Patent Application
20050255189
1. Field of the Invention
The present invention relates to a melt conduit coupler for providing reduced-leakage connections between discrete melt conduits in a molding system. In particular, the melt conduit coupler of the present invention may be configured for interconnecting the melt conduits in a runner system of an injection molding machine. More particularly, the runner system may comprise a hot runner that is configured for metal injection molding.
2. Related Art
The present invention is concerned with the molding of a metal alloy (such as Magnesium) in a semi-solid or fully liquid (i.e. above solidus) state. Detailed descriptions of exemplary apparatus and operations of injection molding systems used for such alloys are available with reference to U.S. Pat. Nos. 5,040,589 and 6,494,703.
The barrel assembly 38, in
The barrel 40 is further configured for connection with a source of comminuted metal feedstock through a feed throat (not shown) that is located through a top-rear portion of the barrel (also not shown). The feed throat directs the feedstock into the bore 48A of the barrel 40. The feedstock is then subsequently processed into a melt of molding material by the mechanical working thereof, by the action of the screw 56 in cooperation with the barrel bore 48A, and by controlled heating thereof. The heat is provided by a series of heaters 50 (not all of which are shown) that are arranged along a substantial portion of the length of the barrel assembly 38.
The clamp unit 12 includes a clamp base 18 with a stationary platen 16 securely retained to an end thereof, a clamp block 22 slidably connected at an opposite end of the clamp base 18, and a moving platen 20 arranged to translate therebetween on a set of tie bars 32 that otherwise interconnect the stationary platen 16 and the clamp block 22. As is known, the clamp unit 12 further includes a means for stroking (not shown) the moving platen 20 with respect to the stationary platen to open and close the injection mold halves 23, 25 arranged therebetween. A clamping means (not shown) is also provided between the clamp block and the moving platen to provide of a clamping force between the mold halves 23, 25 during the injection of the melt of molding material. The hot half of the injection mold 25 is mounted to a face of the stationary platen 16, whereas the complementary cold half of the mold 23 is mounted to an opposing face of the moving platen 20.
In further detail, the injection mold includes at least one molding cavity (not shown) formed between complementary molding inserts shared between the mold halves 23, 25. The mold cold half 23 includes a core plate assembly 24 with at least one core molding insert, not shown, arranged therein. The mold hot half 25 includes a cavity plate assembly 27, with at least one complementary cavity molding insert arranged therein, mounted to a face of a runner system 26. The hot runner system 26 provides a means for connecting the melt passageway 48C of the machine nozzle 44 with at least one molding cavity for the filling thereof. The runner system 26 includes a manifold plate 64 and a complementary backing plate 62 for enclosing melt conduits therebetween, and a thermal insulating plate 60. The runner system 26 may be an offset or multi-drop hot runner system, a cold runner system, a cold sprue system, or any other commonly known melt distribution means.
The process of molding a metal in the above-described system generally includes the steps of: (i) establishing an inflow of metal feedstock into the rear end portion of the barrel 40; (ii) working (i.e., shearing) and heating the metal feedstock into a thixotropic melt of molding material by: (iia) the operation (i.e., rotation and retraction) of the screw 56 that functions to transport the feedstock/melt, through the cooperation of the screw flights 58 with the axial bore 48A, along the length of the barrel 40, past the non-return valve 60, and into an accumulation region defined in front of the non-return valve 60; and (iib) heating the feedstock material as it travels along a substantial portion of the barrel assembly 38; (iii) closing and clamping the injection mold halves 23, 25; (iv) injecting the accumulated melt through the machine nozzle 44 and into the injection mold by a forward translation of the screw 56; (v) optionally filling any remaining voids in the molding cavity by the application of sustained injection pressure (i.e. densification); (vi) opening the injection mold, once the molded part has solidified through the cooling of the injection mold; (vii) removal of the molded part from the injection mold; (viii) optionally conditioning the injection mold for a subsequent molding cycle (e.g., application of mold release agent).
