Method for measuring flatness deviations and curvature directions of components in a punching machine

Abstract

The invention relates to a method for measuring flatness deviations of components (16) in a punching machine, comprising an upper measuring tool (10) and a lower measuring tool in the form of a die (11) comprising a central die part (13) which can be moved downwards. The method has the steps of: - measuring the distance (s0) between the upper starting position of the upper measuring tool (10) and the die (11); - placing a component (16) to be measured on the die (11); - moving the upper measuring tool (10) from the upper starting position thereof until an increase in the force being exerted on the upper measuring tool (10) indicates a contact between the upper measuring tool (10) and the component (16) and measuring the path (s1) of the upper measuring tool (10) up until the upper measuring tool contacts the component (16); and - comparing the distance (s0) of the upper measuring tool (10) to the die (11) and the path (s1) traversed by the upper measuring tool (10) up until contacting the component (16) with a starting thickness (d) of the component (16) and checking whether the central die part (13) has moved downwards or remains in its starting position.

Description

[0001] Method for measuring flatness deviations and curvature directions of components in a punching machine

[0002] The invention relates to a method for measuring flatness deviations and curvature directions of components in a punching machine, a measuring system for carrying out these measurements and a punching machine with such a measuring system.

[0003] When punching sheet metal parts, especially thinner ones, unwanted curvatures can occur. This risk increases as the punching tools wear out. The components of a punching machine are therefore subjected to quality control downstream of the punching process, but this takes place outside the machine. In addition to the extent of the flatness deviations of the components, the direction of the curvature must also be determined in order to be able to readjust the machine's process parameters to avoid further defective components. Determining the direction of the curvature, along with the extent of the flatness deviation, is also important for any possible post-processing of the components. To determine these values ​​on the finished components, cameras, optical and / or tactile sensors are used in conventional processes.

[0004] However, due to downstream quality control, adjustments to the machine's process parameters cannot be made promptly, so a relatively large number of parts must be rejected or reworked. Any rework of components can only be carried out with a delay.

[0005] The invention is based on the object of enabling the measurement of a flatness deviation and the curvature direction of components already in the punching machine. This object is achieved according to the invention by a method for measuring flatness deviations and curvature directions of components in a punching machine, with an upper measuring tool and a lower measuring tool in the form of a die with a central, downwardly movable die part, comprising the following steps:

[0006] - Measurement of the distance between an upper starting position of the upper measuring tool and the die;

[0007] - Placing a component to be measured on the die;

[0008] - moving the upper measuring tool from its upper starting position until an increase in the force exerted on the upper measuring tool indicates contact between the upper measuring tool and the component, and measuring the travel of the upper measuring tool until contact with the component;

[0009] - Comparing the distance of the upper measuring tool from the die and the path travelled by the upper measuring tool until it touches the component with an initial thickness of the component and checking whether the central die part moves downwards or remains in its initial position.

[0010] The term "flatness deviation" is defined here as the smallest distance between two ideal planes, whereby all points on the measured component surfaces must lie between these two planes. For a completely flat component, the flatness deviation is therefore zero. The initial thickness d of the component is its thickness before the punching process, i.e., usually the thickness of the sheet metal used as the blank for the punching process.

[0011] By comparing the difference between the distance traveled by the upper measuring tool until it hits the component and the distance between the upper starting position of the upper measuring tool and the die with the initial thickness of the component, the extent of any flatness deviation of the component can be determined. Checking whether or not the central die part is pressed downwards by the component during the measurement allows a statement to be made about the direction of curvature of the component. A convexly curved component can be identified if movement of the central part of the die is detected. On the other hand, a concavely curved component can be concluded if the difference between the measured distance of the upper measuring tool until it touches the component and the distance between the upper starting position of the upper measuring tool and the die is greater than the initial thickness of the component and the central part of the die remains in its rest position.

[0012] The distance between the upper starting position of the upper measuring tool and the plane of the lower measuring tool can be measured absolutely, i.e. an absolute value for this distance can be determined. Alternatively, the position of the upper and lower measuring tools can be referenced. To do this, in order to measure the distance between the upper starting position of the upper measuring tool and the plane of the lower measuring tool, the upper measuring tool can be moved from its upper starting position towards the lower measuring tool until an increase in the force exerted on the upper measuring tool indicates that the upper measuring tool has hit the lower measuring tool, and the distance traveled by the upper measuring tool until it touches the lower measuring tool is measured. This distance corresponds to the distance between the upper starting position of the upper tool and the lower tool and is saved.

