300, 310, and 320.
Is formed.

When a plurality of output optical sections are used, the average laser output required for forming each section welded section is:
It is desirable that each laser irradiation unit is set to be substantially equal. That is, a plurality of output optical units (n
(N: 2), the temperature rise in the noble metal tip 31 'when the laser beam is simultaneously irradiated becomes large. However, as described above, each of the emission optical portions may share a section welded portion corresponding to substantially (1 / n) circumference with respect to the noble metal tip 31 ', which is different from the case where a single emission optical portion is used. Then, welding can be performed in (1 / n) time. Therefore, if the average laser output is set to be approximately equal for each laser irradiation unit, the noble metal tip 3
Combined with the reduced heat input time for 1 ',
The width of each section weld is made uniform. Further, by simultaneously irradiating the laser beam using the plurality of emission optical units as described above, the welding time can be shortened and the production efficiency can be improved.

For example, in FIG.
The welding portion corresponding to the first laser irradiation pulse P1 to P12 (all around laser welding portion 10 or section welding portion 200, 22)
The average laser output per second of 0) is P = Et
(J / pulse) × 10 (pulse / second) + Eh11 (J / pulse) × 1 (pulse / second) + Eh12 (J / pulse) × 1
(Pulse / second) = 1.25 × 10 + 1.0 × 1 + 0.7
5 × 1 = 14.25 (W). In the case of the conventional example shown in FIG. 10, since P = 1.25 (J / pulse) × 12 (pulses / sec) = 15 (W), energy of 0.75 W is saved per spark plug. be able to.

FIG. 8 shows the ignition section 32 on the ground electrode 4 side.
And the state of formation of the discharge surface 32a.
A laser welding portion 11 similar to the entire circumference is formed.
As shown in FIG. 9A, a side surface of the ground electrode 4 that is to face the spark discharge gap g (FIG. 1) is used as a chip fixing surface, and a concave portion 4a is formed here.
A noble metal tip 32 'is fitted and fixed in the device. In this state, as in FIG. 3 and the like, the entire circumference laser welded portion 11 is formed using the emission optical unit 50 of the laser irradiation unit 150.

In the above, the present invention has been described with reference to the embodiments. However, the present invention is not limited to the above embodiments, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof. Nor. For example, when adjusting the normal laser intensity St and the correction laser intensity Sh (adjustment of the normal irradiation energy Et and the correction irradiation energy Eh), FIGS. 4A, 6A, and 6B show. In the case described with reference to FIG. 4A, the tenth laser irradiation pulse P
Adjustment may be made to lower the laser irradiation energy for 10 to 1 pulse, or both the eleventh and twelfth laser irradiation pulses P11 and P12 may have the lowest laser irradiation energy (for one pulse). The laser irradiation energy may be adjusted so as to reduce the energy.

Further, in a unit weld portion formed by overlapping and overlapping, if the overlapping ratio of the unit weld portions is relatively small, the first first weld portion (that is, the most advanced weld portion) and the last last weld portion. The laser irradiation energy per pulse used to form at least one of the tail weld (that is, the tail weld) is determined by the laser irradiation energy per pulse used to form other unit welds. May be set lower to form a laser weld at the entire circumference.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an example of a spark plug manufactured by a method of the present invention and an enlarged view of a main part thereof.

FIG. 2 is an explanatory view showing one embodiment of the manufacturing method according to the present invention as a manufacturing process of a spark portion on the center electrode side of the spark plug.

FIG. 3 is an explanatory view of a laser irradiation unit.

FIG. 4 is a laser irradiation intensity diagram, an enlarged perspective view, a schematic plan view, and a vertical cross-sectional view of the center electrode tip of the spark plug.

FIG. 5 is an explanatory diagram showing a noble metal tip and a laser weld at the entire circumference developed in a circumferential direction.

FIG. 6 is a laser irradiation intensity diagram showing a modification of FIG. 4 (a).

FIG. 7 is a schematic plan view of a tip portion of a center electrode showing another embodiment of the manufacturing method according to the present invention.

FIG. 8 is a perspective view of a ground electrode side firing portion.

FIG. 9 is an explanatory view of the manufacturing process.

FIG. 10 is an explanatory view showing a problem of a conventional manufacturing method.