A major technical challenge that has plagued the development of a hot runner system 26, suitable for use in metal injection molding, has been the provision of a substantially leak-free means for interconnecting the melt conduits therein. Experience has taught that the traditional connection regime used in a plastics hot runner system (i.e., a face-seal that is compressively loaded under the thermal expansion of the melt conduits) is not suitable in a hot runner system for metal molding. In particular, in a metal hot runner system, the extent to which the melt conduits must be compressed to maintain a face-seal therebetween is also generally sufficient to crush them (i.e., yielding occurs). This is partly the result of the high operational temperatures of the melt conduits (e.g., around 600° C. for a typical Mg alloy), which significantly reduces the mechanical properties of the component material (e.g., typically made from a hot work tool steel such as DIN 1.2888). Another problem is that significant thermal gradients exist across the melt conduits at the high operating temperature cause significant unpredictability in their geometry which complicates the selection of suitable cold clearances.
Another challenge with the configuration of structure for interconnecting melt conduits has been in accommodating the thermal growth of the interconnected melt conduits (i.e., as the conduits are heated between ambient and operating temperatures) without otherwise displacing functional portions thereof that may need to remain fixed relative to other structure. For example, in a single drop hot runner system, with an offset drop, wherein there are two melt conduits, namely a supply and a drop manifold, respectively, it is advantageous to fix the location of a machine nozzle receptacle portion of the supply manifold for sake of alignment with the machine nozzle 44, while also fixing a drop (i.e., discharge) portion of the drop manifold for sake of alignment with an inlet gate of a molding cavity insert. Accordingly, some means for sealing between the supply and drop manifolds must be provided that accommodates an expansion gap therebetween in the cold condition, and that does not rely on a face-seal therebetween in the hot condition. This becomes even more of a challenge in a multi-drop hot runner (i.e., a hot runner with more than one discharge nozzle for servicing a large molding cavity or a mold with more than one molding cavity) wherein there are many fixed drop portions, the drop portions being configured on a corresponding quantity of drop manifolds.
The present invention provides an injection molding machine apparatus and method to overcome the problems noted above, and to provide an effective, efficient means for reduced leakage connection between discrete melt conduits in a molding system.
According to a first aspect of the present invention, structure and/or steps are provided for a molding machine melt conduit coupler including coupling structure having a first surface configured to couple with a first melt conduit, and a second surface configured to couple with a second melt conduit. Cooling structure is configured to provide a coolant to the coupling structure. Preferably, the cooling structure cools the coupling structure to a temperature that causes any melt leaking from the coupling structure to at least partially solidify thereby further sealing the connection(s).
According to a second aspect of the present invention, sealing structure and/or steps are provided whereby a molding hot runner system includes a plate configured to carry at least one melt-carrying manifold. A coupling is configured to couple the at least one melt-carrying manifold with a melt-carrying channel. A cooling structure is configured to cool the coupling.
According to a third aspect of the present invention, control structure and/or steps are provided for an injection molding machine having a mold configured to form a molten material into a molded article. First and second molten material conduits are configured to carry the molten material to the mold. A molten material conduit coupler is configured to couple the first molten material conduit to the second molten material conduit. The melt conduit coupler includes a coolant channel configured to carry a coolant adapted to remove heat from the molten material conduit coupler.
According to a fourth aspect of the present invention, a method of coupling together first and second molten material conduits includes the steps of: (i) placing an end of said first molten material conduit adjacent an end of said second molten material conduit; (ii) placing a coupler about the ends of the first and second molten material conduits; (iii) locating the coupler about the ends of the first and second molten material conduits; and (iv) as molten material flows through the ends of the first and second molten material conduits, cooling said coupler to cause molten material leaking from said coupler to at least partially solidify.
Exemplary embodiments of the presently preferred features of the present invention will now be described with reference to the accompanying drawings in which:
1. Introduction
The present invention will now be described with respect to several embodiments in which an injection molding system is used for the molding of a metal alloy, such as Magnesium, above its solidus temperature (i.e., semi-solid thixotropic, or liquidus state). However, the present invention may find use in other injection molding applications such as plastic, liquid metal, composites, powder injection molding, etc.
