Injection molding manifold with heating element extending between the plates and methods of fabrication

Abstract: An injection molding melt distribution manifold (10) and method of making it with a melt passage (12) extending from a single inlet (14) to a plurality of outlets (18). The melt passage (12) has a branching portion (26) formed by machining matching grooves (54,56) in opposing surfaces (48,50) of two steel plates (42,44) and then integrally brazing them together. The manifold has an embedded electrical heating element (30) received in a channel formed by two other matching grooves (70,72) in the opposing surfaces of the two plates. The channel is then integrally filled with nickel by heating under a partial vacuum. The electrical heating element (30) which extends around and is in or near the same plane as the branching portion (26) of the melt passage (12) to ensure rheological and thermal balance of the melt flowing therethrough.

Description: BACKGROUND OF THE INVENTION This invention relates generally to injection molding and more particularly to a manifold having a heating element and a branching portion of a melt passage which extend in transverse planes not spaced far apart and a method of making it. It is well known to have an injection molding manifold for a multi-cavity molding system in which the melt passage branches from a single inlet to a plurality of outlets. As seen in U.S. Patent Number 4,648,546 to Gellert which issued March 10, 1987, this is made by machining two matching grooves in the abutting surfaces of two steel plates and then brazing the plates together so the matching grooves form the branching portion of the melt passage. U.S. Patent Number 4,648,546 also shows the manifold having an integral electrically insulated electrical heating element. However, the heating element is embedded in a channel in the front face of the manifold and thus is spaced a considerable distance from the branching portion of the melt passage. This has the disadvantage that the temperature gradient in different parts of the manifold due to heat loss to the nozzles and the surrounding mold results in the temperature of the branching portion of the melt passage not being sufficiently uniform and constant. This is particularly a problem for molding materials having a narrow temperature window. Furthermore, a very rapid heat up can result in slight bowing of the manifold. US, 2,227,263 discloses a one-piece manifold which comprises several electrical heating elements. Said individual cartridge heaters are inserted into radial holes from the outside of said circular manifold. The injection molding manifold according to US 2,227,263 comprises a melt passage extending therethrough from the rear surface to a plurality of outlets on the front surface, the melt passage having a branching portion extending in a plane transversally to the inlet bore and the outlet bores of the melt passage wherein the heating elements extend, in the same plan as the branching portion, transversally to the inlet bore and the outlet bores of the melt passage. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to at least partially overcome the disadvantages of the prior art by providing a manifold and a method of making it. Said object is achieved according to the invention by the subject-matters of claims 1, 4 and 5. Further improvements of the invention are indicated in the subdaims. In the following, the invention is explained in more detail with regard to preferred embodiments in connection with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a partially cut-away isometric view of a manifold according to a preferred embodiment of the invention, Figure 2 is an isometric view of the electrical heating element between the rear and front plates, Figure 3A is a view of the front surface of the rear plate, Figure 3B is a view of the rear surface of the front plate, Figure 4 is a view along lines 4-4 in Figure 2 after the plates are bolted together, and Figure 5 is a cross-sectional view of a manifold according to another embodiment of the invention. DETAILED DESCRIPTIONS OF THE INVENTION As best seen in Figure 1, this invention relates to a heated melt distribution manifold 10 to be mounted in a multi-cavity injection molding system. A hot runner melt passage 12 extends through the manifold 10 to convey pressurized melt received from an injection molding machine at a common inlet 14 on the rear face 16 to a plurality of outlets 18 spaced on the front face 20 each aligned with a heated nozzle (not shown) extending to a gate to a cavity. The melt passage 12 has an inlet bore 22 extending forwardly from the inlet 14, a number of outlet bores 24 each extending rearwardly from one of the outlets 18, and a branching portion 26. The branching portion 26 connects each of the outlet bores 24 to the inlet bore 22 and extends in a first plane 28 extending transversely to the inlet and outlet bores 22, 24. The melt passage 12 is shaped to have a smooth finish with no sharp bends or dead spots to avoid deterioration of the pressurized melt which is injected through it. While the branching portion 26 of the melt passage 12 