EP2736661B1 - Segmented press-hardening tool - Google Patents

Description

The invention relates to a press hardening tool for producing hardened sheet-metal shaped parts from a hardenable sheet steel material, according to the preamble of claim 1.

Press hardening tools for producing hardened sheet metal parts are known from the prior art. Such press hardening tools comprise at least two tool parts which are movable relative to one another in a working direction and between which a heated sheet steel material is formed and, at the same time, cooled simultaneously under application of a pressing force, whereby an increase in strength occurs according to the known metallurgical mechanisms.

In order to achieve the best possible cooling and in a good shape retention, a full-surface concerns of the steel sheet material to the tool acting surfaces of the tool parts is required during the press hardening process. This full-surface concern is usually achieved by a complex incorporation of the press-hardening tool. In practice, however, despite this incorporation, a full-surface concerns of the steel sheet material on the tool effective surfaces, especially in steep areas (i.e., steep with respect to the working direction), can not be reliably guaranteed, which z. B. is due to increasing tool wear and / or irregular thickness distributions of the steel sheet material.

This problem is already in the generic WO 2006/015849 A2 explained. To solve this problem is in the WO 2006/015849 A2 proposed a press-hardening tool in which the steel sheet material is only partially clamped in relevant areas between the tool parts during press hardening, for which purpose the tool effective surfaces are formed with corresponding clamping webs (for example in the form of protrusions or oversizes). In the areas where the steel sheet material is not clamped in the press hardening process, this is spaced with an air gap to one or both tool effective surfaces.

A disadvantage of the in the WO 2006/015849 A2 However, the proposed press hardening tool is that the steel sheet material in the non-clamped areas undergoes no or only a relatively smaller increase in strength due to the lower cooling rate. The sheet metal part produced thus has different strength properties. However, such a sheet metal part is not suitable for all uses.

It is therefore an object of the present invention to provide a press-hardening tool that does not have the abovementioned disadvantages or at least only to a lesser extent.

This object is achieved by a press-hardening tool according to the invention having the features of claim 1. The features and feature combinations specified in the dependent claims relate to preferred refinements and developments of the press-hardening tool according to the invention.

The press-hardening tool according to the invention comprises at least two tool parts which are movable relative to one another in a working direction and between which a heated steel sheet material is formed by application of a pressing force acting in the working direction (shaping of the sheet steel material is understood as forming and / or holding, as explained in more detail below). and cooled and this can be cured in a known manner. According to the invention, at least one of the tool parts is formed at least partially segmented and has at least a first segment with a transverse to the working direction extending form portion and at least a second segment with a steeply extending to the working direction form portion, wherein the first segment movable on the respective tool part is arranged and give in against a given pressing force against this applied pressing force or can retreat, thereby enabling further movement of the tool parts and a concomitant increased pressing of the second segment to the steel sheet material. The press-hardening tool according to the invention can be designed for the simultaneous production of a plurality of hardened sheet-metal shaped parts. Furthermore, the production of partially hardened sheet-metal shaped parts is also possible with the press-hardening tool according to the invention.

In order to accomplish the cooling of the steel sheet material during the press hardening process, it is preferably provided that at least one tool part and in particular also the segmented tool part is designed as a coolable tool part, for which purpose this tool part with at least one cooling device for cooling or at least in regions Cooling of the tool effective surface is equipped. In particular, at least one second segment is formed with at least one cooling device (eg cooling channels).

The segments of a segmented trained tool part each have a mold section. A mold section is understood to mean a surface section belonging to a tool effective surface which comes into direct contact with the steel sheet material during the press hardening process. This shape portion may be flat or formed with a spatial shape. A form section extending transversely to the working direction is understood to mean, in particular, a surface section (the tool active surface) which extends substantially perpendicularly to the working direction. Under a steeply extending to the working direction of the mold section is in particular a surface portion (the tool acting surface) understood, which extends substantially at an angle of 0 ° to 15 ° to the working direction. To assess the extension or alignment of a mold section, a mathematical compensation surface for the surface section in question may be considered. The segments of a segmented tool part are preferably designed and arranged such that their mold sections form a substantially gap-free tool effective area at each point in time of the press hardening process.

By at least a first segment yielding or shrinking against this applied pressing force in the press hardening process when exceeding a certain or defined pressing force, the tool parts of the press-hardening tool according to the invention (without appreciable increase of the applied pressing force) can be moved even further together (in the order of a few hundredths or tenths of a millimeter), whereby in the steep areas, the surface portions of the opposing or corresponding tool acting surfaces are moved towards each other in the working direction. By means of the tool-making measures according to the invention, it is thus also possible to provide the sheet-metal material to be hardened with sufficient force to mold and cool in the areas steep to the working direction (eg in the frame areas) with a high surface pressure (in particular in relation to conventional press-hardening tools). be achieved.