Briefly, in accordance with the present invention, a melt conduit coupler is provided for interconnecting discrete melt conduits. Preferably, complementary male and female ‘spigot’ coupling portions are arranged on each of a melt conduit coupler and along portions of the melt conduits to be interconnected, respectively. A ‘spigot’, as used in this description, is a modifier that characterizes the relative configuration of pairs of complementary coupling portions that cooperate to interconnect discrete melt conduits in a substantially leak-free manner. In particular, a complementary pair of ‘spigot’ coupling portions are characterized in that the coupling portions are configured to cooperate in an overlapping, closely-spaced, and mutually parallel relation. The spigot coupling portions are preferably configured to cooperate to provide a ‘spigot connection’ between each of the melt conduit spigot coupling portions and the complementary spigot coupling portion provided on the melt conduit coupler. The ‘spigot connection’ is characterized in that the interface between the complementary spigot coupling portions is cooled. Accordingly, a spigot connection is provided as a cooled engagement between closely-fit complementary cylindrical sealing faces, wherein a weepage or leakage of melt therebetween solidifies to provide a further effective seal that substantially prevents further leakage of melt.
The invention provides a new use for a spigot connection that solves some rather vexing problems in metal molding runner systems, outlined hereinbefore. U.S. Pat. No. 6,357,511, discloses a spigot connection configured between a machine nozzle and a mold sprue bushing. According to the present invention, a melt conduit coupler has been devised that uses the spigot connection to interconnect pairs of melt conduits. The presently preferred form of the invention is as an interconnection between a pair of melt conduits.
Furthermore, a runner system may also make use of the inventive melt conduit coupler to join typical melt distribution manifolds contained therein. For example, a single drop hot runner, in an offset configuration, is disclosed herein that is particularly useful in adapting cold chamber die casting molds for use in a metal injection molding machine. Also disclosed is a multi-drop hot runner for use in a metal injection molding machine.
In a preferred embodiment of the invention, each of the melt conduits includes a spigot coupling portion that is provided on an outer circumferential surface that is arranged along a cylindrical end portion thereof. Similarly, the melt conduit coupler preferably comprises a cooled ring body wherein a complementary spigot coupling portion is arranged along an inner circumferential surface thereon. The ring body is preferably configured for the cooling thereof, in use, to maintain the required temperature at the spigot connection (i.e., provide a seal of relatively cooled, solidified melt). As one example, the temperature of the melt conduit coupler is controlled, in use, to maintain the temperature at the spigot connection at about 350° C., when molding with a typical Magnesium alloy melt.
In the following description, the mold operating temperature is typically around 200-230° C.; the melt temperature is typically around 600° C.; hot work tool steel (DIN 1.2888) is preferably used for manifolds, spigot tip inserts, etc. Also, the sealing/cooling rings are preferably made from regular tool steel (AISI 4140, or P20) because they are kept at a relatively low temperature and are generally isolated from large forces. Alternatively, the sealing/cooling rings can be made from AISI H13 where some force transmission is expected. The manifold insulators are preferably made from a relatively low thermally conductive material that is also capable of withstanding the extremely high processing temperatures without annealing. Presently, the preferred insulators are made from Inconel™. However, the actual mold operating temperature, melt temperature, tool steel, sealing/cooling ring material, and manifold insulators may be selected based on the material being molded, the required cycle times, the available materials, etc. All such alternate configurations are to be included within the scope of the attached claims.
2. Spigot Seal Parameters
In accordance with the preferred embodiment, a melt conduit coupler is provided for interconnecting discrete melt conduits. Accordingly, spigot coupling portions are arranged on each of the melt conduit couplers and along portions of the melt conduits that are to be interconnected. Preferably, the fit between the complementary spigot coupling portions includes a small diametrical gap. The small gap provides for ease of engagement between the complementary coupling portions during assembly. Preferably, the gap is designed so that it is taken-up by the relative expansion of the spigot coupling portions when the melt conduits and the melt coupler are at their operating temperatures. Any diametrical interference between the spigot coupling portions at their operating temperatures may provide supplemental sealing, but is not otherwise relied upon.
In the presently preferred embodiments, a typical gap between the coupling portions is about 0.1 mm per side when the melt conduits and the melt conduit coupler are at ambient temperature. However, this 0.1 mm gap is not essential, the fit between the complementary spigot coupling portions could otherwise be exact or include a slight interference at ambient temperature. Preferably, each melt conduit coupler is independently temperature-controlled.
