Method for manufacturing a cam drum for a transport device

Abstract

The present invention relates to a method for manufacturing a cam drum for a transport device, in particular a rotary indexing table or a linear transport device. The cam drum has a base body with a lateral surface provided with a drive groove for the engagement of at least one driver connected to a rotatably or linearly movable transport element of the transport device. Furthermore, the cam drum has at least one bearing section for mounting the cam drum in a housing of the transport device. In a first hardening process step, the bearing section is hardened at least section by means of a laser beam. In a subsequent second hardening process step, either directly or indirectly, the lateral surface of the base body is hardened at least section by means of a laser beam.

Description

[0001] The invention relates to a method for manufacturing a cam drum for a transport device, in particular a rotary indexing table or a linear transport device.

[0002] Rotary indexing tables typically feature a ring or plate (transport element) that includes drivers engaging in a drive groove of a cam drum (also called a transport cam). The plate can be driven by the cam drum to rotate around a rotary axis, which in turn can be driven by a motor to rotate around its longitudinal axis.

[0003] During the drum's rotation, the drive lugs interact with one of the flanks (drive flank) of the drive groove in a specific direction of rotation. The pitch of the drive flank therefore determines the rotational movement of the disc.

[0004] The term "drive groove" is to be understood broadly in the context of this disclosure. Besides drums into which a groove has been machined that is somewhat wider than the drive teeth (groove curve), there are drums in which more material has been removed, so that one can also speak of a circumferential rib being created on which the drive flank is formed (rib curve). The distance between axially adjacent rib sections is therefore greater in a rib curve than between the flanks of the groove in a groove curve.

[0005] Put simply, a drum with a rib profile has a comparatively wide drive groove, while a drum with a groove profile has a comparatively wide rib. Functionally, however, the two embodiments do not differ, at least with regard to the present invention and the underlying problem.

[0006] Rotary indexing tables of this type, which are known in various embodiments from the prior art, serve, for example, to transport one or more workpieces held on the aforementioned plate or on structures arranged thereon from one processing or assembly station to the next by rotating the plate. This transport usually—but not necessarily—takes place within a cycle operation, in which the plate is rotated by an angular distance with each cycle, which may, for example, correspond to the angular distance between two adjacent workpieces arranged on the plate.

[0007] Especially with heavy workpieces, the components of the rotary indexing table are subjected to considerable stress, which must be taken into account through appropriate drive design. Furthermore, modern production lines are characterized by high speeds. This means that the rotary indexing tables used must exhibit high dynamics.

[0008] Essential for the power transmission of the drive is the coupling between the drive groove (also known as the cam track) of the cam drum and the drive lugs engaging in it. The cam drums are therefore subjected to considerable loads, especially in the area of ​​the drive groove. The cam drum bearings are also subjected to high loads, particularly the radial bearings.

[0009] At the same time, the precision of workpiece positioning by the rotary indexing tables is of paramount importance. For example, in a clocked operating mode, the workpieces must be moved reliably and precisely from a first rest position to a predetermined second rest position. In many cases, it is not only necessary that the second rest position is reached exactly, but also that the workpiece movement profile between the two rest positions adheres to predefined boundary conditions, such as specified speeds or accelerations.

[0010] Despite the considerable stresses that occur during operation, rotary indexing tables must always ensure consistently accurate positioning. The relevant components must therefore be very robust.

[0011] Cam drums can also be used in linear transport systems where transport elements, e.g., transport carriages ("carriers"), are moved along a transport path (e.g., along a rail). An example of such a linear transport system is described in DE 10 2017 116 414 A1. The above statements apply analogously to cam drums of linear transport systems.

[0012] It is generally known that cam drums are hardened during their manufacturing process. Such processes aim to increase the mechanical resistance of the drums, particularly in the most heavily stressed areas, by selectively modifying and transforming the microstructure of the material used. However, they are usually very complex and therefore expensive.

[0013] One objective of the invention is to create an efficient and cost-effective method for manufacturing cam drums that can reliably handle even large loads.

[0014] This problem is solved according to the invention by a method having the features of claim 1.

[0015] The method according to the invention relates – as already mentioned – to the manufacture of a cam drum – both embodiments with a grooved cam and with a web cam are included – for a transport device, in particular for a rotary indexing table or a linear transport device. The cam drum has a base body with a lateral surface provided with a drive groove for the engagement of at least one driver connected to a rotatably or linearly movable transport element of the transport device, and at least one bearing section for mounting the cam drum in a housing of the transport device. In a first hardening process step, the bearing section is hardened at least partially by means of a laser beam. Directly or indirectly thereafter, in a second hardening process step, the lateral surface of the base body is also hardened at least partially by means of a laser beam.