[0013] The degree of flatness deviation of the component can be calculated using the formula h = so - si - d, where so is the distance between the upper starting position of the upper measuring tool, si is the travel of the upper tool from its upper starting position to contact with the component, and d is the initial thickness of the component. The signals from the force sensor, the displacement measuring device, and the central die part can preferably be synchronized in real time to quickly obtain a measurement result for the component.

[0014] If concave or convex curved components are detected, these components can be reworked in the punching machine if the flatness deviation exceeds a specified tolerance value. This allows parts that were previously identified as defective in a quality control process outside the punching machine, even using conventional methods, to be reworked promptly and without manual intervention. This allows the number of reject parts to be reduced cost-effectively.

[0015] In addition, if a convex or concave curved component is detected and the flatness deviation exceeds a specified tolerance value, the process parameters of the punching machine can be adjusted in such a way that curvature of the components is avoided in the production of future components.

[0016] There are various options for determining the position of the central die part. In a preferred embodiment, when measuring a convexly curved component, the central die part can be moved downwards by the component against a dynamic pressure generated in the die, thereby opening a dynamic pressure valve integrated into the die, the opening of which is monitored as an indicator of a convexly curved component. A change in dynamic pressure can preferably be monitored as an indicator of the opening of the dynamic pressure valve. A sudden drop in dynamic pressure indicates the opening of the valve.

[0017] Alternatively, the position of the back pressure valve itself can also be monitored. For example, the opening of an electrical contact can indicate that the valve has opened.

[0018] For precise measurement of the flatness deviation and the curvature direction of the components, a punch-shaped tool with a flat surface on its underside is preferably used as the upper measuring tool. In this case, the surface of the die and the surface on the underside of the upper measuring tool are exactly parallel.

[0019] The upper and lower measuring tools can be inserted into the machine before measurement using a tool changer, so that quality control can be carried out immediately after the punching process.

[0020] The invention also relates to a measuring system for carrying out a method according to the invention, with an upper measuring tool and with a lower measuring tool in the form of a die which has a central, downwardly movable part, which is characterized in that it has a displacement measuring device for the movement of the upper measuring tool, a measuring device for the force exerted on the upper measuring tool, a monitoring device for the movement of the central die part and an evaluation device for synchronizing the signals of the force measuring device, the displacement measuring device and the monitoring device of the central die part.

[0021] The invention further encompasses a punching machine with such a measuring system, wherein the punching machine is also configured to carry out a method according to the invention. For this purpose, the evaluation device of the measuring system can preferably be connected to the control system of the punching machine.

[0022] Further features and advantages of the invention will become apparent from the description, the claims, and the drawings. According to the invention, the above-mentioned and further-described features can be used individually or in combination in any convenient way. The embodiments shown and described are not intended to be exhaustive, but rather are exemplary in nature for describing the invention.

[0023] Detailed description of the invention and drawing

[0024] Fig. 1a, 1b show a schematic representation of the start phase of a method according to the invention and an associated force-displacement diagram and a level-displacement diagram;

[0025] Fig. 2a, 2b show a schematic representation of a reference measurement according to the method according to the invention and an associated force-displacement diagram and a level-displacement diagram;

[0026] Fig. 3a, 3b show a schematic representation of the first measurement phase of a convexly curved component and an associated force-displacement diagram and a level-displacement diagram;

[0027] Fig. 4a, 4b show a schematic representation of the final phase of the measurement of a convex curved component and an associated force-displacement diagram and a level-displacement diagram;

[0028] Fig. 5a, 5b show a schematic representation of the final phase of the measurement of a concavely curved component and an associated force-displacement diagram and a level-displacement diagram;

[0029] Fig. 6 is an enlarged view of the measurement of a convex component according to Fig. 4a;

