EP2353788A2 - Method for pulling a screw connection involving elongation of the screw - Google Patents

Abstract

The method involves using a force nut runner, with which strokes of a force link, particularly a hydraulic jack are converted, into a rotating movement of a screwing tool. The screw connection is operated to a predetermined adding moment, and then operated with a predetermined number of whole of the force link of the force nut runner.

Description

The present invention relates to a method for tightening a screw with elongation of the screw, wherein a power wrench is used, in which strokes of a force member, in particular a hydraulic cylinder, are converted into a rotational movement of a screwing. In particular tools are used as force wrench, in which the angle of rotation per stroke of the force member forms a constant.

In the manufacture of high-strength preloaded screw it is often necessary to adjust the bias to produce a defined elongation of the screw in a relatively small tolerance process reliable.

It is known, the screw elongation z. B. by an ultrasonic measurement continuously and thereby ensure the correct elongation of the screw. Furthermore, methods for tightening screw connections are known, in which the angle of rotation of the screw is measured by a rotation angle sensor during tightening and the power screwdriver is measured by means of the values of Rotation angle sensor is controlled. As a result, however, conventional power wrench without such sensors are no longer applicable. In addition, these methods are technically quite expensive control technology.

Object of the present invention is therefore to provide a method for tightening a screw available, which is simple and inexpensive to implement and still allows a process-reliable reaching a desired Schraubenlängung with low tolerances.

This object is achieved by a method according to claim 1. In the method according to the invention for tightening a screw connection while elongating the screw, a power wrench is used in which strokes of a force member, in particular a hydraulic cylinder, are converted into a rotary movement of a screwing tool. The inventive method is carried out at least in two steps. In a first step, the screw is first tightened to a predetermined torque. In a second step, the screw is then finished with a predetermined number of complete strokes of the power element of the power wrench. Thus, a torque method is combined with a rotation angle method controlled by the number of strokes.

By means of the method according to the invention, controlled elongation with small tolerances of the overall elongation can be achieved even when conventional power wrenches are used. In particular, tolerances of less than +/- 10% can be achieved. This can be dispensed with the use of costly and relatively large rotary screwdriver with rotation angle sensors. Furthermore, complicated controls, which are based on sensor values such. B. based on angle sensors, a volume measurement of the hydraulic fluid or a time measurement, be completely dispensed with.

By the method according to the invention, the influence of friction coefficients during the screwing procedure is minimized compared to pure torque methods, see above that the process security is improved. In particular, the effects of friction are shifted exclusively in the first step, ie in the joining moment range. In the second stroke-controlled step of the method according to the invention, however, the friction no longer has any influence on the screw elongation. In addition, the method is extremely simple and inexpensive to use.

According to the invention, the joining torque is adjusted so that subsequently the desired screw elongation can be achieved with high accuracy and process reliability by completely executed strokes of the tool. The method according to the invention therefore advantageously further comprises the steps of specifying a desired overall elongation and a determination of a joining moment for achieving a joint elongation, which is dimensioned such that the desired overall elongation can be achieved by the joint elongation and a number of complete strokes of the power element of the power wrench. The total elongation is thus composed of the joint elongation by tightening the screwdriver connection to the joining moment and by the elongation by the number of whole strokes of the force member of the power screwdriver.

The inventive method further advantageously comprises the step of determining a rotation angle generated by a whole stroke of the force member of the power wrench used. This results in a tool constant, by which a calculation of the necessary for a required elongation number of whole Huben can be determined.

To determine the total angle of rotation for several whole strokes, it only has to be determined by which angle of rotation the screwdriver of the power wrench is moved through an entire stroke of the force element. Then it can be calculated by simple multiplication by the number of whole strokes, which total rotation angle is effected by the second step of the method. Alternatively, however, the angle of rotation reached by several whole strokes can be determined directly.

Further advantageously, the present invention comprises the step of determining an elongation of the inserted screw generated by an entire stroke of the force member of the power wrench used. If the elongation of the inserted screw is known per entire stroke of the force member, the elongation of the screw achieved during the second step can be calculated by a simple multiplication by the number of whole strokes. Alternatively, however, the elongation achieved by several whole strokes can also be determined directly.

The elongation of the screw by a whole stroke is on the one hand by the rotation angle generated by the power screwdriver by a whole stroke of the force member and on the other hand by the geometry of the screw, in particular of the pitch of the helical turns dependent.

In this case, the method according to the invention can comprise the step of determining a lengthening of the inserted screw produced by a specific angle of rotation. If the elongation of the screw used is known at a certain angle of rotation, the length of rotation produced by a whole stroke of the force element can be determined, knowing the angle of rotation produced by a complete stroke. Alternatively, the elongation of the screw per entire stroke can also be determined directly.

