EP2782689A1

EP2782689A1 - Method and forming tool for hot forming and press hardening work pieces made of sheet steel, in particular galvanized sheet steel

Info

Publication number: EP2782689A1
Application number: EP12778287.8A
Authority: EP
Inventors: Janko Banik; Sascha Sikora; Maria KÖYER; Thomas Struppek
Original assignee: ThyssenKrupp Steel Europe AG
Current assignee: ThyssenKrupp Steel Europe AG
Priority date: 2011-11-23
Filing date: 2012-10-16
Publication date: 2014-10-01
Anticipated expiration: 2032-10-16
Also published as: PL2782689T3; EP2782689B1; MX341647B; CA2856679C; WO2013075888A1; MX2014006178A; DE102011055643A1; ES2569351T3; CN103958087B; JP2014533608A; KR20140094021A; HUE027539T2; CN103958087A; CA2856679A1; RU2606359C2; US9770750B2; US20140311205A1; JP5886977B2; RU2014125268A

Abstract

The invention relates to a method for hot forming and press hardening plate-shaped or preformed workpieces made of sheet steel, in particular galvanized workpieces (1) made of sheet steel, in which the workpiece (1) is heated to a temperature exceeding the austenitizing temperature and subsequently formed and quenched in a cooled forming tool comprising a stamp (2) and a die (3), characterized in that the drawing edge region, which is defined by a positive die radius, of the die (3) used for hot forming and press hardening is provided with a materially bonded coating of a material (6, 6') and/or is provided with an insert (5) having a thermal conductivity that is lower than the thermal conductivity of section (3.1) of the die (3), which is adjacent to the drawing edge region, by at least 10 W/ (m * K), which section comes into contact with the workpiece (1) during hot forming and press hardening of the same. The surface of the material (6; 6') applied to the drawing edge region and facing the workpiece (1) or the surface of the provided insert (5) has a lateral dimension extending across the drawing edge (7), which is in the range of 1.6 times to 10 times the positive die radius of the die (3). The invention also relates to a corresponding forming tool.

Description

Method and molding tool for hot forming and press hardening of workpieces made of sheet steel, in particular galvanized

Workpieces made of sheet steel

The invention relates to a method for hot forming and press hardening of plate-shaped or preformed workpieces made of sheet steel, in particular galvanized workpieces

Sheet steel in which the workpiece is at a temperature

heated above the Austenitisierungstemperatur and

then in a cooled forming tool, the

at least one stamp and at least one die

has, is reshaped and quenched. Furthermore, the invention relates to a forming tool for hot forming and

Press hardening of plate-shaped or preformed workpieces of sheet steel, in particular galvanized workpieces of sheet steel, with at least one punch and a

Stamp associated die, wherein the punch and / or the die cooling channels for passing a cooling fluid

exhibit .

With respect to the hot forming and press hardening of work ^¬ pieces made of sheet steel, devices are known comprising at least two tool halves, which are formed in regions, such that they have different thermal conductivity characteristics, which are used to adjust locally different strength properties in the component to be manufactured. The method carried out with these devices will be familiar to those skilled in the art The term "Tailored-tempering." A corresponding device is for example from the

DE 10 2009 018 798 AI known. Furthermore, it is known to increase the dimensional and accuracy of fit of formed components in that the ^■

Production used tool halves in the range of

Rounding the workpiece have positive radii and form air gaps in the opposite areas, wherein adjacent to the air gaps projections are formed such that a distortion-free terminals is possible. This also allows different degrees of hardness in the component

be set. A corresponding device for

Manufacture of hardened components made of sheet steel is described in DE 10 2004 038 626 B3.

Investigations have shown that during the hot forming of galvanized steel blanks in conventional casting tools, cracks sometimes occur in the zinc coating. The cracks can continue into the board, which can lead to premature component failure.

The present invention has for its object to provide a method or a Ümformwerkzeug of the type mentioned, which improves the flow properties for steel materials during hot working, so that the risk of occurrence of cracks in the hot forming of workpieces made of sheet steel, especially galvanized steel blanks

is significantly reduced. This object is achieved by a method having the features of claim 1 or by a forming tool having the features of claim 8. Preferred and advantageous embodiments of the invention are specified in the subclaims.

