Forming device for a thermoforming tool, thermoforming tool and thermoforming machine

Abstract

Forming device (200, 200a-200c) for a thermoforming tool for producing a molded part (1000) from heated thermoplastic film, comprising: a mold insert (210) and a mold base (220) which together form a mold space (250), wherein the mold base (220) is movable relative to the mold insert (210); and a demoulding device (300, 300a-300c) provided for the local demoulding of a moulded part (1000) formed in the moulding space (250); wherein the demoulding device (300, 300a-300c) comprises at least one actuatable ram which is displaceably mounted in the mould base (220) and is displaceable back and forth relative to the mould base (220) between a moulding position and demoulding position, and wherein the demoulding device (300, 300a-300c) is arranged in the interior of the mould base (220) such that the at least one ram is arranged in or near a mould base region (224) which has a local surface curvature relative to the base surface (222) of the mould base (220).

Description

[0001] The invention relates to a thermoforming tool for producing a molded part from heated thermoplastic film. Specifically, a molding device for such a thermoforming tool is described.

[0002] Thermoforming tools for producing molded parts (such as cups or lids) from heated thermoplastic film comprise a lower tool part (or tool base for short) and an upper tool part (tool top for short), which are movable relative to one another during a thermoforming process. The thermoforming tool further comprises at least one molding device, which, depending on the design of a thermoforming machine, can be accommodated in the lower tool part or the upper tool part. The molding device comprises a mold insert or mold ring and a mold base. The mold base, together with the mold insert, forms a molding space for forming the molded parts. Opposite the molding device and arranged in the upper or lower tool part, is a hold-down device (hold-down device for short).The hold-down device is designed to hold down a plastic film inserted between the upper tool part and the lower tool part during the thermoforming process.

[0003] According to one implementation, the hold-down device can be designed to accommodate a pre-stretching device (pre-stretcher for short). This device is intended for pre-forming the molded parts. For this purpose, the pre-stretcher can be moved back and forth between a rest position and a stretched position. In the rest position, the pre-stretcher is located in an open recess of the hold-down device, while in the stretched position, the pre-stretcher is moved into the mold cavity.

[0004] During a forming process, the plastic film is first heated to forming temperature using a heating device. The heated plastic film is then inserted between the lower and upper tool parts. The thermoforming tool is then closed, for example by moving the lower tool part against the upper tool part using a lifting movement or by moving the upper tool part against the lower tool part using a lowering movement. When the thermoforming tool is closed, the plastic film is cut and the edge of the molded part is held in place by the hold-down device. Furthermore, closing the thermoforming tool seals off the mold space from the environment so that the compressed air forming process and / or vacuum forming process, described in more detail below, can be carried out.

[0005] If a pre-stretcher is present, it is moved into the mold cavity (stretching position) after the edge of the molded part has been fixed. This forces the heated plastic film into the mold cavity and thus pre-forms it. The plastic film is then pressed further against the inner walls of the molding device (i.e. the walls of the mold cavity formed by the mold base and mold insert) with the help of compressed air (compressed air forming) and / or vacuum (vacuum forming), which causes the cup to be completely formed. The film resting against the inner walls of the molding device is cooled using a cooling block surrounding the mold insert, which achieves the necessary strength of the molded part. After forming and cooling, the two tool parts are separated again. The pre-stretcher is moved back from the stretching position to its rest position.The fully formed part located in the molding device is then ejected so that the thermoforming tool is ready for a subsequent molding process.

[0006] To support the ejection process, the thermoforming tool can comprise an ejection device. This is mechanically coupled to the mold base of the at least one mold device and designed to move the mold base relative to the mold insert (and thus relative to the tool parts) during the ejection process. According to one implementation, the ejection device comprises at least one ejection rod and a centrally controlled ejection bar. The at least one ejection rod is mechanically coupled at one end to the at least one mold base and at a second end to the ejection bar, which is displaceable relative to the mold device. By means of a centrally controlled lifting movement of the ejection bar and the at least one ejection rod coupled thereto, the mold base can be raised within the mold device. The lifting movement of the mold base releases the molded part from the walls of the mold device (also called demolding) and ejects it.The ejector bar can be actuated pneumatically, hydraulically, or electromechanically. Electromechanical actuation using a nut-spindle system is known, for example, from DE 10 2004 027 224 A1.

