GB2109737A - Apparatus for cutting sheet metal - Google Patents

Abstract

The apparatus comprises a pneumatically operated chopper with means for controlling the sequence or timing of the chopping cycles. The chopper is in the form of a portable unit arranged to be coupled to an automatic machine tool such as a power operated press and is cycled in synchronism with the movements of the main press tool and of the strip feed mechanism 21. The chopper has top and bottom cutter plates 32, 31. The top plate is actuated by a pneumatic bellows 36 which bears down on the bottom yoke 35, the bellows being pulsed by an automatic valve controlled through a servo system from a valve sensing the movements of the main press tool. <IMAGE>

Description

SPECIFICATION Apparatus for cutting sheet metal This invention relates to a power operated machine for cutting sheet metal, particularly scrap sheet metal, into short lengths.

It is common practice to chop continuous scrap metal strip as it leaves a continuously operated mechanical press or punch, and to pack the short lengths into boxes for return to a scrap metal plant.

To cut the strip into lengths by hand is usual but is expensive and wasteful of time, and the invention is concerned with a novel automatic chopping machine for the purpose.

Broadly stated, the invention consists in apparatus for cutting waste strip metal into separate short lengths, comprising a chopper with a reciprocating blade, a pneumatic motor for actuating the blade and means for controlling the sequence or timing of the chopping cycles.

According to a particular preferred feature of the invention the motor is a pneumatic bellows.

This has numerous unexpected advantages as will be apparent from the following description.

The bellows preferably includes an internal volume displacer, for reasons which will also be described later, and in a particular preferred construction the pneumatic motor is connected to a moving part of the chopper by a pair of bars spaced on opposite sides of the path of movement of the strip, the two bars being displaced also on opposite sides of the line of cut in relation to the direction of movement of the strip.

The apparatus is particularly suited to a system which includes a main compressed air supply line to the motor and a pneumatic trigger or pilot valve system for controlling the supply of air to the motor in response to input signals derived from a power press with which the apparatus is associated.

The strip chopper apparatus is preferably housed in a mobile casing to form a portable unit, and it may include further pneumatic motors for moving the actuator element of the chopper in the reverse direction.

The invention may be performed in various ways and one preferred embodiment with some possible modifications will now be described by way of example with reference to the accompanying drawing, in which:~ Figure 1 is a general diagrammatic front view of an automatic power press with a portable strip chopping machine according to the invention connected thereto, Figure 2 is a diagrammatic end view in the direction of arrow A is Figure 1 of the essential working components of the strip chopper, Figure 3 is a diagrammatic sectional view through the pneumatic bellows of the strip chopper, Figure 4 is a front view partly in section of the upper moving mechanical components of the strip chopper, Figure 5 is a diagrammatic plan view of the strip chopper, and Figure 6 is a diagram illustrating the components of the pneumatic supply and control system.

Referring first to Figure 1 , the mechanical crank or eccentric press tool illustrated is of conventional design and includes a base 10 supporting a table 11 onto which a continuous metal strip 12 is fed progressively from a supply coil 13. A stand 14 extends over the table and carries a heavy crank or eccentric cam 15 on a shaft 16 driven by an electric motor 17. A connecting rod 18 attached to the crank operates a vertical reciprocating plunger head 19 which carries in this example a series of spaced punching tools 20. The press also includes a horizontal stepping feed mechanism 21 actuated automatically in synchronism with the crank 15 to feed the strip 12 horizontally through a preselected distance after each cycle of the crank.

The finished workpieces fall through an aperture in the table 11 and the waste strip emerges horizontally from the press at 22.

The strip chopper illustrated generally at 25 is a portable unit mounted on castors 26 and can thus be wheeled up any selected press tool and is designed to be connected to the crank operating mechanism to function automatically in synchronism with the press, and the movements of the metal strip.

