Core puller unit for injection moulding tool

Abstract

The invention relates to a core puller unit for moving a mould core relative to an injection moulding tool in an exclusively axial direction of movement without superimposed rotation, for demoulding, after the injection process has been completed, an elongate, hollow-cylindrical moulded part such as a housing part of a medical injection device. The core puller unit comprises a slide (11) or carriage on which the mould core is fixedly mounted during the injection moulding process, a slide bearing with linear guide elements for guiding a displacement of the slide in the axial direction of movement, and a safe, precise and space-saving slide drive. The slide drive comprises an electric motor (150) for rotating a threaded rod (151) or spindle which is mounted so as not to be displaceable in the axial direction of movement relative to the injection moulding tool.

Description

[0001] Core pull unit for injection molding tool

[0002] Injection molding systems can be used to produce large quantities of thermoplastic molded parts. The outer shape of the molded part is defined by an injection mold with two outer shells, which are separated by a movement in a first direction after a cooling period of a few seconds following the injection process. Mold cores are used to produce hollow parts; together with the outer shells, they form a mold cavity. To demold the molded part, the mold cores are pulled out of the injection mold by core pull units in a second direction. The molded parts are released from the mold cores by stopping and blocking them against a stripping edge.

[0003] Patent application WO13006883 A2 describes an injection molding tool for producing hollow plastic bodies, comprising an outer mold and a mold core that is displaceable relative to the outer mold between a working position and a release position along an adjustment path, wherein the mold core forms a mold cavity with the outer mold in the closed working position. A drive element with a cylinder-piston assembly pressurized by a pressure medium displaces the mold core along its adjustment path. The piston rod end of a piston rod of the cylinder-piston assembly facing away from the outer mold is coupled to the mold core via an adjusting element extending in the direction of the adjustment path. This results in a smaller projection of the adjusting device beyond the outer mold when the mold core is in the working position.

[0004] Patent application WO12051640 A1 describes a drive for a mold core suitable for demolding complex areas of injection-molded or die-cast parts. The drive comprises two or more electric motors, with the mold core arranged on a physical axis. The axis is connected via a first gear to a first motor for generating a linear movement of the axis and via a second gear to a second motor for generating a rotational movement of the axis. The two motors can be controlled separately to generate different thread pitches or any combination of rotary and linear movements. The linear movement is generated by an axially immovable nut with an internal thread, which engages a non-rotating external thread of the physical axis.

[0005] Drives based on pressure media or hydraulics carry the risk of leaks, which, at least for medical device components, necessitates the disposal of contaminated molded parts. If a hydraulic drive is not sufficiently vented, the compressible air remaining in the hydraulic circuit can lead to imprecise or fluctuating movements. Hydraulic drives allow only limited control of the pressure medium or the force applied to the mold core, and under no circumstances can they slow down the movement of the mold core.

[0006] It is an object of the present invention to provide a core pulling unit for moving a mold core of an injection molding system with a safe, precise and space-saving drive.

[0007] The problem is solved by a core pull unit for displacing a mold core or core element relative to an injection molding tool in an exclusively axial direction of movement without superimposed rotation, for demolding, after the injection molding process, an elongated, hollow-cylindrical molded part, such as a housing part of a medical injection device. The core pull unit comprises a slide or carriage on which the mold core is firmly mounted during the injection molding process, a slide bearing with linear guide elements for guiding a displacement of the slide in the axial direction of movement, and a slide drive. The slide drive comprises an electric motor for rotating a threaded rod or spindle mounted so that it cannot be displaced in the axial direction of movement relative to the injection molding tool.

[0008] The axially immobile rotating drive with gear coupling to the movable slide results in a shorter overall length, corresponding approximately to the single adjustment path, than, for example, with a threaded or gear rack permanently connected to the slide. Since the latter cannot extend into the area of ​​the injection mold and are thus arranged axially next to the mold core, in these cases an axial extension in the release position results in an axial extension corresponding to at least twice the adjustment path. The use of an electric motor for the controlled actuation of the rotation of the threaded rod with a variable torque results in precise movement of the slide and poses no risk of contamination from hydraulic fluid.

