Injection molding system utilizing melt injection pressure to generate mold clamping force

Abstract

In one aspect, an injection molding system comprises a clamp frame including an actuator platen, a mold platen, and a fixing member fixing the actuator platen relative to the mold platen at least during an injection phase. An injection frame defines an injection cylinder within which an injection piston is slidably arranged. A mold has first and second halves collectively defining a molding cavity therebetween, the halves arranged between the mold platen and the injection frame. An injection actuator is operable, during the injection phase, to actuate the injection piston relative to the actuator platen to cause both: injection of melt from the injection cylinder into the molding cavity; and biasing of the injection frame and the second mold half against the first mold half to generate a clamping force between the first and second mold halves by exertion of melt pressure upon an internal surface of the injection cylinder.

Description

INJECTION MOLDING SYSTEM UTILIZING MELT INJECTION PRESSURETO GENERATE MOLD CLAMPING FORCETECHNICAL FIELD

[0001] The present disclosure relates to injection molding, and more particularly to an injection molding system utilizing melt injection pressure to generate mold clamping force. The present disclosure also relates to a method of operating an injection molding system utilizing melt injection pressure to generate mold clamping force.BACKGROUND

[0002] In an inj ection molding system, melted molding material may be inj ected, under pressure, into a molding cavity of a mold. The molding cavity may be defined between two mold halves of the mold. Pressurized molding material inside the molding cavity applies outward force that tends to urge the mold halves apart. Separation of the mold halves may be undesirable, e.g., because molding material may leak from the mold, resulting in waste and / or undesirable flash on the molded article. To prevent this, a clamping device (e.g. , a hydraulic clamp) may be used to clamp the mold halves together during inj ection molding. Such clamping devices may complicate an injection molding system and / or may consume significant energy during operation.SUMMARY

[0003] In one aspect, there is provided an injection molding system, comprising: a clamp frame including an actuator platen, a mold platen, and a fixing member that fixes the actuator platen relative to the mold platen at least during an injection phase of operation of the injection molding system; an injection frame defining an injection cylinder; an injection piston slidably arranged in the injection cylinder; an injection actuator actuatably coupled to the injection piston; and a mold having a first mold half and a second mold half collectively defining a molding cavity therebetween, the first and second mold halves being arranged between the mold platen and the injection frame, the injection actuator operable, during the injection phase of operation of the injection molding system, to actuate the injection piston relative to the actuator platen to cause both: injection of melt from the injection cylinder into the molding cavity; and biasing of the injection frame and the second mold half against the first mold half to generate a clamping force between the first and second mold halves by exertion of melt pressure upon an internal surface of the injection cylinder.

[0004] The injection actuator may be a hydraulic injection actuator comprising a cylinder head proximate to the actuator platen and a receptacle in the injection frame configured to slidably and sealably receive the cylinder head, the cylinder head, the receptacle, and the injection piston collectively defining a hydraulic fluid chamber, and the hydraulic injection actuator may be operable to actuate the injection piston by pressurizing hydraulic fluid within the hydraulic fluid chamber to cause the injection piston to slide, within the injection cylinder, away from the cylinder head.

[0005] The cylinder head may be fixed relative to the actuator platen.

[0006] The receptacle may be defined in part by a clamping force augmentation surface of the injection frame, the clamping force augmentation surface forming part of the hydraulic fluid chamber and facing at least partly away from the mold, and the hydraulic injection actuator may be operable, during the injection phase of operation of the injection molding system, to generate a supplemental clamping force that further biases the injection frame and the second mold half against the first mold half, and thereby augments the generated clamping force between the first and second mold halves, by exerting hydraulic fluid pressure upon the clamping force augmentation surface of the injection frame.

[0007] The clamping force augmentation surface of the injection frame may be annular and coaxial with the injection cylinder.

[0008] The injection frame may further define a nozzle configured to flow the melt from the injection cylinder to the mold, and the internal surface of the injection cylinder may be proximate to the nozzle.

[0009] The injection frame may be fixed relative to the second mold half.

[0010] The injection frame and the second mold half may be integrally formed.

[0011] The fixing member may be integrally formed with each of the mold platen and the actuator platen.

[0012] The fixing member may be configured to selectively fix the actuator platen with respect to the mold platen.

[0013] Embodiments may include combinations of the above features.

[0014] In another aspect, there is provided a method of generating mold clamping force, the method comprising: providing an injection molding system including: a clamp frame including an actuator platen, a mold platen, and a fixing member; an injection frame defining an injection cylinder; an injection piston slidably arranged in the injection cylinder; an injection actuator actuatably coupled to the injection piston; and a mold having a first mold half and a second mold half collectively defining a molding cavitytherebetween, the first and second mold halves being arranged between the mold platen and the injection frame; and actuating, by the injection actuator, with the fixing member fixing the actuator platen relative to the mold platen, the injection piston relative to the actuator platen to cause: injection of melt from the injection cylinder into the molding cavity; and biasing of the injection frame and the second mold half against the first mold half to generate a clamping force between the first and second mold halves by exertion of melt pressure upon an internal surface of the injection cylinder.

