EP0356375B1 - Method of cold pressing a conical exterior screw thread - Google Patents

Abstract

The process is carried out using a press tool which has a plurality of dies which are arranged around a longitudinal axis and are radially displaceable with respect to this axis. The radially inner surfaces of the dies correspond to segments of the conical thread to be pressed. During pressing of a conical thread in cylindrical workpiece, the dies are first drawn apart in the radial direction and the workpiece is then pushed between the dies, along a length which corresponds to only a few thread turns. The dies are then pressed toward one another in order to press into the workpiece a short conical thread in which only the first thread turn may be formed to its full depth. After the dies have been drawn apart, the workpiece is displaced between the dies through a further length which once again corresponds to only a few thread turns. When the dies are pressed toward one another again, the previously pressed thread turns are pressed deep into the workpiece and additional thread turns are formed. This process is repeated several times until the conical thread has been pressed to the predetermined total length.

Description

The present invention relates to a method for cold pressing a conical external thread into one end of a rod-shaped workpiece according to the preamble of claim 1.
and an apparatus for performing this method.

Conical threads enable a large number of threads to be engaged with one or just a few turns. They are therefore particularly suitable for fastening threads if the threaded bolt and / or the nut piece can only be turned with great effort when tightening or should only be displaced slightly in the axial direction.

A known use of conical threads is the mechanical connection of the butt-jointed ends of reinforcing steels for concrete. The ends of the reinforcing steels, which are provided with conical external threads, are screwed together using a nut piece which has two opposing, conical threads.

Several different methods are known for producing conical external threads. In the case of workpieces made of materials with relatively low toughness and hardness, for example wood screws made of aluminum, the conical external thread can be pressed directly into a cylindrical semi-finished product by means of radially displaceable press jaws.

Workpieces made of materials with relatively high toughness and hardness, such as reinforcing steel, are usually first conically formed, and then the thread is cut into the conical surface, using relatively complicated devices with two opposing chasers.

Because when cutting a thread, the fiber path in the workpiece is interrupted, reducing its strength and reducing the load-bearing cross-section of the thread due to the notch effect in the area of the inner thread core, attempts have also already been made to roll highly resilient conical threads. When rolling threads, not only the mentioned disadvantages of thread cutting are avoided, but the surface fastening achieved by the roller pressure enables the production of threads that are more resilient and more wear-resistant. Device for rolling conical threads in relatively hard and tough materials require a high level of design effort, which is why, despite the advantages mentioned, devices of this type have not previously been used.

EP-A-0 187 623 discloses a method for producing a conical external thread on a workpiece from a tough and hard material, in which the thread is cold pressed into a conically shaped end of a workpiece. The pressing tool used to carry out this method has pressing jaws which are displaced in the axial direction in the conical interior of a guide sleeve and are pressed together or pulled apart in the radial direction. This method enables threads to be produced which have the advantages of non-cutting deformation described above, and the relatively light, robust and easy-to-use device requires only those energy sources which are present at every construction site to operate. The only disadvantage of this method or the device is that the part of the workpiece into which the conical thread is to be pressed must first be shaped conically.

The present invention was therefore based on the object of further developing the aforementioned method and the device used for carrying it out in such a way that conical threads can also be pressed into workpieces made of a relatively hard and tough material without the practically cylindrical workpiece having to be previously conically shaped .

According to the invention, this object is achieved with a method of the type mentioned at the outset, which is characterized by the features of the characterizing part of claim 1.

The method according to the invention has the advantage that a conical thread can be cold-pressed into a practically cylindrical workpiece made of a hard and tough material without prior shaping of a conical surface, that only one device is required to carry out this method and that the cold pressing corresponds to a cold forging process , which causes grain refinement in the material and thus an increase in its strength.

To produce relatively long conical threads, the method steps are preferably repeated at least once.

A suitable one for carrying out the method according to the invention The device contains a pressing tool with a guide sleeve, in the conical interior of which several pressing jaws are slidably mounted along surface lines of the interior, as well as a pressure stamp, which is provided for displacing the pressing jaws in the longitudinal direction of the interior, and with a holding device around the workpiece in the longitudinal axis to hold the conical interior of the guide sleeve, and is characterized by the features of the characterizing part of claim 8.

