Patent Application
20170304884
The present disclosure relates to an apparatus and method for manufacturing hot-stamped components suitable for use with motor vehicles. More specifically, a furnace includes multiple heating zones for heating different portions of a blank to different temperatures to create a hot-stamped component having softened zones in select areas to facilitate down-stream assembly of the component to other components of the vehicle.
Press-hardened steel alloys are being used for sheet-metal parts incorporated in vehicle body structures that may be assembled together with rivets or welding. One example of a press-hardened steel is boron steel sold under the designation Usibor® 22MnB5. Press-hardened steel can be water cooled or oil cooled to a desired level of hardness from 450 to 520 HV. Press-hardened steel may be annealed to reduce the hardness to 140 HV.
Press-hardened steel parts may be assembled to other steel parts by welding. But, new automotive assemblies may include combinations of parts made of different materials such as aluminum and composite parts. An Ultra High Strength Steel (UHSS) beam formed by press hardening and a composite part or an aluminum part cannot be efficiently joined together in a welding operation. The preferred technique for joining such part assemblies is to rivet or otherwise fasten the parts together. The hardness of such high strength parts poses significant challenges in high volume manufacturing operations because the rivets have difficulty penetrating the UHSS beam.
According to one embodiment, a hot-stamping furnace includes a housing defining a heating chamber partitioned into compartments configured to have different temperatures. The heating chamber includes an opening that is at least partially covered by a door movably mounted on the housing. The door is configured to extend over only a portion of the opening when in a closed position. A detachable panel extends from an edge of the door such that the panel extends over a portion of the opening that the door does not extend over.
According to another embodiment, a hot-stamping furnace includes a housing defining a heating chamber having an opening. A partition divides the chamber into first and second zones each extending to the opening. The second zone is configured to have a higher temperature than the first zone. A door is mounted to the housing and includes a panel positioned to cover the opening in front of the second zone but not cover the opening in front of the first zone.
According to yet another embodiment, a method of heat treating a component in a furnace is disclosed. The furnace has at least first and second compartments configured to have different temperatures and a door including a panel. The method includes inserting the component through an opening of the furnace such that a first portion of the component is in the first compartment and a second portion of the component is in the second compartment. The method also includes heating the first compartment to a temperature calculated to heat the first portion of the component above an AC3 temperature within a predetermined time, and heating the second compartment to a temperature calculated not to heat the second portion of the component above an AC1 temperature within the predetermined time. The method further includes closing the door over the opening such that the door only partially covers the opening and such that the panel fully covers the opening in front of the first compartment and does not cover the opening in front of the second compartment.
Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations.
Referring to
In the example process 20, a boron steel blank 22 (which is a press-hardenable steel) is placed in a furnace 24 and heated above AC3 forming austenite. AC3 is the transformation temperature at which ferrite fully transforms into austenite. For example, the blank 22 may be heated at 900 to 950° C. for a predetermined time in the furnace 24. The bake time and furnace temperature varies depending upon the material of the blank 22 and the desired properties of the finished part. After heating, a robotic transfer system 26 may transfer the austenized blank 22 to a press 28 having a die arrangement 30. The die arrangement 30 stamps the blank 22 into a desired shape while the blank 22 is still hot to form one or more components 32 from the blank 22. The component 32 is then quenched while the die 30 is still closed using water or other coolant means. Quenching is provided at a cooling speed of 20 to 150° C./sec. for a predetermined duration at the bottom of the stroke. Quenching changes the microstructure of the blank from austenite to martensite. After quenching, the component 32 is removed from the press 28 while the component is still hot (e.g., about 150° C.). The component 32 may then be cooled on racks.
Hot stamping may provide numerous advantages over other high-strength steel forming methods such as cold stamping. One advantage of hot stamping is reduced spring back and warping. Hot stamping also allows complex shapes to be formed in a single stroke of the die. This reduces downstream processing and may increase efficiency in the manufacturing of the vehicle body component.
Hot-stamped components have found broad application in the automotive industry. Hot-stamping components are both lightweight and strong. Example automotive components formed by hot stamping may include: body pillars, rockers, roof rails, bumpers, intrusion beams, carrier understructure, mounting plates, front tunnels, front and rear bumpers, reinforcement members, side rails, and other parts that are designed to resistance deformation during an impact.
Hot-stamped components may be difficult to join to other components. For example, a hot-stamped component may need to be fastened to another component via a self-piercing rivet. Due to their high strength and low ductility, it may be difficult for the rivet to penetrate through the martensite microstructure of the hot-stamped component. In another example, the hot-stamped component may need to be welded to a mild-steel component. Welding the hot-stamped component to the mild-steel component may be unfeasible.
In order to solve these and other problems, a special furnace may be utilized to form softened zones in the blank at select locations. These softened zones remain soft during the stamping and quenching phases and are also present in the finished component. The softened zones are specifically placed in locations where the component is to be attached to other components. The softened zones may have a microstructure consisting of ferrite and perlite, which have lower yield strength and a higher ductility as compared to martensite. For example, the softened zones may have 30-40% less yield strength, and 30-40% more ductility. A self-piercing rivet can more easily penetrate through the softened zones due to the lower yield strength and the higher ductility present in the zone. The material properties at the softened zones also facilitate welding of the press-hardened component to mild steel or aluminum components. Used herein “softened zone” or “soft zone” is to be construed to mean any area of a component that is not fully austenized.
Steel must be fully austenized in order to from martensite. If portions of the blank remain below AC3, then martensite will not be formed in those areas during quenching. Thus, the softened zones can be created by not heating the zones above the temperature at which austenite begins to form (AC1). An Example AC1 temperature is 800° C.
