EP0597212A1 - Method of controlling a punch press during starting and stopping - Google Patents

Abstract

In order to reach the operating speed of rotation from a standstill, the eccentric shaft (5) must, owing to forces arising from the mass moment of inertia, be accelerated to the number of operating strokes via a starting angle ( alpha B). When the punch press is brought to a standstill, the eccentric shaft (5) is rotated in the operating direction of rotation (13) to a position between the upper dead centre (OT) and the lower dead centre (UT), in which position there is no contact between the upper tool (8) and the metal belt (12). From this position, the eccentric shaft (5) is rotated backwards through the starting angle ( alpha B) to a starting angle position (D). In the starting angular position (D) there is also no contact between the upper tool (8) and the belt (12). There is therefore available for the starting of the punch press a starting angle ( alpha B) which is extended beyond the upper dead centre (OT) so that the first punching operation is executed under the same dynamic conditions of the punch press as the following punching operations, which means that accurate parts are produced on starting, from the very first stroke. <IMAGE>

Description

The invention relates to a method for operating a punch press when starting and stopping the same, which punch press is driven by a positionable drive via the clutch unit of a clutch / brake device, an eccentric shaft, a ram driven by the eccentric shaft for carrying at least one upper tool and a press table for carrying at least one Has lower tool, by means of which tools a strip-shaped workpiece arranged in between is machined, which punching press passes through a starting angle due to the overall moment of inertia of the moving components and the drive torque transmitted by the coupling unit to the eccentric shaft for acceleration from standstill to the operating stroke number and the contact between the tools and the belt starts at a given working angle position of the eccentric press.

In the case of high-speed punching machines, the known increase in the inertial forces of the accelerated components as the speed increases is a problem which has an influence in particular on the quality and accuracy of the products produced with such punching machines. Due to the accelerations and decelerations of the predominantly oscillating components and the opposing forces that arise during the machining of a respective workpiece, the punching machine and in particular its moving components suffer elastic deformations, and furthermore there are displacements in the bearings, which conditions have a negative effect on manufacturing accuracy.

The manufacturing accuracy of a stamped product is heavily dependent, among other things, on the respective ram height of the machine. As is generally known, this ram height determines the tool closing height or the immersion depth when the machine is in operation.

If an unchanging ram height is specified for given embossing and cutting work at a given number of strokes, e.g. with a smaller number of strokes the embossments are not deep enough, with a higher number of strokes the embossments are too deep or the immersion depth of the tool stamps is too large, which is known to lead to undesirably large wear of the corresponding tool parts.

Various procedures have become known for regulating the ram height or immersion depth based on the number of strokes. For example, reference is made to CH-A-676 445.

When punching, in particular with follow-up cutting tools, there should also be no rejects caused by the inertia forces mentioned above when starting and stopping the punching machine, and starting and stopping in particular with high-speed punching machines causes problems in this regard.

To start the punching machine, the eccentric shaft is drive-connected by closing the clutch with the drive located at the operating stroke number, in particular the flywheel, and thus accelerated from standstill to the operating speed. The dynamic behavior of the punch press during the first machining process, e.g. The punching process is defined as the first punch behavior, and it is this first punch behavior that determines the quality of the first punched part.

In known start-up methods for high-speed punch presses, the first punch behavior is such that the first punching process does not take place with the number of operating strokes like the subsequent punching processes, i.e. that the dynamic behavior of the machine is not the same for the first and subsequent strokes, which has a negative effect on the accuracy of the first part.

Reducing the number of operating strokes eliminates this disadvantage, but reduces production, i.e. Number of pieces produced within a given period of time.

The invention seeks to remedy this. The invention, as characterized in the claims, solves the problem of creating a method for operating a punch press when starting and stopping the same, in which after the stop has been completed, the eccentric shaft is rotated back into a starting angle position according to which it is started up again after passing through of the approach angle for accelerating to the operating stroke number is on the operating stroke number before the first machining contact takes place between the tool and the workpiece.

The advantages achieved by the invention are essentially to be seen in the fact that the first punch stroke takes place with a dynamic behavior of the punch press which is the same as the dynamic behavior in continuous operation. This means that when starting up, the strip to be processed is precisely machined during the first machining stroke, so that no rejects are produced.

