WO2018138076A1 - Outil de pressage pour le durcissement à la presse et son utilisation pour la production de composants en tôle durcie à la presse - Google Patents

Outil de pressage pour le durcissement à la presse et son utilisation pour la production de composants en tôle durcie à la presse Download PDF

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Publication number
WO2018138076A1
WO2018138076A1 PCT/EP2018/051548 EP2018051548W WO2018138076A1 WO 2018138076 A1 WO2018138076 A1 WO 2018138076A1 EP 2018051548 W EP2018051548 W EP 2018051548W WO 2018138076 A1 WO2018138076 A1 WO 2018138076A1
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WO
WIPO (PCT)
Prior art keywords
shell
pressing tool
core
forming
cooling
Prior art date
Application number
PCT/EP2018/051548
Other languages
English (en)
Inventor
Paul ÅKERSTRÖM
Original Assignee
Opm Innovation Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Opm Innovation Ab filed Critical Opm Innovation Ab
Publication of WO2018138076A1 publication Critical patent/WO2018138076A1/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
    • B21D22/02—Stamping using rigid devices or tools
    • B21D22/022—Stamping using rigid devices or tools by heating the blank or stamping associated with heat treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D37/00—Tools as parts of machines covered by this subclass
    • B21D37/16—Heating or cooling

