JP2004095214A

JP2004095214A - Spark plug and manufacturing method for the same

Info

Publication number: JP2004095214A
Application number: JP2002251168A
Authority: JP
Inventors: Hideki Teramura; 寺村　英己; Mamoru Musasa; 無笹　守; Tomoaki Kato; 加藤　友聡
Original assignee: NGK Spark Plug Co Ltd
Current assignee: Niterra Co Ltd
Priority date: 2002-08-29
Filing date: 2002-08-29
Publication date: 2004-03-25
Anticipated expiration: 2022-08-29
Also published as: JP4070230B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark plug in which an Ir series precious metal anti-wear part is connected to a grounding electrode side by soldering and in which cracking or peeling hardly occurs in the precious metal anti-wear part. <P>SOLUTION: In the central axial line ○ direction of a central electrode, when a parallel beam is radiated toward a grounding electrode 4 from a sparks discharging gap side, the surface receiving the light of the parallel beam in an electrode base material 4m which has Ni as the main component to which the grounding electrode precious metal anti-wear part 32 is stuck is defined as a gap facing electrode surface SC and surfaces other than that are defined as gap non-facing electrode surface SS. Then, a through soldering part 40 in which each constituting metals of the electrode base body 4m and the ground electrode metal precious metal anti-wear part 32 are melted together in a form having a base end surface 40e is exposed on the gap non-facing electrode surface SS and having the tip part 40t reach the inside of the grounding electrode precious metal anti-wear part 32 by going through the electrode base body 4m from the base end surface 40e. Ir contained percentage in the through soldering part 40 is smaller than at the grounding electrode metal anti-wear part 32 and also more than 10 weight % and less than 50 weight %. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明はスパークプラグ及びスパークプラグの製造方法に関する。
【０００２】
【従来の技術】
内燃機関点火用のスパークプラグにおいては、耐火花消耗性向上のために電極の先端にＰｔやＩｒ等を主体とする貴金属チップを溶接して貴金属耐消耗部としたものが多数提案されている。特に、火花放電時に負極性に設定されることの多い中心電極側は、火花の強いアタックを受けて消耗しやすいことから、貴金属耐消耗部の使用の効果が特に大きい。
【０００３】
しかし、高出力エンジンあるいはリーンバーンエンジンへの適用が進むにつれ、接地電極側についても高い耐消耗性が求められるようになってきており、貴金属耐消耗部の採用が進みつつある。例えば、近年、コージェネレーションシステムやヒートポンプの普及に伴い、ガスエンジン用スパークプラグの需要が伸びている。これらの用途は、スパークプラグの使用条件がとりわけ厳しい点で際立っている。例えば、コージェネレーションシステムは工業用の電力あるいは熱源として活用されることが多く、システム停止が前提となるスパークプラグの交換は、可及的に行いたくないという要望がある。そのため、エンジンは基本的に２４時間稼動となり、１０００〜２０００時間もの間ノンストップで運転継続されるのが普通である。接地電極側の貴金属耐消耗部は、従来、主にＰｔ系金属により構成されたものが使用されていたが、このような厳しい使用環境で使用されるスパークプラグについては、接地電極の貴金属耐消耗部も高融点のＩｒ系金属にて構成したものが望まれている。
【０００４】
Ｐｔ系金属からなる貴金属耐消耗部は、ニッケル合金等からなる接地電極の母材に抵抗溶接により接合されている。しかし、Ｉｒ系金属からなる貴金属耐消耗部は、抵抗溶接による接合では、溶け不足等により接合界面が不健全となりやすく、前記したクラックや剥離等がより生じやすい問題がある。そこで、特開２００２−９３５４７号公報には、電極母材にＩｒ系金属チップをレーザー溶接により接合したスパークプラグが開示されている。具体的には、公報図２に等に開示されているように、Ｉｒ系金属チップを電極母材に形成した凹部に埋め込み配置し、その埋設部分に向けて、電極母材の外からレーザービーム照射することにより、電極母材を貫いてＩｒ系金属チップに到達する溶接部（以下、母材貫通溶接部という）が形成されている。このような溶接部は、抵抗溶接部と比較すれば接合強度の向上が期待できる。
【０００５】
【発明が解決しようとする課題】
しかしながら、上記のような母材貫通溶接部を形成する際には、以下のような問題が生ずる。例えば、中心電極の貴金属耐消耗部のように、電極母材先端面に貴金属チップを接合する場合は、チップと母材の境界にまたがるようにレーザービームを照射すれば、両部分の金属が比較的よく溶け合った均質な溶接部を比較的容易に形成できる。これに対し、上記公報のような母材貫通溶接部を形成する場合は、レーザービームは、初めは低融点の電極母材にのみに照射され、母材内の溶融部が照射深さ方向に進展して、貴金属チップに到達して漸く該貴金属チップの溶融が始まる。しかし、Ｎｉ系金属よりなる電極母材はＩｒ系貴金属チップよりも融点がはるかに低いため、通常の方法でレーザービームを照射すると電極母材ばかりが溶融し、貴金属チップ側の溶け不足による接合強度低下を招きやすい問題がある。また、貴金属チップに対して電極母材の溶融が進みすぎるので、得られる溶接部は電極母材側に偏った組成、すなわちＮｉ含有量の高い組成となりやすい。Ｉｒ系金属とＮｉ系金属とは線膨張係数の差が相当大きく、溶接後の冷却時に、貴金属耐消耗部のクラックや剥離を生じやすい問題がある。
【０００６】
本発明の課題は、接地電極側にＩｒ系貴金属耐消耗部が溶接により接合され、かつ、貴金属耐消耗部の界面にクラックや剥離を生じにくいスパークプラグと、その製造方法とを提供することにある。
【０００７】
【課題を解決するための手段及び作用・効果】
上記の課題を解決するために、本発明のスパークプラグは、
中心電極の先端面に、接地電極の周側面を対向させることにより火花放電ギャップが形成されてなり、かつ、接地電極の火花放電ギャップに臨む部位が、Ｉｒを主成分とする接地電極貴金属耐消耗部とされ、
火花放電ギャップの中心電極側から接地電極に向けて平行光線を照射したとき、接地電極貴金属耐消耗部が固着されるＮｉを主成分とする電極母材の、平行光線を受光する表面をギャップ対向電極表面、それ以外の表面をギャップ非対向電極表面と定義し、電極母材を貫いて、先端部が接地電極貴金属耐消耗部の内部に達するとともに、ギャップ非対向電極表面に基端面が露出する形で、それら電極母材と接地電極貴金属耐消耗部との各構成金属が互いに溶け合った母材貫通溶接部が形成されてなり、かつ、該母材貫通溶接部のＩｒ含有率が、接地電極貴金属耐消耗部よりも少なく、かつ１０質量％以上５０質量％以下とされてなることを特徴とする。なお、本明細書において「主成分」とは、最も質量含有率の高い成分をいう。
【０００８】
本発明のスパークプラグにおいては、接地電極側の電極母材を、Ｎｉを主成分とするＮｉ系金属にて構成し、接地電極側貴金属耐消耗部を、Ｉｒを主成分とするＩｒ系金属にて構成する。そして、この両者を接合するために、電極母材を貫通して接地電極貴金属耐消耗部に先端が到達する母材貫通溶接部を形成する。そして、該母材貫通溶接部のＩｒ含有率を、接地電極貴金属耐消耗部よりも低く、かつ、１０質量％以上５０質量％以下に設定する。
【０００９】
溶接部のＩｒ含有率を１０質量％以上５０質量％以下に設定することにより、溶接後の冷却時（あるいは、過酷な冷熱サイクルが加わる場合）に、貴金属耐消耗部のクラックや剥離を効果的に防止ないし抑制することができる。溶接部のＩｒ含有率を上記のように設定することで、溶接部の線膨張係数は、Ｎｉ系金属よりなる電極母材側、あるいはＩｒ系金属よりなる接地電極側貴金属耐消耗部側のいずれかに偏りすぎることなく、適度な中間の値を示すようになり、クラックや剥離の原因となる熱応力の発生が効果的に抑制されるためであると考えられる。また、貫通溶接部はギャップ非対向電極表面にのみ露出するから、溶接部が火花のアタックを受けて消耗する心配もない。
【００１０】
母材貫通溶接部は、Ｉｒ含有率が１０質量％未満になっても、５０質量％を超えても、いずれも前記したクラックや剥離の防止効果が顕著とならない。母材貫通溶接部のＩｒ含有率は、望ましくは１５質量％以上４０質量％以下、さらに望ましくは、２０質量％以上３０質量％以下とされているのがよい。