[0009] In a preferred embodiment, the threaded rod is arranged on the side of the electric motor facing the injection molding tool. This allows a wired control and / or power supply for the drive to be axially separated from the threaded rod and coupling.

[0010] In a preferred embodiment of the core pull unit, the carriage is coupled to the threaded rod via a carriage coupling and a nut with an internal thread, which engages the external thread of the threaded rod. The connection of the nut to the carriage coupling is fixed or even integral, at least in the axial direction of movement. The connection of the carriage coupling to the carriage is easily detachable, allowing the carriage to be moved manually without using the electric motor, for example, on an assembly bench away from the injection molding tool. Further preferably, a rotor axis of the motor is connected to the threaded rod via a drive coupling. a> connected. Replacing the threaded rod and nut, for example, due to wear or if a gear ratio between rotor rotation and carriage propulsion needs to be adjusted, is thus easily possible.

[0011] A preferred embodiment of the core pull unit comprises a carriage support or base that is immovable relative to the injection molding tool, with the carriage bearing connecting the carriage support to the carriage. In this embodiment, the electric motor is mounted on the carriage support. The motor is therefore not located on the carriage, which simplifies its wired control and power supply. In a preferred embodiment, the threaded rod can also be mounted in the carriage support. Thus, in this preferred embodiment, there is no direct connection between the threaded rod and the molded parts. This results in greater stability and easier maintenance.

[0012] In a preferred embodiment of the core pull unit, the slide bearing comprises two parallel linear guide elements or rails arranged in the direction of movement, preferably in the form of crossed roller bearings. The electric motor and the threaded rod are arranged between the two linear guide elements, on the side of the slide bearing facing away from the slide. This compact design offers a significant space advantage, especially in confined spaces. The slide coupling is designed and arranged to connect the nut and slide transversely through the plane between the linear guide elements. This drive arrangement ensures power transmission without deviation from the axial direction of movement and thus supports the most friction-free displacement of the slide.

[0013] In a method for demolding a molded part using a core pull unit according to the invention, a control of the electric motor is configured or adapted for a controlled and precise displacement of the mold core or the carriage in several phases. In a first phase, the molded part and mold core are displaced together toward a stripping edge. During this displacement, or at the latest in a second phase after the molded part has struck the stripping edge, the torque of the electric motor and thus the release force on the mold core is increased. Preferably, the torque of the electric motor is actively increased by a motor control before the mold core reaches the stripping edge. The motor control can be speed-, power-, voltage-, or current-controlled for this purpose. This results in the molded part being released from the mold core.By actively increasing the torque via the motor control, the molded part can be released from the mold core faster and more reliably. In a third phase, the mold core is moved further, and the molded part is completely stripped off, at the latest after a travel distance corresponding to the axial extension of the molded part. Preferably, the carriage movement is decelerated again at the latest in a fourth phase. The electric motor control is therefore specifically used to adjust the forces acting on the carriage, so that towards the end of the... a In particular, this not only results in a reduction in acceleration, as with a hydraulic drive, but also in a real reduction in the speed of the slide, thus reducing or, advantageously, completely avoiding an impact of the slide against a buffer stop. The control system thus enables precise braking and targeted force control.

[0014] The invention is described below with reference to several figures. The features disclosed herein advantageously further develop the invention, both individually and in combination. They show:

[0015] Fig.1 a - 1c a longitudinal sectional view of a first embodiment of a core pull unit in different positions;

[0016] Fig.2 is an oblique view of a slide drive of the core pull unit in the working position;

[0017] Fig.3 is an oblique view of the carriage drive and a longitudinal section through the carriage and the carriage carrier in the release position; and

[0018] Fig.4 the course of a driving force acting on the carriage and the resulting

[0019] Speed ​​of the sled.