[0016] In the context of the present invention, the drive groove is part of the cylindrical surface.

[0017] The manufacturing process therefore comprises two separate process steps that can transition directly into one another. It is also conceivable that the two processes have some overlap, i.e., the bearing section is still being hardened while the base body is already being hardened. In principle, a (short) pause (e.g., between 5 seconds and 2 minutes, preferably between 10 seconds and one minute) or another manufacturing and / or processing step can also be provided between the two process steps.

[0018] According to the invention, laser hardening is used in the hardening process steps. Surprisingly, it has been found that laser hardening of the bearing section, at least partially prior to laser hardening of the outer surface of the base body, improves the result of the second hardening process step. The heat input associated with the first hardening process step ensures an improvement in the desired microstructural change / transformation.

[0019] In particular, the first hardening process step is carried out in such a way that the areas intended for the second hardening process step are heated to a temperature of at least 80°C, in particular at least 100°C or at least 150°C.

[0020] The inventive method incurs only low costs and delivers significantly better results than known hardening processes. In particular, process reliability increases, meaning that the desired or targeted properties or hardness characteristics are achieved with a higher probability in a given process for hardening the base body through the upstream first hardening process step, thus conversely reducing the scrap rate.

[0021] Further embodiments of the invention are specified in the description, the dependent claims and the drawings.

[0022] In particular, the drive groove has a groove base and two groove flanks, the groove flanks being perpendicular to the groove base. In the second hardening process, according to one embodiment of the method, at least one of the groove flanks is hardened. It may be possible to harden both groove flanks.

[0023] According to a further embodiment of the method, in the second hardening process only one or both of the groove flanks are hardened. This means that the other areas of the cylindrical surface are not hardened in the second hardening process.

[0024] Preferably, in the second hardening process, at least that groove flank which is most heavily stressed by the drivers during normal operation of the transport device is hardened.

[0025] According to one embodiment, the bearing section has a radial bearing segment for radially supporting the cam drum and / or an axial bearing segment for axially supporting the cam drum. In particular, the axial bearing segment is arranged on the base body.

[0026] Preferably, the first hardening process step is carried out such that the areas intended for the second hardening process step are heated (preheated) to a temperature of at least 80°C, in particular at least 100°C or at least 150°C. Preheating temperatures in the range of 120°C to 200°C are particularly desirable. It has been shown that this heating already has a very beneficial effect on the second hardening process step.

[0027] In particular, the surface temperature of the area to be hardened, which is targeted in the first and / or second process step, is between 1,100°C and 1,400°C.

[0028] According to a particularly efficient variant of the process, essentially the same process parameters are applied in the first and second hardening process steps. Process parameters include, for example: the axial feed rate and rotational speed of the drum and / or the laser used for hardening during both process steps (relative movement between the laser beam and the drum), the (heat) power applied by the laser and / or introduced into the drum, and / or the temperature targeted and / or achieved on the surface of the drum.

[0029] Other parameters that arise solely from the different geometries of the bearing section and the base body, for example because they have different diameters and the laser must be positioned differently to maintain the same distance from the surface to be treated, are not process parameters in the above sense.

[0030] A pause can be provided between the first and second hardening process steps, during which preferably no heat is introduced into the drum, with the pause having a length of 5 seconds to 2 minutes, preferably between 10 seconds and one minute. This allows the heat introduced in the first process step to distribute itself within the base body.

[0031] In special cases, it may be necessary to cool the curved drum section by section during the first and / or the second process step and / or between the process steps, for example to avoid (local) overheating and / or to influence the heat propagation / distribution.

[0032] The invention is described below by way of example only, using advantageous embodiments of the rotary indexing table according to the invention as reference to the drawings. The drawings show: Fig. 1 a schematic representation of an embodiment of a rotary indexing table in a top view and Fig. 2 an enlargement of part of the Fig. 1.

[0033] Fig. Figure 1 schematically shows a top view of a rotary indexing table 10, which has a rotatably mounted plate 12 (indicated by dashed lines). The plate 12 is in Fig. The plate 12 is kept transparent so as not to obscure the rotatably mounted drivers 14 (rollers) arranged on its underside. The drivers 14 are evenly distributed around the circumference of the plate 12 and lie on an imaginary circle K, the center of which lies on a rotation axis R of the rotatably mounted plate 12. The plate 12 is supported by a housing 20 of the rotary indexing table 10, as described in more detail below. Fig. 2 will be explained.

