CONDUCTION PRE-HEATING OF SHEET FOR HOT FORMING

FIELD

The present patent application relates to a system for producing components by hot forming.

BACKGROUND

Hot forming generally comprises heating a blank in a furnace, followed by stamping the heated blank between a pair of dies to form a shaped part, and quenching the shaped part between the dies. The blank is generally heated in the furnace to achieve an austenitic microstructure, and then quenched in the dies to transform the austenitic microstructure to a martensitic microstructure.

Also, steel continues to be the material of choice when it comes to modern and cost-effective vehicle bodies. In terms of material, new steels that combine high strength with good formability have been developed in response to the demands of the automotive industry for light weight construction materials. In particular, the multiphase steels are used extensively in hot stamping or forming in which a steel blank is heated into the zone of full austenitization (typically 920° C.). The heated steel blank is subsequently inserted into the forming tool or press while still hot, and is rapidly cooled during the pressing operation.

Advantages of the press hardening method include the low forming resistance and the better formability of steel at this temperature, as well as the high strength and good dimensional stability of the obtained component. In general, the use of hot stamping methods and new steel materials results in high-strength but low-weight vehicle bodies.

Due to the increasing use of hot stamping technology in the automotive industry, the press-hardening machinery is becoming faster. Machines that achieve five strokes per minute have been in use for some time already, and newer machines that achieve seven strokes per minute are known. As a result of the reduced cycle length, the efficiency of the hot stamping method is increased. However, the heating of the supplied blanks via heating furnaces has hitherto been the limiting factor. Since the blanks have to be heated to a processing temperature of over 900° C., heating furnaces which are configured as continuous furnaces are used. Over a 30 m length of such a continuous furnace, the blank is heated by 30° C. per meter. Accordingly, the pass-through speed of the blanks and the length of the heating furnaces limits the cycle length of the hot stamping system.

Further, hot stamping ovens are often bottlenecked by patched blanks causing a decrease in through-put. Induction and open flame pre-heat methods have been used to pre-heat the blanks. These methods had issues with providing uniform heat to the sheet which can cause significant distortion (bowing) to the blanks.

The present patent application provides improvements to hot forming/stamping systems and operations.

SUMMARY

One aspect of the present patent application provides a system for producing components by hot forming. The system includes a pre-heat station, a furnace, and a press. The pre-heat station is configured to receive a blank; and to pre-heat at least a portion of the blank to a pre-heat temperature by thermal conduction. The furnace is constructed and arranged to receive the pre-heated blank from the pre-heat station and to heat the entire blank to a deformation temperature. The deformation temperature is higher than the pre-heat temperature. The press is constructed and arranged to receive the heated blank from the furnace and to form the heated blank into the shape of the component.

These and other aspects of the present patent application, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. In one embodiment of the present patent application, the structural components illustrated herein are drawn to scale. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the present patent application. It shall also be appreciated that the features of one embodiment disclosed herein can be used in other embodiments disclosed herein. As used in the specification and in the claims, the singular form of “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a system for producing components by hot stamping procedure or hot forming procedure in accordance with an embodiment of the present patent application;

FIG. 2 shows an exploded view of a pre-heat station of the system for producing components by the hot stamping/hot forming procedure, wherein some portions of the pre-heat station are not shown for sake of clarity and to better illustrate other portions of the pre-heat station, in accordance with an embodiment of the present patent application, wherein FIG. 2 also shows a blank member being received and heated by the pre-heat station;

FIG. 2A shows the blank member being received and heated by the pre-heat station in accordance with an embodiment of the present patent application;

FIG. 3 shows a side view of the pre-heat station of the system for producing components by the hot stamping/hot forming procedure, wherein some portions of the pre-heat station are not shown for sake of clarity and to better illustrate other portions of the pre-heat station, in accordance with an embodiment of the present patent application;

FIG. 4 shows a top perspective view of the pre-heat station of the system for producing components by the hot stamping/hot forming procedure, wherein some portions of the pre-heat station are not shown for sake of clarity and to better illustrate other portions of the pre-heat station, in accordance with an embodiment of the present patent application;

