Device for manufacturing a molded part using the wobble process

Abstract

Device (1) for forming a molded part (2) with a circumferential forming process, wherein the device (1) has a rotationally symmetrical wobble die (3) which is used to transmit a forming force (F) U ) is displaceable onto the molded part (2) held in a die (4) into a wobbling motion with a wobbling axis (6) deviating from a central axis (5) of the device (1) and orbiting the central axis (5), wherein the wobbling punch (3) radially enclosing its die-side edge region and with a preload force (F V ) has a loaded projection (8), characterized in that the projection (8) is designed to be displaceable parallel to the wobble axis (6) relative to the wobble piston (3).

Description

[0001] The invention relates to a device for forming a molded part with a circumferential design, in particular a toothing, using a wobbling process, wherein the device has a rotationally symmetrical wobbling punch which, in order to transmit a forming force to the molded part held in a die, can be moved into a wobbling motion with a wobbling axis that deviates from a central axis of the device, i.e. here of the die, in particular corresponding to its own axis of symmetry, wherein the wobbling punch has a projection radially enclosing its die-side edge region and loaded with a preload force.

[0002] Such a device is known from EP 1 186 363 A1.

[0003] From DE 197 44 639 A1, a method for manufacturing a switching gear with coaxially arranged and axially extended, radially projecting switching teeth with an axial undercut is known. A forming tool is arranged above a lower die, the forming tool having a circular recess on its underside. At its edge are tooth recesses that are open both axially towards the face of the forming tool and radially inwards. The forming tool is set into a wobbling circular motion relative to the lower die by a drive. During this wobbling circular motion, the wobble axis rotates about the central axis of the lower die.This means that the deformation tool is in intensive deformation contact with the relevant switching teeth of the switching gear in one edge area, while at the radially opposite point a partial or complete separation occurs between the deformation tool and the corresponding switching teeth of the switching gear, depending on the wobble angle.

[0004] DE 32 02 254 A1 describes a process in which the material flow is influenced by the application of orbital pressing in such a way that the negative teeth are filled with material as completely as possible in order to obtain a clean profile shape over the entire tooth width.

[0005] DE 102 03 888 A1 addresses the problem of specifying a method for manufacturing a rack in which, preferably using a wobble forming process, the teeth of the rack are perfectly formed. The negative teeth extend far beyond the circular profile of the blank into the areas of the lateral burrs. The burrs are removed by machining after the forming process.

[0006] A disadvantage of this process is that when a circumferential contour is wobbled, a burr forms within the contour, making it mechanically very difficult to remove. Therefore, attempts are made to eliminate or minimize the burr, or to relocate it to a non-critical area.

[0007] For orbital forming of an externally toothed gear, it is advantageous to use a rotationally symmetrical blank whose outer diameter is smaller than the inner diameter (tip circle) of the die. The material to be formed into the die contour must be axially held against the blank. To avoid burrs, it would be beneficial to plunge the orbital punch circumferentially into the die at the start of the forming process, but this is not possible due to the gear geometry. Without special measures, the forming therefore takes place in the open die, the material escapes between the orbital punch and the die, and a burr forms in the upper area of ​​the gear teeth.

[0008] To prevent such undesired movement, it is already known in the art to cover or close the forming cavity holding the workpiece with a blank holder in the orbital forming process. The blank holder is either bolted firmly to the die or hydraulically clamped against it. A disadvantage of this approach is the insertion and demolding of the workpiece, as the die must be opened for this purpose. With a bolted connection, this is very time-consuming. In contrast, a hydraulic clamping device requires a high degree of design complexity. Furthermore, the orbital motion causes the workpiece material to become trapped as soon as the gap between the orbital punch and the blank holder fills. The blank holder has a cylindrical inner diameter, and a gap must be provided between the blank holder and the orbital punch to allow the orbital punch to move freely.Workpiece material accumulates in this gap. During the forming process, this material is transported upwards by the wobbling punch in the blank holder as the wobbling motion continues. This process proves detrimental to the workpiece contour and tool life. The material flow in the gap exerts high axial forces in the z-direction on the blank holder. Therefore, the blank holder must be very robust to withstand this load.

[0009] From DE 195 25 868 A1, it is known to align both the lower and upper dies at an angle to the workpiece and to allow them to wobble together, so that in the current forming area, the upper and lower dies together form an axially closed cavity, thus preventing axial material flow and the corresponding burr formation. However, a device with two wobbling dies that can also be adjusted relative to each other is structurally very complex and also prone to wear.

