EP0642853B1 - Method of joining thin plates and device for carrying out the method - Google Patents

Description

State of the art

The invention is based on a method for connecting superimposed thin plates according to the preamble of claim 1 and on an apparatus for carrying out this method according to the preamble of claim 17.

In a known cold joining method of this type (DE 35 32 899), the plate pieces lying one above the other are punched out and pushed out along the part of their contour lines and pushed out of the plane of the plate. The pressed-out plate pieces are then squeezed out broadly by a counterforce, producing a punching cam which engages behind the plate sections to be connected. In another known method of this type (see DE-A-35 32 900, which corresponds to the preamble of claim 1 and 17, respectively), plate pieces are interspersed together from the plate sections to be connected results, which leads to an engagement of the plate pieces on the superimposed plate sections.

Such processes are used in industrial mass production, for example in automobile construction. Monitoring the quality of the connection points or ensuring certain quality requirements for such connection points is therefore of particular importance in this process. The occurrence of defects in the implementation of this method must be recognized and eliminated as quickly as possible in order to keep the rejects and machine downtimes as short as possible. Such defects can be caused by a material breakage, in particular the stamp or the die. It is important to recognize every faulty connection point in order to sort out the corresponding part or to repeat a connection process. A criterion for the quality of the connection or its lack is the remaining thickness of the remaining material in the area of the joint. In the known methods, quality assurance consists in monitoring the stamp force with regard to a permissible maximum value and in measuring the residual material thickness after the connection has been made. As a result, only a part of the deficiencies that may occur is recorded. The subsequent measurement of the residual material thickness is also cumbersome and time-consuming.

Presentation of the invention

The method according to the invention with the features of claim 1 and the device according to the invention with the features of claim 17 has the advantage that defects occurring to a much greater extent are detected and that no separate measurement of the residual material thickness has to be carried out. Also, the pressing force, that is to say the punch or die force, does not have to be absorbed in the form of a measuring curve against the working stroke during the entire joining process. By measuring the pressing force immediately after the squeezing process has ended, every faulty connection is recognized. Monitoring is carried out by comparison with predetermined maximum and minimum values. If the pressing force is below the specified minimum value, for example stamp or die break is displayed; on the other hand, if it exceeds the specified maximum value, this indicates plates that are too thick or material that is too hard to be joined. In addition to the pressing force, the stripping force required to strip the connected plates from the punch is also measured. By measuring the stripping force, a lining of the material is determined, which is particularly important when using the invention in robot devices.

In a method known from DE 32 41 063, the forces occurring on the tools are monitored by comparison with a target value, but this is a combined punch-bending operation or the like. acts and sources of error are not detected after completion of the generic crushing process.

According to a further advantageous embodiment of the invention, the pressing force is measured immediately after the squeezing process has ended. If the plates connected by the joining process at the joining point only have those for the Joining process characteristic residual floor thickness, the actual joining process is completed. The pressing force assigned to the relevant working stroke is therefore particularly instructive for the joining process.

According to a further advantageous embodiment of the invention, the measured forces are compared with a predetermined maximum value and a predetermined minimum value. If the measured value lies within the interval defined by the maximum and minimum value, the connection that has been made corresponds to the specified quality, but if it lies outside the interval, the connection is faulty. The comparison of the measured value with the interval is therefore sufficient to characterize the connection.

According to further advantageous refinements of the invention, when the predetermined maximum value is exceeded and when the predetermined minimum value is undershot, a signal is generated which can be used to control an optical and / or acoustic display device in order to draw attention to the presence of a defect. The signal can also be used to control the interruption of the joining process, which can reduce waste and downtimes in production.

According to a further advantageous embodiment, a signal is generated if the punch or the die does not cover the specified working stroke during the joining process. The signal is advantageously a control signal with which an optical and / or acoustic display device is activated. The signal can also be used to interrupt the joining process.

According to a further advantageous embodiment of the invention, the maximum and minimum values are available in an electrical memory. This allows the values to be adjusted as required. There can also be several sets of values in the memory in order to quickly meet different requirements, for example when changing tools or materials.

According to a further advantageous embodiment of the invention, the predetermined working stroke is available in a memory. In addition to the possibility of specifying the working stroke manually, for example with the aid of switches, the working stroke can thus also be set using a computer having the memory.

