Abstract
Inconel 601 is one material of choice for intermediate- to high-temperature protective coatings for spark plugs’ ground electrodes. Production of ground electrodes of spark plugs implies the following operations: the tamping of the copper core in an Inconel 601 cup, cold-forming of the assembly, annealing, welding, and bending of the final spark plug. On the production line, the use of Inconel 601 as a protective coating for ground electrodes leads to possible cracking in the welded area after bending. In the present paper, possible causes of cracking are analyzed. It is clearly shown that a combination of Copper –Inconel interface oxidation, Inconel yielding during the heat treatment, and micro-movements during bending lead to cracks in the welded area of the ground electrode. First, the detrimental effect of gaps, between Copper and Inconel 601, is shown experimentally. Second, a thermo-mechanical analysis combined with SEM (Scanning Electron Microscopy) observations identified the annealing treatment and interface oxidation as the main cause of gaps. Third, bending simulations show the relation between these gaps and cracking. Finally, a new ground electrode design, preventing cracks, is suggested.
Highlights
Considering the increased cost of oil and the stringent emission regulations, engine design should satisfy three important expectations: lower fuel consumption, lower emission, and correct function of engine
It is well-known with non-zero strain σ. The latter adds a degree of freedom to the problem. It is wellthat such thermo-mechanical models overestimate the σzz stresses due to the constraint imposed by known that such thermo-mechanical models overestimate the σ stresses due to the constraint the generalized plane strain condition
As damage is observed in the Inconel 601, we focus which are higher with the generalized plane strain model
Summary
Considering the increased cost of oil and the stringent emission regulations, engine design should satisfy three important expectations: lower fuel consumption, lower emission, and correct function of engine. A systematicA analysis confirmed that gaps cause cracking during bending Gaps induced by the heat treatment will not disappear during and 3 confirm the2causes gap formation: bad and yielding of the Inconel mantle during welding. Sections and 3of confirm the causes ofadhesion gap formation: bad adhesion and yielding of the the heat treatment. At this stage, the detrimental effect of possible gaps during the bending. Section presents a new ground electrode design preventing large plastic treatment, we opted for a less expensive solution. Preventing large deformations of the Inconel mantle avoiding the gap formation
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