In contrast to that from the WO 2006/015849 A2 Known press hardening tool, the tool parts of the press-hardening tool according to the invention are preferably designed such that the steel sheet material over the entire surface can rest against the tool-working surfaces of these tool parts. With appropriate training of the cooling devices can here over the Sheet metal part a uniform cooling and good shape retention can be achieved. Irrespective of this, the press hardening tool according to the invention can also be designed in such a way that the steel sheet material to be hardened rests only in regions on the tool acting surfaces during the press hardening process.

It is preferably provided that both the first segment and the second segment are fastened to a base plate belonging to the respective tool part, wherein the first segment (which has a form section extending transversely to the working direction) is supported directly or indirectly resiliently on this base plate. Due to the resilient support of the first segment to a base plate extending transversely to the direction of the mold section remains permanent, d. H. in particular also during the further movement of the tool parts, with the steel sheet material in touching contact and also brings a defined compressive force or surface pressure on the steel sheet material. Furthermore, locally occurring excessive pressing forces can be reduced, which could lead to sheet metal molding errors and / or damage to the press hardening tool.

The resilient support of a first segment can, for. B. by mechanical springs, such as. Belleville springs, be accomplished. Particularly preferably, it is provided that the resilient support of a first segment is accomplished by at least one gas spring and in particular by at least one nitrogen spring. Such gas springs or nitrogen springs are available as purchased parts. The maximum travel of a first segment relative to the base plate may be between 0.5 mm and 1.5 mm, and in particular approximately 1.0 mm. The maximum travel can be limited in both directions by a mechanical stop.

It is particularly preferred that at least one second segment (which has a steeply extending to the working direction mold section) is designed as a slide, which is designed as a slide second segment is moved during further movement of the tool parts in a direction transverse to the direction and this quasi active is pressed against the steel sheet material reinforced. As a result, the steel sheet material is pressed locally in this area reinforced to the corresponding tool effective surface of the opposite tool part, which can be achieved for shaping and cooling optimal surface contact of the sheet steel material to be hardened on the tool effective surfaces with a concomitant optimal surface pressure. The case taking place slide stroke z. B. in the range of a few hundredths to several tenths of a millimeter.

For the mechanical actuation of a second segment designed as a slide, the relevant tool part can have at least one driver. This driver can be designed as a driver block, which is attached directly or indirectly to the tool base plate of the relevant tool part. In particular, it is provided that the driver or driver block and formed as a slider second segment are formed with corresponding inclined surfaces, which slide on each other when moving the tool parts of the press hardening tool, about which in a known manner the displacement of the slider formed as a second segment is accomplished.

Furthermore, it is preferably provided that the second segment designed as a slide has at least one cooling device. Such a cooling device can, for. B. be incorporated in the second segment cooling channels, which can be traversed by a cooling medium. By this measure, an optimal cooling of the steel sheet material during press hardening process can be accomplished even in steep areas.

A particularly preferred embodiment of the press-hardening tool according to the invention provides that only one tool part and in particular only the die is segmented. Such a press-hardening tool will be explained in more detail below in connection with the figures.

Fig. 1

zeigt in einer Schnittansicht ein erfindungsgemäßes Presshärtewerkzeug.

Fig. 2

zeigt in einer Schnittansicht einen Presshärtevorgang mit dem Presshärtewerkzeug der Fig. 1.

Further features and advantages of the invention will become apparent in a non-restrictive manner from the following exemplary description with reference to the schematic figures.

Fig. 1

shows a sectional view of an inventive press hardening tool.

Fig. 2

shows in a sectional view a press hardening process with the press hardening tool of FIG Fig. 1 ,

Fig. 1 shows an inventive press hardening tool 100 for producing hardened sheet metal parts. The press-hardening tool 100 includes a first upper tool part 200 and a second lower tool part 300. As shown, the press-hardening tool 100 is in an opened state. To close the press-hardening tool 100, the upper tool part 200 can be moved relative to the lower tool part 300 in the working direction indicated by D, for which purpose the press-hardening tool 100 is installed in a forming press (not shown).

The upper tool part (upper tool) 200 has an upper base plate 210 on which a cooled die 220 is constructed. The template 220 is segmented and includes a first middle segment 221 that is generally horizontal and perpendicular to the working direction D extending mold portion 222, and a plurality of second lateral segments 223, which are arranged immediately adjacent to the first segment 221 and which have steeply to the working direction D extending mold sections 224. The steeply oriented to the direction of work D form portions 224 of the second segments 223 extend at an angle y of about 15 ° to the working direction D, which is illustrated for the second segment 223 shown on the right with dashed lines (the oblique line represents a compensating surface for the Molding section 224). The mold sections 222 and 224 form a closed die-side tool acting surface. With 230 cooling channels are designated, which are flowed through by a cooling medium for cooling the die-side tool effective surface or the mold sections 222 and 224.

