Patent Publication Number: US-2023160048-A1

Title: Process of manufacturing aluminum alloy workpiece

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority of Taiwanese Invention Patent Application No. 110143561, filed on Nov. 23, 2021. 
     FIELD 
     The disclosure relates to a process of manufacturing alloy workpieces, especially with regard to a process of manufacturing an aluminum alloy workpiece. 
     BACKGROUND 
     Since aluminum alloy has the characteristics of improved formability after heating, a process with specific forming temperature can be used to form the specific type of aluminum alloy workpieces and achieve desired shape. According to the heating temperature, can be divided into two forming processes: warm forming and hot forming. In the warm forming process, the aluminum alloy sheet is heated to a temperature above 100° C. but below the recrystallization temperature, after that, it is sent into the die for forming and cooling. In the hot forming process, the aluminum alloy sheet is first heated to the solid solution temperature for solution heat treatment, then it is sent into the die for forming and quenching. Subsequently, the formed aluminum alloy sheet must undergo an artificial aging treatment after removing from the forming die to achieve the target strength. 
     However, the subsequent aging treatment in the hot forming process takes a considerable amount of operating time, therefore increasing the production cost and energy consumption of the hot forming process. Moreover, the hot forming die continues to work under the condition of repeated high temperature and rapid cooling. The service life is thus shortened and the production cost of the hot forming process is increased. 
     SUMMARY 
     Therefore, an object of the present disclosure is to provide a process of manufacturing an aluminum alloy workpiece which can conquer at least one of the disadvantages of the previous process. 
     A preparation step, an aging and forming step, and an aging out of forming die step are included in the process of manufacturing an aluminum alloy workpiece according to this disclosure. 
     An aluminum alloy sheet, a forming die, and a handling device are prepared in the preparation step. A transfer mechanism for at least one degree of freedom movement and a dismountable temperature control module connected to the transfer mechanism are included in the handling device. The dismountable temperature control module has a second temperature. 
     The aging and forming step includes a heating substep, a transferring substep, and a forming and cooling substep. 
     In the heating substep, the aluminum alloy sheet is heated to a first temperature lower than a solid solution temperature but higher than a solid solution temperature of a Guinier-Preston Zone (G-P zone), and is then transferred to the temperature control module. 
     In the transferring substep, the transfer mechanism is used for transferring the aluminum alloy sheet contained in the temperature control module into the forming die. The aluminum alloy sheet is maintained at the second temperature through the temperature control module. The second temperature is lower than the solid solution temperature but higher than the solid solution temperature of the G-P zone. In the forming and cooling substep, the aluminum alloy sheet is formed into a target shape while cooling in the forming die. 
     In the aging out of forming die step, the formed aluminum alloy sheet is removed from the forming die and is heated to a third temperature that is lower than the solid solution temperature but higher than the solid solution temperature of the G-P zone, and then undergoes another aging treatment to manufacture the aluminum alloy workpiece. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the present disclosure are apparent with detailed description and figures of the embodiments: 
         FIG.  1    is a flow chart, illustrating the steps involved in a process of manufacturing an aluminum alloy workpiece according to the first embodiment of the present disclosure; 
         FIG.  2    is a perspective view of a handling device used in an aging and forming step of the first embodiment; 
         FIG.  3    is a graph of temperature versus time, illustrating a temperature change of treating an aluminum alloy sheet with the process of the first embodiment; 
         FIG.  4    is a flow chart, illustrating the steps involved in a process of manufacturing an aluminum alloy workpiece according to the second embodiment of the present disclosure; 
         FIG.  5    is a graph of temperature versus time, illustrating a temperature change of treating an aluminum alloy sheet with the process of the second embodiment; and 
         FIG.  6    is a schematic top view, illustrating a layout of a pre-processing substep in a preparation step and a heating substep of an aging and forming step of the second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     It should be noted that similar elements are denoted by the same reference numerals throughout the disclosure before describing the present disclosure in more detail with reference to the figures and embodiments. 
     Referring to  FIG.  1   , a process of manufacturing an aluminum alloy workpiece according to the first embodiment of the present disclosure includes a preparation step  11 , an aging and forming step  12 , and an aging out of forming die step  13 . 