[0015] In some embodiments, the injection actuator is a hydraulic injection actuator comprising a cylinder head proximate to the actuator platen and a receptacle in the injection frame configured to slidably and sealably receive the cylinder head, the cylinder head, the receptacle, and the injection piston collectively defining a hydraulic fluid chamber, and the method further comprises pressurizing, by the hydraulic injection actuator, hydraulic fluid within the hydraulic fluid chamber to cause the injection piston to slide, within the injection cylinder, away from the cylinder head.

[0016] In some embodiments, the receptacle is defined in part by a clamping force augmentation surface of the injection frame, the clamping force augmentation surface forming part of the hydraulic fluid chamber and facing at least partly away from the mold, and the method further comprises exerting, by the hydraulic injection actuator, hydraulic fluid pressure upon the clamping force augmentation surface of the injection frame to further bias the injection frame and the second mold half against the first mold half and to thereby augment the generated clamping force between the first and second mold halves with a supplemental clamping force between the first and second mold halves.

[0017] Embodiments may include combinations of the above features.

[0018] Other features will become apparent from the drawings in conjunction with the following description.BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The non-limiting embodiments will be more fully appreciated by reference to the accompanying drawings, in which:

[0020] FIG. 1 is a side elevation view of a cross-section of an example injection molding system in an assembled state;

[0021] FIG. 2 is a side elevation view of the cross-section of the injection molding system of FIG. 1 in a disassembled state;

[0022] FIG. 3 is a perspective view of a subset of the components of the injection molding system of FIGS. 1 and 2 including an injection frame and an injection piston;

[0023] FIGS. 4, 5, and 6 are side elevation views of the injection molding system of FIG. 1 at various stages of an injection molding cycle;

[0024] FIGS. 7A and 7B are side elevation views showing operation of the injection molding system of FIG. 1 for molded article removal;

[0025] FIGS. 8A and 8B are side elevation views showing alternative operation of the injection molding system of FIG. 1 for molded article removal; and

[0026] FIG. 9 is a schematic, side elevation view of an alternative injection molding system in cross section.

[0027] The drawings are not necessarily to scale and may be illustrated by phantom lines, diagrammatic representations, schematic representations, and fragmentary views. In certain instances, details that are not necessary for an understanding of the embodiments or that render other details difficult to perceive may have been omitted.DETAILED DESCRIPTION OF THE NON-LIMITING EMBODIMENT(S)

[0028] In this document, any use of the term “exemplary” should be understood to mean “an example of’ and not necessarily to mean that the example is preferable or optimal in some way. Terms such as “back,” “rearwardly,” “rightwardly,” “leftwardly,” and “vertical” may be used to describe features of some embodiments in this description but should not be understood to necessarily connote an orientation of the embodiments during manufacture or use.

[0029] Referring to FIG. 1, an exemplary injection molding system 100 is illustrated in side elevation view. In FIG. 1, the injection molding system 100 is shown in cross-section and in an assembled state. The depiction of the injection molding system 100 is simplified, with details that are unnecessary for an understanding of the embodiment being omitted. FIG. 2 depicts the injection molding system 100 of FIG. 1, also in cross-section and in side elevation view, but in a disassembled state.

[0030] The injection molding system 100 of FIGS. 1 and 2 includes a clamp frame 102, an injection frame 110, an injection piston 120, an injection actuator 130, and a mold 140. These components will be described in turn.

[0031] The clamp frame 102 generally acts as a structural framework within which injection molding occurs. The clamp frame 102 includes an actuator platen 104, a mold platen 106, and a fixing member 108. The actuator platen 104 provides a mounting point and / or footing for an injection actuator 130, described below. The mold platen 106 is generally opposed to the actuator platen 104 and provides amounting point for a mold half of the mold 140, described below. The fixing member 108 fixes the actuator platen 104 relative to the mold platen 106 at least during an injection phase of operation of the injection molding system 100, which will be described. In the present embodiment, the clamp frame 102 is a unitary component made from a single block of rigid material, e.g., steel. In other words, the fixing member permanently fixes the actuator platen 104 relative to the mold platen 106 in this embodiment. However, as will be described, the clamp frame 102 need not necessarily be integrally formed as a unitary component in alternative embodiments.

[0032] The injection frame 110 is a structural component that defines an injection cylinder 112 in which melted molding material (also referred to as “melt”) is pressurized for injection molding. In the present embodiment, the injection frame 110 is adjacent to the actuator platen 104 and translatable with respect to the clamp frame 102 (and thus also with respect to the actuator platen 104). As will be appreciated, the injection frame 110 may be subjected to small displacements relative to the clamp frame 102 to compensate for dimensional tolerances of the mold and / or due to strain deflections of the mold 140 when subjected to injection pressure. The injection frame 110 may be formed from a unitary block of rigid material (see, e.g., FIG. 3, described below), such as steel, although this is not strictly required.

[0033] The injection cylinder 112 make take the form of a cylindrical bore (or other cavity) in the injection frame 110. In the present embodiment, the injection cylinder 112 has an upstream wider portion 112A and a downstream narrower portion 112B. The wider portion 112A is sized and shaped to slidably receive the injection piston 120. The narrower portion 112B is sized and shaped to slidably receive a plunger 122 that is fixed relative to the injection piston 120 (described below). In some embodiments, the plunger 122 may not be fixed to injection piston 120. Rather, the plunger 122 and the injection piston 120 may simply be in contact with each other.