shown has a configuration for four outlets 18, it can have other configurations leading to other numbers of outlets 18. However, in all configurations, the distance between each of the outlets 18 and the common inlet 14 must be equal to ensure product uniformity. The manifold 10 according to the invention also has an embedded electrical heating element 30 which extends in a second transverse plane 32 from a terminal 34 projecting from the manifold 10. As best seen in Figure 4, the heating element 30 is electrically insulated with compacted magnesium oxide powder 36 extending around a central resistance wire 38 in an outer stainless steel casing 40. In the embodiment of the invention shown in Figures 1-4, the first plane 28 in which the branching portion 26 of the melt passage 12 extends is the same as the second plane 32 in which the heating element 30 extends. Furthermore, the heating element 30 encircles the branching portion 26 of the melt passage 12 which ensures that the melt in all of the branching portion 26 of the melt passage 12 is maintained at a uniform temperature. In use, the manifold 10 as seen in Figure 1 is mounted in a multi-cavity injection molding mold. Electrical power is applied to the terminal 34 to heat the melt distribution manifold 10 to a predetermined operating temperature. Pressurized melt is applied from a molding machine (not shown) to the central inlet 14 of the melt passage 12 according to a predetermined cycle. The melt flows through the melt passage 12 and branches out to the various cavities. After the cavities are filled and a suitable packing and cooling period has expired, the injection pressure is released. The mold is then opened to eject the molded products. After ejection, the mold is closed and the cycle is repeated continuously with a cycle time dependent upon the size of the cavities and the type of material being molded. Reference is now made particularly to Figures 2, 3A, 3B and 4 to describe the method of making the manifold 10 according to the first embodiment. An elongated rear plate 42 and a matching elongated front plate 44 are made with a particular shape. In the preferred embodiment, these manifold plates 42, 44 are made of H13 tool steel, but can also be made of stainless steel. The rear plate 42 has a flat rear surface 46 and a flat front surface 48 with the inlet bore 22 of the melt passage 12 extending forwardly therethrough from the inlet 14. The front plate 44 has a flat rear surface 50 and a flat front surface 52 with the outlet bores 24 extending forwardly therethrough to the outlets 18. While the embodiment shown has only four outlets 18 extending in alignment, in other embodiments the front plate 44 can be made with eight, sixteen or more spaced outlets in different configurations depending upon the application. As seen in Figures 3A and 3B, first a semicircular groove 54 is machined in the front surface 48 of the rear plate 42, and a matching second semicircular groove 56 is machined in the rear surface 50 of the front plate 44. As seen in Figure 4, the rear and front plates 42, 44 are aligned and secured together by bolts 58 extending through holes 60, 62 in the plates 42, 44 with the front surface 48 of the rear plate 42 abutting with reasonable contact pressure against the rear surface 50 of the front plate 44 along an interface 64. The matching grooves 54, 56 are made with a configuration to form the branching portion 26 of the melt passage 12 when the plates 42, 44 are secured together. The branching portion 26 of the melt passage 12 splits several times in connecting the inlet bore 22 to each of the outlet bores 24. Thus, the entire branching portion 26 is in the common first plane 28 which extends along the interface 64 transversely to the inlet and outlet bores 22, 24. The rear plate 42 is also made with a number of spaced brazing ducts 68 which extend from the rear surface 46 to the interface 64. In this embodiment, the plates 42, 44 are also machined to form a third semicircular groove 70 in the front surface 48 of the rear plate 42 and a matching fourth semicircular groove 72 in the rear surface 50 of the front plate 44. These matching grooves 70, 72 are made with a configuration to form a channel 74 in which the electrical heating element 30 is received when the plates 42, 44 are secured together. In this embodiment, the heating element 30 is in the same plane 28 as the branching portion 26 of the melt passage 12 and extends from the terminal 34 in a loop 76 near the outside of the manifold 10 which encircles the branching portion 26 of the melt passage 12. The rear plate 42 is made with a number of filling ducts 78 which extend from the rear surface 46 to the channel 74 and are spaced along the channel 74. While the rear plate 42 is shown having several brazing ducts 68 and filling ducts 78, the number of them can vary from one to quite a large number depending upon the size of the manifold being made. Also, while the brazing ducts 68 and filling ducts 78 are shown extending through the rear plate 42, in other embodiments of the invention they can be made to extend through the front plate 44. This depends upon which