According to the invention, the die used for hot forming and press hardening is coated in its defined by a positive drawing radius Ziehkantenbereich with material and / or provided with at least one insert which has a thermal conductivity which is lower by at least 10 W / (m * K) than the thermal conductivity the portion of the die adjacent the drawing edge region which contacts the workpiece during hot working and press hardening of the workpiece. The applied in the drawing edge region material or arranged there insert part, which according to ^¬ fiction, has a relatively low thermal conductivity, · is formed so that its surface facing the workpiece has a extending over the drawing edge cross-dimension, which is in the range of 1.6 times up to 10 times,

preferably in the range of 1.6 times to β times the positive draw radius of the die. The transverse extent (transverse dimension) of a relatively low thermal conductivity

having arranged in the drawing edge region material or insert is so limited and relatively small.

In particular, in the drawing edge region of the die defined by a positive drawing radius, the coated steel sheet (workpiece) to be formed becomes highly plastic

Subjected to deformations. Due to the action of the tool Stamp undergoes the workpiece in this area first a compressive stress, which transforms during the continued closing movement of the forming tool in a tensile stress. Due to the high temperature difference between the workpiece and the forming tool, the local

Flow properties of the workpiece in a conventional forming tool, especially in the drawing radius of the die of a conventional forming tool adversely affected, which often leads to cracks in the coating, for example

Zinc layer comes. With increasing sheet thickness and in

Dependence of the complexity of the geometry of the

can be produced different components

Form cracks that extend into the sheet of the

coated component can extend.

According to the invention, the material applied in the drawing edge region, for example by coating, having a relatively low thermal conductivity, or the insert part having a relatively low thermal conductivity, is dimensioned to ensure that the component produced by hot forming and press-hardening is essentially completely martensitic Structure has. By the pulling edge of the die., I. the relatively low thermal conductivity material or

The insert-influenced part of the press-hardened component may have a lower hardness than another part or the remaining part of the component, but this so influenced part of the press-hardened component according to the invention always still has a hardness above a required minimum hardness, the one

martensitic structure corresponds. In this way, cracks in the coating, for example in a Zinc layer, as well as in the corresponding coated sheet avoided or significantly reduced at least crack depths in the coating or the coated sheet metal. The stresses occurring in the hot forming of the coated, eg galvanized workpiece (steel sheet) and

Strains and the hardening occurring in the forming process are reduced by the reduced heat or temperature loss in comparison to that in a conventional tempered forming. This also reduces or prevents any local material failure.

By the present invention, therefore, the flow properties of workpieces made of sheet steel during the

Hot forming improves and thus eliminates the risk of cracking during hot forming of workpieces

Sheet steel, preferably galvanized steel plates significantly reduced. In particular, by the present invention, the feasibility of components that a complex

have three-dimensional shape and made of coated, e.g. galvanized steel sheet are improved.

A preferred embodiment of the solution according to the invention provides that the thermal conductivity of the arranged in the drawing edge area insert or applied

Material is less than 40 W / (m * K), preferably less than 30 W / (m * K), more preferably less than 20 W / (m * K). As a result, the heat or temperature loss during hot working of the workpiece is advantageous

reduced and the forming behavior of the workpiece

improved accordingly. A further advantageous embodiment of the solution according to the invention is characterized in that a heat insulating layer is or is arranged between the insert part and the die. In this way, the heat or temperature loss during the hot working of the workpiece can be further reduced. In particular, this embodiment makes it possible to use an insert which is made of a particularly wear-resistant material, but which has a relatively high thermal conductivity, wherein the heat insulating layer, compared to the insert edge forming part of the insert no high mechanical

Stress, in particular no high frictional stress is exposed, may consist of a heat insulating material, for example plastic or wood material, with low wear resistance.

According to a further advantageous embodiment of

According to the invention, it is provided that the insert part has a projection extending over the inner circumference of the die and / or opposite to the edge of the cavity adjacent to the cavity of the die. By this projection representing a local increase, the heat dissipation from the workpiece to be reshaped can be more effectively reduced before the drawing radius.

A further advantageous embodiment of the solution according to the invention is characterized in that the material applied in the drawing edge region of the die by deposition welding, preferably laser deposition welding on the

Matrix is applied. In this way, the heat conductivity in the pulling edge region of the

Reduce matrix reliably. The one relatively small Thermal conductivity having material application can be replaced inexpensively by build-up welding, preferably laser deposition welding, if this is required due to a wear-related wear (removal).

