Abstract:
A seat back frame of a vehicle using a magnesium alloy results in a seat back frame having the properties of a conventional steel press seat back frame. The seat back frame is reinforced regarding its strength and tapers from wider at the lower portion to thinner toward a head rest. The advantageous properties of the alloy seat, such as weight and castability, are much improved over the conventional. The method of molding such a seat back frame include molding the alloy into a mold via even disbursement about a casting gate.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S)  
       [0001]     The present application is based on, and claims priority to Korean Application No. 2004-0041231, filed on Jun. 7, 2004, the disclosure of which is hereby incorporated by reference.  
       TECHNICAL FIELD OF THE INVENTION  
       [0002]     Generally, the present invention relates to a seat back frame of a vehicle. More particularly, the seat back frame is manufactured using a magnesium alloy and a method of manufacturing the same is also provided.  
       BACKGROUND OF THE INVENTION  
       [0003]     In recent years, as vehicles have become more and more luxurious, the requirements for vehicles to comply with the traffic laws and safety regulations has increased, and vehicle owners&#39; growing concerns on conveniences have increased the seats of vehicles have tended to increase in weight. Therefore, as a way to reduce the weight of a seat, seat back frames have been manufactured using light-weight materials instead of steels.  
         [0004]     More specifically, when seat back frames are manufactured using a magnesium alloy, via a high pressure casting, the entire frame can be manufactured as an integral body, thus reducing the number of processing steps. Thereby, the manufacturer has been able to compensate the increased production cost resulting from using a rather expensive light-weighted material. Further, by employing the high pressure casting method, it is possible to perform repeated mass production along with an expected significant reduction in noise due to dimensional accuracy of the components. However, the physical properties of the magnesium alloy are inferior to those of steels, and thus ‘concept designs’ considering the above deficiency should be conducted.  
         [0005]     In particular, the overall shape of a seat back frame can greatly influence its mechanical strength. Therefore, a rib may be inserted into the frame to rectify the strength and it may ease the integrating a bracket for installing auxiliary parts. Again, considering the inferiorities of magnesium alloy in physical properties, as compared to steels, it is essential that ‘concept design’ be conducted in advance. In addition, it is also possible to design a structure having superiorities over steel-made products when the manufacturing process also reflects the casting point of view.  
         [0006]     Furthermore, in molding a seat back frame of a vehicle using a magnesium alloy, the manufacturing process is a most critical step in establishment of the final product in light of the relatively low thickness, 2.0 mm, of the magnesium alloy material. This is often the reason why a manufacturer keeps its manufacturing processes (e.g., the flow of molten metal according to the time passage and the location of casting gate installation) confidential.  
       SUMMARY OF THE INVENTION  
       [0007]     According to an embodiment of the present invention, a seat back frame of a vehicle is manufactured using a magnesium alloy. The magnesium alloy seat back frame has an improved mechanical strength by forming a reinforcing element with a U-shaped cross-section. The U-shaped cross-section is formed as an integral body that spans over the front side, as well as, both right and left sides of a frame housing the seat back frame. The front side of the frame is provided with a belt-shaped reinforcing element as an integral body. Thus, the seat is enabled to selectively install two different kinds of separable head rests and facilitates a relatively easy installation of any newly developed products.  