Advantageously, the invention provides that the determination of the rotation angle generated by a whole stroke of the force member of the power wrench used is determined in advance for the used power wrench or for the type of power wrench used. The angle of rotation per stroke of the force member must thus be determined only once for each power wrench or Kraftschraubertyp, and can then be used in a variety of Verschraubvorgängen.

Further advantageously, it is provided that the determination of the elongation of the inserted screw generated by a certain angle of rotation in advance for the screw type used. As a result, this determination must also be made only once in advance and can then be used in a variety of glands.

Further advantageously, the elongation of the screw used can be determined in advance by the whole stroke of the force member of the power wrench used for the type of screwdriver used and the screw type used.

The determination of the abovementioned values can be effected both by tests and by mathematical calculations from the geometry of the power wrench and / or the screw used. Advantageously, the determination is carried out by a measurement. In particular, a measurement can be carried out on a plurality of similar power wrenches and / or screws and an averaging can be used to determine the required values. Further advantageously, the measurement can be carried out at different torques, wherein the value used is effected by averaging.

After knowing the appropriate values for a desired elongation of the screw, the number of required complete strokes and the necessary joining torque can be determined easily, the joining torque is adjusted so that the desired total elongation is achieved by the then fully executed whole strokes.

As an alternative to this method, the required number of whole strokes and the necessary joining moment can also be determined directly by trial and error for a desired elongation. This determination also advantageously takes place in advance for the power wrench and / or power wrench type used and / or the screw type used. The corresponding values can then be specified for tightening the screw connection.

In the method according to the invention, the joining moment is advantageously between 5% and 50% of the maximum tightening torque. The joining torque is still advantageously between 15% and 35% of the maximum tightening torque, moreover advantageously about 25% of the maximum tightening torque. Advantageously, the joining moment is predetermined such that a certain elongation of the screw already takes place during the first step of the method.

The joining moment need not necessarily be applied via the same power wrench, which in the second step with a predetermined number of complete strokes of the force member, the screw tightened compound is ready. In particular, the joining torque can also be applied by a torque wrench, a torque motor driven by a rotary motor or the like. Advantageously, however, the joining moment is applied via the same power wrench, which is also used in the second step. In particular, this is a torque wrench. Advantageously, the joining moment is adjusted by the pressure of the hydraulic fluid, with which the hydraulic cylinder of the power wrench is acted upon.

The method according to the invention is less sensitive to purely controllable coefficients and other influencing factors during the screwing process than pure torque methods, since the torque control is initially used only for the application of the joining torque, which is significantly lower than the maximum tightening torque. This also limits the effects of friction on this area. Thereupon, by using whole strokes, a simple and effective control of the length of the screw over the angle of rotation takes place.

Advantageously, in the method according to the invention, the maximum tightening torque of the power wrench or the maximum pressure with which the force member is acted upon, adjusted so that the last stroke performed entirely becomes. Advantageously, at least this last stroke is monitored with a simple control.

Alternatively, however, for the maximum tightening torque of the power wrench or the maximum pressure with which the force member is acted upon, a predetermined value can be used, which would also be used as a final value in a pure torque-controlled method. The tightening of a screw connection according to the invention in two steps also allows in this case a particularly process-safe lengths of the screw, wherein the maximum elongation is set to the same value both on the pressure limit, as well as on the Fügelängung and the number of strokes.

As already explained above, the method according to the invention can still be used to achieve a high-precision screw elongation, particularly in a tolerance range of +/- 10%, with the simplest means. Advantageously, no measurement of the helix angle takes place via a rotation angle sensor. In such a measurement of the helix angle by a rotation angle sensor can be omitted, since in the second step, the angle of rotation can be determined by the whole strokes of the tool and the screw geometry. In particular, the method can be carried out with power wrenches, which have no rotation angle sensor.

Furthermore, it is also possible to dispense with a control which activates the power wrench on the basis of sensor data such as angle sensors, volume measurement and time measurement. In particular, can be dispensed with an electronic control. Furthermore, a regulation of the rotational movement generated by the power wrench can be dispensed with via a corresponding control electronics and / or control hydraulics.

Further advantageously, according to the invention, the control of the power wrench is done manually or by means of a simple control of Hubzahlvorgabe.

The present invention further comprises, in addition to the above-described method, the use of a power wrench in which strokes of a force member, in particular a hydraulic cylinder, are converted into a rotary movement of a screwing tool in such a method. Obviously, the use of the power wrench results in the same advantages already described above with regard to the method.

The power wrench used for a method according to the invention can have as a force member in particular a hydraulic piston-cylinder drive whose linear motion is converted by a corresponding device into a rotary movement of a screwing tool. The screwing tool has in particular a connecting element for detachable connection with a screw and / or a nut. The screwing tool may in particular be a wrench or a wrench insert through which a rotational connection with a screw or a nut can be made. In particular, these are positive-fit tool inserts.

