Method for riveting or punching and a device for carrying out the method

Abstract: The method according to the invention for riveting or punching by means of a riveting or punching device (8), having a pick-up device (4) and a male die (3) guided by a pick-up device (4), both of which in each case can be moved towards a female die (5) or a workpiece (6), wherein female die (5) and riveting or punching device (8) are connected to one another via a counterforce structure (9), is characterised in that the relative movement between pick-up device (4) and counterforce structure (9) is measured by a first sensor (1) and the relative movement between counterforce structure (9) and male die (3) is measured by a second sensor (2) and the depth of the riveting or punching is adjusted with the aid of the two measured values. The associated device allows fast, accurate detection of the thickness of a workpiece (6) and precise punching or riveting with constant predetermined depth irrespective of variations in the quality of the material or other parameters, which can result in deformations of the counterforce structure (9) during the punching process.

Description: The present invention relates to a method for riveting or punching and a device for carrying out the method. A method for forming a punch-rivet connection and a joining device for punch-riveting are known from DE 197 31 222 A 1. The large forces on a workpiece which occur when a rivet is set or during punching must be compensated by a counterforce. This is usually achieved by supporting the workpiece on a counterforce structure, which preferably substantially has the shape of a C and is therefore also usually designated as a C-bracket. For the precise setting of a rivet or accurate punching it is important to know how deeply a rivet or a die has penetrated into the workpiece. This problem arises in particular when large workpieces are being processed, where the counterforce structure (C-bracket) is very large. In practice arm lengths of C-brackets occur of up to 1.5 metres. Deformation of the counterforce structure occurs in particular with large forces acting on the workpiece, so the actual punching depth or the rivet head projection is determined only inaccurately. This problem is particularly significant when short rivets, hard materials and large workpieces are used. Distortion of the counterforce structure results in considerable inaccuracies with respect to the punching depth or the rivet head projection. From DE-A-4213421, which forms the basis for the preamble of claims 1, 2 and 6, a riveting device is known having a riveting head and a counterforce structure, in which the joining force is detected by measuring the deformation of the counterforce structure during a riveting process by means of a strain gauge. The riveting head is movably guided at the counterforce structure and the position of the riveting head relative to the counterforce structure is detected by a linear sensor. A process computer compares the measured data with pre-set values for controlling the joining force and the rate of feed of the riveting process. To date it has been usual to construct the counterforce structure as large and as resistant to bending as possible. To keep deformation within an acceptable scope considerable expenditure and costs in the construction of the counterforce brackets have been necessary. Compensation of any deformations of the counterforce bracket took place manually, after the fault had been detected empirically. It is therefore the object of the invention to disclose a method for riveting or punching which overcomes the disadvantages described and allows the setting or punching process to run particularly accurately, as well as to describe a device for carrying out the method. This object is achieved according to the invention by a method with the features according to the independent claims for the method and by the device with the features according to the independent claim for the device. Further special configurations and further developments, which may occur individually or in combination, are the subject of the dependent claims respectively. In the method for riveting or punching with a counterforce bracket according to the invention the deformation of the counterforce structure during a riveting or punching process is detected by a monitoring unit and a course of movement during the riveting or punching process is corrected as a function of the bending. Detection of the deformation of the counterforce structure, which can vary according to the punching or setting force, the materials used, the rivets used and other parameters specific to material or shape, as different forces occur, allows flexible adaptation to every operational situation. The position of the rivet head is precisely achieved by correcting the course of movement during the riveting or punching process as a function of the bending. The inaccuracies during the riveting or punching process due to the deformation of the counterforce structure are compensated in certain limits. An advantageous consequence of this method can even be that counterforce structures can be used which have less stiffness or higher deformability, so they can be more simply constructed and therefore production costs can be saved. Typically a setting device has a female die, a pick-up device and a die guided in the pick-up device, which presses directly or indirectly on a workpiece, located between die plate and pick-up device. When the pick-up device makes contact with the workpiece the riveting depth can be determined from the relative movement between pick-up device and die. A disadvantage of this, however, is that the cable ducts needed for detecting the relative movement between die and pick-up device suffer from the constant movement both of the pick-up device and of the die in longterm operation and in time are subjected to wear phenomena. In a preferred configuration of the method according to the invention the relative movement between pick-up device and counterforce structure is detected by a first sensor and the relative movement between pick-up device and male die or between male die and counterforce