Partial radiation heating method for producing press hardened parts and arrangement for such production

Abstract

The present invention relates to a method, and system for performing such method, for producing a press hardened part (2) of heat treatable material having zones of different structure by partially heating a blank (2) before the blank is processed. The method (100) comprises the steps of arranging (104) the blank in a furnace (10) for heating the blank to a temperature equal to or above the austenitization temperature of the material of the blank to get the blank into an austenitic phase, in a IR heating station (10) partially heating (106), by means of IR radiation (24), at least one first zone (2a) of the blank thereby keeping the at least one first zone of the blank in the austenitic phase, and arranging (108) the blank in a processing unit (30) for forming and quenching the blank to a press hardened part.

Claims

1. A method for producing a press hardened part of heat treatable material having zones of different structure by partially heating a blank before the blank is processed, comprising the steps of; arranging the blank in a furnace for heating the blank to a temperature equal to or above the austenitization temperature of the material of the blank to get the blank into an austenitic phase, arranging the heated blank in an infrared (IR) heating station comprising IR radiation sources configured to provide IR radiation towards an upper side of the blank, wherein the blank is arranged on a support providing shielding of a bottom side of the blank such that the bottom side of the blank is substantially free from radiation exposure from the IR radiation, arranging a mask made of stainless steel or aluminum between the IR radiation sources and the upper side of the blank, in parallel with the blank, to block IR radiation from reaching outside at least one first zone of the blank, partially heating, by means of IR radiation, said at least one first zone of the blank thereby keeping the at least one first zone of the blank in the austenitic phase and letting a second zone of the blank, outside said at least one first zone, to cool below the austenitization temperature, and arranging the blank in a processing unit for forming and quenching the blank to a press hardened part.

2. The method according to claim 1, wherein the mask is provided with one or more opening or recess for radiation to pass through to reach the blank.

3. The method according to claim 1, wherein the mask is arranged in direct contact with the blank.

4. The method according to claim 3, wherein a plane upper surface of the blank is arranged in contact with a plane bottom surface of the mask.

5. The method according to claim 1, wherein the infrared radiation is in the spectral range between 0.7 and 3 m.

6. The method according to claim 5, wherein the infrared radiation is in the near-infrared (NIR) spectrum having a wavelength between 0.8 and 1.5 m.

7. The method according to claim 1, wherein the blank is kept in the IR heating station for a time between 8 and 100 seconds, providing a cooling of the second zone of the blank to between 550 C. and 750 C. depending on the cooling speed.

8. The method according to claim 1, wherein the infrared radiation is in the spectral range between 0.7 and 2 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will in the following be described in more detail with reference to the enclosed drawings, wherein:

(2) FIG. 1 shows a flow chart of a method according to an embodiment of the invention;

(3) FIG. 2 shows a flow chart of a method according to an embodiment of the invention;

(4) FIG. 3 shows a schematic diagram of the internal structure of a blank during a method process according to an embodiment of the invention;

(5) FIG. 4a shows a schematic block diagram of an arrangement according to an embodiment of the invention;

(6) FIG. 4b shows a schematic block diagram of a part of an arrangement according to an embodiment of the invention;

(7) FIG. 5a shows a schematic block diagram of an arrangement according to an embodiment of the invention;

(8) FIG. 5b shows a schematic block diagram of a part of an arrangement according to an embodiment of the invention;

(9) FIG. 6 shows a schematic perspective view of a part of an arrangement according to an embodiment of the invention;

(10) FIG. 7 shows a schematic perspective view of a part of an arrangement according to an embodiment of the invention;

(11) FIG. 8 shows a schematic perspective view of a part of an arrangement according to an embodiment of the invention; and

(12) FIG. 9 shows a schematic side view of a part of an arrangement according to an embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

(13) The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, like numbers refer to like elements.

