Method and device for partially hardening sheet metal components

Abstract

The invention relates to a method for producing partially-hardened components from steel sheets, in which a component that is cold-formed from a hardenable steel sheet material is heated, in a furnace, to a temperature below the austenitization temperature (<AC.sub.3), and a radiating element acts upon the component in sections where said component is to be austenitized (<AC.sub.3), this radiating element having a component-side contour that corresponds to the contour of the component in the section to be austenitized. The invention also relates to a device for carrying out said method.

Claims

1. A method for producing partially hardened components out of sheet steel, comprising: heating a component that is cold formed out of a hardenable sheet steel in a furnace to a temperature below an austenitization temperature (<Ac.sub.3); and acting on the component with a radiating element in regions in which the component should be austenitized (>Ac.sub.3); wherein the radiating element has a three-dimensional contour on a side oriented toward the component, which approximately corresponds to a contour of the component in the region to be austenitized.

2. The method according to claim 1, wherein in a working position, the radiating element is spaced the same distance apart from the surface of the component over the entire area that is to be heated and austenitized.

3. The method according to claim 1, comprising heating the radiating element electrically or with gas and in such a way that the surface of the radiating element oriented toward the component has a uniform temperature and radiation intensity.

4. The method according to claim 1, comprising placing the component on a support and conveying the component through the furnace in a precisely positioned, cyclical fashion.

5. The method according to claim 1, comprising, for action with thermal radiation, raising supports, lowering the radiating elements, lowering the supports, or raising the radiating element, depending on the way in which the support is conveyed through the furnace, and as a result, bringing the component to a desired distance from the radiating element.

6. The method according to claim 1, comprising situating a plurality of radiating elements in the furnace, one after another in the conveying direction, and performing the heating action with a plurality of radiating elements in steps in accordance with a work cycle.

7. The method according to claim 1, comprising, in order to increase a definition between austenitized and non-austenitized regions on a support, positioning an absorption mass on the support; the absorption mass rests against the component in the austenitized region and in the non-austenitized region and acts on the component so that thermal energy that could flow from the austenitized region to the non-austenitized region is absorbed by the absorption mass.

8. The method according to claim 7, wherein additional absorption masses act in regions that should remain ductile within the austenitized region, particularly in regions in which holes are to be subsequently punched.

9. The method according to claim 1, comprising transferring each of the components to a respective support in a precisely positioned and located fashion, conveying each of the components through the furnace along with a support, and at the end of the furnace, taking each of the components from the support in a precisely positioned and located fashion by a manipulator in a second transfer position, and transferring each of the components to a form-hardening tool and cooling the components therein; wherein the cooling of the components takes place at a speed that is greater than a critical hardening speed of a base material of the components in such a way that the austenitized regions undergo a martensitic hardening.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained by way of example below in conjunction with the drawings. In the drawings:

(2) FIG. 1: is a very schematic depiction of a component with a heated region;

(3) FIG. 2: is a cross section through a furnace for carrying out the method;

(4) FIG. 3: is a very schematic longitudinal section through a furnace according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) The device according to the invention (FIGS. 1 through 3) has at least one elongated continuous furnace 1 (FIG. 3) with a furnace chamber 2, through which it is possible to travel along a conveying direction. For this purpose, a conveying device that is not shown in detail can be provided in an underfloor region 4 and supports 5 for components 6 can be conveyed thereon. The supports 5 in this case are fastened to the conveying device so that they can be conveyed along a longitudinally oriented opening or slot that connects the underfloor region 4 to the furnace chamber 2. In an intrinsically know fashion, the furnace chamber contains, for example, gas-heated furnace radiating tubes 7 that emit heat into the furnace chamber 2. The components 6 are arranged on the supports 5 and are heated by the furnace radiating tubes 7.

(6) The furnace chamber 2 in this case is divided into two regions; the division does not have to be three-dimensional, for example with a dividing wall. A first region I serves to heat the components to approx. 700 C. and therefore is equipped with furnace radiating tubes 7. The second region II is also equipped with furnace radiating tubes 7.

(7) In addition to the furnace radiating tubes 7, this region also contains the three-dimensionally contoured radiating elements 8. The three-dimensionally contoured radiating elements 8 in this case can, for example, be lowered onto the components 6 from a furnace ceiling 9 by means of appropriate mechanisms. The components in this case are conveyed through on the supports 5 so that every 15 seconds, for example, they are conveyed farther and then stopped, likewise for 15 seconds, for example.

(8) In addition, it is also possible to design a support 5 so that it can be raised and lowered, as is the case for the supports on the far right in FIG. 3; in this case, the three-dimensionally contoured radiating element is for example affixed to a furnace ceiling in a stationary fashion. After the departure from the furnace, a correspondingly heated component can be moved by a manipulator into an appropriate forming tool or form hardening tool.

(9) A corresponding component can be seen in FIG. 1, which shows a heated region.

