CA2269949A1 - Method of producing screw connections - Google Patents
Method of producing screw connections Download PDFInfo
- Publication number
- CA2269949A1 CA2269949A1 CA002269949A CA2269949A CA2269949A1 CA 2269949 A1 CA2269949 A1 CA 2269949A1 CA 002269949 A CA002269949 A CA 002269949A CA 2269949 A CA2269949 A CA 2269949A CA 2269949 A1 CA2269949 A1 CA 2269949A1
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- Prior art keywords
- screw
- acoustic emission
- screwing
- accordance
- predetermined
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- 238000000034 method Methods 0.000 title claims abstract description 64
- 238000001514 detection method Methods 0.000 claims abstract description 8
- 230000036316 preload Effects 0.000 claims description 21
- 238000004519 manufacturing process Methods 0.000 claims description 9
- 238000012544 monitoring process Methods 0.000 claims description 5
- 238000011156 evaluation Methods 0.000 claims description 4
- 238000009776 industrial production Methods 0.000 abstract description 3
- 230000001105 regulatory effect Effects 0.000 abstract 1
- 238000005259 measurement Methods 0.000 description 31
- 238000013461 design Methods 0.000 description 3
- 238000009434 installation Methods 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 2
- 239000004020 conductor Substances 0.000 description 2
- 238000012423 maintenance Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 230000003068 static effect Effects 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 238000012790 confirmation Methods 0.000 description 1
- 230000002596 correlated effect Effects 0.000 description 1
- 230000002950 deficient Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 238000012806 monitoring device Methods 0.000 description 1
- 238000005025 nuclear technology Methods 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 230000005236 sound signal Effects 0.000 description 1
- 238000002604 ultrasonography Methods 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
- B25B—TOOLS OR BENCH DEVICES NOT OTHERWISE PROVIDED FOR, FOR FASTENING, CONNECTING, DISENGAGING OR HOLDING
- B25B23/00—Details of, or accessories for, spanners, wrenches, screwdrivers
- B25B23/14—Arrangement of torque limiters or torque indicators in wrenches or screwdrivers
- B25B23/142—Arrangement of torque limiters or torque indicators in wrenches or screwdrivers specially adapted for hand operated wrenches or screwdrivers
- B25B23/1422—Arrangement of torque limiters or torque indicators in wrenches or screwdrivers specially adapted for hand operated wrenches or screwdrivers torque indicators or adjustable torque limiters
- B25B23/1425—Arrangement of torque limiters or torque indicators in wrenches or screwdrivers specially adapted for hand operated wrenches or screwdrivers torque indicators or adjustable torque limiters by electrical means
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23P—METAL-WORKING NOT OTHERWISE PROVIDED FOR; COMBINED OPERATIONS; UNIVERSAL MACHINE TOOLS
- B23P19/00—Machines for simply fitting together or separating metal parts or objects, or metal and non-metal parts, whether or not involving some deformation; Tools or devices therefor so far as not provided for in other classes
- B23P19/04—Machines for simply fitting together or separating metal parts or objects, or metal and non-metal parts, whether or not involving some deformation; Tools or devices therefor so far as not provided for in other classes for assembling or disassembling parts
- B23P19/06—Screw or nut setting or loosening machines
- B23P19/065—Arrangements for torque limiters or torque indicators in screw or nut setting machines
- B23P19/066—Arrangements for torque limiters or torque indicators in screw or nut setting machines by electrical means
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
- B25B—TOOLS OR BENCH DEVICES NOT OTHERWISE PROVIDED FOR, FOR FASTENING, CONNECTING, DISENGAGING OR HOLDING
- B25B23/00—Details of, or accessories for, spanners, wrenches, screwdrivers
- B25B23/14—Arrangement of torque limiters or torque indicators in wrenches or screwdrivers
Abstract
The invention concerns a method of producing specific screw connections, two components being urged against each other with predetermined pretension by means of a screw which is rotated by a screwing device which can be regulated, and the screw producing an acoustic emission. The invention is characterized by the following steps: detection of the acoustic emission which is generated in the screw during an actual screwing process; and comparison of the detected acoustic emission occurring during the actual screwing process with predetermined stored data, it being determined according to predetermined criteria whether the screwing process is proceeding correctly. The method can preferably be used in assembly processes in industrial production.
Description
114_9 Method of Producing Screw Connections The invention relates to a method of producing screw connections and can preferably be used in assembly processes in industrial production.
It is known from the prior art that electronically controlled screw systems are increasingly frequently used in industrial production. These have a drive unit and a tool spindle with a screw tool which tightens a screw with a predetermined screwing in torque in order to press the parts to be joined together against one another with a predetermined pre-load. This force is termed the pre-load and arises through the change in length of the shaft of the screw, which will subsequently be termed the elongation. In many applications it is necessary to set the pre-load as accurately as possible to a predetermined value. For this purpose it is necessary to determine the pre-load. It is prior art to determine the pre-load indirectly via the measurement of the screwing in torque during the screwing in process.
Torque measurement systems or angle of rotation measurement systems, which are integrated into the screwing system, are principally used for the measurement of the screwing in torque. When a preset torque is achieved during the screwing in of the screw, a signal transmitted by the torque measuring system or the angle of rotation measuring system is used to switch off the drive unit or the screw is rotated further by a predetermined angle of rotation.
