DE102014104922A1 - Apparatus and method for cooling sheet steel blanks - Google Patents

Abstract

The present invention relates to a method for tempering sheet steel blanks and in particular for cooling sheet steel blanks, wherein steel sheet is drawn from a steel coil and cut into blanks, the steel blanks are then heated to a temperature above AC3 of the respective steel material and the steel material partially or completely in austenite is then thermoformed in a press-hardening tool while hot and simultaneously cooled at a speed above the critical hardening rate such that a quench-hardening microstructure sets in which, after heating above AC3 and before forming and quench-hardening, the steel material is tempered and in particular intermediately cooled, until it has a desired temperature for forming, characterized in that between at least one, the pressure on the board exerting tool plate (3) and the board (2) egg a worktop (6) is arranged, which serves the tempering and wherein in a working surface (7) of the worktop (6) which faces a sheet steel plate (2), narrow slits are introduced, which form a thermal expansion of the worktop (6) Material without distortion of the worktop (6) allows, as well as a device for carrying out the method.

Description

The invention relates to an apparatus and a method for cooling sheet steel blanks.

It is known to produce sheet steel in blanks for producing high-strength sheet steel components, then heat the steel sheet blanks to a temperature above AC3 of the respective steel material and thus convert the steel material into a partial or complete Austenitgefüge and then simultaneously in a press hardening tool in the sheet metal component and thereby To cool a speed above the critical hardness rate such that sets a substantially martensitic structure.

The steel grades used for this purpose are boron-manganese steels, for. Eg 22MnB5.

It has been found that problems arise when using such press-hardening steels when they are provided with a zinc coating to protect against corrosion. If an austenitic structure comes into contact with liquid zinc during forming, the phenomenon known as "liquid metal embrittlement" can result. This leads to cracks in the surface, which can partially protrude deep into the steel material. Although such a steel material has a high hardness, but can quickly tire or tear in the area of cracks.

In order to avoid such a "liquid metal embrittlement" it is known from the applicant to use a so-called conversion-delayed steel material, which is press-hardened even at temperatures below the peritectic temperature of the zinc-iron diagram, so that no liquid zinc phases with come into contact with the austenite during forming.

For this purpose, however, it is necessary that the steel material is first removed from the coil, then cut into the predetermined boards, the cut boards are then heated to a temperature above AC3 and thus at least partially brought into the austenitized state and the steel plates after heating above AC3 be cooled to a temperature below the peritectic temperature of the zinc-iron diagram and then reformed.

For this purpose, a cooling step, which is preferably coordinated with the steel material, must be carried out, which, however, ensures reliable process control and thus a still sufficient temperature for press hardening.

From the EP 2 014 777 A1 are known a method and an apparatus for the thermal treatment of sheet metal, wherein the metal sheet is thermally treated by heat conduction, wherein the sheet is fixed in position and at least a first contact plate is brought into contact with at least a first surface portion of the sheet and at least a second Contact plate is brought into contact with at least a second surface portion of the sheet, the contact plates are formed flat according to the contour of the surface portions of the sheet and are arranged parallel to each other in the state of contact with the sheet and at least one contact plate during contacting of the sheet opposite the sheet has higher or lower temperature, wherein a plurality of contact plates can be interconnected by means of flexible transition elements.

In this device is disadvantageous that the cooling of the corresponding metal sheets is not traceable evenly.

From the EP 2 182 082 A1 a comparable device is known, in which, moreover, a heating device can also be present, in particular an inductive heating device, in order to heat the sheet arranged between the contact plates partially or completely inductively.

From the DE 20 2013 103 764 U1 a tempering station with induction heating is known, which can be incorporated into a hot forming line for hot forming and press hardening of metal sheets, wherein the tempering has an inductor as a heat source and by means of the tempering in the component areas with mutually different temperatures are adjustable, wherein a lower tool and / or an upper tool having at least one Flächeninduktor and on the Flächeninduktor depending a temperature plate for receiving the component to be heated, wherein in the temperature control at least one cooling channel for the passage of a gaseous cooling medium is arranged so that two areas with mutually different temperatures are adjustable, which ultimately This leads to the fact that a component with different hardness ranges can be produced.

