MOLD WITH EJECTION SYSTEM

Abstract

The invention relates to a mold for producing at least one injection-molded part, the mold comprising a movable part and a fixed part, each comprising a mold plate. The mold includes an ejection block (27, 28) for ejecting said molded part, mounted movable relative to said fixed part of the mold between a retracted position and an ejection position. The ejection block includes a first drive device (4) for movement from the retracted position to the ejection position and vice versa, and a second drive device (6) for movement independent of said first device, said second device being capable of moving said ejection block over a predetermined distance (D) from said retracted position to an intermediate position between said retracted position and said ejection position.The first device is mounted with a travel on said ejection block (27, 28), having a length which corresponds to said predetermined distance. Figure for the abbreviation: Figure 3.

Description

Title of the invention: MOLD WITH EJECTION SYSTEM

[0001] The invention relates to the demolding of articles molded in injection molds.

[0002] It relates, in particular, to mechanical means ensuring the ejection of the molded parts.

[0003] The molds usually comprise two parts, one or the other part, or even both parts, of which are mounted to move to allow the opening and closing of the mold. The injection of plastic material into the mold is carried out when the two mold parts are assembled and the ejection of the molded part is carried out after opening the mold.

[0004] In the context of the invention presented, a mold will be considered comprising a fixed mold part, having a first mold impression (die or punch) and a movable mold part, carrying a second mold impression (die or punch, coming to be associated with the first mold impression in the closed position of the mold).

[0005] The invention is particularly concerned with the ejection of the molded part.

[0006] To eject the parts, the impression plate of a part of the mold can be crossed by ejectors to bear against the molded part, so as to detach it from the impression plate.

[0007] In practice, these ejectors are driven in movement by an ejector plate which, itself, is driven in movement by means of hydraulic cylinders. Such cylinders are usually used to fulfill this function because, among all the cylinders, they are the most economical cylinders for generating the power necessary for moving the ejector block.

[0008] Today, it may be necessary to use molds in a clean room. A "clean room" will be understood to mean a room or series of rooms where the particle concentration is controlled in order to minimize the introduction, generation, retention of particles inside, generally for a specific industrial or research purpose (clean rooms are standardized).

[0009] However, hydraulic cylinders are not suitable for use in a clean room: they must therefore be replaced by other cylinders, for example, electric cylinders.

[0010] Since electric cylinders are not as powerful as hydraulic cylinders, it is necessary to provide several of them. The cost of the mold is then considerably increased.

[0011] The invention aims to offer an alternative to the use of hydraulic cylinders associated with an ejection block in a mold.

[0012] The invention proposes, for this purpose, a mold for producing at least one molded part by injection of material, said mold comprising a fixed mold part and a movable mold part, capable of moving from a mold opening position to a mold closing position, and vice versa.

[0013] The mold is remarkable in that it comprises an ejection block for ejecting said molded part from the fixed mold part, said ejection block comprising a plate mounted to move between a retracted position and an ejection position, and vice versa, said ejection block comprising a first device for driving said plate from said retracted position to said ejection position, and vice versa. Furthermore, in accordance with the invention, said ejection block comprises a second device for driving said plate, capable of being fixed to said fixed mold part, said second device being independent of said first device for driving said plate, said second drive device being capable of moving said plate from said ejection block over a predetermined distance to an intermediate position between said retracted position and said ejection position.Finally, said first displacement drive device is fixed with a clearance on said plate of said ejection block, said clearance having a length which corresponds to said predetermined distance.

[0014] The term “fixed with clearance” will be understood to mean that the first drive device is secured at least partially to the ejection block (an element retains the first device to the ejection block) but that this securing (this link) is achieved by allowing a movement of the first device relative to the ejection block, or a movement of the ejection block relative to the first device, or both.

[0015] The implementation of two independent devices ensuring the movement of the ejection block, associated with the assembly with a movement of the first drive device on the ejection block (or vice versa), makes it possible to detach the molded part before its ejection from the mold, which facilitates the demolding step.

[0016] Thus, the combination of two displacement devices makes it possible to facilitate the ejection of a molded part: the devices used to move the ejection block do not need to be as powerful as hydraulic cylinders which can then, advantageously, be replaced by other means of driving the movement of the ejection block.

