Ejector pin with anti-twist device

Description

FIELD OF THE INVENTION

[0001] The present invention relates generally to casting tools, and for example to an ejector pin for ejecting molded parts and to a support plate-ejector pin arrangement with one or more such ejector pins. BACKGROUND OF THE INVENTION

[0002] In injection molding and die casting (e.g., for molding plastics and low-melting metal alloys), the common task is to remove the solidified molded part from the mold at the end of the casting process. This is often done using one or more ejector pins mounted on a movable support plate, each extending through a hole in the mold. Typically, the ejector pins are flush with the inner wall of the mold when the ejector is not activated.

[0003] Ejection of a cast part occurs after opening the casting tool by moving the support plate with the ejector pin(s) towards the mold, whereby the ejector pin(s) penetrates the mold and thus ejects the molded part.

[0004] An example of such ejector pins and the described ejector mechanism is known from DE 43 16 029 C1. Ejector pins are known as sleeve ejectors (with internal clearance) and as solid pins (without internal clearance) (see, for example, the aforementioned DE 43 16 029 C1 and DE 33 45 366 A1).

[0005] In general, the shape of the ejector pin's face corresponds to the shape of the mold at the location where the ejector pin is located. If, for example, the wall of the mold is inclined, the ejector pin's face will have a corresponding inclination (relative to its longitudinal axis). If, for example, the mold has a step at the corresponding location, the ejector pin's face will also have a corresponding step. In such cases, the ejector pin must be installed in a defined position with respect to rotation around its own axis and secured against twisting around its own axis.

[0006] DE 33 45 366 A1 proposes an anti-twist device for ejector pins. This device features an eccentric head molded onto the ejector pin, which is inserted into a correspondingly eccentric recess in the support plate. The positive fit between the eccentricity of the head and that of the recess prevents the ejector pin from twisting in the support plate.

[0007] Although this proposal provides a functional anti-twist device for ejector pins, practical experience has shown that the proposed solution cannot yet be considered optimal. For example, the molded eccentric heads exhibit relatively large tolerances (in the range of 0.2 mm) due to manufacturing reasons. The proposed ejector pins also tend to warp when inserted into the support plate.

[0008] From DE 20 2004 018 293 U1 an ejector pin with an anti-twist device according to the preamble of claim 1 is known.

[0009] From DE 196 07 785 A1 another example of an ejector pin with the features of the preamble of claim 1 is known. SUMMARY OF THE INVENTION

[0010] The invention relates to an ejector pin for ejecting molded parts from casting tools according to claim 1.

[0011] The bevel can be formed by milling or other suitable manufacturing processes. It is preferably formed by forming (e.g., upsetting).

[0012] The bevel is provided in sections on the peripheral surface of the head. However, it is formed circumferentially around the head.

[0013] Furthermore, the bevel has an angle to the shaft longitudinal axis in a range of 3° to 10°.

[0014] The head circumferential surface comprises, in particular in an upper partial section of the head circumferential surface, a contact surface for contact with the complementary recess in the support plate.

[0015] In particular, a center offset can be generated by varying the distance between the opposing straight circumferential sections and the shaft center. This, in turn, results in the creation of different radii and surface lengths, thus allowing for easy visual differentiation of the ejector pin's installation position.

[0016] During use, the circumferential bevel helps pre-center the ejector pin, enabling quick and easy installation in the respective support plate, especially in areas with an inclined angle of 1° to 15°. Additionally, it is advantageous for installation in only one installation position, which is particularly easy to identify visually for the user.

[0017] The different radii due to the center offset enhance visual recognition and even enable tactile recognition for the user. The same applies to the different surface spacings of the peripheral sections. The shorter and longer surface spacings only ensure one installation situation.

[0018] According to the invention, a two-sided anti-twist device is provided which has a higher accuracy than a one-sided anti-twist device.

[0019] Due to the arrangement of the anti-twist device of the ejector pin and its formation on a lower section of the peripheral surface of the head as well as the support surface of the head, a floating bearing of the ejector pin in the support plate is possible, so that no distortion of the ejector pin occurs in the support plate.