With the indirect determination of the pre-load via the torque measurement, the following problems arise: On tightening a screw, only a small part of the applied torque is used for the elongation of the screw, i.e.
for the production of the pre-load. The larger part of the torque is taken in by the friction at the screw of the thread and at the head of the screw. If the friction conditions change, then these changes have a pronounced effect on the pre-load. Accordingly, the above described devices cannot guarantee the maintenance of narrow tolerances of the pre-load.
In order to overcome these difficulties it is necessary to directly measure the pre-load. For this various methods and devices have been proposed.
Thus, it is known to arrange a measurement ring in the form of a washer beneath the screw head. This measurement ring is a sensor which transmits an electrical signal under the action of a force. If the screw is tightened, the screw head presses onto the measurement ring, and the pre-load can be directly measured. This method is very cost intensive, because the measurement ring remains under the screw head after the screw connection has been tightened. Accordingly, this method is restricted to only certain applications, such as for example space-flight or nuclear technology.
A further possibility for determining the pre-load is described in DE 44 10 722. An apparatus is disclosed for the determination of the pre-load of screws located in a component, with the aid of at least one coil, through which AC current flows, with the screw consisting at least partly of electrically conductive material at the surface confronting the coil(s), and wherein a distance to at least one coil which changes in proportion to the pre-load of the screw is detected by the coil as a measurement signal, with the head of the screw having a projecting region facing the component.
This method has the disadvantage that it can only be used for screws ofelectrically conductive material. Changes in length which arise as a result of plastic deformations cannot be detected. The lengths to be measured are so small that this method can hardly be used or can only be used with considerable technical complications under rough production conditions.
In DE 40 17 726 a mounting screw having a shaft which is at least partly provided with a thread and an actuating end is described, on which a head, a pin-projection or the like are provided, with a first end face being provided at the confirmation end of the mounting screw and a second end face being provided at the free end of the shaft and with measurement surfaces for an ultrasonic measurement being provided in both end surfaces, the measurement surfaces extending only over a part of the end surfaces and being axially offset relative to the end surfaces in the sense of an elevation and/or recess.
With this apparatus the change in length of the screw is measured by means of ultrasonics. The pre-load is directly found from the characteristic values of the material and the geometrical dimensions of the screw by means of methods known to the person skilled in the art. The subjects of the patent applications DE 195 07 391 and DE 40 25 430 are based on the same principal.
However, the determination of the change of length of the screw by means of ultrasonics also has disadvantages. In order to precisely detect the change in length, the ultrasound must be introduced in defined manner into the screw. The technical problems to be solved in this connection are considerable. Thus, it is necessary to specially design the sound introduction surfaces and the reflection surfaces. Furthermore, it is necessary for these surfaces to be manufactured with high precision and to be closely toleranced. Standard screws cannot satisfy these demands.
Screws are manufactured with highly effective methods as mass production components. No comparable method are available for the manufacture of screws with introduction surfaces for ultrasonic signals.
Accordingly, the manufacturing costs for these special screws are high. A
further disadvantage lies in the fact that with the ultrasonic method, the introduction of sound and the picking up of the reaction signal must take place directly at the screw, i.e. the ultrasonic transmitter and receiver are integrated into the screwing spindle, which thereby undergoes larger design changes. In cases where the constructional conditions are very restricted, a screwing spindle of this kind with large design dimensions can under some circumstances not be used.
The object of the invention is to provide a method for the direct determination of the pre-load at screw connections which overcomes the above described problems.
This object is satisfied with a method in accordance with patent claim 1, wherein two components are pressed against one another with a predetermined pre-load by means of a screw which is turned by a regulatable screwing in device. An acoustic emission is transmitted from the screw material caused by the elongation of the screw. The method is characterized by the following method steps:
- detection of the acoustic emission, which arises at the screw during an actual screwing in process and - comparison of the detected acoustic emission during the actual screwing up process with predetermined stored data, wherein a determination is made in accordance with predetermined criteria whether the screwing up process takes place in accordance with the operation.
The evaluation of the signals of the acoustic emission takes place with the methods of sound emission analysis known to the prior art.
The advantage of the method lies in the fact that a signal which is closely correlated with the pre-load is obtained and can be used independently of the friction in the thread or at the screw head, and optionally for the control or for the regulation of the screwing up process. It is possible to combine this signal of the acoustic emission with the measurement signals hitherto known from the prior art for the measurement parameters torque, angle of rotation, screw length, apparent limit of elasticity and screw-in depth. These combinations are used in screw connections in which the maintenance of predetermined quality features is particularly closely toleranced. If required, it is also possible to combine more than two measurement parameters. A further and important advantage of the method lies in the fact that the acoustic emission can also be detected in the close vicinity of the screw. Thus, a method for the direct determination of the pre-load of a screw in a screw connection is available for the first time in which the picking up of the measurement parameter does not have to take place directly at the screw itself.