Definitions

  • the present invention concerns a pressing tool for press hardening.
  • the invention also refers to the use of such pressing tool.
  • Press hardening or hot stamping as forming method has since its introduction in the industry grown in popularity and is clearly one of the most promising methods, especially in automotive industry, for reducing the body weight in constructions. A great improvement has been achieved during the last decades but still there is a lot to do. Some car manufacturer's report that up to 20% of the body in white components are today replaced by press hardened products but that up to over 40% could be expected in the future.
  • a typical pressing tool for press hardening comprises a first and a second die, each having a forming surface.
  • the dies are provided with a cooling system constituted by a plurality of bores receiving a flow of cooling medium, typically water. When moved together, the two forming surfaces together define a forming cavity.
  • the bores are typically drilled and to avoid deflection of the drills, and due to the hardness of the tooling material, the die is typically divided into a plurality of blocks to be mounted together to thereby form the die.
  • the intersections between the mating bores are provided with sealings.
  • the prior art tooling technology involves a number of problems.
  • the manufacturing of the pressing tools is complex and time consuming.
  • due to the drilling providing more or less straight extensions of the cooling channels it is hard to optimize the cooling efficiency.
  • the cooling channels should preferably be arranged on a certain distance to the forming surface to protect the sealings from being damaged by the heat and also to permit milling to refurbish the surface when worn.
  • One object of the present invention is to provide a pressing tool for press hardening allowing a simplified manufacturing process and a reduced complexity of the tool design.
  • the tool design should allow an enhanced and even optimized cooling capacity to thereby allow production of more complex components with improved final shape accuracy.
  • a pressing tool for press hardening comprising a first die and a second die, the first and second dies having a forming surface together defining a forming cavity, at least one of said first and second dies comprising a core forming a body of a metallic material having a heat conductivity of at least 1 10 W/mK, and a shell connected to the core and forming the forming surface of said at least one first and second die, the shell being formed of a material having a heat conductivity less than 100 W/mK.
  • a typical tool steel providing good wear resistance usually has a heat conductivity within the range of 25 to 80 W/mK, and even more typically in the range 30-50 W/mK.
  • the present invention also enables cooling channel placements at a greater distance from the forming cavity combined with an improved cooling capacity.
  • a separate heat sink such as a cooling block, could be used instead of, or in combination with, drilled cooling channels in the core.
  • Examples of core materials are: Copper and its alloys, such as brass, Aluminum and its alloys, Magnesium and its alloys and Silver.
  • the heat conductivity varies greatly depending of type of material.
  • Copper has a heat conductivity of about 395 W/mK
  • Aluminium a heat conductivity of about 200 W/mK
  • brass a heat conductivity in the range of 1 10-300 W/mK depending on the alloy.
  • the shell as such may be made of any suitable tool steel. As given above, tool steels providing good wear resistance, usually have limited heat conductivities within the range 25 to 80 W/mK. A typical range is 30-50 W/mK.
  • the core may on its surface facing the shell be provided with a surface pattern providing a surface enlargement.
  • the surface enlargement may be evenly distributed across the interface between the core and the shell or be locally arranged.
  • the surface enlargement provides an improved heat transfer.
  • the surface enlargement may be provided by different matching patterns on both the shell and the core.
  • the type of pattern may be of different kind, e.g. sinusoidal with varying amplitude and periodicity.
  • a surface enlargement pattern may be used in combination with an overall, global thickness reduction of the shell to further increase the cooling rate at specific locations along the forming cavity. This may further shorten the cooling time- temperature evenness of the workpiece.
  • the pattern can be formed by mechanical machining, such as milling, casting or by additive methods such as 3D-printing.
  • the core may comprise integrated cooling elements or heating elements.
  • the core can comprise integrated cooling elements, or channels, with larger dimensions and less in number than in conventional tool steel parts. This simplifies both the manufacturing and assembly of the tool parts.
  • the core can also be equipped with integrated heating elements. Heated tool parts can be used when producing components with customized mechanical properties during manufacturing. The customized properties are obtained by controlling the cooling rate.
  • the shell may be made of a pressed, casted or machined cap.
  • machining can be used to manufacture the shell.
  • Another possible method to manufacture the shell is by press forming of a sheet, with possible following machining, such as milling.
  • the shell can be formed in the cold or hot state. Compared to conventional tool manufacturing techniques, much less material is used.
  • the shell may be provided by a three-dimensional printing technology.
  • the shell may be manufactured by three-dimensional printing or other additive manufacturing technique. It can be manufactured as a separate sub tool part. It may also be manufactured by first printing the body in one material followed by printing the shell in a steel material directly on the core. This manufacturing technique provides a great flexibility in manufacturing and tool design.
  • the shell may comprise a plurality of zones as seen across its surface extension, each zone having a thickness adapted to the expected cooling rate of the part to be formed in said pressing tool. To optimize the evenness of the cooling rate of the part or workpiece formed, numerical simulations can be used. When forming a part or workpiece with areas along its surface extension with a reduced cooling rate, the shell thickness in such area can be reduced and thereby make the cooling rate and the final temperature even across the whole part.