A further advantageous embodiment of the solution according to the invention is characterized in that the drawing edge region of the die by means of integrated in the die

Heat source or a heating fluid channel is locally selectively heated. As a result, the heat dissipation from the workpiece to be formed can be significantly reduced and thus the flow properties of the steel material can be improved during hot forming. It is also within the scope of the present invention to combine several of the aforementioned or all the aforementioned embodiments of the solution according to the invention.

Hereinafter, the invention will be described with reference to a plurality

Exemplary embodiments illustrative drawing explained in more detail. They show schematically:

Fig. 1 shows a portion of an inventive

Forming tool in sectional view;

Fig. 2 shows a section of another invention

Forming tool in sectional view;

Fig. 3 is a sectional view of a pulling edge

comprehensive section of a forming tool according to the invention with a in the drawing edge region arranged, a relatively low thermal conductivity having BeSchichtung;

Figures 4 and 7 are each a sectional view of a

Pulling edge comprehensive section of a forming tool according to the invention with applied in the drawing edge region by build-up welding material, each having a relatively low thermal conductivity; and

Figures 5, 6 and 8 are each a sectional view of a

Pulling edge comprehensive section of a forming tool according to the invention with an arranged in the drawing edge region insert part, which has a relatively low thermal conductivity.

FIGS. 1 and 2 each show sections of cooled forming tools for hot-forming and press-hardening a plate-shaped or preformed workpiece 1 made of sheet steel, in particular a galvanized workpiece made of sheet steel. The reference numeral 2 is a stamp and the reference numeral 3 is a die (die) of the respective forming tool designated. In addition, the forming tool shown in FIG. 1 and / or FIG. 2 may optionally have a holding-down device (blank holder) which presses the workpiece 1 against the die 3 during the forming process. Preferably, however, the forming tool according to the invention is designed as a blank holder (low-holder) forming tool.

Die (die) 3 contains a cavity 4, in which the punch 2 during forming or deep drawing of the workpiece. 1 penetrates. In Figures 1 and 2 is the respective

Forming tool each shown in the closed state with the workpiece 1 formed therein. In the die 2 and / or the die 3, cooling channels (not shown) for passing a cooling fluid are provided near the forming die surface. Before it is placed in the open forming tool, the workpiece 1 to be formed is first heated to a target temperature, preferably to a temperature above the austenitizing temperature, and then shaped and quenched in the cooled forming tool.

The temperature of the heated plate-shaped or preformed workpiece 1 is preferably kept as high as possible prior to the forming in order to achieve an improvement in the flow properties of the workpiece 1 or a reduction of the stresses and / or strains during the forming process. This can be influenced, for example, by the selected height of the heating temperature and / or by short transfer times, ie short handling times between the heating device (not shown), for example a continuous furnace, and the start of the forming. The forming tool according to the invention is characterized by an optimized heat transfer coefficient. As a result, too rapid local cooling of the heated workpiece 1 (for example, the galvanized steel plate) is prevented after positioning and during the forming in the tool. According to the invention, at least the die 3 is optimized with regard to the heat transfer coefficient. For this purpose, the die 3 is in its drawing edge defined by a positive drawing radius. Area coated with material cohesively and / or provided there with at least one insert part 5, which has a thermal conductivity which is at least 10 W / (m * K) is lower than the thermal conductivity of the drawing edge region adjacent section 3.1 of the die 3, the during hot working and press hardening of the workpiece comes into contact with the same. The means with comparatively low thermal conductivity are dimensioned such that it is furthermore ensured that a completely martensitic microstructure sets in the formed component (work piece) 1 after completion of the quenching process (press hardening), whereas the workpiece region affected by the drawing edge region executed according to the invention has a Reduction in hardness, but must be within the required minimum hardness, may have, whereby cracks in the workpiece 1 can be avoided or crack depths can be reduced. The workpiece 1 facing surface of the applied in the drawing edge region material 6 (see Fig. 3) or arranged insert part 5 therefore has according to the invention over the drawing edge 7 extending transverse dimension, which is in the range of 1.6 times to 10 times the positive Drawing radius of the die 3 is located.