FIG. 5 shows another top perspective view of the pre-heat station of the system for producing components by the hot stamping/hot forming procedure, wherein some portions of the pre-heat station are not shown for sake of clarity and to better illustrate other portions of the pre-heat station, in accordance with an embodiment of the present patent application;

FIG. 6 shows a table that provides a comparison of various residence times for the system of the present patent application and for the prior art system;

FIG. 7 shows a graphical representation of various temperature profiles of the blank member heated in the prior art system;

FIG. 8 shows a graphical representation of various temperature profiles of the blank member heated in the system of the present patent application; and

FIGS. 9 and 10 show exemplary pre-heat station in accordance with an embodiment of the present patent application.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIGS. 1, 2 and 2A, in one embodiment, a system 100 for producing components by hot forming or hot stamping is provided. In one embodiment, the system 100 includes a pre-heat station 102, a furnace 104, and a press 106. In one embodiment, the pre-heat station 102 is configured to receive a blank 108. In one embodiment, the blank 108 includes a patched region 112 and a non-patched region 116. In one embodiment, the pre-heat station 102 is configured to pre-heat at least a portion (e.g., the patched region 112) of the blank 108 to a pre-heat temperature PH_Tby thermal conduction. In one embodiment, the furnace 104 is constructed and arranged to receive the pre-heated blank 108 from the pre-heat station 102 and to heat the entire blank 108 to a deformation temperature D_T. In one embodiment, the deformation temperature D_Tis higher than the pre-heat temperature PH_T. In one embodiment, the press 106 is constructed and arranged to receive the heated blank 108 from the furnace 104 and to form the heated blank 108 into the shape of the component.

In one embodiment, thermal conduction pre-heat is a method of transferring energy/heat into the blanks 108 using conduction as the mode of heat transfer. In one embodiment, thermal conduction pre-heat includes contact heating of the blank. In one embodiment, conduction is the most efficient form of heat transfer and provides the least heating time.

In one embodiment, the blank 108 used to manufacture the shaped parts or components are typically formed of metal, but can be formed of other materials. In one embodiment, the blank 108 is formed of steel material, such pure steel or a steel alloy.

In one embodiment, at least the portion of the blank 108 includes the entire blank. In one embodiment, at least the portion of the blank 108 includes a patched region (of the blank 108, where the blank 108 includes both the patched region and a non-patched region). In one embodiment, at least the portion of the blank 108 includes a patched blank (of the blank 108, wherein the blank includes a base blank and the patch blank attached to the base blank).

In one embodiment, the blank 108 is a tailor welded blank. In one embodiment, the tailor welded blank is formed by a tailor welded blank procedure. In one embodiment, the tailor welded blank includes blank members that are welded together during the tailor welded blank procedure. In one embodiment, the blank members being welded together during the tailor welded blank procedure may have different strengths and/or different thicknesses. In one embodiment, at least the portion of the tailor welded blank is pre-heated to the pre-heat temperature PH_Tby thermal conduction in the pre-heat station.

In one embodiment, the blank 108 is a monolithic blank. In one embodiment, at least the portion of the monolithic blank is pre-heated to the pre-heat temperature PH_Tby thermal conduction in the pre-heat station. In one embodiment, the at least the portion of the monolithic blank includes the entire blank.

In one embodiment, the blank 108 is a tailor rolled blank. In one embodiment, the tailor rolled blank is formed by a tailor rolled blank procedure. In one embodiment, the tailor rolled blank includes variable thickness portions. In one embodiment, at least the portion of the tailor rolled blank is pre-heated to the pre-heat temperature PH_Tby thermal conduction in the pre-heat station.

In one embodiment, referring to FIGS. 2 and 2A, the blank 108 includes a base blank 110 and a patch blank 112 attached to the base blank 110. In one embodiment, the base blank 110 and the patch blank 112 are integrally formed.