         [0008]     The present invention provides a method for manufacturing a magnesium alloy seat back frame of a vehicle. A casting gate is provided in the center of a mold so that the molten metal can be dispersed at various directions and flowed into a cast mold during a die casting process to enable a high pressure casting. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The above, and other, objects and features of the present invention will become apparent from the following description of the invention when taken in conjunction with the accompanying drawings, wherein:  
         [0010]      FIG. 1A  shows a front view of a seat back frame of a vehicle manufactured using a magnesium alloy according to an embodiment of the present invention;  
         [0011]      FIG. 1B  shows a rear view of a seat back frame of a vehicle manufactured using a magnesium alloy according to an embodiment of the present invention  
         [0012]      FIG. 2  is a front view of a part of a seat back frame of a vehicle manufactured using a magnesium alloy according to an embodiment of the present invention, wherein a reinforcing element is installed;  
         [0013]      FIG. 3  is a partial view of a seat back frame of a vehicle manufactured using a magnesium alloy according to an embodiment of the present invention, wherein a reinforcing frame is formed on left and right sides of the frame housing;  
         [0014]      FIG. 4  is a perspective view of a guide bracket of an active head rest device which is applicable to a seat back frame of a vehicle manufactured using a magnesium alloy according to an embodiment of the present invention;  
         [0015]      FIG. 5  is a perspective view of a guide bracket of a non-active head rest device which is applicable to a seat back frame of a vehicle manufactured using a magnesium alloy according to an embodiment of the present invention;  
         [0016]      FIG. 6  is a front view of an active head rest bracket installed on a seat back frame of a vehicle manufactured using a magnesium alloy according to an embodiment of the present invention;  
         [0017]      FIG. 7  shows a cross-sectional view taken along line ‘A-A’ of  FIG. 6 ; and  
         [0018]      FIG. 8  shows perspective views for the flow of molten metal according to time passage and a location of gate installation at the time of casting a seat back frame of a vehicle manufactured using a magnesium alloy according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0019]     According to an embodiment of the present invention a seat back frame, shown in  FIGS. 1A, 1B , and  2 , of a vehicle is manufactured using a magnesium alloy. A reinforcing frame  11 , including a U-shaped cross-section, is formed as an integral body spanning over the front side as well as both right and left sides of a frame housing  10 , which is known vulnerable to concentrated stress. The front side of the frame is provided with a belt-shaped reinforcing element  12  as an integral body. The reinforcing element  12  has a structure such that the recliner region is the thickest as well as the widest while it becomes thinner as well as narrower toward the head rest region.  
         [0020]     According to another embodiment, a seat back frame of a vehicle manufactured using a magnesium alloy, shown in  FIGS. 1A, 1B , and  2 , includes guide brackets  13 ,  14 , of  FIGS. 4 and 5 , respectively, that guide the installation of headrest to the frame housing  10 . Further, a separable bracket structure is fixed to an assembly hole  15  of the frame housing by means of an assembly means. The assembly hole  15  protrudes forward at regular intervals so that a nut cannot be protruded over the rear surface of the frame housing  10 .  
         [0021]     In a further embodiment, a casting gate  25 , as shown in  FIG. 8 , is installed in the center of a mold  20  so that a molten metal, in the course of molding via die casting, is dispersed at various directions and flowed into the mold. Preferably, the molten metal is flowed into the mold at the rate of 4.5-5.5 m/sec under the virtual pressure of 500-700 bar, wherein the distance travelled by a piston to reach the above flow rate is set to be 150-250 mm.  
         [0022]     The present invention is further illustrated with reference to the accompanying drawings. Referring to  FIGS. 1A, 1B ,  2 , and  3 , a seat back frame of a vehicle is manufactured by using a magnesium alloy under high pressure casting process. The structural inferiority of magnesium alloy in physical properties, such as mechanical strength, as compared to those of steel are compensated by means of conversion of its shape. Additionally, a rectifying means and improvement in the location of a casting gate  25  via Theological analysis. That is, the physical properties of the magnesium alloy used in manufacturing the seat back frame are greatly reinforced to be comparable to those of steels, in particular with respect to its mechanical strength, while maintaining its superior intrinsic properties of having a light-weight.  
         [0023]     As shown in  FIGS. 1-3 , the seat back frame of this invention is designed to be integrated as a whole by means of a casting method wherein parts such as a panel, a pipe and a bar are assembles together. That is, in order to attain a required strength there is provided a reinforcing frame  11  with a U-shaped cross-section formed as an integral body spanning over the front side as well as both right and left sides of a frame housing  10 . The front side of the frame is provided with a belt-shaped reinforcing element  12  as an integral body. The reinforcing element  12  has a structure that the recliner region is the thickest as well as the widest at a low region, but becomes thinner as well as narrower as it is headed toward the headrest region.  
         [0024]     The reinforcing means, such as the reinforcing frame  11  and the reinforcing element  12 , are formed to overcome the stress being loaded on a region, which is known most vulnerable to a concentrated stress from the outside, such as collision. In this context, a preferred embodiment of a magnesium alloy seat back frame of this invention is to be more than 450 kgf.m in moment experiment, while it is 345 kgf.m at maximum for a steel made seat back frame.  
         [0025]     Generally, seat back frames are provided with a head rest with a view to protecting the head and neck regions of a passenger. Typically, there are two different kinds of head rests: a) an active head rest device which protects the head and neck of a passenger while it is being moved forward along the given track by the suspension installed within a seat back frame when the seat back is being pushed at the time of a vehicle collision, and b) a non-active head rest device which also serves the same function but is fixed.  