[0034] The injection cylinder 112 is defined, in part, by an internal surface 114 located at a downstream end thereof close to the mold 140. In the illustrated embodiment, the internal surface 114 forms part of the downstream-most, narrower portion 112B of the injection cylinder 112. The internal surface 114 has a frustoconical shape in the present embodiment. The frustoconical shape may help to limit melt hang-up areas, e.g., in comparison to a flat transverse surface. Nevertheless, the internal surface 114 could be flat (e.g., annular) in alternative embodiments. The internal surface 114 faces away, at least in part, from the mold 140. A nozzle 115 provides a channel for egress of melt from the injection cylinder 112. In the present embodiment, the nozzle 115 is coaxial with the injection cylinder 112 and surrounded by (proximate to) the internal surface 114 of the injection cylinder 112.

[0035] The injection piston 120 is used to pressurize and inject melt from the injection cylinder 112 into the mold 140. In the present embodiment, the injection piston 120 is a cylindrical element made from a rigid material, such as steel. The injection piston 120 of the present embodiment has a circularface 121 that defines, in part, a hydraulic fluid chamber 118 (described below). In this embodiment, the injection piston 120 has an associated plunger 122. The plunger 122 is coaxial with the injection piston 120 and, in the depicted embodiment, is fixed with respect thereto, optionally being integrally formed therewith. In alternative embodiments incorporating a plunger, the plunger is not necessarily fixed with respect to the injection piston. In the depicted embodiment, the distal end 124 of plunger 122 has a frustoconical shape that is complementary to the frustoconical shape of internal surface 114 of the injection cylinder 112. In alternative embodiments, the distal end of the plunger may have another shape, e.g., flat, which is complementary to that of the internal surface of the injection cylinder.

[0036] FIG. 3 is a perspective view of the injection frame 110 and injection piston 120 in isolation from other components of the injection molding system 100. FIG. 3 may facilitate appreciation of the three-dimensional shape of these components in the example embodiment.

[0037] Referring again to FIG. 1, the injection actuator 130 is actuatably coupled to the injection piston 120 and is operable to cause the injection piston 120 to move relative to the actuator platen 104. In the present embodiment, the injection actuator 130 is a hydraulic injection actuator 130 that includes a cylinder head 132 and a hydraulic pressure source 134. The cylinder head 132 is a rigid component that is proximate (e.g., adjacent) to the actuator platen 104. In the present embodiment, the cylinder head 132 is fixed relative to the actuator platen 104, e.g., is affixed or attached thereto, although this is not strictly required. In the present embodiment, the cylinder head 132 has a cylindrical or puck shape. The hydraulic pressure source 134, which is schematically depicted in FIG. 1, could for example be a hydraulic pump or a valve in fluid communication with a source of pressurized hydraulic fluid.

[0038] The injection actuator 130 of the present embodiment also includes a receptacle 116 defined in the injection frame 110. The receptacle 116 is configured to slidably and sealably receive the cylinder head 132. Collectively, the cylinder head 132, the receptacle 116, and the injection piston 120 (specifically, its exposed face 121) define a hydraulic fluid chamber 118 (FIG. 1) with which the hydraulic pressure source 134 is in fluid communication. As will be appreciated, the hydraulic pressure source 134 is operable to actuate the injection piston 120 for injection molding by supplying pressurized hydraulic fluid to the hydraulic fluid chamber 118 to cause the injection piston 120 to slide, within the injection cylinder 112, away from the cylinder head 132 and the actuator platen 104.

[0039] In the present embodiment, the receptacle 116 is cylindrically shaped and coaxial with the injection cylinder 112, as perhaps best seen in FIG. 3. To the extent that alternative embodiments utilize an analogous receptacle defined in the injection frame 110, the receptacle may have a different shape.

[0040] In the depicted embodiment, the receptacle 116 is defined, in part, by a clamping force augmentation surface 119 of the injection frame 110, which is an optional feature. The clamping forceaugmentation surface 119 forms part of the hydraulic fluid chamber 118 and faces at least partly away from the mold 140 (or, as in the depicted embodiment, faces fully away from the mold 140, i.e., is vertical in FIG. 1). The clamping force augmentation surface 119 can be used to augment the clamping force applied to the mold 140 during injection molding, as will be described. In the present embodiment, the clamping force augmentation surface 119 is annular and coaxial with the injection cylinder (see FIG. 3), although neither is strictly required.

[0041] Referring again to FIGS. 1 and 2, mold 140 includes a first mold half 142 and a second mold half 144 collectively defining a molding cavity 146 therebetween. The first mold half 142 is mountable to the mold platen 106. The second mold half 144 is arranged between the first mold half 142 and the injection frame 110. As such, the mold halves 142, 144 are arranged between the mold platen 106 and the injection frame 110. A gate 148 in the second mold half 144 (not to scale) provides in ingress channel for melted molding material into the molding cavity 146. In embodiments where the article to be molded is a container or closure, the first mold half 142 may be a core mold half, and the second mold half 144 may be a cavity mold half.