In one embodiment, the patched region 112 includes the patch blank 112 and a portion 114 of the base blank 110 that is attached to the patch blank 112. In one embodiment, the non-patched region 116 includes portions 116 of the base blank 110 that are surrounding the patch blank 112. In one embodiment, portions 116 of the base blank 100 that are surrounding the patch blank 112 are not pre-heated to the pre-heat temperature in the pre-heat station 102. In one embodiment, the non-patched region 116 includes portions 116 of the base blank 110 that are surrounding at least two sides of the patch blank 112. In one embodiment, the non-patched region 116 includes portions 116 of the base blank 110 that are surrounding at least three sides of the patch blank 112. In one embodiment, the non-patched region 116 includes portions 116 of the base blank 110 that are surrounding the entire (e.g., all four sides) patch blank 112. In one embodiment, the non-patched region 116 includes portions 116 of the base blank 110 that are adjacent the patch blank 112. In one embodiment, the non-patched region 116 does not include the patch blank 112.

In one embodiment, the base blank 110 may also be referred to as a parent blank. In one embodiment, the base blank 110 and the patch blank 112 have the same thickness. In another embodiment, the base blank 110 and the patch blank 112 have different thicknesses. In one embodiment, the base blank 110 and the patch blank 112 are made of the same material. In another embodiment, the base blank 110 and the patch blank 112 are made of different materials. In one embodiment, the base blank 110 and the patch blank 112 are made of the same material grade. In another embodiment, the base blank 110 and the patch blank 112 are made of different material grades.

In one embodiment, the non-patched region 116 includes portions 116 of the blank 108 that are surrounding the patch region 112. In one embodiment, the non-patched region 116 includes portions 116 of the blank 108 that are adjacent the patch region 112. In one embodiment, the patched region 112 and the non-patched region 116 have different thicknesses. In one embodiment, the patched region 112 has a thickness greater than the non-patched region 116. In one embodiment, the patched region 112 and the non-patched region 116 are made of the same material. In another embodiment, the patched region 112 and the non-patched region 116 are made of different materials. In one embodiment, the patched region 112 and the non-patched region 116 are made of the same material grade. In another embodiment, the patched region 112 and the non-patched region 116 are made of different material grades.

In one embodiment, the patch blank 112 has an area smaller than the area of the blank 108. In one embodiment, the patch blank 112 is surrounded by portions (e.g., unpatched or remaining portions 116) of the base blank 110. In one embodiment, the portions of the base blank 110 surrounding the patch blank 112 are referred to as non-patched/unpatched portions or the remaining portions of the blank 108. In one embodiment, the patch blank 112 is configured to overlap at least a portion (i.e., portion 114) of the base blank 110. In one embodiment, the patch blank 112 is attached to the base blank 110 by welding, adhesive or mechanical joining operation/procedure. In one embodiment, edge or internal portion of the patch blank 112 is joined to the base blank using resistance spot welding (RSW), metal inert gas welding (MIG), laser welding, friction stir welding, self-piercing rivet (SPR) or flow drill screw (FDS) procedures. In one embodiment, the patch blank 112 may be used to provide local reinforcements (i.e., with improved load transfer and/or distribution of stresses) to the blank 108. In another embodiment, the patch blank 112 is provided where greater strength, stiffness and Noise, vibration and harshness (“NVH”) performance are desired.

In one embodiment, the system 100 includes one or more robots 500, 502, 504, 506 that are operatively connected to a controller C. In one embodiment, the number of robots may vary.

In one embodiment, the robot 502 is constructed and arranged to de-stack (i.e., for removing) the topmost (i.e., single) blank 108 from a stack of sheet metal blanks 510 and to automatically dispose the blank 108 in the pre-heat station 102.

In one embodiment, the system 100 is constructed and arranged to stamp date and/or bench mark indicia on the blank 108 after the de-stacking the blank 108 and before positioning the blank 108 in the pre-heat station 102.

In one embodiment, the controller C includes a computer and is configured to control the operations of various components (robots, furnace, pre-heat station, press, etc.) of the system 100. In one embodiment, the controller C is configured to verify that each component of the system 100 is operating correctly in order to maximize the efficiency. In one embodiment, each of the components (robots, furnace, pre-heat station, press, etc.) are controlled independently by their own controllers, but the controller C is configured to share signals between the controllers of the robots, furnace, pre-heat station, press, etc.