[0030] Fig. 7 is an enlarged detailed view of the lower measuring tool from Fig. 6. Fig. 1a shows a schematic representation of an upper measuring tool 10 and a lower measuring tool 11 of a punching machine (not shown in detail). The upper measuring tool 10 is shown in its upper starting position. It can be moved towards the lower measuring tool 11 by exerting a force 12. The distance traveled by the upper measuring tool 10 is recorded by a distance measuring system (not shown). In the illustrated embodiment, a force sensor 14 is also integrated into the upper measuring tool 10. However, the measurement of the force exerted on the upper measuring tool 10 can also take place in a drive unit of the machine. The lower measuring tool 11 is a die with a central part 13 that can be moved downwards. The signals from the force sensor 14 and the distance measuring system are synchronized and shown in the force-distance diagram shown in Fig. 1b.In this initial phase of the process, the diagram shows a displacement and force of zero. Furthermore, the position of the central die part 13 is recorded in a level-displacement diagram. The signal level in Fig. 1b is high over the entire travel distance of the upper measuring tool 10, thus indicating that the central die part 13 is in its upper starting position.

[0031] Fig. 2a shows the performance of a reference measurement. The upper measuring tool 10 was moved downwards until it came into contact with the lower measuring tool 11. The corresponding force-displacement diagram in Fig. 2b shows a sharp increase in the force measured by the force sensor 14 after the upper measuring tool 10 has traveled a distance s 0. The distance s 0 is the distance that the upper measuring tool 10 has traveled until it comes into contact with the lower measuring tool 11 and thus corresponds to the distance between the upper starting position of the upper measuring tool 10 and the lower measuring tool 11. The value s 0 is saved as a reference value. The signal level of the central die part 13 remains elevated during the reference measurement because its position does not change.

[0032] The upper measuring tool 10 is then returned to its upper

[0033] Starting position and a component 16 - here a convexly curved sheet metal part

[0034] - placed on the die 11, as illustrated in Fig. 3a. The corresponding force-displacement diagram in Fig. 3b still shows a displacement and force of zero, and the signal level of the central die part 13 is increased.

[0035] To measure the flatness deviation h of the curved component 16 and its direction of curvature, as shown in Fig. 4a, the upper measuring tool 10 is moved downwards from its upper starting position by exerting a force 12 until it impacts the component 16. The corresponding force-displacement diagram in Fig. 4b shows a sharp increase in the force measured by the force sensor 14 as soon as the upper measuring tool has traveled a distance si until it impacts the component 16. The force-displacement diagram in Fig. 4b also shows the reference value so. From the two variables so and si, the flatness deviation can then be calculated using the formula h = so - si - d, where d is the initial thickness of the component 16, which is already known before the component is manufactured.

[0036] Since the component 16 is convexly curved, it also pushes the central die part 13 downward as soon as the upper measuring tool 10 touches it and pushes it downward. The level-displacement diagram in Fig. 4b therefore shows an abrupt level drop after the distance si through the upper measuring tool 10. This level drop can therefore be used to conclude that the component 16 is concavely curved, while the flatness deviation h indicates the degree of curvature.

[0037] Fig. 5a, on the other hand, shows the measurement of the flatness deviation and curvature direction of a concave component 17. The upper measuring tool 10 was moved downward by the force 12 until it impacts the component 17. The upper measuring tool has traveled the distance si. As soon as the measuring tool 10 impacts the component 17, there is a sharp increase in the force measured by the force sensor 14, as shown in the force-displacement diagram in Fig. 5b. The central die part 13, on the other hand, is not touched by the component 17 due to the concave curvature of the latter. The signal level of the position measurement of the central die part 13 therefore remains unchanged over the entire distance traveled by the upper measuring tool 10. The flatness deviation can also be calculated for concave components 17 using the formula h = so - si - d.The unchanged high signal level of the central die part 13 indicates that the flatness deviation h results from a concave and not a convex curvature of the component 17.

[0038] Fig. 6 and Fig. 7 illustrate, in an enlarged view, the structure of the die 11 with the central die part 13 and the processes during the measurement of a convexly curved component 16. The central die part 13 can be moved downward in the direction of the arrow. This movement is counteracted by a dynamic pressure (negative pressure) built up in a chamber 19 in the die 11. The chamber 19 is sealed off from the ambient air by a valve 20. If the central die part 13 moves downward due to the pressure exerted by the convex component 16, the valve 20 opens. This leads to a drop in the dynamic pressure, the measurement of which can therefore indicate whether the component 16 being measured is a convexly curved component or a flat or concavely curved component. The level-displacement diagrams shown in Figures 1b, 2b, 3b, 4b and 5b are pressure levels measured in chamber 19.Of course, the position of the central matrix part 13 could also be achieved in another way.