way up the assembled plates 42, 44 are positioned for filling, and the only requirement is that the brazing ducts 68 and filling ducts 78 must all extend through the same plate. The heating element 30 is positioned in one of the third or fourth grooves 70, 72, and the two plates 42, 44 are secured together by the bolts 58 with the heating element 30 extending in the channel 74. Of course, the number and position of the bolts 58 required also depend on the size and shape of the manifold 10. In this embodiment, as seen in Figure 4, a hollow filling tube 80 is seated in a recess 81 in the rear surface 46 of the rear plate 42 and tack welded in place over each of the filling ducts 78 leading to the heating element channel 74 except for one. One of ducts 78 is left as an air duct 82 to allow air to escape from the channel 74 as the plates 42, 44 are heated. With the plates 42, 44 positioned with the brazing ducts 68 and filling ducts 78 extending downwardly, a first quantity 84 of a conductive material such as nickel alloy in a powder form is inserted into each brazing duct 68. A larger second quantity 86 of nickel alloy in a powder form is inserted into each filling duct 78 and the filling tube 80 above it. The assembled plates are then loaded in batches into a vacuum furnace and gradually heated to a temperature of approximately 1050°C (1925°F) which is above the melting temperature of the nickel alloy. As the furnace is heated, it is evacuated to a relatively high vacuum to remove substantially all of the oxygen and then partially backfilled with an inert gas such as argon or nitrogen. When the melting point of the nickel alloy is reached, the nickel alloy 84 in the brazing ducts 68 melts and flows downwardly to the interface 64 between the front surface 48 of the rear plate 42 and the rear surface 50 of the front plate 44. These surfaces 48, 50 are roughened and the nickel alloy spreads between them by capillary action to integrally braze the two plates 42, 44 together to form an integral manifold 10. Similarly, the nickel alloy 84 in the filling ducts 78 and filling tubes 80 melts and flows downwardly into the channel 74 where it flows around the heating element 30 to integrally embed the heating element 30 in the manifold 10. Brazing in a vacuum provides a metallurgical bonding of the nickel alloy to the steel for very efficient heat transfer from the heating element 10 to the manifold around the melt passage 12. The position of the heating element 30 in the same plane 28 as the branching portion 26 of the melt passage 12 ensures the melt is maintained at a more uniform temperature as it flows through the melt passage 12 during the injection cycle. After the nozzles 10 are removed from the vacuum furnace and cooled, they are machined to remove the filling tubes 80 and to provide the manifold 10 with smooth rear and front faces 16, 18. Pressure disc location holes 88 and manifold lift holes 90 are then drilled in the rear face 16 of the manifold 10 as required. Reference is now made to Figure 5 to briefly describe a method of making the manifold 10 according to another embodiment of the invention. As most of the elements and steps are the same as described above, their description will not be repeated and elements common to this embodiment will be described and illustrated using the same reference numerals. As can be seen, in this case, a third groove 92 having a predetermined depth d is machined in the rear surface 50 of the front plate 44 and no matching groove is machined in the front surface 48 of the rear plate 42. The heating element 30 is positioned in the third groove 94 and the two plates 42, 44 are secured together as described above. Thus, the third groove 94 forms a channel 96 in which the heating element 30 extends and to which the filling ducts 78 connect. Then the assembled plates 42, 44 are heated as described above to melt the nickel alloy powder to integrally braze the plates 42, 44 together and embed the heating element 30 in the manifold 10. The difference from the embodiment described above is that the heating element 30 extends in a second plane 32 which extends transversely and is spaced apart from the first plane 28 in which the branching portion 26 of the melt passage 12 extends not further than the depth d and of the third groove 94. While the third groove 94 is shown in the rear surface 50 of the front plate 44, in another embodiment it can be in the front surface 48 of the rear plate 42 with the manifold 10 inverted in the filling and heating positions. A manifold 10 having the two planes 28, 32 offset from each other like this does not have quite as good thermal characteristics as the one described above where they are in the same plane, but it is slightly easier to make because machining one less groove is required. While the description of the injection molding manifold and method of making it according to the invention has been given with respect to preferred embodiments, it will be evident that various other modifications are possible without departing from the scope of the invention as understood by those skilled in the art and as defined in the following claims.