A comparable device is from the DE 10 2012 110 649 B3 known to be produced with the sheet metal parts with partially different strength properties with low energy requirements. It is provided that in the tempering by the thermally conductive contact of the sheet with the adjacent Heat transfer plates heat is transferred to the plate and the sheet is heated in this case, in particular to temperatures above the AC3 point. In addition, areas of the sheet metal blank can also be cooled by the plates. In one embodiment, sheet metal blanks may be preheated to a temperature in a separate furnace, in particular homogeneously, for example at a temperature above AC1 but below AC3, in which case the further heating within the tempering station from at least the first type to a temperature above AC3 and areas of the second kind, which are to remain softer, are maintained at a temperature level between AC1 and AC3.

All previously known methods for direct heating has in common that they are to be used as evidence of the cited prior art for cooling. However, it has been found that the mentioned devices lead to different component properties during cooling.

The object of the invention is to provide a method for cooling sheet metal blanks, which is simple and safe to carry out and results in a comprehensible cooling.

The object is achieved by a method having the features of claim 1.

It is a further object of the invention to provide an apparatus for carrying out the method.

The object is achieved with a device having the features of claim 6.

Advantageous developments are characterized in the respective dependent subclaims.

The inventors have found that, when applying a metal sheet already heated to above AC3 in a tempering or cooling tool, it is due to the thermal expansion of the cooling plates that they bulge. By this bulge is not to be expected in all areas of the sheet steel plate with a full-surface contact, at least a full-surface uniform contact, and a full-surface uniform pressure, so that the heat transfer between the sheet steel plate and the cooling plates are non-uniform. This results in different material properties, which - at least if it is untargeted - is undesirable.

According to the invention, this problem is eliminated by arranging between a pressure plate on the board and two tool plates and the respective board a worktop, which is formed with a plurality of narrow slots, so that the thermal expansions only in small local areas occur and be balanced so that the global warping of the plate can be prevented.

Optionally, an insulating layer may be present between the work surface and the tool plate.

In addition, the worktop can be formed with connections for a gas and / or water flow and in particular coolant flow.

In a further advantageous embodiment, the worktop for processing of sheets of different thicknesses (taylored blanks) is formed with corresponding stages such that taylored blanks having one or more stages or offsets can be cooled safely and uniformly.

When using a slotted work surface between the tool plate and board is an advantage that it allows uniform uniform cooling without distortion and with the appropriate pressure.

x

... Tiefe der Schlitze

D

... Dicke der Arbeitsplatte

d

... Dicke des zu kühlenden Bleches

b

... Schlitzbreite

a

... Schlitzabstand

α

... linerarer Wärmeausdehungskoeffizient [1/K]

T_Start

... Ausgangstemperatur der Arbeitsplatte (Umgebungstemperatur)

T_Blech

... Ausgangstemperatur des zu kühlernen Bleches

Under the following conditions

x

... depth of the slots

D

... thickness of the worktop

d

... thickness of the sheet to be cooled

b

... slit width

a

... slot spacing

α

... linear thermal expansion coefficient [1 / K]

T_Start

... exit temperature of the worktop (ambient temperature)

T_Blech

... initial temperature of the sheet to be cooled

• 1. 0,1 <= x/D <= 0,9 insbesondere 0,25 <= x/D <= 0,8 insbesondere 0,5 <= x/D <= 0,75
• 2. d/D <= 0,2 insbesondere 0,1
• 3. b/a >= α·(T_Blech – T_Start)/2 d.h. bei z.B.: 800 T_Blech – 20 T_Start (RT)/2 = 390 °C Dies mal α, bei Stahl ca. 1·10 ^–5 [1/K]

It had turned out to be advantageous to comply with the following conditions:

• 1. 0.1 <= x / D <= 0.9, in particular 0.25 <= x / D <= 0.8, in particular 0.5 <= x / D <= 0.75
• 2. d / D <= 0.2, in particular 0.1
• 3. b / a> = α · (T_Blech - T_Start) / 2 ie eg: 800 T_Blech - 20 T_Start (RT) / 2 = 390 ° C This time α, for steel approx. 1 · 10 ^ -5 [1 / K]

Since no cooling takes place in the area of the slot itself, b must not be too wide here. A second condition is therefore that b <d / 2.

