Abstract:
Embodiments of a method of injection molding with two molding steps and tools for this method are described. The transfer tool for high-volume manufacturing allows transfer of molded parts from one injection molding tool to another injection molding tool without separating the molded part from runners and without degating. The single step transfer, which can be performed without degating and without separating the molded parts from one another, can reduce cycle time as well as complexity.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of Chinese Patent Application No. 201110361910.9 filed on Sep. 30, 2011, which is hereby incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to methods of injection molding and a tool for forming injection molded parts. More particularly, the present invention relates to a method of injection molding parts with two molding steps and injection molding tools to make molding more efficient. 
     2. Description of the Related Art 
     Injection molding is one of the most popular processes for manufacturing plastic products. A typical injection molding process generally includes (1) injecting molten plastic material into a closed mold, (2) allowing the plastic to cool down and solidify, and (3) ejecting the finished product from the mold. This process may be used to form molded plastic parts, including for example, be used to form housings and accessories for various electronic products. 
     In some cases, injection molding can also be used to place decorative features on the outer surfaces of a part. In other cases, plastic can be molded over an already molded part to produce, for example, parts having two or more different colors or formed of two or more different materials. Formation of such features may be accomplished in two molding steps. 
     For example, the first molding step can be used to form the part (as described above for example), and the second molding step can be used to create an outer layer around some or all of the part (or vice versa). By way of example, injection molding in two steps may be used to place a soft layer on top of a hard layer, a transparent layer on top of an opaque layer, or create multicolored layers. In some cases, this molding process can be used to form the structural walls of the enclosure. 
     When one machine and tool set molds both shots, the tool is typically known as double-shot tool. Transferring a molded part from a first tool to a second tool for the second shot is known as transfer molding. A basic process can include injection molding a part, transferring this molded part to a second tool, and molding the second component on the transferred part. The transfer process can add complexity as well as cycle time to the process. 
     SUMMARY OF THE DESCRIBED EMBODIMENTS 
     This paper describes various embodiments that relate to systems, methods, and apparatus for injection molding parts with two molding steps. 
     According to one embodiment, an injection molding device for high-volume manufacturing is provided. The injection molding device includes a first tool and a second tool. The first tool, which is for performing a first injection molding shot to form molded parts, includes first shot gates that allow molten material to flow into cavities of the first tool. The second tool is for performing a second injection molding shot on the molded parts transferred from the first tool. The second tool has cavity spacing that matches the cavity spacing of the first tool and the second tool is configured to receive the molded parts transferred from the first tool with the first shot gates attached to the molded parts. The molded parts can be transferred from the first tool to the second tool without degating. 
     In accordance with another embodiment, an injection molding process is provided. According to the process, molded parts are transferred simultaneously from a first injection molding tool to a second injection molding tool. The molded parts are then loaded into the second injection molding tool prior to degating the molded parts. 
     According to yet another embodiment, an injection molding apparatus for high volume manufacturing is provided. The apparatus includes a first injection molding tool and a second injection molding tool. The first injection molding tool includes cavities spaced apart at a distance. The second injection molding tool has cavities spaced apart at a same distance as in the first injection molding tool, and the second injection molding tool also includes gate punches configured to remove gates from the first injection molding tool. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
         FIG. 1  is a top perspective view of four molded parts held together by and still connected to the runners from a first tool used to mold the parts. 
         FIG. 2  shows molded parts from the first injection molding tool still connected to the gates being loaded into a second injection molding tool. 
         FIG. 3  is a side cross-sectional view of the molded part in the second injection molding tool prior to being degated. 
         FIG. 4  is a side cross-sectional view of the molded part in the second injection molding tool after being degated. 
         FIG. 5  is a top perspective view of molded parts, still connected to one another and the gates from the first tool, loaded in their respective mold cavities of the second injection molding tool. 
         FIG. 6  is a top perspective view of the molded parts of  FIG. 5  with the gate punches of the second tool contacting the gates of the first tool. 
         FIG. 7  is a flow chart of an injection molding process method according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the described embodiments as defined by the appended claims. 
     The embodiments described herein allow for much faster production rates since molded parts can be removed from a first injection molding tool and loaded into a second tool very quickly. Furthermore, a separate station is not needed for removal of the first shot gates. 
     In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order to avoid unnecessarily obscuring the present invention. 
