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(11) | EP 2 208 930 A3 |
(12) | EUROPEAN PATENT APPLICATION |
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(54) | Manufacturing method of heater tube of glow plug and glow plug |
(57) [Objective] An object is to maintain at a predetermined amount the projection length
of a projecting mouth portion projecting frontward from a tapered-off portion at the
front end of a heater tube, to thereby prevent occurrence of welding failure, which
would otherwise occur when a front end of a heat generation coil disposed within the
heater tube is welded to the projecting mouth portion. [Means for Solution] The diameter D21 of a straight hole portion 123 of a forming hole 121 of a die 101 used in each of press steps including the final press step is made greater than the outer diameter of a heater tube finished product. A blank material 20 to undergo forming is pressed, with a support member 151 disposed on the front end side of the forming hole 121, whereby the projection length L1 of a projecting mouth portion 35 is maintained at a predetermined projection length. When the blank material 20 is excessively long, its outer diameter increases. Therefore, the blank material 20 is then passed through an ironing hole so as to adjust the outer diameter of the straight tube portion 21 of the heater tube in-process product to a predetermined dimension. When the overall length is greater than a maximum allowable dimension, a rear-end unnecessary portion of the straight tube portion 21 is cut for adjustment. Desired dimensions can be imparted to the projecting mouth portion, etc. |