When using slotted worktops on both sides of a board, it is also advantageous to offset the slots against each other in both directions of Kühlebene by half the slot width.

Preferably, the slots are arranged above or in the machining direction in alignment with the cooling channels.

In an advantageous embodiment, the slots to improve the cleaning, wider in the region of its top plate mouth than in the foot area to facilitate the precipitation of contaminants or the expulsion of dirt.

In the invention, advantageously, the slotted worktop can be arranged on a water-cooled tool plate.

Moreover, it is possible according to the invention that corresponding cooling coils or cooling lines are also arranged in the worktop itself.

The invention will be explained by way of example with reference to a drawing. It shows:

1 an embodiment of the structure according to the invention with a tool plate, a slotted work surface and a board to be cooled;

2 a graph showing the hardness or strength profile over the plate length in a worktop without cuts;

3 : a diagram with the hardness or strength profile over the worktop thickness and the achievable equalization when using slotted plates.

The device according to the invention 1 for tempering and in particular cooling a sheet steel plate 2 has at least one massive tool plate 3 , which with a processing page 4 ahead on a circuit board 2 to (arrow direction 5 ) and is movable away from it. The tool plate 3 it has an extension, preferably the spatial extent of a board 2 equals or slightly larger, leaving a circuit board 2 for the purpose of tempering and in particular cooling is completely thermally conductive contactable.

For the purpose of tempering can over the area 4 an additional worktop 6 arranged.

The plates 3 . 6 may be formed from corresponding hot-work steels or other metals and metal alloys commonly used.

The tool plate 3 or worktop 6 can be traversed by known lines and / or holes (not shown), through which a gaseous or liquid temperature control medium and in particular a cooling gas or a cooling liquid can be passed. Accordingly, the worktop has 6 via at least one inflow port and a drain port (not shown).

In an advantageous embodiment of the worktop 6 this has a plurality of different line and / or hole arrangements, so that the board 2 in direct contact with a work surface 7 the worktop 6 cooled zonally different.

The worktop 6 is with a printing surface 8th formed, which to the work surface 7 runs parallel and towards the tool plate 3 is directed and in particular with the area 4 the tool plate 3 is in preferably thermally conductive contact.

In a particular thermally conductive contacting of worktop 6 and tool plate 3 can also use the tool plate 3 an actively cooled and in particular water-cooled plate.

Is only the worktop 6 Chilled, can between the countertop 6 and the water-cooled plate may also be provided with thermal insulation (not shown).

To the slots 9 in the tool plate 3 or worktop 6 to bring in the plates 3 . 6 from a work page 4 . 7 slit-shaped eroded so that the slit areas form. Here, the depth of the slots can vary widely from about 10% to almost 90% of the plate thickness. The width is here kept relatively narrow, with the width defined in principle on the thermal expansion of the area. The slots here have a slightly sloping course to impurities, eg. B. by iron or zinc oxide, by a cleaning liquid (eg., Acids) to remove efficiently.

In addition, the slots are preferably introduced eroded such that the slot mouth 10 wider than the slot bottom 11 , so that even in this way a slight cleaning is given.

x

... Tiefe der Schlitze

D

... Dicke der Arbeitsplatte

d

... Dicke des zu kühlenden Bleches

b

... Schlitzbreite

a

... Schlitzabstand

α...

linearer Wärmeausdehungskoeffizient [1/K]

T_Start

... Ausgangstemperatur der Platte (Umgebungstemperatur)

T_Blech

... Ausgangstemperatur des zu kühlenden Bleches

On condition that:

x

... depth of the slots

D

... thickness of the worktop

d

... thickness of the sheet to be cooled

b

... slit width

a

... slot spacing

α ...