In one embodiment, thermal conduction pre-heat of patched blank 108 provides a heating solution to reduce overall oven residence time of the blank in the furnace 104.

In one embodiment, as shown in FIGS. 1 and 2, the pre-heat station 102 includes an induction contact oven. In one embodiment, the pre-heat station 102 includes upper and lower contact platens 118 and 120. In one embodiment, the upper and lower platens 118 and 120 are configured to only heat up the patch area/blank 112 of the blank 108 to an intermediate temperature or the pre-heat temperature PH_T.

In one embodiment, the intermediate temperature or pre-heat temperature PH_Tis below the Al—Si coating eutectic temperature for the coated steel. In another embodiment, the intermediate temperature or pre-heat temperature PH_Tis lower than 700° C. In yet another embodiment, the intermediate temperature or pre-heat temperature PH_Tis in the range of 200° C. and 700° C.

In one embodiment, at least one of the upper and lower platens 118 and 120 is a moveable platen. In one embodiment, the pre-heat station 102 is operatively connected to the controller C. In one embodiment, the controller C is configured to actuate the upper and/or lower platens 118 and 120 (after the blank 108 is properly placed between the upper and lower platens 118 and 120 (e.g., by the robot 500)) such that the upper platen 118 and the lower platen 120 are brought into contact with each other.

In one embodiment, as shown in FIGS. 2-4, each of the lower platen 120 and the upper platen 118 includes a plurality of induction coils 516 therein. In one embodiment, the induction coils 516 are made of copper material. In one embodiment, the induction coils 516 are configured to heat the respective lower and upper platens 120 and 118. In one embodiment, the induction coils 516 are connected to an external power source 522. For example, as shown in FIG. 3, the induction coils 516 may have offset inductions leads 518. In one embodiment, the offset induction leads 518 are configured to prevent electrical coupling. In one embodiment, as shown in FIG. 4, the induction coils 516 are connected to a source of coolant (e.g., via connectors 520) located at the ends of the inductive coils 516. In one embodiment, the induction coils 516 are cooled by water.

In one embodiment, the induction coils 516 are used to provide energy into the platens 118 and 120 to heat the respective platens 118 and 120 and keep them at the desired temperature (i.e., equal to or higher than pre-heat temperature PH_T). In one embodiment, any source of heating may be used to heat and keep the platens 118 and 120 at the desired temperature (i.e., equal to or higher than pre-heat temperature PH_T) as long as it provides energy to the platens 118 and 120. For example, in one embodiment, the sources of heating, such as cartridge, open flame etc. may be used to provide energy/heat to the platens 118 and 120 and maintain the platens 118 and 120 at the desired temperature (i.e., equal to or higher than pre-heat temperature PH_T).

In one embodiment, the blank 108 is the work piece of which the patch area/blank 112 is configured to receive the heat energy from the platens 118 and 120. In one embodiment, the heated platens 118 and 120 are used to pre-heat sheets for the purpose of hot stamping. In one embodiment, only patch areas/blank 112 of sheets or blanks 108 are pre-heated in the pre-heat station 102 through thermal conduction procedure.

In one embodiment, the upper platen 118 is constructed and arranged to provide pressure to the patch blank 112. In one embodiment, the upper platen 118 is heated to a desired platen temperature (i.e., equal to or higher than pre-heat temperature PH_T) and then moved into contact with the patch area 112 of the blank 108. In one embodiment, the lower platen 120 is constructed and arranged to be used as a base for the blank 108 to be placed on. In one embodiment, the lower platen 120 is also heated to a desired platen temperature (i.e., equal to or higher than pre-heat temperature PH_T). In one embodiment, either the upper platen 118 or the lower platen 120 is configured to apply contact pressure on the at least portion of the blank 108 received in the pre-heat station 102.