Advantageously, while the movement of the force member is converted in one direction into a rotational movement of the screwing, while the screwing remains unmoved in the return movement of the force member. Further advantageously, the power wrench comprises a ratchet device, by which this intermittent movement of the force member is converted into a rotational movement in a certain direction.

Advantageously, the stroke monitoring of the power wrench can continue to be carried out by means of a simple sensor system close to the force member, whereby the tool geometry does not have to be changed. As a result, an end position monitoring of all strokes is given.

Figur 1:

ein Diagramm, in welchem die Schraubenlängung während der Durchführung eines erfindungsgemäßen Verfahrens dargestellt ist.

The present invention will now be described in more detail by means of embodiments and a drawing. Showing:

FIG. 1:

a diagram in which the screw elongation during the implementation of a method according to the invention is shown.

Before carrying out the actual screwing, a tool constant φ must be determined for the power wrench used or for the type of power wrench used, which describes the rotation angle generated by a complete stroke of the force element. This constant φ must be determined only once for each tool or for each tool type. This tool constant can be determined both by appropriate tests, and theoretically based on the tool geometry.

The method according to the invention can be used for all screwdriver tools in which such a relationship between tool stroke and elongation or angle of rotation can be determined.

Furthermore, for the screw type used, the elongation I of the screw must be determined as a function of the angle of rotation. This can be done in advance for each screw type. Again, this can be done either by a measurement, or by a corresponding theoretical calculation based on the screw geometry.

From these two values, it is now possible to calculate the elongation Iφ per full stroke for each combination of power wrench and inserted screw. Alternatively, the elongation per entire stroke of the force member can be determined directly for a particular combination of power wrench and screw.

The actual screwing process then takes place in two stages. In stage 1, a predetermined joining moment is introduced into the screw connection. In stage 2 then a number of stroke controlled screw elongation. The specified screw elongation can be achieved process-safe in the required tolerance range by the joining torque is adjusted so that then carried out by completely executed tool strokes the desired Gesamtlängung.

The required joining moment can be z. B. be determined by means of experiment. Usually, a joining moment of approximately 25% of the total required tightening torque should be used. The joining torque can be applied, for example, by torque wrench, torque wrench and the like. The required number of strokes of the tool in the subsequent screw elongation by means of entire strokes can be determined by experiment.

wobei

• L die Gesamtlängung (geforderte bzw. berechnete Schraubenlängung),
• Fü die Fügelängung,
• n die Anzahl der Hübe,
• I die Schraubenkonstante (Längung der Schraube pro Winkelgrad) und
• ϕ die Werkzeugkonstante (Winkelgrad pro Werkzeughub)

darstellen.The total length of the screw can be calculated as follows: $$\mathrm{L}\mathrm{=}\mathrm{F}\ddot{\mathrm{u}}\mathrm{+}\mathrm{n}\mathrm{*}\mathrm{l}\mathrm{*}\mathrm{\phi }$$

in which

• L is the total elongation (required or calculated screw elongation),
• For the bondage,
• n the number of strokes,
• I the screw constant (elongation of the screw per angle degree) and
• φ the tool constant (angular degree per tool stroke)

represent.

Alternatively, instead of the screw constant I and the tool constant φ, a single constant k can be used, which describes the elongation of the screw per tool stroke, so that L = Fü + n * k.

The inventive method is again based on FIG. 1 shown in more detail. The screw elongation L is plotted over the time t in a diagram. In phase 1, an elongation takes place by applying a predetermined Add Moments. Then the remaining elongation of the screw is made by one or more whole strokes 3. At point 4 now the required screw elongation is reached. The joining torque is adjusted so that the required elongation can be achieved by the subsequent whole strokes of the screwing.

The plateau phases 2 in the diagram between the joint extension and the whole strokes correspond to the return stroke of the force member. Here, the force member is returned to its original position, without rotation of the screw or screw elongation would take place.

Furthermore, the torque or the pressure is limited so that the last stroke is completed. For this purpose, a corresponding control device may be provided which monitors at least the last stroke. The torque or pressure limitation can be done over the maximum provided by the tool unit operating pressure for the power screwdriver.

With the method according to the invention, an equally simple and highly accurate screw elongation in the ± 10% tolerance range is possible without any sensors or control on the power wrench. In particular, angle sensors, a volume measurement, a time measurement and the like can be dispensed with. As a result, an increased accuracy is possible even when using conventional torque wrench screwdriver.

The method according to the invention realizes torque Drehwikelverschraubungen by elongation is carried out by whole strokes of the piston in tools with piston drive. The tool and screw geometry determined the joining moment and the final elongation of the screw connection.