• Figur 1 zeigt schematisch eine Stanzpresse mit den das Verständnis der Erfindung erleichternden Baueinheiten,
• Figur 2 zeigt ein Diagramm, in dem das Anfahrverhalten eine Stanzpresse dargestellt ist,
• Figur 3 zeigt schematisch die Stellung einer nach dem erfindungsgemässen Verfahren betriebenen Stanzpresse nach dem Stillsetzen, und
• Figur 4 zeigt schematisch die Stellung einer nach dem erfindungsgemässen Verfahren betriebenen Stanzpresse vor dem Anfahren.

The invention is explained in more detail below with the aid of drawings which illustrate only one embodiment.

• FIG. 1 schematically shows a punch press with the structural units that facilitate understanding of the invention,
• FIG. 2 shows a diagram in which the starting behavior of a punch press is shown,
• Figure 3 shows schematically the position of a punch press operated according to the inventive method after stopping, and
• Figure 4 shows schematically the position of a punch press operated according to the inventive method before starting.

Figure 1 shows schematically a punch press. It has a positionable drive 1. This drive 1 contains an electric motor which can be controlled in any desired angular position and which drives the flywheel of the high-speed punch press according to generally known designs via a belt drive. The flywheel is connected to a clutch / brake device 2, 3, which in turn is connected to the eccentric shaft 5, which is mounted in the machine frame 4.

The clutch / brake device 2, 3 has a clutch unit 2, by means of which the eccentric shaft 5 can be coupled or uncoupled from the drive 1, or its flywheel, and has a brake unit 3 with a brake disc 14, via which Brake disc 14, the eccentric shaft 5 can be braked against the machine housing 4. Details of this braking device can be found in CH-A-546 141 and US-A-3 805 931. It should be noted here that the clutch unit 2 and the brake unit 3 are non-positive designs, i.e. they grind when engaging or braking.

Connecting rods 6, which carry the tappet 7, are articulated on the eccentric shaft 5. This plunger 7 is connected to the upper tool 8. The press table 10, which carries the lower tool 9, is also shown in FIG. Reference numeral 11 generally designates the balance weight arrangement for balancing the rotating and oscillating forces occurring during the operation of the punch press.

In operation, the eccentric shaft rotates through all angular positions of a 360 _° angle and can obviously assume any angular position at a standstill driven by the positionable drive. An upper dead center UD and a lower dead center LD are generally defined for the eccentric shafts 5 of the punch presses, the articulation point of the connecting rod (s) on the eccentric shaft 5 being taken as the structural reference. The ram 7 has the largest distance from the press table 10 at the top dead center UD and the smallest distance at the bottom dead center UT. These positions UD and LD can be seen from FIGS. 3 and 4.

To interrupt operation, a punch press is usually shut down or positioned approximately at top dead center UD. The distance between the ram 7 and the press table 10 has the greatest value, the tool (consisting of upper tool 8 and lower tool 9) is open. When operation is interrupted, the clutch unit 2 is opened and the brake 3 is closed, i.e. the eccentric shaft 5 is uncoupled from the drive 1, the drive 1 with the flywheel idling at the operating speed and the crankshaft 5 stopped.

Reference is now made to FIG. 2. The abscissa relates to the angular position a of the eccentric shaft 5, the ordinate to the speed n of the same.

wobei

• M = von der Kupplung abgegebenes Antriebsmoment [Nm],
• J = Massenträgheitsmoment der bewegten Bauteile der Stanzmaschine [kg_M ²] = Anfahr- bzw. Bremswinkel [ _° ].

If, with the eccentric shaft stationary and the drive running at the operating speed n _B , the brake is opened and the clutch to the eccentric shaft located in the top dead center position OT is closed, the speed n of the eccentric shaft increases under the influence of the torque transmitted from the clutch to the eccentric shaft. This increase in the speed n relative to the angular position a is shown in FIG. 2 by the curve line. After a certain period of time, ie after passing through a certain angle of rotation a, the operating speed n is reached. The speed change takes place according to the formula

in which

• M = drive torque given by the clutch [Nm],
• J = moment of inertia of the moving components of the punching machine [kg _M ² ] = approach or braking angle [ _° ].

The tool closure, ie the machining contact between the upper tool and the strip to be processed, takes place shortly before bottom dead center LD, at which the eccentric shaft has passed through an angle of rotation or approach angle a _A , the distance between the approach angle being shown in the diagram in FIG a _A and a = 180 _° can be seen.