In one embodiment, either the upper platen or the lower platen is configured to apply contact pressure on the patched region of the blank received in the pre-heat station. In one embodiment, each of the upper and lower platens are heated by at least one process selected from conduction, convection, resistance, induction, heat radiation and gas that are configured to provide energy to heat and maintain the respective upper and lower platens at a desired platen temperature. In one embodiment, the desired platen temperature is higher than the pre-heat temperature. In another embodiment, the desired platen temperature is equal to the pre-heat temperature.

In one embodiment, as shown in FIG. 5, each of the lower platen 120 and the upper platen 118 includes one or more thermocouples 514 therein. In one embodiment, the thermocouples 514 are configured to control and/or monitor the surface temperature of the respective lower and upper platens 120 and 118.

In one embodiment, the controller C is configured to determine whether the patch blank 112 of the blank 108, in the pre-heat station 102, has reached the pre-heat temperature PH_T. In one embodiment, this may be determined either with sensors or the thermocouples 514 associated with the pre-heat station 102 or by monitoring the amount of time that each blank 108 remains in the pre-heat station 102. In one embodiment, the controller C is also configured to adjust the amount of time that the blank 108 is in the pre-heat station 102.

In one embodiment, the controller C is also configured to adjust the surface temperatures of the lower and upper platens 120 and 118 based on the monitored surface temperature data of the lower and upper platens 120 and 118 obtained from the respective thermocouples 514. In one embodiment, the controller C is also configured to adjust the amount of time that the blank 108 is heated between the upper and lower platens 118 and 120. In one embodiment, surface temperatures of the lower and upper platens 120 and 118 can also be adjusted by controllers associated with the pre-heat station 102.

In one embodiment, the system 100 includes the robot 502 that is constructed and arranged to lift the blank 108 from the pre-heat station 102 and place the blank 108 on a blank loader 506 of the furnace 104. In another embodiment, the system 100 includes a blank feeder that is disposed between the pre-heat station 102 and the furnace 104 and is operatively connected to both the pre-heat station 102 and the furnace 104. In one embodiment, the blank feeder is constructed and arranged to convey the blank 108 from the pre-heat station 102 to the furnace 104. That is, the blank feeder is constructed and arranged to extend continuously from the pre-heat station 102 to the furnace 104. In one embodiment, the blank feeder is an indexing blank feeder and includes a plurality of driven rollers. In one embodiment, the indexing feature of the blank feeder comprises a plurality of indexing fingers for aligning the blank 108 in a predetermined position prior to entering the furnace 104. In one embodiment, the blank feeder is insulated from the surrounding environment, or includes a heater (not shown) so that the temperature of the patch blank 112 of the heated blank 108 is maintained at the desired, pre-heat temperature PH_Twhen the blank 108 enters the furnace 104.

FIGS. 9 and 10 show exemplary pre-heat station in accordance with an embodiment of the present patent application.

In one embodiment, the blank 108 is then transferred from the pre-heat station 102 into the roller hearth furnace 104 where the temperature of remaining areas/portions (i.e., without pre-heat) 116 are heated to the deformation temperature D_T, as well as that in the pre-heated patch area/blank 112. In one embodiment, the final/deformation temperatures between unpatched and patched areas can be different.

In one embodiment, the non-patched region 116 of the blank 108 is first heated in the roller hearth furnace 104 to the pre-heat temperature and the non-patched region 116 of the blank 108 is then further heated to the deformation temperature. In one embodiment, as the patched region 112 of the blank 108 is already at the pre-heat temperature, when received by the roller hearth furnace 104, the patched region 112 of the blank 108 is heated in the roller hearth furnace 104 to the deformation temperature.

In one embodiment, the furnace 104 includes a housing 124 and a heating system 126 (e.g., direct or indirect). In one embodiment, the furnace 104 may include a plurality of driven rollers. In one embodiment, the furnace 104 may include a flat surface 122 to support the pre-heated blank 108 during the furnace heating. In one embodiment, the furnace 104 is a continuous furnace. In one embodiment, the furnace 104 is a roller hearth furnace. In one embodiment, the heating in the furnace 104 is not only limited to roller hearth radiant heating, but can include other heating methods, e.g., induction, conduction, electrical resistance, flame impingement, etc.