     A typical injection molding apparatus includes a runner system for transporting molten plastic or another molten material to a mold cavity where a molded part is formed. A moldable material, such as plastic or metal, can be used in the injection molding apparatus described herein. 
     The runner system can include a gate, which is the location at which molten material can enter the mold cavity to form the molded part. The runner system can also include sprues, which are typically larger diameter channels through which molten material can flow. The runner system can also include several runners, which are smaller diameter channels that run from the sprue to the gate. Thus, molten material can flow through the runner system and enters the mold cavity through one or more gates to form a molded part in the mold cavity when the material cools and hardens. 
     After the molded part has hardened and cooled, it can be removed from the mold cavity and degated. Degating is a process of cutting runners away from the molded parts. Degating is typically performed to separate the molded part from the runner system when the molded part is removed from the mold cavity. 
     Sometimes, as noted above, the geometry or other processes require that the first molded part be physically transferred to a different mold before the second part is molded. Such a process is known as transfer molding. In transfer molds with more than one mold cavity, molded parts are usually ejected from the tool, degated (if needed), and then individually put into a second tool for the second molding shot. 
     Existing methods and tooling for a transfer molding process require molded parts to be collected from the first tool, degated, and then individually loaded into the second tool. Often, all of the first shot molded parts are either degated in the first tool, or in a separate fixture. An embodiment described herein combines the second shot molding process with the degating and therefore eliminates a separate degating step, and allows faster loading of the molded parts in the second tool. It also eliminates the need for a separate degating fixture, as the degating can be performed in the second molding tool. 
     An embodiment described herein allows the easy transfer of a large number of molded parts from a first molding tool to a second molding tool without separating the molded parts and without degating. Instead, in this embodiment, a first set of molded parts can be transferred from the first molding tool and loaded into the second molding tool while still connected by the runner system. The second molding tool can include integrated punches that remove the runner system to degate as it closes. 
       FIG. 1  shows four individual molded parts  100  that are held together by and still connected to the gates  120  from a first tool used to mold the parts  100 . The molded parts  100  remain connected by gates. As shown in  FIG. 1 , a gate  120  is positioned between two molded parts. It will be understood that, in the embodiment illustrated in  FIG. 1 , four molded parts  100  are shown but that any number of molded parts can be provided. According to an embodiment, the molded parts  100 , which are formed in a first injection molding tool, can be transferred to a second injection molding tool  200  ( FIG. 2 ) for the second shot of an injection molding process without separating the molded parts  100  from the gates  120  of the first tool. By eliminating the degating step, cycle times can be reduced and the need for a separate degating fixture can be eliminated. Furthermore, since the molded parts  100  remain connected to the gates  120 , they can be loaded into the second injection molding tool  200  together in a single transfer step rather than having individual molded parts separately loaded into the second tool  200 . Thus, after the first shot, the molded parts  100  are transferred simultaneously from the first tool to the second tool  200  for the second shot of the injection molding process. 
     In the illustrated embodiment, molten material flows into the gates  120  from runners (not shown) and the molten material then flows into each of the four corners of the cavity to form the molded part. Thus, as shown in  FIG. 1 , a gate  120  is connected at each of the four corners to the molded part  100  so that molten material can flow into the mold cavity through each one of the gates in the corners. It will be understood, however, that any number of gates can be provided for each cavity, depending on the geometry of the part. 
       FIG. 2  shows the molded parts  100  being loaded into a second injection molding tool  200  while the molded parts  100  are still connected to each other via the gates  120  from the first tool. In the second injection molding tool  200 , the spacing D between the mold cavities  220  is the same as that of the first tool (minus a small amount to account for runner shrinkage during cooling in some embodiments) so that the molded parts  100  can be easily transferred in one step, while still connected to each other via the gates  120 , from the first tool to the second tool  200 . That is, the molded parts  100  can be transferred directly from the first tool to the second tool without being separated from one another or degated. Thus, a separate degating fixture is not necessary. Further, the transfer of the molded parts  100  can be done in a single step with the molded parts  100  connected via the gates  120 . 