(10) FIG. 2 shows the radiating element that has been lowered onto the component and is preferably spaced approximately the same distance apart from the surface of the work piece 6 in all regions so that a uniform heating is possible. In order to embody the temperature progression between the heated region 10 and the surrounding warmed region 11 in as sharply defined a manner as possible, corresponding absorption masses or an appropriately frame-shaped absorption mass 12 can be provided in the boundary region between the area heated by the three-dimensionally contoured radiating element 8 and the surrounding areas. The absorption mass in this case ensures that no heat or as little heat as possible is transmitted from the region 10 heated by the radiating element 8 into the remaining region 11 and into the furnace chamber. In this case, in regions that are within the heated region and should remain ductile, for example in the vicinity of a hole 12a that is to be subsequently punched, the absorption mass 12 can also have an absorption mass so that this region remains ductile.

(11) The complete sequence of the method according to the invention is as follows:

(12) A blank is stamped out of a steel band composed of an austenitizable steel, for example a 22MnB5 steel or a comparable steel that can be hardened through quench hardening. The stamped blank is then deep drawn into a component using a conventional shaping process; this component can already have the three-dimensional final contour of the desired component or else certain thermal expansions or expansions due to changes in the structure can be taken into account such that after a quench hardening step, which nevertheless occurs without significant further shaping, the component has the desired final contour and final size.

(13) This component is in particular a component provided with a zinc coating or a zinc-based coating.

(14) These components are placed onto furnace supports by a manipulation tool in a first transfer station. For this purpose, the components can have corresponding holes that are engaged by pick-up pins or bolts of the support. In this connection, it is important for the method that the component is placed onto the support in an absolutely precisely positioned fashion, with an absolutely uniquely defined position of the component. Then the support travels into the furnace; in the furnace, the component on the support first travels through a first region in which the furnace temperature is between 650 C. and 800 C., in particular between 700 C. and 750 C., preferably 730 C.; this temperature is achieved by means of furnace radiating tubes. The length of the furnace or of the first furnace section in this case is dimensioned so that at the end of this section, the components have a temperature of 700 C. to 750 C., preferably 730 C.

(15) In this case, the components are conveyed through the furnace in a cyclical fashion. This means that a furnace support is transported by a respectively fixed distance from station to station and then in this station, in whose position it is precisely kept, is stopped for a certain amount of time, for example 15 seconds, before the furnace support together with the component is advanced exactly to the next station and remains in it in turn for a holding time. After the furnace section I, the support together with the component travels into the furnace section II, in which a three-dimensionally contoured radiating element is situated above all or part of the cycle stations. After the arrival at the station, either the three-dimensionally contoured radiating element is lowered onto the component or the component is raised and positioned with a predetermined, always equal distance from the component; in the region covered by the radiating element, the component is acted on with thermal radiation in such a way that either by means of a single radiating element or by means of a plurality of radiating elements arranged one after the other in the cycle sequence, a sufficient amount of thermal energy is imparted to the component such that this region is heated at least to the austenitization temperature (>Ac.sub.3).

(16) In order to embody the definition between the heated region and unheated region as sharply as possible, the furnace support can have an absorption mass that is embodied, for example, in the form of a frame around the heated region and comes to rest against the component from the side opposite from the radiating element. As explained above, thermal energy that tends to flow from the heated region into the cooler region can thus be conveyed into the absorption mass.

(17) After the component has been sufficiently heated even in the heated region, then the component is cyclically transported out of the furnace and is immediately picked up by a manipulation tool and transferred to a form hardening tool. In the form hardening tool, the form hardening tool surfaces of the form hardening tool rest against the component and cool it rapidly. The cooling in at least the regions that are heated (by the three-dimensionally contoured radiating elements) occurs at a speed greater than the critical hardening speed of the respective steel material so that the initially austenitic phase is essentially transformed into martensite and as a result, achieves a high degree of hardness.

(18) The support, possibly provided with the absorption masses, travelsfor example driven by a conveyor chainthrough the furnace and after exiting from the furnace, for example underneath the furnace, travelseither in an encapsulated underfloor region or in a manner that provides open air coolingback to the transfer station (at the beginning of the furnace).

(19) Since according to the invention, both the support and the absorption masses do not intrinsically require cooling, it is suitable for the support, possibly together with the absorption mass, to be conveyed back in an encapsulated region so that the support and the absorption mass do not need to be heated again in the furnace, but instead, the already warm absorption masses can additionally feed thermal energy into the component. A cooling, however, is likewise possible.

(20) With the invention, it is advantageous that such a device can be implemented at a comparatively low cost; the control-related costs are also low.

(21) It is also advantageous that with the method, less heat is discharged from the furnace than with conventional methods, making it more energy efficient and thus less expensive.

(22) In addition, the three-dimensionally contoured radiating elements make it possible to meter the heat into the components in a very precise fashion so that the results can be reproducibly achieved with a high degree of uniformity.

(23) With flat sheet metal parts that are to undergo a subsequent shaping in the hot state or when it is only necessary to act on flat regions of an otherwise contoured component, the three-dimensionally contoured radiating elements can naturally also be embodied as only two-dimensional.

REFERENCE NUMERAL LIST

(24) 1 continuous furnace 2 furnace chamber 3 conveying direction 4 underfloor region 5 support 6 component 7 furnace radiating tubes 8 three-dimensionally contoured radiating element 9 furnace ceiling 10 heated region 11 warmed region 12 absorption mass 12a hole to be punched I first region II second region