  • the shell may comprise at least two zones as seen across its surface extension, said at least two zones being formed of materials with different heat conductivity. Using at least two zones with different heat conductivity gives the advantage to optimize the evenness of the formed parts cooling rate.
  • the different zones may be welded together or mounted separately.
  • the core may be connected to the shell by soldering and/or bolting. These connections make it easy to exchange the shell when worn out.
  • At least one of said dies on its surface facing away from the shell may be provided with a heat sink.
  • the heat sink(s) may be placed at a distance far exceeding the distance at which conventional cooling channels may be placed from the forming surface.
  • the number of cooling channels may be reduced in number.
  • the size of used cooling channels may be larger in size, e.g. diameter, than conventional employed.
  • the heat sink(s) may be designed as simple "blocks" with drilled coarse cooling channels.
  • the material in the heat sink may be of high conductivity type or be made of conventional steel/tool steel.
  • the invention refers to the use of a pressing tool according to any of claims 1 -9 in the production of press hardened sheet metal components.
  • Fig. 1 discloses a typical pressing tool according to prior art.
  • Fig. 2 discloses highly schematic a pressing tool according to the present invention.
  • Fig. 3 discloses highly schematic optional features of a pressing tool according to the present invention.
  • the pressing tool 100 comprises an upper die 1 attached to an upper plate 2 or directly to a pillar stand (not shown) and a lower die 3 attached to a lower plate 4 or directly to a pillar stand (not shown).
  • the upper die 1 is arranged to be given a driving motion from a driving source (not shown).
  • the upper die 1 can be displaced in the y-direction (up and down direction) indicated by an arrow in Fig. 1 .
  • a flat plate shaped metal workpiece 5 is heated to 800 -1000 °C by a heating device, e.g. furnace (not shown) and after heating moved to lay between the upper and lower dies 1 , 3.
  • a heating device e.g. furnace (not shown)
  • the upper die 1 can be lowered.
  • the surface of the upper die 1 comes into contact with the metal workpiece 5 and the upper die 1 lowers further, the upper die 1 presses the workpiece 5.
  • the initially flat workpiece 5 is deformed along the shapes of the upper die 1 and the lower die 3.
  • a convex part 1 a of the upper die 1 enters into a concave part 3a of the lower die 3.
  • the upper die 1 is displaced to a bottom end point and is held in this state for a predetermined period of time, by which the workpiece 5 is formed into a predetermined part.
  • the formed part is cooled down through contact with the colder upper and lower dies 1 , 3, whereby it reaches desired final mechanical properties.
  • the upper and lower dies 1 , 3 are commonly water cooled via drilled holes or channels 6 placed in the vicinity of the forming cavity of the upper and lower dies 1 , 3.
  • the diameters of the drilled holes or channels 6 are usually in the range of 5 - 10 mm.
  • each hole of channel 6 is surrounded by a cavity 7 adapted to receive a sealing 8, such as a rubber O-ring, which prevents water leakage.
  • a sealing 8 such as a rubber O-ring
  • the material used for the upper and lower dies 1 , 3 are tool steels aimed for hot forming applications providing a compromise between wear resistance and heat conductivity.
  • Tool steels providing good wear resistance usually have limited heat conductivities within the range 25 to 80 W/mK. A typical range is 30-50 W/mK.
  • the pressing tool 200 has the same overall design as a prior art pressing tool, i.e. it comprises an upper die 20 attached to an upper plate 21 or directly to a pillar stand (not shown) and a lower die 22 attached to a lower plate 23, or directly to a pillar stand (not shown).
  • the upper die 20 is arranged to be given a driving motion from a driving source (not shown).
  • At least one of the upper and lower dies 20, 22 comprises a core 24.
  • both the upper and lower dies 20, 22 do each comprise a core 24.
  • the core 24 acts as a support for a shell 25 to be described below.
  • the core 24 consists of a high conductivity metallic material.
  • high conductivity we here refer to materials providing a heat conductivity of at least 1 10 W/mK.
  • Materials providing this level of heat conductivity are e.g. Copper, Aluminum, Magnesium and Silver, and alloys based on these metals.
  • the heat conductivity varies greatly depending of type of material.
  • Copper has a heat conductivity of about 395 W/mK
  • Aluminium a heat conductivity of about 200 W/mK
  • brass a heat conductivity in the range of 1 10-300 W/mK depending on type of alloy.
  • the core 24 provides the pressing tool 200 with a high cooling capability due to its high conductivity properties.
  • the core 24 may be manufactured by machining, e.g. milling, from a billet, by forging, casting or by three-dimensional printing technology (additive manufacturing). Combinations of the different manufacturing techniques are also possible, followed by machining of its surfaces to reach desired tolerances and surface finish.
  • the core 24 is covered by a shell 25.
  • the shell 25 forms a cap having a geometry defining the actual forming cavity and thereby the surface that during operation is arranged to be in direct contact with the part to be formed. Accordingly, when the upper and lower dies 20, 22 are moved together, the shells 25 of the upper and lower dies 20, 22 together define a forming cavity.
  • the shell 25 can be manufactured by pressing, casting, three- dimensional printing technology or by machining. When using three- dimensional printing technology, the shell 25 can be directly printed on its respective core 24 or on a temporary support. In the latter case, the thus formed shell 25 is later transferred and joined to the core 24.
  • the shell 25 may be subjected to optional heat treatments and/or surface treatments to further improve the mechanical material strength and wear resistance.
  • Final machining such as milling and/or grinding, may be applied to obtain desired tolerances and surface finish.
  • the material of the shell 25 is a tool steel capable of providing high mechanical strength, ductility and wear resistance in combination with a heat conductivity less than 100 W/mK. Tool steels providing good wear
  • resistance usually have limited heat conductivities within the range 25 to 80 W/mK.
  • a typical range is 30-50 W/mK.