The strip chopper includes a horizontal fixed platform or bolster 30 on which is mounted a lower cutting blade or bed 31. An upper cutting knife 32 is secured to a horizontal top yoke 33 which is connected by a pair of tie-bars 34 to a bottom yoke 35. A pneumatic bellows 36 is interposed between the bolster 30 and the bottom yoke 35 and by admitting compressed air to the bellows the bottom yoke is driven downwards thus exerting a heavy downward force on the top cutting knife 32. The top yoke is raised between strokes by a pair of pneumatic lifting rams 37 acting as separator cylinders, and located between the bolster 30 and the opposite ends of the top yoke 33. In order to minimise undesirable tilting forces and outof-balance loads on the top yoke, the two tie-bars 34 are preferably on a transverse centre line or on opposite sides thereof, as illustrated in Figure 5.Buffers 38 cushion the movement of the top yoke.

The pneumatic cylinder 36 is a heavy duty unit selected to be capable of providing the required operating force and having a potential working life preferably in excess of ten million cycles. By comparison with a pneumatic piston and cylinder assembly it is relatively frictionless, has a completely positive air seal eliminating air leakage, and has a greatly improved operating efficiency. The overall diameter of the bellows related to the pressure of the compressed air supply determines the effective output load. The operating stroke or travel required at the moving knife 32 may be no more than 5 to 10 mm but the length of the bellows must be considerably greater to provide the necessary flexibility and ability for expansion without over strain, and hence the required long operating life.For this purpose a solid displacement block 40 is mounted within the bellows as illustrated in Figure 3. This is spaced by a small radial clearance from the internal surface of the bellows convolutions 43, 44, so that the total internal volume is greatly reduced, thus also reducing the air consumption on each cycle, and the quantity of air to be transmitted through the exhaust valves which in turn increases the speed of operation.

The pneumatic circuit for operating the machine is illustrated diagrammatically in Figure 6. The bellows is connected via a rapid exhaust valve 50 to a two-way valve 51 which connects the bellows alternatively to the supply line 52 via a pressure regulator valve 53 or to relief 54. This valve 51 is operated by a servo pilot valve 55 which is itself controlled by a pneumatic signal at S, and acts to connect a servo control line 56 either to line pressure at 57 or to exhaust 58. The control signal S is derived from the crank press itself via a cam operated shuttle valve 59 (see Figure 1).

The signal at S also acts on a further control valve 61, which controls admission of compressed airfrom line 62 to the upper volumes of the two lifting rams 34, the lower volumes being permanently connected to the supply via a pressure regulator valve 63. The pressure in the lower volumes is set at a value just sufficient to counterbalance the weight of the moving parts, and the admission of air to the upper volumes, which cancels this balance effect and starts the shear blade accelerating downwards, is timed by valves 61, 57 to occur shortly before the bellows 40 is actuated.

Thus the strip chopper is operated automatically in synchronism with the movements of the main crank 1 5 and of the strip feed mechanism 21 so that the strip is fed horizontally in steps by the feed mechanism 21 in the intervals between the punching operation of the tools 20, and severed by the chopper 25 during each pause while it is stationary.

Claims (9)

1. Apparatus for cutting strip metal into separate short lengths, comprising a chopper with a reciprocating blade, a pneumatic motor for actuating the blade and means for controlling the sequence or timing of the chopping cycles.

2. Apparatus according to claim 1, in which the motor is a pneumatic bellows.

3. Apparatus according to claim 2, in which the bellows includes an internal volume displacer.

4. Apparatus according to any of the preceding claims, in which the pneumatic motor is connected to a moving part of the chopper by a pair of bars spaced on opposite sides of the path of movement of the strip.

5. Apparatus according to claim 4, in which the two bars are displaced also on opposite sides of the line of cut in relation to the direction of movement of the strip.

6. Apparatus according to any of the preceding claims, including a main compressed air supply line to the motor and a pneumatic trigger or pilot valve system for controlling the supply of air to the motor in response to input signals derived from a press tool with which the apparatus is associated.

7. Aparatus according to any of the preceding claims, housed in a mobile casing to form a portable unit.

8. Apparatus according to any of the preceding claims, including further pneumatic motors for moving the actuator element of the chopper in the reverse direction.

9. Apparatus for cutting waste strip metal substantially as described with reference to the accompanying drawings.