[0017] The mold according to the invention may also include the following characteristics, taken separately or in combination: - said second displacement drive device comprises an elastic return device, capable of elastically deforming between a compressed state and a decompressed state, - in the retracted position of the plate of said ejection block, said second displacement drive device is positioned against said plate of said ejection block, - said second movement drive device comprises at least one gas cylinder, - said first device for driving the plate of the ejection block to move comprises a worm screw system driven in rotation by an electric motor, said system comprising a fixing device on said ejection block, said fixing device being fixed with said clearance on said ejection block, said fixing device comprising a threaded sleeve receiving said worm screw, said sleeve being able to move on said worm screw driven in rotation in one direction or the other depending on the direction of rotation imposed on said worm screw by said electric motor, - said fixing device comprises at least one oblong-shaped through hole, forming a guide rail for a fixing bolt screwed into said plate of said ejector block, said fixing device being free to move on either side of said bolt between two ends of said through hole, said predetermined distance corresponding to the length of said oblong-shaped through hole, - the ejection plate is secured to ejection rods, said ejection rods passing through said fixed mold part, - the movable mold part comprises arms capable of coming into contact with the plate of said ejection block in the intermediate position and capable of pushing the plate of said ejection block from the intermediate position to said retracted position.

[0018] The invention also relates to a method for implementing a mold as defined above, which comprises the following steps: - opening of the mold by moving the moving part, - first movement, over said predetermined distance, of the plate of said ejection block from the retracted position to the intermediate position, under the action of a thrust exerted by the second movement device on the ejection block, said first movement leading to the detachment of a molded part, - second movement of the plate of said ejection block from the intermediate position to said ejection position, controlled by the first movement device, said second movement leading to the ejection of said detached part, - third movement of the plate of said ejection block from the ejection position to the intermediate position, controlled by said first movement device, - fourth movement of the plate of said ejection block from the intermediate position to the retracted position, under the action of a thrust exerted by the movement of the movable part of the mold passing from the opening position to the closing position of the mold.

[0019] Advantageously, the implementation method may also comprise steps, according to which the plate of said ejection block is shifted by said predetermined distance relative to the first displacement device:

[0020] - during said second movement to ensure the detachment of the molded part by die elastic formation of an elastic return device which comprises said second displacement device, and - during said fourth movement, to ensure the tensioning of said elastic return device.

[0021] The invention will be better understood with regard to the embodiment which will now be presented, with reference to the appended drawings among which:

[0022] [Fig-1] is a schematic sectional view of an injection mold conforming to the invention, in the closed position,

[0023] [Fig.2] is a schematic sectional view of the mold according to the invention, in opening position and before ejection of the molded part,

[0024] [Fig.3] is a schematic sectional view of the mold, in the open position and at the time of pre-ejection,

[0025] [Fig.4] is also a schematic sectional view of the mold, in position opening and at the time of ejection,

[0026] [Fig.5] still shows the mold, following a first closing step,

[0027] [Fig.6] still shows the mold, following a second closing step, and

[0028] [Fig.7] is a partial view of an example of a ball screw with which a block can be equipped ejection of a mold according to the invention.

[0029] Figures 1 to 6 show a mold 1 comprising a mold cavity 2 for producing a part (not shown) by injecting material.

[0030] The mold 2 comprises, in a conventional manner, a matrix (not visible) and a punch 21, of a shape substantially complementary to the shape of the matrix.

[0031] The die and the punch 21 are carried respectively in blocks 23 and 22 of the mold, respectively.

[0032] The mold block 23, constituting the movable part of the mold and carrying the matrix, is fixed on a first sole 24.

[0033] The mold block 22 carrying the punch 21 is fixed to cleats 25, and the cleats 25 are fixed to a second sole 26.

[0034] The cleats 25 make it possible to create a space between the block 22 of the mold carrying the punch 21 and the sole 26.

[0035] The mold comprises an ejector block (or ejection block) comprising a plate 27 which is mounted to move between a retracted position (or rest position of the ejector block) and an ejection position.

[0036] The ejection block comprises ejection rods 28 which pass through the block 22 and the ends of which can, in the ejection position of the ejection block, project from the punch 21 to push a molded part in order to eject it (see figures 3 and 4).

[0037] The plate 27 and the rods 28 which it carries are driven in displacement in a direction of opening of the mold by means of two displacement drive systems 4, each comprising a ball screw 3 (worm screw) and a device for driving the ball screw in rotation, each of the two systems 4 being fixed at least partially on the plate 27, as well as on the second sole 26 and on the fixed block 22 of the mold.