  • the shell 25 is provided with a uniform thickness t.
  • the shell 25 and core 24 are preferably assembled by screwing.
  • the screws (not disclosed) may pass through drilled holes extending from the bottom of the core 24 to the top of the said core into threaded holes in the shell 25.
  • the screws are tightened to a specified tension so that adequate, even contact pressure between the core 24 and shell 25 is obtained.
  • Thermal interface materials may be arranged to further enhance the heat transfer between the core 24 and the shell 25.
  • the thermal interface material may be placed in the interface between the core 24 and shell 25 and aims to fill a potential gap formed due to the randomly distributed asperities on interface surfaces between the core 24 and the shell 25.
  • the interface material may be designed to deform and adjust itself to the roughness of the surfaces and thereby increase the real contact area of the interface and consequently increase the thermal contact conductance, i.e. heat transfer of the interface.
  • Interface material can also be applied between the core 24 and a heatsink (to be described below) to further improve the cooling capability.
  • the pressing tool may comprise a heatsink 26 being placed in connection to the respective core 24 and act as a main cooling element for the shell 25 and the core 24 transporting away the heat that is emitted from the formed part during cooling thereof.
  • the heatsink 26 is a sheet or block provided with a thickness sufficiently large to contain drilled cooling channels 27. Since the channels 27 are arranged in the heatsink 26, their extension and size do not interfere with the actual forming surface or the available volume of the core 24.
  • the material used for the heatsink 26 can with advantage be of high conductivity type such as Copper, Brass, Aluminum, Aluminum alloys or high conductivity steel.
  • high conductivity steel the same high strength and wear resistance as for the material of the shell 25 is not needed. Thereby there are more steel candidates to select from.
  • Copper or Copper alloys is preferred.
  • Manufacturing of the heatsink 26 can preferable be through machining of a thick hot rolled sheet or casted body with appropriate initial dimensions.
  • the heatsink 26 can be mounted to one or both of the cores 24 of the upper and lower dies 20, 22 depending on the particular need and design of the cores 24.
  • a pressing tool 200' for press hardening according to the invention is disclosed.
  • the purpose of this illustration is to disclose a number of optional features that can be applied to the inventive concept, either alone or in combination. Accordingly, the features to be described below may be optionally applied to the pressing tool 200 of Fig. 2.
  • the upper die 20' is disclosed.
  • the upper die 20' has the overall general design as previously described with reference to Fig. 2, i.e. it comprises a core 24', a shell 25' and a heatsink 26'.
  • the core 24' and the shell 25' are on their mating interface surfaces provided with complementary surface patterns 30a, 30b providing a surface enlargement.
  • the surface pattern 30a arranged on the surface of the core 24' adapted to face the shell 25' corresponds to the surface pattern 30b arranged on the shell 25' and which is adapted to face the core 24'.
  • the surface patterns 30a, 30b increase heat conduction between the shell 25' and the core 24' by providing a surface enlargement in the interface.
  • the surface pattern 30a, 30b can cover the whole interface between the shell 25' and the core 24' or only a part thereof.
  • the core 24' may comprise integrated cooling elements and/or heating elements 31 .
  • Cooling elements 31 may be in the form of drilled holes or channels 32 adapted to be connected to a fluid flow, or cooling elements which are introduced during casting or during manufacturing of the core 24'.
  • the cooling or heating elements 31 may be provided during manufacturing by using direct metal printing technology.
  • the heating elements 31 within the core 24' can be used to maintain certain areas of the core 24' at elevated temperatures to reduce and better control the hardness of the parts to be formed by using the pressing tool 200'. This may be desired e.g. in order to provide deformation zones in parts to be used in crash applications.
  • the heating elements 31 can be inserted into the drilled holes or channels 32 in the core 24' or be arranged during casting of the body 24'.
  • the position and number of cooling elements and/or heating elements 31 are determined by the complexity and desired function of the part to be formed by using the pressing tool 200'.
  • the position and number of cooling and/or heating elements can be determined and also optimized by numerical simulations, e.g. by using the Finite Element Method.
  • the shell 25' may comprise a plurality of zones 33a, 33b as seen across its surface extension, each zone 33a, 33b having a thickness ta, tb adapted to the expected cooling rate of the part to be formed in said pressing tool 200'.
  • the shell thickness t may be adapted to provide an even cooling rate of the part to be formed, meaning that the shell thickness t may be reduced in areas where the contact situation is one sided, e.g. close to a radii or where the contact between part to be formed and the shell 25' exhibits a low surface pressure when the upper die 20' during operation of the pressing tool 200' has reached its bottom end point in view of a mating lower die (not shown).
  • the thickness t of the shell 25' as seen across its surface extension can be determined by numerical simulations, e.g. by using the Finite Element Method in order to provide an even cooling rate and consequently even final temperature distribution of the formed part when removed from the forming tools.
  • the shell 25' may comprise at least two zones 35a, 35b as seen across its surface extension, said at least two zones 35a, 35b being formed of materials with different heat conductivity.
  • a shell 25' consisting of different materials or alloys enable an alternative way to control the cooling rate and final temperature of the part to be formed. This can also be in combination with adapted thicknesses t of the shell 25' across its surface extension.
  • the different zones 35a, 35b may be joined, e.g. by welding, manufactured by three-dimensional printing technology with different materials or mounted as separate parts, each consisting of different materials, to the core.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Mounting, Exchange, And Manufacturing Of Dies (AREA)

