Patent Application
20180222099
The invention is directed to an injection molding machine with a stack mold. Different embodiments of stack molds and injection molding machines with stack molds are known in the art.
A stack mold is typically composed of several mold parts, namely:
a mold part that is fixed on the fixed platen of an injection molding machine, hereinafter also referred to as fixed stack mold part;
a mold part that is fixed on of the movable platen of the injection molding machine, hereinafter also referred to as movable stack mold part;
one or several central parts, which are disposed between the fixed and the mobile stack mold part.
Depending on number of the central parts, stack molds with two or more stacks are obtained. In the closed state of the stack mold, one or several mold cavities are formed on each stack, in which melt is introduced and solidifies to form a molded part. To distribute of the melt in the mold cavities, the center platens are provided with suitable melt distribution channels. Various measures are known in the art for supplying melt from the injection unit of the injection molding machine into the central plate(s).
It is known from U.S. Pat. No. 4,207,051 to provide above of the fixed platen two telescopically collapsible pipe pieces and to connect these pieces at of the top side of the center plate of the stack mold to a melt distribution system in the center plate.
It is known from WO 2014/153676 A1 to feed the melt to the melt distribution system in the center plate via a feed line located on the central injection axis. The feed line includes at least two mutually displaceable telescopic pipe pieces. There is no need for valves for closing the feed lines when the stack mold is opened.
An injection molding machine with a stack mold is known from JP-Y-62-18418, wherein, the injection unit can be moved relative to the stationary stack tool by way of a piston-cylinder unit. The JP-Y-62-18418 is cited in the EP0576837B1 as state of the art and is described therein as follows. The injection unit is connected with the central part by way of an elongated injection cylinder, which extends through a through-opening of the stationary stack mold part, wherein in the central part a mouthpiece of the injection cylinder is pressed against a port opening of central part. The contact pressure of the mouthpiece can be preset by means of the piston-cylinder unit. When the stack mold is now closed, it can be attained by suitable control of the piston-cylinder unit that the injection unit follows the likewise moving central part and the mouthpiece of the injection cylinder remains in contact at the port opening of the central part. In this way, the injection unit forms with the central part of the stack mold a unit, which does not become separated even during the opening and closing movement of the stack mold.
It is suggested in EP0576837B1 to directly connect the injection unit with the central part. In particular, a direct mechanical connection between the injection unit and the central part of the stack mold is proposed. In one embodiment, the central part of the stack mold has on its side facing the fixed platen a protruding tubular connection fitting, which is usually referred to as snorkel. The fixed platen and the fixed stack mold part each have a center opening, into which the snorkel can protrude in certain situations so far, that the port opening protrudes from the back side of the fixed platen when the stack mold is closed. The injection unit can be axially displaced with hydraulic actuating cylinders in order to press the mouthpiece of the injection cylinder against a port opening of the snorkel to thereby establish a connection between the injection cylinder and the central part of the stack mold which is sealed to the outside. The piston rods of the hydraulic actuating cylinders pass through openings in the fixed platen and are anchored on the central part of the stack mold. By pressurizing the chamber in front the piston of the actuating cylinder, the injection cylinder is pressed against the snorkel, and the central part of the stack mold and the injection unit form a rigidly coupled unit, so that the injection unit follows the opening and closing movement of the central part. With this entrainment of the injection unit on the central part, the coupling of the mouthpiece to the port opening of the snorkel remains unchanged during the entire injection molding process and over many injection cycles, including the mold closing and mold opening movements. The central part and the injection unit may also be connected by way of screws instead of with the hydraulic actuating cylinders.
When an increased output capacity of parts is desired, it may become necessary to perform so-called injection compression molding with one stack mold. Various embodiments of injection compression molding are known in the art, obviating the need for a detailed discussion here. It is important with injection compression molding with stack molds that the mouthpiece or the nozzle of the injection unit is pressed against the snorkel so as to be able to inject, although the snorkel is displaced during the compression molding movement in the direction of the injection unit. The contact force on the snorkel during the compression molding process should preferably be constant. The snorkel could sustain damage under a heavy load or the position of the central part of the stack mold could change.
