Patent Issued for Method and Forming Tool for Hot Forming and Press Hardening Workpieces of Sheet Steel, in Particular Galvanized Workpieces of Sheet Steel (USPTO 9770750)
By a News Reporter-Staff News Editor at Journal of Engineering -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventors Banik, Janko (Altena, DE); Sikora, Sascha (Lunen, DE); Koeyer, Maria (Dortmund, DE); Struppek, Thomas (Werne, DE), filed on October 16, 2012, was published online on September 26, 2017.
The patent's assignee for patent number 9770750 is ThyssenKrupp Steel Europe AG (Duisburg, DE).
News editors obtained the following quote from the background information supplied by the inventors: "Field of the Invention
"The invention relates to a method for hot forming and press hardening plate-shaped or preformed workpieces of sheet steel, in particular galvanized workpieces of sheet steel, in which the workpiece is heated to a temperature above the austenitisation temperature and is then formed and quenched in a cooled forming tool having at least one punch and at least one female mold. The invention also relates to a forming tool for hot forming and press hardening plate-shaped or preformed workpieces of sheet steel, in particular galvanized workpieces of sheet steel, having at least one punch and a female mold associated with said punch, the punch and/or the female mold having cooling ducts for conducting a cooling fluid.
"Description of Related Art
"Devices are known for hot forming and press hardening workpieces of sheet steel, which devices have at least two tool halves, regions of these tool halves being configured such that they have different thermal conduction characteristics which are used to enable the adjustment of locally differing strength characteristics in the component to be produced. The method implemented by these devices is known by experts as 'tailored tempering'. A corresponding device is disclosed, for example, in DE 10 2009 018 798 A1.
"It is also known to increase the dimensional accuracy and fitting accuracy of formed components in that the tool halves used for production have positive radii in the region of curves of the workpiece and they form air spaces in the opposite regions, projections being configured adjacently to the air spaces such that a non-warping clamping is facilitated. As a result, different hardness degrees can also be set in the component. A corresponding device for producing hardened components of sheet steel is described in DE 10 2004 038 626 B3.
"Tests have shown that when galvanized steel blanks are hot formed in conventional forming tools, cracks sometimes appear in the zinc coating. The cracks can spread into the blank and thus the component may fail prematurely.
"The object of the present invention is to provide a method and a forming tool of the type mentioned at the outset, which improve the flow characteristics of steel materials during the hot forming procedure, thereby significantly reducing the risk of cracks appearing during the hot forming of workpieces of sheet steel, in particular of galvanized steel blanks."
As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "According to the invention, the female mold used for hot forming and press hardening is coated in its corner region, defined by a positive die radius, with material and/or is provided with at least one insert part having a thermal conductivity which is at least 10 W/(m*K) lower than the thermal conductivity of the portion of the female mold, which portion is adjacent to the drawing edge region and comes into contact with the workpiece when said workpiece is being formed and press hardened. The material applied in the drawing edge region, or the insert part arranged there, which according to the invention has a relatively low thermal conductivity is configured such that the surface thereof facing the workpiece has a transverse dimension which extends over the drawing edge and is within the range of 1.6 times to 10 times, preferably within the range of 1.6 times to 6 times the positive radius of the female mold. The transverse extent (transverse dimension) of the material or insert part having a relatively low thermal conductivity and arranged in the drawing edge region is thus limited and relatively small.
"The coated sheet steel (workpiece) to be formed is subjected to high plastic deformations particularly in the drawing edge region, defined by a positive die radius, of the female mold. Due to the action of the punch, in this region the workpiece initially experiences a compressive stress which changes into a tensile stress during the continued closing movement of the forming tool. The high temperature difference between the workpiece and the forming tool adversely affects the local flow characteristics of the workpiece in a conventional forming tool, particularly in the die radius of a conventional forming tool, and cracks frequently appear in the coating, for example in the layer of zinc. With an increasing sheet thickness and subject to the complexity of the shape of the component to be produced, differing crack depths can appear which can extend right into the sheet of the coated component.