[0034] The drivers 14 have a perpendicular orientation to the image plane of the Fig. 1. The longitudinal extension of the cam drum engages in a drive groove 16 of a cam drum 18. The cam drum 18 is rotatably mounted about a pivot axis R' in the housing 20, which also serves to mount the plate 12.

[0035] To set the plate 12 into rotation, the cam drum 18 is set into a rotary motion. The drive groove 16, which spirals around the cam drum 18, engages the drivers 14 during rotation, thereby setting the plate 12 into a rotary motion. This type of drive for the plate 12 is known in principle from the prior art. It is also known that the design of the drive groove 16, together with the drive rotary motion of the cam drum 18, controls the rotary motion of the plate 12. In other words, the drive groove 16 can, in a different embodiment than shown, have areas with different or varying pitches. Detent areas of the drive groove 16 can also be provided, which extend perpendicular to the axis of rotation R' in a top view.With a suitable arrangement and number of drivers 14, a pulsed operation of the plate 12 can be generated, for example, without changing the drive speed of the cam drum 18. Such operation can also be achieved with a constant pitch of the drive groove 16 by means of a correspondingly controlled drive of the cam drum 18.

[0036] The cam drum 18 is driven by an electric motor 22, whose axis of rotation R'' is, in this example, arranged parallel to the axis of rotation R' of the cam drum 18. A drive torque generated by the motor 22 is transmitted, in a manner known per se, via a gearbox 24 – in this case a spur gear gearbox – to a drive shaft 26 of the cam drum 18, thereby driving the disc 12 to a rotary motion about the axis of rotation R, as described above. The axis of rotation R is perpendicular to the axes of rotation R' and R''.

[0037] As explained at the beginning, the coupling between the drive lugs 14 and the flanks of the drive groove 16 represents a mechanically limiting factor for a reliable drive of the platter 12, especially under high loads. Specifically, this means that the left flank of the drive groove 16, which spirals around the cam drum 18, is subjected to load when the platter 12 is driven into a counterclockwise rotation.

[0038] In Fig. 2 is an enlarged section of the Fig. Figure 1 is shown to further explain the bearing of the cam drum 18.

[0039] The cam drum 18 comprises a base body G with a lateral surface M into which the drive groove 16 is integrated. The drive groove 16 has lateral flanks 16F that extend perpendicular to a groove base 16G.

[0040] A pin 30 is arranged on each end face of the base body G. The pins 30 serve for the axial support of the drum 18. Each section of the pin 30 forms a radial bearing segment rL, which interacts with a radial bearing 28r held – directly or indirectly – in the housing 20. The right-hand pin 30 is coupled to the drive shaft 26 in a manner not shown in detail.

[0041] Furthermore, ring-shaped axial bearing segments aL are provided on the two end faces of the base body G, each of which interacts with an axial bearing 28a held - directly or indirectly - in the housing 20.

[0042] As explained at the beginning, the bearing segments rL, aL, and especially the flank 16F of the groove 16 (which is in contact with the drivers 14 during operation of the table 10 and depends on the direction of rotation of the drum 18) are subject to particularly high loads. To minimize wear on these components, the journals 30, the end faces of the base body G, and the cylindrical surface M are hardened, at least partially and especially in the areas described above, using laser beams. The order in which segments aL and rL are hardened can be determined as required. Simultaneous hardening of segments aL and rL is also possible. Hardening of segment rL or aL can be omitted if the radial or axial bearing of the drum is subject to lower loads in the specific application.

[0043] At least one of the segments aL, rL is hardened using a laser. This process (first hardening step) takes place before laser hardening (second hardening step) of at least a section of the cylindrical surface M. It has surprisingly been found that the heat introduced into the cam drum 18 during the first hardening step improves the second hardening step. Preferably, only the two groove flanks 16F, which—as defined above—are part of the cylindrical surface M of the base body G, are subjected to the second process step. Generally, it is unnecessary to harden the groove base 16G or the remainder of the cylindrical surface M.

[0044] In the area of ​​segments aL and rL, the requirements for hardness quality and case hardening depth are generally lower than for the areas of the drum 18 that are in effective contact with the drive lugs 14 and are subjected to the second hardening process step. Therefore, it is conceivable that different process parameters could be used for the two process steps. However, for simplification, the same parameters can also be used in both process steps.

[0045] Heat-treatable steels are typically used for the cam drum. Common materials include 31CrMoV9 (1.8519) and 42CrMo4 (1.7225). Their heat-treatable condition is preferably greater than 1,000 MPa. However, the type and properties of the material can be selected according to requirements.