linear thermal expansion coefficient [1 / K]

T_Start

... output temperature of the plate (ambient temperature)

T_Blech

... starting temperature of the sheet to be cooled

• 1. 0,1 <= x/D <= 0,9 insbesondere 0,25 <= x/D <= 0,8 insbesondere 0,5 <= x/D <= 0,75
• 2. d/D <= 0,2 insbesondere 0,1
• 3. b/a >= α·(T_Blech – T_Start)/2 d.h. bei z.B.: 800 T_Blech – 20 T_Start (RT)/2 = 390 °C dies mal α, bei Stahl ca. 1·10^–5 [1/K]

it is advantageous if the following conditions are met:

• 1. 0.1 <= x / D <= 0.9, in particular 0.25 <= x / D <= 0.8, in particular 0.5 <= x / D <= 0.75
• 2. d / D <= 0.2, in particular 0.1
• 3. b / a> = α · (T_Blech - T_Start) / 2 ie for example: 800 T_Blech - 20 T_Start (RT) / 2 = 390 ° C this time α, for steel approx. 1 · 10 ^ -5 [1 / K]

Since no cooling takes place in the region of the slot, it is provided as a further condition that b <d / 2.

In the event that two slotted plates 3 . 6 can be used, advantageously, a displacement of the slots of the plates against each other in both directions of Kühlebene done and preferably by half the slot width to allow good cooling or temperature control.

In a further advantageous embodiment (not shown), the plates have 3 . 6 over at least one step or paragraph. Here is the board 2 formed as so-called taylored blank, ie due to different material grades and / or different desired properties, the sheet has different thicknesses over its extension. To compensate for these different sheet thicknesses in terms of height and despite different heights uniform contact of the work surfaces 4 . 7 on the board 2 To ensure the level is provided in the range of the thickness jump of the board.

Of course, this is also possible with more complex shapes and more complex thickness jumps.

An inventive device 1 Of course, you can also use two opposite tool plates 3 and / or two opposite worktops 6 which correspond to the direction of the arrow 5 be guided towards each other and away from each other, leaving a circuit board 2 between the corresponding worktops 6 held in positive engagement with pressure to allow heat transfer from both sides.

Even with a corresponding embodiment with a thickness jump or multiple thickness jumps in taylored blanks and the corresponding steps in the countertops 6 opposite worktops may be formed with the correspondingly extending steps.

In the invention it is advantageous that a global deformation of the worktops previously used by compensation of the voltage in the slots of the worktop is avoided.

In the invention it is also advantageous that the device according to the invention for tempering and in particular cooling hardenable by quench hardening steel blanks a full-surface, traceable positive engagement while a full-surface, traceable heat transfer without distortion of the work surfaces allows.

LIST OF REFERENCE NUMBERS

1

 contraption

2

 Steel sheet metal blank

3

 tool plate

4

 edit page

5

 arrow

6

 countertop

7

 working surface

8th

 print area

9

 slots

10

 slot mouth

11

 slot base

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 2014777 A1 [0008]
• EP 2182082 A1 [0010]
• DE 202013103764 U1 [0011]
• DE 102012110649 B3 [0012]

Claims (18)

