JP3769766B2

JP3769766B2 - Manufacturing method of spark plug

Info

Publication number: JP3769766B2
Application number: JP33076394A
Authority: JP
Inventors: 県司堀部; 明夫加藤
Original assignee: Denso Corp
Current assignee: Denso Corp
Priority date: 1994-12-06
Filing date: 1994-12-06
Publication date: 2006-04-26
Anticipated expiration: 2021-04-26
Also published as: JPH08162256A

Description

【０００１】
【産業上の利用分野】
本発明は，中心電極の先端部の円弧状側面に設けた金属チップと，接地電極とが対向する，スパークプラグの製造方法に関する。
【０００２】
【従来技術】
最近，内燃機関のメンテナンスフリーが求められていることに伴い，スパークプラグは長寿命化が要求されている。
長寿命のスパークプラグとしては，中心電極の放電面に耐火花消耗性に優れた金属チップを接合したものが多数提案されている。
【０００３】
金属チップを接合したスパークプラグとしては，図１３に示すごとく，中心電極９１の側面の平面部９１１，９１２に金属チップ３１，３２を接合したものが知られている。中心電極９１への金属チップ３１，３２の接合は，まず，中心電極の側面に平面部９１１，９１２を設け，次いで，２枚の金属チップ３１，３２を順次抵抗溶接により接合する方法が採られている。
【０００４】
【解決しようとする課題】
しかしながら，上記従来のスパークプラグの製造方法においては，次の問題がある。
即ち，円弧状である中心電極９１の側面に平面部９１１，９１２を設けるには，切削，研磨，塑性加工等が必要となり，コスト高となる。
【０００５】
また，得られたスパークプラグは，図１３に示すごとく，接地電極９２１，９２２に対して中心電極９１の平面部９１１，９１２が角度θだけ回転ズレを生じた場合には，火花ギャップＧ２は，金属チップ３１，３２以外の場所で形成される。そのため，耐火花消耗性に劣る中心電極９１が短期間で劣化し，スパークプラグの長寿命化を実現することができない。
【０００６】
また，長寿命化を図るスパークプラグとして，中心電極に平面部を設けず，円弧状側面に直接金属チップを接合させ，金属チップ表面を円弧状にしたスパークプラグが提案されている（図３，図５参照）。このスパークプラグにおける中心電極への金属チップの接合方法としては，図１４に示すごとく，平面状の第１溶接電極９６と平面状の第２溶接電極９７との間に中心電極１及び金属チップ３１を挟み込み，抵抗溶接させる方法がある。
【０００７】
この方法においては，図１４に示すごとく，金属チップ３１と中心電極１との接触部Ａ１及び中心電極と上記第２溶接電極との接触部Ａ２は，ともに線接触となり，接触面積が小さい。そのため，上記両接触部Ａ１，Ａ２は，加圧通電時には高抵抗となり，過度に加熱される。それ故，両接触部Ａ１，Ａ２においては，中心電極１及び金属チップ３１が過度に溶融し，バリ，座屈，変形の発生といった不具合が発生する。この不具合を防止するには，通電電流を低下させることが考えられるが，この場合には安定した接合強度を得ることができない。
【０００８】
本発明は，かかる従来の問題点に鑑みてなされたもので，優れた耐火花消耗性を有し，かつ中心電極と金属チップとの接合部におけるバリ，座屈，変形がない優れた接合状態を有するスパークプラグを，低コストで製造することができる，スパークプラグの製造方法を提供しようとするものである。
【０００９】
【課題の解決手段】
本発明は，先端部に円弧状側面を有する中心電極と，該中心電極の上記円弧状側面に対向配設した接地電極とを有し，かつ上記円弧状側面には上記中心電極に比較して耐火花消耗性に優れた金属又はその合金よりなる金属チップを接合してなるスパークプラグの製造方法において，
第１溶接電極と第２溶接電極との間に上記中心電極を挟持して，上記中心電極の上記円弧状側面に上記金属チップを抵抗溶接するに当たり，
上記第１溶接電極は上記金属チップに当接する第１凹部を有し，
また上記第２溶接電極は上記中心電極の先端部に直接当接する第２凹部を有しており，
かつ上記第１凹部及び第２凹部は，上記中心電極の先端部の上記円弧状側面と同形状を有しており，
また，上記中心電極の上記円弧状側面の曲率半径をＲ１ｍｍ，上記第１溶接電極の上記第１凹部の曲率半径をＲ２ｍｍとしたとき，Ｒ２ｍｍは次の関係式
Ｒ１ｍｍ−０．２ｍｍ≦Ｒ２ｍｍ≦Ｒ１ｍｍ＋０．２ｍｍ
で示される範囲内にあることを特徴とするスパークプラグの製造方法にある。
【００１０】
本発明において最も注目すべきことは，上記第１溶接電極は上記第１凹部を有し，また上記第２溶接電極は上記第２凹部を有しており，かつ上記第１凹部及び第２凹部は，上記中心電極の先端部の上記円弧状側面と同形状を有していることにある。
【００１１】