     Referring to  FIGS.  1  and  2   , an aluminum alloy sheet (not shown), a forming die (not shown), and a handling device  2  are prepared in the preparation step  11 . 
     A transfer mechanism  21  for at least one degree of freedom movement and a dismountable temperature control module  22  are included in the handling device  2 . The transfer mechanism  21  includes a robotic arm  29  for detachable connection with the temperature control module  22 . 
     The aluminum alloy sheet in the first embodiment is the AA 7075 aluminum alloy sheet with required pre-aging treatment. Furthermore, the aluminum alloy sheet is manufactured into an automotive stamping part as an example for the first embodiment. The transfer mechanism  21  and the temperature control module  22  can be connected to or separated from each other through a programmable logic control to arrange the layout of automated operations. 
     Referring to  FIGS.  1  to  3   , the aging and forming step  12  includes a heating substep  121 , a transferring substep  122 , and a forming and cooling substep  123 . In the heating substep  121 , the aluminum alloy sheet is heated in a heating station to a first temperature lower than a solid solution temperature (T1) but higher than a solid solution temperature (T2) of a Guinier-Preston Zone (G-P zone) at a rate of more than 10° C. per second. Then, it is transferred to the temperature control module  22  of the handling device  2 . 
     The aluminum alloy sheet is held in the heating station for a period of time at the first temperature to achieve a uniform temperature distribution and also to carry out the first aging treatment. Specifically, the first temperature is 130 to 270° C. if it is the 6000 series of aluminum alloy sheet; and, the heating temperature is 150 to 250° C. if it is the 7000 series of aluminum alloy sheet. 
     The AA 7075 aluminum alloy sheet of AA 7000 series aluminum alloy is taken as an example to illustrate in this embodiment, so the first temperature is set at 200° C. It is worth noting that the holding time of the first temperature is preferably to be chosen as two minutes, which is sufficient for the aluminum alloy sheet to reach a uniform temperature distribution and prepare required heat energy for the subsequent aging treatment. Especially, a strengthening phase of the aluminum alloy sheet is started precipitating and a metastable state is initially reached when the heating temperature is maintained above the solid solution temperature (T2) of the G-P zone. 
     In the transferring substep  122 , the aluminum alloy sheet contained in the temperature control module  22  is transferred through the robotic arm  29  of the transfer mechanism  21  to the forming die within a transport time. The temperature control module  22  has a second temperature. 
     The aluminum alloy sheet is maintained at the second temperature in the temperature control module  22 . The second temperature is lower than the solid solution temperature (T1) but higher than the solid solution temperature (T2) of the G-P zone. 
     The sum of the holding time of the first temperature and the transport time is 5 to 300 seconds to transfer the aluminum alloy sheet into the forming die as soon as possible to prevent the temperature of the aluminum alloy sheet from dropping. A certain formability of the aluminum alloy sheet is ensured when transferring into the forming die and thus the quality of the formed part is optimized. It is noteworthy that the forming die has to be clamped immediately after transferring the aluminum alloy sheet into the forming die to prevent the temperature of the aluminum alloy sheet from dropping after leaving the temperature control module  22 . 
     In the forming and cooling substep  123 , the aluminum alloy sheet is held in the forming die for more than 5 seconds to be formed into a desired shape under condition of improved formability, and the aluminum alloy sheet is formed into a target shape while cooling in the forming die. That is, in the forming and cooling substep  123 , an aluminum alloy plate is formed during the aging process. 
     In the aging out of forming die step  13 , the formed part is removed from the forming die and is heated in another heating station to a third temperature, which is lower than the solid solution temperature (T1) but higher than the solid solution temperature (T2) of the G-P zone. The aluminum alloy workpiece is manufactured after aging treated again. The third temperature is 170 to 190° C. 
     To be specific, the aging out of forming die step  13  is preferable to go with a paint bake process since the aluminum alloy sheet is manufactured to be an automotive stamping part in this embodiment. 
     The temperature and the holding time are set to be 185° C. and 20 minutes, respectively, for the second aging treatment, which can be matched with the parameters of the paint bake process. 
     Besides the advantage of being aging treated again through the paint bake process, the automotive stamping part can also achieve a peak strength and obtain a strengthening phase after the paint bake process. The strength loss of the automotive stamping part due to the paint bake process is avoided. Therefore, the strength of the aluminum alloy workpiece is maintained at a peak state after the paint bake process and the aging treatment and the heating process are coordinated through the manufacture process of the first embodiment. 