"According to the invention, the material applied, for example by coating in the drawing edge region, having a relatively low thermal conductivity, or the insert part arranged there, having a relatively low thermal conductivity, is dimensioned to ensure that the component produced by hot forming and press hardening has a substantially completely martensitic structure. In this respect, the part of the press-hardened component, influenced by the drawing edge of the female mold, i.e. by the material or insert part having a relatively low thermal conductivity, can have a tower hardness than another part or than the remaining part of the component, although according to the invention, this part, influenced thus, of the press-hardened component always has a hardness which is above the required minimum hardness and corresponds to a martensitic structure. In this manner, cracks in the coating, for example in a zinc layer, and also in the correspondingly coated sheet are avoided or at least the crack depths in the coating or in the coated sheet are considerably reduced.
"The stresses and strains which occur when the coated, for example galvanized, workpiece (sheet steel) is hot formed and also the solidification which occurs in the forming process are reduced by the reduced loss of heat or temperature compared to that in a conventional temperature-controlled forming process. Consequently, a possible local material failure is also reduced or prevented.
"The present invention thus improves the flow characteristics of workpieces of sheet steel during hot forming and thereby significantly reduces the risk of cracks appearing during the hot forming of workpieces of sheet steel, preferably galvanized steel blanks.
"In particular, the present invention improves the feasibility of components which have a complex three-dimensional shape and are to be produced from coated sheet steel, for example from galvanized sheet steel.
"A preferred configuration of the solution according to the invention provides that the thermal conductivity of the insert part, arranged in the drawing edge region, or of the applied material, is less than 40 W/(m*K), preferably less than 30 W/(m*K) and particularly preferably less than 20 W/(m*K). This measure advantageously reduces the loss of heat or temperature during the hot forming of the workpiece and accordingly improves the forming behaviour of the workpiece.
"A further advantageous configuration of the solution according to the invention is characterised in that a heat insulating layer is arranged between the insert part and the female mold. This measure can further reduce the loss of heat or temperature during the hot forming of the workpiece. In particular, this configuration allows the use of an insert part which is produced from a particularly wear-resistant material but which has a relatively high thermal conductivity, it being possible for the heat insulating layer which, compared to the insert part forming the drawing edge region, is not exposed to a high mechanical stress, and in particular is not exposed to a high frictional stress, to consist of a thermally insulating material, for example a plastics material or wood material, having low wear resistance.
"A further advantageous configuration of the solution according to the invention provides that the insert part has a projection which protrudes with respect to the inner periphery of the female mold and/or with respect to the peripheral surface adjoining the cavity of the female mold. This projection, by forming a local elevation, can reduce even more effectively the dissipation of heat from the workpiece to be formed upstream of the die radius.
"A further advantageous configuration of the solution according to the invention is characterised in that the material applied in the drawing edge region of the female mold is applied to the female mold by build-up welding, preferably by laser build-up welding. In this manner, the thermal conductivity in the drawing edge region of the female mold can be reduced in a reliable and relatively simple manner. The material application having a relatively low thermal conductivity can be renewed economically by build-up welding, preferably by laser build-up welding, when this is necessary due to abrasion (erosion) caused by wear.
"A further advantageous configuration of the solution according to the invention is characterised in that the drawing edge region of the female mold is heated in a locally selective manner by a heat source, integrated into the female mold, or by a duct conducting a heating fluid. This configuration can also significantly reduce the dissipation of heat from the workpieee to be formed and can thereby improve the flow characteristics of the steel material during hot forming.
"It also lies within the scope of the present invention to combine together a plurality of the aforementioned configurations or all the aforementioned configurations of the solution according to the invention."
For additional information on this patent, see: Banik, Janko; Sikora, Sascha; Koeyer, Maria; Struppek, Thomas. Method and Forming Tool for Hot Forming and Press Hardening Workpieces of Sheet Steel, in Particular Galvanized Workpieces of Sheet Steel. U.S. Patent Number 9770750, filed October 16, 2012, and published online on September 26, 2017. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=9770750.PN.&OS=PN/9770750RS=PN/9770750
Keywords for this news article include: ThyssenKrupp Steel Europe AG.
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