Thus must the Betriebshubzahl n _A at the latest when actuating a _A be obtained when the first punch when starting with the same dynamic conditions to be executed, as in the next punching. There are therefore no difficulties with any number of operating strokes nA.

However, if the number of operating strokes n _{B is} above n _A , i.e. nB n _A , which property prevails in high-speed punch presses, a starting angle a _B that is greater than a _A is required if the same dynamic conditions as for the subsequent ones are used for the first punching Punchings should prevail.

The same considerations apply when stopping the punch press. A reduction in the number of strokes may only be initiated after passing through the bottom dead center LD, the complete standstill before a 360 _° rotation before the tool and the metal strip have come into contact.

The parameters M (drive torque or braking torque) and J (moment of inertia) of a punch press can only be changed with difficulty or not at all. The method according to the invention is thus used, which will now be described with reference to FIGS. 3 and 4.

Since the operating speed n and the machine parameters M and J are known, both the approach angle a _B and, accordingly, the braking angle can be calculated in a control unit for the punch press.

When stopping, the punch press is not stopped at top dead center UD, but at angular position C, which lies after top dead center UD.

Obviously, f B may at most be so large that reaching bottom dead center LD and thus further punching is avoided. When a punch press is stopped, the clutch is opened and the brake is closed, the drive with the flywheel still rotating at the operating speed.

After stopping the punch press, ie the eccentric shaft, the drive is now also stopped. Thereafter, the drive is set in motion in the opposite direction, the eccentric shaft is coupled and thus rotated backwards through the angle 2 x 'β 2 = aB into the angular position D according to FIG. 4. After reaching the angular position D, the clutch 2 is opened and the drive 5 is raised to the operating speed n _B. The eccentric shaft 5 is in the angular position D and thus the punch press is ready for engaging and starting with an extended approach angle a _B.

Normally, a punch press is stopped at top dead center UD so that it can be manipulated in the open tool. The press can thus be stopped at top dead center UD when rotating back from point C to point D (intermediate stop).

Claims (4)

1.Method for operating a punch press when starting and stopping the same, which punch press is driven by a positionable drive (1) via the clutch unit (2) of a clutch / brake device (2; 3) eccentric shaft (5), one by the eccentric shaft (5 ) driven plunger (7) for carrying at least one upper tool (8) and a press table (10) for carrying at least one lower tool (9), by means of which tools (8; 9) an intermediate belt (12) is processed, which punch press due to the total moment of inertia of the moving components and the drive torque transmitted by the coupling unit (2) to the eccentric shaft (5) for acceleration from standstill to the number of operating strokes passes through a starting angle (a _A ) and the contact between the tool stamp (15) and the belt ( 12) begins at a predetermined working angle position (C) of the eccentric shaft (5), characterized in that after a St When the punch press is set, the eccentric shaft (5) is rotated into a starting angle position (D) for starting without going through its bottom dead center position (LD), according to which it moves in the direction of the operating rotation before the next start after passing through the starting angle (a _B ) Working angle position (C) is at operating speed. 2. The method according to claim 1, wherein the contact between the tools (8; 9) and the metal strip (12) at a predetermined release angle position (D) after passing through the bottom dead center position (LD) in the direction of the operating rotation (13) ends and the eccentric shaft (5) when the punch press is stopped due to the total moment of inertia of the moving components and the braking torque exerted by the brake unit (3) of the clutch / brake device (3; 4) to delay the speed of the eccentric shaft (5) from the operating stroke number to Standstill passes through a stopping angle, characterized in that the deceleration of the speed of the eccentric shaft (5) is initiated by the braking unit (3) immediately after passing through the release angle position (D) in the direction of the operational rotation. 3. The method according to claim 1 or 2, wherein the stopping angle (a _A ) is greater than the angle between the release angle position (D) and the top dead center position (LD) of the eccentric shaft (5) in the direction of the operating rotation (13), characterized that the eccentric shaft (5) is rotated back into the approach angle position (D) by an operation of the drive (1) opposite to the direction of the operating rotation, via the top dead center position (LD). 4. The method according to any one of the preceding claims, characterized in that the eccentric shaft is temporarily stopped at top dead center (UD) when rotating back into the approach angle position (D).

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