Advantageous further developments of the method of the invention are the subject of the subordinate claims, in accordance with claim 2 of which an actual pattern of the acoustic emission which arises during the elongation of the screw in an actual screwing in process is detected. Parallel to this the actual pattern is compared with a stored characteristic pattern and a determination is made by means of predetermined criteria whether the screwing in process takes place within permissible tolerances.
In accordance with patent claim 3 a suitable environment is selected atthe screw in dependence on the screw geometry, the screw size and the installation conditions, i.e. in dependence on the environment of the screw, in which the acoustic emission can be readily detected. A suitable position is preferably the end or side surface of the screw head or the end surface of the end of the screw. In dependence on the specific installation conditions another position can also be selected which permits a direct contact between the sensor for picking up the acoustic emission and the screw.
In accordance with patent claim 4 a suitable position at which the acoustic emission can be readily detected is selected in dependence on the screw geometry, the screw size and on the installation conditions in the immediate vicinity of the screw. In choosing the suitable position, the sound transmission conditions are to be taken into account. An ideal position is determined by means of a few tests.
In accordance with patent claim 5 the acoustic emission is detected both directly at the screw and also at a suitable position in the immediate vicinity of the screw. This method offers a higher reliability of the outcome in the evaluation of the acoustic emission with special requirements and under special conditions.
In accordance with patent claim 6, the screw connection is additionallymonitored via the angle of rotation or via the apparent limit of elasticity or via the screw length in addition to the control and/or regulation by means of the acoustic emission, with three preferred method variants existing:
Variant 1:
During the manufacture of a screw connection the screw-in depth of the screw is continually determined by means of a depth sensor. When the screw head comes into contact, the signal of the depth sensor exceeds a predetermined, limiting value T and the detection of the acoustic emission is started. After reaching a predetermined limit value El, the angle of rotation measurement is started. When the acoustic emission has reached a further predetermined value E2, the screwing spindle with which the screw is turned in is switched off. Subsequently, a check is made whether the angle of rotation lies in a predetermined range. When the angle of rotation lies in the predetermined range, the screw connection is assessed as good, when the angle of rotation lies outside of the predetermined range, the screw connection is evaluated as deficient.
Variant 2:
During the manufacture of a screw connection, the torque at the screw is continually determined by means of a torque sensor. When the screw head comes into contact, the signal of the torque sensor exceeds a predetermined limit value M, and the detection of the acoustic emission is started. After achieving a predetermined limit value E 1, a measurement of the angle of rotation is started. The ratio is calculated from two parameters, from the torque that is found and from the angle of rotation.
If the acoustic emission achieves a further predetermined boundary value E2, the screwing spindle is switched off and a check is made whether the ratio torque / angle of rotation and/or the angle of rotation and/or the torque lie within predetermined ranges.
Variant 3:
Before turning in the screw, its length Ll is measured. Thereafter, the screw is turned in until the screw head comes into contact, with simultaneous measurement of the screw-in depth by means of a depth measuring instrument and the measurement of the torque. When the head comes into contact, the measurement signal of the depth measurement reaches a limit value T, after which the detection of the acoustic emission is started. If the acoustic emission reaches a predetermined value El, the angle of rotation measurement is started. If the acoustic emission reaches a further predetermined value E2, the screwing spindle is switched off and the length L2 of the screw is measured. The pre-load is calculated from the length difference L2 - Ll via the known geometrical dimensions and via the characteristic strength values of the screw.
In accordance with patent claim 7 the production of the screw connection is controlled via the torque or the angle of rotation or the apparent limit of elasticity, with the monitoring taking place via the acoustic emission.
There are three preferred method variants:
Variant 1:
The screw is turned in with simultaneous measurement of the torque until the head enters into contact. When the head enters into contact, the torque achieves a predetermined value M 1, after which the detection of the acoustic emission is started. If the torque reaches a predetermined value M2, the screwing spindle is switched off. Thereafter, a check is made whether the acoustic emission lies within a predetermined range or satisfies predetermined criteria. Thus, the elongation of the screw can be checked without the disturbing influence of the thread friction and head friction.
Variant 2:
The screw is turned in with simultaneous measurement of the torque until the head enters into contact. When the head enters into contact, the torque achieves a predetermined value M 1, after which the detection of the acoustic emission and of the angle of rotation is started. After reaching a predetermined angle of rotation D 1, the screwing spindle is switched off.
Thereafter a check is made whether the acoustic emission lies within a predetermined range or satisfies specific criteria. With this method it can in particular be determined whether the screw has not been drawn into the region of plastic deformation or has been drawn too far into the region of plastic deformation.
Variant 3:
The screw is turned in with simultaneous measurement of the torque until the head enters into contact. After the head has entered into contact, the torque rises strongly and achieves a predetermined value M 1. At this point in time the ratio of the torque / angle of rotation is determined and the measurement of the acoustic emission is started. After a predetermined ratio of torque / angle of rotation, the screwing spindle is switched off.
Thereafter a check is made whether the acoustic emission lies within a predetermined range or satisfies predetermined criteria.
In accordance with patent claim 8, the method of the invention is used for a redundant monitoring of the screwing in process. It can be combined with the methods known from the prior art. One of these combination possibilities should be explained as an example for further possibilities.