In one embodiment, the pre-heated blank 108, received from the pre-heat station 102, is transported through the furnace 104 using the driven rollers. That is, in one embodiment, the plurality of driven rollers are configured to convey the blank through the furnace 104. In one embodiment, the driven rollers comprises mechanically driven (e.g., ceramic material) rollers or rollers of the type used in the hearth type furnaces. In one embodiment, the driven rollers of the furnace 104 are constructed and arranged to rotate continuously, remain stationary for periods of time, or oscillate forward and backward, depending on the amount of heating desired.

In one embodiment, the heating system 126 includes a gas burner, an electric heater, or another type of heater. In one embodiment, the heating system 126 comprises a single heating element or a plurality of heating elements. For example, the heating system 126 includes a plurality of tubes containing burning gas, or a plurality of heated coils.

In one embodiment, the furnace 104 is operatively connected to the controller C. In one embodiment, the controller C is configured to determine whether the blank 108, in the furnace 104, has first reached the pre-heat temperature PH_Tand then has reached the deformation temperature D_T. In one embodiment, this may be determined either with sensors associated with the furnace 104 or by monitoring the amount of time that each blank 108 remains in the furnace 104. In one embodiment, the controller C is also configured to adjust the amount of time that the blank 108 is in the furnace 104. In one embodiment, the deformation temperature D_Tis higher than 700° C. In another embodiment, the deformation temperature D_Tis in the range of 700° C. and 1000° C.

In one embodiment, the system 100 includes the robot 503 that is constructed and arranged to lift the blank 108 from a blank loader 508 of the furnace 104 and place the blank 108 in position in the press 106. In another embodiment, the system 100 includes a blank feeder that is disposed between the furnace 104 and the press 106 and is operatively connected to both the furnace 104 and the press 106. In one embodiment, the blank feeder is constructed and arranged to convey the blank 108 from the furnace 104 to the press 106. That is, the blank feeder is constructed and arranged to extend continuously from the furnace 104 to the press 106. In one embodiment, the blank feeder is an indexing blank feeder and includes a plurality of driven rollers. In one embodiment, the indexing feature of the blank feeder comprises a plurality of indexing fingers for aligning the blank 108 in a predetermined position prior to entering the press 106. In one embodiment, the blank feeder is insulated from the surrounding environment, or includes a heater (not shown) so that temperature decrease from deformation temperature D_Tof the heated blank 108 can be minimized, when the blank 108 enters the press 106.

In one embodiment, the press 106 includes a pair of dies 128 and 130. In one embodiment, the press 106 is constructed and arranged to stamp the heated blank 108 between the pair of dies 128 and 130 to form the shaped part or component. That is, the heated blank 108 (i.e., heated to the deformation temperature, D_Tin the furnace 104) is stamped between the pair of dies 128 and 130 to form the shaped part or component.

In one embodiment, at least one of the dies 128 and 130 is moveable. In one embodiment, the press 106 is operatively connected to the controller C. In one embodiment, the controller C is configured to actuate the dies 128 and 130 (after the heated blank 108 from the furnace 104 is properly placed between the dies 128 and 130 (e.g., by the robot 503)) such that the dies 128 and 130 are brought into contact with each other to form the shaped part or component therebetween. For example, in one embodiment, the shaped parts or components may include parts or components for use as chassis or body components of an automobile. In one embodiment, shaped parts or components alternatively may be used in other applications.

In one embodiment, the press 106 is also constructed and arranged to quench the shaped part between the dies 128 and 130. In one embodiment, the controller C is also configured to adjust the amount of time that the parts are quenched between the dies 128 and 130. In one embodiment, the blank 108 is typically heated in the furnace 104 to achieve an austenitic microstructure, and then quenched in the dies 128 and 130 to transform the austenitic microstructure to a martensitic and/or mixed microstructure. In one embodiment, the hot forming procedures (i.e., pre-heat in the pre-heat station 102, heating in the furnace 104, and shaping in the press 106) run continuously to produce a plurality of the shaped parts at a high rate and low cost.