Abstract

La présente invention concerne un outil de pressage (200, 200') pour le durcissement à la presse. L'outil de pressage comprend une première matrice (20) et une seconde matrice (22), les première et seconde matrices (20, 22) ayant une surface de formation respective définissant conjointement une cavité de formation. La première et/ou la seconde matrice (20, 22) comprennent un noyau (24) formant un corps d'un matériau métallique ayant une conductivité thermique d'au moins 110 W/mK, et une coque (25) raccordée au noyau (24) et formant la surface de formation desdites première et seconde matrices (20, 22). La coque (25) est fabriquée dans un matériau ayant une conductivité thermique inférieure à 100 W/mK.
PCT/EP2018/051548 2017-01-26 2018-01-23 Outil de pressage pour le durcissement à la presse et son utilisation pour la production de composants en tôle durcie à la presse WO2018138076A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE1750062 2017-01-26
SE1750062-0 2017-01-26

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WO2018138076A1 true WO2018138076A1 (fr) 2018-08-02

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110947853A (zh) * 2019-10-16 2020-04-03 马春江 一种基于加热冲压的高精度凸部的加工方法

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2335842A2 (fr) * 2009-12-16 2011-06-22 Benteler Automobiltechnik GmbH Procédé de fabrication d'un outil de formage à chaud et outil de formage à chaud doté d'une protection contre l'usure
EP2851138A1 (fr) * 2013-09-18 2015-03-25 Benteler Automobiltechnik GmbH Outil de formage à chaud partiellement refroidi
US20150246383A1 (en) * 2014-02-28 2015-09-03 Ford Motor Company System and process for producing a metallic article
DE102014107210A1 (de) * 2014-05-22 2015-11-26 Benteler Automobiltechnik Gmbh Modulares Warmformwerkzeug

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2335842A2 (fr) * 2009-12-16 2011-06-22 Benteler Automobiltechnik GmbH Procédé de fabrication d'un outil de formage à chaud et outil de formage à chaud doté d'une protection contre l'usure
EP2851138A1 (fr) * 2013-09-18 2015-03-25 Benteler Automobiltechnik GmbH Outil de formage à chaud partiellement refroidi
US20150246383A1 (en) * 2014-02-28 2015-09-03 Ford Motor Company System and process for producing a metallic article
DE102014107210A1 (de) * 2014-05-22 2015-11-26 Benteler Automobiltechnik Gmbh Modulares Warmformwerkzeug

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110947853A (zh) * 2019-10-16 2020-04-03 马春江 一种基于加热冲压的高精度凸部的加工方法

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