Abstract:
The present invention discloses a die-casting mold structure for a thin-walled mini zinc alloy shell. The mold structure includes a longitudinal runner, a transverse runner, an end runner, and a mold cavity all connected serially to provide a path for a liquid metal. The end runner and the mold cavity are connected through an in-gate. The liquid metal flows through the in-gate and enters the mold cavity at an incidence angle of approximately 30 to 45 degrees. The liquid metal is incident on the mold cavity near the rear end surface of the mold cavity. The direction of the liquid metal flow is controlled as the liquid metal flows through the runners and into the cavity so as to reduce the amount of air mixed into the liquid metal. The result is that the liquid metal can fill the mold cavity more satisfactorily, reducing casting defects and increasing product yield.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority, under the Paris Convention, of Chinese patent application, application number 201310292753.X, filed on Jul. 12, 2013 in the Intellectual Property Office of the People&#39;s Republic of China. The disclosure of the Chinese application is hereby incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a casting technology for thin-walled mini castings and, in particular, to a die-casting mold structure for thin-walled zinc alloy shells used in electrical connectors. 
         [0004]    2. Description of Related Art 
         [0005]    Currently, thin-walled mini zinc alloy shells refer to a zinc alloy product that has a wall thickness about 0.1-0.5 mm. In a die casting process for thin-walled mini zinc alloy shells, the filling speed for the zinc alloy is about 40 m/s. Under the high pressure and high speed action of a molding machine, the molten or liquid metal will enter the mold cavity in the form of jet flow to fill the cavity. During the filling process, the liquid metal may encounter collision, friction and resistance, causing the liquid metal to become a pressurized fluid that exhibits a filling characteristic inferior to that of a jet flow. The pressurized fluid may introduce defects, such as entrapping air bubbles, which may lead to porous castings. In particular, the thin-walled zinc alloy shells may be prone to entrap bubbles and may have an incomplete filling. Therefore, a well-designed casting process and mold design has an important influence on molding the shells. Other common defects in the zinc alloy shells are surface bubbles and loose structure, which may reduce the tensile strength and the electrical conductivity of the shells. The result is that the shells may fail to meet quality standards, lowering product yield, and causing a serious impact on normal production of the shells. Even more seriously, it may be difficult for some defects to be detected in the semi-finished products in the casting process. The latent defects may not be found until at a later stage in the process; for example, the defects may not become visible until the electroplating process. Such a late detection of defects would cause an even more severe loss in product yield and greater economic loss. 
         [0006]    There are many factors that may lead to such defects. In conventional die casting technology, the end runner, which is the channel through which the liquid metal flows into the mold cavity, is oriented perpendicular to the mold cavity. The vertical orientation of the runner to the mold cavity is intended to allow the flow vector of the liquid metal to be free of any speed component horizontal to the mold cavity so as to reduce the speed loss when the liquid metal enters the mold cavity, resulting in an improved filling effect. However, the results have been less than satisfactory. As such, there is a need for an improved die-casting mold structure. 
       SUMMARY OF THE INVENTION 
       [0007]    An object of the present invention is to provide a simple, inexpensive die-casting mold structure for thin-walled zinc alloy shells used in electrical connectors such as USB connectors to overcome the shortcomings of the conventional technology. Another object is to reduce the vortexes and the entrapped gases in the filling processing for a complete filling so as to reduce surface bubbles and surface flow mark, improve surface smoothness and strength, and increase yield of the die casting process. 
         [0008]    A die-casting mold structure for thin-walled zinc alloy shells for connectors such as USB connectors is disclosed. The die-casting mold structure includes a longitudinal runner, a transverse runner, an end runner, and a mold cavity, all of which are connected serially to provide a path for the flow of molten or liquid metal. The end runner and the mold cavity are connected through an in-gate. The cross-sectional areas of the longitudinal runner, the transverse runner, the end runner, and the in-gate are progressively smaller in the direction of the flow of the liquid metal. The liquid metal flows through the in-gate and enters the mold cavity at an incidence angle of approximately 30 to 45 degrees. The incidence angle is subtended by the end runner and the plane of the in-gate. The liquid metal enters the mold cavity from the in-gate near the rear end surface of the mold cavity. 
         [0009]    In other embodiments, the incidence angle of the liquid metal jet flow subtended by the end runner and the plane of the in-gate may be set at approximately 30 to 40 degrees. 