[0042] Operation of the injection molding system 100 of FIG. 1 for injection molding an article will be described in conjunction with FIGS. 4-6, which adopt conventions similar to those of FIG. 1. In FIGS. 4-6, the injection molding system 100 is depicted at various points in time of an injection molding cycle.

[0043] Referring to FIG. 4, the injection molding system 100 is depicted at the beginning of an injection cycle. The injection frame 110 is translated slightly rearwardly (rightwardly in FIG. 4) with respect to the clamp frame 102 compared to its position in FIG. 1, resulting in a gap G between the injection frame 110 and the mold 140. As will be described, this gap G may facilitate molded article removal in some embodiments (see, e.g., FIGS. 7A and 7B, described below). The gap G may also facilitate loading of a suitable mold 140 into the clamp frame 102 for molding a desired type of article. In other words, the gap G may facilitate the swapping of molds 140 between injection molding runs.

[0044] In preparation for injection molding, the injection piston 120 and associated plunger 122 are pulled back (translated axially rightwardly) within the injection cylinder 112 in FIG. 4. Moreover, a downstream part of the narrower injection cylinder portion 112B, between the distal end 124 of plunger 122 and the internal surface 114, has been filled with melt 150. The melt 150 may for example be supplied to the injection cylinder 112 from an injection unit (not expressly depicted) via suitable supply channels within the injection frame 110 (also not expressly depicted). Hydraulic fluid 160 fills the hydraulic fluid chamber 118 in FIG. 4 but is insufficiently pressurized to cause appreciable movement of the injection piston 120 relative to the injection frame 110.

[0045] FIG. 5 depicts the injection molding system 100 during injection molding, i.e., aftercommencement, but prior to completion, of injection molding. In FIG. 5, the injection actuator 130 has been actuated by activating the hydraulic pressure source 134 to increase the hydraulic fluid pressure within the hydraulic fluid chamber 118. Actuation of the injection actuator 130 has three outcomes.

[0046] A first outcome is that the injection piston 120 and associated plunger 122 are actuated, relative to the actuator platen 104, to commence injection molding. More specifically, the injection piston 120 and plunger 122 are both translated within the injection cylinder 112 away from the actuator platen 104 and cylinder head 132. This outcome is a result of the increased pressure of the hydraulic fluid 160 acting axially (leftwardly in FIG. 5) upon the face 121 of the injection piston 120. More specifically, an axial force F0, which is a product of the hydraulic fluid pressure within the hydraulic fluid chamber 118 multiplied by the cross-sectional area of the piston (i.e., the area of the exposed face 121 in the depicted embodiment), is applied to the injection piston 120. The resultant translation of the injection piston 120 and plunger 122 away from the actuator platen 104 pressurizes the melt 150 inside the injection cylinder 112 (specifically, portion 112B of the injection cylinder 112) and causes to the melt 150 to be injected into the molding cavity 146 via nozzle 115 and gate 148.

[0047] A second outcome of actuation of the injection actuator 130 is that the injection frame 110 and second mold half 144 are biased against first mold half 142. More specifically, as the injection piston 120 and plunger 122 begin to translate within the injection cylinder 112, melt pressure within the injection cylinder 112 increases. The pressurized melt 150 exerts outward pressure upon all of the internal surfaces of the injection cylinder 112 with which it is in contact, including the internal surface 114. The resultant force Fl, acting in the axial dimension towards the mold 140, is sufficient in this example to cause the injection frame 110 to shift towards the mold platen 106, thereby eliminating the gap G of FIG. 4. The shift may occur before any melt 150 is injected into the molding cavity 146. The force Fl biases the injection frame 110 against the second mold half 144, which in turn is biased against the first mold half 142 (i.e., the second mold half 144 transmits the forces imparted by the injection frame 110 through to the first mold half 142). A clamping force Fl (which may be alternatively referred to as the “injection clamping force Fl”) is thereby generated between the confronting faces of the first and second mold halves 142, 144.

[0048] A third outcome of the actuation of the injection actuator 130 in the present embodiment is that the mold clamping force Fl is augmented due to the presence of the clamping force augmentation surface 119. More specifically, pressurized hydraulic fluid 160 within the hydraulic fluid chamber 118 exerts pressure outwardly against all of the internal surfaces of the hydraulic fluid chamber 118, including the annular clamping force augmentation surface 119. The hydraulic fluid pressure upon clamping force augmentation surface 119 creates an axial force F2, away from the actuator platen 104, that further biases the injection frame 110 and second mold half 144 against first mold half 142. Theforce F2 thus augments (supplements) clamping force Fl, resulting in a total or net clamping force of Fl + F2 between the confronting faces of the mold halves 142, 144. It will be appreciated that the pressure of the hydraulic fluid 160 that is exerted oppositely upon the cylinder head 132 does not counteract force F2 because the injection frame 110 is free to slide (translate) relative to the cylinder head 132. The mold clamping forces Fl and F2 may accordingly be considered as primary and secondary mold clamping forces, respectively.

[0049] It will be noted that the generating of supplemental clamping force F2 as described above is optional and is not necessarily performed in all embodiments. For example, mold clamping force augmentation may not occur in embodiments of the injection molding system 100 having a hydraulic fluid chamber 118 that lacks a clamping force augmentation surface 119 or in the alternative embodiment depicted in FIG. 9, described below.