Claims

Patent claims 1 . Method for measuring flatness deviations and curvature directions of components (16, 17) in a punching machine, with an upper measuring tool (10) and a lower measuring tool in the form of a die (11) with a central, downwardly movable die part (13), comprising the steps: - measuring the distance (so) between an upper starting position of the upper measuring tool (10) and the die (11); - placing a component to be measured (16, 17) on the die (11); - moving the upper measuring tool (10) from its upper starting position until an increase in the force exerted on the upper measuring tool (10) indicates contact between the upper measuring tool (10) and the component (16, 17), and measuring the path (si) of the upper measuring tool (10) until contact with the component (16, 17); - comparing the distance (so) of the upper measuring tool (10) from the die (11) and the path (si) travelled by the upper measuring tool (10) until it comes into contact with the component (16, 17) with an initial thickness (d) of the component (16, 17) and checking whether the central die part (13) moves downwards or remains in its initial position.

2. Method according to claim 1, characterized in that a concavely curved component (16) is detected when a movement of the central part (13) of the die (11) is detected.

3. Method according to claim 1 or 2, characterized in that a convexly curved component (17) is detected when the difference between the measured path (si) of the upper measuring tool (10) until contact with the component (17) and the distance (so) between the upper starting position of the upper measuring tool (10) and the die (11) is greater than the Initial thickness (d) of the component is (17) and the central part (13) of the die (11) remains in its rest position.

4. Method according to one of the preceding claims, characterized in that for measuring the distance (so) between the upper starting position of the upper measuring tool (10) and the plane of the die (11), the upper measuring tool (10) is moved from its upper starting position towards the die (11) until an increase in the force exerted on the upper measuring tool (10) indicates that the upper measuring tool (10) has struck the die (11), and the distance (so) traveled by the upper measuring tool (10) until it touches the die (11) is measured.

5. Method according to one of the preceding claims, characterized in that the degree of flatness deviation of the component (16, 17) is calculated from the formula h = so - si - d, where so is the distance between the upper starting position of the upper measuring tool (10) and the die (11), si is the path of the upper tool (10) from its upper starting position to contact with the component (16, 17) and d is the starting thickness of the component (16, 17).

6. Method according to one of the preceding claims, characterized in that when concavely or convexly curved components (16, 17) are detected, a reworking of these components (16, 17) is carried out in the punching machine if the flatness deviation (h) exceeds a predeterminable tolerance value.

7. Method according to one of the preceding claims, characterized in that when a convexly or concavely curved component (16, 17) is detected, and if the flatness deviation (h) exceeds a predeterminable tolerance value, process parameters of the punching machine are adapted in such a way that curvature of the components (16, 17) is avoided during the production of future components (16, 17).

8. Method according to one of the preceding claims, characterized in that when measuring a convexly curved component (16), the central die part (13) is moved downwards by the component (16) against a dynamic pressure generated in the die (11), whereby a dynamic pressure valve (20) integrated in the die (11) is opened, the opening of which is monitored as an indicator for a concavely curved component (16).

9. Method according to claim 8, characterized in that a change in the back pressure is monitored as an indicator for opening of the back pressure valve (20).

10. Method according to claim 8, characterized in that the position of the back pressure valve (20) is monitored.

11. Method according to one of the preceding claims, characterized in that a stamp-shaped tool with a flat surface on its underside is used as the upper measuring tool (10).

12. Method according to one of the preceding claims, characterized in that the upper and lower measuring tools (10, 11) are exchanged into the machine by a tool changer before the measurement.

13. Measuring system for carrying out a method according to one of the preceding claims, with an upper measuring tool (10) and with a lower measuring tool in the form of a die (11) which has a central, downwardly movable part (13), characterized in that it comprises a path measuring device for the movement of the upper measuring tool (10), a measuring device for the force exerted on the upper measuring tool (10), a monitoring device for the movement of the central die part (13) and an evaluation device for synchronizing the Signals from the force measuring device (14), the position measuring device and the monitoring device of the central die part (13).

14. Punching machine with a measuring system according to claim 13 and which is configured to carry out a method according to one of claims 1 to 12.

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