Patent Publication Number: US-2022212242-A1

Title: A hot press forming apparatus and a method for hot press forming a blank

Description:
TECHNICAL FIELD 
     Aspects of the present invention relate to a hot press forming apparatus for forming a blank, wherein the hot press forming apparatus comprises a first die and a second die. The first die has at least one die cavity, and the second die has at least one die protrusion, the die protrusion of the second die being complementary to the die cavity of the first die. The hot press forming apparatus is configured to, by means of the first and second dies, press form the blank placed between the first and second dies. Further, aspects of the present invention relate to a method for hot press forming a blank. 
     BACKGROUND 
     Hot pressed metal parts, for example parts of aluminium, are often used in the car industry for various parts of the car, e.g. thresholds, bumpers, support elements and structures etc. Other fields of application are also possible. When hot press forming a blank between two dies to form a metal part, blank material may remain on the press forming surface of a die after press forming. This may be called “cladding” and impairs the process of hot press forming metal parts and impairs the quality of the resulting metal parts. 
     SUMMARY 
     An object of embodiments of the invention is to provide a solution which mitigates or solves the drawbacks and problems of conventional solutions. 
     According to a first aspect of the invention, the above-mentioned and other objects of the embodiments of the present invention are attained by providing a hot press forming apparatus for forming a blank, wherein the hot press forming apparatus comprises a first die and a second die. The first die has at least one die cavity, and the second die has at least one die protrusion. The die protrusion of the second die being complementary to the die cavity of the first die. The hot press forming apparatus is configured to, by means of the first and second dies, press form the blank placed between the first and second dies. At least one of the first and second dies has a draw radius. A member is attached to a die which has a draw radius, at least a portion of the member being positioned adjacent to or on the draw radius. The member defines a first press forming surface, and the die holding the member defines a second press forming surface outside the first press forming surface. The member and the die, which holds the member, are configured such that during the same hot press forming, a first friction arises between the blank and the first press forming surface when the blank is in contact with the member and a second friction arises between the blank and the second press forming surface when the blank is in contact with the die holding the member. The first friction is lower than the second friction. Since the member is attached to a die of the apparatus, the apparatus comprises the member. 
     An advantage of the apparatus according to the first aspect is that an increased or improved deformability, or suitability for forming, is provided. The reason, which has been identified by the inventor, is that a higher force is required to pull the blank material over the draw radius when the friction is high adjacent to or on the draw radius, which results in an increased strain or elongation of the blank material and an increased risk of fractures in or breaking of the resulting metal part. The inventor has found that a reduction of the friction adjacent to or on the draw radius by means of the innovative member and the innovative position of the member means that less force is required to pull the blank material over the draw radius and an excessive strain or elongation of the blank material is thus avoided. The result is an improved quality of the resulting metal parts. 
     A further advantage of the apparatus according to the first aspect is reduced cladding on the die, whereby inter alia the wear on the dies is reduced and the amount of required maintenance is reduced. Since the cladding is reduced, also the overall friction is more stable which results in improved tolerances of the resulting metal parts. When cladding occurs, the friction experienced by the blank is changed, for example increased. When this happens, the force required to form the resulting part from the blank is increased, which in turn increases the risk of fractures in and breaking of the resulting metal part. The result is also an excessive strain or elongation of the blank material, which negatively affects the tolerances of the resulting metal parts, since the movement of the blank during hot press forming is not identical between the different pressings. Further, an advantage of the apparatus according to the first aspect is that an improved surface quality is attained. When cladding occurs, the result is often that scratches are produced from the pulling of the blank when hot press forming, which is a problem especially for resulting metal parts which are to be visible when mounted. 
     Another advantage of the apparatus according to the first aspect is that less lubricant is required, which results in reduced costs and less pollution from the hot press forming to the environment, which in turn provides for a hot press forming which has less negative impact on the environment. 
     The inventor has found that the above-mentioned problems solved by the apparatus according to the first aspect are most prominent adjacent to or on the draw radius, because the biggest lateral displacement of the blank takes place adjacent to or on the draw radius. 
     According to an advantageous embodiment of the hot press forming apparatus according to the first aspect, at least a portion of the member is positioned, or located, on the draw radius. The positive technical effects associated with this embodiment are mentioned above. 
