Flat die thread rolling machine and method for operating such a machine

This application claims the benefit of German Patent Application DE 10 2024 110 057.5, filed on Apr. 11, 2024, the content of which is incorporated by reference in its entirety.

A flat die thread rolling machine is a type of industrial machine used to produce threads on cylindrical workpieces-like screws, bolts, and studs—by cold forming instead of cutting. It can be designed with a vertical tool arrangement, i.e. the movable rolling die moves in a horizontal or slightly inclined direction. Horizontal tool arrangements are also known, i.e. the movable rolling die moves in a horizontal direction. The movable rolling die is driven using a crank drive, which consists of a rotating crank disc (eccentric disc) at which one end of a connecting rod is arranged; the other end of the connecting rod is connected to the movable rolling die or to a carriage which supports the latter. On rotation of the crank disc, the movable rolling die moves back and forth in an oscillatory manner. This produces the required relative movement between the two rolling dies.

Functional sequences are reproduced in the machine using cams. The machines are characterized by a high output.

A disadvantage with the previously known machine concept is that components with a large component length or complex bending geometries consisting of rods, wire sections or tube material cannot be machined, or only to an extremely limited extent.

The disclosure relates to a flat die thread rolling machine, comprising at least one thread rolling module, which has a stationarily arranged first tool part (first rolling die) and second tool part (second rolling die) that moves relative thereto in an oscillatory manner. The two tool parts have a profiled surface which can be rolled into a workpiece arranged between the tool parts. The second tool part is connected to a drive that can cause the oscillatory motion of the second tool part. Furthermore, the disclosure relates to a method for operating such a flat die thread rolling machine.

The disclosure describes a flat die thread rolling machine as well as a method for the operation of same, with which it is possible to provide workpieces and in particular workpiece ends with a profiled surface and in particular with a thread in a more flexible manner. In particular, the manufacturing process is improved.

This improvement is achieved in that the drive comprises a servomotor that is controlled by a machine controller.

The term “workpiece” means in particular rod, wire or tube sections, more particularly the ends thereof. The term also covers screw blanks with a head and headless bolt parts.

A servomotor is a special electric motor that allows the angle position of the motor shaft as well as the rotational velocity and the rotational acceleration to be controlled and regulated. Accordingly, the electric motor comprises a sensor, which allows the rotary position to be determined; the rotary position determined by the sensor is transmitted to a controller (servo controller) that controls the movement of the motor according to a specified setpoint value.

Accordingly, the machine controller specifies the setpoint movement and in particular the setpoint velocity of the servomotor over one complete stroke cycle of the movable tool part, which is then executed by the servomotor in the closed control loop as precisely as possible. A stroke cycle includes a working stroke (forward stroke, forming stroke) and a return stroke.

In the process, the servomotor preferably directly or indirectly drives a spindle, in particular a threaded spindle, which engages in a nut, in particular in a threaded nut. The nut is directly or indirectly connected to the second tool part.

Preferably, a transmission is arranged between servomotor and spindle, by means of which the rotary motion of the servomotor can be transmitted to the spindle; the transmission is preferably a belt drive transmission. However, it is also possible that the servomotor acts directly on the spindle and drives the latter. The tool arrangement, be it vertical or horizontal, as well as the direction of motion of the movable rolling die in the horizontal or vertical direction can be used in a flexible manner.

One preferred embodiment provides that two thread rolling elements are arranged at a specified distance from each other, each of which comprises a stationarily arranged first tool part and a second tool part driven in an oscillatory manner, as well as a servomotor. The distance is preferably adjustable. This solution has proven very advantageous particularly when it is necessary to make a thread or a profile at two ends of a workpiece. With previously known solutions, the machine must have a very stable construction in order to accommodate the total necessary tool height. The implementation with and use of a servomotor affords a simpler and more flexible solution to this.

The proposed design of the machine therefore enables two thread rolling modules, which can be placed at a specified distance, to be arranged in substantially mirror image fashion, in order to be able to provide a workpiece with two threads or profiles in a single operation without additional handling. The distance can be adjusted in order to machine different lengths of raw material. Owing to the respective servomotors of each thread rolling module, axis-synchronised machining can take place. Complicated mechanical coupling can therefore be dispensed with. It is also possible, however, to operate a module in a sequential arrangement in order to execute several machining operations in sequence (e.g. knurling following by thread application). This is also possible at two places on the workpiece. The sequence and arrangement can be made flexible, so that different and also consecutive profiled surfaces can be made on each side of the workpiece.