In a preferred embodiment of this device, the feed device is assigned a compensating cylinder which compensates for a change in length of the workpiece caused by the axial component of the displacement of the pressing jaws and by the flow of the material during the pressing process.

Fig. 1

die schematische Darstellung einer Vorrichtung zur Ausführung des Verfahrens,

Fig. 2

den Längsschnitt durch eine Ausführungsform des Presswerkzeugs der Vorrichtung gemäss der Fig. 1,

Fig. 3

den Querschnitt durch das Presswerkzeug längs der Linie A-A in Fig. 2 und

Fig. 4

ebenfalls in schematischer Darstellung eine bevorzugte Ausführungsform der Verschiebeeinrichtung und des Ausgleichszylinders.

The method according to the invention and a device suitable for carrying it out are described below with the aid of the figures. Show it:

Fig. 1

the schematic representation of an apparatus for performing the method,

Fig. 2

the longitudinal section through an embodiment of the Press tool of the device according to FIG. 1,

Fig. 3

the cross section through the pressing tool along the line AA in Fig. 2 and

Fig. 4

likewise a schematic representation of a preferred embodiment of the displacement device and the compensating cylinder.

The device shown schematically in FIG. 1 contains a machine bed, not shown, to which a rotating device 11 and a feed device 12 can be fastened at an adjustable distance from one another. A pressing tool 13 and a press 14 are held on the rotating device on the side facing the feed device. A holding device 16 is arranged on the feed device 12. This holding device is provided for holding a rod-shaped workpiece 91 and is designed in the manner of a hydraulically actuated multi-jaw chuck.

The axis of rotation of the rotating device 11, the axis of symmetry of the pressing tool 13, and the axis of symmetry of the holding device 16 lie one inside the other, so that the pressing tool can be rotated about a rod-shaped workpiece held in the holding device with a suitable distance between the pressing tool and the holding device.

The rotating device 11 and the press 14 as well as the feed device 12 and the holding device 16 are actuated hydraulically and are connected to a hydraulic system 17 via hydraulic lines 21, 22, 23 and 24. The hydraulic system contains a hydraulic pump, not shown, which generates a constant pressure of the hydraulic fluid during operation of the device. At least one electrically controllable valve 26, 27, 28 and 29 is arranged in each hydraulic line and is connected to an electronic control circuit 36 via an electrical line 31, 32, 33 and 34. The hydraulic lines 21 and 24 are designed in pairs between the valves 27 and 29, which makes it possible to reverse the direction of rotation of the rotating device 11 and to close and open the holding device 16. The line 23 to the feed device consists of several lines (not shown) running parallel to one another, each of which contains a valve which can be controlled independently of the other valves, which will be described in detail with the aid of FIG. 4. The electronic control circuit 36 is programmable for various uses of the device. A control panel 37 is also provided, with a keypad for switching the device on and off and for setting the control circuit to a selected program.

2 shows a longitudinal section of a press tool 13 and a press 14 intended for its actuation. The press 14 contains a hydraulic cylinder 41, in which a piston 42 is fitted so as to be displaceable in the axial direction. The cylinder base 43 has a bore 44 which is provided for the connection of the hydraulic line 22. A piston rod 46 is formed on the surface facing away from the working surface of the piston 42, the free end of which protrudes from the cylinder through the central opening of an annular cylinder cover 47. At the free end of the piston rod, a pressure stamp 48 is attached, the diameter of which is greater than is the diameter of the piston rod. A compression spring 49 is placed around the part of the piston rod located in the cylinder, the ends of which abut the rear surface of the piston or the inner surface of the cylinder cover.

The pressing tool 13 contains a guide sleeve 51 which is fastened to the hydraulic press 14 in the region of the cylinder cover 47. The guide sleeve has a conical interior 52, the largest diameter or base circle of which is adjacent to the plunger 48 and the smallest diameter or cover circle of which forms an opening 53 in the top surface of the press tool facing away from the press 14. In the wall of the conical interior 52, four grooves 56, 57, 58, 59, offset by 90 ° and having a T-shaped cross section, are incorporated (FIG. 3). The grooves run parallel to the surface lines of the conical interior and are therefore inclined at an angle α with respect to the longitudinal axis 61 of the pressing tool.