The injection molding machines with a stack mold known from JP-Y-62-18418 and EP0576837B1 can also be used to perform injection compression molding processes, because the injection unit abuts the central part or a snorkel of the central part in every position of the stack mold. However, the JP-Y-62-18418 disadvantageously requires more complex control technology. In the EP0576837B1, the mold closing must move with it the entire aggregate. This requires either an increased drive power, which makes injection compression molding less interesting. Or the movement is slowed down which makes the cycle time less interesting. Lastly, rapid movement of the injection unit has certain safety risks, unless the injection unit is enclosed in an expensive housing, which in turn impedes accessibility.
Based on this state of the art, it is the object of the invention to provide a different injection molding machine with a stack mold that is suitable for injection compression molding processes.
The object is solved with an injection molding machine having the features of claim 1. Advantageous embodiments and refinements are recited in the dependent claims.
Because a position of the injection unit can be locked or held at least during the injection process, especially during an injection process before or during the execution of an injection compression molding stroke of the stack mold, as seen in the longitudinal direction of the machine, in which the nozzle of the injection unit is pressed against a biased, movable part of snorkel, wherein the bias and the stroke to be performed by the movable part is adjusted or can be adjusted so that the nozzle and the snorkel remain pressed against each other during the injection process, the injection unit needs not be moved with the center plate, as was necessary in the prior art. This saves energy. The cycle time is also not adversely affected because the closing motion occurs independently from of the motion of the aggregate. Since the aggregate does not move fast, safety is enhanced. The control complexity is manageable.
According to one embodiment, one or several mechanical stops may be provided for establishing the position of the injection unit, to which stop(s) the injection unit can be moved and against which the injection unit can be pressed. Preferably, the position of the mechanical stops should be variable or adjustable in longitudinal machine direction. An operator has then the option to adjust a suitable position for one or more stops for a certain compression molding stroke of the stack mold. A clamping half-shell or counter-threaded stops can be used as a stop. These stops can for example be placed on the piston rods of a hydraulic linear drive for moving the injection unit. It would also be feasible to arrange one or several suitable stops on the front end of the injection unit, which can be supported on the fixed platen. This could be, for example, a circular stop element which surrounds the nozzle or the injection unit. Alternatively, several stop pins may be arranged on a circle around the injection unit. Moreover, one or several stops for supporting the guide shoe(s) of the injection unit may be arranged on the machine bed.
In another embodiment, a position of the injection unit in longitudinal machine direction may be fixed or is fixed by a mechanical blockade of its linear drive. With a hydraulic linear drive, this could be realized by a hydraulic blockade of the spaces occupied by the pressure medium. With an electrical linear drive, a brake may be provided which mechanically blocks an element driven by the electric motor.
According to another embodiment, a position of the injection unit in the longitudinal machine direction may be fixed or is fixed by regulating the driving force of its linear drive. It should hereby be taken into account that a counterforce is exerted on the injection unit which is variable over one injection cycle. On the one hand, the force with which the snorkel of the stack mold is pressed against the nozzle has to be considered. This force depends on of the position of the stack mold parts. The force increases when the stack mold closes. Furthermore, the force generated during injection of the melt into the stack mold must be taken into account.
The aforementioned possibilities for establishing the position of the injection unit may if necessary also be combined.
The snorkel may be designed to have a first snorkel part connected with a central part standing and a second snorkel part which is movable relative to the first snorkel part and faces the nozzle of the injection unit. These two snorkel parts are telescopically movable relative to one another, so that a continuous melt channel is formed that runs through both snorkel parts. Melt from the injection unit can be fed through this melt channel to the central part(s). The second snorkel part is preferably biased with respect to the first snorkel part in the direction of the nozzle and displaceable with respect to the first snorkel part by a snorkel stroke, wherein the snorkel stroke should be designed commensurate with a defined compression molding stroke of the stack mold. This snorkel stroke should be sized to correspond at least to the compression molding stroke of the stack mold. The compression molding stroke of the stack mold typically conforms to the molded part to be produced and may hence vary from one molded part to the next. However, different compression molding strokes may also be executed for the same molded part in dependence of the defined injection molding process.
A nozzle sealing mechanism, which seals on the plasticizing side, may be arranged on the front end of the plasticizing cylinder. For thinner plastic melts, a so-called valve gate is used as nozzle seal mechanism. When the valve gate is open, the melt can freely flow from there until reaching the mold. Nozzle needles may be arranged in the mold which block or open the path for the melt into the cavities. No additional closure element is required between these two closures. Moreover, the nozzle is rarely lifted from the snorkel in normal operation. However, if this occurs, leakage from the snorkel and to a lesser degree also from the nozzle may occur. If, however, these two parts are to be separated, the screw can preferably be retracted before the separation, i.e. the screw is withdrawn by a certain stroke in order to decompress the melt in the hot runner and in the nozzle tip. This can reduce leakage.