In the exemplary embodiments illustrated in FIGS. 1 and 2, the respective die 3 has at least one insertion part 5 in its pulling edge region defined by a positive drawing radius, whose thermal conductivity is preferably less than 40 W / (m * K), particularly preferably less than 30 W / ( m * K). The at least one insert part 5 is annular or strip-shaped and inserted into a formed in the drawing edge region of the die 3 recess 3.2. In the figures 3 to 8 further embodiments of a forming tool according to the invention, preferably a die 3 are shown schematically. In the exemplary embodiment shown in FIG. 3, a die 3 serving for hot-forming and press-hardening is coated, in its drawing edge region defined by a positive drawing radius, with material 6 which has a relatively low thermal conductivity. The material (coating) 6 is preferably ceramic, for example alumina or zirconia. The selective coating of the drawing edge region can be effected, for example, by flame spraying, in particular powder flame spraying or wire flame spraying, or by arc spraying or plasma spraying.

The transverse dimension of extending over the pulling edge 7

Coating 6 is, for example, in the range of 1.6 times to 4 times, preferably in the range of 1.6 times to 2 times, the positive drawing radius of the die 3. The coating 6 is or can face the adjacent surface 3.1 slightly protrude the die 3, for example, about 0.25 mm to 0.5 mm or more.

In the illustrated in Fig. 4 embodiment, the serves for hot forming and press hardening die 3 is provided in the edge region with a drawing produced by build-up welding material application 6 ', which has a relatively low thermal conductivity ^¬. Before the build-up welding is in the drawing edge region of the die 3, for example by machining a transverse to the drawing edge extending

Well 3.3 made. In this recess (recess) 3.3 is then by deposition welding material 6 'with arranged relatively low thermal conductivity. This application material 6 'may be, for example, chromium steel, titanium or high alloy steel, such as X5CrNil8-10, which has a thermal conductivity of about 30 W / (m * K) or less than 30 W / (m * K ) exhibit. The applied by contract ^¬ welding on the handle edge portion of material 6 'is so far applied and subsequently removed by milling or grinding, that it is substantially flush with the surface of the die 3 closes or in the surface of 3.1 low- fügig protruding from the surface 3.1 of the die. 3

The die 3 shown in a section in FIG. 5 substantially corresponds to the exemplary embodiment shown in FIG. Again, in the pulling edge region of the die 3 is a strip-shaped insert member 5 with relatively less

Thermal conductivity arranged. The insert 5 consists for example of ceramic, preferably of aluminum oxide (Al 2 O 3) or zirconium oxide. The outer edge of the insert part 5 forming the pulling edge region terminates substantially flush with the surface 3.1 of the die 3.

FIG. 5 also shows a further option or alternative for reducing the heat loss of the heated workpiece. This alternative or additional option is that in the die 3, a heat source or a heating channel leading channel 8 is integrated, by means of which the drawing edge region of the die 3 is locally selectively heated. According to a further preferred embodiment, it is provided that the heat source, for example in the form of one or more electrical heating wires, or the channel 8 carrying a heating fluid is integrated in the insert part 5 forming the drawing edge region. The illustrated in Fig. 6 embodiment differs from that shown in Figures 1, 2 and 5 ^¬ execution examples in that a heat insulating layer 9 is disposed between the insert 5 and the die 3. The heat insulating layer 9 is single-layered or multi-layered and consists for example of plastic

and / or mineral wool. In the embodiment shown in FIG. 7, the die 3 used for hot forming and press hardening in the drawing edge region is again provided with a material application 6 'produced by build-up welding, which has a relatively low thermal conductivity. In contrast to the embodiment according to FIG. 4, however, the material application 6 'is designed such that it has a position opposite to that of FIG

Inner circumference of the die 3 or with respect to the adjacent to the cavity 4 of the die 3 edge peripheral surface projecting projection 6.1. Through this local increase or

this local projection 6.1 from a one relatively small

Thermal conductivity material having the heat dissipation from the heated workpiece 1 is reduced. In addition to this material order 6 'can in the matrix turn a

Heat source or a heating fluid leading channel 8 may be integrated, by means of which / / the drawing edge region of the die 3 can be locally selectively heated.

The embodiment shown in FIG. 8 differs from the exemplary embodiment according to FIG. 6 in that the insert part 5 has a relative to the inner circumference of the cavity 4 of the die 3 or opposite to the cavity 4

adjacent edge peripheral surface projecting projection 5.1 having. The reference numeral 9 again denotes a disposed between the insert part 5 and the die 3 heat insulating layer. The embodiment of the present invention is not on the above-described and / or in the drawing

limited embodiments shown. On the contrary, numerous variants or modifications are conceivable which make use of the invention specified in the appended claims, even if the design deviates from the exemplary embodiments. Thus, for example, in addition, the stamp and / or possibly also the sheet holder (Nieder ^¬ holder) with means 5, 5.1, 6, 6 ', 6.1 and / or 9 are provided with low thermal conductivity ^¬ to optimize the heat transfer coefficients.