また，上記同形状とは，寸法的に全く同一であることを意味するのではなく，寸法的にはほぼ同程度でありその形状が相似形であることを意味する。即ち，中心電極の上記円弧状側面の形状が略真円形状でれば，上記第１凹部及び第２凹部も略真円形状であり，上記円弧状側面が楕円形状であれば，上記第１凹部及び第２凹部も楕円形状であることを意味する。
【００１２】
また，上記金属チップとしては，例えば白金（Ｐｔ），イリジウム（Ｉｒ），Ｐｔ−Ｉｒ合金，Ｐｔ−Ｉｒ−ニッケル（Ｎｉ）合金等の貴金属又はその合金，又は，クロム（Ｃｒ），Ｃｒ合金等がある。そして，上記金属チップは，ほぼ厚みが一定の平板状のものを用いるが，その形状は，ディスク状（円形状），四角形状等，種々の形状を適用できる。
【００１３】
また，上記中心電極の上記円弧状側面の曲率半径をＲ１ｍｍ，上記第１溶接電極の上記第１凹部の曲率半径をＲ２ｍｍとしたとき，Ｒ２ｍｍは次の関係式
Ｒ１ｍｍ−０．２ｍｍ≦Ｒ２ｍｍ≦Ｒ１ｍｍ＋０．２ｍｍ
で示される範囲内（単位はｍｍ。以下同様）にある。
これにより，上記中心電極と金属チップとは，バリ，座屈，変形等を発生させることなく，強固に接合させることができる。
【００１４】
また，上記Ｒ２がＲ１−０．２より小さい場合（図６参照）には，第１溶接電極は金属チップの周縁部の２か所のみに接触し，その接触面積が小さい（図６符号Ａ３，Ａ４参照）。そのため，上記接触部は，加圧通電時に過度に加熱され，バリ，座屈，変形等が発生するという問題がある。また，上記Ｒ２がＲ１＋０．２より大きい場合（図７参照）には，上記第１溶接電極は金属チップの中央部に線接触し，その接触面積が小さい（図７符号Ａ５参照）。そのため，第１凹部を持たない場合と同様に，接触部にバリ，座屈，変形等が発生するという問題がある。
【００１５】
次に，先端部に円弧状側面を有する中心電極と，該中心電極の上記円弧状側面に対向配設した接地電極とを有し，かつ上記円弧状側面には上記中心電極に比較して耐火花消耗性に優れた金属又はその合金よりなる金属チップを接合してなるスパークプラグの製造方法において，
第１溶接電極と第２溶接電極との間に上記中心電極を挟持して，上記中心電極の上記円弧状側面に上記金属チップを抵抗溶接するに当たり，
上記第１溶接電極は上記金属チップに当接する第１凹部を有し，
また上記第２溶接電極は上記中心電極の先端部に直接当接する第２凹部を有しており，
かつ上記第１凹部及び第２凹部は，上記中心電極の先端部の上記円弧状側面と同形状を有しており，
また，上記中心電極の先端部の上記円弧状側面の曲率半径をＲ１，上記第２溶接電極の上記第２凹部の曲率半径をＲ３ｍｍ，上記第２溶接電極の上記第２凹部の深さをＨｍｍとしたとき，Ｒ３ｍｍ及びＨｍｍは次の関係式Ｒ１ｍｍ−０．１ｍｍ≦Ｒ３ｍｍ≦Ｒ１ｍｍ＋０．１ｍｍ
Ｒ１ｍｍ＞Ｈｍｍ≧（１／４）×Ｒ１ｍｍ
で示される範囲内にあることを特徴とするスパークプラグの製造方法がある。
上記関係式で示される範囲内にある場合には，上記中心電極と第２溶接電極との接触部分に，バリ，座屈，変形等を発生させることなく，上記金属チップと中心電極を抵抗溶接することができる。
【００１６】
また，上記Ｒ３がＲ１−０．１より小さい場合（図８参照）には，中心電極は，上記第２凹部の２か所の頂部と線接触し，その接触面積が小さい（図８符号Ａ６，Ａ７参照）。そのため，上記接触部は，加圧通電時に過度に加熱され，バリ，座屈，変形等が発生するという問題がある。また，Ｒ３がＲ１＋０．１より大きい場合（図９参照）には，上記第２凹部の底部が中心電極に線接触し，その接触面積が小さい（図９符号Ａ８参照）。そのため，第２溶接電極が第２凹部を有さない場合と同様に，接触部にバリ，座屈，変形等が発生するという問題がある。
【００１７】
また，上記ＨがＲ１以上の場合には，上記中心電極を第２凹部にセットすることができないという問題がある。また，上記Ｈが（１／４）×Ｒ１より小さい場合には，中心電極と第２溶接電極との接触面積が小さすぎる。そのため，上記接触部は，加圧通電時に過度に加熱され，接触部にバリ，座屈，変形等が発生するという問題がある。
【００１８】
また，上記金属チップは，上記中心電極の先端部の上記円弧状側面に添った曲面形状に予め曲げ加工してあることが好ましい。これにより，抵抗溶接時のセッティングを容易にすることができる。
【００１９】
【作用および効果】
本発明のスパークプラグの製造方法においては，上記第１溶接電極は上記第１凹部を有し，かつ該第１凹部は，上記中心電極の先端部の上記円弧状側面と同形状を有している。そのため，抵抗溶接における加圧通電の際には，第１溶接電極の第１凹部と金属チップ，及び金属チップと中心電極は，それぞれ比較的広い面積において面接触する。それ故，金属チップと中心電極とは，バリ，座屈，変形等を発生させることなく，強固に接合する。
【００２０】
また，上記第２溶接電極は上記第２凹部を有し，かつ該第２凹部は，上記中心電極の先端部の上記円弧状側面と同形状を有している。そのため，抵抗溶接における加圧通電の際には，第２溶接電極の第２凹部と中心電極は，比較的広い面積において面接触する。それ故，中心電極の第２溶接電極との接触部には，バリ，座屈，変形等が発生することはない。
【００２１】