The first segment 221 is supported by several gas pressure springs 260 directly to the upper base plate 210 and can move back by compression of these gas springs 260 against the working direction D. In order to limit the travel, a spacer 225 is optionally provided. Due to the number and design of the gas springs 260, a force acting on the first segment 221 spring force can be adjusted.

The second segments 223 are designed as slides, which can be moved transversely to the working direction D. The displacement of the slider formed as second segments 223 is carried out by the driver pads 240 which are attached directly to the upper base plate 210. The driver pads 240 and the second segments 223 designed as slides have corresponding oblique surfaces which can slide on one another when moving the upper tool part 200 in the working direction D, whereby the displacement of the second segments 223 designed as slides is accomplished in a known manner transversely to the working direction D. , In addition, not shown actuators (eg. Hydraulic Kurzhubzylinder) may be installed in the upper tool part 200. Sliding plates 250 are attached to the inclined surfaces of the driver pads 240. Sliding plates or the like may also be fastened to the corresponding inclined surfaces of the second segments 223 designed as slides. Means for resetting the slider formed as second segments 223 are not shown. The reset could z. B. by spring elements (such as, for example, gas springs) accomplished.

The lower tool part (lower tool) 300 has a lower base plate 310 on which a cooled punch 320 is constructed. The punch 320 is designed as a rigid punch and has a closed punch-side tool acting surface. The stamp 320 may also be of a different type. Corresponding to the die-side tool acting surface, the punch-side tool acting surface comprises a region (or molding section) 322, the extends substantially perpendicular to the working direction D, and a plurality of portions (or mold portions) 324, which extend steeply to the working direction D. With 330 cooling channels are referred to, which are flowed through by a cooling medium for cooling the punch-side tool effective area. The lower tool part 300 may further include a hold-down (not shown). This is preferably a cooled down holder which has a corresponding cooling device (such as, for example, cooling channels).

For producing a hardened sheet metal part, a heated steel sheet material is inserted into the opened press hardening tool 100. Typically, the steel sheet material to be cured is heated to a temperature greater than 900 ° C prior to loading into the press hardening tool 100. In a first variant of the method, the steel sheet material to be hardened, when placed in the press-hardening tool, can be in the form of a flat sheet-metal blank (direct press-hardening method, wherein the press-hardening tool has a deforming function). In a second variant of the method, the steel sheet material to be hardened when inserted into the press hardening tool may have the form of an already cold preformed sheet metal part or intermediate molded part (indirect press hardening, wherein the press hardening tool has a deforming or shape-retaining function). After inserting a heated sheet steel material, the press hardening tool 100 is closed to perform a press hardening operation by moving the upper die 200 in the working direction D.

Fig. 2 shows the press hardening tool 100 in the closed state. Between the die 220 and the punch 320 is a steel sheet material 400 to be hardened, which was formed upon closing of the press hardening tool 100 in accordance with the punch and die contour and bears against the tool effective surfaces. The die 220 is in a lower end position as a whole and can not be moved further in the working direction D.

When the die 220 is in the lower end position shown, a pressing force F required for press-hardening is applied to the press-hardening tool 100 by the forming press, which is illustrated by the force arrow F directed onto the upper base plate 210. The applied pressing force F leads to an increase in pressure in the gas pressure springs 260, which initially served only to transmit power during the firing of the press hardening tool 100. When exceeding a certain or defined by design pressing force F, the gas springs can spring 260, which in this case is synonymous with a yielding of the first segment 221 against the applied pressing force F, at least until this the optional spacer element 225 abuts (as in FIG Fig. 2 shown). By compressing the gas pressure springs 260, the tool parts 200 and 300 can be moved further together (or the upper tool part 200 can be further fed in the working direction D on the lower tool part 300), this collapse is accomplished by the effective pressing force F.

The further collapse of the tool parts 200 and 300 is accompanied by an analog compression of the gas springs 260. This compression of the gas springs 260 causes a continuous yielding of the first segment 221. This yielding can be considered a retraction of the inherently stationary first segment 221 within the upper tool part 200, in which the first segment 221, as illustrated by the movement arrow A, almost moves towards the upper base plate 210, although the upper base plate 210 actually moves towards the first segment 221. The gas pressure springs 260 also cause the first segment 221 and its mold section 222 at any time of the press hardening process in contact with the steel sheet material 400, wherein in the region concerned a certain pressure force generated by the gas pressure springs 260 (which may be with one on the Spacer 225 transmitted compressive force superimposed) is applied to the steel sheet 400, which leads to a flat abutment of the sheet steel 400 to be hardened on the mold sections 222 and 322 with a defined surface pressure.

