PUNCHING MACHINE

The present invention relates to a punching machine.

The object of the invention is to provide a punching machine which also radiuses the edge of the hole formed by the punch. This object is attained according to the invention by a punching machine for sheet metal strip as described in claim 1 .

A preferred embodiment of the present invention is further clarified hereinafter with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section through a punching machine according to the invention,

Figures 2, 3, 4, 5 and 6 show it in its various operating stages, and Figure 7 is a detailed view of the punch head.

As can be seen from the figures, the punching machine of the invention comprises substantially a base 2 provided with columns 4 for guiding an upper horizontal plate 6 drivable vertically by a piston 8.

The plate 6 is provided with a seat 10 for housing the heads 12 of threaded bolts 14 which with their lower end engage in a second plate 16 supporting a punch guide 18 within which a punch 20 slides rigid with the plate 6. The plate 16 is guided along the columns 4, and is also guided along columns 22 provided lowerly with a plate 24 housed in a seat 26 provided in the base 2.

The plate 24 is provided upperly with a die 28 within which a counter- punch slides rigid with the plate 2. The die is provided internally with two channels 32, 34 for feeding an air jet and discharging scrap respectively.

Pairs of springs 36 are interposed between the plate 6 and the plate 16, with pairs of springs 38 interposed between the bottom of the seat 26 and the lower surface of the plate 24.

The springs 36 have a rigidity less than that of the springs 38. The head 40 of the punch 20 has smaller dimensions than those of its shank 42 (the diameter of which is less than the diameter of the counter- punch 30) and is connected to it by a frusto-conical portion 44.

The upper surface of the counter-punch is provided with a frusto- conical portion 46, the outer diameter of which is greater than the diameter of the head 40 of the punch 20 but less than the diameter of the shank 42.

The machine of the invention operates in the following manner.

When not in use, the plate 6 is in the configuration of maximum distance from the plate 2, the springs 36 and 38 maintaining the plate 6 with the plate 16, and the plate 24 with the base 2, in the configuration of greatest distance apart (see Figure 1 ). The punch 20 is completely inserted into the punch guide 18.

The metal sheet 48 is advanced so that it becomes positioned on the die 28, after which the piston 8 is operated to lower the plate 6 and hence the plate 16 (by means of the springs 36) until the punch guide 18 rests on the die 28 to retain the metal sheet (see Figure 2).

Subsequent lowering of the plate 2 has the following effect (see Figure

3):

- emergence of the punch from the punch guide,

- commencement of the punching step by the punch head, - lowering of the plate 24 into the seat 26.

As the descent of the plate 24 continues, the initial effect (Figure 4) is as follows:

- further lowering of the plate 24,

- total punching of the metal sheet, - compression of the springs 36 and 38, followed by (see Figure 5):

- fall of the punched-out scrap,

- its expulsion along the channel 34 by the programmed air jet,

- 90° flanging of the profile edge about the hole by the mutual interaction between the die 28 and the punch guide 18.

At this point the plate 2 is made to rise by the piston 8, resulting in (see Figure 6):

- raising of the punch 20 along the punch guide, this being always in contact with the die 28 by virtue of the elastic reaction of the spring 38, which is greater than the elastic reaction of the spring 36,

- interaction between the frusto-conical portion 46 of the counter-punch 30 and the flanged edge of the metal sheet to bend it U-shaped against the punch guide 18.