【００１１】
また、本発明のスパークプラグの製造方法は、上記本発明のスパークプラグを製造するために、
接地電極の電極母材の表面の、ギャップ対向電極表面として予定された領域に、Ｉｒを主成分とする貴金属チップ（以下、Ｉｒ系貴金属チップという）を重ね合わせ、ギャップ非対向電極表面からパルスレーザービームを照射することにより、該レーザー照射位置から電極母材を貫いて貴金属チップに到達させる形で、それら電極母材と接地電極貴金属耐消耗部との各構成金属が、Ｉｒ含有率が１０質量％以上５０質量％以下となるように互いに溶け合った母材貫通溶接部を形成することを特徴とする。
【００１２】
Ｉｒ系金属よりなる接地電極側貴金属耐消耗部は融点が高いため、電極母材側からこれを貫通する溶接部を形成しようとすると、既に説明した通り、通常の溶接条件では溶接部のＩｒ含有率が電極母材側の組成（一般にはＩｒをほとんど含有しない）に偏りやすい。従って、特開２００２−９３５４７号公報のような通常のレーザー溶接を用いると、本発明のように溶接部のＩｒ含有率を１０質量％以上とすることが事実上不可能だったのである。すなわち、溶接対象物の奥に位置するＩｒ系貴金属チップを十分溶融させようとして、高エネルギーのレーザービームを連続照射すると、電極母材の溶融が進みすぎる結果、Ｉｒ系貴金属チップの溶融量は相対的に減少する。他方、レーザービームのエネルギーが低すぎると、Ｉｒ系貴金属チップの溶融が不完全となる。いずれの場合も、溶接部のＩｒ含有率が不足することは明白である。
【００１３】
そこで、本発明のスパークプラグの製造方法においては、１つの溶接部を形成するのに、一箇所に連続的なレーザービームを照射するのではなく、パルス状のレーザービームを複数回断続照射することにより、上記の問題を解決することに成功した。パルスレーザービームは、照射深さ方向への熱集中効率が高く、断続照射を繰り返すことにより、照射位置周囲の電極母材部分への熱拡散を抑制しつつ、電極母材のさらに奥に位置するＩｒ系貴金属チップを効率的に溶融できる。その結果、母材貫通溶接部のＩｒ含有率を１０質量％以上に問題なく確保することができる。
【００１４】
なお、本明細書の特許請求の範囲において、各要件に付与した符号は、添付の図面の対応部分に付された符号を援用して用いたものであるが、あくまで発明の理解を容易にするために付与したものであり、本発明における各構成要件の概念を何ら限定するものではない。
【００１５】
【発明の実施の形態】
以下、本発明の実施の形態を、図面を用いて説明する。図１に示す本発明の一例たるスパークプラグ１００は、筒状の主体金具１、先端部２１が突出するようにその主体金具１の内側に嵌め込まれた絶縁体２、先端に設けられた中心電極貴金属耐消耗部３１を突出させる形で絶縁体２の内側に設けられた中心電極３、及び主体金具１に一端が溶接等により結合されるとともに他端側が側方に曲げ返されて、その周側面が中心電極３の先端部と対向するように配置された接地電極４等を備えている。また、接地電極４には、上記中心電極貴金属耐消耗部３１に対向する接地電極貴金属耐消耗部３２が形成されており、それら中心電極貴金属耐消耗部３１と、対向する接地電極貴金属耐消耗部３２との間の隙間が火花放電ギャップｇとされている。なお本明細書でいう「耐消耗部」とは、接合された貴金属チップのうち、溶接による組成変動の影響を受けていない部分（例えば、溶接により接地電極ないし中心電極の材料と合金化した部分を除く残余の部分）を指すものとする。
【００１６】
絶縁体２は、例えばアルミナあるいは窒化アルミニウム等のセラミック焼結体により構成され、その内部には自身の軸方向に沿って中心電極３及び端子金具８を嵌め込むための孔部６を有している。また、主体金具１は、低炭素鋼等の金属により円筒状に形成されており、スパークプラグ１００のハウジングを構成するとともに、その外周面には、プラグ１００を図示しないエンジンブロックに取り付けるためのねじ部７が形成されている。
【００１７】
他方、中心電極３及び接地電極４の電極母材３ｍ，４ｍは、インコネル６００（商標名）等のＮｉ合金にて構成されている。一方、上記中心電極貴金属耐消耗部３１及び対向する接地電極貴金属耐消耗部３２は、Ｉｒを主成分とする貴金属を主体に構成されている。具体的には、Ｉｒ−Ｒｕ合金（例えばＩｒ−１〜３０質量％Ｒｕ合金）、Ｉｒ−Ｐｔ合金（例えばＩｒ−１〜１０質量％Ｐｔ合金）、Ｉｒ−Ｒｈ合金（例えばＩｒ−５〜２５質量％Ｒｈ合金）、Ｉｒ−Ｒｈ−Ｎｉ合金（例えば、Ｉｒ−１〜４０質量％Ｒｈ−０．５〜８質量％Ｎｉ合金）等を使用できる。なお、Ｉｒ系の貴金属材料を使用する場合には、元素周期律表の３Ａ族（いわゆる希土類元素）及び４Ａ族（Ｔｉ、Ｚｒ、Ｈｆ）に属する金属元素の酸化物（複合酸化物を含む）を０．１〜１５質量％の範囲内で含有させることができる。これにより、Ｉｒ成分の酸化・揮発を効果的に抑制でき、ひいては耐消耗部の耐火花消耗性を向上させることができる。上記酸化物としてはＹ_２Ｏ_３が好適に使用されるが、このほかにもＬａ_２Ｏ_３、ＴｈＯ_２、ＺｒＯ_２等を好ましく使用することができる。この場合、金属成分はＩｒ合金のほか、Ｉｒ単体を使用してもよい。
【００１８】
中心電極３は、先端側が縮径されるとともに、その先端面に上記中心電極貴金属耐消耗部３１を構成する合金組成からなる円板状の貴金属チップを重ね合わせ、その接合面外縁部に沿ってレーザー溶接することにより形成されたものである。そして、中心電極３の中心軸線Ｏ方向において、火花放電ギャップｇ側から接地電極４に向けて平行光線を照射したとき、接地電極貴金属耐消耗部３２が固着される電極母材４ｍの、平行光線を受光する表面（光の回折は生じないと仮定する）を、ギャップ対向電極表面ＳＣとし、それ以外の表面をギャップ非対向電極表面として定義する。図２に示すように、接地電極貴金属耐消耗部３２は母材貫通溶接部４０により電極母材４ｍに接合されている。該母材貫通溶接部４０は、ギャップ非対向電極表面ＳＳに基端面４０ｅが露出し、該基端面４０ｅから電極母材４ｍを貫いて、先端部４０ｔが接地電極貴金属耐消耗部３２の内部に達する形で、それら電極母材４ｍと接地電極貴金属耐消耗部３２との各構成金属が互いに溶け合ったものとして形成されている。そして、母材貫通溶接部４０のＩｒ含有率は、接地電極貴金属耐消耗部３２よりも少なく、かつ１０質量％以上５０質量％以下（望ましくは１５質量％以上４０質量％以下、さらに望ましくは、２０質量％以上３０質量％以下）である。なお、平行光線の照射方法については、上述したように、図１に示すような接地電極４の側面が中心電極３の先端面と対向する、いわゆる平行接地電極タイプのスパークプラグの場合には、中心軸線Ｏ方向において平行光線を照射するものと考える。その他のタイプのスパークプラグについては、中心電極と接地電極との最短距離を示す仮想線と平行に、火花放電ギャップｇ側から接地電極に向けて平行光線を照射すればよい。
【００１９】
接地電極貴金属耐消耗部３２は、以下のようにして形成できる。図１１に示すように、電極母材４ｍの表面のギャップ対向電極表面ＳＣとして予定された領域に、Ｉｒ系貴金属チップ３２’を重ね合わせる。そして、ギャップ非対向電極表面ＳＳからパルスレーザービームＬＢを照射する。レーザービームＬＢは、最初は電極母材４ｍのみに照射され、照射深さ方向にＮｉ系金属の溶融部を生ずる。この溶融部が深さ方向に進展して貴金属チップ３２’に到達すると、Ｉｒ系貴金属チップ３２’の溶融が始まり、溶融部にＩｒ系金属が溶け込む。パルスレーザービームＬＢは、照射深さ方向への熱集中効率が高いが、１回のパルス照射のみでは十分な溶接部を形成できない。そこで、図１２に示すように、適当なピークパワーＥ_Ｌ及びパルス幅τ１を有するレーザーパルスを同一箇所に複数回照射することにより、レーザー照射方向を法線とする面内の溶融部の拡張を抑制しつつ、溶融部の形成を段階的に深くすることができる。その結果、溶融部がＩｒ系貴金属チップ３２’に到達した後は、該Ｉｒ系貴金属チップ３２’にレーザーエネルギーを効率的に集中でき、Ｉｒ系貴金属チップ３２’の溶融を促進することができる。つまり、照射位置周囲の電極母材４ｍの過度の溶融を抑制しつつ、該電極母材４ｍのさらに奥に位置するＩｒ系貴金属チップ３２’を効率的に溶融でき、得られる貫通溶接部４０のＩｒ含有率を効果的に高めることができる。
【００２０】
各照射位置におけるパルス照射回数及びピークパワーＥ_Ｌを同じに設定する場合、パルス幅τ１を大きくすると、電極母材の溶融が進みやすくなり、母材貫通溶接部４０のＩｒ含有率が小さくなる傾向となる。他方、ピークパワーＥ_Ｌを大きくすると、これとは逆の傾向となる。
【００２１】
図２に示すように、母材貫通溶接部４０は、深さ方向（つまりレーザービームＬＢの照射方向）と直交する断面積が、電極母材４ｍ側にて大きく、接地電極側貴金属耐消耗部３２内に位置する先端部４０ｔ側にて小さくなるように形成される。そして、母材貫通溶接部４０は、上記の軸断面積が、電極母材４ｍと接地電極側貴金属耐消耗部３２との境界位置にて階段状に変化するように形成されることが、電極母材４ｍと接地電極側貴金属耐消耗部３２とを適度な混合比率にて溶融させ、前記Ｉｒ組成範囲を充足する母材貫通溶接部４０を得る上で望ましい。すなわち、電極母材４ｍ側に溶融部を多少広く形成しておけば、Ｉｒ系貴金属チップ３２’との接触面中央に、該溶融部との接触により比較的高温に昇温された領域を広く確保することができる。そして、該準領域の中央にレーザービームＬＢを照射すれば、高融点のＩｒ系貴金属チップ３２’の溶融を効果的に促進することができる。
【００２２】
なお、パルスレーザービームＬＢを用いた母材貫通溶接部４０の形成は、希ガス（例えばアルゴンガス）や窒素ガス等の不活性ガス雰囲気中にて行なうことが、電極母材４ｍをなすＮｉ合金の過度の溶融を抑制して、得られる母材貫通溶接部４０のＩｒ含有率を高める上で望ましい。電極母材４ｍをなすＮｉ合金は、大気中で溶融すると酸化される。Ｎｉ金属が酸化される反応は発熱反応であり、Ｎｉ酸化物の生成が著しくなると、その反応熱により温度上昇がさらに著しくなり、電極母材４ｍの溶融が助長される。しかし、不活性ガス雰囲気中では該酸化反応が抑制される分だけ、反応熱による温度上昇も起こりにくく、電極母材４ｍの過度の溶融、ひいては母材貫通溶接部４０のＩｒ含有率の低下を抑制することができる。本実施形態では、Ａｒガスを流通したチャンバー８０内にて溶接を行なう例を示しているが、開放雰囲気中にてＡｒガスの吹き付けにより被溶接部の周囲をシールドして溶接を行なうこともできる。特に後者の方法では、Ａｒガスが空気よりも比重が多少大きいため、シールドを行ないやすい利点がある。