[0050] FIG. 6 depicts the injection molding system 100 at the completion of injection molding. At this stage, substantially all of the melt from the injection cylinder 112 has been injected into the molding cavity 146. Force Fl continues to be applied to the internal surface 114 of the injection cylinder 112, possibly directly by the plunger 122 (if no melt remains in the injection cylinder 112). The clamping force Fl between the confronting faces of the mold halves 142, 144 is accordingly maintained. The melt 150 within the molding cavity 146 remains pressurized as it cools.

[0051] It will be appreciated that the pressurized melt 150 within the molding cavity 146 exerts an outward force F3 in the axial dimension, tending to cause the mold halves 142, 144 to separate. The mold separating force F3 may be computed, or at least estimated, by multiplying the maximum transverse cross-sectional area of molding cavity 146 by the pressure of the melt 150 within the molding cavity 146. For clarity, the term “transverse” in this context refers to a dimension orthogonal to the moldopening dimension. In some embodiments, the maximum transverse cross-sectional area of molding cavity 146 is its projected parting area, i.e., the area of the molding cavity 146 at the parting line of the mold 140.

[0052] To prevent, or at least limit, separation of the mold halves 142, 144 during injection molding, the net mold clamping force Fl + F2 acting axially upon the mold 140 should exceed the mold-separating force F3 (where, in embodiments lacking a mold clamp augmentation surface 119, the mold clamping force F2 may be considered to be zero). To reduce a risk of mold separation, it may be desirable to maintain a ratio of the net mold clamping force F 1 + F2 to the mold separating force F3 above a threshold value greater than one. For example, the ratio of clamping force Fl + F2 to mold-separating force F3 may be kept at or above 1.1 or 1.2, i.e., 10% or 20% over equality. These values may be application specific.

[0053] It will be appreciated that the magnitude of the net clamping force F 1 + F2 applied to the mold 140 in FIGS. 4 and 5 may depend upon multiple factors. One factor is the transverse cross-sectional area of the internal surface 114 of the injection cylinder 112 upon which melt pressure is exerted. Another factor is the pressure of the melt within the injection cylinder 112, which in turn depends at least partly upon the force F0 of hydraulic fluid acting upon the face 121 of the injection piston 120 (as described above). Another factor is the transverse cross-sectional area of the clamping force augmentation surface 119 (if present) of the injection frame 110 upon which hydraulic fluid pressure is exerted. A further factor is the pressure of the hydraulic fluid in the hydraulic fluid chamber 118 (in embodiments having a clamping force augmentation surface 119). These parameters can be customized, e.g., to achieve the desired ratio (referenced above) of net mold clamping force Fl + F2 to expected mold separation force F3.

[0054] Regardless of whether a clamping force augmentation surface 119 is present, it will be appreciated that the clamping force Fl upon the mold 140 is adaptive to melt pressure: the greater the melt pressure, the greater the mold clamping force. This effect may facilitate automatic maintenance of appropriate clamping force upon a mold even as melt pressure changes over the course of an injection molding cycle. For example, in some embodiments of injection molding system 100, melt pressure within the molding cavity 146 may be increased during a final hold / pack phase of injection molding, e.g., in order to fill any gaps in the molded article as melt within the molding cavity 146 cools and shrinks. Such a hold / pack melt pressure increase may intensify the magnitude of the mold-separating force F3 (FIG. 6). However, such a melt pressure increase would also automatically correspondingly increase the force Fl counteracting the mold-separating force F3, i.e., clamping mold halves 142, 144 together. The adaptivity of the clamping force relative to melt pressure may diminish the need for externally powered clamping mechanisms whose clamping forces must be continuously dynamically adjusted. Accordingly, the complexity and / or power consumption demands of the injection molding system 100 may be reduced in comparison to such systems.

[0055] Once the melt 150 within the molding cavity 146 has sufficiently hardened, the resultant molded article 152 may be removed from the molding cavity 146 of the mold 140. FIGS. 7A and 7B are schematic diagrams showing operation of the injection molding system 100 for molded article removal. The conventions of FIGS. 7A and 7B are similar to those of FIGS. 4-6. The operations depicted in FIGS. 7A and 7B may be suitable for embodiments of the injection molding system 100 in which the cylinder head 132 is affixed to the actuator platen 104.

[0056] In a first stage of operation of the injection molding system 100 for molded article removal (FIG. 7A), the mold 140 is removed from the clamp frame 102, i.e., from between the mold platen 106 and the injection frame 110. Prior to removal of the mold 140, clamping force Fl + F2 (as describedabove in connection with FIG. 6) may be reduced to zero, e.g., by deactivation of the injection actuator 130. In some embodiments, the injection actuator 130, or another actuator (not expressly depicted), may also be used to shift the injection frame 110 slightly away from the mold 140 towards the actuator platen 104. This may create a gap G between the mold 140 and the injection frame 110 (e.g., as in FIG. 4), which may facilitate mold 140 removal. The mold 140 may be removed from the clamp frame 102 as shown in FIG. 7A by one or more actuators, such as hydraulic linear actuators, ball screw actuators, or the like (not expressly depicted).

