| 摘要 |
In a method of making through-passages in a perforated U-shaped sheet metal part, an inner core is positioned between confronting legs of the sheet metal part in an area of holes, and a support bar is inserted through one hole into the sheet metal part for support of a backside of the inner core. A shaping punch is inserted through another opposite hole into the inner core, thereby forming an inwardly directed collar. After retracting the support bar and the shaping punch and transferring the sheet metal part to replace the first inner core with a second inner core, a centering bar is inserted through the collared hole into the sheet metal part to center the sheet metal part in relation to the centering bar and to support a backside of the other inner core. A further shaping punch is then inserted into the second inner core through the first hole, thereby forming an inwardly directed collar so that the two collars are aligned and form through-passages.
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