[0020] In addition, the compression of the head also enables a space-saving design of the head shape, so that narrow distances can be provided between the ejector pins in a support plate.

[0021] A further aspect relates to a support plate-ejector pin arrangement comprising a support plate with one or more bores with receptacles into which ejector pins of the above-mentioned type are inserted. The receptacles are complementary to the ejector pin head shape and accommodate the heads. The shafts extend through the bores. The bores have a diameter so much larger than the shafts that the position of the ejector pin(s) in the support plate, transverse to the opposite rectilinear circumferential sections, is defined by these circumferential sections in cooperation with complementary circumferential sections of the receptacles, but not by the bores.

[0022] Further features are implicit in the disclosed devices or will become apparent to those skilled in the art from the following detailed description of embodiments and the attached drawings. SHORT DESCRIPTION OF THE DRAWING

[0023] Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Fig. 1 shows a side view of an exemplary injection mold in section in which embodiments of the ejector pins according to the invention are installed; Fig. 2 shows a top view and a side view of a first embodiment of an ejector pin; Fig. 3 shows a top view and a side view of a second embodiment of an ejector pin; Fig. 4 shows a top view and a side view of a third embodiment of an ejector pin; Fig. 5 a top view of an exemplary support plate for ejector pins of the Fig. 2 illustrated embodiment; Fig. 6 a sectional view of the support plate of Fig. 5 along the line AA; Fig. 7 shows a perspective view of another embodiment of an ejector pin according to the invention; Fig. 8a a top view of the ejector pin design from Fig. 7 shows; and Fig. 8b a side view of the embodiment of the ejector pin according to Fig. 7 shows. DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Fig. 1 shows a side view of an injection mold in which embodiments of the ejector pins according to the invention are installed. Before a detailed description of the Fig. 1 First, various explanations of the embodiments follow.

[0025] The described embodiments show an ejector pin with a shaft and a head formed by forming (e.g., upsetting). The head can also be formed by milling or other suitable processes. In the embodiments, the head has two opposite, straight circumferential sections, viewed in the longitudinal direction of the shaft. The opposite, straight circumferential sections serve to prevent rotation when the ejector pin is mounted in a complementary support plate. For this purpose, the support plate has a complementary recess for receiving the head, which recess has at least two opposite, straight circumferential sections, depending on the shape of the head. In some embodiments, the opposite, straight circumferential sections run parallel to one another. In some of these embodiments, they are at the same distance from the shaft center, i.e., are symmetrical to it.In other of these designs, however, they run at different distances from the shaft center, i.e. they are asymmetrical to it.

[0026] A different distance between the opposing straight circumferential sections and the shaft center generates a center offset. This allows for different radii and surface lengths to be created, allowing for easy visual differentiation of the ejector pin's installation position.

[0027] In other embodiments, the opposing rectilinear circumferential sections do not run parallel to each other, but rather, for example, at a small angle to each other. In some embodiments, one or more of the opposing rectilinear circumferential sections are composed of subsections at an angle. The property "reciprocal" in these cases therefore refers to the fact that they are composed of rectilinear subsections. For example, the head can essentially have the shape of a hexagon, in which two subsections adjacent to each other at 60 degrees together form a "reciprocal circumferential section composed of subsections at an angle," and two such composite sections are opposite each other (however, with such a hexagon, a "symmetry-reducing measure to eliminate the 60-degree symmetry" is also required, see below).

[0028] The head is also shaped so that the ejector pin can only be mounted in the complementary support plate in one specific installation position. In other words, this means that the head shape (only) exhibits 360-degree symmetry, meaning it only becomes congruent with itself after a 360-degree rotation (in contrast, for example, a head with symmetrically connected and symmetrically arranged straight circumferential sections has 180-degree symmetry, and a hexagon head (which becomes congruent with itself after a 60-degree rotation) has 60-degree symmetry).

[0029] In embodiments with an asymmetrical arrangement of the opposing rectilinear circumferential sections, this 360-degree symmetry is already provided by the asymmetry of the aforementioned circumferential sections; therefore, a further "symmetry-removing" measure in the head design is not necessary (although not excluded).