(14) FIG. 1 illustrates a method 100 for producing a press hardened part according to an embodiment of the invention. The method 100 comprises a step 102 of arranging a blank in a furnace. In the furnace, the blank is heated 104 to a temperature equal to or above the austenitization temperature of the material of the blank. Such heating puts the blank in an austenitic phase. The entire blank may be heated in the furnace, or a section of the blank may be heated in the furnace. For instance, a first section of the blank may be inserted into the furnace for heating, while a second section of the blank may extend outside the furnace during heating. The blank may be held in place into the furnace by an apparatus holding the blank at the second section.

(15) The method 100 further comprises a step 106 of keeping at least one first zone of the blank at a temperature for the austenitic phase using radiation heating. At the same time, parts of the blank outside said at least one first zone is allowed to cool to a temperature exiting the austenitic phase.

(16) After the step 106 of radiation heating of the at least one first zone, the blank is arranged 108 in a processing unit to be formed and quenched to a press hardened part. When the blank is formed, the at least one first zone is in the austenitic phase. Further, when being formed in the processing unit, the blank is cooled, such that the at least one first zone of the blank being in the austenitic phase becomes hardened.

(17) The method 100 may use infrared heating as radiation heating to keep the first zone in the austenitic phase.

(18) FIG. 2 illustrates another embodiment of the method 100 of FIG. 1, further comprising a step of arranging 105 a mask between the radiation source and the blank in the radiation heating station. The mask and the use thereof will be further discussed below.

(19) The method 100 above may use infrared heating as radiation heating to keep the first zone in the austenitic phase.

(20) FIG. 3 illustrates how the internal structure in a steel blank may change in different zones using a method according to the present invention. In the figure, the temperature of the second zone 2b of the blank 2 outside the at least one first zone and the temperature of the least one first zone 2a of the blank 2 is illustrated. In the first stage 210, the entire blank is heated in the furnace to the austenitic phase. This includes heating the blank to a temperature equal to or above the AC.sub.3 temperature of the blank, and keeping the blank at this temperature for an amount of time. In the second stage 220, the blank has been moved to the radiation heating station in which the at least one first zone 2a is kept at a temperature keeping it in the austenitic phase. Such temperature may be above the AC.sub.3 temperature. The second zone 2b is cooling reaching ferrite, pearlite and bainite phase. In the third stage 230, the blank 2 is formed and quenched in the processing unit. When the at least one first zone 2a is rapidly cooled from the austenitic phase, it reaches martensite phase. When the second zone 2b is quenched, it stays in the pearlite phase which it had reached when previously been cooling. However, the second zone 2b may, before being quenched, have a mixture of ferrite, pearlite, bainite and/or austenite. Depending on the composition of phase in the second zone 2b before quenching, the internal structure and material strength level becomes different.

(21) FIG. 4a illustrates an arrangement 1 according to an embodiment of the present invention, and FIG. 4b a detailed view of the infrared heating station 20 according to the same embodiment. The arrangement 1 comprises a furnace 10 configured to receive a blank 2, or several blanks at once. The blank 2 is heated in the furnace 10 to a temperature equal to or above the austenitization temperature of the material of the blank 2. The material of the blank 2 is thereby put into the austenitic phase of the material.

(22) The arrangement 1 further comprises an infrared heating station 20 configured to receive a blank 2 in a furnace interior 12. In the following, an embodiment of the arrangement 1 comprising an infrared heating station and using infrared heating will be discussed. However, what is said below may as well be applied on an embodiment using other kind of radiation and radiation heating station for the partial heating of the blank.

(23) The blank 2 heated in the furnace 10 is moved to the infrared heating station 20. In the infrared heating station 20, at least one first zone 2a is exposed to infrared radiation 24 from an infrared light source 22. The at least one first zone may in this embodiment also be referred to as IR heated zone or zones. The IR heated zone 2a is thereby heated to be kept in the austenitic phase. The second zone or zones 2b of the blank 2 not being exposed to the infrared radiation 24 are permitted to cool to a temperature below the austenitization temperature and further out of the austenitic phase.