[0007] GB 1546369 A also discloses a thermoforming machine and a method for forming plastic lids. The thermoforming machine comprises an upper and a lower tool part, which are movable relative to one another. The upper tool part comprises a base plate with a forming element, a cutting element, and a preloaded clamping ring. The lower tool part also comprises a base plate, a clamping ring arranged thereon, and an ejection ring inserted therein, which in turn accommodates an annular ejector. By moving the annular ejector, the lid is lifted along its peripheral edge, thus initiating an ejection process.

[0008] Furthermore, FR 1 238 421 A discloses a deep-drawing tool for producing a container with a concave bottom. The deep-drawing tool comprises a mold insert with a bottom, the bottom consisting of an inner bottom part connected to a ram, and a stationary outer bottom part. The ram with the inner bottom part is designed to be raised against the mold movement before the molded film has completely cooled in order to invert the bottom. The ram is then raised further to eject the molded container.

[0009] As an alternative to the design described in DE 10 2004 027 224 A1, thermoforming tools without ejector bars and ejector rods are also known. In this case, demolding of the molded parts is achieved by connecting webs to the residual film grid, so-called holding films. The molded parts are then transported further along with the film by a chain conveyor of the thermoforming machine.

[0010] Regardless of the ejection mechanisms described above, the ejection process is considered critical for parts with (severe) surface curvatures (e.g., dome-shaped surface bulges) or undercuts. This is because the molded part shrinks slightly during the cooling process. Due to the shrinkage process, the molded plastic film can adhere or wedge to the mold base, particularly in areas with severe surface curvatures. Although molded parts are generally designed for thermoforming, such bulges or domes are often necessary, especially in the mold base, for example, to increase the rigidity of the molded part or to serve as a support surface for inserts.

[0011] The global ejection mechanism described above often fails to release molded parts from curved mold base surfaces. This creates the risk that molded parts will stick to the mold base despite the (rapid) lifting movement of the mold base and thus not be ejected. If, in a subsequent molding process, another molded part is molded in a mold cavity that has not been emptied, this is referred to as double punching. Double punching can have a significant impact on process reliability. Firstly, double punching can damage the thermoforming tool. Secondly, double punching increases the reject rate of unusable molded parts. In particular, if several molded parts become jammed in the molding device, the thermoforming machine must be stopped, which leads to an undesirable interruption of the molding process.

[0012] To prevent so-called double punching, the state of the art uses compressed air to blow off the molded part. For this purpose, appropriate holes are provided in the mold base. However, depending on the geometry of the molded part, this solution does not always offer the desired process reliability, as the film can be molded into the holes, thus creating an insufficient surface area for the compressed air to penetrate. Furthermore, the blowing impulse can lead to uneven blowing off of the molded parts in a thermoforming tool with multiple forming devices. This can then cause problems with the part transfer to a stacking / automation system of the thermoforming machine.

[0013] The invention is based on the object of eliminating the above-mentioned demoulding problems using simple structural means so that articles of the highest quality and with high process reliability can be manufactured.

[0014] To achieve this object, a molding device for a thermoforming tool for producing a molded part from heated thermoplastic film is provided. The molding device comprises a mold insert and a mold base, which together form a molding cavity, wherein the mold base is movable relative to the mold insert; and a demolding device provided for the local demolding of a molded part formed in the molding cavity, wherein the demolding device comprises at least one actuatable ram, which is displaceably mounted in the mold base and is displaceable back and forth relative to the mold base between a molding position and a demolding position, wherein the demolding device is arranged inside the mold base such that the at least one ram is arranged in or near a mold base region which has a local surface curvature relative to the bottom surface of the mold base.

[0015] The term "molding position" can refer to an initial position of the at least one ram, in which the ram remains in the mold base during a molding process. The at least one ram can be mounted relative to the mold base in such a way that it does not influence the molding process. The "ejection position" can refer to the position of the ram into which the ram can be moved after the molding process has ended, in order to assist in the demolding of the molded part.