As will be described in detail hereinafter, active cooling of the melt conduit coupler is preferred to control the temperature at the interface between the spigot coupling portions to maintain a substantially leak-free spigot connection. However, by configuring the melt conduit within cooled runner system plates (manifold and manifold backing plates which are maintained at about 200-230° C.) it may also be possible to rely solely on passive heat transfer therewith. Preferably, the melt conduit components to be interconnected are arranged in the melt conduit coupler such there is a longitudinal cold clearance therebetween when the melt conduit components are at ambient temperature. In particular, there is a cold clearance gap between complementary annular mating faces that are disposed at the ends of each of the complementary melt conduits when the melt conduits are at ambient temperature.
Preferably, the clearance between the mating faces is taken up when the melt conduits are at their operating temperatures, due to the thermal expansion thereof. Accordingly, the preload between the mating faces of the melt conduit components, if any, can be controlled to avoid excessive compressive forces that could otherwise crush the melt conduit components. In the preferred embodiments, a typical cold clearance for a melt conduit that is heated to 600° C. is about 1 mm. Any face-seal that is provided between the complementary mating faces, at operating temperature, is supplemental.
With reference to
The melt conduit coupler 80 is also shown to include a thermocouple installation 86 that includes a bore that is configured for receiving a thermocouple. Adjacent to the thermocouple installation is a thermocouple retainer 88 that includes a bore that is configured to receive a fastener, the fastener retains, in use, a clamp (not shown) that retains the thermocouple within the thermocouple installation 86. Preferably, the thermocouple installation 86 is located very close to a spigot coupling portion 76′ disposed around an inner circumferential surface of the melt conduit coupler 80 so that the temperature at a spigot connection with complementary spigot coupling portions 76, disposed around end portions of the melt conduits 70, 70′, can be controlled. Each of the melt conduits 70, 70′ may have a heater 50 to maintain the temperature in the melt in conduits at the prescribed operating temperature, which again is about 600° C. for Magnesium alloy molding.
As described hereinbefore, the spigot coupling portions 76, 76′ are preferably configured to have a small gap therebetween. In use, a Magnesium alloy at 600° C. has a viscosity like water and is therefore generally able to seep between complementary mating faces 120, 120′ of the melt conduits 70, 70′, and to thereafter seep between spigot coupling portions 76, 76′. However, because the melt conduit coupler 80 is kept at a relatively low temperature by active or passive cooling (i.e., around 350° C.), the melt will fully or at least partially solidify in such gaps and provide a seal that substantially prevents the further leakage of melt.
A thermocouple 74 may be disposed at the end portions of either or both of the melt conduits 70, 70′, to detect the temperature of the melt conduit adjacent the melt conduit coupler 80. Preferably, the thermocouple 74 is located very close to the interface between the spigot coupling portions 76, 76′, so that the temperature of the melt within the melt passageway 148A, 148B adjacent the spigot connection can be controlled (for example, by controlling the power to the heaters 50 disposed about the melt conduits 70, 70′), to prevent the formation of a plug in the melt passageway 148A, 148B adjacent the cooled spigot connection.
The mating faces 120, 120′ of the melt conduits 70 and 70′ are shown to preferably include a longitudinal cold clearance 116 of about 1 mm therebetween when the melt conduits are at that ambient temperature. This gap is selected (predetermined) to be taken up (or substantially closed) as the melt conduits expand in length as they are heated to the operating temperatures. Accordingly, there is substantially no gap, and maybe even some compression between the mating faces of the melt conduits 70 and 70′. Any such compression may act to provide a supplemental seal against leakage of melt. In this fashion, excessive compressive forces between the melt conduits 70, 70′, due to thermal expansion, that may otherwise cause local yielding in the melt conduits 70, 70′ is substantially avoided.