【００２３】
接地電極貴金属耐消耗部３２の外径Ｄは、０．３ｍｍ以上２ｍｍ以下とすることが望ましい。Ｄが０．３ｍｍ　未満では耐消耗性が不十分となり、２ｍｍを超えると着火性が悪化することにつながる。
【００２４】
次に、図２に示すように、接地電極貴金属耐消耗部３２は、中心電極３の中心軸線Ｏ方向において少なくとも一部を、電極母材４ｍ中に埋設された埋設部３２ｖとすることができる。母材貫通溶接部４０は、その先端部４０ｔが埋設部３２ｖの内部に達するように形成することができる。接地電極貴金属耐消耗部３２の一部を電極母材４ｍ中に埋設することにより、接地電極貴金属耐消耗部３２と電極母材４ｍとの接合強度を高めることができ、ひいては、接地電極貴金属耐消耗部３２の剥離やクラック発生がさらに生じにくくなる。また、電極母材４ｍとの接触面積が増加するので、接地電極貴金属耐消耗部３２の熱引きが進みやすく、ひいては耐消耗性が向上する利点もある。
【００２５】
上記のような埋設形態の接地電極貴金属耐消耗部３２は、図１１に示す工程にて形成することができる。すなわち、Ｉｒ系貴金属チップ３２’に対応する形状の凹部４ｋを電極母材４ｍに形成し、ここにＩｒ系貴金属チップ３２’をはめ込む。そして、該凹部４ｋ内にＩｒ系貴金属チップ３２’を位置決めしつつ、電極母材４ｍ側からレーザービームＬＢを照射して母材貫通溶接部を形成する。このような凹部４ｋを形成することで、溶接中のＩｒ系貴金属チップ３２’の位置ずれが生じにくくなり、良好な母材貫通溶接部を容易に得ることができる。
【００２６】
図１３に示すように、電極母材４ｍに形成する凹部４ｋは、Ｉｒ系貴金属チップ３２’の挿入軸断面形状に対応する開口形状を有したものとして形成される（本実施形態では円状：例えば、ドリリングやレーザー穿孔を用いることができる）。ここで、Ｉｒ系貴金属チップ３２’の挿入を容易とするためには、凹部４ｋの内径をＩｒ系貴金属チップ３２’の外径よりも少し大きく形成しておけばよい。このとき、凹部４ｋの内周面とＩｒ系貴金属チップ３２’の外周面との間には、隙間４ｇが形成される。そして、パルスレーザービームＬＢの照射により母材貫通溶接部４０を形成すると、母材貫通溶接部４０の形成に伴い発生する溶融金属により、隙間４ｇの少なくとも一部を充填され、隙間充填金属部４０ｆが形成される。この結果、中心電極３の中心軸線Ｏ周りにおいて、接地電極貴金属耐消耗部３２の埋設部３２ｖの外周面と電極母材との間に、外周面の周方向の少なくとも一部区間に沿うように、母材貫通溶接部４０と一体の隙間充填金属部４０ｆが形成された構造が得られる。
【００２７】
上記隙間充填金属部４０ｆは、接地電極貴金属耐消耗部３２の接合強度向上に寄与するほか、スパークプラグ使用時には、接地電極貴金属耐消耗部３２から電極母材４ｍへの熱伝導を促進し、接地電極貴金属耐消耗部３２の温度上昇抑制ひいては耐消耗性向上に寄与する。また、隙間充填金属部４０ｆは電極母材４ｍと接地電極貴金属耐消耗部３２との中間の組成を有し、接地電極貴金属耐消耗部３２を周方向に取り囲むように形成されることから、接地電極貴金属耐消耗部３２の半径方向の熱応力を緩和する効果が高く、ひいては接地電極貴金属耐消耗部３２の耐剥離性がより向上する。
【００２８】
隙間充填金属部４０ｆは、上記の効果をより顕著なものとするために、隙間４ｇの周方向のなるべく多くの区間に形成されることが望ましい。そのためには、前述のように、母材貫通溶接部４０の軸断面積が、電極母材４ｍと接地電極側貴金属耐消耗部３２との境界位置にて階段状に変化するように形成されること、すなわち、パルスレーザービームＬＢを用いた溶接時に、電極母材４ｍ側に溶融部をある程度広く形成して、一種の溶融金属溜めを形成することが有効である。このようにすると、Ｉｒ系貴金属チップ３２’の外周面が、隙間４ｇを充填した溶融金属と、周方向の比較的長い区間にわたって接触し、その保温効果によりＩｒ系貴金属チップ３２’の昇温が促進されて、母材貫通溶接部４０へのＩｒの溶け込み量を増加させることができる。なお、隙間４ｇの幅δ（母材貫通溶接部４０の幅にも相当する）は０．０１ｍｍ以上０．１５ｍｍ以下に調整するのがよい。幅δが０．１５ｍｍを超えると母材貫通溶接部４０の形成が困難となり、０．０１ｍｍ未満になると、凹部４ｋへのＩｒ系貴金属チップ３２’の挿入作業が面倒になる。
【００２９】
母材貫通溶接部は、例えば図３あるいは図４及び図５に示すように、１つのみ設ける構成とすることができる。母材貫通溶接部の形成個数が少なければ、それだけ工程も簡略化され、製造能率を高めることができる。しかし、接地電極側貴金属耐消耗部３２の接合強度をより高レベルに確保したい場合は、図２、図６、図７、図８、図９及び図１０に示すように、母材貫通溶接部４０，４１は、中心軸線Ｏの周りに複数個設けることが有効である。この場合、周方向の母材貫通溶接部の形成個数が増える分だけ、隙間充填金属部４０ｆの合計形成区間長も増加し、接地電極貴金属耐消耗部３２の接合強度向上効果と、温度上昇抑制効果をさらに高めることができる。
【００３０】
なお、接地電極４のギャップ対向電極表面ＳＣの幅は、一般には２．０ｍｍ以上３．５ｍｍ以下に調整される。他方、着火性を高めるためには、図２、図３あるいは図７のように、中心軸線Ｏの周りに複数個の母材貫通溶接部を設ける場合は、接地電極貴金属耐消耗部３２の外径Ｄを小さく設定することが望ましい。この場合、接地電極貴金属耐消耗部３２の外径Ｄが過度に小さくなると、いくつかの母材貫通溶接部の深さが大きくなりすぎ、Ｉｒ系貴金属チップ３２’の溶融が不十分となる場合がある。この観点において、Ｉｒ系貴金属チップ３２’ひいては接地電極貴金属耐消耗部３２の外径Ｄは、図８、図９あるいは図１０に示すように、多少大きめに調整すること、例えば１ｍｍ以上２ｍｍ以下に調整することが望ましい。これにより、極度に深い母材貫通溶接部が生じにくくなり、ひいては母材貫通溶接部のＩｒ含有率を本願発明の範囲に調整しやすくなる。
【００３１】
母材貫通溶接部の形成形態は、ギャップ非対向電極表面のどこにパルスレーザービームを照射するかによって、種々の態様が可能である。図２においては、母材貫通溶接部４０は、ギャップ対向電極表面ＳＣの幅方向Ｗの少なくとも一方の側において、該ギャップ対向電極表面ＳＣの端縁ＬＥに連なる電極母材４ｍの側面領域ＳＳに、母材貫通溶接部４０の基端面４０ｅが露出するように形成されている。本明細書において、接地電極４の幅方向Ｗは、以下のように定義する。図１に示すように、すなわち、中心軸線Ｏ方向において、主体金具１の、接地電極４が接合されている端面から１ｍｍ隔たった位置にて、中心軸線Ｏと直交する平面Ｐ２にて切断したときの、接地電極４の断面の幾何学的重心位置をＫとする。そして、該位置Ｋを通り、かつ、中心軸線Ｏと直交する基準方向Ｆを定め、中心軸線Ｏと基準方向Ｆとの双方と直交する向きを、接地電極４のギャップ対向電極表面ＳＣの幅方向Ｗと定義する。側面領域ＳＳは幅方向Ｗの両側に生ずるので、図２にように、各ギャップ対向電極表面ＳＣに１つ、計２つの母材貫通溶接部４０を少なくとも形成することができ、接地電極側貴金属耐消耗部３２の接合強度向上に有効である。
【００３２】
また、図３に示すように、基端面４１ｅを接地電極４の先端面ＳＴに露出させた母材貫通溶接部４１を形成することもできる。特に、着火性向上効果を優先するために、接地電極貴金属耐消耗部３２の外径Ｄを小さく設定する場合、ギャップ対向電極表面ＳＣにおいて、接地電極貴金属耐消耗部３２の外周縁から接地電極４の先端側の端縁ＴＥまでの距離をｔ２、同じく幅方向Ｗの端縁ＬＥまでの距離ｔ１としたとき、ｔ２がｔ１よりも小さく設定することができる。これにより、先端面ＳＴ側から形成する母材貫通溶接部４１の溶接深さを小さくすることができ、ひいては母材貫通溶接部４１のＩｒ含有率を本願発明の範囲に調整しやすくなる。外径Ｄを例えば０．３ｍｍ以上１ｍｍ以下に設定する場合、ｔ１を０．５ｍｍ以上１．５ｍｍ以下、ｔ２を０．３ｍｍ以上１．０ｍｍ以下に設定することが望ましい。
【００３３】
また、図４に示すように、中心軸線Ｏ方向において、電極母材４ｍのギャップ対向電極表面ＳＣと反対側の面ＳＢに基端面４２ｅが露出するように、母材貫通溶接部４２を形成することもできる。この態様は、例えば埋設部３２ｖの埋設深さ（つまり、図１１の凹部４ｋの深さ）の調整により、接地電極貴金属耐消耗部３２の外径Ｄに関係なく、母材貫通溶接部４１の溶接深さを削減できる利点がある。また、電極母材４ｍの厚さが比較的薄い場合は、図５に示すように、凹部を形成せずにＩｒ系貴金属チップを電極母材４ｍに重ねて溶接すること、つまり、埋設部３２ｖを省略することも可能である。
【００３４】
また、図６、図９及び図１０においては、電極母材４ｍの先端角部にテーパ面４ｊを形成した電極母材４ｍの幅を減少させ、そのテーパ面に基端面４０ｅが露出するように、母材貫通溶接部４０を形成している。図６では、接地電極貴金属耐消耗部３２の外径Ｄが小さく（例えば０．３ｍｍ以上１ｍｍ以下）設定されているが、テーパ面４ｊにより、形成される母材貫通溶接部４０の深さを縮小することができる。また、中心軸線Ｏの周りに複数個の母材貫通溶接部を形成する場合は、例えば、図７あるいは図８に示すように、２つの側面領域ＳＳと先端面ＳＴとのそれぞれから溶接を行なうことにより、３つの母材貫通溶接部４０，４１は比較的容易に形成できる。しかし、さらに多くの母材貫通溶接部が必要な場合は、図９あるいは図１０に示すように、テーパ面４ｊを設けることにより、溶接深さの比較的小さい母材貫通溶接部４０を、電極母材４ｍの先端角部に比較的容易に増設することが可能となる。
【００３５】
【実施例】
本発明の効果確認のために、以下の実験を行なった。
図１に示すスパークプラグ１００（母材貫通溶接部の形成形態は図８）の種々の試験品を以下のようにして準備した。すなわち、Ｉｒ−５質量％Ｐｔ合金により、図１１に示すＩｒ系貴金属チップ３２’を、厚さが１．０ｍｍ、直径Ｄが１．８ｍｍとなるように作製した。これを用いてインコネル６００よりなる電極母材４ｍに、図１１の工程に従い溶接した。なお、電極母材４ｍには切削（エンドミル）により深さ０．５ｍｍ、内径１．８５ｍｍの凹部４ｋを形成した（なお、隙間４ｇの幅δは０．２５ｍｍである）。また、溶接は、アルゴンガスの吹き付けによるアルゴン雰囲気中にて、ＹＡＧレーザー光源により、表１に示す種々のピークパワー及びパルス幅を有するレーザービームを、各溶接部に３パルス照射して行なった。そして、溶接により得られた接地電極貴金属耐消耗部３２を周辺部分とともに切断し、溶接部の平均的なＩｒ含有率をＥＰＭＡ面分析により測定した。その結果、表１に示すように、溶接条件によりＩｒ含有率が５〜５５質量％の範囲にて変動していることがわかった。
【００３６】
【表１】