[0057] In a second stage of operation of the injection molding system 100 for molded article removal (FIG. 7B), the first mold half 142 and the second mold half 144 are separated for ejection of the molded article 152. Either one or both of the mold halves 142, 144 may be made to move away from the other. The actuator(s) used to move the mold halves 142, 144 into a separated condition is / are not expressly depicted in FIG. 7B but may for example be one or more linear hydraulic actuators, ball screw actuators, or the like. The injection molding system 100 may incorporate mechanisms to facilitate article ejection, such as ejector pins or stripping mechanisms, which too are not expressly depicted.

[0058] An alternative approach for molded article ejection by the injection molding system 100 is depicted in FIGS. 8A and 8B. The molded article ejection operations shown in FIGS. 8A and 8B may be suitable for embodiments of the injection molding system 100 in which the cylinder head 132 is not fixed relative to (e.g., not affixed or attached to) the actuator platen 104. The conventions of FIGS. 8A and 8B are similar to those of FIGS. 7A and 7B.

[0059] In a first stage of operation of the injection molding system 100 for molded article removal (FIG. 8A), the mold 140 and injection frame 110 are removed as a unit from the clamp frame 102, i.e., from between the actuator platen 104 and the mold platen 106. Prior to removal of the mold 140, clamping force Fl + F2 may be reduced to zero, e.g., by deactivation of the injection actuator 130. The cylinder head 132 may be held in place relative to the receptacle 116, e.g., by a locking mechanism (not expressly depicted), to avoid egress of hydraulic fluid 160. To that end, the cylinder head 132 may contain, in some embodiments, a return spring (not expressly depicted) that reacts against injection frame 110 to aid in cylinder head retraction relative to the injection frame 110. Such a return spring could also assist in removal of oil volume from hydraulic fluid chamber 118. Alternatively, in some embodiments, oil may be removed from hydraulic fluid chamber 118 via suction. The suction may result in reactive forces on injection piston 120 and cylinder head 132. In some embodiments, the injection molding system 100 may be designed to effect preferential movement of cylinder head 132 as compared to the injection piston 120, e.g., via a larger hydraulic area and lower running friction of the former versus the latter. As well, the mold 140 may be locked relative to the injection frame 110 to permit movement of the two as a unit without separation. The actuator(s) used to achieve the movement shown in FIG. 8Amay for example be one or more hydraulic linear actuators, one or more ball screw actuators, or the like (not expressly depicted).

[0060] In a second stage of operation of the injection molding system 100 for molded article removal (FIG. 8B), the first mold half 142 is separated from the second mold half 144 for ejection of the molded article 152. This stage may entail keeping mold half 144 and inj ection frame 110 stationary while moving the first mold half 142 away from the second mold half 144 (which may expend less energy than causing second mold half 144 and injection frame 110 to move away from the first mold half 142 during mold separation). As with the injection molding system 100 shown in FIGS. 7A and 7B, the injection molding system 100 of FIGS. 8A and 8B may employ additional mechanisms to facilitate molded article ejection, such as ejector pins or stripping mechanisms, which too are not expressly depicted.

[0061] A possible benefit of the molded article ejection approach of FIGS. 7A and 7B may be that only the mold 140, and not injection frame 110, is moved during molded article ejection. This may consume less energy than if the weight of inj ection frame 110 were also required to move during molded article ejection. However, it will be appreciated that the operations depicted in FIGS. 7A and 7B cause the melt nozzle 115 of the injection frame 110 to be taken out of alignment with — and then realigned with — the gate 148 of second mold half 144, during each injection molding cycle. The mechanism(s) used for such alignment actions may contribute to system complexity. Moreover, many repeated injection cycles over time may risk wear and / or misalignment of the melt nozzle 115 with respect to the gate 148 of second mold half 144. Over time, this may lead to an increasing risk of melt flow anomalies and / or melt leakage.

[0062] Conversely, a possible benefit of the molded article ejection approach of FIGS. 8A and 8B may be that the melt nozzle 115 and gate 148 are kept in alignment throughout molded article ejection. This may reduce the risk of melt flow anomalies and / or melt leakage in comparison to the embodiment of FIGS. 7A and 7B. However, this approach may come at the cost of the additional energy expended to move not only mold 140 but injection frame 110 during each injection molding cycle.

[0063] As described above, the injection molding system of FIGS. 1-6, 7A, 7B, 8A, and 8B incorporates an injection actuator that is hydraulically driven. It will be appreciated that, in alternative embodiments of the injection molding system, the injection actuator may be non-hydraulic. For example, the injection actuator may be mechanical and / or electrical.

[0064] An alternative embodiment of the injection molding system 200 employing a mechanical and / or electrical injection actuator 230 is depicted schematically in FIG. 9. In many respects, the injection molding system 200 is similar to the injection molding system 100 of FIGS. 1-6, 7A, and 7B. For example, the injection molding system 100 comprises a clamp frame 202, an injection frame 210,an injection piston 220, and a mold 240 that are analogous to the respective components of the same name of FIG. 1, described above.

[0065] More specifically, the clamp frame 202 includes an actuator platen 204, a mold platen 206, and a fixing member 208. The actuator platen 204 provides a mounting point for an injection actuator 230. The mold platen 206 is generally opposed to the actuator platen 104 and provides a mounting point for a mold half of the mold 240. The fixing member 208 fixes the actuator platen 104 relative to the mold platen 106 at least during an injection phase of operation of the injection molding system 200. In the present embodiment, the clamp frame 202 is a unitary component made from a single block of rigid material, e.g., steel. However, as will be described, the clamp frame 202 need not necessarily be integrally formed as a unitary component in alternative embodiments.