As discussed above, the melt also has a way of working its way through the gaps between the spigot coupling surfaces 76, 76′, and is only substantially prevented by carefully controlling the temperature at the interface between these spigot coupling portions 76, 76′ well below the melting point of the molding material. For the preferred embodiments, it is preferable that a cold clearance gap of about 0.1 mm between the spigot coupling portions 76, 76′ be provided at ambient temperature. In use, the relative thermal expansion of the melt conduit coupler 80 and the melt conduits 70, 70′ is such that this diametrical gap will be substantially taken up and preferably there is as an intimate contact between the accompanying portions at the operating temperature. Such intimate contact would provide a supplemental seal against further leakage of the melt, although a small residual gap is tolerable in view of the main mode of sealing (i.e. seal of solidified melt). Alternatively, there could be an exact fit, or even a small compressive preload between the spigot coupling portions 76, 76′ at ambient temperature. This would ensure that there is supplemental sealing from the compression between the spigot coupling portions 76, 76′ at the operating temperatures. Accordingly, the melt coupler 80 of the present invention provides a substantially leak-free seal between melt conduits 70, 70′ that operates without requiring a compressive sealing force between the mating faces 120, 120′ of the melt conduits 70, 70′.
In, an alternative embodiment (not shown), the melt conduit coupler may be integrated onto an end of one of the melt conduits.
In, an alternative embodiment, the melt conduit coupler 180 is a parallelepiped, as shown with reference to
As previously mentioned, the specific features of the melt conduit coupler 180 are substantially similar to those discussed above with respect to melt conduit coupler 80 in
Also shown in
Also shown in
4. Supplemental Expansion Bushing
With reference to
5. Use in Offset Applications
With reference to
The supply and drop manifolds 170 and 172 are preferably interconnected with a melt conduit coupler 180. Preferably, the manifolds themselves are located in manifold pockets 65 provided in the manifold plate 64 and as shown with reference to
Also shown in
Also shown in
With reference to
With reference to
The cooling ring seat includes a mating portion 200 and a locating shoulder 201. The mating portion 200 preferably cooperates with a complimentary mating portion provided on the cooling ring 185, to conduct heat between the supply manifold and the cooling ring for cooling the spigot coupling portion 174. Preferably, the locating shoulder 201 retains the cooling ring 185 adjacent the free end of the first elbow portion 206.
The cooling ring 185 is shown in
The remaining outer circumferential surface of the first elbow portion 206 is configured to receive a heater 50. The heater maintains the temperature of the melt in the melt passageway 148A at the prescribed operating temperature. A controller (not shown) controls the heater 50 through feedback from one or more thermocouples, located in thermocouple installation cavities 186, that monitor the temperature of the melt passageway 148A. The feedback from the thermocouples could also be used to control the temperature in the cooling ring 185. A thermocouple clamp retainer 188 may be used to retain one or more of the thermocouples in their respective thermocouple installation cavities 186.
The second elbow portion 208 is generally perpendicular to the first elbow portion, and also includes a melt passageway 148B that extends through a free end thereof and interconnects with the melt passageway 148A of the first elbow portion at substantially right angles thereto. An annular planar front face at the free end of the second elbow portion 208 provides a mating space 220 that is configured to cooperate with a complimentary mating face on the drop manifold 172, as will be described hereinafter. Also shown is a shallow diametrical relief in the outer surface of the second elbow portion 208 that provides a seat for receiving the melt conduit coupler 180.
In further detail, the melt conduit coupler seat includes a spigot coupling portion 76 which is provided along an outer circumferential surface of the relief portion and a locating shoulder 79 which retains the melt conduit coupler adjacent the free end of the second elbow portion 208. As with the first elbow portion 206, the second elbow portion 208 is configured to receive a heater 50 for maintaining the temperature of the melt within the melt passageway 148B at the prescribed operating temperature. Also, there is preferably a thermocouple installation cavity provided along second elbow portion 208, for providing temperature feedback to the heater controller and the temperature controller for the melt conduit coupler 180.
