Drawing tool for sheet metal processing with at least one holding device and method for operating this drawing tool

Abstract

Drawing tool (100) for sheet metal processing, with at least one retaining device for influencing the sheet metal material flow, which has a drawing bead (130) and a corresponding opposite drawing groove (140), wherein the sheet metal material (M) is guided around the drawing bead (130) by the drawing groove (140) during a drawing process and is thereby braked, characterized in that in the sheet metal infeed direction (E) upstream of the retaining device (130 / 140) there is at least one bore (150) for lubricant application in at least one tool working surface (121) coming into contact with the sheet metal material (M) and / or in the retaining device (130 / 140), through which a lubricant (S) can be applied in a defined manner during the drawing process in order to adjust the braking effect achieved in the retaining device (130 / 140).

Description

The invention relates to a drawing tool for sheet metal machining, which tool has at least one retaining device for influencing the flow of sheet metal material.The invention further relates to a method for operating such a drawing tool.A drawing tool of the relevant type is typically a press-bonded drawing tool, such as in particular a deep-drawing tool for sheet metal forming, which comprises a lower tool part and an upper tool part, wherein one of the tool parts has at least one die and the other tool part has at least one punch and at least one hold-down device.Retaining devices for influencing and in particular for locally influencing the flow of sheet metal material during a drawing process are known from the prior art. These are usually draw bead-draw bead combinations, which are effective in particular between the holding-down device and the die. A drawing bead is a profile body (also referred to as a drawing strip) which projects from the active tool surface and engages during the drawing process in a corresponding groove-like drawing bead which is incorporated in the counteracting active tool surface. The sheet metal material entering the tool cavity during the drawing process is directed by the drawing bead around the drawing bead, wherein the material flow is inhibited or braked.From the prior art, adjustable restraining devices, i.e. restraining devices whose braking or inhibiting action can be varied, are known. The closest DE 10 2012 014 201 B3 proposes that at least one actuating element is arranged in the region of the pull bead, which actuating element can act variably on the sheet metal material directed through the pull bead and around the pull bead, in order to thereby be able to adapt the braking effect achieved. With regard to the prior art and for understanding the invention, reference is also made in addition to the patent specifications DE 10 2009 015 671 A1 and DE 10 2006 003 268 B4.It is the object of the invention to specify a drawing tool of the relevant type that does not have at least one disadvantage associated with the prior art, or at least only to a reduced extent.This is achieved with a drawing tool according to the invention corresponding to the features of claim 1. Preferred refinements and refinements emerge analogously for both subject matter of the invention both from the dependent patent claims and from the explanations which follow.The drawing tool according to the invention has at least one retaining device for influencing the material flow, which retaining device comprises a drawing bead and a corresponding opposing drawing bead, wherein the sheet metal material is directed through the drawing bead around the drawing bead during a drawing process and is braked or inhibited in the process. According to the invention, it is provided that in the sheet metal inlet direction upstream of this retaining device, at least one bore (or a microchannel or the like) for (active) lubricant discharge is located in at least one effective tool surface coming into contact with the sheet metal material and / or in the retaining device itself, through which bore lubricant can be discharged in a defined manner during the drawing process and can be applied in particular to the sheet metal material in order thereby to be able to adapt the braking action achieved in the retaining device or in order thereby to influence the inhibition achieved in the retaining device. The bore for supplying lubricant can also be referred to as a lubricant supply bore or as a nozzle.The inventive drawing tool allows the defined (i.e. determined in time and quantity) application of lubricant into the tool gap during the drawing process, namely in the sheet metal inlet direction upstream and / or directly in the retaining device. The lubricant is discharged directly on the retaining device (i.e. in situ) by means of pressurization through the at least one bore and / or discharged in front of the retaining device and entrained by the incoming sheet metal material, whereby the retention achieved in the retaining device is reduced locally or in the relevant region as a result of the friction reduction. (This is achieved in contrast to the procedure described in DE 10 2012 014 201 B3, without additional mechanical and / or movable components.) The effective braking or inhibiting effect (or else retaining force) can thus be changed during the drawing process or forming process (i.e. during the press closing or working stroke). As a result, it is possible to produce, for example, shaped sheet metal parts and, in particular, complex shaped sheet metal parts which cannot be produced with a constant or constant braking action. In addition, the process window (for goods) can be enlarged and the process safety can thus be increased. Furthermore, the installation outlay of the drawing tool can be reduced, in particular with regard to the retaining devices which are otherwise difficult to install.The drawing tool according to the invention is preferably a deep-drawing tool and / or a draw-stage tool. Particularly preferably, the drawing tool according to the invention has (at least) one die and (at least) one counteracting hold-down device, in the corresponding effective surfaces of which the drawing bead and the drawing bead of the retaining device are worked, wherein the at least one bore for lubricant discharge can be provided on the die side and / or on the hold-down device side, so that both a one-sided lubricant application and an independent two-sided lubricant application (optionally also with different lubricants) are possible. In addition, the height of the drawing bead of the retaining device can be variable (as is known from the prior art). The drawing tool according to the invention can have a plurality of retaining devices which can be influenced independently of one another in the sense according to the invention.Preferably, a plurality of bores are provided for lubricant discharge, which open into a common supply channel arranged in the tool body or into a supply line. The common supply channel can be formed by a pipeline integrated in the tool body, which can also have a spatial course. The pipeline can be cast, for example, in the tool body or inserted into a corresponding (subsequently or generatively introduced) bore in the tool body. New bores can advantageously be set to the supply channel at required locations. Likewise, existing bores can be closed.The supply channel can be connected to a lubricant pump, with which in particular a time-variable pressurization or a time-variable lubricant pressure can be generated in the supply channel, in order thereby to bring about the discharge of the lubricant through the at least one lubricant discharge bore. Valves and other devices (for example a pressure vessel) can also be provided for controlling the lubricant pressure. The invention also extends, at least indirectly, to a device for sheet metal machining and in particular sheet metal forming, comprising a drawing tool according to the invention, a lubricant supply system connected thereto (having a lubricant pump which can be controlled in terms of its pumping capacity, wherein the latter is preferably an oil pump, a lubricant storage container, at least one supply line, in particular for