従って，従来のように抵抗溶接前に予め中心電極の側面に平面部を設けるという工程を省略することができ，低コストでスパークプラグを製造することが出来るまた，得られたスパークプラグの中心電極と金属チップの接合部は優れた接合状態を有し，耐火花消耗性にも優れる。
【００２２】
上述のごとく，本発明によれば，優れた耐火花消耗性を有し，かつ中心電極と金属チップとの接合部におけるバリ，座屈，変形がない優れた接合状態を有するスパークプラグを，低コストで製造することができる，スパークプラグの製造方法を提供することができる。
【００２３】
【実施例】
実施例１
本発明の実施例にかかるスパークプラグの製造方法につき，図１〜図９を用いて説明する。
本例のスパークプラグの製造方法は，図１〜図５に示すごとく，先端部１０に円弧状側面１１，１２を有する中心電極１と，該中心電極１の上記円弧状側面１１，１２に対向配設した接地電極２１，２２（図４）とを有し，かつ上記円弧状側面１１，１２には上記中心電極１に比較して耐火花消耗性に優れた金属チップ３１，３２を接合してなるスパークプラグの製造方法である。
【００２４】
上記中心電極１に金属チップ３１，３２を接合するに当たっては，図１，図２に示すごとく，まず，第１溶接電極６と第２溶接電極７との間に上記中心電極１を挟持して，上記中心電極１の一方の円弧状側面１１に上記一方の金属チップ３１を抵抗溶接する。
【００２５】
上記第１溶接電極６は，図１，図２に示すごとく，上記金属チップ３１に当接する第１凹部６１を有し，また上記第２溶接電極７は上記中心電極１の先端部１０に直接当接する第２凹部７１を有している。また，上記第１凹部６１及び第２凹部７１は，上記中心電極１の先端部１０の上記円弧状側面１１，１２と同形状を有している。
【００２６】
次いで，金属チップ３１を接合した中心電極１を１８０度回転させて，第１溶接電極６と第２溶接電極７との間に挟持し，かつ上記中心電極１のもう一方の円弧状側面１２に他方の上記金属チップ３２を抵抗溶接する。この場合，第２凹部には，上記中心電極１と接合して一体化した金属チップ３１が当接するが，その他は上記１回目の抵抗溶接時と同様である。
【００２７】
なお，上記中心電極１は，Ｎｉ−Ｃｒ−Ｆｅ合金（商標：インコネル６００）よりなり，その先端部１０は，図１，図３，図４に示すごとく，脚部１１０に比べ細い円柱形状をなしている。そして，上述したごとく，この先端部１０の直径方向の一対の円弧状側面１１，１２に金属チップ３１，３２を接合する。
また，上記金属チップ３１，３２としては，Ｐｔ−Ｉｒ−Ｎｉ合金よりなる，直径１．２ｍｍφ，厚み０．３ｍｍのディスク状のものを用いた。
【００２８】
次に，上記金属チップ３１，３２を接合した中心電極１は，次のようにスパークプラグに組付ける。
まず，図４に示すごとく，碍子４の内孔４０内に，上記中心電極１の脚部１１０を挿入した後，導電性ガラス１３４，内蔵抵抗１３５を投入し，次いで端子１３６を挿入する。
【００２９】
次いで，上記碍子４を加熱し，上記導電性ガラス１３４を溶融固着させる。これにより，碍子４，中心電極１，導電性ガラス１３４，内蔵抵抗１３５，及び端子１３６が一体化する。
一方，接地電極２１，２２は，予め金属ハウジング５に溶接し，所定の形状及び方向に曲げ加工しておく。
【００３０】
次に，中心電極１と一体化した碍子４を金属ハウジング５の内孔５０内に挿入固定し，中心電極１の金属チップ３１，３２と接地電極２１，２２を対向配設させる。
このとき，碍子４と金属ハウジング５との間には，両者の気密性を確保するために，ガスケット１３１，１３２を組付ける。
【００３１】
次いで，金属ハウジング５の上下両端に高電圧をかけると共に，金属ハウジング５の腹部５１を押圧し，かしめる。
これにより，中心電極１と一体化した碍子４が金属ハウジング５に固定され，スパークプラグが得られる。
【００３２】
また，本例においては，上記中心電極１の上記円弧状側面１１，１２の曲率半径をＲ１，上記第１凹部６１の曲率半径をＲ２，上記第２凹部７１の曲率半径をＲ３，第２凹部７１の深さをＨとし，それぞれの値を種々変化させ，比較例とともに，バリ，座屈，変形等の発生状況を調査した。
尚，抵抗溶接の条件はすべての場合において，印加電圧３０ｋＶ，印加電流１２５０Ａ，加圧力３０ｋｇとした。
【００３３】
まず，上記Ｒ１＝１ｍｍ，Ｒ３＝１ｍｍ，Ｈ＝０．５ｍｍの値を，それぞれ一定とし，第１凹部６１の曲率半径であるＲ２を０．７ｍｍ〜１．３ｍｍまで０．１ｍｍピッチで変化させた。そして，金属チップ３１と円弧状側面１１との接触部あるいは金属チップ３１の表面における，バリ，座屈，変形等の発生状況を観察した。
【００３４】
観察の結果，表１に示すごとく，上記Ｒ２が本発明の範囲内にある場合，即ち，Ｒ２＝０．８〜１．２ｍｍの場合においては，バリ，座屈，変形等の発生が見られなかった。一方，Ｒ２が本発明の範囲を外れる場合には以下のような不具合が見られた。
【００３５】
即ち，Ｒ２＝０．７ｍｍの場合には，図６に示すごとく，第１凹部６１と金属チップ３１の周縁部の２か所の接触部Ａ３，Ａ４において，バリ，座屈，変形等の発生が見られた。また，Ｒ２＝１．２ｍｍの場合には，図７に示すごとく，金属チップ３１の中央部と中心電極１との接触部Ａ５において，バリ，座屈，変形等の発生が見られた。
【００３６】
【表１】