Claims

Paten tan sayings

Process for hot forming and press hardening

plate-shaped or preformed workpieces (1) made of sheet steel, in particular galvanized workpieces (1) made of sheet steel, in which the workpiece is heated to a temperature above the austenitizing temperature and then placed in a cooled forming tool which has at least one punch (2) and at least one die (3 ), is formed and quenched, characterized in that the die (3) used for hot forming and press hardening is characterized by a positive

Drawing radius defined drawing edge area with material (6,

6') Cohesively coated and/or provided there with at least one insert part (5) which has a thermal conductivity that is at least 10 W/(m*K) lower than the thermal conductivity of the section (3.1) of the die adjacent to the drawing edge area (3), which comes into contact with the workpiece (1) during forming and press hardening, the surface of the material (6; 6') applied in the drawing edge area or the insert part (5) facing the workpiece (1) being positioned over the Drawing edge

(7) has an extending transverse dimension that is in the range of 1.6 times to 10 times the positive drawing radius of the die (3).

Method according to claim 1,

characterized in that the thermal conductivity of the insert part (5) arranged in the drawing edge area or applied material (6, 6') is less than 40 W/(m*K), preferably less than 30 W/(m*K).

Method according to claim 1 or 2,

characterized in that the at least one

Insert part (5) is strip-shaped and inserted into a recess (3.2) formed in the drawing edge area of the die (3).

Method according to one of claims 1 to 3,

characterized in that a thermal insulating layer (9) is arranged between the insert part (5) and the die (3).

Method according to one of claims 1 to 4,

characterized in that the insert part (5) is opposite the inner circumference of the die (3) and/or

compared to the cavity (4) of the matrix (3)

adjacent peripheral edge surface (3.1) has a projecting projection (5.1).

Method according to one of claims 1 to 5,

characterized in that the material (6') applied in the drawing edge area of the die (3) passes through

Deposition welding is applied to the die (3).

Method according to one of claims 1 to 6,

characterized in that the drawing edge area of the die (3) is heated by means of a heat source integrated in the die or a channel carrying a heating fluid

(8) is locally selectively heated. Forming tool for hot forming and press hardening

plate-shaped or preformed workpieces (1) made of sheet steel, in particular galvanized workpieces (1) made of sheet steel, with at least one stamp (2) and a die (3) assigned to the stamp, the stamp (2) and/or the die (3) Have cooling channels for passing a cooling fluid through, characterized in that the die (3) is filled with material (6; 6') in its drawing edge area defined by a positive drawing radius.

Cohesively coated and/or provided there with at least one insert part (5) which has a thermal conductivity which is at least 10 W/(m*K) lower than the thermal conductivity of the section (3.1) of the die (3) adjacent to the drawing edge area. , which comes into contact with the workpiece (1} during hot forming and press hardening, the surface of the material (6; 6') or inserted part (5) applied in the drawing edge area facing the workpiece (1) extending over the drawing edge (7 ) has an extending transverse dimension that is in the range of 1.6 times to 10 times the positive drawing radius of the die (3).

9. Forming tool according to claim 8,

characterized in that the thermal conductivity of the insert part (5) or applied material (6, 6') arranged in the drawing edge area is less than 40 W/(m*K), preferably less than 30 W/(m*K).

10. Forming tool according to claim 8 or 9,

characterized in that the at least one

Insert part (5) is strip-shaped and in an in Recess (3.2) formed in the drawing edge area of the die (3) is inserted.

11. Forming tool according to one of claims 8 to 10,

Forming tool according to one of claims 8 to 11,

compared to the cavity (4) of the matrix (3)

adjacent peripheral edge surface (3.1) has a projecting projection (5.1).

Forming tool according to one of claims 8 to 12,

characterized in that the material (6') applied in the drawing edge area of the die (3) is applied to the die (3) by deposition welding.

Forming tool according to one of claims 8 to 13,

characterized in that there is one in the die (3).

Heat source or a channel carrying heating fluid (8)

is integrated, by means of which the drawing edge area of the die (3) can be locally selectively heated.