     According to an advantageous embodiment of the hot press forming apparatus according to the first aspect, at least a portion of the member surrounds the die cavity or the die protrusion. An advantage of this embodiment is that cladding on the die is further reduced, and the positive technical effects mentioned above are further enhanced. 
     According to a further advantageous embodiment of the hot press forming apparatus according to the first aspect, at least a portion of the member is positioned outside the die cavity or the die protrusion. An advantage of this embodiment is that cladding on the die is further reduced, and the positive technical effects mentioned above are further enhanced. 
     According to another advantageous embodiment of the hot press forming apparatus according to the first aspect, the member is provided as a coating applied to a die that has a draw radius. An advantage of this embodiment is that the member is attached to the die in an efficient manner, whereby the positive technical effects mentioned above are further enhanced. 
     According to still another advantageous embodiment of the hot press forming apparatus according to the first aspect, the member is provided as a liquid applied to a die, which has a draw radius, and is subsequently cured. An advantage of this embodiment is that the member is attached to the die in an efficient manner, whereby the positive technical effects mentioned above are further enhanced. 
     According to yet another advantageous embodiment of the hot press forming apparatus according to the first aspect, the member comprises an adhesive tape having a first surface and a second surface, wherein the first surface of the adhesive tape forms the first form pressing surface of the member, and the second surface of the adhesive tape is provided with at least one adhesive substance, and wherein the second surface of the adhesive tape is attached to a die, which has a draw radius, by means of the at least one adhesive substance. An advantage of this embodiment is that the member is attached to the die in an efficient and uncomplicated manner, whereby the positive technical effects mentioned above are further enhanced. 
     According to an advantageous embodiment of the hot press forming apparatus according to the first aspect, a die, which has a draw radius, is provided with at least one recess holding the member. An advantage of this embodiment is that the member is attached to the die in an efficient manner, whereby the positive technical effects mentioned above are further enhanced. 
     According to a further advantageous embodiment of the hot press forming apparatus according to the first aspect, the member is resilient. An advantage of this embodiment is that the displacement of the blank, for example the lateral displacement of the blank, during hot press forming is further improved. An advantage of this embodiment is also that the positive technical effects mentioned above are further enhanced. 
     According to another advantageous embodiment of the hot press forming apparatus according to the first aspect, the first die has a draw radius, and the member is attached to the first die. The inventor has identified that the problems mentioned above in relation to the draw radius are especially prominent with regard to the die cavity. An advantage of this embodiment is that the lateral displacement of the blank during hot press forming is further improved. An advantage of this embodiment is also that the positive technical effects mentioned above are further enhanced. 
     According to yet another advantageous embodiment of the hot press forming apparatus according to the first aspect, the member is a polymer member. An advantage of this embodiment is that the lateral displacement of the blank during hot press forming is further improved. An advantage of this embodiment is also that the positive technical effects mentioned above are further enhanced. 
     According to still another advantageous embodiment of the hot press forming apparatus according to the first aspect, the polymer member is made of an elastomer or a mixture of elastomers. An advantage of this embodiment is that the lateral displacement of the blank during hot press forming is further improved. An advantage of this embodiment is also that the positive technical effects mentioned above are further enhanced. 
     According to an advantageous embodiment of the hot press forming apparatus according to the first aspect, the polymer member is at least partly made of polyimide. An advantage of this embodiment is that the displacement of the blank during hot press forming is further improved. An advantage of this embodiment is also that the positive technical effects mentioned above are further enhanced. 
     According to a further advantageous embodiment of the hot press forming apparatus according to the first aspect, one of the first and second dies is an upper die placed above the other die, which is a lower die, wherein at least one of the first and second dies is essentially vertically movable in relation to the other die, and wherein the essentially vertically movable die is configured to move essentially vertically towards the other die for press forming the blank. An advantage of this embodiment is that the positive technical effects mentioned above are further enhanced. 