A screw is screwed in with simultaneous measurement of the torque, withan "operating mode fast". On reaching a threshold torque Ml which signals and ensures the contact of the screw head, an "operating mode slow" is switched on and simultaneously an angle of rotation monitoring device is switched on. A slow further turning of the screw takes place until a technologically predetermined switch-off torque M2 is achieved. After the switching off, a determination can be made, from the size of the angle of rotation between M 1 and M2, whether the measured angle of rotation corresponds with a predetermined angle of rotation, and thus the screw has been tightened in accordance with the technological requirement.
With the method of the invention, a redundant monitoring of the angle of rotation check takes place in that a determination is made whether a characteristic pattern of the acoustic emission transmitted by the screw corresponds with a comparison pattern stored in the memory unit. This redundant check increases the statistical reliability with which the quality of the screw connection is assessed with respect to the contact pressure force. This method can preferably be used with tightly toleranced screw connections. A further advantage lies in the fact that the redundant monitoring can be retro-fitted to existing screwing in devices.
Further measures and advantages of the invention result from the following description of the embodiment in connection with the accompanying schematic drawing, with the invention being directed to all new features or combinations of features which can be deduced therefrom, even if these are not expressly set forth in the claims.
Fig. 1 shows the schematic layout of a preferred embodiment of the method of the invention.
Two plate-like components, of which one component has a threaded bore, are screwed together by means of a screw M 10. For this the following working processes are carried out:
The screw is mounted on the component and turned in, with the screw-in depth being simultaneously measured with a depth sensor. When the screw head comes into contact with the component, a signal is transmitted by the depth sensor, which starts the measurement of the acoustic emission (AE). The high frequency AE signals arising in the screw are detected by an AE sensor releasably coupled to the screw and lie in the present example in the range from 130 to 300 kH. The AE signals are processed into a quasi static signal. For this purpose, first of all bandpass filtering takes place in order to increase the signal to noise ratio. The bandpass filter is so dimensioned that disturbing sound signals, which arise through the frictional processes in the thread or from other sound sources, can be separated from the useful signal, which is produced by the elongation of the screw. Thereafter, the signal is squared and an average value formation is carried out. The average value formation and also the width and position of the frequency range is dependent on the screw, or on the type of screw, and is found by tests. If empirical values for a specific screw type are already present, only an optimization is required if necessary. In order to increase the quality of the measured signals, further bandpass filters can be used. If the filtered, quasi static signal of the acoustic emission exceeds a predetermined limit value E1, the angle of rotation measurement is started. If a further limit value E2 is achieved, the switching off of the screwing spindle takes place. After the switching off of the screwing spindle, a check is made whether the angle of CA 02269949 l999-04-26 rotation measured at the screw head lies within a technologically permissible tolerance.
It should be emphasized that this embodiment does not represent any restriction of the invention. In the knowledge of the technical teaching disclosed in the present description of the invention, it is possible for a person skilled in the art to develop further possibilities of use of the invention without, however, departing from the scope of protection of the patent claims.
It is known from the prior art that electronically controlled screw systems are increasingly frequently used in industrial production. These have a drive unit and a tool spindle with a screw tool which tightens a screw with a predetermined screwing in torque in order to press the parts to be joined together against one another with a predetermined pre-load. This force is termed the pre-load and arises through the change in length of the shaft of the screw, which will subsequently be termed the elongation. In many applications it is necessary to set the pre-load as accurately as possible to a predetermined value. For this purpose it is necessary to determine the pre-load. It is prior art to determine the pre-load indirectly via the measurement of the screwing in torque during the screwing in process.
Torque measurement systems or angle of rotation measurement systems, which are integrated into the screwing system, are principally used for the measurement of the screwing in torque. When a preset torque is achieved during the screwing in of the screw, a signal transmitted by the torque measuring system or the angle of rotation measuring system is used to switch off the drive unit or the screw is rotated further by a predetermined angle of rotation.
With the indirect determination of the pre-load via the torque measurement, the following problems arise: On tightening a screw, only a small part of the applied torque is used for the elongation of the screw, i.e.
for the production of the pre-load. The larger part of the torque is taken in by the friction at the screw of the thread and at the head of the screw. If the friction conditions change, then these changes have a pronounced effect on the pre-load. Accordingly, the above described devices cannot guarantee the maintenance of narrow tolerances of the pre-load.
In order to overcome these difficulties it is necessary to directly measure the pre-load. For this various methods and devices have been proposed.
Thus, it is known to arrange a measurement ring in the form of a washer beneath the screw head. This measurement ring is a sensor which transmits an electrical signal under the action of a force. If the screw is tightened, the screw head presses onto the measurement ring, and the pre-load can be directly measured. This method is very cost intensive, because the measurement ring remains under the screw head after the screw connection has been tightened. Accordingly, this method is restricted to only certain applications, such as for example space-flight or nuclear technology.
A further possibility for determining the pre-load is described in DE 44 10 722. An apparatus is disclosed for the determination of the pre-load of screws located in a component, with the aid of at least one coil, through which AC current flows, with the screw consisting at least partly of electrically conductive material at the surface confronting the coil(s), and wherein a distance to at least one coil which changes in proportion to the pre-load of the screw is detected by the coil as a measurement signal, with the head of the screw having a projecting region facing the component.