【００３７】
次に，上記Ｒ１＝１ｍｍ，Ｒ２＝１ｍｍ，Ｈ＝０．５ｍｍの値を，それぞれ一定とし，第２凹部７１の曲率半径であるＲ３を０．８ｍｍ〜１．２ｍｍまで０．１ｍｍピッチで変化させた。そして，第２凹部６１と円弧状側面１２との接触部における中心電極１のバリ，座屈，変形等の発生状況を観察した。
【００３８】
観察の結果，表２に示すごとく，上記Ｒ３が本発明の範囲内にある場合，即ち，Ｒ３＝０．９〜１．１ｍｍの場合においては，バリ，座屈，変形等の発生が見られなかった。一方，Ｒ３が本発明の範囲を外れる場合には，以下のような不具合が見られた。
【００３９】
即ち，Ｒ３＝０．８ｍｍの場合には，図８に示すごとく，中心電極１と第２凹部７１の２か所の頂部７１０との接触部Ａ６，Ａ７において，バリ，座屈，変形等の発生が見られた。また，Ｒ３＝１．１ｍｍの場合には，図９に示すごとく，中心電極１と第２凹部７１の底部との接触部Ａ８において，バリ，座屈，変形等の発生が見られた。
【００４０】
【表２】

【００４１】
次に，上記Ｒ１＝１ｍｍ，Ｒ２＝１ｍｍ，Ｒ３＝１ｍｍの値を，それぞれ一定とし，第２凹部７１の深さであるＨを種々変化させた。そして，第２凹部６１と円弧状側面１２との接触部における中心電極１のバリ，座屈，変形等の発生状況を観察した。
【００４２】
観察の結果，上記Ｈが本発明の範囲内，即ち，０．２５ｍｍ≦Ｈ＜１ｍｍの場合には，特に問題は発生しなかった。一方，上記Ｈが０．２５ｍｍ未満，即ち，Ｈ＜（１／４）×Ｒ１の場合には，中心電極１と第２凹部７１との接触面積が小さすぎるため，熱伝導が悪化し，中心電極の座屈，変形が発生した。また，上記Ｈが１ｍｍ以上，即ちＨ≧Ｒ１の場合には，中心電極１を第２凹部７１にうまくセットすることができなく，不適であった。
【００４３】
上述のごとく，本例においては，上記第１溶接電極６は第１凹部６１を有し，かつ該第１凹部６１の曲率半径Ｒ２は，上記中心電極１の上記円弧状側面１１，１２の曲率半径Ｒ１に対して，Ｒ１−０．２≦Ｒ２≦Ｒ１＋０．２の関係にある。そのため，２回の抵抗溶接における加圧通電の際には，第１溶接電極６の第１凹部６１と金属チップ３１，３２，及び金属チップ３１，３２と中心電極１は，それぞれ比較的広い面積において面接触する。それ故，金属チップ３１，３２と中心電極１とはバリ，座屈，変形等を発生させることなく，強固に接合する。
【００４４】
また，上記第２溶接電極７は第２凹部７１を有し，かつ該第２凹部７１の曲率半径Ｒ３は，上記中心電極１上記円弧状側面１１，１２の曲率半径Ｒ１に対して，Ｒ１−０．１≦Ｒ３≦Ｒ１＋０．１の関係にある。そのため，２回の抵抗溶接における加圧通電の際には，第２溶接電極７の第２凹部７１と中心電極１とは，比較的広い面積において面接触する。それ故，中心電極１における第２溶接電極７との接触部には，バリ，座屈，変形等が発生することはない。
【００４５】
従って，本例においては，中心電極１の側面に特に平面部を設ける工程を，抵抗溶接前に採ることなく，低コストでスパークプラグを製造することができる。また，本例の製造方法において得られたスパークプラグは，図５に示すごとく，中心電極１の円弧状側面１１，１２に金属チップ３１，３２が接合されており，金属チップ３１，３２の表面も円弧状である。そのため，中心電極１と接地電極２１，２２とが角度θだけ回転ズレしても，火花ギャップＧ１は，殆どばらつかない。それ故，得られたスパークプラグは，優れた耐火花消耗性を発揮することができる。
【００４６】
実施例２
本例のスパークプラグの製造方法においては，図１０に示すごとく，中心電極１の先端部１０の円弧状側面１１，１２に，金属チップ３１の径よりも狭い極僅かの極小平面部１１５，１２５を設けた。また，この極小平面部１１５，１２５は，中心電極１の押し出し成形と同時に設けた。その他は，実施例１と同様である。
【００４７】
本例においては，中心電極１の先端部１０に上記極小平面部１１５，１２５を設けてある。そのため，中心電極１の円弧状側面１１，１２部分への金属チップ３１，３２のセッティングを簡単に行うことができる。また，この極小平面部１１５，１２５は，極僅かの幅である。そのため，金属チップ３１，３２の表面は，実施例１と同様に，中心電極１の円弧状側面１１，１２と同様の円弧状形状をなす。それ故，従来のように金属チップ３１，３２以外のところで火花ギャップを形成させるということはない。その他，実施例１と同様の効果が得られる。
【００４８】
実施例３
本例のスパークプラグの製造方法においては，図１１に示すごとく，実施例１における第１溶接電極６を下方に，第２溶接電極７を上方に配設し，金属チップ３１を中心電極１の下方に挟持して抵抗溶接する。その他は，実施例１と同様である。
【００４９】
本例においては，金属チップ３１を中心電極１の下方に配置させて抵抗溶接するため，金属チップ３１のセッティングが容易である。
その他，実施例１と同様の効果が得られる。
【００５０】
実施例４
本例のスパークプラグの製造方法においては，図１２に示すごとく，金属チップ３１０を，中心電極１の先端部１０の円弧状側面１１に沿った曲面形状に予め曲げ加工してある。その他は，実施例３と同様である。
【００５１】
本例においては，金属チップ３１０が上記曲面形状に予め曲げ加工されている。そのため，金属チップ３１０は，第１溶接電極６の第１凹部６１に載置してわずかな振動を与えることにより，上記第１凹部６１に十分に面接触する。それ故，金属チップ３１０のセッティングが容易である。
その他，実施例３と同様の効果が得られる。
【図面の簡単な説明】
【図１】実施例１における，抵抗溶接時のセッティング状態の斜視図。
【図２】実施例１における，抵抗溶接時のセッティング状態の正面図。
【図３】実施例１における，中心電極の金属チップ接合部の（ａ）平面図，（ｂ）正面図。
【図４】実施例１における，スパークプラグの一部切欠断面図。
【図５】実施例１における，中心電極の金属チップと接地電極の配置状態を示す説明図。
【図６】実施例１の比較例における，抵抗溶接時の不具合の説明図。
【図７】実施例１の比較例における，抵抗溶接時の不具合の説明図。
【図８】実施例１の比較例における，抵抗溶接時の不具合の説明図。
【図９】実施例１の比較例における，抵抗溶接時の不具合の説明図。
【図１０】実施例２における，抵抗溶接時のセッティング状態の正面図。
【図１１】実施例３における，抵抗溶接時のセッティング状態の正面図。
【図１２】実施例４における，抵抗溶接時のセッティング状態の正面図。
【図１３】従来例における，中心電極の金属チップと接地電極の配置状態を示す説明図。
【図１４】従来例における，抵抗溶接時のセッティング状態の（ａ）正面図，（ｂ）側面図。
【符号の説明】
１．．．中心電極，
１０．．．先端部，
１１，１２．．．円弧状側面，
２１，２２．．．接地電極，
３１，３２．．．金属チップ，
６．．．第１溶接電極，
６１．．．第１凹部，
７．．．第２溶接電極，
７１．．．第２凹部，[0001]
[Industrial application fields]
The present invention relates to a method for manufacturing a spark plug in which a metal tip provided on an arcuate side surface of a tip portion of a center electrode and a ground electrode face each other.
[0002]
[Prior art]
With the recent demand for maintenance-free internal combustion engines, spark plugs are required to have a longer life.
Many long-life spark plugs have been proposed in which a metal tip with excellent spark wear resistance is joined to the discharge surface of the center electrode.
[0003]
As shown in FIG. 13, a spark plug in which