Furthermore, attention should preferably be paid to the design of the components of the injection molding machine carrying the melt, hereinafter also referred to as melt channels, so as to minimize shear energy which would damage the plastic. Moreover, suitable heating of the melt channels must be provided in order to maintain a suitable viscosity of the plastic. After the melt transitions from plasticizing into a stack mold, the melt still travels a significant distance in the snorkel, which forms the connection between plasticizing and the center plate of the mold. The center plate has additional melt channels, which are also referred to as hot runners or as hot runner manifold. Nozzles are also arranged at the transition from the hot runners to the cavities in the stack molds. Preferably, the melt channel in the snorkel is generously designed for optimum rheology. Moreover, stack molds are especially employed in conjunction with low viscosity plastics which exhibit little shear heating during passage through the melt channels. To regulate the temperature around the ideal process temperature, the snorkel can be heated along its entire length or along sections. The snorkel can therefore also be designated as a hot runner. In the center plate of a stack mold, the melt stream is divided among distribution channels into individual streams and transported to the mold nozzles located proximate to the cavities. Such distribution channels are frequently also referred to as hot run manifolds. The nozzle in front of the cavity is also heated to prevent solidification of the plastic melt awaiting injection into the nozzle antechamber.
Heating occurs preferably by way of resistance heaters disposed in suitable areas of the melt channels. Heating tapes may be used for the externally accessible areas. This applies especially to the plasticizing cylinder, the nozzle at of the plasticizing unit and the snorkel. Optionally, so-called thick film heaters may also be provided.
The invention will now be described in more detail based on embodiments and with reference to the
A first embodiment of an injection molding machine according to the invention and its operation during injection compression molding will be described hereinafter in more detail with reference to the
The central part 6b and the movable stack mold part 6c move in direction of the support plate 5 when the mold opens. An unillustrated sprue and distribution system is integrated in the central part 6b, via which the melt can be distributed in the work planes or stacks of the stack mold, in order to supply melt to the mold cavities formed in the stacks. This necessitates a tubular extension toward to the nozzle 11 on the cylinder 2a of injection unit 2, a so-called snorkel 12, through which the melt can be directed to the central part 6b. The snorkel 12 moves in conjunction with the central part 6b when the stack mold 6 opens and closes, which may cause the snorkel 12 to lift off the nozzle 11. The snorkel 12 protrudes at least into the recess of the fixed platen 3. When the stack mold 6 is closed, the snorkel 12 may even protrude past the fixed platen 3.
In the illustrated embodiment, the snorkel 12 is provided toward the nozzle 11 with a biased, movable element. The construction of such snorkel 12 is shown in more detail in
The second snorkel part 16b is biased with respect to the first snorkel part 16a in direction of the nozzle 11 and is movable with respect to the first snorkel part 16a by a snorkel stroke Hs, wherein the snorkel stroke Hs is designed commensurate with a certain compression molding stroke HP of the stack mold 6 and sized so as to correspond to at least this compression molding stroke of the stack mold 6, i.e. Hs≥HP. The biased, displaceable element may conceivably also be constructed differently, i.e.
The biased, displaceable element can also be integrated in the nozzle. The construction of such a nozzle equipped with a biased, displaceable element appointed is shown in more detail in
In injection molding without injection compression molding, the injection unit 2 presses via the nozzle 11 of the plasticizing 2a against the snorkel 12 of the stack mold 6. When injecting with comparatively high pressures, for example with pressures greater than 1500 bar and in particular with pressures greater than 2000 bar, the nozzle 11 and thus the injection unit 2 could lift off the snorkel 12, unless they are pressed against the snorkel 12, because the melt stream in the mold experiences a resistance. Moreover, in an injection compression molding process, as in the present example, the nozzle 11 or the injection unit 2 are not allowed to lift off the snorkel 12 during injection. It should be noted with injection compression molding that the stack mold 6 is not completely closed at the start of the injection, but has instead an opening of the size of the so-called compression molding stroke. To completely fill the mold, a smaller mold stroke, the so-called compression molding stroke HP, is executed which affect a stroke of the snorkel 12. This stroke of the snorkel 12 can be compensated directly at the snorkel 12 by an element, for example the aforedescribed biased movable element, namely the snorkel part 16b. As soon as the injection starts, a force between the nozzle 11 and the snorkel 12 must be built up to prevent a leakage.