structure is detected by a second sensor and the depth of the riveting or punching is adjusted with the aid of the two measured values. The two sensors are preferably constructed as path sensors, in particular digital step counters. It is important herein that not only the relative displacement between pick-up device and die is detected, but additionally also the movement of the pick-up device due to deformations of the counterforce structure. According to an advantageous further development of the method the setting of the male die and the pick-up device on the female die or on a workpiece is detected by a measurement of the force on the drive of the die. By measuring a reference position at a defined force when the male die and the pick-up device are set, calibration can be performed in a simple manner. The measurement of the force takes place via the housing, so the forces exerted by the male die and the holding-down clamp are measured together. With this information the actual depth of the riveting or punching and also the length of the riveting can then be accurately determined. These reference measurements can also be used to determine the thickness of workpieces accurately and quickly. The relative displacement between male die and pick-up device at the deepest point corresponds exactly to the pressing depth or the rivet head projection. The method according to the invention in a particularly preferred embodiment has the effect that a predetermined movement path of the die towards the workpiece, based on a desired punching depth or a desired rivet head projection, is lengthened by the relative movement between counterforce structure and pick-up device measured by the first sensor during the riveting or punching process. With different hardness of the material to be processed, but also even with different temperatures, etc., the forces occurring during riveting or punching are different, leading to deformations of the counterforce structure which cannot be accurately determined empirically. By means of the compensation according to the invention with the relative movement measured by the first sensor, which exactly corresponds to the deformation of the counterforce structure, a constant setting or punching depth can nevertheless be achieved. In addition, however, the measurement of the deformation of the counterforce structure can also provide further valuable information, in other words, for example, on the quality of the material to be processed, the state of the counterforce structure, the quality of the process carried out itself, etc. This is another substantial advantage of the invention. A riveting or punching device according to the invention, in particular for carrying out the above method, has a pick-up device and a male die guided by the pick-up device, which in each case can be moved towards a female die or a workpiece, wherein female die and riveting or punching device are connected to one another via a counterforce structure, in particular a C-shaped counterforce bracket. In that a first sensor is present which measures the relative movement between pick-up device and counterforce structure and a second sensor is present which measures the relative movement between pick-up device and male die or between male die and counterforce structure, an exact detection of the actual position of the male die relative to the female die or the workpiece is possible. Deviations from the target position can for the first time be corrected by adjusting during the course of movement and no longer have to be manually input based on empirical observations. Preferably the first path recorder is a linear path recorder, preferably a digital counter, which, for example, counts stroke-shaped markings on a kind of ruler. This enables fast and accurate processing of the signals in a monitoring unit. Further special configurations and advantages of the invention are explained in the following drawing using a rivet setting machine. The drawing is to be seen as a special, demonstration example of the invention, which is, however, not intended to restrict it. The invention can also be used in punching machines and similar devices, in which a die is guided in an outer guide, for example, a holding-down clamp or pick-up device. The figure shows a riveting device 8 with a counterforce structure 9 surrounding a workpiece 6 in the form of a C-shaped bracket. The workpiece 6 is supported on a female die 5. A pick-up device 4 picks up rivets, which are driven into the workpiece 6 with the aid of a die 3 driven by a drive unit. A first sensor 1 measures the relative movement between pick-up device 4 and counterforce structure 9. This sensor is preferably a linear path recorder consisting of a kind of ruler which makes the same movement as the pick-up device 4 and a counter which is fixed to the counterforce structure 9 and counts markings on the ruler going past it. A second sensor 2 measures the relative movement between counterforce structure 9 and male die 3. Sensors of this kind are known per se and usually integrated into the drive unit 10 of the male die 3. With spindle drives they are, for example, step counters. The first sensor 1 and the second sensor 2 are connected to a monitoring unit 7, which can thereby detect the bending of the counterforce structure 9 during action of force by the die 3 and the pick-up device 4 on the workpiece 6. With the knowledge of the bending of the counterforce structure 9 detected in this way the movement of the male die 3 can be adjusted in such a way that a constant penetration depth of the rivets is always ensured. Owing to the correction the counterforce bracket 9 can possibly be constructed as even lighter, smaller and more economical. The method for riveting or punching, in which the deformation of the counterforce structure 9 during a riveting or punching process is detected by a monitoring unit 7 and a course of movement during the riveting or punching process is corrected as a function of the bending, is particularly suitable for guaranteeing particularly good reproducibility of the setting depth or of the rivet head projection and therein gaining additional information on the working process.