         [0010]    In other embodiments, the connection between the transverse runner and the end runner forms an arc. The arc has an arc radius of approximately 10 mm to 15 mm. 
         [0011]    In other embodiments, the distance between the mid-point of the in-gate and the rear end surface of the mold cavity is approximately 2 to 3 mm. 
         [0012]    In other embodiments, the distance between the mid-point of the in-gate and the rear end surface of the mold cavity is about 2.5 mm. 
         [0013]    Advantages of the disclosed die-casting mold structure for thin-walled zinc alloy shells for electrical connectors include simplicity in structure and design. In addition, the runners of the mold structure allow the liquid metal to flow through the in-gate and enter the mold cavity at an angle not perpendicular to the mold cavity. Rather, the direction of flow of the liquid metal makes an incidence angle of between 30 and 45 degrees where the incidence angle is subtended by the end runner and the plane of the in-gate. The direction of flow of the liquid metal is controlled as the liquid metal flows through the runners and into the mold cavity so as to reduce the amount of air mixed into the liquid metal. The result is that the liquid metal can fill the mold cavity more effectively, since casting defects such as surface bubbles, surface flow marks, loose structure, low strength, and low electrical conductivity can be reduced, thereby increasing the product yield of the casting process. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The accompanying drawings are provided together with the following description of the embodiments for a better comprehension of the present invention. The drawings and the embodiments are illustrative of the present invention, but are not intended to limit the scope of the present invention, wherein: 
           [0015]      FIG. 1  show a schematic view of a die-casting mold structure for thin-walled zinc alloy shells for electrical connectors according to one embodiment of the present invention; and 
           [0016]      FIG. 2  shows an enlarged view for the “A” portion indicated in  FIG. 1  according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The following paragraphs describe several embodiments of the present invention in conjunction with the accompanying drawings. It should be understood that the embodiments are used only to illustrate and describe the present invention, and are not to be interpreted as limiting the scope of the present invention. 
         [0018]    Referring to  FIGS. 1 and 2 , a die-casting mold structure for thin-walled zinc alloy shells for electrical connectors is shown. The die-casting mold structure includes a longitudinal runner  4 , two transverse runners  3 , two end runners  5 , and two mold cavities  1 , all of which are connected in the order shown to provide a path for molten or liquid metal to flow into the mold cavities  1 . Each of the end runners  5  and its associated mold cavity  1  are connected through an in-gate  2 . The cross sectional areas of the longitudinal runner  4 , the transverse runner  3 , the end runner  5 , and the in-gate  2  are progressively smaller in the direction of the flow of the liquid metal. As such, the flow speed of the liquid metal may be increased gradually to achieve sufficient velocity at the in-gate  2  to allow each mold cavity to be filled properly. The liquid metal flows through the in-gate  2  and enters its associated mold cavity at an incidence angle (α) of approximately 30 to 45 degrees where the incidence angle (α) is subtended by the end runner  5  and the plane of the in-gate  2 . The jet flow of liquid metal in the end runner  5  enters the mold cavity  1  near the rear end surface of the mold cavity  1 . The proper incidence angle (α) allows the mold cavity to be filled completely. 
         [0019]    Furthermore, the connection between each transverse runner  3  and its associated end runner  5  forms an arc R. The arc R has an arc radius of approximately 12 mm. The arc R allows the liquid metal to flow smoothly from each transverse runner  3  to its associated end runner  5 . 
         [0020]    The distance between the mid-point of each in-gate  2  and the rear end surface of the associated mold cavity  1  is about 2.5 mm. This distance may alleviate the impact from the excessively high speed of the liquid metal at the in-gate  2  to prevent the mold cavity  1  from eroding. 
         [0021]    The incidence angle (α) of the liquid metal flowing through the in-gate  2  and entering the associated mold cavity  1  significantly affects the quality of the casting. The incidence angle (α) may be determined from two sub-vectors of the speed vector of the liquid metal. As shown in  FIG. 2 , the horizontal sub-vector (a) represents the horizontal speed component of the liquid metal; the vertical sub-vector (b) represents the vertical speed component of the liquid metal; the speed vector of the liquid metal forms an incidence angle (α) with the plane of the in-gate ( 2 ). 
         [0022]    In one embodiment, the following parameters may be used in molding a front metal shell of an electrical connector for USB 3.0:
       Product name: front metal shell of an USB 3.0 connector   Material: zinc alloy (Zemark3)   Melting temperature: 420 degrees C.°   Casting weight: 0.830 g   Runner weight: 6.349 g       
 