In one embodiment, the system 100 includes the robot 504 that is constructed and arranged to lift the shaped components or parts from the press 106 and place the shaped components or parts in position on cooling racks 512.

The table shown in FIG. 6 provides a comparison of various residence times between the system of the present patent application and the prior art system. For example, in one embodiment, the residence time in the furnace 104 for the center of the patch blank 112 is reduced from 361 seconds when using the prior art system to 273 seconds when using the system 100 of the present patent application. In one embodiment, the residence time in the furnace 104 for the edge(s) of the patch blank 112 is reduced from 300 seconds when using the prior art system to 249 seconds when using the system 100 of the present patent application. In one embodiment, the residence time for the patched area/blank 112 of the blank 108 was reduced by 24% in the present patent application compared to the residence time for the blank 108 the prior art system. In one embodiment, the residence time for the unpatched portions 116 (i.e., portions surrounding the patch blank 112) of the blank 108 remained about the same using the prior art system and using the system 100 of the present patent application.

FIGS. 7 and 8 show graphical representations of the various temperature profiles of the blank heated using the prior art system and using the system of the present patent application, respectively. The temperatures (i.e., measured in ° C.) of the various portions of the blank are shown on the left hand side Y-axis of the graphs in FIGS. 7 and 8 and the residence times of the various portions of the blank (i.e., measured in seconds) are on the X-axis of the graphs FIGS. 7 and 8.

As can be seen from the graph of FIG. 7, in the prior art system, all the heating of the blank is done in the furnace and there is no pre-heat of the blank in the prior art system. Referring to FIG. 7, the temperature profiles of the patch center (PC), the patch edge (PE) and the unpatched portion (UP) show gradual increase in their corresponding temperatures (till they reach the deformation temperature D_T) because of the furnace heating. The temperature profiles clearly show that the temperatures of the patch area/blank do not reach the deformation temperature D_Ttill the residence time of 361 seconds in the furnace.

Referring to the graph of FIG. 8, in the system of the present patent application, the patch area/blank of the blank is pre-heated in the pre-heat station 102 by contact, thermal conduction heating. The temperature profiles of the patch center (PC) and the patch edge (PE) show that temperatures of the patch center (PC) and the patch edge (PE) reach an intermediate/pre-heat temperature PH_Twhen the patch blank/area is being pre-heated in the pre-heat station 102, while the temperature profile of the unpatched portion (UP) shows a very slight or no increase in the temperature of the unpatched portion when the patch blank/area is being pre-heated in the pre-heat station 102. The temperature profile of the unpatched portion (UP) shows that the temperature of the unpatched portion when the blank is being heated in the furnace 104 first catches up to the intermediate/pre-heat temperature PH_Tof the patch center (PC) and the patch edge (PE) and from thereon reaches the deformation temperature D_T. The temperature profiles of the patch center (PC) and the patch edge (PE) shows that the temperatures of the patch center (PC) and the patch edge (PE) when the blank is being heated in the furnace 104 reaches the deformation temperature D_Tat about the residence time of 273 seconds and 249 seconds, respectively.

In one embodiment, the timings (i.e., furnace residence timing for the patch center, the patch edge, and the unpatched regions with preheat) of the present patent application shown in FIGS. 6 and 8 are exemplary and are not construed to be limiting in anyway. In one embodiment, the timings (i.e., furnace resistance timing for the patch center, patch edge, and unpatched regions with preheat) may vary and depend on various factors, such as, thickness of the blank, geometry of the blank, pre-heat temperature, contact pressure, etc. and any combination thereof.

Although the present patent application has been described in detail for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that the present patent application is not limited to the disclosed embodiments, but, on the contrary, is intended to cover modifications and equivalent arrangements that are within the spirit and scope of the appended claims. In addition, it is to be understood that the present patent application contemplates that, to the extent possible, one or more features of any embodiment can be combined with one or more features of any other embodiment.

CONDUCTION PRE-HEATING OF SHEET FOR HOT FORMING

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