connection to the supply channel in the tool, and / or at least one valve), and a control device, in particular for controlling the lubricant pump, the valves and / or other devices belonging to the lubricant supply system.A bore for lubricant discharge preferably has a diameter of less than 1.0 mm, particularly preferably of less than 0.8 mm and in particular of less than 0.6 mm. The bore opening or outlet opening in the active tool surface should be formed so small that no grooves are formed in the sheet metal material. The lubricant flow through this bore can be influenced via the cross-sectional size of the bore. If a plurality of bores are provided, these can have different diameters as required.The retaining device can function as a scraper with respect to the lubricant located on the sheet metal material and applied in particular during the drawing process. It is preferably provided that in the retaining device, in particular in the draw bead, there is at least one outlet for scraped-off lubricant.The method according to the invention for operating a drawing tool according to the invention provides that lubricant is only discharged through the at least one lubricant discharge bore during a specific phase (possibly also only at a specific point in time) or optionally also during a plurality of phases of the drawing process. This phase is preferably a critical phase of the drawing process or forming process, wherein the lubricant can also be discharged with regard to other objectives. The beginning and end of the phase can be defined, for example, on the basis of the position of the press ram. The lubricant can be discharged during this phase with constant pressure (by which in particular the pressure in the supply channel is meant) and a constant lubricant flow resulting therefrom or with variable pressure and a variable lubricant flow resulting therefrom.It is preferably provided that the sheet metal material to be processed, when being inserted into the drawing tool, has only one base oil, in particular applied by the manufacturer or in the cleaning installation. A preceding additional oil treatment for the drawing process or forming process is accordingly omitted, wherein the lubricant typically required for forming is applied directly in the drawing tool according to the invention.The lubricant used is preferably a low-viscosity oil (or else an oil emulsion or the like) (for example having a viscosity of less than and in particular significantly less than 100 mm^2 / s), in particular a special drawing oil.Low viscosity drawing oils are commercially available. In order to reduce the viscosity, the oil can be heated, which can also be effected, for example, with the aid of a heater integrated in the drawing tool.The lubricant is preferably discharged during the drawing process in a control loop. The regulation can be effected, for example, with the aid of the control device already mentioned above. It is particularly preferably provided that the regulation takes place based on a measurement of the sheet metal inlet, in particular in the region of the retaining device, for which purpose at least one suitable sensor (for example a sheet metal edge inlet sensor or the like) can be installed in the drawing tool according to the invention. The setpoint variable (which can be a constant setpoint variable or possibly also a temporally varying setpoint variable) is in this case the sheet metal inlet which, if necessary, is influenced by a defined lubricant discharge (in particular by adaptive variation of the pump output of the lubricant pump or oil pump by corresponding actuation) and the friction reduction (or friction increase after termination of the lubricant discharge) associated therewith in the retaining device. However, the regulation can also be carried out on the basis of other measured process variables (for example. The pressing force, the holding-down force and the like) can be effected. With such a control system, it is also possible to react in particular to tolerance fluctuations within a batch of sheet material in order to reduce the reject scrap shot rate. Instead of a regulation, a control according to specification (for example by a permanently specified time profile of the pump output of the lubricant pump or oil pump) can also be provided. If the drawing tool according to the invention has a plurality of retaining devices, these can be influenced in the sense according to the invention by separate and independent control or regulation.The invention is explained in more detail below by way of example and in a non-limiting manner with reference to the drawings. However, the features shown in the drawing and / or explained below can be general features of the invention, independently of specific feature combinations. Illustrated in the drawing FIG. 1 is a schematic sectional view of the principle according to the invention on the basis of a preferred embodiment.FIG. 1 shows a detail of a drawing tool 100 according to the invention, having a die 110 which has an effective surface 111, and a holding-down device 120 which has an effective surface 121. Between die 110 and hold-down device 120 there is a sheet metal material M (so-called flange region or flange section) which runs or flows into the tool cavity via the pulling edge 115 in a manner known per se. The arrow E indicates the sheet metal running direction in the flange region. The drawing tool 100 further comprises, in the region shown, a retaining device for influencing the flow of sheet metal material, which retaining device has a die-side drawing bead 130, which is designed as an inserted drawing strip, and a draw bead 140 on the holding-down device side, wherein the sheet metal material M is directed or drawn around the drawing bead 130 by the drawing bead 140 during a drawing process and is braked or inhibited in the process.According to the invention, the holding-down device 120 has at least one bore 150 for the lubricant discharge in the sheet metal inlet direction E upstream of the retaining device 130 / 140. The bore opening or outlet opening in the active tool surface 121 is designated 151. During the drawing process, a lubricant S, which is in particular a drawing oil or the like, can be introduced through the bore 150 in a defined manner into the tool gap (distance between the corresponding effective surfaces 111 and 121) and / or applied to the sheet metal material M (which can also be referred to as targeted oiling), whereby the braking or inhibiting effect achieved in the retaining device 130 / 140 is reduced. This allows an adaptation of the braking or inhibiting effect during the drawing or forming process, as explained in detail above.The lubricant discharge bore 150 opens into a supply channel 160 which is formed from a pipe piece cast into the holding-down device 120 or integrated in some other way. Accordingly, the bore 150 is expressly not a blind bore for forming a lubricant depot, but rather a permeable connecting bore from the supply channel 160 to the tool surface or effective surface 121. A plurality of bores 150 may extend from the supply channel 160. The lubricant S is discharged by pressurizing the supply channel 160, for which purpose it can be connected to a lubricant pump or oil pump which generates the required lubricant pressure if necessary. Designated at 170 is a scraped lubricant S drain formed in the pull bead 140. Instead of such a drain, a collection reservoir or the like can also be provided.In a manner analogous to the embodiment shown in FIG. 1, the die 110 can also have at least one bore for defined lubricant discharge during the drawing process. Such a lubricant discharge bore in the die 110 is shown in dashed lines and designated 150', wherein the bore 150' ends directly at the draw strip 130 and thus opens into the retaining device 130 / 140. The invention is also suitable in particular for retrofitting existing drawing tools.List of reference characters100 Drawing tool 110 Die 111 Effective surface 115 Drawing edge 120 Holding-down device 121 Effective surface 130 Drawing bead (drawing strip) 140 Drawing bead 150 Lubricant discharge bore 151 Bore opening 160 Supply channel 170 Outlet E Sheet metal inlet direction M Sheet metal material S Lubricant