According to an advantageous development of these features, the input of the values into the memory is protected. This ensures that changes can only be made by authorized persons.

According to a further advantageous embodiment of the invention, the forces are measured at several joints at the same time, the values determined being evaluated by a common device.

According to a further advantageous embodiment of the invention, the measured values determined are displayed optically. The visual display makes it easier to distinguish between different types of errors so that the appropriate countermeasures can be taken. For this purpose, the measured values determined can be saved in order to enable subsequent evaluation. At the same time, the measurement values are saved quality control, since the joining process can be checked in the event of later complaints.

The device according to the invention for carrying out the method with the features of claim 19 is advantageously adapted to the requirements of the method. Force measuring devices are provided in the die holder, or in the punch holder, or on the stripper, preferably strain gauges or piezoelectric sensors are used, for example a piezo force transducer in the die holder, a piezo transverse dowel in the punch holder and a piezo measuring ring on the stripper. A position detector ensures that the measurement is carried out exactly at the previously set working stroke. The position indicator can advantageously be accommodated in a stamp stroke limiter.

Further advantages and advantageous embodiments of the invention can be found in the following description, the drawing and the claims.

drawing

• Figur 1 eine Seitenansicht einer erfindungsgemäßen Vorrichtung im Teilschnitt und
• Figur 2 ein Diagramm in dem die Stempelkraft (Ordinate) über dem Stempelweg (Abszisse) aufgetragen ist.

An embodiment of the invention is shown in the drawing and described in more detail below.
Show it:

• Figure 1 is a side view of a device according to the invention in partial section and
• Figure 2 is a diagram in which the stamp force (ordinate) is plotted against the stamp path (abscissa).

Description of the embodiment

The press 1 shown in FIG. 1 has a C-shaped frame 2, the lower part of which serves as a press table 3 on which the die holder 4 for the die 5 is arranged. On the upper arm 6 of the frame 2, opposite the die holder 4, there is a stamp holder 7 for receiving the stamp 8. A stripping device 9 is arranged around the stamp holder 8 for stripping plates hanging on the stamp. The punch 8 is moved up and down via a pressure cylinder 10 by a press drive 11 provided on the upper side of the C-shaped frame 2.

In the die holder 4 there is a piezo force transducer with which the die force exerted by the die is determined. A piezo transverse dowel 12 is provided in the stamp holder 7 to determine the stamping force exerted. Finally, a piezo measuring ring 13 arranged around the pressure cylinder 10 is provided on the stripper 9 to determine the stripping force. The pressure cylinder 10 has a position indicator 14, which activates the force measuring devices for a given stamp path to measure the stamp force and possibly the die force. The position detector can also be included in the stroke limiter 15. The evaluation devices and the electrical connections between the evaluation devices and the measuring devices are not shown.

The diagram in FIG. 2 shows an example of the course of the stamp force as a function of the stamp path during a joining process. As can be seen from the diagram, the punch force increases steadily until the end of the joining process, but not linearly, but differently depending on the joining phase. The various joining phases, in the order of their sequence during the joining process, are first a combined sinking and pushing through, followed by upsetting and widthing, then filling in the upper contour of the die engraving, filling the ring channel of the die and finally backward extrusion to interlock the plate elements to be connected. The stamp force is measured by the force measuring device on the value of the stamp path marked with I in the diagram, the measured value is marked with II. An interval V is defined by the minimum value III and the maximum value IV. If the measured value II lies within the interval V, the joining process that has taken place corresponds to the specified quality. If, on the other hand, the measured value VI exceeds the predetermined maximum value IV, the joining is faulty. Possible causes in this case are too thick a sheet, too much sheet layer, too high sheet strength or wrong tool combination. A faulty joining is also present if the measured value VII falls below the minimum value III. In this case the breakage of the punch or die, a missing sheet position or wrong tool combination can be the cause. Another possibility of an incorrect joining is indicated by the point marked with VIII. Here the position detector could not activate the force measuring device because the stamp did not cover the specified stamp path. The cause can either be a press force that is set too low, a press stroke that has not been carried out completely or the failure to reach the remaining floor thickness at the joining point.