Four threaded press jaws 62, 63, 64, 66 trapezoidal in side view are arranged in the conical interior. The press jaws have a T-shaped cross section with a two-armed guide beam and a press ram protruding therefrom. Each press jaw is mounted with its guide bar in an associated groove in the guide sleeve in the longitudinal direction of the press tool and connected by means of a screw 67, 68 to the pressure ram 48. The screw heads are guided in the plunger in radial slots 69 in order not to block the displacement in the radial direction which is superimposed on any displacement of the pressing jaws in the axial direction. The inner surfaces of the press jaws facing the center of the conical interior 52 are inclined at an angle β with respect to the longitudinal axis 61. The direction of inclination of this angle β is opposite to the direction of inclination of the angle α, and the angle β is smaller than the angle α. The inner surfaces of the press jaws are circular in cross-section and have a surface profile that corresponds to a corresponding part of a nut piece for the conical external thread to be pressed.

4 shows a feed device 12, to which a length compensation device 71 is assigned. The feed device contains a housing 72, in which several and in the exemplary embodiment shown three series-connected piston-cylinder arrangements are installed. The first piston-cylinder arrangement consists of a first cylinder 73 permanently installed in the housing, to which pressure fluid lines 123 'and 123' 'are connected. A cylinder 77, which is displaceable in the second housing 72, is fastened to the piston rod 76 of the piston 74 sliding in the first cylinder. The pressure fluid lines 223 'and 223' 'are connected to this second cylinder. On the piston rod 79 of the piston 78 sliding in the second cylinder, a third cylinder 81 is attached, to which pressure fluid lines 323 'and 323' 'are connected. The piston 82 sliding in the third cylinder is rigidly connected by means of a piston rod 83 to a piston 84 of the length compensation device 71.

The stroke of the pistons in the three piston-cylinder arrangements is of different lengths, which makes it possible to move the piston 84 in the length compensation device by predetermined total lengths by shifting one, two or even all three pistons. The work space 86 of the length compensation device is connected to the hydraulic system 17 via the line 23A and is filled with the pressurized fluid at the beginning of each working cycle, so that each time the piston 84 is displaced (to the right in FIG. 4), the cylinder 87 acts like the cylinder of the displacement device in the housing 72 is slidably shifted to the right. The cylinder 87 is mechanically or indirectly mechanically connected to the holding device 16 for the workpiece, so that the holding device 16 is also displaced in accordance with the displacement of the cylinder 87.

A further pressure fluid line 23B is connected to the cylinder 87 of the length compensation device 71 or to the pressure fluid line 23A connected to this cylinder. This line contains a pressure relief valve 88, which opens as soon as the pressure in the working space 86 exceeds a predetermined value, as will be explained below.

When using the device according to the invention for cold pressing a conical thread into a rod-shaped, practically cylindrical workpiece, the "ON" button is first pressed on the control panel 37, which then activates the electronic control circuit 36 and the hydraulic system 17. The control circuit sets the valve 27 in a first position, in which hydraulic fluid flows into the cylinder 41 of the press 14 and displaces the piston 42 against the force of the spring 49 (to the right in FIG. 2). As a result, the pressing jaws 62, 63, 64 and 65 are also displaced in the axial direction and, due to the inclination of the guide grooves 56, 57, 58, 59, are also moved together in the radial direction with respect to the longitudinal axis of the pressing tool until their side faces abut one another. At the same time, the valve 29 is also in a adjusted first position in which the inflowing hydraulic fluid pulls the holding jaws of the holding device 16 apart in the radial direction. Then the rod-shaped workpiece 91 can be inserted in the direction of arrow 92 between the open holding jaws as far as the stop on the pressed-together pressing jaws.

Before the start of the actual work cycle, the key data of the workpiece important for the cycle, in particular the diameter of the workpiece, or the nominal diameter and the length of the conical thread to be pressed and at least one the material are entered into the electronic control circuit using the keypad on the control panel 27 characteristic of the workpiece. The entered characteristic values then determine which of several work programs stored in the control circuit is to be carried out.