[0016] The mold base can be block-shaped. The block-shaped mold base (or mold base block for short) can be formed in one piece or in multiple pieces. It can be arranged (movably) inside an annular mold insert. The mold base block can have a surface forming the mold base. The demolding device is accommodated inside the mold base block. The demolding device is arranged inside the block-shaped mold base such that the at least one movable ram is arranged in a mold base region or near a mold base region with a strong surface curvature. According to one variant, the at least one movable ram can be arranged in the center of a mold base region with a strong surface curvature. If the mold base has several regions with a strong surface curvature, a separate ram can be provided for each curved region.In this way, local demoulding of the moulded part can be supported by moving the rams relative to the mould base surface.

[0017] A mold base area with strong surface curvature can refer to a local surface area of ​​the mold base (i.e., a mold base surface area with a limited extent) that exceeds a specified curvature threshold. The surface curvature can be negative or positive. Such surface areas can thus represent local dome-shaped bulges or trough-shaped depressions on the base surface. For comparison with the specified curvature threshold, the absolute value of the curvature value can be used for negative surface curvature. An inverse radius of curvature, an angle of curvature, or another parameter suitable for describing a surface curvature can be used as a parameter to describe the curvature.The specified curvature threshold can thus represent a limit value for a surface curvature, above which the independent demoulding of the moulded part from the mould base no longer occurs with a specified probability.

[0018] The demolding device can be arranged inside the block-like mold base in such a way that the displacement of the at least one ram occurs substantially perpendicular to the mold base surface. This enables particularly effective local demolding of the molded part.

[0019] According to one variant, the demolding position can be achieved by pushing the ram toward the mold cavity (and thus against the molded part). Accordingly, the demolding device inside the mold base can be designed and arranged such that the at least one ram can be moved into the mold cavity for demolding purposes.

[0020] Alternatively, the demolding position can be achieved by moving the ram away from the mold cavity (and thus from the molded part), so that a cavity is created locally in the mold base between the molded part and the base. Accordingly, the demolding device inside the mold base can be designed and arranged such that the at least one ram can be moved out of the mold cavity for the purpose of demolding.

[0021] For slidably receiving the at least one ram in the mold base, the demolding device can comprise at least one bore formed in the mold base. The at least one bore can exit at one end at the base surface and open into the mold cavity. The at least one bore can be cylindrical or have another shape.

[0022] The at least one plunger accommodated in the at least one bore can be annular or cylindrical. Regardless of the specific design of the plunger, it can be configured such that an end of the plunger facing the mold cavity is shaped such that the plunger locally replicates the mold base in the molding position. The plunger can thus be part of the mold base surface in the molding position.

[0023] The demolding device may further comprise an actuating device for actuating the at least one ram. The actuating device may be implemented as a hydraulic, pneumatic, electromagnetic, and / or electromechanical actuating device. Additionally or alternatively, the actuating device may comprise a spring device designed and arranged to hold or preload the at least one ram in the molding or demolding position.

[0024] When implementing a pneumatic or hydraulic actuation device, each ram housed in the mold base can be coupled to a compressed air or hydraulic fluid source via corresponding compressed air channels or hydraulic fluid channels. The respective compressed air channels or hydraulic fluid channels can be implemented, at least partially, in the form of bores in the mold base. Controllable valves for selectively coupling / decoupling the ram with the compressed air or hydraulic fluid source can be arranged in the compressed air channels or hydraulic fluid channels. When implementing an electromechanical actuation device, the ram can be mechanically coupled to a linear drive. The linear drive can comprise a nut-spindle arrangement for transmitting a translational movement to the ram.

[0025] According to one variant, the actuating device can comprise a spring device which is designed to hold the at least one plunger in the molding position, as well as a pneumatic or hydraulic actuating device which is designed to move the at least one plunger from the molding position into the demolding position against a restoring force of the spring device.

[0026] According to a further variant, the actuating device can comprise a spring device which is designed to hold the at least one plunger in the demolding position, as well as a pneumatic or hydraulic actuating device which is designed to move the plunger from the demolding position into the molding position against a restoring force of the spring device.