A method for tempering steel sheet blanks, wherein steel sheet is removed from a Stahlcoil and cut into blanks, the steel sheet blanks are then heated to a temperature in particular above AC3 of the respective steel material and thus the steel material is partially or completely converted into austenite and then in a press hardening tool in hot Deep-drawn condition and at the same time cooled at a speed above the critical hardening speed such that a quench hardening structure sets in which, after heating above AC3 and before forming and quench hardening, the steel material is tempered and in particular cooled until it has a desired temperature for forming, characterized in that in a, the pressure on the board exerting tool plate ( 3 ) or worktop ( 6 ) in workspaces ( 4 . 7 ) narrow slits are introduced, which is a thermal expansion of the countertops ( 3 . 6 ) forming material without in particular global distortion of the plates ( 3 . 6 ). Method according to claim 1, characterized in that the plates ( 3 . 6 ) is cooled by gas and / or water flow. A method according to claim 1 or 2, characterized in that between the worktop and the tool plate a single or multi-layer sliding and / or insulating layer is arranged. Method according to claim 1, characterized in that the tool plate ( 3 ) is cooled. Method according to one of the preceding claims, characterized in that the sheet steel plate ( 2 ) on one or both sides of plates ( 3 . 6 ) is tempered and / or cooled, the plates ( 3 . 6 ) are arranged so that the slots are arranged offset from each other. Apparatus for tempering, and in particular cooling, sheet steel blanks previously heated to a temperature greater than AC3 and, after being cooled, subjected to a forming step in which they are also quench hardened, in particular apparatus for carrying out the method according to one of Claims 1 to 5 therefrom characterized in that in at least one, the pressure on a board ( 2 ) performing tool plate ( 3 ) or worktop ( 6 ), which on the tool plate ( 3 ) is arranged in the one to be processed board ( 2 ) ( 4 . 7 ) are provided from the surface thereof a plurality of slots to compensate for temperature-induced strains and shrinkages. Apparatus according to claim 6, characterized in that the slots are eroded introduced, wherein the depth of the slots is between 10% and 90% of the plate thickness. Apparatus according to claim 6 or 7, characterized in that the slots over their longitudinal extent have a sloping course and / or the slots of their slot mouth ( 10 ) to the slot bottom ( 11 ) become narrowing or conical. Device according to one of claims 6 to 8, characterized in that with respect to the slot geometry the following applies: 0.1 <= x / D <= 0.9 in particular 0.25 <= x / D <= 0.8, in particular 0.5 <= x / D <= 0.75 where x is the depth of the slot and D is the thickness of the plate ( 3 . 6 ). Device according to one of claims 6 to 9, characterized in that in the slotted plate ( 3 . 6 ): d / D <= 0.2, in particular 0.1 where D is the thickness of the worktop and d is the thickness of the sheet to be cooled. Device according to one of claims 6 to 10, characterized in that: b / a> = α · (T_Blech - T_Start) / 2 ie at eg: 800 T_Blech - 20 T_Start (RT) / 2 = 390 ° C this time α for steel approx. 1 · 10 ^ -5 [1 / K] where b is the slot width, a is the slot spacing, α is the linear thermal expansion coefficient, T_Blech is the starting temperature of the sheet to be cooled and T_Start is the starting temperature of the plates ( 3 . 6 ). Apparatus according to claim 11, characterized in that also applies b <d / 2. Device according to one of claims 6 to 12, characterized in that in the presence of two tool plates ( 3 ) or one of each worktop ( 6 ) an offset of the slots ( 9 ) is present such that the slots of the one plate ( 3 . 6 ) not with the slots of the other plate ( 3 . 6 ) are aligned and preferably offset by half a slot width. Device according to one of claims 6 to 13, characterized in that between the worktop ( 6 ) and the tool plate ( 3 ) an insulating layer and / or sliding layer is present. Apparatus according to claim 14, characterized in that the sliding and / or insulating layer is formed in multiple layers. Device according to one of claims 6 to 15, characterized in that the plates ( 3 . 6 ) is formed with connections for a gas and / or water flow and in particular coolant flow and corresponding holes and / or lines. Device according to one of claims 6 to 16, characterized in that the plates ( 3 . 6 ) is designed for processing of sheets of different thicknesses (taylored blanks) with corresponding steps such that taylored blanks, which have one or more steps or offsets or differences in thickness, can be touched and cooled safely, uniformly and over the entire surface. Device according to one of claims 6 to 17, characterized in that the plates ( 3 . 6 ) is formed of a hot working steel and / or an Ampco alloy or other suitable hot working alloys, wherein an optionally present insulating and / or sliding layer of a bearing bronze, in particular formed with graphite inserts bearing bronze, and / or a ceramic is formed.

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