Method and device for perforating a pipe wall

A method for perforating a pipe wall with a punch comprising a body (1), a cutting punch (2) and a three-part die (3, 5, 8) with an upper die part (3), a lower die part (5) and a wedge (8) between the die parts (3, 5), the method comprising the following stages:

• moving the pipe in its longitudinal direction to a punching position where the die (3, 5, 8) is inside the pipe,
• expanding the die (3, 5, 8) in the direction of movement of the cutting punch by moving the wedge (8) in a first direction of transfer towards the end of the die,
• perforating the wall of the pipe with a cutting punch (2) while supporting the wall with an expanded die (3, 5, 8) during punching, whereupon the piece punched off from the pipe falls into a hole (16) in the upper die part (3),
• contracting the die (3, 5, 8) by moving the wedge (8) in a second direction of transfer opposite to the first direction of transfer,
• moving the perforated pipe away from the punching position in its longitudinal direction, and
• moving the pipe to a position for finishing the rims of the hole,
• characterised in that the die (3, 5, 8) is supported by a support bushing (14) attached to the body (1), that the die (3, 5, 8) is kept out of contact with the inner surface of the pipe surrounding the die during the transfer movement of the pipe and brought into contact during the expansion such that the upper wedge part is turned upwards and the lower wedge part downwards as a result of the wedge being moved in the first direction of transfer, that after punching, the wedge (8) is moved by a first transfer distance in the second direction of transfer, which contracts the die by allowing the die parts (3, 5) to turn in an articulated manner towards each other, that the perforated pipe is moved away from the punching position and that the lower part (5) of the die and the wedge (8) are then moved together by a second transfer distance in the said second direction of transfer thus opening the base of the hole (16) in the upper die part, whereupon the piece punched off from the pipe falls out through the hole (16).