[0027] According to a further aspect, a thermoforming tool for producing a molded part from heated thermoplastic film is provided. The thermoforming tool comprises an upper and a lower tool part, which are movable relative to one another; at least one molding device, wherein the at least one molding device is arranged in the lower or upper tool part and comprises the following: a mold insert and a mold base, which together form a molding space, wherein the mold base is movable relative to the mold insert;and a demolding device provided for the local demolding of a molded part formed in the mold cavity, wherein the demolding device comprises at least one actuatable ram that is displaceably mounted in the mold base and displaceable back and forth relative to the mold base between a molding position and a demolding position, and wherein the demolding device is arranged inside the mold base such that the at least one ram is arranged in or near a mold base region that has a local surface curvature relative to the bottom surface of the mold base; and an ejection device comprising an ejection rod that is movable relative to the tool parts, wherein the ejection rod is coupled to the mold base of the molding device in order to move the mold base relative to the mold insert during an ejection process.

[0028] The thermoforming tool may further comprise a pre-stretching device with a pre-stretcher that can be moved back and forth between a rest position and a stretched position. In the rest position, the pre-stretcher may be accommodated within a cavity of the blank holder. In the stretched position, the pre-stretcher may be moved into the molding space of the molding device to pre-form a molded part.

[0029] The thermoforming tool may further comprise at least one recess formed coaxially with the corresponding forming device in the upper tool part or lower tool part and open towards the lower or upper tool part, in which a hold-down device is slidably arranged

[0030] According to a further aspect, a thermoforming machine is provided, comprising: the thermoforming tool described above, and a control unit which is designed to activate an actuating device of the molding device after forming a molded part in order to actuate the at least one ram and to release the molded part from the molding device, wherein the control unit is further designed to activate the ejection device of the thermoforming tool in order to move the mold base relative to the mold insert and thus eject the molded part. The activation of the ejection device and the actuating device can take place essentially simultaneously or with a time delay of a predetermined time period. According to one implementation, the actuating device is activated with a time delay of a predetermined time period with respect to the ejection device.

[0031] Thus, the molded part is first lifted in the mold cavity with the help of the ejector and then removed from the mold base. This prevents the molded part from becoming jammed in the mold cavity (caused by a slight tilt of the molded part during the bottom removal with the help of the ram).

[0032] Furthermore, the thermoforming machine can include a pneumatic or hydraulic pressure source for actuating the actuating device. The pneumatic or hydraulic pressure source can be pneumatically or hydraulically coupled to the actuating device of the forming device. The coupling can be realized via corresponding channels. Valves can be provided in the channels for selectively coupling and decoupling the actuating device with the pressure source. The pressure source can be implemented as a hydraulic pump, hydraulic fluid pressure accumulator, or air pressure accumulator.

[0033] Further details and advantages of the invention are explained in more detail with reference to the drawings. They show: Fig. 1 a cup-shaped molded part produced by means of a thermoforming machine; Fig. 2a a cross-section of a thermoforming tool for producing the Fig. 1 shown cup-shaped molded part; Fig. 2b a section of the Fig. 2a shows a thermoforming tool for illustrating an ejection process of a cup-shaped molded part; Fig. 3a an excerpt from the Fig. 2a and Fig. 2b shown molding device in molding position; Fig. 3b shows an excerpt from the Fig. 2a and Fig. 2b shown molding device in demolding position; Fig. 4 shows a section of another forming device for a thermoforming tool; Fig. 5 a section of another forming device for a thermoforming tool; and Fig. 6 a section of another forming device for a thermoforming tool.

[0034] In Fig. 1 shows an example of a cup 1000 made of thermoplastic film, which can be produced by thermoforming using a thermoforming machine. The cup 1000 has a cup bottom 1020 and an outer cup wall 1010 that tapers conically toward the cup bottom 1020. The cup bottom 1020 further has an inwardly directed curvature 1030 (dome-shaped elevation) located in the center of the cup bottom 1020. The curvature 1030 comprises, viewed from the cup bottom 1020, two steeply rising flanks 1032, 1034, which merge into a concavely curved region 1036 at the upper end (i.e., in the interior of the cup 1000). The inclination of the flanks 1032, 1034 can be determined with respect to a perpendicular bisector 1038 of the dome-shaped elevation 1030. The flanks have an inclination angle of approximately 20°.