【００３７】
他方、中心電極貴金属耐消耗部３１は、Ｉｒ−２０質量％Ｒｈ合金からなる直径１．２ｍｍ、高さ０．８ｍｍの貴金属チップを、インコネル６００よりなる中心電極３の先端面にレーザー溶接することにより形成した。図１５は、表１の番号４の試験品における接地電極貴金属耐消耗部３２の断面光学顕微鏡観察画像である（図中、黒っぽく表れている楔状の領域が母材貫通溶接部である）。いずれの母材貫通溶接部も、先端部が接地電極貴金属耐消耗部３２の内部に達している。また、母材貫通溶接部の軸断面積（あるいは母材貫通溶接部の幅）は、深さ方向において、電極母材と接地電極側貴金属耐消耗部との境界位置にて階段状（つまり不連続）に変化している。さらに、凹部の内周面と接地電極側貴金属耐消耗部の外周面との間には隙間が形成され、ここに溶接金属が略全周にわたって充填されている。
【００３８】
そして、それら接地電極４及び中心電極３を用いて、図１に示すスパークプラグ１００を、火花放電ギャップｇのギャップ長Ｇが０．８ｍｍとなるように組立てた（接地電極貴金属耐消耗部３２の各組成毎に１０個ずつ）。そして、該スパークプラグを試験用エンジン（６気筒、総排気量２０００ｃｃ）に取り付け、スロットル全開、エンジン回転数５０００ｒｐｍにて１分運転した後、エンジン回転数７００ｒｐｍにて１分アイドリングするサイクルを１００時間繰り返す冷熱サイクル試験を行った。そして、試験後、接地電極貴金属耐消耗部３２に剥離を生じたスパークプラグの個数から、剥離率を求めた。図１４にその結果を示す。これにより、母材貫通溶接部のＩｒ含有率を１０質量％以上５０質量％未満とすることにより、接地電極貴金属耐消耗部３２の剥離が効果的に抑制されていることがわかる。
【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２】接地電極貴金属耐消耗部に対する母材貫通溶接部の形成形態の第１例の説明図。
【図３】同じく第２例の説明図。
【図４】同じく第３例の説明図。
【図５】同じく第４例の説明図。
【図６】同じく第５例の説明図。
【図７】同じく第６例の説明図。
【図８】同じく第７例の説明図。
【図９】同じく第８例の説明図。
【図１０】同じく第９例の説明図。
【図１１】母材貫通溶接部の形成工程の説明図。
【図１２】パルスレーザービームの波形を模式的に示す図／
【図１３】隙間充填金属部の形成過程を説明する図。
【図１４】冷熱サイクルテストの試験結果を示すグラフ。
【図１５】表１の番号４の接地電極貴金属耐消耗部の断面光学顕微鏡観察画像。
【符号の説明】
３　中心電極
４　接地電極
４ｍ　電極母材
ｇ　火花放電ギャップ
３２　接地電極貴金属耐消耗部
３２ｖ　埋設部
ＳＣ　ギャップ対向電極表面
ＳＳ，ＳＴ，ＳＢ　ギャップ非対向電極表面
ＳＳ　側面領域
ＳＴ　先端面
４０ｅ，４１ｅ，４２ｅ　基端面
４０ｔ，４１ｔ，４２ｔ　先端部
４０，４１，４２　母材貫通溶接部
ＬＢ　パルスレーザービーム[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a spark plug and a method for manufacturing a spark plug.
[0002]
[Prior art]
Many spark plugs for ignition of an internal combustion engine have been proposed in which a noble metal tip mainly composed of Pt, Ir, or the like is welded to the tip of an electrode to form a noble metal wear-resistant portion in order to improve spark wear resistance. In particular, the use of the noble metal wear-resistant portion is particularly effective because the center electrode, which is often set to a negative polarity during spark discharge, is likely to be consumed due to a strong attack of the spark.
[0003]
However, as the application to a high-output engine or a lean-burn engine progresses, high wear resistance is required also on the ground electrode side, and the adoption of a noble metal wear-resistant portion is progressing. For example, in recent years, with the spread of cogeneration systems and heat pumps, demand for spark plugs for gas engines has increased. These applications are distinguished by the particularly harsh conditions of use of the spark plug. For example, a cogeneration system is often used as industrial power or a heat source, and there is a demand that it is not desirable to replace a spark plug on the premise of stopping the system as much as possible. Therefore, the engine is basically operated for 24 hours, and is usually operated non-stop for 1000 to 2000 hours. Conventionally, the noble metal wear resistant portion on the ground electrode side is mainly composed of a Pt-based metal. However, for a spark plug used in such a severe use environment, the noble metal wear resistant portion of the ground electrode is used. It is desired that the portion is also made of a high melting point Ir-based metal.
[0004]
The noble metal wear-resistant portion made of a Pt-based metal is joined by resistance welding to a base material of a ground electrode made of a nickel alloy or the like. However, the noble metal wear-resistant portion made of an Ir-based metal has a problem that the joining interface is apt to be unhealthy due to insufficient melting or the like in joining by resistance welding, and the above-mentioned cracks and peeling are more likely to occur. Therefore, Japanese Patent Application Laid-Open No. 2002-93547 discloses a spark plug in which an Ir-based metal tip is joined to an electrode base material by laser welding. More specifically, as disclosed in FIG. 2 and the like, an Ir-based metal chip is buried in a recess formed in an electrode base material, and a laser beam is applied from outside the electrode base material toward the buried portion. Irradiation forms a welded portion that penetrates the electrode base material and reaches the Ir-based metal tip (hereinafter referred to as a base material penetration welded portion). Such a welded portion can be expected to have improved bonding strength as compared with a resistance welded portion.
[0005]
[Problems to be solved by the invention]
However, the following problems occur when forming the base metal penetration weld as described above. For example, when joining a noble metal tip to the tip surface of the electrode base material, such as the noble metal wear-resistant part of the center electrode, irradiate the laser beam across the boundary between the tip and the base material and compare the metals in both parts. A well welded homogeneous weld can be formed relatively easily. In contrast, when forming a base metal penetration weld as in the above publication, the laser beam is initially irradiated only on the electrode base material having a low melting point, and the molten portion in the base material is irradiated in the irradiation depth direction. As it progresses and reaches the noble metal tip, melting of the noble metal tip begins. However, since the electrode base material made of Ni-based metal has a much lower melting point than the Ir-based noble metal tip, when the laser beam is irradiated in the usual way, only the electrode base material is melted, and the bonding strength due to insufficient melting of the noble metal tip side. There is a problem that is likely to cause a decrease. Further, since the melting of the electrode base material proceeds too much with respect to the noble metal tip, the resulting welded portion tends to have a composition biased toward the electrode base material, that is, a composition having a high Ni content. The difference in linear expansion coefficient between the Ir-based metal and the Ni-based metal is considerably large, and there is a problem that cracks and peeling of the noble metal wear-resistant portion easily occur during cooling after welding.
[0006]
An object of the present invention is to provide a spark plug in which an Ir-based noble metal wear-resistant portion is joined to a ground electrode by welding, and a crack or peeling is not easily generated at an interface of the noble metal wear-resistant portion, and a method of manufacturing the same. is there.
[0007]
[Means for Solving the Problems and Functions / Effects]
In order to solve the above problems, the spark plug of the present invention
A spark discharge gap is formed by opposing the peripheral side surface of the ground electrode to the front end surface of the center electrode, and the portion of the ground electrode facing the spark discharge gap is a ground electrode precious metal wear resistant mainly composed of Ir. Department and
When a parallel light beam is radiated from the center electrode side of the spark discharge gap toward the ground electrode, the surface of the electrode base material mainly composed of Ni, to which the noble metal wear-resistant portion is fixed, which receives the parallel light beam, faces the gap. The electrode surface and the other surface are defined as the gap non-facing electrode surface, penetrate the electrode base material, the tip reaches the inside of the ground electrode noble metal wear-resistant part, and the base end surface is exposed on the gap non-facing electrode surface In the form, a base metal through-welded portion in which the constituent metals of the electrode base material and the ground electrode noble metal wear-resistant portion are mutually melted is formed, and the Ir content rate of the base-material through-welded portion is equal to that of the ground electrode. It is characterized in that it is less than the noble metal wear-resistant portion and is not less than 10% by mass and not more than 50% by mass. In this specification, the “main component” refers to a component having the highest mass content.
[0008]
In the spark plug of the present invention, the electrode base material on the ground electrode side is made of a Ni-based metal mainly containing Ni, and the ground electrode-side noble metal wear-resistant portion is made of an Ir-based metal mainly containing Ir. Configure. Then, in order to join the two, a base metal penetrating weld is formed, which penetrates the electrode base metal and reaches the end to the ground electrode noble metal wear-resistant part. Then, the Ir content of the base metal penetration weld is set to be lower than that of the ground electrode noble metal wear-resistant portion and to be 10% by mass or more and 50% by mass or less.
[0009]
By setting the Ir content of the welded portion to 10% by mass or more and 50% by mass or less, it is possible to effectively prevent cracking and peeling of the noble metal wear-resistant portion during cooling after welding (or when a severe cooling / heating cycle is applied). Can be prevented or suppressed. By setting the Ir content of the welded portion as described above, the coefficient of linear expansion of the welded portion can be either the electrode base material side made of a Ni-based metal or the ground electrode side made of an Ir-based metal or the noble metal wear-resistant portion side. This is considered to be due to the fact that an appropriate intermediate value is shown without being excessively biased, and the generation of thermal stress which causes cracks and peeling is effectively suppressed. In addition, since the through-welded portion is exposed only on the surface of the non-gap electrode, there is no fear that the welded portion is consumed by the attack of the spark.
[0010]
Regardless of whether the Ir content of the base metal through-welded portion is less than 10% by mass or more than 50% by mass, the above-described effect of preventing cracking and peeling is not remarkable. The Ir content of the base metal through-welded portion is desirably 15% by mass or more and 40% by mass or less, and more desirably 20% by mass or more and 30% by mass or less.
[0011]
In addition, the method for manufacturing a spark plug of the present invention includes the steps of:
A noble metal tip containing Ir as a main component (hereinafter referred to as an Ir-based noble metal tip) is superimposed on a region of the surface of the electrode base material of the ground electrode, which is to be a gap-facing electrode surface, and a pulse laser is applied from the surface of the non-gap electrode. By irradiating the laser beam, the constituent metals of the electrode base material and the ground electrode noble metal wear-resistant portion have an Ir content of 10% by mass so as to reach the noble metal tip through the electrode base material from the laser irradiation position. % To 50% by mass or less.
[0012]
Since the ground electrode-side noble metal wear-resistant portion made of an Ir-based metal has a high melting point, if an attempt is made to form a welded portion that penetrates from the electrode base material side, as described above, under normal welding conditions, the Ir-containing portion of the welded portion will be used. The ratio tends to be biased toward the composition on the electrode base material side (generally containing almost no Ir). Therefore, when ordinary laser welding as disclosed in JP-A-2002-93547 is used, it was practically impossible to make the Ir content of the welded portion 10% by mass or more as in the present invention. That is, when a high-energy laser beam is continuously irradiated to sufficiently melt the Ir-based noble metal tip located deep in the welding target, the melting of the Ir-based noble metal tip is relatively advanced as a result of excessive melting of the electrode base material. Decrease. On the other hand, if the energy of the laser beam is too low, the melting of the Ir-based noble metal tip becomes incomplete. In each case, it is clear that the Ir content of the weld is insufficient.
[0013]