[0066] The injection frame 210 is a structural component that defines an injection cylinder 212. The injection frame 210 may be adjacent to the actuator platen 204 and is translatable away therefrom towards the mold platen 206. The injection frame 210 may be formed from a unitary block of rigid material, e.g., similar to the injection frame 110 of FIG. 3, although this is not strictly required.

[0067] The injection cylinder 212 make take the form of a cylindrical cavity within the injection frame 210 that slidably receives the injection piston 220. The injection cylinder 212 is defined, in part, by an internal surface 214 located at a downstream end thereof. The internal surface 214 has a frustoconical shape in the present embodiment, with the internal surface 214 facing away, in part, from the mold 240. A channel that connects with the injection cylinder 212, which is referred to as a piston shaft guide 216, slidably receives a piston shaft 222.

[0068] A nozzle 215 that is coaxial with the injection cylinder 212 provides a channel for egress of melt during injection molding. In the present embodiment, the nozzle 215 is surrounded by (or, more generally, proximate to) the internal surface 214 of the injection cylinder 212.

[0069] The injection piston 220 is used to pressurize and inject melt from the injection cylinder into the mold 240. In the present embodiment, the injection piston 220 is a cylindrical element made from a rigid material, such as steel. In the present embodiment, the injection piston 220 is driven by an associated piston shaft 222. The piston shaft 222 is coaxial with the injection piston 220 and is fixed with respect thereto, optionally being integrally formed therewith. In the present embodiment, the distal end 224 of the injection piston 220 has a frustoconical shape that is complementary to the frustoconical shape of internal surface 214 of the injection cylinder 212.

[0070] The mechanical or electrical injection actuator 230 of the present embodiment is schematically represented as a set of screw threads 232 upon piston shaft 222 that are received within corresponding screw grooves of the actuator platen 204. A motor 234 (e.g., an electric DC motor orpneumatic motor) selectively causes the piston shaft to rotate clockwise or counterclockwise to cause the injection piston 220 to move leftwardly or rightwardly, respectively, in FIG. 9. The motor 234 is actuatably coupled to the injection piston 220 — in this case, via the piston shaft 222 — and is operable to cause the injection piston 220 to move relative to (e.g., away from or towards) the actuator platen 204.

[0071] Mold 240 includes a first mold half 242 and a second mold half 244 collectively defining a molding cavity 246 therebetween. The first mold half 142 may be mounted to the mold platen 206. A gate 248 in the second mold half 244 provides in ingress channel for melted molding material into the molding cavity 246. The mold halves 242, 244 are arranged between the mold platen 206 and the injection frame 210. In embodiments where the article to be molded is a container or closure, the first mold half 242 may be a core mold half and the second mold half 244 may be a cavity mold half.

[0072] Operation of the injection molding system 200 of FIG. 9 may be analogous to the operation of the injection molding system 100, described above. A difference is that the depicted injection molding system 100 of FIG. 9 generates an axial mold clamping force toward mold 240 based primarily or solely upon the melt pressure within injection cylinder 212 acting upon internal surface 214. The injection molding system 200 of FIG. 9 does not generate any mold clamping augmentation force F2 as in FIGS. 5 and 6 above because, unlike the embodiment described above in connection with FIGS. 1-6, the injection frame 210 does not have any sort of clamping force augmentation surface upon which the injection actuator 230 of FIG. 9 can apply force. A molded article formed by the injection molding system 200 could for example be ejected from mold 240 using an analogous approach to that of FIGS. 7A and 7B, described above.

[0073] Various alternative embodiments are contemplated.

[0074] Alternative embodiments of the inj ection molding system 100 could be implemented in which the injection piston 120 lacks an associated plunger 122. For example, the injection piston 120 may act directly upon melt within the injection cylinder 112 during injection molding, similarly to injection piston 220 of FIG. 9.

[0075] It is not strictly required for the internal surface 114, 214 of the injection cylinder 112, 212 (upon which pressurized melt acts to generate a mold clamping force Fl) to be frustoconical or in any way conical. The internal surface 114, 214 could have other shapes, e.g., flat.

[0076] The fixing member 108, 208 need not necessarily be integrally formed with the actuator platen 104, 204 and mold platen 106, 206. The fixing member 108, 208 could be configured to selectively unfix the actuator platen 104, 204 from the mold platen 106, 206, e.g., using selectively disengageable clamping means, such as a tie bar clamping mechanism or the like. In other words, the fixing member 108, 208 may be configured to selectively fix the actuator platen 104, 204 relative to the mold platen106, 206, e.g., to facilitate injection molding, and then disengaged to unfix the actuator platen 104 relative to the mold platen 106, e.g., to facilitate mold opening and / or molded article ejection.

[0077] In the embodiments depicted above, the second mold half 144, 244 and the injection frame110, 210 are separate components. In some embodiments, the second mold half 144, 244 and the injection frame 110, 210 may be integrally formed. In such embodiments, the injection cylinder 112, 212 may effectively be defined within the second mold half 144, 244.