[0030] In embodiments with a symmetrical arrangement of the opposing rectilinear circumferential sections, without further "symmetry-dissolving" measures, a 180-degree symmetry or, for example, a 60-degree symmetry would be present (i.e., the ejector pin could also be installed in a support plate rotated by 180 degrees or 60 degrees). In these embodiments, the head therefore has a shape that precludes such installation, e.g., only rotated by 180 degrees or 60 degrees. For example, in some of these embodiments, to create the clear installation position, another rectilinear circumferential section is provided, which runs at right angles to the opposing rectilinear circumferential sections, as well as a curved circumferential section opposite this section. The design with the rectilinear circumferential section on the one hand and the curved circumferential section on the other hand cancels out the (otherwise existing) 180-degree symmetry in favor of 360-degree symmetry.Of course, this is only an example - any other symmetry-breaking design can be used equally.

[0031] Some embodiments, for example, are manufactured by first forming the head in its raw form by forming the shaft material (e.g., by upsetting), and then machining the opposing, straight peripheral sections by material removal, e.g., milling or grinding. The upsetting can be performed centrally to the longitudinal axis of the shaft. In other embodiments, the head is already manufactured with the straight peripheral sections by uniform processes (e.g., upsetting), for example, by arranging the end of the shaft to be formed in a suitable shape during the forming process.

[0032] The flat surfaces corresponding to the straight circumferential sections can be manufactured with significantly greater precision than, for example, the eccentric heads proposed in DE 33 45 366 A1. For example, the opposing straight circumferential sections of the described embodiments are manufactured with tolerances of less than or equal to 0.02 mm relative to one another. With the eccentric heads mentioned, on the other hand, tolerances in the order of magnitude of 0.2 mm were usually only achieved in practice. With the embodiments of the invention, an increase in precision of approximately one order of magnitude (i.e. a factor of 10) can therefore be achieved in a relatively simple manner - the precision in defining the angular position of the ejector pin is increased even further because the surfaces mentioned are generally supported against rotation in a complementary receptacle with a larger lever arm than an eccentric head of a corresponding size.

[0033] The embodiments further describe a support plate-ejector pin arrangement, i.e., a support plate with one or more built-in ejector pins of the type mentioned. The support plate has one or more receptacles that complement the ejector pin head shape, for example, also two opposing, straight peripheral sections. The receptacles can be manufactured, for example, by milling.

[0034] It was recognized that the eccentric ejector pins known from DE 33 45 366 A1 tend to become distorted in the support plate. The likely reason for this was found to be that when the head is manufactured by forming (e.g. upsetting), the shaft is also upset, and that this causes the shaft to become somewhat thicker (typically by 0.02 to 0.05 mm, although this can vary considerably from case to case). Since the eccentric head of DE 33 45 366 A1 does not act as a torsion lock in a complementary support plate recess on its own, but only in conjunction with the shaft, which is supported in the shaft bore by the support plate, the diameter of the shaft bore in DE 33 45 366 A1 had to be selected in practice without any air, i.e. equal to the nominal shaft diameter. Due to the aforementioned (varying) thickening of the shaft, this led to a more or less pronounced distortion of the ejector pin in the support plate.

[0035] In contrast, the situation is different in the embodiments of the invention, since here the two opposing rectilinear circumferential sections, together with the corresponding complementary circumferential sections of the recess, form an anti-rotation device on their own—that is, without supporting the shaft against the shaft bore. Against this background, in some embodiments, the ejector pin is mounted "floating" in the shaft bore; that is, the diameter of the shaft bore is chosen to be large enough that the position of the ejector pin in the support plate, transverse to the opposing rectilinear circumferential sections, is defined by these circumferential sections in cooperation with the complementary circumferential sections of the receptacle, but not by the shaft bore. For example, in some embodiments, the shaft bore has a diameter 0.1 mm larger than the shaft, and in other embodiments, even 0.2 mm larger.