metal tips

31 and 32 are joined to

flat portions

911 and 912 on the side surface of a center electrode 91 is known as a spark plug to which metal tips are joined. For joining the

metal tips

31 and 32 to the center electrode 91, first,

flat portions

911 and 912 are provided on the side surfaces of the center electrode, and then the two

metal tips

31 and 32 are joined sequentially by resistance welding. ing.
[0004]
[Problems to be solved]
However, the conventional spark plug manufacturing method has the following problems.
That is, in order to provide the

flat portions

911 and 912 on the side surface of the arc-shaped center electrode 91, cutting, polishing, plastic working and the like are required, which increases the cost.
[0005]
In addition, as shown in FIG. 13, when the

flat portion

911, 912 of the center electrode 91 is rotated by an angle θ with respect to the

ground electrodes

921, 922, the spark plug G2 obtained as shown in FIG. It is formed at a place other than the

metal chips

31 and 32. For this reason, the center electrode 91 that is inferior in spark wear resistance deteriorates in a short period of time, and the life of the spark plug cannot be extended.
[0006]
Further, as a spark plug for extending the life, a spark plug in which a metal tip is directly joined to an arc-shaped side surface without providing a flat portion on the center electrode and the surface of the metal tip is arc-shaped has been proposed (FIG. 3, FIG. 3). (See FIG. 5). As a method of joining the metal tip to the center electrode in this spark plug, as shown in FIG. 14, the center electrode 1 and the metal tip 31 are disposed between the planar first welding electrode 96 and the planar second welding electrode 97. There is a method of resistance welding.
[0007]
In this method, as shown in FIG. 14, the contact portion A1 between the metal tip 31 and the center electrode 1 and the contact portion A2 between the center electrode and the second welding electrode are both in line contact, and the contact area is small. Therefore, both the contact portions A1 and A2 have high resistance when energized with pressure and are excessively heated. Therefore, in both the contact portions A1 and A2, the center electrode 1 and the metal tip 31 are excessively melted, causing problems such as burrs, buckling, and deformation. In order to prevent this problem, it is conceivable to reduce the energization current, but in this case, it is impossible to obtain a stable bonding strength.
[0008]
The present invention has been made in view of such conventional problems, and has excellent spark wear resistance and an excellent bonded state without burrs, buckling, and deformation at the joint between the center electrode and the metal tip. It is an object of the present invention to provide a spark plug manufacturing method capable of manufacturing a spark plug having a low cost.
[0009]
[Means for solving problems]
The present invention has a center electrode having an arc-shaped side surface at a tip portion and a ground electrode disposed opposite to the arc-shaped side surface of the center electrode, and the arc-shaped side surface has a ground electrode compared to the center electrode. In a method of manufacturing a spark plug formed by joining a metal tip made of a metal having excellent spark wear resistance or an alloy thereof,
In the resistance welding of the metal tip to the arcuate side surface of the center electrode by sandwiching the center electrode between the first welding electrode and the second welding electrode,
The first welding electrode has a first recess abutting against the metal tip;
In addition, the second welding electrode has a second recess that directly contacts the tip of the center electrode,
And the said 1st recessed part and the 2nd recessed part have the same shape as the said circular arc side surface of the front-end | tip part of the said center electrode,
When the radius of curvature of the arc-shaped side surface of the center electrode is R1 mm and the radius of curvature of the first recess of the first welding electrode is R2 mm , R2 mm is the following relational expression R1 mm −0.2 mm ≦ R2 mm ≦ R1 mm +0.2 mm
It exists in the range shown by this, It exists in the manufacturing method of the spark plug characterized by the above-mentioned.
[0010]
The most notable aspect of the present invention is that the first welding electrode has the first recess, and the second welding electrode has the second recess, and the first and second recesses. Has the same shape as the arc-shaped side surface of the tip of the center electrode.
[0011]
Further, the same shape does not mean that the dimensions are exactly the same, but means that the dimensions are almost the same and the shapes are similar. That is, if the shape of the arc-shaped side surface of the center electrode is substantially perfect circle shape, the first recess and the second recess are also substantially true circle shape, and if the arc-shaped side surface is elliptical shape, It means that the recess and the second recess are also elliptical.
[0012]
Examples of the metal tip include noble metals such as platinum (Pt), iridium (Ir), Pt—Ir alloy, Pt—Ir—nickel (Ni) alloy or alloys thereof, or chromium (Cr), Cr alloy, etc. There is. The metal chip is a flat plate having a substantially constant thickness, and various shapes such as a disk shape (circular shape) and a square shape can be applied.
[0013]
When the radius of curvature of the arc-shaped side surface of the center electrode is R1 mm and the radius of curvature of the first recess of the first welding electrode is R2 mm , R2 mm is the following relational expression R1 mm −0.2 mm ≦ R2 mm ≦ R1 mm +0.2 mm
(The unit is mm. The same shall apply hereinafter) .
As a result, the center electrode and the metal tip can be firmly bonded without causing burrs, buckling, deformation, or the like.
[0014]
When R2 is smaller than R1-0.2 (see FIG. 6), the first welding electrode contacts only two places on the peripheral edge of the metal tip, and its contact area is small (reference A3 in FIG. 6). , A4). For this reason, the contact portion is excessively heated when energized under pressure, and there is a problem that burrs, buckling, deformation, etc. occur. When R2 is larger than R1 + 0.2 (see FIG. 7), the first welding electrode is in line contact with the central portion of the metal tip, and the contact area is small (see A5 in FIG. 7). Therefore, there is a problem that burrs, buckling, deformation, etc. occur in the contact portion, as in the case where the first recess is not provided.
[0015]
Next, a center electrode having an arc-shaped side surface at the tip and a ground electrode disposed opposite to the arc-shaped side surface of the center electrode, and the arc-shaped side surface has a fire resistance compared to the center electrode. In a spark plug manufacturing method in which a metal tip made of a metal having excellent flower wearability or an alloy thereof is joined,
In the resistance welding of the metal tip to the arcuate side surface of the center electrode by sandwiching the center electrode between the first welding electrode and the second welding electrode,
The first welding electrode has a first recess abutting against the metal tip;
In addition, the second welding electrode has a second recess that directly contacts the tip of the center electrode,
And the said 1st recessed part and the 2nd recessed part have the same shape as the said circular arc side surface of the front-end | tip part of the said center electrode,
The radius of curvature of the arcuate side surface of the tip of the center electrode is R1, the radius of curvature of the second recess of the second welding electrode is R3 mm , and the depth of the second recess of the second welding electrode is R3 mm . When H mm , R3 mm and H mm are the following relational expressions: R1 mm −0.1 mm ≦ R3 mm ≦ R1 mm + 0.1 mm
R1 mm > H mm ≧ (1/4) × R1 mm
There is a manufacturing method of a spark plug characterized by being within the range indicated by.
If within the range indicated by the above relational expression, the metal tip and the center electrode are resistance welded without causing burrs, buckling, deformation, or the like at the contact portion between the center electrode and the second welding electrode. can do.
[0016]
When R3 is smaller than R1-0.1 (see FIG. 8), the center electrode is in line contact with the two top portions of the second recess, and the contact area is small (reference A6 in FIG. 8). , A7). For this reason, the contact portion is excessively heated when energized under pressure, and there is a problem that burrs, buckling, deformation, etc. occur. When R3 is larger than R1 + 0.1 (see FIG. 9), the bottom of the second recess is in line contact with the center electrode, and the contact area is small (see A8 in FIG. 9). Therefore, as in the case where the second welding electrode does not have the second recess, there is a problem that burrs, buckling, deformation, etc. occur at the contact portion.
[0017]
Further, when H is equal to or greater than R1, there is a problem that the center electrode cannot be set in the second recess. When H is smaller than (1/4) × R1, the contact area between the center electrode and the second welding electrode is too small. For this reason, the contact portion is excessively heated when energized under pressure, and there is a problem that burrs, buckling, deformation, etc. occur in the contact portion.
[0018]
The metal tip is preferably bent in advance into a curved shape along the arcuate side surface of the tip of the center electrode. Thereby, the setting at the time of resistance welding can be made easy.
[0019]
[Action and effect]
In the spark plug manufacturing method of the present invention, the first welding electrode has the first recess, and the first recess has the same shape as the arc-shaped side surface of the tip of the center electrode. Yes. Therefore, during pressurization energization in resistance welding, the first recess of the first welding electrode and the metal tip, and the metal tip and the center electrode are in surface contact with each other over a relatively wide area. Therefore, the metal tip and the center electrode are firmly joined without causing burrs, buckling, deformation, or the like.
[0020]
The second welding electrode has the second recess, and the second recess has the same shape as the arc-shaped side surface of the tip of the center electrode. Therefore, during pressurization energization in resistance welding, the second recess of the second welding electrode and the center electrode are in surface contact over a relatively wide area. Therefore, no burr, buckling, deformation or the like occurs at the contact portion of the center electrode with the second welding electrode.
[0021]
Therefore, it is possible to omit the step of providing a flat portion on the side surface of the center electrode in advance before resistance welding as in the prior art, and it is possible to manufacture a spark plug at low cost. Also, the center electrode of the obtained spark plug can be manufactured. The joint between the metal chip and the metal chip has an excellent bonding state and is excellent in spark wear resistance.
[0022]
As described above, according to the present invention, a spark plug having excellent spark wear resistance and an excellent joined state free from burrs, buckling, and deformation at the joint between the center electrode and the metal tip can be obtained. A spark plug manufacturing method that can be manufactured at low cost can be provided.
[0023]
【Example】
Example 1
A method for manufacturing a spark plug according to an embodiment of the present invention will be described with reference to FIGS.
As shown in FIGS. 1 to 5, the spark plug manufacturing method of the present example is opposed to the center electrode 1 having arcuate side surfaces 11 and 12 at the tip 10 and the arcuate side surfaces 11 and 12 of the center electrode 1. Metal chips 31 and 32 having a grounding electrode 21 and 22 (FIG. 4) disposed thereon and having excellent arc wear resistance compared to the center electrode 1 are joined to the arc-shaped side surfaces 11 and 12. This is a method for manufacturing a spark plug.
[0024]
In joining the