[0038] The two ball screw systems 4 thus each comprise three parts: - A first part, comprising a first device 40 for fixing and guiding a first end of the ball screw, is fixed on the sole 26 which is fixed and which is associated with the block 22 of the mold carrying the punch 21, - A second part, comprising a second device 41 for fixing and guiding a second end of the ball screw, is fixed on the block 22 of the mold carrying the punch 21, and - A third part, comprising a third device 43 for fixing and guiding the ball screw, is fixed on the plate 27 of the ejection block.

[0039] The first and second devices 40 and 41 are fixed and do not move relative to the ball screw 3, while the third device 42 is mounted to move on the screw 3 when the screw 3 is rotated about its axis. The third device 42 is therefore mounted to move relative to the first and second devices 40 and 4L

[0040] The third device 42 being fixed on the plate 27 of the ejection block, its movement causes the plate 27 / rods 28 assembly of the ejection block to move: in one direction if the ball screw 3 is rotated in one direction, and in the other direction if the ball screw 3 is rotated in the other direction.

[0041] The movement of the third device 42, fixed to the plate of the ejection block, thus makes it possible to move the plate 27 of the ejection block from a retracted position to an ejection position, making it possible to eject a molded part, and vice versa: from the ejection position to the retracted position.

[0042] To drive the ball screw 3 in rotation, each system 4 is equipped with a motor 5 fixed to the block 22.

[0043] The motor 5 may preferably be a “brushless” motor. It is, for example, a motor of the self-controlled synchronous machine type with magnets permanent, belonging to the category of synchronous machines, whose rotor is made up of one or more permanent magnets and can be equipped with a rotor position sensor.

[0044] The advantage of using such a motor 5 is that it is much more precise than other motors. This makes it possible to solve problems of synchronizing movements of the ejection block in the mold.

[0045] By rotating the worm screw 3, the device 42 moves along the screw, following the direction of rotation given to the screw 3.

[0046] This is how the device 42 moves on the screw 3 towards the fixed block 22 of the mold, causing the plate 27 of the ejection block to move. When the device 42 is as close as possible to the fixed block 22, the ejection block is in its ejection position.

[0047] When the device 42 is located closest to the second fixed sole 26, it is in the retracted position.

[0048] The ball screw 3 and the fixing device 42 are more particularly shown in [Fig.7]: the ball screw 3 is a worm screw which is rotatably mounted in a threaded sleeve 45, the sleeve being integral with a plate 43. Balls 46 are placed between the thread of the worm screw and the internal thread of the sleeve 45 and promote the rotation of the screw in the thread by limiting, or even eliminating, friction.

[0049] The plate 43 is fixed to the plate 27 of the ejection block by bolts 44, visible in figures 1 to 6: to do this, the plate 43 is crossed by holes 47 of oblong shape and the bolts 44 are fixed to the fixing device 42 by crossing the oblong holes 47.

[0050] Thanks to this oblong shape, the device 42 can be moved between two positions on the plate 27 of the ejection block: in a first position, shown in [Fig.l] or in [Fig.6], the device 42 is positioned as close as possible to the second sole 26 and the bolt 44 is placed in abutment against a first end 51 of the oblong through hole 47. In a second position, shown in [Fig.3] or 4, the device 42 is positioned as far as possible from the second sole 26 and is oriented towards the block 22: the bolt 44 is then placed in abutment against a second end 52 internal to the oblong through hole 47, opposite the first end 51.

[0051] In this way, the plate 27 of the ejection block can move over a short distance D on either side of the device 42: it is thus movable relative to the fixing device 42.

[0052] This short distance D allows a displacement of the plate 27 of the ejection block beyond that permitted by the rotation of the ball screw: this displacement allows, in the context of this embodiment, to actuate an elastic return device 6 fixed on the block 26.

[0053] The elastic return device 6 works in compression. In the context of this mode of realization, the elastic return devices are gas cylinders. However, they could be replaced by devices ensuring elastic return (i.e. they can return to an initial shape after being deformed) for example a device comprising one or more springs.

[0054] The function of this elastic return device 6 is to automatically push the plate 27 of the ejection block back a short distance D, corresponding to the permitted displacement distance of the bolt 44 in the through hole 47 of the device 42, when the elastic return device 6 is no longer constrained. This makes it possible to push the ejection block towards the block 22, the rods 28 of the ejection block thus passing through the punch 21 to exert a force on a molded part, against the punch, thus making it possible to detach it before its ejection.