This method has the disadvantage that it can only be used for screws ofelectrically conductive material. Changes in length which arise as a result of plastic deformations cannot be detected. The lengths to be measured are so small that this method can hardly be used or can only be used with considerable technical complications under rough production conditions.
In DE 40 17 726 a mounting screw having a shaft which is at least partly provided with a thread and an actuating end is described, on which a head, a pin-projection or the like are provided, with a first end face being provided at the confirmation end of the mounting screw and a second end face being provided at the free end of the shaft and with measurement surfaces for an ultrasonic measurement being provided in both end surfaces, the measurement surfaces extending only over a part of the end surfaces and being axially offset relative to the end surfaces in the sense of an elevation and/or recess.
With this apparatus the change in length of the screw is measured by means of ultrasonics. The pre-load is directly found from the characteristic values of the material and the geometrical dimensions of the screw by means of methods known to the person skilled in the art. The subjects of the patent applications DE 195 07 391 and DE 40 25 430 are based on the same principal.
However, the determination of the change of length of the screw by means of ultrasonics also has disadvantages. In order to precisely detect the change in length, the ultrasound must be introduced in defined manner into the screw. The technical problems to be solved in this connection are considerable. Thus, it is necessary to specially design the sound introduction surfaces and the reflection surfaces. Furthermore, it is necessary for these surfaces to be manufactured with high precision and to be closely toleranced. Standard screws cannot satisfy these demands.
Screws are manufactured with highly effective methods as mass production components. No comparable method are available for the manufacture of screws with introduction surfaces for ultrasonic signals.
Accordingly, the manufacturing costs for these special screws are high. A
further disadvantage lies in the fact that with the ultrasonic method, the introduction of sound and the picking up of the reaction signal must take place directly at the screw, i.e. the ultrasonic transmitter and receiver are integrated into the screwing spindle, which thereby undergoes larger design changes. In cases where the constructional conditions are very restricted, a screwing spindle of this kind with large design dimensions can under some circumstances not be used.
The object of the invention is to provide a method for the direct determination of the pre-load at screw connections which overcomes the above described problems.
This object is satisfied with a method in accordance with patent claim 1, wherein two components are pressed against one another with a predetermined pre-load by means of a screw which is turned by a regulatable screwing in device. An acoustic emission is transmitted from the screw material caused by the elongation of the screw. The method is characterized by the following method steps:
- detection of the acoustic emission, which arises at the screw during an actual screwing in process and - comparison of the detected acoustic emission during the actual screwing up process with predetermined stored data, wherein a determination is made in accordance with predetermined criteria whether the screwing up process takes place in accordance with the operation.
The evaluation of the signals of the acoustic emission takes place with the methods of sound emission analysis known to the prior art.
The advantage of the method lies in the fact that a signal which is closely correlated with the pre-load is obtained and can be used independently of the friction in the thread or at the screw head, and optionally for the control or for the regulation of the screwing up process. It is possible to combine this signal of the acoustic emission with the measurement signals hitherto known from the prior art for the measurement parameters torque, angle of rotation, screw length, apparent limit of elasticity and screw-in depth. These combinations are used in screw connections in which the maintenance of predetermined quality features is particularly closely toleranced. If required, it is also possible to combine more than two measurement parameters. A further and important advantage of the method lies in the fact that the acoustic emission can also be detected in the close vicinity of the screw. Thus, a method for the direct determination of the pre-load of a screw in a screw connection is available for the first time in which the picking up of the measurement parameter does not have to take place directly at the screw itself.
Advantageous further developments of the method of the invention are the subject of the subordinate claims, in accordance with claim 2 of which an actual pattern of the acoustic emission which arises during the elongation of the screw in an actual screwing in process is detected. Parallel to this the actual pattern is compared with a stored characteristic pattern and a determination is made by means of predetermined criteria whether the screwing in process takes place within permissible tolerances.
In accordance with patent claim 3 a suitable environment is selected atthe screw in dependence on the screw geometry, the screw size and the installation conditions, i.e. in dependence on the environment of the screw, in which the acoustic emission can be readily detected. A suitable position is preferably the end or side surface of the screw head or the end surface of the end of the screw. In dependence on the specific installation conditions another position can also be selected which permits a direct contact between the sensor for picking up the acoustic emission and the screw.
In accordance with patent claim 4 a suitable position at which the acoustic emission can be readily detected is selected in dependence on the screw geometry, the screw size and on the installation conditions in the immediate vicinity of the screw. In choosing the suitable position, the sound transmission conditions are to be taken into account. An ideal position is determined by means of a few tests.
In accordance with patent claim 5 the acoustic emission is detected both directly at the screw and also at a suitable position in the immediate vicinity of the screw. This method offers a higher reliability of the outcome in the evaluation of the acoustic emission with special requirements and under special conditions.