[0036] As mentioned, significantly reduced tolerances can be achieved with these ejector pin designs. While the tolerance of the pin's angular position in ejector pins with eccentric heads depends on a number of factors (which are difficult to control), such as the head diameter, head position, shaft thickness, machining of the shaft bore into the support plate, and machining of the head shape into the support plate, this tolerance in the designs of the invention depends only on the tolerance of the linear circumferential sections relative to one another and their machining into the support plate. It has also been shown that the tendency toward distortion observed with eccentric heads is eliminated in these ejector pin designs. Furthermore, the linear circumferential sections allow for precise definition of the angular position of an ejector pin, unlike with conventional eccentric heads.This allows the front sides of the ejector pins to be machined outside the casting mold and before they have been installed in the support plate, whereas with conventional ejector pins with eccentric heads, this machining could usually only be carried out in practice when the ejector pin was installed in the support plate or the casting mold due to a lack of sufficiently precise angular position definition.

[0037] Now returning to Fig. 1 , this shows a side sectional view of an exemplary casting mold 1 with ejection device in a known construction (known, for example, from the aforementioned DE 33 45 366 A1). The casting mold 1 is essentially constructed from an upper and a lower mold half 2, 3 (designations such as "top" and "bottom" refer to the Fig. 1 illustrated orientation of the casting mold 1). Between the two mold halves 2, 3 there is a mold cavity 4. The lower mold half 3 is equipped with the ejection device. This is constructed from several (here: two) ejector pins 5 according to the embodiments of the invention described in more detail below, which are received in bores of the lower mold half 3 so as to be longitudinally displaceable. The ejector pins 5 have a cylindrical (e.g. circular cylindrical) shaft 6 and a flange-like, protruding head 7 formed thereon. They are installed with their heads 7 in a rotationally secure manner in a support plate 8, which is movable in the longitudinal direction of the shafts 6 by an ejection drive in the direction of the mold cavity 4. After opening the mold (ieAfter removing the upper mold half 2), the molded article produced in the mold cavity 4 is ejected by moving the support plate 8 in the direction mentioned, whereby the ejector pins 5 move upwards; these accordingly press the molded article upwards and thus push it away from the lower mold half 3.

[0038] As the exemplary Fig. 1 shows, end faces 9 of the ejector pins 5 in the non-ejection position each form a part of the wall of the lower mold half 3. In the exemplary casting mold 1, this wall runs inclined to the longitudinal axis of the ejector pins 5; consequently, the end faces 9 are also designed with a corresponding inclination relative to the ejector pin longitudinal axis. The shaping of the heads 7 of the ejector pins 5 described below and their reception in complementary recesses 10 of the support plate 8 ensure that the ejector pins 5 cannot twist, and thus their inclined end faces 9 always remain in the correct position and thus always present the correct inclination. Of course, the Fig. 1 The embodiment shown is only exemplary; in particular, the end region of the ejector pins 5 can have any desired shape determined by the desired shape of the mold cavity 4. An anti-twist device is always necessary if this shape is not rotationally symmetrical with respect to the longitudinal axis of the ejector pins 5.

[0039] Fig. 2 shows a first embodiment of the ejector pin 5, whose head 7 has two opposing, straight circumferential sections 11, which run parallel to each other at the same distance from the longitudinal axis 13 of the ejector pin 5. To clearly define the installation position (i.e., to create 360-degree symmetry), the head 7 also has another straight circumferential section 19 on one side, but a curved circumferential section 12 on the opposite side. The straight sections 11, 19 do not touch each other; rather, a radius 14 lies between them.

[0040] In this embodiment, the head 7 additionally has a circumferential bevel S. This bevel is also present in the embodiments according to Figs. 3 and inserted and designed accordingly. The head peripheral surface K comprises, particularly in an upper portion of the head peripheral surface, a contact surface AF for engaging the complementary recess in the support plate. The head 7 comprises a support surface A on its underside for resting on the support plate 8.

[0041] The bevel S can have an angle to the longitudinal axis in a range of 1° to 25°. This range is preferably between 1° and 15°; particularly preferably, the angle W is 5°. This serves as a pre-centering element for simple and quick assembly of the ejector pin 5‴ in the support plate.

[0042] Another example of an ejector pin (here designated 5') is shown in Fig. 3 shown. In this embodiment, the head 7 also has two opposing, straight, parallel circumferential sections 11, which, however, extend at different distances from each other to the longitudinal axis 13 of the ejector pin 5'. This already ensures a clear definition of the installation position (360-degree symmetry), so that the straight circumferential sections 11 are adjoined on both sides by similarly curved circumferential sections 12.