Therefore, in the spark plug manufacturing method of the present invention, a pulsed laser beam is intermittently irradiated a plurality of times instead of irradiating a continuous laser beam to one place to form one welded portion. As a result, the above problem was successfully solved. The pulsed laser beam has a high heat concentration efficiency in the irradiation depth direction, and is located further inside the electrode base material while suppressing heat diffusion to the electrode base material part around the irradiation position by repeating intermittent irradiation. The Ir-based noble metal tip can be efficiently melted. As a result, the Ir content of the base metal penetration welded portion can be secured to 10% by mass or more without any problem.
[0014]
In addition, in the claims of the present specification, reference numerals given to respective requirements are used with the aid of reference numerals attached to corresponding parts in the attached drawings, but they are used to facilitate understanding of the invention. Therefore, the concept of each component in the present invention is not limited at all.
[0015]
BEST MODE FOR CARRYING OUT 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 has a cylindrical metal shell 1, an insulator 2 fitted inside the metal shell 1 so that a tip 21 protrudes, and a center electrode provided 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 so that the noble metal wear-resistant portion 31 projects, and the other end is bent back to the side. A ground electrode 4 and the like are disposed such that the side faces the tip of the center electrode 3. The ground electrode 4 is provided with a ground electrode noble metal wear-resistant portion 32 facing the center electrode noble metal wear-resistant portion 31. The center electrode noble metal wear-resistant portion 31 and the opposite ground electrode noble metal wear-resistant portion are provided. 32 is defined as a spark discharge gap g. In this specification, the “consumable portion” refers to a portion of the joined noble metal tip that is not affected by the composition change due to welding (for example, a portion that is alloyed with the material of the ground electrode or the center electrode by welding). (The remaining part excluding).
[0016]
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. I have. The metal shell 1 is formed of a metal such as low-carbon steel in a cylindrical shape, constitutes a housing of the spark plug 100, and has, on its outer peripheral surface, a screw for attaching the plug 100 to an engine block (not shown). A part 7 is formed.
[0017]
On the other hand, the electrode base materials 3m and 4m of the center electrode 3 and the ground electrode 4 are made of a Ni alloy such as Inconel 600 (trade name). On the other hand, the center electrode noble metal wear-resistant portion 31 and the opposing ground electrode noble metal wear-resistant portion 32 are mainly composed of a noble metal mainly composed of Ir. Specifically, an Ir-Ru alloy (for example, Ir-1 to 30% by mass Ru alloy), an Ir-Pt alloy (for example, Ir-1 to 10% by mass Pt alloy), and an 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) and the like can be used. When an Ir-based noble metal material is used, an oxide (including a 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 the Elements. Can be contained in the range of 0.1 to 15% by mass. Thereby, the oxidation and volatilization of the Ir component can be effectively suppressed, and the spark erosion resistance of the erosion resistant portion can be improved. As the above oxide, Y ₂ O ₃ Is preferably used. In addition, La ₂ O ₃ , ThO ₂ , ZrO ₂ Etc. can be preferably used. In this case, as the metal component, Ir alone may be used in addition to the Ir alloy.
[0018]
The center electrode 3 has a reduced diameter at the tip end side, a disc-shaped noble metal tip made of an alloy composition constituting the center electrode noble metal wear-resistant portion 31 overlapped on the tip end surface, and along the outer edge of the joining surface. It is formed by laser welding. When a parallel light beam is irradiated from the spark discharge gap g side toward the ground electrode 4 in the direction of the center axis O of the center electrode 3, the parallel light beam of the electrode base material 4m to which the ground electrode noble metal wear-resistant portion 32 is fixed. Is defined as a gap opposing electrode surface SC, and the other surfaces are defined as gap non-opposing electrode surfaces. As shown in FIG. 2, the ground electrode noble metal wear-resistant portion 32 is joined to the electrode base material 4 m by the base material penetration welding portion 40. The base metal penetration welding portion 40 has a base end surface 40e exposed on the gap non-opposing electrode surface SS, penetrates the electrode base material 4m from the base end surface 40e, and has a front end portion 40t inside the ground electrode noble metal wear resistant portion 32. In this manner, the constituent metals of the electrode base material 4m and the ground electrode noble metal wear-resistant portion 32 are formed as being melted together. The Ir content of the base metal penetration welded portion 40 is smaller than that of the ground electrode noble metal wear-resistant portion 32 and is 10% by mass or more and 50% by mass or less (preferably 15% by mass or more and 40% by mass or less, more preferably, 20% by mass or more and 30% by mass or less). As described above, in the case of a so-called parallel ground electrode type spark plug in which the side surface of the ground electrode 4 faces the tip surface of the center electrode 3 as shown in FIG. It is assumed that parallel rays are emitted in the direction of the central axis O. For other types of spark plugs, parallel rays may be emitted from the spark discharge gap g side toward the ground electrode in parallel with the imaginary line indicating the shortest distance between the center electrode and the ground electrode.
[0019]
The ground electrode noble metal wear-resistant portion 32 can be formed as follows. As shown in FIG. 11, an Ir-based noble metal tip 32 ′ is superimposed on a region of the surface of the electrode base material 4 m that is to be the gap facing electrode surface SC. Then, the pulse laser beam LB is irradiated from the non-gap electrode surface SS. The laser beam LB is initially irradiated only on the electrode base material 4 m, and a molten portion of the Ni-based metal is generated in the irradiation depth direction. When the molten portion advances in the depth direction and reaches the noble metal tip 32 ', melting of the Ir-based noble metal tip 32' starts, and the Ir-based metal melts into the molten portion. Although the pulse laser beam LB has a high heat concentration efficiency in the irradiation depth direction, a sufficient welded portion cannot be formed by only one pulse irradiation. Therefore, as shown in FIG. _L And irradiating a laser pulse having a pulse width τ1 to the same portion a plurality of times, thereby suppressing the expansion of the in-plane fusion portion in the direction normal to the laser irradiation direction and gradually increasing the fusion portion formation. Can be. As a result, after the molten portion reaches the Ir-based noble metal tip 32 ', the laser energy can be efficiently concentrated on the Ir-based noble metal tip 32', and the melting of the Ir-based noble metal tip 32 'can be promoted. That is, while suppressing excessive melting of the electrode base material 4 m around the irradiation position, the Ir-based noble metal tip 32 ′ located further inside the electrode base material 4 m can be efficiently melted, and the resulting penetration welding portion 40 The Ir content can be effectively increased.
[0020]
Pulse irradiation frequency and peak power E at each irradiation position _L Is set to be the same, when the pulse width τ1 is increased, the melting of the electrode base material tends to proceed easily, and the Ir content rate of the base material penetration welded portion 40 tends to decrease. On the other hand, the peak power E _L When the value of is increased, the opposite tendency occurs.
[0021]
As shown in FIG. 2, the base metal penetrating welded portion 40 has a large cross-sectional area orthogonal to the depth direction (that is, the irradiation direction of the laser beam LB) on the electrode base material 4 m side, and the ground electrode-side noble metal wear resistant portion. It is formed so as to be smaller on the side of the tip portion 40t located in the inside 32. The base metal penetration welded portion 40 is formed such that the axial cross-sectional area changes stepwise at the boundary position between the electrode base material 4 m and the ground electrode-side noble metal wear-resistant portion 32. It is desirable to melt the base metal 4m and the ground electrode-side noble metal wear resistant part 32 at an appropriate mixing ratio to obtain a base metal penetration welded part 40 that satisfies the Ir composition range. That is, if the molten portion is formed somewhat wide on the electrode base material 4m side, the region heated to a relatively high temperature by contact with the molten portion is widened in the center of the contact surface with the Ir-based noble metal tip 32 '. Can be secured. By irradiating the center of the subregion with the laser beam LB, the melting of the high melting point Ir-based noble metal tip 32 'can be effectively promoted.
[0022]
The base metal penetration welding portion 40 using the pulsed laser beam LB is formed in an inert gas atmosphere such as a rare gas (eg, argon gas) or a nitrogen gas. It is desirable to suppress excessive melting of the alloy and increase the Ir content of the obtained base metal penetration welded portion 40. The Ni alloy constituting the electrode base material 4m is oxidized when melted in the atmosphere. The reaction of oxidizing Ni metal is an exothermic reaction. When the generation of Ni oxide is remarkable, the temperature of the reaction is further remarkably increased by the reaction heat, and the melting of the electrode base material 4m is promoted. However, in an inert gas atmosphere, the temperature rise due to the reaction heat is unlikely to occur due to the suppression of the oxidation reaction, and excessive melting of the electrode base material 4m and, consequently, reduction of the Ir content of the base material through-welded portion 40 are reduced. Can be suppressed. In the present embodiment, an example is shown in which welding is performed in the chamber 80 through which Ar gas is circulated, but welding may be performed by blowing Ar gas in an open atmosphere to shield the periphery of the welded portion. . In particular, the latter method has an advantage that shielding is easily performed since the specific gravity of Ar gas is somewhat higher than that of air.
[0023]
It is desirable that the outer diameter D of the ground electrode noble metal wear-resistant portion 32 be 0.3 mm or more and 2 mm or less. If D is less than 0.3 mm, the wear resistance will be insufficient, and if it exceeds 2 mm, the ignitability will deteriorate.
[0024]
Next, as shown in FIG. 2, at least a part of the ground electrode noble metal wear-resistant portion 32 in the direction of the central axis O of the center electrode 3 can be a buried portion 32v buried in the electrode base material 4m. . The base metal penetration welded portion 40 can be formed such that the tip portion 40t reaches the inside of the embedded portion 32v. By embedding a part of the ground electrode noble metal wear-resistant portion 32 in the electrode base material 4m, it is possible to increase the bonding strength between the ground electrode noble metal wear-resistant portion 32 and the electrode base material 4m. Peeling of the consumable part 32 and generation of cracks are further less likely to occur. In addition, since the contact area with the electrode base material 4m increases, there is an advantage that the heat extraction of the ground electrode noble metal wear-resistant portion 32 proceeds easily, and the wear resistance is improved.
[0025]
The ground electrode noble metal wear resistant portion 32 of the buried form as described above can be formed by the process shown in FIG. That is, a recess 4k having a shape corresponding to the Ir-based noble metal tip 32 'is formed in the electrode base material 4m, and the Ir-based noble metal tip 32' is fitted therein. Then, while positioning the Ir-based noble metal tip 32 'in the concave portion 4k, a laser beam LB is irradiated from the side of the electrode base material 4m to form a base material penetration weld. By forming such a concave portion 4k, displacement of the Ir-based noble metal tip 32 ′ during welding is less likely to occur, and a good base metal penetration weld can be easily obtained.