• Mit diesem Verfahren ist eine hochgenaue Schraubenlänung im +-10% Toleranzbereich, ohne jegliche Sensoren, oder Steuerung (Winkelsensoren, Volumenmessung, Zeitmessung, usw, ...) möglich!
• Verhinderung kostenintensiver Werkzeugumstellung (konventionelle Werkzeuge, bei welchen der Drehwinkel pro Hub bestimmbar ist, sind einsetzbar, z.B. übliche Drehmomentschrauber)
• Minimierung der Werkzeugbaugröße
• Platzbedarf für marktübliche Drehwinkelschrauber (Drehwinkelsensoren) nicht gegeben
• Reibbeiwerteinfluss beim Verschraubungsvorgang minimiert
• Verbesserung der Prozeßsicherheit
• Prüfkostenreduktion, fortlaufende Prüfungen (Ultraschall-Messungen) können reduziert werden
• Realisierung von Drehmoment-Drehwinkelverschraubungen ohne Drehwinkelsensoren bei Werkzeugen mit Kolbenantrieb
• Werkzeug- und Schraubengeometrie bestimmen Fügemoment, Hubzahl und Endlängung der Schraubenverbindung
• Nach dem Fügen wird durch die Ausführung von vollständigen Werkzeughüben die erforderliche Schraubenlängung erreicht
• Eine Druckbegrenzung (Werkzeugaggregat max. Druckeinstellung) verhindert eine Überlastung der Schraube
• Reibeinflüsse werden ausschließlich in den Fügemomentbereich (Drehmomentverfahren Fü) verlagert

In particular, the following advantages result from the method according to the invention:

• With this method, a high-precision screw clearance in the -10% tolerance range, without any sensors, or control (angle sensors, volume measurement, time measurement, etc ...) is possible!
• Prevention of cost-intensive tool changeover (conventional tools in which the angle of rotation per stroke can be determined, can be used, for example, conventional torque screwdrivers)
• Minimization of tool size
• Space requirement for commercially available turning angle screwdrivers (rotation angle sensors) not given
• Reibbeiwerteinfluss minimizes the screwing
• Improvement of process safety
• Test cost reduction, continuous testing (ultrasound measurements) can be reduced
• Realization of torque-angle screw connections without rotation angle sensors on tools with piston drive
• Tool and screw geometry determine the joining moment, number of strokes and final elongation of the screw connection
• After joining, the required screw elongation is achieved by executing complete tool strokes
• A pressure limitation (tool unit maximum pressure setting) prevents overloading of the screw
• Frictional influences are exclusively shifted to the joining moment range (torque method Fü)

Claims (10)

Method for tightening a screw connection while elongating the screw,
wherein a power wrench is used, in which strokes of a force member, in particular a hydraulic cylinder, are converted into a rotational movement of a screwing tool,
characterized,
that in a first step, the screw is first tightened to a predetermined torque, and
in a second step, the threaded connection with a predetermined number of whole strokes of the power member of the power wrench is completed. The method of claim 1, further comprising the steps of: Specification of a desired total elongation, Determining a joining moment to achieve a joint elongation, which is so dimensioned that the desired total elongation can be achieved by the joint elongation and a number of complete strokes of the power element of the power wrench. Method according to claim 1 or 2, with the further step: Determining a rotation angle generated by an entire stroke of the force member of the power wrench used. Method according to one of the preceding claims, with the further step: Determining an elongation of the inserted screw generated by a whole stroke of the force member of the power wrench used and / or by a certain angle of rotation. A method according to claim 3 and / or 4, wherein the determination of the rotation angle generated by a whole stroke of the force member of the power wrench used and / or by a whole stroke of the force member of the used power wrench and / or generated by a certain angle of rotation elongation of the screw used in advance for the type of power screwdriver used and / or the screw type used. Method according to one of the preceding claims, wherein the joining torque between 5% and 50% of the maximum tightening torque, advantageously between 15% and 35% of the maximum tightening torque, further advantageously about 25% of the maximum tightening torque. Method according to one of the preceding claims, wherein the maximum tightening torque of the power wrench and / or the maximum pressure, with which the force member is acted upon, is set so that the last stroke is carried out in its entirety. Method according to one of the preceding claims, wherein no measurement of the helix angle takes place via a rotation angle sensor and / or the power wrench used has no rotation angle sensor. Method according to one of the preceding claims, wherein the control of the power wrench manual or by means of a simple control of Hubzahlvorgabe. Use of a power wrench in which strokes of a force member, in particular a hydraulic cylinder, are converted into a rotational movement of a screwing tool, in a method for tightening a screw according to one of the preceding claims.

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