[0010] From the aforementioned generic patent EP 1 186 363 A1, a wobbling device is known in which the wobbling punch engages in a recess of the workpiece held in a die, in order to exert a forming force, directed essentially radially outwards, on its side walls during wobbling. To ensure good centering of the die and wobbling punch, both are enclosed by a centering ring. In its axial section encompassing the wobbling punch, the guide ring is provided – depending on the embodiment, either directly or via an intermediate ring – with an inner surface designed as a spherical surface section, which slides on a corresponding spherical surface section formed by the outer surface of the wobbling punch in this area. This allows the wobbling movement of the wobbling punch while simultaneously centering this wobbling movement relative to the die or the workpiece.The aforementioned intermediate ring is held to the wobble punch itself by springs; it thus forms a projection of the punch subjected to a preload force. However, the problem of undesired axial material flow is only indirectly solved. On the (radial) side where the punch, immersed in the workpiece, processes its inner wall, material can escape axially upwards; on the radially opposite side, however, a circumferential projection belonging to the punch exerts an axially downward forming force on the upper edge of the workpiece. With continuous wobble motion, material that has flowed undesirably axially upwards is therefore pressed axially downwards again after half a punch revolution. This device is not suitable for applying essentially purely axial forming forces that are merely deflected radially outwards within the workpiece to form, for example, an external toothing.

[0011] Against this background, the invention aims to prevent the undesirable flow of the workpiece material out of the die and the formation of burrs with minimal design effort.

[0012] WO 96 / 33030 A1 discloses a wobble pressing process for the production of non-externally toothed, fully rotationally symmetrical devices, in particular cookware, wherein the blank to be formed is placed in a lower die with a conical wall shape.

[0013] This problem is solved by a device according to the features of claim 1. It is particularly characterized in that the projection is designed to be displaceable relative to the wobble die parallel to the wobble axis. The dependent claims relate to particularly advantageous embodiments of the invention.

[0014] According to the invention, a device is provided in which the wobble punch has a radial projection enclosing the circumferential edge region, acting as a blank holder. This projection is axially displaceable relative to the wobble punch and is subjected to a preload force. The invention is based on the understanding that, during its wobble movement, the wobble punch makes line contact with the workpiece in the currently forming area while the die is being fed. Therefore, the blank holder is only required in the circumferential area subjected to the forming force. According to the invention, an axially displaceable radial projection is provided on the wobble punch so that the wobble movement not only results in a line contact area between the wobble punch and the workpiece, but also provides a partial blank holder in the area encompassing this contact area.To ensure a secure installation and reliable contact of the projection with the die, and at the same time to reliably compensate for the feed movement between the wobble punch and the die, the projection is pre-tensioned against the die.

[0015] The radial projection is preferably guided against rotation on the wobble punch and follows the wobble motion of the wobble punch, while the preload presses it against the die moving in the wobble punch direction. In the forming zone, the die cavity is thus partially closed from the start of the forming process. Naturally, the projection can also be mounted on the wobble punch by means of a bearing arrangement to achieve optimal guidance and to minimize frictional resistance during axial displacement.

[0016] The projection could be pre-tensioned against the die by means of a hydraulically or pneumatically actuated actuator, or it could be displaceable against the die's pre-tensioning force due to the feed movement between the die and the wobble ram. However, it proves particularly advantageous if the projection is pre-tensioned against the die by means of a spring element, thus enabling a simple design without external connecting elements or supply lines.

[0017] According to a further preferred embodiment, if the spring element comprises a spring assembly including a coil spring, a disc spring, and / or a plastic spring, which are designed as compression springs and enclose the wobble piston, then in addition to a space-saving design, the spring force can also be easily adjusted. For this purpose, the spring can, for example, be supported by an adjusting element which can be fixed in different axial positions by means of an internal thread on an external threaded section of the wobble piston. Furthermore, the spring element can, for example, have a progressive or degressive spring characteristic to compensate for the feed movement.

[0018] Furthermore, it has already proven to be particularly practical if the wobble punch and the die can be moved relative to each other at a constant speed in order to achieve a continuous forming process, whereby the movement is carried out against the restoring force of the spring element.

[0019] The projection could exhibit limited elastic deformability to achieve an optimal contact surface between the projection and the die. Preferably, the radial projection has a contact surface that can be applied to the die and is inclined to the cross-sectional plane of the wobble die.