Claims: An injection molding manifold (10) comprising a rear plate (42) with a front surface (48) and a rear surface (46), a front plate (44) with a rear surface (50) and a front surface (52), the rear plate (42) and the front plate (44) being joined together with a melt passage (12) extending therethrough from the rear surface (46) of the rear plate (42) to a plurality of outlets (24) on the front surface (52) of the front plate (44), the melt passage (12) having a branching portion (26) formed by a first groove (54) in the front surface (48) of the rear plate (42) and a matching second groove (56) in the rear surface (48) of the front plate (44), the branching portion (26) extending in a plane transversally to the inlet bore and the outlet bores of the melt passage (12) wherein at least one of the front surface (48) of the rear plate (42) and the rear surface (50) of the front plate (44) has a groove in which at least a portion of the heating element (30) is received whereby the heating element (30) is fully embedded in the manifold (10), this groove having a maximal depth (d) corresponding to the diameter of the heating element (30), wherein the heating element (30) extends in a plane extending transversally to the inlet bore and the outlet bores of the melt passage (12). An injection molding manifold (10) as claimed in claim 1, characterized in that the front surface (48) of the rear plate (42) has a groove (70) and the rear surface (50) of the front plate (44) has a matching groove (72), the matching grooves (70, 72) forming a channel (74) in which the heating element (30) is embedded. An injection molding manifold (10) as claimed in claim 1, characterized in that one of the front surface (48) of the rear plate (42) and the rear surface (50) of the front plate (44) has a groove in which the heating element is received. Method of making an injection molding manifold having a rear face (16), a front face (20), and a melt passage (12) extending therethrough from a common inlet (14) on the rear face (16) to a plurality of outlets (18) spaced on the front face (20), the melt passage (12) having an inlet bore (22) extending forwardly from the common inlet (14) on the rear face (16) and a plurality of outlet bores (24) each extending rearwardly from a respective one of the outlets (18) spaced on the front face (20), and an electrically insulated electrical heating element (30) extending in a second transverse plane (32) and having a predetermined diameter and a terminal (34) being provided at the manifold (10), the method comprises the steps of: forming an elongated steel rear plate (42) having a rear surface (46), a front surface (48), and the inlet bore (22) extending therebetween, forming an elongated steel front plate (44) having a rear surface (50), a front surface (52), and the outlet bores (24) extending therebetween, one of the rear plates (42) and the front plate (44) having at least one brazing duct (68) extending therethrough, wherein the front surface (48) of the rear plate (42) and the rear surface (50) of the front plate (44) are provided for abutting against each other at an interface (64) extending along a first transverse plane (28), machining a first groove (54) in the front surface (48) of the rear plate (42) extending from the inlet bore (22) and a matching second groove (56) in the rear surface (50) of the front plate (44) extending to all of the outlet bores (24), machining a third groove (94) having a predetermined depth (d) corresponding to the predetermined diameter of the heating element (30) in one of the front surface (48) of the rear ptate (42) and the rear surface (50) of the front plate (44) to receive the electrical heating element (30), forming said one of the rear plates (42) and the front plate (44) with at least one filling duct (78) extending therethrough, wherein a brazing duct (68) and said at least one filling duct (78) are formed in the same plate, positioning the electrical heating element (30) in the third groove (94), securing the rear and the front plate (42,44) together with the front surface (48) of the rear plate (42) abutting against the rear surface (50) of the front plate (44) at the interface (64) extending along the first transverse plane (28) in a position wherein the matching first and second grooves (54,56) form a branching portion (26) of the melt passage (12) extending in said first interfacing transverse plane (28) to connect each of the outlet bores (24) to the inlet bore (22), wherein when the front and rear plates (42,44) are secured together the third groove (94) forms a channel (96) to which the at least one filling duct (78) connects, orienting the rear and the front plate (42,44) with the at least one brazing duct (68) extending downward to the interface (64), providing a first quantity of conductive material (84) at each of the at least one brazing ducts (18), and providing a second quantity of conductive material (86) at each of the at least one filling duct (78), heating the rear and the front plate (42,44) in a partial vacuum in a position and to a sufficient temperature whereby the first quantity of conductive material (84) melts and flows downwardly from the at least one brazing duct (68) to the