In addition to presses with a reciprocating stamp movement, the method according to the invention can also be used for methods with a rotary movement of the stamp. Instead of the stroke movement, the rotary movement is then determined by means of an angle encoder. In addition to the force measurement, an acceleration measurement can also be carried out, for example by measuring the structure-borne noise generated during the stroke, in order to ensure compliance with a target value with a tolerance range. Accelerations that are too high lead to high material wear and an increased risk of tool breakage.

List of reference numbers

1

Press

2nd

frame

3rd

Press table

4th

Die holder

5

die

6

boom

7

Stamp holder

8th

stamp

9

Wipers

10th

Impression cylinder

11

Press drive

12th

Piezo dowel

13

Piezo measuring ring

14

Position detector

15

Stamp stroke limiter

I.

predefined stamp path

II, VI, VII

possible measured values

III

Minimum value

IV

Maximum value

V

interval

Claims (23)

1. Method of joining thin mating plates especially sheet metal or plate sections by cold joining in which the mating surfaces of the plates or plate sections to be joined are deep drawn and squeezed flat in a single working stroke by an interaction of the die (8) and the mold (5) with or without partial punching of the surfaces, characterized in that

   - the pressing force exercised on the plates as stamping force by the die (8) or as matrix force by the mold (5) is measured immediately after squeezing and that

   - the skimming force needed by the die (8) to skim off the joined plates or plate sections is measured.
2. Method according to claim 1., characterized in that the measured values (II, VI, VII) for pressing force and skimming force are compared to a set maximum value (IV) and a set minimum value (III).
3. Method according to claim 2., characterized in that a signal is effected when the maximum value (IV) is exceeded or the minimum value (III) falls short.
4. Method according to one of the above claims characterized in that a signal is effected when either the die (8) or the mould (5) do not travel the set working stroke (I) in the joining process.
5. Method according to claims 3. or 4., characterized in that the signal is a control signal controlling an acoustic and/or visual display.
6. Method according to claims 3., 4., or 5., characterized in that the signal is used to interrupt the respective joining process.
7. Method according to claim 6., characterized in that in the case of an interruption the process can only be continued after unlocking.
8. Method according to one of the claims 2. through 7., characterized in that the maximum (IV) and minimum (III) values are stored in an electronic memory for recall.
9. Method according to claim 8., characterized in that the maximum and minimum values can be adjusted by a force measuring device (12, 13) either manually or using a computer featuring the above mentioned memory.
10. Method according to claims 8. or 9., characterized in that the memory stores different sets of maximum (IV) and minimum (III) values.
11. Method according to one of the above claims, characterized in that a set working stroke (I) is stored in the electronic memory for recall.
12. Method according to claim 11., characterized in that the set working stroke (I) can be adjusted at a position indicator (14) either manually or by a computer featuring a memory.
13. Method according to one of the claims 8. through 12., characterized in that the input of the maximum (IV) and minimum (III) values and/or the set working stroke is protected against misuse or loss.
14. Method according to one of the above claims characterized in that the forces are measured at several cold joining points at the same time, and the values are processed by the same data processing device.
15. Method according to one of the above claims, characterized in that the elicited values (II, VI, VII) are displayed visually.
16. Method according to one of the above claims, characterized in that the elicited values (II, VI, VII) are stored electronically.
17. Device for carrying out the method according to one of the above claims using a mould (5) positioned in a mechanical press (1) and a die (8) driven to and fro at right angles to the plates to be joined, characterized in that a position indicator (14) and at least one force measuring device (12) for measuring the pressing force and a force measuring device for measuring the skimming force are present.
18. Device according to claim 17., characterized in that a transmitter is connected motion-locking to the die (8) to effect a linear or rotary motion.
19. Device according to claims 17. or 18., characterized in that one or several piezo elements serve as force measuring devices (12, 13).
20. Device according to claim 17. or 18., characterized in that one or several strain gauges serve as force measuring devices (12, 13).
21. Device according to one of the claims 17. through 20., characterized in that the force measuring device for measuring the pressing force is positioned in a mould mount (5) or on the press table (3).
22. Device according to one of the claims 17. through 21., characterized in that the force measuring device (12) is positioned between die (8) and pressure cylinder (10).
23. Device according to one of the claims 17. through 22., characterized in that the position indicator (14) is integrated into a stroke limiter (15).

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