In accordance with patent claim 6, the screw connection is additionallymonitored via the angle of rotation or via the apparent limit of elasticity or via the screw length in addition to the control and/or regulation by means of the acoustic emission, with three preferred method variants existing:
Variant 1:
During the manufacture of a screw connection the screw-in depth of the screw is continually determined by means of a depth sensor. When the screw head comes into contact, the signal of the depth sensor exceeds a predetermined, limiting value T and the detection of the acoustic emission is started. After reaching a predetermined limit value El, the angle of rotation measurement is started. When the acoustic emission has reached a further predetermined value E2, the screwing spindle with which the screw is turned in is switched off. Subsequently, a check is made whether the angle of rotation lies in a predetermined range. When the angle of rotation lies in the predetermined range, the screw connection is assessed as good, when the angle of rotation lies outside of the predetermined range, the screw connection is evaluated as deficient.
Variant 2:
During the manufacture of a screw connection, the torque at the screw is continually determined by means of a torque sensor. When the screw head comes into contact, the signal of the torque sensor exceeds a predetermined limit value M, and the detection of the acoustic emission is started. After achieving a predetermined limit value E 1, a measurement of the angle of rotation is started. The ratio is calculated from two parameters, from the torque that is found and from the angle of rotation.
If the acoustic emission achieves a further predetermined boundary value E2, the screwing spindle is switched off and a check is made whether the ratio torque / angle of rotation and/or the angle of rotation and/or the torque lie within predetermined ranges.
Variant 3:
Before turning in the screw, its length Ll is measured. Thereafter, the screw is turned in until the screw head comes into contact, with simultaneous measurement of the screw-in depth by means of a depth measuring instrument and the measurement of the torque. When the head comes into contact, the measurement signal of the depth measurement reaches a limit value T, after which the detection of the acoustic emission is started. If the acoustic emission reaches a predetermined value El, the angle of rotation measurement is started. If the acoustic emission reaches a further predetermined value E2, the screwing spindle is switched off and the length L2 of the screw is measured. The pre-load is calculated from the length difference L2 - Ll via the known geometrical dimensions and via the characteristic strength values of the screw.
In accordance with patent claim 7 the production of the screw connection is controlled via the torque or the angle of rotation or the apparent limit of elasticity, with the monitoring taking place via the acoustic emission.
There are three preferred method variants:
Variant 1:
The screw is turned in with simultaneous measurement of the torque until the head enters into contact. When the head enters into contact, the torque achieves a predetermined value M 1, after which the detection of the acoustic emission is started. If the torque reaches a predetermined value M2, the screwing spindle is switched off. Thereafter, a check is made whether the acoustic emission lies within a predetermined range or satisfies predetermined criteria. Thus, the elongation of the screw can be checked without the disturbing influence of the thread friction and head friction.
Variant 2:
The screw is turned in with simultaneous measurement of the torque until the head enters into contact. When the head enters into contact, the torque achieves a predetermined value M 1, after which the detection of the acoustic emission and of the angle of rotation is started. After reaching a predetermined angle of rotation D 1, the screwing spindle is switched off.
Thereafter a check is made whether the acoustic emission lies within a predetermined range or satisfies specific criteria. With this method it can in particular be determined whether the screw has not been drawn into the region of plastic deformation or has been drawn too far into the region of plastic deformation.
Variant 3:
The screw is turned in with simultaneous measurement of the torque until the head enters into contact. After the head has entered into contact, the torque rises strongly and achieves a predetermined value M 1. At this point in time the ratio of the torque / angle of rotation is determined and the measurement of the acoustic emission is started. After a predetermined ratio of torque / angle of rotation, the screwing spindle is switched off.
Thereafter a check is made whether the acoustic emission lies within a predetermined range or satisfies predetermined criteria.
In accordance with patent claim 8, the method of the invention is used for a redundant monitoring of the screwing in process. It can be combined with the methods known from the prior art. One of these combination possibilities should be explained as an example for further possibilities.
A screw is screwed in with simultaneous measurement of the torque, withan "operating mode fast". On reaching a threshold torque Ml which signals and ensures the contact of the screw head, an "operating mode slow" is switched on and simultaneously an angle of rotation monitoring device is switched on. A slow further turning of the screw takes place until a technologically predetermined switch-off torque M2 is achieved. After the switching off, a determination can be made, from the size of the angle of rotation between M 1 and M2, whether the measured angle of rotation corresponds with a predetermined angle of rotation, and thus the screw has been tightened in accordance with the technological requirement.
With the method of the invention, a redundant monitoring of the angle of rotation check takes place in that a determination is made whether a characteristic pattern of the acoustic emission transmitted by the screw corresponds with a comparison pattern stored in the memory unit. This redundant check increases the statistical reliability with which the quality of the screw connection is assessed with respect to the contact pressure force. This method can preferably be used with tightly toleranced screw connections. A further advantage lies in the fact that the redundant monitoring can be retro-fitted to existing screwing in devices.
Further measures and advantages of the invention result from the following description of the embodiment in connection with the accompanying schematic drawing, with the invention being directed to all new features or combinations of features which can be deduced therefrom, even if these are not expressly set forth in the claims.
Fig. 1 shows the schematic layout of a preferred embodiment of the method of the invention.
