Method for trimming and punching thermoformed part, and trimming and punching die

Abstract

Provided is a method for trimming and punching a thermoformed part and a trimming and punching die. The method includes the following steps: S 1 : in a hot stamping die, subjecting a workpiece to hot stamping, initial quenching, and temperature preservation; S 2 : when a temperature of the workpiece is cooled to a preset temperature, taking out the workpiece and moving the workpiece into a trimming and punching die; S 3 : determining a to-be-trimmed position and a to-be-punched position, and heating the to-be-trimmed position and the to-be-punched position; S 4 : after a set condition is reached, trimming and punching the workpiece; and S 5 : subjecting the workpiece to secondary quenching, so that a hot stamped part can be rapidly punched and trimmed. By accurately controlling cooling rate of the workpiece during machining, temperatures of the workpiece at various positions can be cooled, which helps prevent deformation or cracks and ensures performance of the workpiece.

What is claimed is: 
     
         1 . A method for trimming and punching a thermoformed part, comprising following steps:
 S 1 : in a hot stamping die, subjecting a workpiece to hot stamping, initial quenching, and temperature preservation;   S 2 : when a temperature of the workpiece is cooled to a preset temperature, taking out the workpiece and moving the workpiece into a trimming and punching die;   S 3 : determining a to-be-trimmed position and a to-be-punched position, and heating the to-be-trimmed position and the to-be-punched position;   S 4 : after a set condition is reached, trimming and punching the workpiece, wherein the set condition includes a temperature of a region on the workpiece within a set distance from notches corresponding to the to-be-trimmed position and the to-be-punched position is within a set temperature range; and   S 5 : subjecting the workpiece to secondary quenching.   
     
     
         2 . The method for trimming and punching a thermoformed part according to  claim 1 , wherein during the initial quenching or the secondary quenching, the workpiece is subjected to liquid cooling, and a plurality of cooling channels are used for liquid cooling; and
 the subjecting the workpiece to liquid cooling comprises:   S 01 : determining cooling time and initial coolant flow rates at inlets of the cooling channels according to heat dissipation requirements of pre-selected key points on the workpiece and initial coolant temperatures;   S 02 : determining, according to the cooling time, a relationship between target flow rates at the inlets of the cooling channels and time, target temperatures at the key points at different moments within the cooling time, and monitoring actual temperatures at the key points;   S 03 : controlling flow rates at the inlets of the cooling channels according to the relationship between the target flow rates at the inlets of the cooling channels and the time;   S 04 : during the cooling, comparing actual temperatures of the key point at a current moment with the target temperature, and correcting the relationship between the target flow rates at the inlets of the cooling channels and the time according to comparison results; and   S 05 : controlling coolant flow rates at the inlets of the cooling channels according to a relationship between the target flow rates at the inlets of the cooling channels and the time after correction; and repeating step S 04  and step S 05  until the cooling time ends.   
     
     
         3 . The method for trimming and punching a thermoformed part according to  claim 2 , wherein in step S 02 , the determining a relationship between target flow rates at the inlets of the cooling channels and time comprises:
 S 021 : determining cooling capacities of the cooling channels for the key points;   S 022 : determining a ratio of degrees of influence of the cooling channels on the key points;   S 023 : determining cooling intensity requirements of the key points;   S 024 : determining a relationship between a total target flow rate at the inlets of the cooling channels and time according to the cooling intensity requirements of the key points, the cooling capacities of the cooling channels for the key points, and the ratio of degrees of influence of the cooling channels on the key points; and   S 025 : allocating the target flow rates at the inlets of the cooling channels according to the cooling intensity requirements of the key points and a ratio of the target flow rates at the inlets of the cooling channels.   
     
     
         4 . The method for trimming and punching a thermoformed part according to  claim 3 , wherein in step S 021 , the relationship between the target flow rates at the inlets of the cooling channels and the time is determined by the cooling capacities of the cooling channels for the key points; and
 the cooling capacities of the cooling channels for the key points are determined by following formula:   
       
         
           
             
               
                 sa 
                 = 
                 
                   
                     ∫ 
                     
                       t 
                       1 
                     
                     
                          
                       
                         t 
                         2 
                       
                     
                   
                   
                     
                       
                         
                           a 
                           1 
                         
                         ⁢ 
                         
                           cSv 
                           ⁡ 
                           ( 
                           
                             
                               T 
                               m 
                             
                             - 
                             
                               T 
                               s 
                             
                           
                           ) 
                         
                       
                       
                         
                           l 
                           ⁡ 
                           ( 
                           t 
                           ) 
                         
                         2 
                       
                     
                     ⁢ 
                     dt 
                   
                 
               
               , 
             
           
         
         where sa denotes a cooling capacity, a 1  denotes a constant coefficient, c denotes a specific heat capacity of coolant, S denotes a cross-sectional area of a cooling channel, v denotes a flow rate of the coolant, Tm denotes a temperature at a wall surface of the cooling channel, and Ts denotes a temperature of the coolant; t1 denotes a time for the coolant to flow from an inlet of the cooling channel to a first endpoint of a cooling section; t2 denotes a time for the coolant to flow from the inlet to a second endpoint of the cooling section; and l(t) denotes a distance between a position of the coolant at a certain point at time t and the corresponding key point starting from the inlet. 
       