It has proven to be very advantageous if the loading of the machine with blanks and the removal of the rolled or profiled parts is done in a special way. For this purpose, provision is specifically made that a first side area of the machine is defined in the area in which the second tool part is in its first end position and a second side area of the machine is defined where the second tool part is in its other end position. A first handling element for feeding in a raw workpiece is arranged in the first side area and a second handling element for the removal of a rolled workpiece is arranged in the second side area.

In this case, the oscillatory motion of the second tool part defines a direction of motion, wherein preferably the first and the second handling element are designed to be displaceable in said direction of motion.

The proposed configuration of the machine therefore enables it to have a very advantageous operating procedure. The proposed method provides in general that the machine controller specifies a defined motion profile for the servomotor.

Specifically, to do this, a path-speed profile is specified for the servomotor, in the case of which the second tool part travels at a constant speed at least over a part of its path. In this case, preferably, the second tool part travels at a constant speed over at least 50% of its stroke length.

A further option is that a path-speed profile is specified for the servomotor, in the case of which the second tool part travels at a lower speed during its working stroke than during the return stroke of the second tool part.

Preferably, the different speeds between working stroke and return stroke relate to the areas of the stroke length of the second tool part in which the latter travels at a constant speed.

It can furthermore be provided that during the working stroke of the second tool part, it travels at two different speed levels, with a lower speed level being followed by a higher speed level.

Furthermore, one advantageous configuration of the method provides that the machine controller specifies a path-speed profile for the servomotor, which is shifted by a specified displacement in the path direction with respect to a nominal profile. This makes it possible to optimally adjust the thread matching (see below in conjunction with).

It is possible to use the proposed machine as a standalone machine and to then equip it with a corresponding interface for the loading with blanks and for the removal of rolled parts (e.g. multi-axis robots and bar loaders).

The proposed machine can also be used as a module in a manufacturing plant, in which even more work steps are performed on a workpiece. By way of example, reference is made in this regard to EP 4 295 968 A1, which describes a plurality of such workstations. The interfaces of the module are used for feeding in the workpiece and for removing the finished workpiece that has been provided with a thread or a profile. This interface is discussed in more detail hereinbelow inwhich describes the handling devices used for this (feeding and removal grippers).

The proposed concept for the use of a servomotor enables a compact and space-saving construction. The servomotor offers the advantage that it can be freely programmed via the machine controller and thus allows any course of the path or speed to be realized to a certain extent over a motion cycle (working stroke and return stroke).

A sensor system for detecting rotary positions, torques and currents can be integrated into the servomotor, meaning that the useful process and status information can be retrieved.

shows a flat die thread rolling machinein which a stationarily arranged first tool partin the form of a rolling die as well as a movable second tool partin the form of a rolling die are provided for machining a thread in a workpiece (not shown here). The movable tool partperforms an oscillatory motion, i.e. over one motion cycle, the tool partfirstly moves in a translational direction (working stroke) and then back in the other translational direction (return stroke) to the starting position. Both rolling dies,have a profiled surface, which is imparted to a workpiece placed between the two rolling dies,during the working stroke. The movable tool partthus moves in the direction of motion B.

The required drivefor the oscillation motion of the movable rolling diecomprises a servomotorwhich is controlled by a machine controllerwith a specified path or speed profile over the motion cycle (i.e. over one complete working stroke and return stroke of the movable tool part).

In the exemplary embodiment, the rotary motion of the servomotoris transmitted via a transmissionin the form of a belt drive transmission to a spindlewhich cooperates with a nut (cannot be seen in), so that as the servomotor rotates, the movable tool partis correspondingly moved translationally.

As a result of the machine controllerspecifying a corresponding path or speed profile over the motion cycle for the servomotor, advantageous operating modes can be made possible (see below).

shows an advantageous embodiment in which two thread rolling modulesandare placed at a distance from each other. The distance a can be adjusted as desired by an apparatus (not shown). The two thread rolling modulesandcorrespond to those that were described in connection with.

shows a workpiece, the two end areas of the workpiece being simultaneously provided with one thread each by the shown machine.

Preferably, a loading and unloading process is used here, which is described hereinbelow.

For this, reference is first made to, which outlines a previously known loading and unloading process. The figure shows six consecutive process stepsto; the subsequent process step, step, corresponds in turn to process step. Accordingly, the temporal sequence of the individual sub-steps of loading the machine with a workpiece as well as removing the finished workpiece is shown here.