[0026]
As shown in FIG. 13, the concave portion 4k formed in the electrode base material 4m is formed as having an opening shape corresponding to the cross-sectional shape of the insertion shaft of the Ir-based noble metal tip 32 '(in the present embodiment, circular: For example, drilling or laser drilling can be used). Here, in order to facilitate the insertion of the Ir-based noble metal tip 32 ', the inner diameter of the recess 4k may be formed slightly larger than the outer diameter of the Ir-based noble metal tip 32'. At this time, a gap 4g is formed between the inner peripheral surface of the recess 4k and the outer peripheral surface of the Ir-based noble metal tip 32 '. When the base metal penetrating weld 40 is formed by the irradiation of the pulse laser beam LB, at least a part of the gap 4g is filled with the molten metal generated with the formation of the base metal penetrating weld 40, and the gap filling metal part 40f Is formed. As a result, around the central axis O of the center electrode 3, between the outer peripheral surface of the buried portion 32 v of the ground electrode noble metal wear-resistant portion 32 and the electrode base material, along at least a part of the outer peripheral surface in the circumferential direction. Thus, a structure in which the gap filling metal portion 40f integral with the base material through-welded portion 40 is formed is obtained.
[0027]
The gap filling metal portion 40f not only contributes to improving the bonding strength of the ground electrode noble metal wear-resistant portion 32, but also promotes heat conduction from the ground electrode noble metal wear-resistant portion 32 to the electrode base material 4m when a spark plug is used. This contributes to the suppression of the temperature rise of the electrode noble metal wear-resistant portion 32 and the improvement of wear resistance. The gap filling metal portion 40f has an intermediate composition between the electrode base material 4m and the ground electrode noble metal wear-resistant portion 32, and is formed so as to surround the ground electrode noble metal wear-resistant portion 32 in the circumferential direction. The effect of alleviating the thermal stress in the radial direction of the electrode noble metal wear-resistant portion 32 is high, and the peel resistance of the ground electrode noble metal wear-resistant portion 32 is further improved.
[0028]
The gap filling metal portion 40f is desirably formed in as many sections as possible in the circumferential direction of the gap 4g in order to make the above effect more remarkable. For this purpose, as described above, the axial cross-sectional area of the base metal penetration welded portion 40 is formed so as to change stepwise at the boundary position between the electrode base material 4m and the ground electrode-side noble metal wear-resistant portion 32. That is, at the time of welding using the pulse laser beam LB, it is effective to form a kind of molten metal reservoir by forming a molten portion to a certain extent on the electrode base material 4 m side. By doing so, the outer peripheral surface of the Ir-based noble metal tip 32 'comes into contact with the molten metal filling the gap 4g over a relatively long section in the circumferential direction, and the temperature retention effect of the Ir-based noble metal tip 32' increases. It is possible to increase the penetration amount of Ir into the base metal penetration weld 40 by being promoted. The width δ of the gap 4g (corresponding to the width of the base metal penetration welded portion 40) is preferably adjusted to 0.01 mm or more and 0.15 mm or less. When the width δ exceeds 0.15 mm, it is difficult to form the base metal through-welded portion 40, and when the width δ is less than 0.01 mm, the work of inserting the Ir-based noble metal tip 32 ′ into the recess 4 k becomes troublesome.
[0029]
For example, as shown in FIG. 3 or FIGS. 4 and 5, only one base metal penetration weld may be provided. If the number of base metal penetration welds formed is small, the process can be simplified accordingly, and the production efficiency can be increased. However, when it is desired to secure the bonding strength of the ground electrode side noble metal wear-resistant portion 32 to a higher level, as shown in FIGS. 2, 6, 7, 8, 9, and 10, It is effective to provide a plurality of 40 and 41 around the central axis O. In this case, the total formation section length of the gap filling metal portion 40f increases as the number of formed base metal penetration welds in the circumferential direction increases, thereby improving the bonding strength of the ground electrode noble metal wear-resistant portion 32 and suppressing the temperature rise. The effect can be further enhanced.
[0030]
In addition, the width of the gap counter electrode surface SC of the ground electrode 4 is generally adjusted to 2.0 mm or more and 3.5 mm or less. On the other hand, in order to improve the ignitability, as shown in FIG. 2, FIG. 3 or FIG. It is desirable to set the diameter D small. In this case, when the outer diameter D of the ground electrode noble metal wear-resistant portion 32 is excessively small, the depth of some base metal penetration welds becomes too large, and the melting of the Ir-based noble metal tip 32 'becomes insufficient. There is. From this point of view, the outer diameter D of the Ir-based noble metal tip 32 ′ and, consequently, the ground electrode noble metal wear-resistant portion 32 may be adjusted to be slightly larger as shown in FIG. 8, FIG. 9 or FIG. It is desirable to adjust. As a result, an extremely deep base metal penetration weld is less likely to occur, and thus the Ir content of the base metal penetration weld can be easily adjusted within the range of the present invention.
[0031]
Various forms of the base metal penetration welding portion can be formed depending on where the pulsed laser beam is irradiated on the surface of the non-gap electrode. In FIG. 2, the base metal penetrating welded portion 40 is provided on at least one side in the width direction W of the gap opposing electrode surface SC in the side surface region SS of the electrode base material 4 m continuing to the edge LE of the gap opposing electrode surface SC. The base end face 40e of the base metal through-welded portion 40 is formed so as to be exposed. In this specification, the width direction W of the ground electrode 4 is defined as follows. As shown in FIG. 1, that is, when the metal shell 1 is cut along a plane P2 orthogonal to the central axis O at a position 1 mm away from the end face of the metal shell 1 to which the ground electrode 4 is joined in the direction of the central axis O. The geometrical center of gravity of the cross section of the ground electrode 4 is denoted by K. Then, a reference direction F passing through the position K and orthogonal to the center axis O is determined, and the direction orthogonal to both the center axis O and the reference direction F is set to the width direction of the gap opposing electrode surface SC of the ground electrode 4. Defined as W. Since the side surface regions SS are formed on both sides in the width direction W, as shown in FIG. 2, at least two base metal through-welded portions 40 can be formed, one at each gap counter electrode surface SC. This is effective for improving the joining strength of the wear-resistant portion 32.
[0032]
Further, as shown in FIG. 3, a base metal penetration welded part 41 in which the base end face 41 e is exposed to the front end face ST of the ground electrode 4 can be formed. In particular, when the outer diameter D of the ground electrode noble metal wear-resistant portion 32 is set small in order to give priority to the effect of improving the ignitability, the ground electrode 4 extends from the outer peripheral edge of the ground electrode noble metal wear-resistant portion 32 on the gap counter electrode surface SC. When the distance to the end edge TE on the front end side is t2 and the distance t1 to the edge LE in the width direction W is t2, t2 can be set to be smaller than t1. Thereby, the welding depth of the base metal penetration welded part 41 formed from the front end surface ST side can be reduced, and the Ir content rate of the base metal penetration welded part 41 can be easily adjusted within the range of the present invention. When the outer diameter D is set to, for example, 0.3 mm or more and 1 mm or less, it is preferable that t1 is set to 0.5 mm or more and 1.5 mm or less, and t2 is set to 0.3 mm or more and 1.0 mm or less.
[0033]
In addition, as shown in FIG. 4, in the direction of the central axis O, the base metal penetrating welded portion 42 is formed such that the base end surface 42 e is exposed on a surface SB of the electrode base material 4 m opposite to the gap opposing electrode surface SC. You can also. This mode is achieved by adjusting the burying depth of the buried portion 32v (that is, the depth of the concave portion 4k in FIG. 11) regardless of the outer diameter D of the ground electrode noble metal wear-resistant portion 32. There is an advantage that the welding depth can be reduced. When the thickness of the electrode base material 4m is relatively thin, as shown in FIG. 5, an Ir-based noble metal tip is overlapped and welded to the electrode base material 4m without forming a concave portion, that is, the buried portion 32v is formed. May be omitted.
[0034]
6, 9 and 10, the width of the electrode base material 4m in which the tapered surface 4j is formed at the tip corner of the electrode base material 4m is reduced so that the base end surface 40e is exposed on the tapered surface. , A base material through-welded portion 40 is formed. In FIG. 6, the outer diameter D of the ground electrode noble metal wear-resistant portion 32 is set to be small (for example, 0.3 mm or more and 1 mm or less), but the tapered surface 4j reduces the depth of the base material penetration welded portion 40 formed. Can be reduced. When a plurality of base metal penetration welds are formed around the center axis O, for example, as shown in FIG. 7 or FIG. 8, welding is performed from each of the two side surface regions SS and the front end surface ST. Thereby, the three base metal penetration welds 40 and 41 can be formed relatively easily. However, when more base metal penetration welds are required, as shown in FIG. 9 or FIG. 10, by providing the tapered surface 4j, the base metal penetration welds 40 having a relatively small welding depth can be connected to the electrode. It can be relatively easily added to the tip corner of the base material 4m.
[0035]
【Example】
The following experiment was performed to confirm the effects of the present invention.
Various test samples of the spark plug 100 shown in FIG. 1 (the formation of the base metal through-welded portion is FIG. 8) were prepared as follows. That is, an Ir-based noble metal tip 32 ′ shown in FIG. 11 was manufactured from an Ir-5 mass% Pt alloy so as to have a thickness of 1.0 mm and a diameter D of 1.8 mm. Using this, it was welded to 4 m of the electrode base material made of Inconel 600 according to the process of FIG. A recess 4k having a depth of 0.5 mm and an inner diameter of 1.85 mm was formed in the electrode base material 4 m by cutting (end mill) (the width δ of the gap 4 g was 0.25 mm). In addition, welding was performed by irradiating a laser beam having various peak powers and pulse widths shown in Table 1 with an YAG laser light source at three pulses to each welded part in an argon atmosphere by blowing argon gas. The ground electrode noble metal wear-resistant portion 32 obtained by welding was cut together with the peripheral portion, and the average Ir content of the welded portion was measured by EPMA surface analysis. As a result, as shown in Table 1, it was found that the Ir content varied in the range of 5 to 55% by mass depending on the welding conditions.
[0036]
[Table 1]