[0020] Figures 1a to 1c each show schematically a longitudinal section through a core pulling unit 1 for a mold core 2 according to the invention, which cooperates with an injection molding tool 4 to produce an elongated molded part 3. In Fig. 1a, two outer shells or half shells 40a, 40b of the injection molding tool are closed and, together with the mold core 2 in the working position, delimit the freshly injection-molded molded part 3. In Fig. 1b, the first outer shell 40a is removed and the second outer shell 40b is slightly raised vertically and removed from the mold part 3. In Fig. 1c, the mold core 2 is displaced horizontally by a maximum adjustment path D into a release, demolding or end position, wherein the mold part 3 is held back on a non-displaced stripping edge 10 of the core pulling unit 1 and detached from the mold core 2.

[0021] The stripping edge forms a closed structure with a clear opening through which the mold core can at least approximately fit. If the second outer shell is not lifted and the molded part is pushed out of the second outer shell by an ejector after the mold core has moved, a separate stripper can be omitted.

[0022] The core pull unit 1 comprises a slide 11 or carriage, on which a core holder 12 is mounted, which in turn supports the mold core 2 and optionally additional mold cores. As a result, the mold core is not mounted directly on a longitudinal axis of the slide, in other words at a distance from the longitudinal axis of the slide, which simplifies the assembly and disassembly of the mold core or multiple mold cores. Furthermore, the slide and a slide guide are not arranged in the parting plane of the outer shells, which allows for greater flexibility. Having multiple mold cores on the core enables more flexible and efficient production. The core pull unit 1 further comprises a slide carrier 13 or base, relative to which the slide 11 is mounted on a slide bearing so that it can be displaced in the axial direction of movement. A slide drive 15 comprises an electric motor 150 and a threaded rod 151 or spindle, which is enclosed by a nut 152.The nut 152, in turn, is axially fixed to the slide 11, so that a rotation of the threaded rod 151 is converted into an axial displacement of the slide 11 in the direction of movement.

[0023] Fig. 2 shows an oblique view of the carriage drive and the carriage bearing 14 in the working position. The carriage bearing 14 comprises parallel linear guide elements 140a, 140b or rails for precise guidance of the carriage movement. The two linear guide elements 140 have a lateral spacing that exceeds the width or transverse extent of the electric motor 150. The motor is mounted on the carriage carrier 13 on a side of the carriage bearing 14 opposite the carriage 11, between the linear guide elements 140.

[0024] The linear guide elements 140 are preferably cross-roller guides or plain-bearing linear guides with precision rollers, which are characterized, among other things, by low-maintenance operation and insensitivity to temperature fluctuations. Cross-roller guides are also suitable for absorbing the considerable forces that arise when the half-shells of the injection mold are closed.

[0025] Fig. 3 shows an oblique view of the slide drive 15 and a longitudinal section through the slide 11 and the slide support 13 in the release position. The threaded rod 151 is supported at its ends in the slide support 13 by two ball bearings 130a, b designed as roller or angular contact ball bearings and is coupled on the drive side to the rotor of the electric motor 150 via a drive coupling 153 designed as an elastomer coupling. The threaded rod 151 is designed as a recirculating ball screw and the nut 152 as a recirculating ball nut and is detachably screwed to the slide 11 via a slide coupling 110.

[0026] Fig. 4 is a representation of a typical curve of a driving force acting on the slide and the resulting speed of the slide as a function of the displacement d of the mold core from the working to the release position D. The positions or positions of the slide are designated Pos1 (starting position, working position of the mold core), Pos2 (impact of the molded part on the stripping edge), Pos3 (initiation of the braking process). The force on the slide is maximum in Pos2 at the beginning of the release of the mold part, the speed is throttled at Pos3 towards the end of the movement and driven in a controlled manner towards zero. With a hydraulic drive, the speed of the slide upon impact is typically

[0027] The slide travel is either maximally decelerated or only slightly decelerated by friction. Motor-controlled deceleration of the slide means that at the end of the travel, it no longer has any significant speed, eliminating the need for a dedicated buffer to absorb the slide's kinetic energy. To reduce cycle time, the slide can be briefly accelerated further after the molded part has been released at position 2. The prior and / or subsequent displacement of the slide in the opposite direction requires much lower forces.

