Method and apparatus for setting a screw

Abstract

The invention relates to a method and to an apparatus for setting a screw, in particular a flow drilling screw. In accordance with the method, the screw is driven at a first revolution speed and at a first axial feed force during a time-limited first phase to drive the screw through at least one component. In the event that the screw does not penetrate the component during the first phase, the screw is automatically driven at a second revolution speed that is higher than a first rotation speed and/or at a second axial feed force that is greater than a first axial feed force during a second phase subsequent to the first phase.

Claims

1. A screwing apparatus for setting a screw, the screwing apparatus comprising a drive unit that is configured to set the screw into rotation and to exert an axial feed force on the screw to drive the screw through at least one component; a device, configured to detect a penetration of the screw through the component during a first phase, that determines at least one of a feed path, a feed rate of the screw, and the axial feed force applied to the screw; and a drive control configured to automatically increase at least one of a revolution speed of the screw and the axial feed force on the screw during a second phase if at least one of the feed path, the feed rate, and the axial feed force, determined by the device, does not change substantially or characteristically during the first phase.

2. The screwing apparatus in accordance with claim 1, wherein the screw is a flow-drilling screw.

3. The screwing apparatus in accordance with claim 1, wherein at least one determination device is provided that determines at least one of the revolution speed, the axial feed force, and a point in time at which the screw penetrates the component.

4. The screwing apparatus in accordance with claim 3, further comprising a processor that determines a mechanical resistance of the component with reference to at least one of the revolution speed, the axial feed force, and the point in time at which the screw penetrates the component.

5. The screwing apparatus in accordance with claim 4, wherein the mechanical resistance of the component is at least one of a thickness of the component and a strength of the component.

6. The screwing apparatus in accordance with claim 4, further comprising a processor that is configured to establish an increased tightening torque for the screw in dependence on the mechanical resistance of the component.

7. The screwing apparatus in accordance with claim 1, wherein the drive control is configured to automatically increase at least one of the revolution speed of the screw and the axial feed force on the screw during a second phase only if at least one of the feed path, the feed rate, and the axial feed force does not change substantially or characteristically during a first phase.

Description

(1) The invention will be described in the following with reference to a purely exemplary embodiment and to the enclosed drawings. There are shown:

(2) FIG. 1 a flowchart of a method in accordance with the invention;

(3) FIG. 2 a screw that has penetrated a component;

(4) FIG. 3 a progression characteristic for the revolution speed;

(5) FIG. 4 a progression characteristic for the axial force; and

(6) FIG. 5 a schematic representation of an apparatus in accordance with the invention.

(7) FIG. 1 shows a flowchart of a method in accordance with the invention with which a screwing apparatus 10 (FIG. 5) can be operated. In a first step A, a flow-drilling screw 12 (FIG. 2) is driven by a drive unit 14 during a time-limited first phase to (FIGS. 3 and 4) that lasts approximately 0.5 seconds at a first revolution speed no % and a first axial feed force F.sub.a 0% to drive the screw 12 through a component 16, for example through two metal sheets disposed areally over one another and accessible at one side. In this respect, in parallel with step A, it is continuously established by a detection apparatus 18 whether the screw 12 has penetrated the component 16. With flow-drilling screws, the screw 12 has penetrated the component when—as shown in FIG. 2—a conically tapering tip 20 of the screw 12 again passes out of the component 16 and the hole 22 in the component 16 generated by the screw 12 has a minimal diameter 23 that corresponds to the diameter of a threadless shaft of the screw 12.

(8) If the screw 12 has not yet penetrated the component 16 after the end of the first phase t.sub.A, a drive control 24 starts a second phase t.sub.B that comprises a boost stage t.sub.Boost in a step B following step A. During the second phase t.sub.B, the revolution speed n (FIG. 3) is constantly increased up to a maximum revolution speed n.sub.max provided that the screw 12 does not previously penetrate the component 16. At the same time, the axial feed force F.sub.a (FIG. 4) is likewise constantly increased up to a maximum axial feed force F.sub.a max, provided that the screw 12 has not previously penetrated the component 16. A detection is further continuously made during the increase of the revolution speed n or of the axial feed force F.sub.a whether the screw 12 has penetrated the component 16. If the latter is the case, the revolution speed n and the axial feed force F.sub.a are reduced to values that are suitable for forming a thread.

(9) If the screw 12 does not penetrate the component 16 up to a point in time at which a maximum revolution speed n.sub.100% and a maximum axial feed force F.sub.a 100% have been reached, the screw 12 is further driven at the maximum revolution speed n.sub.100% and at the maximum axial feed force F.sub.a 100% until either the screw 12 has penetrated the screw 12 or a maximum time t.sub.max has been reached. If the maximum time t.sub.max has been reached, the screwing apparatus 10 aborts the setting of the screw 12. if the screw penetrates the component before reaching the maximum time t.sub.max, the revolution speed n and the axial feed force F.sub.a are reduced to values that are suitable for forming a thread.