The third elbow portion 210 is also preferably substantially perpendicular to the second elbow portion 208, and is generally coaxial with the first elbow portion 206. The third elbow portion 210 includes a shallow cylindrical bore that provides a seat 214 configured for receiving an axial insulator 108, as shown in
The fourth elbow portion 212 is also generally perpendicular to the third elbow portion 210, and is substantially coaxial with the second elbow portion 208. The fourth elbow portion 212 includes an insulator stand 216 that is configured on the end face of a free end of the fourth elbow portion, and includes generally parallel sidewalls that are configured to cooperate with a complimentary slot and a side insulator 106, as shown in
As introduced hereinbefore, the location of the first elbow 206 (i.e. inlet portion) of the supply manifold 170 is preferably substantially fixed with respect to a first axis. With reference to
In
The drop manifold 172 is shown in
Accordingly, the first elbow portion 306 includes a melt passageway 148C that extends through the free end thereof and along the length of the first elbow portion 306, and is interconnected with a melt passageway 148D that extends along the second elbow portion 308. As with the second elbow portion 208 of the supply manifold, the first elbow portion 306 of the drop manifold includes a diametrically relieved portion adjacent the free end that provides a seat for the melt conduit coupler 180. As explained previously, the seat preferably comprises a spigot coupling portion 76 and a locating shoulder 79. An annular planer face at the free end of the first elbow portion 306 provides a mating face 220 that cooperates with the complimentary mating face on the supply manifold 170. The remaining outer portion of the first elbow portion 306 is configured to receive a heater 50 and one or more thermocouple installations 186, as explained previously.
The second elbow portion 308, or discharge portion, is substantially perpendicular to the first elbow portion 306. The second elbow portion 308 includes the melt passageway 148D that extends through the free end of the second elbow portion 308 and interconnects with the melt passageway 148C of the first elbow portion 306. The free end of the second elbow portion 308 is preferably configured to include a seat for receiving a spigot tip insert 145. Of course, the spigot tip insert could otherwise be made integrally with the second elbow portion as shown with reference to
The third elbow portion 310 is configured similarly to the fourth elbow portion 212 of the supply manifold 170 and accordingly includes an insulator stand 216 for receiving the side insulator 106, as shown in
The fourth elbow portion 312 is configured similarly to the third elbow portion 210 of the supply manifold 170, and accordingly includes a insulator seat 214. The insulator seat 214 is preferably configured to receive an end of an axial insulator 110 that can be seen in
Also shown in
As explained previously with reference to
Also shown in
With reference to
As shown with reference to
The sprue bushing 252 is arranged within a front housing 254 such that a spigot ring portion 288, configured at the front of the sprue brushing 252, is received within a complimentary spigot coupling portion provided in the front portion 290 of front housing 254. A rear portion of the sprue bushing 252 is received within a cooling insert 256 that is located within a rear portion of the front housing 254. The cooling insert 256 functions to cool an inlet portion of the sprue bushing 252 such that a spigot connection can be maintained between a spigot coupling portion 174, configured along an inner circumferential surface of a shallow cylindrical bore formed through the end of the sprue bushing 252, and the complementary spigot coupling portion disposed on the drop manifold 172.
Also shown is a plurality of heaters that are arranged along the length of the sprue bushing 252 to maintain the temperature of the melt within a melt passageway therein at a prescribed operating temperature.
The configuration of the supply 270 and drop manifolds 172, 172′ that are shown arranged between the manifold plate 64 and the manifold backing plate 62 with reference to
As described hereinbefore, the hot runner 26 could be reconfigured to include any quantity and/or configuration of drops. Accordingly, many variations on the number and configuration of the manifolds are possible. For example, an intermediate manifold (not shown) could be configured between the supply and drop manifolds.
Any type of controller or processor may be used to control the temperature of the melt and structure, as described above. For example, one or more general-purpose computers, Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), gate arrays, analog circuits, dedicated digital and/or analog processors, hard-wired circuits, etc., may receive input from the thermocouples described herein. Instructions for controlling the one or more of such controllers or processors may be stored in any desirable computer-readable medium and/or data structure, such floppy diskettes, hard drives, CD-ROMs, RAMs, EEPROMs, magnetic media, optical media, magneto-optical media, etc.
Thus, what has been described is a method and apparatus for the coupling of molding machine structures to provide enhanced sealing while allowing for the thermal expansion of the components.
The individual components shown in outline or designated by blocks in the attached Drawings are all well-known in the injection molding arts, and their specific construction and operation are not critical to the operation or best mode for carrying out the invention.
While the present invention has been described with respect to what is presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
All U.S. and foreign patent documents discussed above are hereby incorporated by reference into the Detailed Description of the Preferred Embodiment.