The work cycle begins as soon as the "START" button is pressed on the control panel. In the first step, the valve 29 is switched to a second position in which the holding jaws move together until the workpiece is clamped. In the second step, the valve 27 is controlled into its second position, in which the cylinder 41 of the press is ventilated and the spring 49 retracts the piston 42 together with the press jaws 62, 63, 64, 66 into the rest position shown in FIG. 2. In the subsequent third work step, the valve 28 is controlled into a first position in which the hydraulic fluid flowing through displaces the feed device 12 and thus also the holding device 16 and the workpiece 91 held by it by a predetermined distance in the direction of the pressing tool 13 or between the pressing jaws . The last fourth step the valve 27 is controlled again in its first position, in which the pressing jaws are displaced in the axial direction and at the same time pressed together and pressed into the workpiece until their side faces abut one another.

When the press jaws are pressed into the workpiece, the axial component of their displacement generates a pressure acting on the holding device. This pressure is increased when the material of the workpiece flows in the direction of the larger workpiece diameter when the press jaws are pressed in. If this pressure exceeds a predetermined value, the pressure relief valve 88 opens and enables a rearward displacement of the cylinder 87 together with the holding device attached to it, until the pressure of the workpiece has dropped to a tolerable value.

In the subsequent fifth step, the valve 27 is controlled into the second position, whereby the press jaws are pulled apart again in the radial direction. In the next sixth working step, the valve 26 is controlled into the first position, so that the rotating device 11 and with it the press 14 and the pressing tool are rotated 45 ° to the left. In the seventh working step, the valve 27 is again moved into the first position, the pressing jaws of the pressing tool being moved together again in the radial direction and the burr which has formed during the pressing of the conical thread in the region of the lateral edges of the pressing jaws being pressed out. In the eighth step, by actuating the valves 27 and 26, the pressing jaws are first pulled apart again and then the pressing tool is turned 45 ° to the right into its starting position. The workpiece with a cold pressed conical Threads can then be removed from the device.

Workpieces with a large diameter and / or made of a relatively tough material or conical thread with more than five gears, for example, are advantageously pressed in several working cycles. In the second and each subsequent working cycle, the pressing jaws remain in the pressing position after the fourth working step described above, while in a first intermediate working step the valve 24 is controlled in the first position and the holding jaws of the holding device 16 are thereby moved apart. In a second intermediate work step, the valve 28 is controlled into the second position and the feed device 12 is thereby moved back into its starting position. Then each of the first, second, third and fourth steps described above is repeated, i.e. the holding jaws are moved together, the pressing jaws are pulled back into the rest position, the workpiece is inserted deeper into the pressing tool by moving the feed device and the pressing jaws are pressed together again.

The end of a work cycle is always the work steps six and seven described above, with which the burr that is unavoidable when pressing the conical thread is pressed into the workpiece.

When pressing a thread in several work cycles, the workpiece is pushed deeper into the press tool for each work cycle. The previously pressed threads are pressed and new threads pressed in. In order to limit the overall deformation of the workpiece in the area of the thread, which increases with increasing number of working cycles, it can be advantageous to set the feed of the workpiece into the pressing tool somewhat shorter in each subsequent working cycle than in the previous working cycle.

In the practical testing of the device according to the invention, conical threads were pressed into reinforcing steels. Each reinforcing steel had a diameter of 40 mm. The conical thread had a cone of 6 °, a pitch of 4 mm and a flank angle of 90 °, corresponding to a pitch of 2 mm or half the pitch. The pressing tool used contained four pressing jaws, each of which had a cross section when viewed in the axial direction, that corresponded to a quarter circle. The pressure of the press was up to 650 bar in the axial direction, whereby a pressing pressure of the press jaws of up to 850 t was achieved in the radial direction.

Five working cycles were carried out for cold-pressing a conical thread with 15 threads, the reinforcing steel being fed into the pressing tool in the first cycle of the (axial) length of five thread turns and in the second to fifth cycle the length of four, three, two or one thread turn corresponded. The total machining time was about 90 seconds. The finished pressed conical thread showed neither chipping nor burr.

It is understood that the described device and its devices can be modified in many ways and adapted to special working conditions. For example Instead of a press that is moved hydraulically into the working position and into the rest position by means of a spring, a press can be used that is moved hydraulically in both directions. Furthermore, a feed device with only one cylinder can be used, the feed of which is controlled by the amount of hydraulic fluid introduced. In the case of a feed device with only one cylinder, the pressure relief valve 88 can also be connected to this cylinder and the longitudinal compensation device can be dispensed with.