[Explanation of symbols]

3 center electrode 3s chip fixed surface 4 ground electrode 10, 11, 20, 30 whole circumference laser weld 200, 220, 300, 310, 320 section weld 10t, 200t, 220t, 300t, 310t, 3
20t Top welded part 10e, 200e, 220e, 300e, 310e, 3
20e Tail welding part 101-112, 201-212, 221-232, 3
01-308, 311-318, 321-328 Unit weld 31, 32 Noble metal firing part 31 ', 32' Noble metal tip 31a, 32a Discharge surface 40 Laser oscillation part 50 Emission optical part 70 Superposition assembly 100 Spark plug 150 Laser Irradiation unit LB pulsed laser light

Claims (10)

[Claims] 1. A spark discharge gap is formed by welding a noble metal tip to at least one of the center electrode and a ground electrode disposed opposite to the center electrode. A method of manufacturing a spark plug having a noble metal firing portion, wherein the noble metal tip is superimposed on a tip fixing surface of the center electrode and / or the ground electrode to form a superimposed assembly, By irradiating a pulsed laser beam from the emission optical unit of the laser irradiation unit to the joining assembly, in the circumferential direction of the noble metal chip, the noble metal chip and the chip fixing surface forming site are straddled, and each laser irradiation pulse A unit weld corresponding to is formed to form an all-around laser weld that is sequentially overlapped, and , Welds head portion so that the number of overlapping of the unit weld increases (hereinafter,
The laser irradiation energy per pulse (hereinafter referred to as “corrected irradiation energy”) used for forming at least one of the first welded portion and the last welded portion (hereinafter referred to as “last welded portion”) is used for other welding portions. Characterized in that the energy is set lower than the laser irradiation energy per pulse (hereinafter, referred to as normal irradiation energy) used in forming the spark plug. 2. The laser beam welding unit according to claim 1, wherein the laser welding unit is configured to rotate the superimposed assembly and the single emission optical unit relatively around a central axis of the superimposed assembly, and to control the pulse from the emission optical unit. 2. The method for manufacturing a spark plug according to claim 1, wherein the spark plug is formed by irradiating a laser beam. 3. The correction irradiation energy used when forming the tail welded portion in which the number of overlaps of the unit welded portion among the entire circumference laser welded portion is increased,
2. The method according to claim 1, wherein the energy is set lower than the normal irradiation energy.
Or the method of manufacturing a spark plug according to 2. 4. The laser irradiation energy per pulse is set to be lower from the laser irradiation pulse of the irradiation order that arrives before the laser irradiation pulse for forming the tail welding portion. 4. The method for producing a spark plug according to 3. 5. The laser irradiation energy per pulse used for forming the head welding portion in the entire laser welding portion is set substantially equal to the normal irradiation energy. Spark plug manufacturing method. 6. The laser welding section around the entire circumference, while relatively rotating the superimposed assembly and the plurality of emission optical sections around a central axis of the superimposed assembly, the plurality of emission optical sections are configured to rotate from the plurality of emission optical sections. By irradiating the pulsed laser light substantially in synchronization, the unit welds are sequentially overlapped and formed by a plurality of section welds corresponding to the number of the output optical sections, among the section welds, The correction irradiation energy used when forming at least one of the head weld and the tail weld where the number of overlaps of the unit weld is to be increased, the normal used when forming other welds The method for manufacturing a spark plug according to claim 1, wherein the energy is set lower than the irradiation energy. 7. The correction irradiation energy used for forming the tail welding portion in which the number of overlaps of the unit welding portion increases in the section welding portion is set lower than the normal irradiation energy. The method for producing a spark plug according to claim 6, wherein 8. The laser irradiation energy per one pulse is set to be lower from the laser irradiation pulse of the irradiation order that arrives before the laser irradiation pulse for forming the tail welding portion. A method for producing a spark plug according to claim 7. 9. The spark according to claim 7, wherein a laser irradiation energy per pulse used for forming the head weld in the section weld is set substantially equal to the normal irradiation energy. Plug manufacturing method. 10. The method for manufacturing a spark plug according to claim 6, wherein an average laser output required for forming the section welded portion is set substantially equal for each of the laser irradiation units.