         [0028]      FIG. 1  shows a whole raw casting where the two castings of the shells for the USB connectors occupy a small portion of the raw casting (the weight of the raw casting is about 8.009 g whereas the two castings of the shells weigh about 0.830 g each). The shapes and dimensions for the longitudinal runner  4 , the transverse runners  3 , the end runners  5 , and the in-gates  2  may be determined according to the weight and shape of the casting. 
         [0029]    From the structure of the casting and the fluid analysis of the liquid metal, five configurations for the runners of the raw casting may be obtained. The shapes and dimensions of the longitudinal runner  4 , the transverse runners  3 , the end runners  5 , and the in-gates  2  are the same in each configuration. However, by changing the configuration of the end runner and in-gate  2 , such as changing the direction at which the liquid metal enters the mold cavity  1  and the incidence angle (α) subtended by the end runner  5  and the plane of the in-gate  2 , the five configurations may be obtained. The incidence angles (α) of the five configurations are 45, 40, 35, 33 and 30 degrees. 
         [0030]    The filling process of the castings of the above five configurations was digitally simulated by INTER-CAST software (a simulation software). The simulation results are listed as follows: 
         [0000]    
       
         
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                 change in the 
                   
                   
                   
                   
               
               
                 incidence 
                 temperature 
                 confluence 
                 Entrapped 
                   
                 filling state 
               
               
                 angle (α) 
                 field 
                 zone 
                 gas 
                 Vortex 
                 as a whole 
               
               
                   
               
             
             
               
                 30° 
                 extremely 
                 small 
                 none 
                 none 
                 good 
               
               
                   
                 small 
                   
                   
                   
                   
               
               
                 33° 
                 extremely 
                 small 
                 none 
                 none 
                 good 
               
               
                   
                 small 
                   
                   
                   
                   
               
               
                 35° 
                 very small 
                 very small  
                 extremely 
                 none 
                 good 
               
               
                   
                   
                   
                 little 
                   
                   
               
               
                 40° 
                 small 
                 small 
                 extremely 
                 extremely 
                 good 
               
               
                   
                   
                   
                 little 
                 little 
                   
               
               
                 45° 
                 small 
                 small 
                 little 
                 little 
                 better 
               
               
                   
               
             
          
         
       
     