The device can be assembled from commercially available components and groups, and it is assumed that the electronic control and hydraulic system for controlling or actuating the individual devices are known to any person skilled in the art, for which reason a detailed description of these devices is dispensed with.

Claims (12)

1. Method of cold-pressing a conical external thread into an end of a bar-shaped workpiece (91), preferably of a reinforcing bar, with a pressing tool (13) which comprises a plurality of pressing jaws (62, 63, 64, 66) which are disposed about a longitudinal axis (61) and are displaceable at least radially relative thereto, and the radially inner surfaces of which correspond to individual segments of a nut component for the thread to be pressed, wherein

   (a) the pressing tool is opened by pulling the pressing jaws apart in the radial direction,

   (b) the pressing tool and the workpiece aligned with its longitudinal axis are displaced relative to each other until the pressing jaws surround the workpiece in the longitudinal direction by a predetermined amount,

   (c) the pressing jaws are brought together in the radial direction and pressed into the workpiece until their lateral edges of the internal surfaces, extending parallel to the longitudinal axis, bear against one another, and

   (d) the pressing jaws are again moved apart,

   characterized in that a virtually cylindrical workpiece (91) is pushed between the pressing jaws (62, 63, 64, 66), so that with the process steps (a) to (d) a short conical thread is pressed into the workpiece (91), at least the first thread turn being formed to its full depth, and

   (e) after the pressing jaws (62, 63, 64, 66) have been moved apart, the pressing tool (13) and the workpiece (91) are rotated relative to each other about the longitudinal axis (61), the rotation corresponding to a part of the circular sector corresponding to the cross-section of each pressing jaw, and

   (f) the process steps (c) and (d) are then repeated.
2. Method according to Claim 1, characterized in that

   (g) the workpiece (91), after the process step (f), is pushed further into the pressing tool (13) and process steps (c) to (f) are repeated.
3. Method according to Claim 1, characterized in that, for a conical thread with a cone of 6°, the pressing tool and the workpiece are displaced relative to each other in the axial direction by five times the pitch of the conical thread.
4. Method according to Claim 2, characterized in that, before process step (g) the relative rotation according to process step (e) is cancelled.
5. Method according to Claim 3, characterized in that, when process step (b) is repeated, the amount of the displacement corresponds to the pitch of the conical thread or to a whole-number multiple thereof.
6. Method according to Claim 2, characterized in that the length of the relative displacement of pressing tool and workpiece decreases with increasing repetition of process steps (c) to (f).
7. Method according to Claim 1, characterized in that, for a pressing tool having four pressing jaws, the pressing tool and the workpiece are rotated through 45° relative to each other about the longitudinal axis.
8. Apparatus for carrying out the method according to Claim 1, comprising a pressing tool (13) having a guide sleeve (51), in the conical internal space of which a plurality of pressing jaws (62, 63, 64, 66) are mounted displaceable along generatrices of the internal space, and comprising a pressing plunger (48), which is provided for displacing the pressing jaws in the longitudinal direction of the internal space, and comprising
   a holding device (16) for holding the workpiece (91) in the longitudinal axis (61) of the conical internal space of the guide sleeve, characterized by
   a feed device (12), for displacing the holding device and/or the pressing tool relative to each other along the axis of the conical internal space by a preadjustable feed distance,
   and by a rotating device (11) for rotating the holding device and/or the pressing tool relative to each other about the axis of the conical internal space through a preadjustable angle, wherein
   the feed device (12) cooperates with a device (71) for compensating a displacement of the workpiece caused by the axial component of the displacement of the pressing jaws and by the flow of the material of the workpiece.
9. Apparatus according to Claim 8, characterized in that the feed device (12) possesses a plurality of sections (73, 74; 77, 88; 81, 82), which can be controlled independently of one another and each of which is provided for a different feed distance.
10. Apparatus according to Claim 8, characterized in that a hydraulic power plant (17) is provided, which is connected to at least some of the devices (11, 12, 13, 14, 16), for the purpose of moving them.
11. Apparatus according to Claim 10, characterized in that furthermore an electronic control circuit (36) is provided, which in accordance with input programmes controls the valves (26, 27, 28, 29) in the hydraulic lines (21, 22, 23, 24).
12. Apparatus according to Claim 11, characterized by an electronic control desk (37) comprising a keyboard for manually inputting the characteristic data necessary for the conical thread to be pressed.

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