[0043] Another example of an ejector pin (here marked 5") is shown in Fig. 4 In this embodiment, the head 7 has two opposing, straight circumferential sections 11, 11', one of which is formed by two angularly joined subsections 11'. This already ensures a clear definition of the installation position (360-degree symmetry), so that the straight circumferential sections 11, 11' are adjoined on both sides by similarly curved circumferential sections 12.

[0044] In some of the embodiments shown, the head 7 is produced by upsetting and subsequent machining of the straight and curved sections 11, 11', 12, 19 and the radii 14 by milling or grinding. The opposite straight sections 11, 11' are in the embodiments of the Fig. 2 bis Fig. 4 and 7 bis 8b with a tolerance of approximately 0.02 mm relative to each other. Since the other circumferential sections 12, 19 do not serve to define the angular position of the ejector pin 5, 5', 5", 5‴, they are manufactured with larger tolerances in some embodiments. In other embodiments, the head 7 is already formed together with the sections 11, 11', 12, 19 by upsetting, without subsequent material-removing machining of these sections 11, 11', 12, 19.

[0045] In some embodiments, the ejector pin 5, 5', 5", 5‴ is a solid pin (without internal clearance). In other embodiments, however, it is a sleeve pin (with internal clearance) which can, for example, be received in a fixed pin projecting into the mold cavity 4 (see, for example, the DE 43 16 029 C1 mentioned above).

[0046] Fig. 5 shows a top view of an exemplary support plate 8 for several ejector pins 5, e.g. the one in Fig. 2 shown embodiment. The support plate 8 has a through hole 15 for each ejector pin 5 to be accommodated, with a diameter that is larger than the shaft 6 for the purpose of floating accommodation (e.g., increased by 0.2 mm), as well as a recess 16 for the positive, play-free accommodation of the head 7 within the tolerances (Note: larger tolerances - and thus greater play - can exist parallel to the straight circumferential sections 11 than perpendicular to them, since this parallel direction does not need to be used to define the ejector pin angular position). As in Fig. 5 As can be seen, the exemplary support plate 8 has two concentric circular arrangements of such bores 15 and recesses 16, the inner arrangement being designed for smaller ejector pins than the outer one for larger ejector pins. The shape of the recesses 16 is complementary to that of the head 7 of the embodiment of Fig. 2 ; i.e., the recesses 16 have two opposite rectilinear circumferential sections 17, a further rectilinear circumferential section 17' (with intermediate radii), and a curved circumferential section 18. The arrangement and dimensions of the circumferential sections 17, 17', 18 are complementary to those (11, 19, 12) of the head 7, which allows the head 7 to be received with virtually no play, and thus a virtually play-free form fit (within the given tolerances) between the head 7 and the recess 16 despite the floating reception of the shaft 6 in the through-bore 15.

[0047] Another embodiment of an ejector pin (here designated 5‴) is shown in Fig. 7 In this embodiment, the head 7 additionally has a circumferential bevel S. This bevel is also present in the embodiments according to Figs. 2-4be used and designed accordingly. The head peripheral surface K comprises, particularly in an upper section of the head peripheral surface, a contact surface AF for engaging the complementary recess in the support plate. The head 7 comprises a support surface A on its underside for resting on the support plate 8.

[0048] In one embodiment, the bevel S can have an angle to the longitudinal axis in a range of 1° to 25°. In another embodiment, this range is preferably between 1° and 15°; particularly preferably, the angle W is 5°. This serves as a pre-centering feature for simple and quick assembly of the ejector pin 5‴ in the support plate.

[0049] In this embodiment, the head 7 also has two opposing, straight, parallel circumferential sections 11, which, however, extend at different distances from the longitudinal axis 13 of the ejector pin 5‴. This already ensures a clear definition of the installation position (360-degree symmetry).