Two plate-like components, of which one component has a threaded bore, are screwed together by means of a screw M 10. For this the following working processes are carried out:
The screw is mounted on the component and turned in, with the screw-in depth being simultaneously measured with a depth sensor. When the screw head comes into contact with the component, a signal is transmitted by the depth sensor, which starts the measurement of the acoustic emission (AE). The high frequency AE signals arising in the screw are detected by an AE sensor releasably coupled to the screw and lie in the present example in the range from 130 to 300 kH. The AE signals are processed into a quasi static signal. For this purpose, first of all bandpass filtering takes place in order to increase the signal to noise ratio. The bandpass filter is so dimensioned that disturbing sound signals, which arise through the frictional processes in the thread or from other sound sources, can be separated from the useful signal, which is produced by the elongation of the screw. Thereafter, the signal is squared and an average value formation is carried out. The average value formation and also the width and position of the frequency range is dependent on the screw, or on the type of screw, and is found by tests. If empirical values for a specific screw type are already present, only an optimization is required if necessary. In order to increase the quality of the measured signals, further bandpass filters can be used. If the filtered, quasi static signal of the acoustic emission exceeds a predetermined limit value E1, the angle of rotation measurement is started. If a further limit value E2 is achieved, the switching off of the screwing spindle takes place. After the switching off of the screwing spindle, a check is made whether the angle of CA 02269949 l999-04-26 rotation measured at the screw head lies within a technologically permissible tolerance.
It should be emphasized that this embodiment does not represent any restriction of the invention. In the knowledge of the technical teaching disclosed in the present description of the invention, it is possible for a person skilled in the art to develop further possibilities of use of the invention without, however, departing from the scope of protection of the patent claims.
Claims (8)
1. Method of producing a defined threaded connection, wherein two components are pressed against one another with a predetermined pre-load by means of a screw, which is rotated by a regulatable screwing in device, wherein the screw gives off an acoustic emission, characterized by the following method steps:
- detection of the acoustic emission, which is produced in the screw during an actual screwing in process, and - comparing the detected acoustic emission which arises during the actual screwing in process with predetermined stored data, wherein - a determination is made in accordance with predetermined criteria whether the screwing in process takes place in accordance with the operation.
- detection of the acoustic emission, which is produced in the screw during an actual screwing in process, and - comparing the detected acoustic emission which arises during the actual screwing in process with predetermined stored data, wherein - a determination is made in accordance with predetermined criteria whether the screwing in process takes place in accordance with the operation.
2. Method in accordance with patent claim 1, characterized by the following method steps:
- detecting an actual pattern of the acoustic emission which arises during the elongation of the screw in an actual screwing in process;
- comparison of the actual pattern of the acoustic emission during the actual screwing in process with a stored characteristic pattern, with a determination being made by means of predetermined criteria whether the screwing in process takes place within permissible tolerances.
- detecting an actual pattern of the acoustic emission which arises during the elongation of the screw in an actual screwing in process;
- comparison of the actual pattern of the acoustic emission during the actual screwing in process with a stored characteristic pattern, with a determination being made by means of predetermined criteria whether the screwing in process takes place within permissible tolerances.
3. Method in accordance with patent claim 1 or 2, characterized in that the signal of the acoustic emission is picked up directly at the screw, with the position at which the acoustic emission is taken up being so selected that the acoustic emission is available in a quality capable of evaluation.
4. Method in accordance with patent claim 1 or 2, characterized in that the signal of the acoustic emission is taken up from the direct vicinity of the screw, with the position of the take-up of the acoustic emission being so selected that the acoustic emission is available in a quality which can be evaluated.
5. Method in accordance with patent claim 1 or 2, characterized in that the signal of the acoustic emission is taken up directly at the screw and in parallel thereto the signal of the acoustic emission is taken up from the direct vicinity of the screw, with the locations of taking up the acoustic emission being so selected that the acoustic emission is available in a quality which can be evaluated.
6. Method in accordance with patent claim 1 to 5, characterized in that, in addition to the control or regulation by means of acoustic emission, the screw connection is additionally monitored via the angle of rotation or via the apparent limit of elasticity or via the screw length.
7. Method in accordance with patent claim 1 to 5, characterized in that the production of the screw connection is monitored by - the evaluation of the acoustic emission and - is controlled via the torque or via the angle of rotation or via the apparent limit of elasticity.