Claims: Method for riveting, punching or punch-riveting with a counterforce structure (9), in particular an approximately C-shaped counterforce bracket (9), in which the deformation of the counterforce structure during a riveting or punching process is detected by a monitoring unit (7), characterised in that a course of movement during the riveting or punching process is corrected as a function of the deformation. Method of riveting, punching or punch-riveting by means of a riveting or punching device (8), having a pick-up device (4) and a male die (3) guided by the pick-up device (4), both of which can be moved in each case towards a female die (5) or a workpiece (6), wherein female die (5) and riveting or punching device (8) are connected to one another via a counterforce structure (9), characterised in that the relative movement between counterforce structure (9) and pick-up device (4) is measured by a first sensor (1) and the relative movement between pick-up device (4) and male die (3) or between male die (3) and counterforce structure (9) is measured by a second sensor and the depth of the riveting or punching or the rivet head projection is adjusted with the aid of the two measured values. Method according to claim 2, characterised in that , for calibrating, the setting of the pick-up device (4) and the male die on the female die (5) or on the workpiece (6) is detected by a force measurement, wherein the measured values of the two sensors (1 and 2) are recorded as reference values at a previously defined force. Method according to claim 2 or 3, characterised in that a movement path of the male die (3) based on a desired punching depth or a desired rivet head projection is lengthened towards the workpiece (6) by the relative movement between counterforce structure (9) and pick-up device (4) measured by the first sensor (1) during the riveting or punching process. Method according to any one of the preceding claims, characterised in that the measured deformation of the counterforce structure (9) is recorded as a quality signal for the state of the counterforce structure, the nature of the workpiece, the rivets and the die plate and/or the quality of the process carried out. Riveting or punching device (8) having a pick-up device (4) and a male die (3) guided by the pick-up device (4), both of which can be moved in each case towards a female die (5) or a workpiece (6), wherein female die (5) and riveting or punching device (8) are connected to one another via a counterforce structure (9), in particular an approximately C-shaped counterforce bracket (9), characterised in that a first sensor (I) is present, which is adapted to measure the relative movement between pick-up device (4) and counterforce structure (9) and a second sensor (2) is present which is adapted to measure the relative movement between pick-up device (4) and male die (3) or between male die (3) and counterforce structure (9), and means are provided for adjusting the depth of the riveting or punching or the rivet head projection with the aid of the two measured values. Riveting or punching device (8) according to claim 6, characterised in that the first sensor (1) is a linear path recorder, preferably a digital counter. Riveting or punching device (8) according to claim 6 or 7, characterised in that a monitoring unit (7) is present, to which in use the measured values of the two sensors (1 and 2) are fed and which is adapted to calculate and record the deformation of the counterforce structure (9) from the measured values and/or correspondingly drive a drive unit (10) for the male die (3).

Inventors: BLOECHER MICHAEL, MOESER JOACHIM, OPPER REINHOLD, BLOECHER, MICHAEL, MOESER, JOACHIM, OPPER, REINHOLD, Blöcher, Michael
Applicants: NEWFREY LLC
Application year: 2001
Main classification: B21J15
IPC codes: B21J15