| 摘要 |
A method and structure for joining a harder to a softer sheet are disclosed. Sharp projections are formed surrounding a hole on the harder sheet, and these projections are penetrated through the softer sheet and then bent back and around so as to engage with the softer sheet. In a preferred embodiment, the projections are formed by boring a conical hole in the harder sheet, cutting radial slots which lead outwards from the hole, and bending the periphery of the hole perpendicular to the sheet. The acute angle formed by the conical surface of the hole and one face of the sheet ensures that the projections are sharp.
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