         [0026]     In this invention, an integrated bracket is excluded but it is converted to a separable bracket which can select either type of head rest and assemble it to a frame housing  10 . Thereby being more readily adapted to a new type of product while eliminating the welding process which results in reducing the production cost.  
         [0027]     Referring to  FIGS. 4 and 5 , they are perspective views showing guide brackets of an active head rest device as well as non-active head rest device which are applicable to a seat back frame of the present invention. The guide brackets  13  and  14  are fixed to the seat back frames by means of an assembly means such as a bolt, for example. The guide bracket  13  of an active head rest device shown in  FIG. 4  is a bracket which guides the movement of the active head rest device along the given track. The bracket  13  has a simple structure because it is usually freed from a large force. Further, the bracket  13  is restricted to have only three bracket holes  16  which can be mounted onto the frame housing  10  and also is designed to minimise its weight.  
         [0028]     As shown in  FIG. 5 , the guide bracket  14  of a non-active head rest device has five bracket holes  16  for the frame housing  10  so that it can endure a relatively larger force than that delivered to the above guide bracket  13 . When the bracket hole  16  fixes its respective guide bracket they can be used allowing an overlap.  
         [0029]     Referring to the bolt assembly hole  15 , as its cross-sectional view is shown in  FIG. 7 , nuts protrude forward at regular intervals over the rear surface of the frame housing  10  so problems during assembly will be minimised. Therefore, the seat back frame of a vehicle manufactured using a magnesium alloy according to this invention can achieve equally powerful physical properties as those manufactured using the conventional steel material while still maintaining its intrinsic advantage of having light weight. Meanwhile, the step of forming a seat cushion of a vehicle is the most critical step to reflect a given design at its optimum level. In particular, the optimisation of a casting process is one of the essential steps of this invention. In forming a seat back frame using a magnesium alloy, solidification process can be performed rapidly under the optimised condition of a casting gate  25 . Therefore, the casting should be performed using a high speed die casting process, and accordingly, it is essential to select a most appropriate location for installing a casting gate  25  via Theological analysis. That is, when a molten metal fills in a certain area with limited space through a rather complex passage, the way of filling-in differs greatly depending on from which location of the casting gate  25  the molten metal is introduced, and preferred embodiments can be derived based on the variations of the location.  
         [0030]     Referring to  FIG. 8 , it shows the flow of molten metal according to the passage of time and the location of gate installation at the time of casting the seat back frame. In the process of molding a seat back frame of a vehicle, as shown in the  FIG. 8 , a molten metal flows into a nearby area to thereby uniformly fills in the area. When a casting gate  25  is installed in the center of the mold  20 , the molten metal becomes dispersed in various directions, thus firstly filling in the recliner that connects the frame housing  10  and the cushion frame, its lower part, then filling in its left and right sides, and finally filling in its top portion. That is, instead of being united in the middle, the molten metal fills in the very near end first thereby reducing the occurrences of casting defects. This was made possible based on the notion that the left and right sides are the major seat back supporting parts, and in this way, the insertion time of the molten metal into a mold is much reduced as compared to that of the conventional one. Therefore, it is suitable for using a magnesium alloy material which is rapidly solidified. When the molding is performed using the aforementioned molding process, it is preferable to have an insertion rate of 4.0-5.0 m/sec for a molten metal through the casting gate  20 , more preferably 5.0 m/sec, and virtual pressure of 500-700 bar, more preferably 600 bar. The distance travelled by a piston to reach the injection speed is preferred to be 150-250 mm, more preferably 200 mm. Here, the optimal forming conditions in this invention were obtained as a result of numerous experiments by varying the forming conditions.  
         [0031]     Therefore, in the event of a casting according to this invention where molten metals are allowed to be united, it can prevent casting defects due to gas entrapment in the mold or by the presence of a hot flow of the molten metals, thereby enabling to maximally mold a seat back frame of a vehicle to a maximum level.  
         [0032]     The invention has been described in detail with reference to preferred embodiments thereof. However, it will be appreciated that those skilled in the art, upon consideration of the disclosure, may make modifications and improvements within the scope and spirit of the invention that is defined by the appended claims.