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The U-Groove Design
In 1972, we received a patent for the popular U-Groove ground electrode design. This electrode was developed to meet the demand for improved ignitability, which is necessary for an increase of efficiency in emission gas purification and fuel consumption. The U-Groove gives the flame a groove to grow in, thereby creating a larger flame front for a more complete combustion even in the case of lean air-fuel mixture. A conventional, flat ground electrode design of regular plugs crushes the flame preventing full spark potential. Iridium Alloy In a never-ending effort to improve upon success, DENSO developed an Iridium alloy that is superior to platinum based on hardness, strength and melting point. The new Iridium alloy is composed primarily of Iridium with rhodium mixed in for oxidation wear.  Pure Iridium has a melting point of almost 700ºC higher than platinum, and had the greatest potential for resistances against wear. Iridium by itself is susceptible to oxidation wear at temperatures over 900ºC, however, ordinary driving around town an engine would never reach these temperatures. Further testing proved that Iridium alone would not meet DENSO's demanding standards. After testing other pure metals combined with Iridium, rhodium proved to be the best choice to meet the needs of DENSO's spark plug engineers.
 Laser Welding Process 
DENSO's Iridium Alloy had all of the qualities to produce the world's best spark plug, but conventional tooling prevented DENSO from mass manufacturing. Due to the high melting point there wasn't a welding process hot enough to join the Iridium tip to the nickel base. Necessity to melt the Iridium to the nickel base forced DENSO to pioneer its third patent, the 360º Laser Welding Process, to provide a seal so reliable; the electrode resists wear even in the worst combustion conditions.
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