Furthermore, due to the further movement of the tool parts 200 and 300 made possible by compression of the gas pressure springs 260, a shift of the second segments 223 in the direction of the punch 320 initiated by the drive blocks 240 occurs, so that these segments 223, as with the movement arrows B illustrated in the steep areas reinforced with a certain compressive force against the steel sheet material 400 are pressed. This results in a flat and in particular large-area concerns of the sheet steel 400 to be hardened in the steep areas to the corresponding tool effective surfaces or to the corresponding mold sections 224 and 324 with a relatively high surface pressure. This allows a rapid and uniform cooling of the steel sheet material 400 even in the steep areas, which is brought about in an optimal strength increase in the steel sheet material 400. Regardless, the second segments 223 formed as sliders also have a forming (ie, reshaping or at least shape-retaining) function. With regard to this forming function, it is also possible to provide greater displacement movements or slide strokes which exceed the above-mentioned orders of magnitude in the range of a few hundredths to several tenths of a millimeter go out, in which case preferably also the maximum travel or travel of a first segment relative to the base plate can be more than 1.5 mm.

Otherwise, the displacement movement B of the second segments 223 in the form of slides overlaps with the movement of the upper tool part 200 in the working direction D during the further movement of the tool parts 200 and 300. By appropriate design of the driver 240 and / or the second segments 223 designed as slides For example, it is possible to produce a slider movement directed essentially perpendicular to the punch-side tool effective surface region 324, which is illustrated by the arrow C as an example for the right-hand second segment 223.

After cooling the steel sheet material 400, which takes place while maintaining the pressing force F, the press-hardening tool 100 can be opened by moving the upper tool part 200 counter to the working direction D and the hardened sheet metal part can be removed. The hardened sheet metal part is, for. B. to a vehicle tunnel for a motor vehicle body, which by design has steep area.

LIST OF REFERENCE NUMBERS

100

Press hardening tool

200

upper tool part (upper tool)

210

upper base plate

220

die

221

first segment

222

Molding section (first segment)

223

second segment / slider

224

Molding section (second segment)

225

spacer

230

Cooling device, cooling channels

240

driver

250

sliding plate

260

Gas spring

300

lower tool part (lower tool)

310

lower base plate

320

stamp

330

Cooling device, cooling channels

400

Steel sheet material

A

Back-off movement (of the first segment)

B

Movement movement (of the second segment)

C

resulting slider movement

D

working direction

F

pressing force

y

angle

Claims (9)

1. Press-hardening tool (100) for producing hardened shaped sheet metal parts from a sheet steel material (400), comprising at least two tool parts (200, 300), which are movable in relation to each other in a working direction (D) and between which, by applying a pressing force (F) acting in the working direction (D), a heated sheet steel material (400) can be shaped and cooled and thereby hardened, characterized in that at least one of the tool parts (200, 300) is formed in a segmented manner and has at least a first segment (221) having a shaped section (222) extending transversely to the working direction (D) and at least a second segment (223) having a shaped section (224) extending steeply with respect to the working direction (D), wherein the first segment (221) is arranged in a movable manner on the relevant tool part (200, 300) and, when a certain pressing force (F) is exceeded, can yield to the pressing force (F) applied, in order as a result to allow further moving together of the tool parts (200, 300) and associated intensified pressing of the second segment (223) against the sheet steel material (400).
2. Press-hardening tool (100) according to Claim 1, characterized in that the tool parts (200, 300) are formed in such a way that the sheet steel material (400) can lie with its full surface area against the effective tool surfaces of these tool parts (200, 300).
3. Press-hardening tool (100) according to Claim 1 or 2, characterized in that both the first segment (221) and the second segment (223) are fastened to a base plate (210) belonging to the relevant tool part (200), wherein the first segment (221) is supported resiliently on this base plate (210).
4. Press-hardening tool (100) according to Claim 3, characterized in that the resilient support of the first segment (221) on the base plate (210) is accomplished by at least one gas pressure spring (260).
5. Press-hardening tool (100) according to Claim 3 or 4, characterized in that the maximum spring excursion of the first segment (221) in relation to the base plate (210) is between 0.5 mm and 1.5 mm, and in particular is approximately 1.0 mm.
6. Press-hardening tool (100) according to one of the preceding claims, characterized in that at least a second segment (223) is formed as a slide, wherein this second segment (223), formed as a slide, is displaced during the further moving together of the tool parts (200, 300) in a direction (B) transverse to the working direction (D) and thereby pressed more intensely against the sheet steel material (400).
7. Press-hardening tool (100) according to Claim 6, characterized in that the relevant tool part (200) has at least one driver (240) for the mechanical actuation of the second segment (223) formed as a slide.
8. Press-hardening tool (100) according to Claim 6 or 7, characterized in that the second segment (223), formed as a slide, has at least one cooling device (230).
9. Press-hardening tool (100) according to one of the preceding claims, characterized in that only one tool part (200), and in particular only the die (220), is formed in a segmented manner.

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