[0050] In addition, the two head circumferential surfaces 11, 11' have different lengths A and B, which are determined by the center offset from the center axis. The different head circumferential surface lengths A and B also ensure a clear definition of the installation position. The circumferential sections 12 also have different radii KR1 and KR2, which further enables visual differentiation and recognition of the corresponding installation positions of the ejector pin 5‴.

[0051] This anti-twist device for the ejector pin can be mounted floating in a support plate.

[0052] The described embodiments of the invention allow, compared to ejector pins of the prior art, a non-tensioning and repeatable ejector pin anti-twist device in the installation position in the support plate.

[0053] The angular position of a correspondingly anti-twist ejector pin is precisely defined, allowing the face shape of the ejector pins to be machined before they are installed in the carrier plates and molds. The two straight head surfaces 11, 11' form reference surfaces that can be used to align the ejector pin. The bevel S enables pre-centering.

Claims

1. An ejector pin (5, 5', 5") for ejecting moulded parts from a casting tool (1), comprising: a shaft (6), and a head (7) formed thereon, the head (7) being shaped such that the ejector pin (5, 5', 5") can be mounted in a complementary support plate (8) in one unique installation position only, the head (7), when viewed in the longitudinal direction of the shaft, having at least two opposing straight circumferential sections (11) which serve to prevent rotation when the ejector pin (5, 5', 5") is mounted in a complementary support plate (8), wherein the head (7) comprises, at its lower side, a bearing surface (A) for bearing against the support plate (8) and, at an upper subsection of its circumferential surface (K), a contact surface (AF) for contacting a complementary recess in the support plate (8), characterized in that the head (7) comprises, at a lower section of its circumferential surface (K), a slope (S) for pre-centring, wherein the slope (S) is formed circumferentially around the head (7) and adjacent to the bearing surface (A), and the slope (S) is at an angle of 3 to 10 degrees to the longitudinal axis of the shaft.

2. The ejector pin (5) according to claim 1, wherein the opposing straight circumferential sections (11) extend parallel to each other at the same distance from the centre of the shaft.

3. The ejector pin (5') according to claim 1, wherein the opposing straight circumferential sections (11) extend parallel to each other at a different distance from the centre of the shaft.

4. The ejector pin (5") according to claim 1, wherein the opposing straight circumferential sections (11, 11) are not parallel to each other.

5. The ejector pin (5") according to claim 1, wherein one or more of the opposing straight circumferential sections (11, 11') are formed of subsections (11') arranged at angles to each other6. The ejector pin (5) according to one of claims 1 to 3, wherein the head (7) has a further straight circumferential section (19) and a curved circumferential section (12) arranged opposite thereto to provide the unique installation position.

7. A method for manufacturing an ejector pin (5, 5', 5") according to one of claims 1 to 6, wherein the head (7) is produced by reshaping the shaft material and the opposing straight circumferential sections (11) are produced by milling or grinding.

8. The method for manufacturing an ejector pin (5, 5', 5") according to one of claims 1 to 6, wherein the head (7) with the opposing straight circumferential sections (11) and its slope (S) are produced by reshaping the shaft material.

9. The method according to claim 7 or 8, wherein the reshaping process is a centric upsetting process.

10. An ejector pin (5, 5', 5") according to one of claims 1 to 6 or manufactured according to one of the methods 7 to 9, wherein the opposing straight circumferential sections (11) are manufactured with tolerances of less than or equal to 0.02 mm.

11. A support-plate ejector-pin arrangement having a support plate (8) comprising one or more bores (15) with receptacles (16), into which the ejector pins (5, 5', 5") according to one of claims 1 to 6 are inserted, wherein the receptacles (16) are complementary to the ejector-pin head shape and receive the heads (7), and wherein the shafts (6) pass through the bores (15), and the bores have a diameter greater than the shafts (6) by such an extent that the position of the ejector pin or pins (5, 5', 5") in the support plate (8), in the direction transverse to the opposing straight circumferential sections, is defined by these circumferential sections in cooperation with the complementary circumferential sections (17) of the receptacles (16), but not by the bores (15).

12. The support-plate ejector-pin arrangement according to claim 11, wherein the bore (15) has a diameter which is greater than the diameter of the shaft (6) by at least 0.1 mm, in particular by at least 0.2 mm.