     
     
         5 . The method for trimming and punching a thermoformed part according to  claim 4 , wherein the cooling section is selected by using the key point as a center of a circle and using a preset distance as a radius to form a sphere, and a portion of the cooling channel located in a spherical surface is the cooling section. 
     
     
         6 . The method for trimming and punching a thermoformed part according to  claim 3 , wherein a formula for correcting the relationship between the target flow rates at the inlets of the cooling channels and the time according to comparison results is: 
       
         
           
             
               
                 
                   q 
                   ⁡ 
                   ( 
                   t 
                   ) 
                 
                 = 
                   
                 
                   Sv 
                   = 
                   
                     
                       Q 
                       ⁡ 
                       ( 
                       t 
                       ) 
                     
                     + 
                     
                       b 
                       ⁢ 
                       Δ 
                       ⁢ 
                       q 
                     
                   
                 
               
               , 
             
           
         
         where q(t) denotes the relationship between the target flow rates at the inlets of the cooling channels and the time after the correction, Q(t) denotes the relationship between the target flow rates at the inlets of the cooling channels and the time before the correction, b denotes an adjustment factor, and Δq denotes a unit adjustment amount of a target flow rate; and 
         a calculation formula for the adjustment factor is: 
       
       
         
           
             
               
                 b 
                 = 
                 
                   
                     a 
                     2 
                   
                   ⁢ 
                   
                     
                       
                         T 
                         sj 
                       
                       - 
                       
                         T 
                         mb 
                       
                     
                     
                       
                         ❘ 
                         "\[LeftBracketingBar]" 
                       
                       
                         
                           T 
                           sj 
                         
                         - 
                         
                           T 
                           mb 
                         
                       
                       
                         ❘ 
                         "\[RightBracketingBar]" 
                       
                     
                   
                 
               
               , 
             
           
         
         where a 2  denotes a constant coefficient, T sj  denotes an actual temperature at the corresponding key point, and T mb  denotes a target temperature of the corresponding key point. 
       
     
     
         7 . The method for trimming and punching a thermoformed part according to  claim 3 , wherein a middle portion of at least one of the cooling channels is provided with a plurality of branches. 
     
     
         8 . The method for trimming and punching a thermoformed part according to  claim 1 , wherein step S 1  comprises following steps:
 S 11 : placing a blank material into the hot stamping die, and heating the blank material; 
 S 12 : stamping the blank material to form the workpiece; and 
 S 13 : carrying out the initial quenching and the temperature preservation for a set time; 
 wherein the heating processes in step S 11  and step S 3  are both controlled by proportional-integral-derivative (PID). 
 
     
     
         9 . A trimming and punching die, applied for the method according to  claim 2 , comprising: a first die ( 1 ), a second die ( 2 ), and a third die ( 3 );
 wherein the first die ( 1 ) and the second die ( 2 ) are configured to be pressed on a to-be-trimmed-and-punched workpiece from two sides;   the first die ( 1 ) is provided with a plurality of first holes ( 11 ), a side of the first die ( 1 ) close to the workpiece is provided with a punching portion ( 12 ), and the first holes ( 11 ) pass through the punching portion ( 12 ); a first heating element ( 15 ) is embedded into the punching portion ( 12 ); and the first heating element ( 15 ) is configured to heat a temperature of a to-be-punched region to a set temperature range prior to punching;   the second die ( 2 ) is provided with a plurality of second holes ( 21 ) corresponding to the first holes ( 11 );   a side wall of the first die ( 1 ) is provided with a trimming region ( 13 ), the trimming region ( 13 ) is provided with at least one second heating element ( 22 );   the third die ( 3 ) and the first die ( 1 ) are located on a same side of the workpiece, the third die ( 3 ) is arranged along a circumferential side of the first die ( 1 ), and the third die ( 3 ) is provided with the second heating element ( 22 ) configured to heat a trimming position; and   the first die ( 1 ) is provided with cooling channels configured to carry out the liquid cooling in step S 01  to step S 05 .   
     
     
         10 . The trimming and punching die according to  claim 9 , wherein the trimming region ( 13 ) is provided with a groove ( 14 ), and the second heating element ( 22 ) is arranged in the groove ( 14 ); the second heating element ( 22 ) is configured to heat the trimming region of the workpiece; and a gap is provided between a circumferential side of the second heating element ( 22 ) and a wall of the groove ( 14 ).