     Not only the thermal energy of the paint bake process is properly utilized, the thermal energy consumption is also reduced dramatically compared with the existing heat treatment with parameters of heating to 120° C. and holding for 24 hours. 
     Furthermore, thermal accumulation of the forming die because of frequent contact with heated sheets or mass production is reduced due to lower target forming temperature. The forming die life is effectively increased and the production cost is thus reduced. 
     Referring to  FIGS.  4  and  5   , a process of manufacturing an aluminum alloy workpiece according to the second embodiment of the present disclosure is shown, which is similar with the first embodiment. 
     The difference between the first and second embodiments is that the prepared aluminum alloy sheet in the preparation step  11  of the second embodiment is untreated (F state), and a pre-processing substep  111  is thus concluded in the preparation step  11 . In the pre-processing substep  111 , the aluminum alloy sheet is heated to the solid solution temperature (T1) and is held for a period of time, and is then quenched. Additionally, the aluminum alloy sheet requires further heat treatment in the heating substep  121  to ensure the strength after the entire manufacture process due to not being heat treated compared with the first embodiment. Therefore, the aluminum alloy sheet is slowly heated to the first temperature for 20 minutes, and is then held for 5 minutes. 
     In addition, the overall holding time and transfer time at the first temperature is 5 to 20 minutes since it does not take too much time to transfer the aluminum alloy sheet contained in the temperature control module  22  into the forming die. The second embodiment mainly processes the aluminum alloy sheet that is not being heat treated. The heating substep  121  is preferably conducted in 30 minutes after the pre-processing step  111 . 
     Relative slower heating and longer holding time are required in the heating substep  121  to ensure that the aluminum alloy sheet is completely pre-aged before the forming and cooling substep  123 . Besides the differences mentioned above, the effect of the first embodiment can be achieved by the second embodiment. 
     Referring to  FIG.  6    and  FIG.  4   , a solid solution heating furnace zone (Z1) for conducting the pre-processing substep  111  and a warm-forming heating furnace zone (Z2) for conducting the heating substep  121  can be placed respectively (see  FIG.  6   ) if different aluminum alloy sheets are needed to be manufactured separately by the first embodiment and the second embodiment at the same time. 
     Multiple handling devices  2  are arranged between the solid solution heating furnace zone (Z1) and the warm-forming heating furnace zone (Z2) to achieve the configuration of production lines. The efficiency of whole manufacturing process is optimized and it is conducive to mass production. 
     In summary, the aluminum alloy sheet is contained in the temperature control module  22  to maintain required aging treatment while transferring into the forming die through the handling device  2  by combining heating process of the pre-aging treatment with transfer process of the aluminum alloy sheet of this disclosure. 
     It not only solves the problem of dropping temperature during the transfer process of heated aluminum alloy sheet, but also avoid consumption of time by reheating process. Besides the improved formability after heating is maintained and the quality of workpiece is optimized, the aging treatment process of the aluminum alloy sheet can also be flexibly arranged. 
     Furthermore, the forming and cooling processes are completed in the forming die at the same time, and the aging treatment can also be conducted by going with subsequent process, such as the paint bake process. 
     The peak strength of the aluminum alloy sheet is achieved after completing subsequent processes. 
     In addition to the prevented strength loss, it is beneficial for improving production efficiency by reduced manufacturing time and efficiency costs. Therefore, the object of this disclosure can indeed be achieved. 
     In the description above, numerous specific details have been set forth in order to provide a thorough understanding of the embodiments for the purposes of explanation. 
     However, it will be apparent to those one skilled in the art that one or more other embodiments may be practiced without some of these specific details. 
     It should also be appreciated that reference throughout this specification to “one embodiment,” “an embodiment,” an embodiment with an indication of an ordinal number and so forth means that a particular feature, structure, or characteristic may be included in the practice of the disclosure. It should be further appreciated that in the description, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of various inventive aspects, and that one or more features or specific details from one embodiment may be practiced together with one or more features or specific details from another embodiment, where appropriate, in the practice of the disclosure. 
     While the disclosure has been described in connection with what are considered the exemplary embodiments, it is understood that this disclosure is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.