[0028] For an example maximum travel range D of 150 mm, the maximum speed Vmax is up to 750 mm / s, and the peak force Fmax is up to 1 kN per mold core. For this travel range D, a spacing of at least 50 mm between the linear guide elements is preferred. For example, a 42 mm wide SVM-FP34-RN-NTC servo motor from Infranor fits into this gap.

[0029] Reference symbol:

[0030] 1 core pull unit

[0031] 10 scraper edge

[0032] 11 sleds

[0033] 110 Slide coupling

[0034] 12 core holders

[0035] 13 sled carriers

[0036] 130a, b ball bearings

[0037] 14 Sled bearing

[0038] 140a, b Linear guide elements

[0039] 15 Carriage drive

[0040] 150 electric motor

[0041] 151 threaded rod

[0042] 152 Mother

[0043] 153 Drive coupling

[0044] 2 mold core

[0045] 3 molded part

[0046] 4 injection molding tool

[0047] 40a, b outer shells

Claims

Claims 1. Core pulling unit (1) for displacing a mold core (2) relative to an injection molding tool (4) in an axial direction of movement, comprising - a carriage (11) for mounting the mold core (2), - a slide bearing (14) for guiding the slide (11) in the axial direction of movement, and - a slide drive (15), characterized in that the slide drive comprises an electric motor (150) for rotating a threaded rod (151) which is non-displaceably mounted in the axial direction of movement relative to the injection molding tool.

2. Core pulling unit according to claim 1, characterized in that the threaded rod (151) is arranged on the side of the electric motor (150) facing the injection molding tool.

3. Core pull unit according to claim 1 or 2, characterized in that the slide (11) is coupled to the threaded rod (151) via a releasable slide coupling (110) and a nut (152).

4. Core pull unit according to claim 3, characterized in that the threaded rod (151) is coupled to the electric motor (150) via a releasable drive coupling (153).

5. Core pull unit according to one of claims 1 to 4, comprising a carriage carrier (13) which is provided so as to be non-displaceable relative to the injection molding tool for receiving the carriage bearing (14), characterized in that the electric motor (150) is fastened to the carriage carrier (13).

6. Core pull unit according to one of claims 1 to 5, wherein the carriage bearing (14) comprises two parallel linear guide elements (140a, 140b), characterized in that the electric motor (150) is arranged between the two linear guide elements (140a, 140b) on the side of the carriage bearing (14) facing away from the carriage (11).

7. Core pull unit according to one of claims 1 to 6, comprising a control of the electric motor (150), characterized in that the control is designed to brake the carriage (11) before reaching a maximum adjustment path (D).

8. Core pulling unit according to claim 7, characterized in that the control is designed to increase a torque of the electric motor (150) after the start of the displacement of the mold part (3) and the mold core (2).

9. Method for demolding a molded part (3) by means of displacement of a mold core (2) by a core pulling unit (1) according to one of claims 1 to 6, by stripping the molded part (3) on a stripping edge (10) of the core pulling unit (1), characterized by an increase in a torque of the electric motor (150) after the start of the displacement of the mold part (3) and mold core (2) towards the stripping edge (10).

10. Method for demoulding a moulded part (3) according to claim 9, characterised by braking the carriage (11) before reaching a maximum displacement path (D).

11. Use of a core pulling unit according to one of claims 1 to 8 and / or a method according to one of claims 9 or 10 for producing hollow cylindrical molded parts for medical injection devices.

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