     According to a second aspect of the invention, the above-mentioned and other objects of the embodiments of the present invention are attained by providing a method for hot press forming a blank, the method comprising the steps of:
         Placing the blank between a first die and a second die, wherein the first die has at least one die cavity, and the second die has at least one die protrusion, the die protrusion of the second die being complementary to the die cavity of the first die, wherein at least one of the first and second dies has a draw radius, wherein a member is attached to a die that has a draw radius, at least a portion of the member being positioned adjacent to or on the draw radius, wherein the member defines a first press forming surface, and the die holding the member defines a second press forming surface outside the first press forming surface;   Heating the blank; and   Press forming the blank placed between the first and second dies by means of the first and second dies, wherein during the same hot press forming, a first friction arises between the blank and the first press forming surface when the blank is in contact with the member and a second friction arises between the blank and the second press forming surface when the blank is in contact with the die that holds the member, the first friction being lower than the second friction.       

     Advantages of the method according of the second aspect of the present invention correspond to advantages mentioned above in connection with the hot press forming apparatus according to the first aspect. 
     According to an advantageous embodiment of the method according to the second aspect, one of the first and second dies is an upper die placed above the other die, which is a lower die, and the method is characterized by essentially vertically moving at least one of the first and second dies towards the other die for press forming the blank. An advantage of this embodiment is that the positive technical effects mentioned above are further enhanced. 
     The above-mentioned features and embodiments of the hot press forming apparatus and the method, respectively, may be combined in various possible ways providing further advantageous embodiments. 
     Further advantageous embodiments of the hot press forming apparatus and method according to the present invention and further advantages with the embodiments of the present invention emerge from the dependent claims and the detailed description of embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects of the present invention will now be described, for exemplary purposes, in more detail by way of embodiments and with reference to the enclosed drawings, in which: 
         FIG. 1  is a schematic side view of first embodiments of the hot press forming apparatus according to the first aspect; 
         FIG. 2  is a schematic top view of the first die of the apparatus of  FIG. 1 ; 
         FIG. 3  is a schematic side view of a second embodiment of the hot press forming apparatus according to the first aspect; 
         FIG. 4  is a schematic top view of the first die of the apparatus of  FIG. 3 ; and 
         FIG. 5  is a flow chart illustrating embodiments of the method according to the second aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIGS. 1 and 2 , a hot press forming apparatus  102  for forming a blank  104  is provided. The blank  104  may comprise or consist of a metal or a metal alloy. The blank  104  may comprise or consist of aluminium or a metal alloy including aluminium. The blank  104  may be a sheet of a material, for example a sheet comprising or consisting of a metal or a metal alloy. The hot press forming apparatus  102  includes a first die  106  and a second die  108 . The first die  106  has at least one die cavity  110 , which is surrounded by the remainder of the first die  106 . The second die  108  has at least one die protrusion  112 . The die protrusion  112  of the second die  108  is complementary to the die cavity  110  of the first die  106 . The first die  106  may be called a female die, and the second die  108  can be called a male die. Each of the first and second dies  106 ,  108  may comprise or consist of a metal or a metal alloy. In the embodiment shown in  FIGS. 1 and 2 , one of the first and second dies  106 ,  108  is an upper die  108  placed above the other die  106 , which is a lower die  106 . At least one of the first and second dies  106 ,  108  is essentially vertically movable in an essentially vertical direction  114  in relation to the other die  106 ,  108 . The essentially vertically movable die  106 ,  108  is configured to move essentially vertically towards the other die  106 ,  108  for press forming the blank  104 . The first die  106  can be a lower die  106 , or an upper die, in relation to the second die  108 . The second die  108  can be an upper die  108 , or a lower die, in relation to the first die  106 . In the embodiment shown in  FIGS. 1 and 2 , the first die  106  is a lower die  106 , and the second die  108  is an upper die  108 . However, other positions of the first and second dies  106 ,  108  are possible. 
     With reference to  FIGS. 1 and 2 , the hot press forming apparatus  102  is configured to, by means of the first and second dies  106 ,  108 , press form the blank  104  placed between the first and second dies  106 ,  108 . At least one of the first and second dies  106 ,  108  has a draw radius  116 , or defines or presents a draw radius  116 . In the embodiment shown in  FIGS. 1 and 2 , at least the first die  106  has a draw radius  116 . The draw radius  116  may be adjacent to the die cavity  110  of the first die  106 . When the second die  108 , i.e. the male die, has a draw radius, the draw radius may be adjacent to the die protrusion  112  of the second die  108 . 
