| 摘要 |
A rapidly rotatable piercing tool for forming, substantially by frictional heat and pressure, a bossed hole in a metal plate or tube wall, said tool comprising a head of greater diameter, whereby a shoulder facing the leading end of the tool is formed for so shaping one of the end faces of the boss surrounding the hole, as to round off, to bevel off or to deepen said end face towards the hole in an annular region bordering the hole.
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