Claims

Drawing tool (100) for sheet metal machining, having at least one retaining device for influencing the flow of sheet metal material, which retaining device has a drawing bead (130) and a corresponding, opposite drawing bead (140), wherein the sheet metal material (M) is guided by the drawing bead (140) around the drawing bead (130) during a drawing process and is braked in the process, characterized in that, in the sheet metal inflow direction (E), upstream of the retaining device (130 / 140), at least one bore (150) for lubricant discharge is located in at least one tool active surface (121) coming into contact with the sheet metal material (M) and / or in the retaining device (130 / 140), a lubricant (S) can be discharged through said bore in a defined manner during the drawing process, in order thereby to be able to adapt the braking action achieved in the retaining device (130 / 140).Drawing tool (100) according to claim 1, characterised in that a plurality of bores (150) are provided for the lubricant discharge, which bores open into a common supply channel (160) arranged in the tool body.Drawing tool (100) according to claim 2, characterised in that the supply channel (160) is formed by a pipe integrated in the tool body.Drawing tool (100) according to one of the preceding claims, characterized in that the bore (150) for lubricant discharge has a diameter of less than 1.0 mm, preferably of less than 0.8 mm and in particular of less than 0.6 mm.Drawing tool (100) according to one of the preceding claims, characterized in that at least one outlet (170) for scraped-off lubricant (S) is located in the drawing bead (140) of the retaining device.Method for operating a drawing tool (100) according to one of the preceding claims, wherein lubricant is only discharged through the bore (150) during a specific phase of the drawing process.Method according to Claim 6, characterized in that the sheet metal material (M) to be processed has only one base oiling during the insertion into the drawing tool (100).Method according to Claim 6 or 7, characterized in that a low-viscosity oil is used as lubricant (S).Method according to claim 6, 7 or 8, characterised in that the lubricant is discharged during the drawing process in a control loop.Method according to Claim 9, characterized in that the regulation takes place on the basis of a measurement of the sheet metal inlet (E) and / or other process variables.

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