[0035] It is understood that the cup shape described here is achieved by the shape of the forming device used in the thermoforming machine. To realize the Fig. 1, the molding device must have a mold insert corresponding to the cup shape with downwardly tapered inner surfaces and a mold base with a dome-shaped raised base located centrally in the mold base. A molding device with such a shape is described in the Fig. 2a, Fig. 2b, Fig. 3a, Fig. 3b (see mold device 200) and is used in conjunction with the Fig. 2a, Fig. 2b, Fig. 3a, Fig. 3b will be described in more detail below.

[0036] As described above, the molded thermal film contracts as the cup 1000 cools. The resulting shrinkage of the cup 1000 can cause the cup 1000 to become wedged against the mold base in the concave region 1036 (and / or in the regions 1033, 1035, where the horizontal cup base 1020 abruptly transitions into the steeply rising flanks 1032, 1034). This wedging can be so severe that the ejection process described above is unable to release the cup 1000 from the mold base. To assist the demolding of the cup 1000 from the mold base, the invention uses movable rams in the mold base. These rams support local demolding on mold base surfaces with pronounced surface curvature. This technology for assisting cup demolding is described further with reference to the following figures.

[0037] In connection with the Fig. 2a and Fig. 2b, a thermoforming tool and a molding device according to the invention for producing cup-shaped molded parts are now described.

[0038] Fig. 2a shows in the form of a cross-sectional view the structure of a thermoforming tool 100 according to the invention, which is used, for example, to produce the Fig. 1. The thermoforming tool 100 comprises an upper tool part 110 and a lower tool part 120, which are movable relative to one another, at least one molding device 200 arranged in the lower tool part 120 and forming a molding space 250, a cooling device 160 provided for cooling the molding device 200, and a hold-down device 130 arranged opposite the at least one molding device 200 and received in the upper tool part 110. The thermoforming tool 100 further comprises a pre-stretching device 150 and an ejection device 140.

[0039] It should be noted that the present invention does not depend on the number of forming devices 200 arranged in the lower tool part 120. In the Fig. The cross-sectional view shown in Figure 2a shows two parallel molding devices 200 as an example. It is understood that the lower tool part 120 can also be designed to accommodate a larger number of molding devices 200 in order to simultaneously form a plurality of cups 1000 in a single molding process cycle.

[0040] The hold-down device 130 accommodated in the upper tool part 110 has at least one cavity 135 for accommodating at least one pre-stretcher 156 of the pre-stretcher device 150. The at least one cavity 135 is open toward the mold space device 200 and arranged coaxially thereto. Fig. 2a again shows two cavities 135, each designed to accommodate a piston-shaped pre-stretcher 156. It is understood that the number of cavities 135 corresponds to the number of existing molding devices 200. The hold-down device 130 can thus also have more than two cavities 135, depending on the number of molding devices 200.

[0041] The at least one pre-stretcher 156 is mechanically coupled via at least one pre-stretcher rod 152 to a pre-stretcher plate 154 of the pre-stretching device 150. By actuating the pre-stretcher plate 154, the at least one pre-stretcher 156 can be moved back and forth between a rest position and a stretched position. Actuating the pre-stretcher plate 154 here means lowering or raising the pre-stretcher plate 154 relative to the upper tool part 110. Accordingly, the pre-stretcher 156 is lowered from the cavity 135 into the mold space 250 of the molding device 200 (stretched position of the pre-stretcher 156) or raised from the mold space 250 back into the recess 135 (rest position of the pre-stretcher 156, as in Fig. 2a).