     The apparatus  102  includes a member  118  attached to a die  106  which has a draw radius  116 . The apparatus  102  could include a plurality of members  118  attached to a die  106 . Thus, in the embodiment shown in  FIGS. 1 and 2 , the member  118  is attached to the first die  106 . At least a portion  119  of the member  118  is positioned adjacent to or on the draw radius  116 . The member  118  defines a first press forming surface  120 . The die  106  holding the member  118 , in the present case the first die  106 , defines a second press forming surface  122  outside the first press forming surface  120 . The area of the first press forming surface  120  may be less than 25% of the area of the second press forming surface  122 , for example less than 10% of the area of the second press forming surface  122 . 
     The member  118  and the die  106 , which holds the member  118 , are configured such that during the same hot press forming, a first friction arises, or is present, between the blank  104  and the first press forming surface  120  when the blank  104  is in contact with, and possibly moves in relation to, the member  118  and a second friction arises between the blank  104  and the second press forming surface  122  when the blank  104  is in contact with, and possibly moves in relation to, the die  106  which holds the member  118 . As mentioned above, in the embodiment shown in  FIGS. 1 and 2 , the first die  106  holds the member  118 . The first friction, i.e. the friction between the blank  104  and the first press forming surface  120 , is lower than the second friction, i.e. the friction between the blank  104  and the second press forming surface  122 . 
     Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. Dry friction is a force that opposes the relative lateral motion of two solid surfaces in contact, i.e. the blank  104  and the first press forming surface  120 , or the blank  104  and the second press forming surface  122  with regard to the solution described in this disclosure. Dry friction may be subdivided into static friction (“stiction”) between non-moving surfaces, and kinetic friction between moving surfaces. Said first friction is reduced in relation to said second friction, i.e. the first friction is lower than the second friction. The coefficient of friction, COF, of the first press forming surface  120  is lower than the COF of the second press forming surface  122 , which is valid for both static friction and kinetic/sliding friction. The first friction may be at least 10% lower, for example at least 30% lower, or at least 50% lower, than the second friction. For example, the COF of the first press forming surface  120  may be at least 10% lower, for example at least 30% lower, or at least 50% lower, than the COF of the second press forming surface  122 . The member  130  may be called a friction-reducing member  130 . 
     The member  118  is advantageously elongated. The material of the member  118 , or the material of the first press forming surface  120 , may be different from the material of the die  106  holding the member  118 , or different from the material of the second press forming surface  122 . Each of the first and second press forming surfaces  120 ,  122  may be provided with a structure or a pattern. The structure or pattern may include grooves and/or bars. The structure or pattern of the first press forming surface  120  may be different from the structure or pattern of the second press forming surface  122 . The member  118  may be adjacent to die cavity  110  of the first die  106 . If the second die  108  were holding a member, the member may be adjacent to the die protrusion  112 . Both the first and second dies  106 ,  108  could hold its own member  118  or members  118 . The member  118  may be a polymer member  118 . The polymer member  118  may be made of an elastomer or a mixture of elastomers. Advantageously, the polymer member  118  is at least partly made of polyimide. The entire member  118  may be made of polyimide. 
     With reference to  FIG. 2 , at least a portion of the member  118  or the entire member  118  surrounds the die cavity  110  of the first die  106 . If the second die  108  were holding a member  188 , the member  118  could surround the die protrusion  112  of the second die  108 . At least a portion of the member  118  is positioned outside the die cavity  110  of the first die  106 . If the second die  108  were holding a member  188 , at least a portion of the member  118  could be positioned outside the die protrusion  112  of the second die  108 . 
     With reference to the first embodiments of  FIGS. 1 and 2 , the member  118  may be provided as a coating applied to the die  106  that has a draw radius  116 , for example to the first die  106 . Alternatively, the member  118  may be provided as a liquid applied to the die  106  that has a draw radius  116  and may subsequently be cured. Alternatively, the member  118  may comprise an adhesive tape having a first surface  120  and a second surface  124 . The first surface  120  of the adhesive tape forms the first form pressing surface  120  of the member  118 , and the second surface  124  of the tape is provided with at least one adhesive substance. The second surface  124  of the tape is attached to the die  106 , which has a draw radius  116 , i.e. the first die  106  in the embodiment shown in  FIGS. 1 and 2 , by means of the at least one adhesive substance. 