[0055] To pressurize the elastic return device 6 (or to load the elastic return device by constraining the elastically deformable element that it comprises), it is provided to equip the movable block 23 of the mold with two arms 7 which are positioned against the plate 27 of the ejection block.

[0056] When the mold is closed, the ends of the two arms 7 come into abutment against the plate 27 of the ejection block and push it back over the distance D: this makes it possible to push back (return) the ends of the rods 28 into the punch 21 and to compress the elastic return devices 6, thanks to the movement of the bolts 44 in the through holes 47 of the fixing and guiding devices 42.

[0057] In the embodiment shown in Figures 1 to 5, it is provided to implement two ball screw systems 4 to move the plate 27 of the ejection block. It could be provided to equip the mold with several other ball screw systems, or with a single ball screw system 4, without departing from the scope of the invention.

[0058] Thanks to the invention, the pressure no longer works by means of hydraulic systems: it only works by electrical or gas means.

[0059] Reference will now be made to Figures 1 to 6 to describe the operation of the mold equipped with the ejection block with ball screw system according to the invention.

[0060] In [Fig. 1], the mold is in the closed position, the mold is closed and material is injected into the mold 2 (first step of a method for implementing a mold according to the invention).

[0061] To eject the molded part (not shown) from the mold, the mold is first opened, as shown in [Fig.2] (second step of the method according to the invention), by moving, in the opening direction SI, the blocks 23 and the first sole 24 of the mold (moving part of the mold 1).

[0062] In this position, the molded part (illustrated here) remains stuck for a few moments to the punch 21 of the other part of the mold, which itself remains fixed for a few moments.

[0063] Then, the molded part is automatically detached in the following way: by opening the mold, the arms 7 of the movable part of the mold cease to exert pressure on the plate 27 of the ejection block. As a result, the elastic return devices 6 are no longer constrained and resume their shape by pushing on the plate 27 of the ejection block.

[0064] The plate 27 then moves over a short distance D ([Fig.3]) in the same direction as the opening direction SI.

[0065] The ends of the rods 28 then pass through the punch 21 and detach the molded part from the punch 21 of the mold (third step aimed at detaching the part, illustrated in [Fig.3]).

[0066] To allow complete ejection of the molded part (made easier due to the part being detached), the plate 27 of the ejection block is driven in movement towards the block 22 of the fixed mold thanks to the rotational drive of the endless screw 3, by control of the motor 5 (the rotation of the screw causing the movement of the devices 42 fixed to the plate 27). The rods 28, also driven in movement with the plate 27, push the molded part to release it from the mold 2 (fourth ejection step shown in [Fig.4]).

[0067] Once the molded part is ejected, the mold must return to its initial position.

[0068] To do this, following a fifth step of closing the mold, shown in [Fig.5] ,1a plate of the ejection block passes from its ejection position to its retracted position following a first phase of movement, by controlling the rotation of the worm screw 3 in the opposite direction to the opening direction SI (actuated by the motor 5), which causes the movement of the plate 27 of the ejection block and the rods 8 (see the arrow in [Fig.5]).

[0069] It is noted that the bolts 44 are always positioned against the internal end 52 of the oblong hole which is oriented towards the block 22 of the mold.

[0070] Following a second phase of closing of the mold, shown in [Fig.6], the movable part of the mold (block 23) fixed to the first sole 24 of the mold (the block 23 carrying the mold matrix) is moved in the closing direction S2, opposite to the opening direction SL

[0071] The movement of the movable part of the mold, to open or close the mold, is done by any means known to those skilled in the art.

[0072] When the movable part of the mold 2 is moved in the closing direction S2, the punch 21 will enter the matrix carried by the block 23 of the mold and the ends of the arms 7 will come into contact with the plate 27 of the ejection block ([Fig.6]).

[0073] In doing so, the arms 7 will push on the plate 27 of the ejection block and, at the end of closing of the mold, the plate will be moved by a short distance D (see [Fig.6]) corresponding to the movement of the bolts 44 in the through hole 47 of the fixing and guiding devices 42 between the first end 51 of the oblong shape and the second end 52 of the oblong shape of the hole 47.

[0074] This final movement of the plate 27 of the ejection block makes it possible to exert pressure on the elastic return devices 6 (still visible in the relaxed position in [Fig.5]) to force them into the compressed position (compressed position shown in [Fig.6]). This final movement also makes it possible to fully insert the ends of the rods 28 of the ejection block into the punch 21.

[0075] It is understood from the preceding description how the invention makes it possible to implement a mold without having to implement hydraulic circuits.