[0037]
On the other hand, the center electrode noble metal wear-resistant portion 31 is formed by laser welding a noble metal tip made of an Ir-20 mass% Rh alloy and having a diameter of 1.2 mm and a height of 0.8 mm to the front end surface of the center electrode 3 made of Inconel 600. Formed. FIG. 15 is a cross-sectional optical microscope observation image of the ground electrode noble metal wear-resistant portion 32 in the test sample of No. 4 in Table 1 (in the figure, a black wedge-shaped region is a base metal penetration welded portion). The leading end of each of the base metal penetration welds reaches the inside of the ground electrode noble metal wear-resistant portion 32. Also, the axial cross-sectional area of the base metal penetration weld (or the width of the base metal penetration weld) is stepwise (that is, non-uniform) at the boundary position between the electrode base material and the ground electrode-side noble metal wear-resistant part in the depth direction. Continuous). Further, a gap is formed between the inner peripheral surface of the concave portion and the outer peripheral surface of the ground electrode-side noble metal wear-resistant portion, and the weld metal is filled over substantially the entire periphery.
[0038]
Then, using the ground electrode 4 and the center electrode 3, the spark plug 100 shown in FIG. 1 was assembled so that the gap length G of the spark discharge gap g was 0.8 mm. 10 for each composition). The spark plug was attached to a test engine (6 cylinders, total displacement: 2000 cc), the throttle was fully opened, the engine was operated at an engine speed of 5,000 rpm for 1 minute, and then a cycle of idling at an engine speed of 700 rpm for 1 minute was performed for 100 hours. A repeated thermal cycle test was performed. Then, after the test, the peeling rate was determined from the number of spark plugs that peeled off the ground electrode noble metal wear-resistant portion 32. FIG. 14 shows the result. Thus, it can be seen that the peeling of the ground electrode noble metal wear-resistant portion 32 is effectively suppressed by setting the Ir content of the base metal penetration welded portion to 10% by mass or more and less than 50% by mass.
[Brief description of the drawings]
FIG. 1 is a longitudinal section showing one embodiment of a spark plug of the present invention.
FIG. 2 is an explanatory view of a first example of a form of forming a base metal through-welded portion with respect to a ground electrode noble metal wear-resistant portion.
FIG. 3 is an explanatory diagram of a second example.
FIG. 4 is an explanatory view of a third example.
FIG. 5 is an explanatory view of a fourth example.
FIG. 6 is an explanatory view of a fifth example.
FIG. 7 is an explanatory view of a sixth example.
FIG. 8 is an explanatory view of a seventh example.
FIG. 9 is an explanatory view of an eighth example.
FIG. 10 is an explanatory view of a ninth example.
FIG. 11 is an explanatory view of a step of forming a base metal penetration weld.
FIG. 12 is a diagram schematically showing a pulse laser beam waveform /
FIG. 13 is a diagram illustrating a process of forming a gap filling metal part.
FIG. 14 is a graph showing test results of a thermal cycle test.
FIG. 15 is a cross-sectional optical microscope observation image of the ground electrode noble metal wear-resistant portion of No. 4 in Table 1.
[Explanation of symbols]
3 Center electrode
4 Ground electrode
4m electrode base material
g spark discharge gap
32 Ground electrode noble metal wear resistant part
32v buried part
SC gap counter electrode surface
SS, ST, SB Gap non-facing electrode surface
SS side area
ST Tip surface
40e, 41e, 42e Base end face
40t, 41t, 42t Tip
40,41,42 Base metal penetration weld
LB pulse laser beam