     With reference to  FIGS. 3 and 4 , a second embodiment of the apparatus  202  is illustrated. In most parts, the apparatus  202  of the second embodiment of  FIGS. 3  and  4  corresponds to the apparatus  102  of the first embodiments of  FIGS. 1 and 2 . The difference is that the die  206 , for example the first die  206  with the die cavity  210 , which has a draw radius  216 , is provided with at least one recess  226  or groove holding the member  218 . At least a portion  219  of the member  218  is positioned adjacent to or on the draw radius  216 . The member  218  may essentially correspond to the member  118  of  FIGS. 1 and 2 . For example, the member  218  also defines a first press forming surface  220 . However, the member  218  of  FIGS. 3 and 4  is resilient or flexible, such that before hot press forming the first press forming surface  220  of the member  218  is slightly elevated above the second press forming surface  222  of the first die  206 , the second press forming surface  222  being outside the first press forming surface  220 . When the blank  104  is pressed by the first and second dies  206 ,  108  the resilient member  218  is compressed and the first press forming surface  220  of the member  218  is thus moved towards the same level as the second press forming surface  222  of the first die  206 . Otherwise, the features of the apparatus  202  of the second embodiment of  FIGS. 3 and 4  correspond to the features of the apparatus  102  of first embodiments of  FIGS. 1 and 2  and are thus not repeated here. For example, the second die  108  of the apparatus  202  of the second embodiment of  FIGS. 3 and 4  corresponds to the second die  108  of the apparatus of the first embodiments of  FIGS. 1 and 2 . 
     With reference to  FIG. 5 , a flow chart illustrates embodiments of the method for hot press forming a blank  104  according to the second aspect of the present invention. The method includes the steps of:
         Placing  301  the blank  104  between a first die  106  and a second die  108 , wherein the first die  106  has at least one die cavity  110 , and the second die  108  has at least one die protrusion  112 , the die protrusion  112  of the second die  108  being complementary to the die cavity  110  of the first die  106 , wherein at least one of the first and second dies  106 ,  108  has a draw radius  116 , wherein a member  118  is attached to a die  106  that has a draw radius  116 , at least a portion  119  of the member  118  being positioned adjacent to or on the draw radius  116 , wherein the member  118  defines a first press forming surface  120 , and the die  106  holding the member  118  defines a second press forming surface  122  outside the first press forming surface  120 ;   Heating  302  the blank  104 ; and   Press forming  303  the blank  104  placed between the first and second dies  106 ,  108  by means of the first and second dies  106 ,  108 , wherein during the same hot press forming, a first friction arises between the blank  104  and the first press forming surface  120  when the blank  104  is in contact with, and possibly moved in relation to, the member  118  and a second friction arises between the blank  104  and the second press forming surface  122  when the blank  104  is in contact with, and possibly moved in relation to, the die  106  that holds the member  118 , the first friction being lower than the second friction.       

     The step of press forming  303  may include, when one of the first and second dies  106 ,  108  is an upper die  108  placed above the other die  106 , which is a lower die  106 , essentially vertically moving at least one  106 ,  108  of the first and second dies  106 ,  108  towards the other die  106 ,  108  for press forming the blank  104 . The step of placing  301  the blank  104  between the first die  106  and the second die  108  may be performed by moving the blank  104  in relation the first and/or second die  106 ,  108 , for example by lateral movement of the blank  104 , or by moving the first and/or second die  104 ,  106  in relation to the blank  104 , for example by lateral movement of the first and/or second die  104 ,  106 . The blank  104  may be heated  302  before the blank  104  is placed between the first and second dies  106 ,  108 , or after the blank  104  is placed between the first and second dies  106 ,  108 . However, the blank  104  is always heated before press forming  303 . After press forming  303 , a step of cooling the blank  104  may be performed. 
     The features of the different embodiments of the apparatus and method disclosed above may be combined in various possible ways providing further advantageous embodiments. The invention shall not be considered limited to the embodiments illustrated, but can be modified and altered in many ways by one skilled in the art, without departing from the scope of the appended claims.