[0076] It will also be understood how the permitted movement of the plate 27, relative to the device 42 which connects it to the ball screw system, makes it possible to implement devices making it possible to actuate, over a short distance, the ejection block, to detach the molded part before completely ejecting it (which facilitates demolding).

Claims

Claims

1. Mold (1) for producing at least one molded part by injection of material, said mold (1) comprising a fixed part (21, 22, 26) and a movable part (23, 24) capable of passing from a mold opening position to a mold closing position, and vice versa, said mold comprising an ejection block (27, 28), for ejecting said molded part from the fixed part (21, 22) of the mold, said ejection block (27, 28) comprising a plate (27) mounted movable in movement between a retracted position and an ejection position, and vice versa, said ejection block comprising a first device (4) for driving the movement of said plate (27) from said retracted position to said ejection position, and vice versa, characterized in that said ejection block comprises a second device (6) for driving in moving said plate (27), which is fixed on said fixed part (26) of mold,said second device (6) being independent of said first displacement drive device (4), said second drive device (6) being capable of moving, over a predetermined distance (D), said plate (27) of said ejection block (27, 28) from said retracted position to an intermediate position between said retracted position and said ejection position, in that said first displacement drive device (4) is fixed with a clearance on said plate (27) of said ejection block (27, 28), said clearance having a length which corresponds to said predetermined distance (D), in that said second displacement drive device (6) comprises an elastic return apparatus, capable of elastically deforming between a compressed state and a decompressed state, and in that in the retracted position of the plate (27) of said ejection block,said second displacement drive device (6) is positioned against said plate (27) of said ejection block (27, 28) in a compressed state.,

2. Mold according to claim 1, characterized in that said second displacement drive device (6) comprises at least one gas cylinder.

3. Mold according to any one of the preceding claims, characterized in that said first device (4) for driving the plate (27) of said ejection block in movement comprises a system (4) of worm screw (3) driven in rotation by an electric motor (5), said system (4) comprising a fixing device (42) on said ejection block, said fixing device (42) being fixed with said clearance on said ejection block (27), said fixing device (42) comprising a threaded sleeve (45) receiving said worm screw (3), said sleeve (45) being able to move on said worm screw (3) driven in rotation in one direction or the other depending on the direction of rotation imposed on said worm screw (3) by said electric motor (5).

4. Mold according to claim 3, characterized in that said fixing device (42) comprises at least one through hole (47) of oblong shape, forming a guide rail for a fixing bolt (44) screwed into said plate (27) of said ejection block, said fixing device (42) being free to move on either side of said bolt (44) between two ends (51, 52) of said through hole (47), said predetermined distance (D) corresponding to the length of said through hole (47) of oblong shape.

5. Mold according to claim 3, characterized in that the ejection plate (27) is integral with ejection rods (28), said ejection rods (28) passing through said fixed mold part (21).

6. Mold according to any one of the preceding claims, characterized in that the movable mold part (23) comprises arms (7) capable of coming into contact with the plate (27) of said ejection block (27, 28) in the intermediate position and capable of pushing the plate (27) of said ejection block (27, 28) from the intermediate position to said retracted position.

7. Method for implementing a mold according to any one of the preceding claims, characterized in that it comprises the following steps: - opening the mold by moving the movable part (23), - first movement, over said predetermined distance (D), of the plate (27) of said ejection block (27, 28) from the retracted position to the intermediate position, under the action of a thrust exerted by the second movement device (6) on the ejection block (27, 28), said first movement leading to the detachment of a molded part by passage of the second device from a compressed state to a decompressed state, - second movement of the plate (27) of said ejection block (27, 28) from the intermediate position to said ejection position, controlled by the first movement device (4), said second movement

8. leading to the ejection of said detached part, - third movement of the plate (27) of said ejection block (27, 28) from the ejection position to the intermediate position, controlled by said first movement device (4), - fourth movement of the plate (27) of said ejection block (27, 28) from the intermediate position to the retracted position, under the action of a thrust exerted by the movement of the movable part (23) of the mold passing from the open position to the closed position of the mold, constraining the second device from said decompressed state to said compressed state. Implementation method according to claim 7, characterized in that the plate (27) of said ejection block (27, 28) is shifted by said predetermined distance (D) relative to the first displacement device (4): - during said second displacement to ensure the detachment of the molded part by elastic deformation of an elastic return device that said second displacement device comprises, and - during said fourth displacement, to ensure the tensioning of said elastic return device.

Images