       FIG. 3  is a side cross-sectional view of the second tool  200  with a molded part  100 , which has been molded in the first tool, held in a mold cavity  220  of the second tool. As noted above, the second tool  200  has cavity spacing that matches that of the first tool (minus any shrinkage) in order to receive the molded part  100  from the first tool with the gates  120  still attached. The second molding tool  200  can also have integrated gate punches  260  for degating to remove the gates  120  as the mold cavity  220  closes. As the mold cavity  220  of the second tool  200  closes, a spring loaded retention block  240  can hold the molded part  100  in place before gate punches  260  make contact with the gate  120 . Thus, in this embodiment, the degating process for the gates  120  from the first tool is integrated with the second injection molding tool  200 . 
     A spring biased retention block  280  can be provided to hold the molded part  100  in place before the gate punches  260  make contact with the gates  120 . In this embodiment, the gate punches  260  make contact with the gates  120  as the mold cavity block  220  closes onto the core  290 . As the mold cavity block  220  and core  290  are closing but before they are fully closed, the gate punches  260  make contact with each gate  120 , as shown in  FIG. 3 . As can be seen in  FIG. 3 , the gate punches  260  are positioned such that they move with the moving side of the cavity block  220 .  FIG. 4  shows that, as the mold cavity block  220  closes, the gate punches  260  move downward and apply force to each gate  120  to degate the molded part  100 . In this embodiment, the gate punches  260  can move in a downward motion and apply force to the gates  120  from above when the mold cavity blocks  220  are in the closed position. 
     As degating of the first molded parts  100  occurs, each of the gates  120  is removed from the molded parts  100  and falls through a channel  270  provided under each gate  120  in the direction of arrow G, as shown in  FIG. 3 . As illustrated in  FIG. 3 , the channels  270  can pass through the core  290  of the second tool  200 . As shown in  FIG. 4 , the gates  120  can then pass out of the second tool  200  through another channel  272 . In an embodiment, the gates  120  can be air blasted out of the channel  272 . 
       FIGS. 5 and 6  show details of the degating process of the first molded part  100  in the second tool  200 . It will be understood that, in this embodiment, the part  100  that was molded in the first tool is degated to separate the molded part  100  from the gates  120  of the first tool before the second injection molding shot takes place in the second tool  200 . 
       FIG. 5  is a top perspective view of molded parts  100 , still connected to one another and the gates  120  from the first tool, loaded in their respective mold cavities  220  of the second injection molding tool  200 .  FIG. 6  is a top perspective view of the molded parts  100  shown in  FIG. 5  with the gate punches  260  of the second tool  200  contacting the gates  120  of the first tool. 
     As discussed above, the gate punches  260  in this embodiment contact the gates  120  from above and move to push the gates  120  in a downward motion to detach them from the molded parts  100 . As shown in the illustrated embodiment shown in  FIG. 6 , the gate punches  260  contact the central portions of the gates  120  to push the gates  120  in a downward motion. When the gates  120  are detached from the molded parts  100 , the gates  120  fall into the channels  270  located below the gates  120 . In some embodiments, the degated gates  120  can be stacked in the channels  270 . In an embodiment, the channels  270  can be shaped accordingly so that the gates  120  can be stacked in the channels  270 . For example, each channel  270  can have a cross-sectional shape that corresponds with that of the gate  120 . In an embodiment, the channel  270  can have a shape such that when the gate  120  is pushed downward, the gate  120  cannot shift horizontally, thereby forcing the gate  120  to be pulled from the molded part  100 . 
     A molding process in which molded parts are transferred from one injection molding tool to another injection molding tool will be described with reference to  FIG. 7 . A molding process will be described below with reference to steps  700 - 750 . In step  700 , a first injection molding process is performed in a first injection molding tool to form molded parts. 
     In step  710 , a second injection molding tool is provided. The second injection molding tool has mold cavities that are spaced apart from each other the same distance as in the first injection molding tool. This spacing allows molded parts from the first injection molding tool to be transferred to the second tool together in a single step. Thus, in step  720 , the molded parts are transferred from the first tool to the second tool without separating and degating the molded parts. The molded parts are therefore transferred simultaneously from the first injection molding tool to the second injection molding tool. 
     In step  730 , the molded parts are separated from the gates of the first tool while the molded parts are in the second tool. After degating the molded parts, a second injection molding process (or the second shot) can be performed on the molded parts in the second tool in step  740 . In step  750 , the injection molded part made from two injection molding processes steps can be removed from the second tool. 
     The foregoing description, for purposes of explanation, uses specific nomenclature to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the invention. Thus, the foregoing descriptions of specific embodiments of the present invention are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings. 
     The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.