metal tips

31 and 32 to the center electrode 1, as shown in FIGS. 1 and 2, first, the center electrode 1 is sandwiched between the first welding electrode 6 and the second welding electrode 7. The one metal tip 31 is resistance welded to one arcuate side surface 11 of the center electrode 1.
[0025]
As shown in FIGS. 1 and 2, the first welding electrode 6 has a first recess 61 that abuts on the metal tip 31, and the second welding electrode 7 is directly on the tip 10 of the center electrode 1. It has the 2nd recessed part 71 which contact | abuts. The first recess 61 and the second recess 71 have the same shape as the arcuate side surfaces 11 and 12 of the tip portion 10 of the center electrode 1.
[0026]
Next, the center electrode 1 to which the metal tip 31 is joined is rotated by 180 degrees and is sandwiched between the first welding electrode 6 and the second welding electrode 7, and on the other arcuate side surface 12 of the center electrode 1. The other metal tip 32 is resistance welded. In this case, the metal chip 31 joined and integrated with the center electrode 1 is brought into contact with the second recess, but the others are the same as in the first resistance welding.
[0027]
The center electrode 1 is made of a Ni—Cr—Fe alloy (trademark: Inconel 600), and the tip 10 has a columnar shape that is narrower than the legs 110 as shown in FIGS. There is no. As described above, the

metal chips

31 and 32 are joined to the pair of arcuate side surfaces 11 and 12 in the diameter direction of the tip portion 10.
Further, as the

metal tips

31 and 32, disk-shaped ones made of Pt—Ir—Ni alloy and having a diameter of 1.2 mmφ and a thickness of 0.3 mm were used.
[0028]
Next, the center electrode 1 to which the

metal tips

31 and 32 are joined is assembled to the spark plug as follows.
First, as shown in FIG. 4, after inserting the leg 110 of the center electrode 1 into the inner hole 40 of the insulator 4, the conductive glass 134 and the built-in resistor 135 are inserted, and then the terminal 136 is inserted.
[0029]
Next, the insulator 4 is heated to melt and fix the conductive glass 134. Thereby, the insulator 4, the center electrode 1, the conductive glass 134, the built-in resistor 135, and the terminal 136 are integrated.
On the other hand, the