(24) The infrared heating station comprises a plurality of infrared radiation sources. When exposing the blank to the radiation, the infrared radiation sources can be controlled to provide radiation to the first zone 2a. Specific radiation sources can be activated in a desired pattern to create a desired pattern of the at least one first zone 2a.

(25) Further, the arrangement 1 comprises a processing unit 30 configured to receive a heated blank 2. The partially heated blank 2 is moved from the infrared heating station 20 to the processing unit 30, preferably rapidly. In the processing unit 30, the blank 2 is arranged in a tool 32. By being pressed by a pressing force F, and quenched, the blank 2 is formed to a press hardened part 2. The press hardened part 2 has a hardened zone 2a corresponding to the IR heated zone 2a on the blank 2.

(26) In an exemplary embodiment, the blank 2 may in the furnace 10 be heated to a temperature around 930 C. and kept there to put the blank in the austenitic phase. The austenitization temperature for the blank 2 may typically be around 850 C. Using the infrared heating, the IR heated zone 2a of the blank is kept in the austenitic phase, and may when reaching the processing unit 30 for the forming and quenching have reached a temperature of about 780 C., i.e. still in the austenitic phase.

(27) FIG. 5a illustrates the arrangement 1 according to an alternative embodiment of the present invention, wherein the infrared heating station 20 further comprises a radiation mask 26. FIG. 5b further illustrates a detailed view of the infrared heating station 20 according to the same embodiment. The radiation mask 26 is arranged between the infrared light source 22 and the blank 2. The radiation mask 26 is provided with one or more openings or recesses 26a. The radiation mask 26 thereby blocks the infrared radiation 24 from reaching the blank 2 except at the openings 26a, through which the infrared radiation 24 extends to the blank 2.

(28) The openings 26a in the radiation mask 26 may be designed in a pattern corresponding to specific first zone or zones 2a of the blank 2 desired to be exposed to the radiation 24 to become hardened when being formed and quenched. The first zones 2a of the blank 2 are thereby heated while the second zones 2b outside the first zones 2a are not. When the blank 2 thereafter is moved to the processing unit 30 and formed to a press hardened part 2, different structure in different zones 2a, 2b of the blank 2 is achieved due to the different temperatures in the different zones 2a, 2b. The different temperatures may be related to the material of the zones 2a, 2b being in the austenitic phase or not. The different structured zones 2a, 2b of the blank 2 result in different structured or different hardened zones 2a, 2b on the press hardened part 2.

(29) This is further illustrated in FIGS. 6 and 7, wherein a mask 26 having opening/recess 26a to enable infrared radiation 24 from the infrared light source 22 to reach the blank 2 at the intended IR heated zone 2a, and to block the radiation 24 from reaching outside (2b) the intended IR heated zone 2a. The mask 26 is arranged in a plane in parallel with the blank 2. The size of the mask 26 is larger than the size of the blank 2 to enable tailored heating of the entire blank 2. The mask 26 is provided with openings and recesses 26a that may be small to provide a detailed tailoring of the IR heated zone or zones 2a on the blank 2. However, in some embodiments, the openings and recesses 26a may be large, i.e. that most area of the blank 2 is not covered by the mask 26, and only small areas are covered to provide cooled soft zones.

(30) As illustrated in FIG. 8, an embodiment of the invention may comprise a radiation heating station 20 in which the radiation source 22 extends over only a section of the blank 2. The radiation 24 will thereby only reach the first zone 2a of the blank 2 that will be hardened. Optionally, a shield 29 may be used to block radiation 24 from reaching outside the intended first zone 2a. The second zone 2b may thereby be kept from radiation exposure and not heated by the radiation 24.

(31) As illustrated in the embodiment of FIG. 9, the radiation heating station 20 comprises a mask 26 in plane and parallel direct contact with the blank 2. The opening 26a thereby in very detail control the extension of the radiation from the radiation source 22 to the first zone 2a of the blank 2. The mask 26 may further be in plane direct contact with the radiation source 22.

(32) In the drawings and specification, there have been disclosed preferred embodiments and examples of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation, the scope of the invention being set forth in the following claims.