8. Method in accordance with patent claim 1 to 7, characterized in that the acoustic emission which arises during the screwing in process is utilized for the redundant monitoring.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19643933.7 | 1996-10-30 | ||
| DE1996143933 DE19643933C1 (en) | 1996-10-30 | 1996-10-30 | Screw connection method for industrial assembly process |
| PCT/EP1997/004986 WO1998018601A1 (en) | 1996-10-30 | 1997-09-11 | Method of producing screw connections |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2269949A1 true CA2269949A1 (en) | 1998-05-07 |
Family
ID=7809682
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002269949A Abandoned CA2269949A1 (en) | 1996-10-30 | 1997-09-11 | Method of producing screw connections |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP0935514A1 (en) |
| JP (1) | JP2001511073A (en) |
| CN (1) | CN1235570A (en) |
| AU (1) | AU719448B2 (en) |
| BR (1) | BR9712394A (en) |
| CA (1) | CA2269949A1 (en) |
| DE (1) | DE19643933C1 (en) |
| WO (1) | WO1998018601A1 (en) |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE518436C2 (en) * | 1998-05-14 | 2002-10-08 | Atlas Copco Tools Ab | Method for determining the axial force of a threaded fastener when tightening over the tension limit |
| DE19944702A1 (en) * | 1999-09-17 | 2001-03-22 | Weber Schraubautomaten Gmbh | Screwing device |
| DE19944717A1 (en) * | 1999-09-17 | 2001-03-22 | Weber Schraubautomaten Gmbh | Method for operating a screwing device |
| DE10042291C1 (en) * | 2000-08-29 | 2002-02-14 | Fraunhofer Ges Forschung | Method to monitor screwing process; involves using pulse-echo technique before and during screwing process and comparing echo times for screw material and screwing tension |
| US20080131228A1 (en) * | 2006-11-30 | 2008-06-05 | Caterpillar Inc. | Fastener tightening system utilizing ultrasonic technology |
| JP5163270B2 (en) * | 2008-05-13 | 2013-03-13 | マツダ株式会社 | Bolt fastening method and apparatus |
| FR3006765B1 (en) * | 2013-06-11 | 2015-07-03 | Airbus Operations Sas | METHOD AND DEVICE FOR DETECTING AN ACOUSTIC TRANSMITTING PHENOMENON |
| US20170321502A1 (en) * | 2016-05-06 | 2017-11-09 | Baker Hughes Incorporated | Use of acoustic emission technology in oilfield tubular make ups |
| CN107470896B (en) * | 2017-09-05 | 2019-04-12 | 天合汽车零部件（上海）有限公司 | Fastener external screw thread just matches internal screw thread monitoring device and monitoring method |
| DE102019211303A1 (en) * | 2019-07-30 | 2021-02-04 | Robert Bosch Gmbh | Method for recognizing the work progress of a hand machine tool |
| DE102021124669A1 (en) | 2021-09-23 | 2023-03-23 | Bayerische Motoren Werke Aktiengesellschaft | Procedure for process control in screwing processes |
| CN114952239B (en) * | 2022-06-07 | 2023-10-20 | 江苏悦阳光伏科技有限公司 | Automatic installation and effect detection device for junction box cover of photovoltaic module |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| LU84553A1 (en) * | 1982-12-24 | 1984-10-22 | Benoit De Halleux | METHOD OF MEASURING CONSTRAINT IN A MEDIUM AND ELEMENT AND ASSEMBLY FOR IMPLEMENTING THE METHOD |
| JPS60150919A (en) * | 1984-01-13 | 1985-08-08 | Hitachi Ltd | Automatic fastener for screw for mold-frame |
| JPH02274441A (en) * | 1989-04-18 | 1990-11-08 | Honda Motor Co Ltd | Looseness detecting device for thread member |
| JP2913322B2 (en) * | 1989-09-08 | 1999-06-28 | 横浜ゴム株式会社 | Runflat pneumatic radial tires |
| DE4017726C2 (en) * | 1990-06-01 | 1993-12-16 | Kellermann Fa Rudolf | Fastening screw |
| DE4025430A1 (en) * | 1990-08-10 | 1992-02-13 | Psm Drucklufttechnik Vertrieb | Torque controlled screwing head - has electroacoustic sensor to measure distortion of bolt under torque |
| US5277261A (en) * | 1992-01-23 | 1994-01-11 | Makita Corporation | Tightening tool |
| DE4410722A1 (en) * | 1994-03-28 | 1995-10-05 | Bosch Gmbh Robert | Non-contact bolt tightening force measurement appts. for quality control |
| JPH0858284A (en) * | 1994-08-29 | 1996-03-05 | Kotobuki:Kk | Propelling pencil |
| DE19507391C2 (en) * | 1994-09-06 | 2003-08-14 | Bosch Gmbh Robert | Screwing device for ultrasound-controlled tightening of screw connections |
-
1996
- 1996-10-30 DE DE1996143933 patent/DE19643933C1/en not_active Expired - Fee Related
-
1997
- 1997-09-11 JP JP51995898A patent/JP2001511073A/en active Pending
- 1997-09-11 CN CN 97199364 patent/CN1235570A/en active Pending
- 1997-09-11 AU AU45549/97A patent/AU719448B2/en not_active Ceased
- 1997-09-11 WO PCT/EP1997/004986 patent/WO1998018601A1/en not_active Application Discontinuation
- 1997-09-11 EP EP97943860A patent/EP0935514A1/en not_active Withdrawn
- 1997-09-11 CA CA002269949A patent/CA2269949A1/en not_active Abandoned
- 1997-09-11 BR BR9712394-3A patent/BR9712394A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| DE19643933C1 (en) | 1998-03-12 |
| BR9712394A (en) | 1999-08-31 |
| WO1998018601A1 (en) | 1998-05-07 |
| CN1235570A (en) | 1999-11-17 |
| AU719448B2 (en) | 2000-05-11 |
| EP0935514A1 (en) | 1999-08-18 |
| AU4554997A (en) | 1998-05-22 |
| JP2001511073A (en) | 2001-08-07 |
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Legal Events
| Date | Code | Title | Description |
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| FZDE | Discontinued |