As seen in the direction of motion B of the movable tool part, two handling elementsand(grippers) are arranged in a side areaof the machine. First of all (see stepsand), the gripperfeeds a workpieceinto the work area between the two tool partsand. If the gripperis retracted (see step), the movable tool partmoves (in step) so as to machine the desired thread in the workpiece. In step, the grippermoves forwards, so as to grip the finished workpieceand (in step) retract or unload it. Gripperis then used once more with a new workpiece.

In contrast thereto,describes a method, which in general can also be used without using a servomotor, although preferably, of course, with the use thereof, in order to feed and remove workpieces in and from a machine of the type in question.

As seen in the direction of motion B, the two side areas of the machine, namely a first side areaand a second side area, are used for handling purposes. There is one handling element arranged in each side area,, namely a first handling element (gripper)and a second handling element (gripper).

In step, the first gripperfirstly supplies a blank of the workpiecein the first side area. In step, the gripperadvances in the direction of motion B and places the workpiecebetween the two tool partsand. Subsequently, the gripperretracts again (step).

The machining procedure takes place in step, i.e. the movable tool parttravels in the direction of motion B to the end position of the working stroke.

Now (according to step), the second grippercomes into play, which is advanced in the direction of motion B and grips the finished workpiece. The second grippernow travels back with the finished workpiece, while the first gripperhas already provided the next workpiece. Process stepthen accordingly corresponds to process stepagain.

The proposed method according tomeans that the machine's output can be substantially increased; this is not possible with the previously known solution according toas this involves having to perform the unloading and loading sequentially. In the proposed procedure, work can be partially carried out in parallel. The proposed procedure enables processing of the workpiece to be machined in the flow and transport direction. This considerably increases the output rate of workpieces.

By using the proposed servomotors for the drive of the movable rolling die, it is advantageously possible to freely program the movement sequence of the movable rolling die, which has substantial advantages for the method. This is illustrated in the subsequent figures.

The drive by a servomotor makes it possible to freely adapt the travel profile of the rolling carriage or the movable tool part and thus of the profile-forming or thread-forming process, independently of mechanical or geometric connections—in contrast to the previously known crank drive.

While the motion curve of the movable tool part is largely specified in the case of previously known machines that have a crank drive, this is not the case with the proposed solution. Instead, adapted speed-path profiles can be programmed. While that also includes a substantially sinusoidal curve of the motion cycle, it goes beyond that. It is namely possible to adapt the course of the motion curve to within certain limits, with it being of particular benefit to keep the strain rate constant over a substantial part of the metal forming process. Furthermore, it is possible to travel at a higher speed for the return stroke than during the (profile-forming or thread-forming) working stroke. This leads to a further increase in output.

shows such a case in which both for the working stroke (range between 0 and 180) and for the return stroke (range between 180 and 360), a constant speed of the movable tool partis provided (namely in each case at approx. +/−100 cm/s) over substantial distances. Advantageously, the profiling or threading process is designed to be carried out (during the working stroke) at a constant feed rate of the movable tool part.

illustrates substantially the same principle, wherein here, however, the return stroke is designed to have approximately double the speed of the working stroke (working stroke: approx. 100 cm/s; return stroke: approx. 200 cm/s). Accordingly, this can substantially shorten the process time, as the return stroke can be performed in a considerably shorter amount of time.

Another variant is illustrated in: here, the working stroke takes place substantially at two different speed levels. At the start of the working stroke (between approx. 10 to 45), a relatively lower speed (approx. 40 cm/s) is employed; in the subsequent region of the working stroke (between approx. 60 to 140), the speed increases (to approx. 100 cm/s). Meanwhile, the return stroke is again performed at a largely constant speed (of approx. 100 cm/s). The lower starting speed has advantages in the metal forming process.

illustrates a further example, in which a substantially triangular curve of the feed and return rate is provided.

It is apparent from the curves shown that the path, the speed and the acceleration can be largely adapted within certain physical limits. The manufacturing process can thus be performed optimally.

As is known, the metal forming process in the flat die thread rolling machine takes place on a rotating blank via the two opposite rolling dies (short/long die). To obtain an optimally formed thread or profile, the profile peaks of the two rolling tools have to be exactly opposite each other. The matching position is determined according to the prior art in a run-in test, in which the blank is formed through half a turn. As a result, it is checked whether the two thread tracks meet. If they do not meet, then the thread match (track position) must be adapted by an adjustment (forward or back) until the thread peaks match (setting the thread matching).