[0046] Preferably, the first process step introduces sufficient heat into the curved drum 18 to achieve preheating temperatures of 120°C to 200°C in the area of ​​the surface section to be hardened in the second step (especially in the area of ​​the groove flanks 16F). A (short) pause without active heat input can be provided between the steps to allow sufficient time for the heat flow from the first hardened areas to preheat the areas for the second process step.

[0047] The following is a brief, example of a process: (1) Clamping the cam drum in a laser hardening device, e.g. using points that are pressed in an axial direction against the pins 30. (2) First process step: Laser hardening of the two radial bearing segments rL (especially simultaneously), wherein the desired spot surface temperature is preferably between 1,100°C and 1,400°C. This temperature can be determined, for example, "axis-parallel" to the laser beam during the process. The power of the laser(s) is then adjusted accordingly. On the one hand, it is necessary to reach a sufficiently high temperature to achieve the desired hardening result. On the other hand, care must be taken to ensure that these high temperatures are not maintained for too long, as this makes the onset of martensitization more difficult.

[0048] The entire surface of the radial bearing segments is hardened.

[0049] The feed rate of the laser beam on the surface to be hardened (relative movement between the beam and the drum) can range from 4 to 20 mm / second. However, the specific feed rate to be selected depends on the properties of the surface to be hardened and / or the desired hardening depth.

[0050] (3) Optional pause before the second process step to achieve distribution of the heat introduced in step (2). The length of the pause can be 5 seconds to 2 minutes, preferably 10 seconds to one minute. Preferably, no active heat input into the drum takes place during the pause.

[0051] (4) Second process step: Laser hardening of the groove flanks 16F with preferably the same process parameters as in step (2).

[0052] In addition to the measures described above, further process steps may be provided, such as measures to cool the drum, especially after step (4).

[0053] The method according to the invention has been described above purely by way of example using a rotary indexing table with a cam drum 18 with a grooved cam. However, it can also be used with cam drums with a ribbed cam.

[0054] Without significant additional effort, the inventive method produces cam drums that are better hardened and therefore more wear-resistant and have a higher load-bearing capacity. These have longer service lives, which in turn leads to reduced maintenance requirements. Furthermore, the process reliability of the manufacturing process is significantly improved. Reference symbol list 10 Rotary indexing table 12 plates 14 drivers 16 drive groove 16G Nutgrund 16F slot flank 18 Curved drum 20 cases 22 Electric motor 24 gearboxes 26 Drive shaft 28a Axial bearing 28r radial bearing 30 cones R, R', R'' axis of rotation K Circle G Basic body rL radial bearing segment aL axial bearing segment QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2017 116 414 A1

[0011]

Claims

[1] Method for manufacturing a cam drum for a transport device, in particular a rotary indexing table or a linear transport device, where the cam drum (18) a base body (G) with a lateral surface (M) which is provided with a drive groove (16) which is intended for the engagement of at least one driver (14) which is connected to a rotatably or linearly movable transport element (12) of the transport device, and at least one bearing section (aL, rL) for supporting the cam drum in a housing (20) of the transport device, wherein the bearing section (aL, rL) is hardened at least section by means of a laser beam in a first hardening process step, and wherein the outer surface (M) of the base body (G) is hardened at least section by means of a laser beam in a second hardening process step - directly or indirectly - following. [2] Method according to claim 1, wherein the drive groove (16) has a groove base (16G) and two groove flanks (16F), in particular wherein the groove flanks run perpendicular to the groove base, and wherein in the second hardening process step at least one of the groove flanks (16F), in particular both groove flanks (16G), is / are hardened. [3] Method according to claim 2, wherein in the second hardening process step only one of the groove flanks (16F) or only the two groove flanks (16F) is / are hardened. [4] Method according to at least one of claims 1 to 3, wherein the bearing section has a radial bearing segment (rL) for radial support of the cam drum (18) and / or an axial bearing segment (aL) for axial support of the cam drum (18), in particular wherein the axial bearing segment (aL) is arranged on the base body (G). [5] Method according to at least one of the preceding claims, wherein the first hardening process step is carried out such that the areas intended for the second hardening process step are heated to a temperature of at least 80°C, in particular at least 100°C or at least 150°C. [6] Method according to at least one of the preceding claims, wherein the surface of the area to be hardened is heated to a temperature between 1,100°C and 1,400°C in the first and / or in the second process step. [7] Method according to at least one of the preceding claims, wherein substantially the same process parameters are applied in the first hardening process step and the second hardening process step. [8] Method according to at least one of the preceding claims, wherein a pause is provided between the first hardening process step and the second hardening process step, in which preferably no heat is introduced into the cam drum, in particular wherein the pause has a length of 5 seconds to 2 minutes, preferably 10 seconds to one minute.

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