         [0031]    When the incidence angle (α) is 45 degrees, with the aid of video analysis of the filling process of the castings, it is found that the change in the temperature field is small; the confluence zone in the liquid metal is small; there is little entrapped gas in the liquid metal; there is little vortex in the liquid metal; the filling state as a whole is better, and consequently the quality of the casting is better. 
         [0032]    When the incidence angle (α) is 40 degrees, with the aid of video analysis on the filling process of the castings, it is found that the change in the temperature field is small; the confluence zone in the liquid metal is small; there is extremely little entrapped gas in the liquid metal; there is extremely little vortex in the liquid metal; and the filling state as a whole is good. 
         [0033]    When the incidence angle (α) is 35 degrees, with the aid of video analysis on the filling process of the castings, it is found that the change in the temperature field is very small; the confluence zone in the liquid metal is very small; there is extremely little entrapped gas; there is no vortex in the liquid metal; and the filling state as a whole is good. 
         [0034]    When the incidence angle (α) is 33 degrees, with the aid of video analysis on the filling process of the castings, it is found that the change in the temperature field is extremely small; the confluence zone in the liquid metal is small; there is no entrapped gas; there is no vortex in the liquid metal; and the filling state as a whole is good. 
         [0035]    When the incidence angle (α) is 30 degrees, with the aid of video analysis on the filling process of the castings, it is found that the change in the temperature field is extremely small; the confluence zone in the liquid metal is small; there is no entrapped gas; there is no vortex in the liquid metal; and the filling state as a whole is good. 
         [0036]    From the above simulation of the filling process of the castings, it is seen that when the incidence angle (α) is 30°, the filling effect appears to be the best. 
         [0037]    Comparisons may also be made of casting samples from sample mold designs. According to the drawings of the castings, corresponding mold designs may be obtained. A die-casting machine made by FRECH is used to produce the casting samples according to the mold designs. The following table shows the results: 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                   
               
               
                 incidence 
                 number of  
                 bubble  
                 surface flow 
                 surface 
               
               
                 angle (α) 
                 surface bubbles 
                 volume 
                 mark 
                 smoothness 
               
               
                   
               
             
             
               
                 30° 
                 extremely few 
                 small 
                 none 
                 good 
               
               
                 33° 
                 extremely few 
                 small 
                 none 
                 good 
               
               
                 35° 
                 few 
                 very small 
                 little 
                 better 
               
               
                 40° 
                 very few 
                 very small 
                 little 
                 better 
               
               
                 45° 
                 very few 
                 very small 
                 little 
                 better 
               
               
                   
               
             
          
         
       
     
         [0038]    For the casting sample made from the mold design with an incidence angle (α) of 45 degrees, there are very few surface bubbles; the bubble volume is very small; there is little surface flow mark; and the surface smoothness is better. 
         [0039]    For the casting sample made from the mold design with an incidence angle (α) of 40 degrees, there are very few surface bubbles; the bubble volume is very small; there is little surface flow mark; and the surface smoothness is better. 
         [0040]    For the casting sample made from the mold design with an incidence angle (α) of 35 degrees, there are few surface bubbles; the bubble volume is very small; there is little surface flow mark; and the surface smoothness is better. 
         [0041]    For the casting sample made from the mold design with an incidence angle (α) of 33 degrees, there are extremely few surface bubbles; the bubble volume is small; there is no surface flow mark; and the surface smoothness is good. 
         [0042]    For the casting sample made from the mold design with an incidence angle (α) of 30 degrees, there are extremely few surface bubbles; the bubble volume is small; there is no surface flow mark; and the surface smoothness is good. 
         [0043]    Through an analysis of the above digital simulation results of the filling of the mold designs, in combination with the actual application of the mold designs to obtain casting samples, it is found that, for thin-walled mini zinc alloy shells, the filling effect of liquid metal is good when the incidence angle is between 30 and 45 degrees. Therefore, when designing a mold to produce a thin-walled zinc alloy shell that has few and smaller bubbles, high strength, good electrical conductivity, and thus high product yield, the incidence angle (α), which is the angle between the end runner  5  and the mold cavity  1 , may be designed to be between 30 and 45 degrees. In particular, when the incidence angle (α) is about 30 degrees, the filling effect appears to be optimal, and may produce the highest product yield. 
         [0044]    The descriptions set forth above are provided to illustrate one or more embodiments of the present invention and are not intended to limit the scope of the present invention. Although the invention is described in details with reference to the embodiments, a person skilled in the art may obtain other embodiments of the invention through modification of the disclosed embodiment or replacement of equivalent parts. It is understood that any modification, replacement of equivalent parts and improvement are within the scope of the present invention and do not depart from the spirit and principle of the invention as hereinafter claimed.