[0078] Other modifications may be made within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. An injection molding system (100, 200), comprising: a clamp frame (102, 202) including an actuator platen (104, 204), a mold platen (106, 206), and a fixing member (108, 208) that fixes the actuator platen relative to the mold platen at least during an injection phase of operation of the injection molding system; an injection frame (110, 210) defining an injection cylinder (112, 212); an injection piston (120, 220) slidably arranged in the injection cylinder; an injection actuator (130, 230) actuatably coupled to the injection piston; and a mold (140, 240) having a first mold half (142, 242) and a second mold half (144, 244) collectively defining a molding cavity (146, 246) therebetween, the first and second mold halves being arranged between the mold platen and the injection frame, the injection actuator operable, during the injection phase of operation of the injection molding system, to actuate the injection piston relative to the actuator platen to cause both: injection of melt from the injection cylinder into the molding cavity; and biasing of the injection frame and the second mold half against the first mold half to generate a clamping force (Fl) between the first and second mold halves by exertion of melt pressure upon an internal surface of the injection cylinder.

2. The injection molding system of claim 1 wherein the injection actuator is a hydraulic injection actuator comprising a cylinder head (132) proximate to the actuator platen and a receptacle (116) in the injection frame configured to slidably and sealably receive the cylinder head, the cylinder head, the receptacle, and the injection piston collectively defining a hydraulic fluid chamber (118), and wherein the hydraulic injection actuator is operable to actuate the injection piston by pressurizing hydraulic fluid within the hydraulic fluid chamber to cause the injection piston to slide, within the injection cylinder, away from the cylinder head.

3. The injection molding system of claim 2 wherein the cylinder head is fixed relative to the actuator platen.

4. The injection molding system of claim 2 or claim 3 wherein the receptacle is defined in part by a clamping force augmentation surface (119) of the injection frame, the clamping force augmentation surface forming part of the hydraulic fluid chamber and facing at least partly awayfrom the mold, and wherein the hydraulic injection actuator is operable, during the injection phase of operation of the injection molding system, to generate a supplemental clamping force (F2) that further biases the injection frame and the second mold half against the first mold half, and thereby augments the generated clamping force between the first and second mold halves, by exerting hydraulic fluid pressure upon the clamping force augmentation surface of the injection frame.

5. The injection molding system of claim 4 wherein the clamping force augmentation surface of the injection frame is annular and coaxial with the injection cylinder.

6. The injection molding system of any one of claims 1 to 5 wherein the injection frame further defines a nozzle (115, 215) configured to flow the melt from the injection cylinder to the mold and wherein the internal surface of the injection cylinder is proximate to the nozzle.

7. The injection molding system of any one of claims 1 to 6 wherein the injection frame is fixed relative to the second mold half.

8. The injection molding system of claim 7 wherein the injection frame and the second mold half are integrally formed.

9. The injection molding system of any one of claims 1 to 8 wherein the fixing member is integrally formed with each of the mold platen and the actuator platen.

10. The injection molding system of any one of claims 1 to 8 wherein the fixing member is configured to selectively fix the actuator platen with respect to the mold platen.

11. A method of generating mold clamping force, the method comprising: providing an injection molding system (100, 200) including: a clamp frame (102, 202) including an actuator platen (104, 204), a mold platen (106, 206), and a fixing member (106, 206); an injection frame (110, 210) defining an injection cylinder (112, 212); an injection piston (120, 220) slidably arranged in the injection cylinder; an injection actuator (130, 230) actuatably coupled to the injection piston; anda mold (140, 240) having a first mold half (142, 242) and a second mold half (144, 244) collectively defining a molding cavity (146, 246) therebetween, the first and second mold halves being arranged between the mold platen and the injection frame; and actuating, by the injection actuator, with the fixing member fixing the actuator platen relative to the mold platen, the injection piston relative to the actuator platen to cause: injection of melt from the injection cylinder into the molding cavity; and biasing of the injection frame and the second mold half against the first mold half to generate a clamping force (Fl) between the first and second mold halves by exertion of melt pressure upon an internal surface of the injection cylinder.

12. The method of generating mold clamping force of claim 11 wherein the injection actuator is a hydraulic injection actuator comprising a cylinder head (132) proximate to the actuator platen and a receptacle (116) in the injection frame configured to slidably and sealably receive the cylinder head, the cylinder head, the receptacle, and the injection piston collectively defining a hydraulic fluid chamber (118), and wherein the method further comprises pressurizing, by the hydraulic injection actuator, hydraulic fluid within the hydraulic fluid chamber to cause the injection piston to slide, within the injection cylinder, away from the cylinder head.

13. The method of generating mold clamping force of claim 12 wherein the receptacle is defined in part by a clamping force augmentation surface (119) of the injection frame, the clamping force augmentation surface forming part of the hydraulic fluid chamber and facing at least partly away from the mold, and wherein the method further comprises exerting, by the hydraulic injection actuator, hydraulic fluid pressure upon the clamping force augmentation surface of the injection frame to further bias the injection frame and the second mold half against the first mold half and to thereby augment the generated clamping force between the first and second mold halves with a supplemental clamping force (F2) between the first and second mold halves.

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