interface (64) between the abutting front surface (48) of the rear plate (42) and rear surface (50) of the front plate (44) to integrally join the rear and the front plate (42,44) together to form the manifold (10) and seal the melt passage (12) against leakage, and the second quantity of conductive material (86) melts and flows from the at least one filling duct (78) into the channel (96) around the heating element (30) to embed the heating element (30) in the manifold (10). Method of making an injection molding manifold having a rear face (16), a front face (20), and a melt passage (12) extending therethrough from a common inlet (14) on the rear face (16) to a plurality of outlets (18) spaced on the front face (20), the melt passage (12) having an inlet bore (22) extending forwardly from the common inlet (14) on the rear face (16) and a plurality of outlet bores (24) each extending rearwardly from a respective one of the outlets (18) spaced on the front face (20), and an electrically insulated electrical heating element (30) with a terminal (34) being provided at the manifold (10), the method comprises the steps of: forming an elongated steel rear plate (42) having a rear surface (46), a front surface (48), and the inlet bore (22) extending therebetween, forming an elongated steel front plate (44) having a rear surface (50), a front surface (52), and the outlet bores (24) extending therebetween, one of the rear plates (42) and the front plate (44) having at least one brazing duct (68) extending therethrough, machining a first groove (54) in the front surface (48) of the rear plate (42) extending from the inlet bore (22) and a matching second groove (56) in the rear surface (50) of the front plate (44) extending to all of the outlet bores (24), machining a third groove (70) in the front surface (48) of the rear plate (42), and machining a fourth groove (72) in the rear surface (50) of the front plate (44) to match the third groove (70) in the front surface (48) of the rear plate (42), for receiving the electrical heating element (30), forming said one of the rear plates (42) and the front plate (44) with at least one filling duct (78) extending therethrough, wherein said brazing and filling ducts (68,78) are formed in the same plate, positioning the electrical heating element (30) extending in a second transverse plane (32) in one of the third and the fourth groove (70,72), securing the rear and the front plate (42,44) together with the front surface (48) of the rear plate (42) abutting against the rear surface (50) of the front plate (44) at an interface (64) extending along a first transverse plane (28) in a position wherein the matching first and second grooves (54,56) form a branching portion (26) of the melt passage (12) extending in said first transverse plane (28) to connect each of the outlet bores (24) to the inlet bore (22), wherein when the front and rear plates (42,44) are secured together the third and the fourth groove (70,72) forms a channel (74) to which the at least one filling duct (78) connects, orienting the rear and the front plate (42,44) with the at least one brazing duct (68) extending downward to the interface (64), providing a first quantity of conductive material (84) at each of the at least one brazing ducts (18), and providing a second quantity of conductive material (86) at each of the at least one filling duct (78), heating the rear and the front plate (42,44) in a partial vacuum in a position and to a sufficient temperature whereby the first quantity of conductive material (84) melts and flows downwardly from the at least one brazing duct (68) to the interface (64) between the abutting front surface (48) of the rear plate (42) and rear surface (50) of the front plate (44) to integrally join the rear and the front plate (42,44) together to form the manifold (10) and seal the melt passage (12) against leakage, and the second quantity of conductive material (86) melts and flows from the at least one filling duct (78) into the channel (74) around the heating element (30) to embed the heating element (30) in the manifold (10), wherein the heating element (30) and the branching portion (26) of the melt passage (12) are extending in the same transverse plane (28,32). A method of making an injection molding manifold as claimed in claim 5 further including the steps of attaching a hollow filling tube to one of the rear surface of the rear plate and the front surface of the front plate in communication with each of the at least one filling duct, inserting the second quantity of conductive material into each filling tube prior to heating, whereby when the plates are heated the second quantity of conductive material melts in the filling tube and flows through the at least one filling duct into the channel around the heating element, and then machining the manifold to remove the filling tube. A method of making an injection molding manifold as claimed in claim 6, wherein the first quantity of conductive material is inserted directly into each of the at least one brazing ducts.

Inventors: RENWICK CRAIG W, RENWICK, CRAIG W.
Applicants: MOLD MASTERS LTD, MOLD-MASTERS LIMITED
Application year: 1995
Main classification: B29C45
IPC codes: B29C45, B29C33