ground electrodes

21 and 22 are previously welded to the metal housing 5 and bent in a predetermined shape and direction.
[0030]
Next, the insulator 4 integrated with the center electrode 1 is inserted and fixed in the inner hole 50 of the metal housing 5, and the

metal tips

31, 32 of the center electrode 1 and the

ground electrodes

21, 22 are arranged to face each other.
At this time,

gaskets

131 and 132 are assembled between the insulator 4 and the metal housing 5 in order to ensure the airtightness of both.
[0031]
Next, a high voltage is applied to the upper and lower ends of the metal housing 5 and the abdomen 51 of the metal housing 5 is pressed and caulked.
Thereby, the insulator 4 integrated with the center electrode 1 is fixed to the metal housing 5, and a spark plug is obtained.
[0032]
In this example, the radius of curvature of the arc-shaped side surfaces 11 and 12 of the center electrode 1 is R1, the radius of curvature of the first recess 61 is R2, the radius of curvature of the second recess 71 is R3, and the second recess. The depth of 71 was set to H, each value was changed variously, and the occurrence state of burrs, buckling, deformation, etc. was investigated together with the comparative example.
In all cases, the resistance welding conditions were applied voltage 30 kV, applied current 1250 A, and applied pressure 30 kg.
[0033]
First, the values of R1 = 1 mm, R3 = 1 mm, and H = 0.5 mm are fixed, and the radius of curvature R2 of the first recess 61 is changed from 0.7 mm to 1.3 mm at a pitch of 0.1 mm. It was. Then, the occurrence of burrs, buckling, deformation, and the like at the contact portion between the metal tip 31 and the arc-shaped side surface 11 or the surface of the metal tip 31 was observed.
[0034]
As a result of observation, as shown in Table 1, when R2 is within the range of the present invention, that is, when R2 = 0.8 to 1.2 mm, burrs, buckling, deformation, etc. are observed. There wasn't. On the other hand, when R2 was outside the scope of the present invention, the following problems were observed.
[0035]
That is, when R2 = 0.7 mm, burrs, buckling, deformation, etc. occur at the two contact portions A3 and A4 of the first recess 61 and the peripheral edge of the metal tip 31, as shown in FIG. It was observed. In the case of R2 = 1.2 mm, as shown in FIG. 7, the occurrence of burrs, buckling, deformation, etc. was observed at the contact portion A5 between the central portion of the metal tip 31 and the central electrode 1.
[0036]
[Table 1]

[0037]
Next, the values of R1 = 1 mm, R2 = 1 mm, and H = 0.5 mm are made constant, and R3, which is the radius of curvature of the second recess 71, is changed from 0.8 mm to 1.2 mm at a pitch of 0.1 mm. I let you. Then, the state of occurrence of burrs, buckling, deformation and the like of the center electrode 1 at the contact portion between the second recess 61 and the arc-shaped side surface 12 was observed.
[0038]
As a result of observation, as shown in Table 2, when R3 is within the range of the present invention, that is, when R3 = 0.9 to 1.1 mm, burrs, buckling, deformation, etc. are observed. There wasn't. On the other hand, when R3 was outside the scope of the present invention, the following problems were observed.
[0039]
That is, when R3 = 0.8 mm, as shown in FIG. 8, burr, buckling, deformation, etc. occur at the contact portions A6 and A7 between the center electrode 1 and the two top portions 710 of the second recess 71. Occurrence was seen. In the case of R3 = 1.1 mm, as shown in FIG. 9, burrs, buckling, deformation, and the like were observed at the contact portion A8 between the center electrode 1 and the bottom of the second recess 71.
[0040]
[Table 2]

[0041]
Next, the values of R1 = 1 mm, R2 = 1 mm, and R3 = 1 mm were made constant, and H, which is the depth of the second recess 71, was changed variously. Then, the state of occurrence of burrs, buckling, deformation and the like of the center electrode 1 at the contact portion between the second recess 61 and the arc-shaped side surface 12 was observed.
[0042]
As a result of observation, when H is within the range of the present invention, that is, when 0.25 mm ≦ H <1 mm, no particular problem has occurred. On the other hand, when the H is less than 0.25 mm, that is, H <(1/4) × R1, the contact area between the center electrode 1 and the second recess 71 is too small, so that the heat conduction deteriorates and the center Electrode buckling and deformation occurred. Further, when H is 1 mm or more, that is, H ≧ R1, the center electrode 1 cannot be set well in the second recess 71, which is inappropriate.
[0043]
As described above, in this example, the first welding electrode 6 has the first recess 61, and the radius of curvature R2 of the first recess 61 is the curvature of the arcuate side surfaces 11 and 12 of the center electrode 1. There is a relationship of R1-0.2 ≦ R2 ≦ R1 + 0.2 with respect to the radius R1. For this reason, when applying pressure in two resistance weldings, the first recess 61 of the first welding electrode 6 and the

metal tips

31, 32, and the

metal tips

31, 32 and the center electrode 1 have a relatively large area, respectively. In surface contact. Therefore, the

metal tips

31 and 32 and the center electrode 1 are firmly joined without causing burrs, buckling, deformation, or the like.
[0044]
The second welding electrode 7 has a second recess 71, and the radius of curvature R3 of the second recess 71 is R1− with respect to the radius of curvature R1 of the central electrode 1 and the arcuate side surfaces 11 and 12. The relationship is 0.1 ≦ R3 ≦ R1 + 0.1. For this reason, the second recess 71 of the second welding electrode 7 and the center electrode 1 are in surface contact with each other over a relatively large area when pressure is applied in two resistance weldings. Therefore, no burr, buckling, deformation or the like occurs at the contact portion of the center electrode 1 with the second welding electrode 7.
[0045]
Therefore, in this example, a spark plug can be manufactured at a low cost without taking the step of providing a flat portion on the side surface of the center electrode 1 before resistance welding. Further, as shown in FIG. 5, the spark plug obtained in the manufacturing method of this example has

metal tips

31 and 32 joined to the arc-shaped side surfaces 11 and 12 of the center electrode 1, and the surface of the

metal tips

31 and 32. Is also arcuate. Therefore, even if the center electrode 1 and the

ground electrodes

21 and 22 are rotated by an angle θ, the spark gap G1 hardly varies. Therefore, the obtained spark plug can exhibit excellent spark wear resistance.
[0046]
Example 2
In the spark plug manufacturing method of this example, as shown in FIG. 10, on the arc-shaped side surfaces 11 and 12 of the tip portion 10 of the center electrode 1, there are very few minimal