The figures and related text disclose example furnaces configured to heat different portions of the blank 22 to different temperatures in order to create the softened zones at select locations. Referring to
The furnace 50 may be configured to have multiple chambers or zones of different temperature within the heating chamber 64 to heat different portions of the blank to different temperatures. One way to create the zones is to physically divide the heating chamber 64 into separate compartments or zones. For example, one or more partitions 80 are disposed within the heating chamber 64 to divide heating chamber into at least two compartments. The partition 80 may include a top surface 82 that engages or nearly engages the ceiling 68 of the chamber 64, and a bottom surface 84 that engages with one of the pillars 76. In one embodiment, the bottom surface 84 defines a groove 88 that receives a top surface 78 of the pillar 76 to connect the partition 80 to the pillar 76. The partition 80 also includes a rear surface 85 that engages, or nearly engages, the back 70. Thus, the partition 80 extends between the floor 66 and the ceiling 68, and extends between the back 70 and the opening 74 to fully divide the heating chamber 64. The partition 80 includes major sides 86 that each forms a boundary of one of the zones. The partitions 80 also define a part receiving area 94. The part receiving area 94 may be a slot or similar feature that receives the blank therein to support the blank within the heating chamber 64. In the illustrated embodiment, each of the partitions 80 includes a top portion 90 and a bottom portion 92 that cooperate to define a slot 94. The partitions 80 are modular structures that can be moved around within the heating chamber 64 to create different heating-zone configurations. The heating chamber 64 includes the plurality of pillars 76 to provide a plurality of different placement locations for the partitions 80. It is understood that the heating chamber 64 may include more or less than three different zones.
In the illustrated embodiment, the furnace 50 includes a pair of partitions 80 that divide the heating chamber 64 into a first zone 96, a second zone 98, and a third zone 100. Each of the zones may be set to a different temperature, or two of the zones may be a same temperature and the third zone is a different temperature. The first zone 96 may be a cooler zone that is set below the AC1 temperature (e.g., below 850° C.), and/or is set to a temperature calculated to not heat the blank above the AC1 temperature within the predetermined baking time. The third zone 100 may also be a cooler zone. The second zone 98 may be a hotter zone that is set at or above the AC3 temperature (e.g., above 900° C.), and/or is set to a temperature calculated to heat the blank above the AC3 temperature within the predetermined baking time. It is understood that the heating chamber 64 may include more or less than three different zones by increasing or decreasing the number of partitions. Each of the zones may include its own set of heating elements 97. Each set of heating elements 97 may be independently controlled to a different temperature by a control module of the furnace 150. The heating element may be electric heating elements or may be infrared heating elements for example.
The furnace 50 includes a movable door 102 that may be mounted on the front 54 to cover the opening 74 reducing heat loss from the heating chamber 64 through the opening 74. The door 102 is movable between an open position, a close position and a plurality of in-between positions. The term “closed position” does not necessarily mean that the door 102 fully covers the entire surface area of the opening 74. For example, the door may be configured such that in the closed position it only partially covers the opening 74. The door 102 may be a sliding door that moves up-and-down along vertical door tracks 104 to move between the open and closed positions. In other embodiments, the door may swing between the open and closed position along hinges. The door tracks 104 may be disposed on the front 54. A door actuator 116, such as mechanical gear motor or hydraulic cylinder, moves the door up-and-down along the tracks. The door 102 may include a planar body 106 defining a front panel 108 that faces away from the furnace 50, a back panel 110 that faces the opening 74, a top edge 112, and a bottom edge 114. The door 102 may be shaped as a rectangular, plate-like structure (as shown) or may be any shape known by a person skilled in the art.
Referring to
In the illustrated example, the heating chamber 64 includes two cooler zones 96, 101 and hotter zone 98.
The illustrated embodiment shows a door that moves downwardly from the open position to the closed position. But, the furnace could also be configured such that the door moves upwardly from the open position to the close position. Here, the panels would extend from the top edge 112 of the door. Of course, the door could also be a hinged door that swings from the open position to the close position. In that case, the panel could be positioned on either the top, or the bottom, depending upon the vertical positioning of the door relative to the opening of the heating chamber.
Referring to
Referring to
In one embodiment, the heating chamber 182 may be configured to have a generally uniform temperature (i.e., a single zone). Here, a blank 196 is inserted into the heating chamber 182 such that a first portion 198 of the blank is disposed within the heating chamber, and a second portion 200 of the blank is external to the heating chamber 182. The opening 184 acts as a window allowing the second portion 200 to extend out of the heating chamber 182 as shown in
In another embodiment, the heating chamber 182 may be configured to have multiple heating zones as described above with reference to
The floor 260 defines an array of locating features 270. The locating features 270 may be slots (as shown) or may be projections, brackets or any other feature known in the art. The slots 270 may extend from the back 264 to the front 254. The slots 270 may be spaced along a width direction of the heating chamber 256 (i.e., between the sidewalls 266) at spaced intervals, such as 3, 6, or 9 inch spacing for example.
The heating camber 256 includes one or more partitions 258 that divide the chamber into zones or compartments configured to have a different temperature. Each of the partitions may be a panel-like structure that extends between the floor 260 and the ceiling 262 and between the back 264 and the front face 254. The partitions 258 cooperate with the locating features 270 to locate the partitions within the heating chamber 256. In some embodiments, the locating feature 270 also is an attachment feature. In the illustrated embodiment, a lower portion 272 of each partition is disposed within one of the slots 270 to locate and retain the partition 258 in a desired location. Each of the partitions 258 may define a blank-receiving area 274 as described above in the other embodiments.
While example embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.