(10) If the screw 12 enters into the component 16 during the second phase t.sub.B, a duration t.sub.Boost from the start of the second phase t.sub.B up to the penetration of the screw 12 through the component 16 is established by means of a determination device 26 in a step C. The duration t.sub.Boost is dependent on a mechanical resistance of the component 16, i.e. inter alia on the thickness 27 of the component 16 and on its strength, and can therefore be used as a characteristic for the mechanical resistance. An increased tightening torque M.sub.a is calculated for the screw 12 in a step D by means of the duration t.sub.Boost, and indeed according to the formula
M.sub.a=M.sub.a 0%+(M.sub.a 100%−M.sub.a 0%)×t.sub.Boost/t.sub.Duration,
where M.sub.a 0% is a minimal tightening torque required for a reliable screw connection; M.sub.a 100% is a maximum tightening torque applicable to the screw; t.sub.Boost is the time duration of the second phase up to the penetration of the screw 12; and t.sub.Duration is the duration of the second phase up to the reaching of the maximum possible revolution speed n.sub.100% and/or maximum possible axial feed force F.sub.a 100%.

(11) In a step E, the screw 12 is tightened with the increased tightening torque M.sub.a. Each screw is thus tightened in dependence on the respective material thickness or metal sheet thickness of the component. It is thus ensured that every screw 12 set using this method is tightened ideally, i.e. neither too weakly nor too tightly, while taking account of the mechanical load capacity of the component 16.

(12) FIGS. 3 and 4 show the progression of the revolution speed n and of the axial feed force F.sub.a during the method outlined in FIG. 1. The revolution speed n is constantly maintained at a minimum revolution speed n.sub.0% in the first phase to for approximately 0.5 seconds. The same applies to the axial feed force F.sub.a that is maintained at a minimum feed force F.sub.a 0%. If the screw 12 has not yet penetrated the component 16 after the end of the first phase t.sub.A, the revolution speed n and the axial feed force F.sub.a are constantly increased from a starting time t.sub.start onward for the second phase over a time period of a maximum of 0.5 to 1.5 seconds until the screw 12 penetrates the component 16 after a boost time t.sub.Boost. The boost time t.sub.Boost thus stands for the time duration during the second phase t.sub.B until the screw 12 has penetrated the component 16.

(13) It can occur—as described above—that the screw 12 has also not yet penetrated the component 16 up to the reaching of a maximum possible revolution speed n.sub.100% and of a maximum possible axial feed force F.sub.a 100%. After the end of a time t.sub.Duration in which the revolution speed n and/or the axial feed force F.sub.a is/are increased up to their maximum values n 100%, F.sub.a 100%, the screw 12 is driven at an unchanged revolution speed n.sub.100% and an unchanged axial feed force F.sub.a 100% up to a maximum duration t.sub.max. If the screw 12 has not yet entered into the component 16 after the end of the maximum duration t.sub.max, the screwing apparatus 10 is switched off and the setting process is aborted as incomplete.

(14) FIG. 5 schematically shows a screwing apparatus 10 for performing the method outlined in FIG. 1. The screwing apparatus 10 is in particular suitable to introduce flow-drilling screws 12 into a component 16. The screwing apparatus 10 comprises the drive unit 14 that is configured to set the screw 12 into rotation and simultaneously to exert an axial feed force onto the screw 12. The screwing apparatus 10 further comprises the detection device 18 that determines a feed path and/or a feed rate of the screw 12 and/or that determines a feed force applied to the screw 12 to determine when the screw 12 has penetrated the component 16. It can, for example, be recognized by an increase of the feed rate or a reduction of the feed force to be applied to the screw 12 that the screw 12 has penetrated the component 16. The screwing apparatus 10 further comprises the drive control 24 that increases the revolution speed n of the screw 12 and/or the axial feed force F.sub.a on the screw 12 during the second phase if the feed path, the feed rate, or the feed force does not substantially or characteristically change over the duration of the first phase and thus the screw 12 has not yet penetrated the component 16. The drive control 24 is connected to the detection device 18 that communicates to the drive control 24 that the screw 12 has penetrated the component 16.

(15) The screwing apparatus 10 additionally comprises the determination device 26 that establishes the point in time at which the screw 12 has penetrated the component 16 or establishes the boost time t.sub.Boost. The screwing apparatus 10 comprises a processor 28 that has a characteristic value for the mechanical resistance of the component 16 communicated to it. The mechanical resistance of the component 16 is expressed in the present example by the required time during the second phase t.sub.B until the screw 12 has penetrated the component 16, i.e. the boost time t.sub.Boost. The processor 28 calculates an increased tightening torque M.sub.a for the screw 12, that increases as the boost time t.sub.Boost increases, from the determined boost time t.sub.Boost.

REFERENCE NUMERAL LIST

(16) 10 screwing apparatus 12 screw 14 drive unit 16 component 18 detection device 20 tip 22 hole 23 diameter 24 drive control 26 determination device 27 thickness 28 processor A step 1 B step 2 C step 3 D step 4 E step 5 t.sub.A first phase t.sub.B second phase n revolution speed F.sub.a axial feed force n.sub.0% first revolution speed F.sub.a 0% first axial feed force n.sub.100% maximum revolution speed F.sub.a 100% maximum axial feed force t.sub.start start time of the boost phase t.sub.Boost boost phase t.sub.Duration time duration up to n.sub.100% and/or F.sub.a 100% t.sub.max maximum time M.sub.a tightening torque M.sub.a 0% minimal tightening torque M.sub.a 100% maximum tightening torque