flat portions

115 and 125 narrower than the diameter of the metal tip 31. Was established. Further, the minimal

flat portions

115 and 125 were provided simultaneously with the extrusion of the center electrode 1. Others are the same as in the first embodiment.
[0047]
In this example, the minimum

flat portions

115 and 125 are provided at the distal end portion 10 of the center electrode 1. Therefore, the setting of the

metal tips

31 and 32 to the arcuate side surfaces 11 and 12 of the center electrode 1 can be easily performed. Further, the minimal

flat surface portions

115 and 125 have a very small width. Therefore, the surfaces of the

metal tips

31 and 32 have the same arcuate shape as the arcuate side surfaces 11 and 12 of the center electrode 1 as in the first embodiment. Therefore, the spark gap is not formed in places other than the

metal tips

31 and 32 as in the prior art. In addition, the same effects as those of the first embodiment can be obtained.
[0048]
Example 3
In the spark plug manufacturing method of this example, as shown in FIG. 11, the first welding electrode 6 and the second welding electrode 7 in Example 1 are disposed below and the metal tip 31 is disposed on the center electrode 1 as shown in FIG. Clamp downward and resistance weld. Others are the same as in the first embodiment.
[0049]
In this example, since the metal tip 31 is disposed below the center electrode 1 and resistance welding is performed, the setting of the metal tip 31 is easy.
In addition, the same effects as those of the first embodiment can be obtained.
[0050]
Example 4
In the spark plug manufacturing method of this example, as shown in FIG. 12, the metal tip 310 is bent in advance into a curved shape along the arcuate side surface 11 of the tip 10 of the center electrode 1. Others are the same as in the third embodiment.
[0051]
In this example, the metal tip 310 is previously bent into the curved surface shape. Therefore, the metal tip 310 is sufficiently in surface contact with the first recess 61 by being placed in the first recess 61 of the first welding electrode 6 and applying slight vibration. Therefore, setting of the metal tip 310 is easy.
In addition, the same effects as those of the third embodiment can be obtained.
[Brief description of the drawings]
1 is a perspective view of a setting state during resistance welding in Example 1. FIG.
2 is a front view of a setting state during resistance welding in Example 1. FIG.
3A is a plan view and FIG. 3B is a front view of a metal tip joint portion of a center electrode in Embodiment 1. FIG.
4 is a partially cutaway cross-sectional view of a spark plug in Embodiment 1. FIG.
5 is an explanatory diagram showing an arrangement state of a metal tip of a center electrode and a ground electrode in Example 1. FIG.
FIG. 6 is an explanatory diagram of defects during resistance welding in a comparative example of Example 1.
FIG. 7 is an explanatory diagram of defects during resistance welding in a comparative example of Example 1.
FIG. 8 is an explanatory diagram of defects during resistance welding in a comparative example of Example 1.
FIG. 9 is an explanatory diagram of defects during resistance welding in a comparative example of Example 1;
10 is a front view of a setting state during resistance welding in Example 2. FIG.
11 is a front view of a setting state during resistance welding in Example 3. FIG.
12 is a front view of the setting state during resistance welding in Example 4. FIG.
FIG. 1 3 is an explanatory view showing an arrangement state of a metal tip of a center electrode and a ground electrode in a conventional example.
[1 4] in a conventional example, (a) a front view of the setting state at the time of resistance welding, (b) a side view.
[Explanation of symbols]
1. . . Center electrode,
10. . . Tip,
11,12. . . Arcuate sides,
21,22. . . Ground electrode,
31, 32. . . Metal chips,
6). . . First welding electrode,
61. . . First recess,
7). . . Second welding electrode,
71. . . Second recess,

Claims

A center electrode having an arc-shaped side surface at a tip portion, and a ground electrode disposed opposite to the arc-shaped side surface of the center electrode, and the arc-shaped side surface has a spark wear resistance compared to the center electrode. In a method of manufacturing a spark plug formed by bonding a metal tip made of a metal excellent in metal or an alloy thereof,
In the resistance welding of the metal tip to the arcuate side surface of the center electrode by sandwiching the center electrode between the first welding electrode and the second welding electrode,
The first welding electrode has a first recess abutting against the metal tip;
In addition, the second welding electrode has a second recess that directly contacts the tip of the center electrode,
And the said 1st recessed part and the 2nd recessed part have the same shape as the said circular arc side surface of the front-end | tip part of the said center electrode,
When the radius of curvature of the arc-shaped side surface of the center electrode is R1 mm and the radius of curvature of the first recess of the first welding electrode is R2 mm , R2 mm is the following relational expression R1 mm −0.2 mm ≦ R2 mm ≦ R1 mm +0.2 mm
A method for producing a spark plug, characterized by being within the range indicated by.

A center electrode having an arc-shaped side surface at a tip portion, and a ground electrode disposed opposite to the arc-shaped side surface of the center electrode, and the arc-shaped side surface has a spark wear resistance compared to the center electrode. In a method of manufacturing a spark plug formed by bonding a metal tip made of a metal excellent in metal or an alloy thereof,
In the resistance welding of the metal tip to the arcuate side surface of the center electrode by sandwiching the center electrode between the first welding electrode and the second welding electrode,
The first welding electrode has a first recess abutting against the metal tip;
In addition, the second welding electrode has a second recess that directly contacts the tip of the center electrode,
And the said 1st recessed part and the 2nd recessed part have the same shape as the said circular arc side surface of the front-end | tip part of the said center electrode,
The radius of curvature of the arcuate side surface of the tip of the center electrode is R1 mm , the radius of curvature of the second recess of the second welding electrode is R3 mm , and the depth of the second recess of the second welding electrode the when the H mm, R3 mm and H mm following relationship R1 mm -0.1 is mm ≦ R3 mm ≦ R1 mm +0.1 mm
R1 mm > H mm ≧ (1/4) × R1 mm
A method for producing a spark plug, characterized by being within the range indicated by.

3. The spark plug manufacturing method according to claim 1, wherein the metal tip is bent in advance into a curved shape along the arcuate side surface of the tip of the center electrode.