[0020] Preferably, the die is designed such that jamming of the formed part due to elastic tool deformation in the die or lower tool is avoided after forming. Furthermore, an ejector system can be provided with which the formed part is ejected from the die. In the case of helical gears, the ejector system is preferably rotatable so that the formed part can be ejected while rotating.

[0021] In a further advantageous embodiment of molded parts with straight or helical teeth, the tooth thickness of the die or lower tool is designed conically and decreases towards the die. This creates a clearance angle of the tooth flanks in the demolding direction, and the molded part only needs to be released from the lower tool or die by the ejector. A gap then forms in both flank directions, which facilitates demolding. In particular, this significantly reduces demolding forces and minimizes lower tool wear and component deformation.

[0022] The invention allows for numerous embodiments. To further illustrate its basic principle, one of these is shown in the drawing and described below. This drawing shows a cutaway side view of a device 1 for producing a molded part 2 with circumferential teeth using a known wobble forming process. For this purpose, the device 1 has a rotationally symmetric wobble die 3, which is set into a wobble motion, i.e., a rotational movement about its wobble axis 6, which is tilted relative to the central axis 5 of the die 2 and revolves around the central axis 5, in order to transmit a forming force to the molded part 2 held in a die 4. This results in a forming force F acting concentrically to the central axis 5 in a circumferential edge region 7 corresponding to a momentary linear contact surface. Uof the wobble punch 3 onto the molded part 2 held in a die 4. To prevent the undesired flow of the material out of the die 4 in the axial direction, a hold-down device is provided, which is formed by an annular projection 8 that radially encloses the wobble punch 3. The projection 8 is designed to be axially displaceable on the wobble punch 3 parallel to the wobble axis 6 and is subject to a preload force F. Va spring element is loaded. The radial projection 8 has a contact surface 9 that can be applied against the die 4 and is conical according to a wobble angle α relative to a cross-sectional plane of the wobble punch 3. This results in the chamfered contact surface 9 forming a conical or frustoconical flat surface. When the radial projection 8 contacts the die 4 during the feed movement, the die 4 pushes the radial projection 8 upwards along the wobble axis 6 on the wobble punch 3 against the preload force F. VThe die 4 is displaced. In this process, the die 4 is partially closed in the forming area. Since, during the wobbling motion, only this circumferential edge region 7 is incrementally formed, and the wobbling punch 3 and the projection 8 perform a synchronous wobbling motion, the die 4 is permanently closed in the forming area by the projection 8. The workpiece material cannot escape from the die 4 in the tooth region. As can be seen, the projection 8 is located in the edge region 7 where the forming force F is applied. U The material acts in a continuous, almost gap-free contact with the die 4, thus preventing the unwanted flow of material out of the die 4. Reference symbol list 1 Device 2 Molded part 3 tumbling stamps 4 dies 5 Central axis 6 wobble axle 7 Forming area 8 lead 9 Contact area α wobble angle F U Forming force FV Preload force

Claims

[1] Device (1) for forming a molded part (2) with a circumferential forming process, wherein the device (1) has a rotationally symmetrical wobble die (3) which is used to transmit a forming force (F U ) is displaceable onto the molded part (2) held in a die (4) into a wobbling motion with a wobbling axis (6) deviating from a central axis (5) of the device (1) and orbiting the central axis (5), wherein the wobbling punch (3) radially enclosing its die-side edge region and with a preload force (F V ) has a burdened lead (8), characterized by , that the projection (8) is designed to be displaceable parallel to the wobble axis (6) relative to the wobble piston (3). [2] Device (1) according to claim 1, characterized by , that the projection (8) can be pre-tensioned relative to the die (4) by means of a spring element. [3] Device (1) according to claim 2, characterized bythat the spring element comprises a spring assembly including a coil spring, disc spring and / or plastic spring. [4] Device (1) according to one of claims 2 to 3, characterized by , that the projection (8) can be hydraulically pre-tensioned relative to the die (4). [5] Device (1) according to any one of the preceding claims, characterized by , that the wobble die (3) and the die (4) can be moved relative to each other at a particularly constant speed. [6] Device (1) according to any one of the preceding claims, characterized by , that the wobble axis (6) is oriented at an angle of wobble (α) to the central axis (5) of the die (4) and the radial projection (8) has a contact surface (9) which can be applied to the die (4) and which conically surrounds the central axis (6) of the wobble punch (3) and which runs obliquely to the cross-sectional plane of the wobble punch (3) according to the angle of wobble (α).

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