In the embodiment of
In the illustrated example, the mechanical stop is affixed to the piston rods 17 of the pressure cylinder 18. However, the mechanical stop may also be placed at other locations of the machine. For example, a rim which is supported on of the fixed platen 3 may be placed on the head of the cylinder 2a. It is also conceivable to provide one or several other suitable stops at the front end of the injection unit, which may be supported on the fixed platen. For example, several stop pins could be provided which are arranged on a circle around the injection unit 2 and are supported on the fixed platen 3. Alternatively, stops could be attached on the guide rail(s) 20 of the injection unit 2, against which the unillustrated guide shoe(s) of the injection unit 2 bump.
The mechanical stop(s) 19 should be designed so that their position can be adjusted by the machine operator. This enables an operator to adjust a suitable position of the stop(s), for a certain compression molding stroke HP of the stack mold in order to fix the injection unit 2 at this position.
At the start of a cycle or at start of the production, the injection unit 2 approaches the mechanical stop 19 with a certain force and presses against the stop 19. Subsequently or at the same time, the stack mold 6 closes down to the injection compression molding gap or the compression molding stroke HP. Shortly before the mold parts 6a, 6b and 6c of the stack mold 6 reach the position for the compression molding stroke HP during closing, the snorkel 12 and the nozzle 11 make contact. During further closure to the injection compression molding gap or the compression molding stroke HP, the spring 15 in the biased movable element (fitting 12c) is slightly compressed and the fitting 12c pressed against the nozzle 11 with a small force. This state is shown in
When injection is completed, the injection unit 2 with its nozzle 11 can again be lifted from the snorkel 12 and retracted rearward from the stop 19. Alternatively, the injection unit 2 may be held permanently pressed against the mechanical stop 19. The biased movable element, such as the fitting 12c, is cyclically relieved by the mold opening stroke when the aggregate is continuously fully pressed against the stop 19. Moreover, the mechanical stop 19 is subjected to the full force by the injection unit 2 only when the snorkel 12 is lifted from of the nozzle 11. During the mold movements (closing and opening) outside of actual embossing and injection process, i.e. when the snorkel 12 is detached from of the nozzle 11, the pressure can be relieved in the pressure cylinder 18, to reduce the risk of leakage of the pressure cylinder 18. It would be advantageous to make relieving the pressure in the pressure cylinder 18 contingent on whether the snorkel 12 and the nozzle 11 make contact. In the absence of contact, the pressure cylinder 18 can be depressurized.
The injection unit 2 may be held at the predetermined, desired position in various ways. Both with an electrical and a hydraulic linear drive the position can be held by controlling a force. For example, an electrical spindle drive may be employed as a linear drive for moving the injection unit 2. In this case, the inverter can control the servomotor of the spindle drive so as to control the position of the injection unit 2 and to hold it at the predetermined, desired position. Alternatively or additionally, a brake may also be provided in the electrical or hydraulic linear drive. It is also possible with a hydraulic linear drive to hold the pressure cylinder in position by hydraulically blocking the spaces for the pressure medium.
Not shown in the figures are facilities for heating the components of the injection molding machine carrying the melt, in the following also referred to as hot runners. Heating is preferably performed with resistance heaters disposed in suitable areas of the hot runners. Heating tapes may be employed for the externally accessible areas. This applies especially for the plasticizing cylinder, the nozzle and the snorkel. In the present exemplary embodiment, the snorkel 12 is preferably heated in the area 12a and 12b, because the simple geometries allow a heating tape to be placed around the cylindrical parts. The area 12c need not be additionally heated, because of its small width. Alternatively, only the area 12a may be heated, whereas areas 12b and 12c may not be heated, and whereas area 12b may possibly be insulated, depending on the required accessibility of the components. The approach for the nozzle is comparable to the snorkel. Here, the area 11 is preferably heated, whereas the area 11b is not heated. Preferably, the area of the nozzle 11 farther back, which is not visible in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2015 112 508.0 | Jul 2015 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2016/067986 | 7/28/2016 | WO | 00 |