Claims

A spark discharge gap (g) is formed by making the peripheral side surface of the ground electrode (4) face the tip end surface of the center electrode (3), and the spark discharge gap (g) of the ground electrode (4) is formed. ) Is a ground electrode noble metal wear resistant portion (32) mainly composed of Ir,
When a parallel light beam is irradiated from the side of the center electrode (3) of the spark discharge gap (g) toward the ground electrode (4), Ni is attached to the ground electrode noble metal wear-resistant portion (32) as a main component. The surface of the electrode base material (4m) that receives the parallel rays is defined as a gap opposing electrode surface (SC), and the other surfaces are defined as gap non-opposing electrode surfaces (SS, ST, SB). The tip (40t, 41t, 42t) penetrates through the material (4m) and reaches the inside of the ground electrode noble metal wear-resistant part (32), and the base end face is formed on the non-gap electrode surface (SS, ST, SB). The base metal penetration welds (40, 41, 42) in which the constituent metals of the electrode base material (4m) and the ground electrode noble metal wear-resistant part (32) are melted together with the (40e, 41e, 42e) exposed. ) Is formed Further, the Ir content of the base metal through-welded portion (40, 41, 42) is smaller than that of the ground electrode noble metal wear-resistant portion (32), and is 10% by mass or more and 50% by mass or less. Features spark plug.

2. The spark plug according to claim 1, wherein an Ir content of the base metal through-welded portion is in a range of 15% by mass to 40% by mass. 3.

2. The spark plug according to claim 1, wherein an Ir content of the base material through-welded portion (40, 41, 42) is 20% by mass to 30% by mass. 3.

The spark plug according to any one of claims 1 to 3, wherein the ground electrode noble metal wear-resistant portion (32) has an outer diameter D of 0.3 mm or more and 2 mm or less.

At least a part of the ground electrode noble metal wear-resistant portion (32) in the direction of the center axis (O) of the center electrode (3) is at least partially formed of the electrode base material (4m) of the ground electrode (4) mainly containing Ni. ) Is buried in the buried portion (32v), and the tip portions (40t, 41t, 42t) of the base metal penetration welds (40, 41, 42) reach the inside of the buried portion (32v). The spark plug according to any one of claims 1 to 4, wherein the spark plug is formed.

The base end of the ground electrode (4) is joined to the end face of the metal shell (1), and the ground electrode (4) of the metal shell (1) is joined in the direction of the central axis (O). At a position 1 mm away from the end face, passing through the geometric center of gravity (K) of the cross section of the ground electrode (4) when cut along a plane orthogonal to the central axis (O), and A reference direction (F) orthogonal to the center axis (O) is determined, and a direction orthogonal to both the center axis (O) and the reference direction (F) is set to the surface of the gap opposing electrode of the ground electrode (4). Is defined as the width direction (W) of
On at least one side in the width direction (W), the base material penetration welded portion is formed on a side surface region (SS) of the electrode base material (4m) connected to an edge (LE) of the gap opposing electrode surface (SC). The spark plug according to claim 5, wherein the base end face (40e) of (40) is exposed.

The base end of the ground electrode (4) is joined to the end face of the metal shell (1), and the ground electrode (4) of the metal shell (1) is joined in the direction of the central axis (O). At a position 1 mm away from the end face, passing through the geometric center of gravity (K) of the cross section of the ground electrode (4) when cut along a plane orthogonal to the central axis (O), and A reference direction (F) orthogonal to the center axis (O) is determined, and a direction orthogonal to both the center axis (O) and the reference direction (F) is set to the surface of the gap opposing electrode of the ground electrode (4). Is defined as the width direction (W) of
On the gap opposing electrode surface (SC), the distance from the outer peripheral edge of the ground electrode noble metal wear-resistant portion (4) to the edge (TE) on the tip end side of the ground electrode (4) is t2, and in the width direction ( When the distance t1 to the edge (LE) of W) is set to t1, t2 is set to be smaller than t1, and the base end face (40e) of the base metal penetration welded portion (40) is connected to the ground electrode (4). 6. The spark plug according to claim 5, wherein the spark plug is exposed on the tip end surface (ST) of the spark plug.

Around the center axis (O) of the center electrode (3), between the outer peripheral surface of the buried portion (32v) of the ground electrode noble metal wear-resistant portion (32) and the electrode base material, the periphery of the outer peripheral surface is formed. The spark plug according to any one of claims 5 to 7, wherein a gap filling metal part (40f) integral with the base metal penetration welded part (40) is formed along at least a part of the direction of the spark plug. .

The spark plug according to any one of claims 1 to 8, wherein a plurality of the base metal penetration welds (40, 41) are provided around the central axis (O).

The base metal penetration weld (42) is provided on the surface (SB) of the electrode base material (4m) on the opposite side to the gap opposing electrode surface (SC) in the direction of the center axis (O) by the base end surface (42e). 10. The spark plug according to claim 1, wherein the spark plug is exposed.

It is a manufacturing method of the spark plug according to any one of claims 1 to 10,
A noble metal tip (32 ') containing Ir as a main component is superimposed on a region of the surface of the electrode base material (4m) of the ground electrode (4) which is to be the gap opposing electrode surface (SC). By irradiating a pulse laser beam (LB) a plurality of times from the gap non-opposing electrode surface (SS, ST, SB), the laser irradiation position penetrates the electrode base material (4 m) to the noble metal tip (32 ′). A base material in which the constituent metals of the electrode base material (4m) and the ground electrode noble metal wear-resistant portion (32) are melted together so that the Ir content is 10% by mass or more and 50% by mass or less. A method for manufacturing a spark plug, comprising forming through-welded portions (40, 41, 42).

The method for manufacturing a spark plug according to claim 11, wherein the formation of the base metal through-welded portion (40, 41, 42) using the pulsed laser beam (LB) is performed in an inert gas atmosphere.

A recess (4k) having a shape corresponding to the Ir-based noble metal tip (32 ') is formed in the electrode base material 4m, the Ir-based noble metal tip (32') is fitted therein, and the recess (4k) is inserted into the recess (4k). 13. The spark according to claim 11, wherein a laser beam LB is irradiated from the side of the electrode base material (4 m) while positioning the Ir-based noble metal tip 32 ′ to form the base material penetration welds (40, 41). Plug manufacturing method.

A gap 4g is formed between the inner peripheral surface of the concave portion (4k) and the outer peripheral surface of the Ir-based noble metal tip (32 '). The method for manufacturing a spark plug according to claim 13, wherein at least a part of the gap (4g) is filled to form a gap filling metal part (40f).