[0042] To form the cup 1000, the pre-stretcher 156 is moved from its rest position to the stretched position with the thermoforming tool 100 closed. A plastic film, which is inserted between the upper tool part 110 and the lower tool part 120 when the pre-stretcher 156 is in its rest position and secured by the fixing device 137, is pressed into the forming chamber 250 and thus pre-formed. For complete forming, compressed air (also called forming air) is supplied to the forming chamber 250 via a compressed air duct 170, whereby the pre-formed plastic film is pressed against the inner walls of the forming device 200 and thus completely formed. After the forming process is completed, the forming chamber 250 is vented (the forming air is discharged from the forming chamber 250) and the two tool parts 110, 120 are moved apart to eject the formed cups.

[0043] To carry out the ejection process, the ejection device 140 is provided in the thermoforming tool 100. This comprises an ejection rod 142 and ejection bar 144 mechanically coupled to a rear side of the mold base 220 (this is only Fig. 2b), which is displaceable relative to the lower tool part 120 by means of an actuating device. During the ejection process, the ejection rod 142 is moved upwards, i.e., in the direction of the mold space 250 (see arrow 410 in Fig. 2b). The mold base 220 coupled to the ejector rod 142 is moved by the lifting movement of the ejector rod 142 from a mold position (see Fig. 2a) into an ejection position. This lifting movement is in Fig. 2b by arrow 420. The position of the mold base 220 in the ejection position is shown in Fig. 2b also shown.

[0044] In the ejection position, the mold base 220 is shifted towards the top of the mold cavity. This causes the cup 1000 resting on the mold base 220 (the cup 1000 is in the Fig. 2b not shown) from the mold cavity 250. As already mentioned at the beginning and in connection with Fig. 1, for certain cup geometries with curved bottom surfaces, the global lifting movement of the ejection device 140 (even if this occurs quickly or jerkily) is not sufficient to completely release and eject the cup from the mold bottom 220.

[0045] With the help of the Fig. 2a and Fig. 3a, the molding device 200 according to the invention will now be further described, which is designed to actively support the cup demolding. Fig. 3a shows the bottom area of ​​the Fig. 2a in an enlarged form. Components of the molding device 200 that are structurally and functionally identical are provided with the same reference numerals in both figures.

[0046] As in Fig. 2a, the molding device 200 comprises a mold insert 210, the mold base 220 and a demolding device 300. The mold insert 210 is annular or hollow-cylindrical with an inner surface 212 tapering downwards (i.e., towards the mold base 220). The mold base 220 is block-shaped with a mold base surface 222, which, depending on the design of the cup 1000 to be formed, can have one or more elevations or depressions. The mold base 220 comprises, for example, a dome-shaped base elevation 224 or bulge arranged in the center for forming the Fig. 1. It is understood that, depending on the desired cup shape, the mold base surface 222 may have a plurality of such base elevations 224 or base depressions. The invention does not depend on the number of elevations 224 or depressions arranged in the base. Likewise, the invention does not depend on the geometry of the mold insert 210 described above. It is understood that, depending on the desired cup shape, the mold insert 210 may also have a different geometry.

[0047] As in the Fig. 2a and Fig. As shown in Figure 3a, the mold base 220 is surrounded by the mold insert 210 and, in the molding position, rests on an (annular) projection 214 at the lower end of the mold insert 210. The mold base 220 and the mold insert 210 thus form a molding space 250 that is delimited by the inner surface 212 of the mold insert 210 and the mold base surface 222. The molding position of the mold base 220 refers to the position of the mold base 222 in which the mold base 222 rests on the projection 214 of the mold insert 210 to form the molding space 250 provided for forming the cup 1000.

[0048] In connection with Fig. 3a, the demolding device 300 is further described. The demolding device 300 is designed for demolding the molded cup 1000 from the mold base surface 222. The demolding device 300 comprises at least one plunger 310 and at least one bore 330 in the mold base 220 for displaceably receiving the at least one plunger 310. The plunger 310 is displaceably mounted in the bore 330 and can be displaced back and forth between a molding position and a demolding position (see arrow 410 in Fig. 3a). For displacing (actuating) the ram 310, the demolding device 300 has an actuating device. The actuating device comprises a spring device 320 and a hydraulic or pneumatic actuating device, which is entirely or at least partially accommodated in the block-shaped mold base 220.

[0049] As in Fig. As shown in Figure 3a, the plunger 310 is received in the mold base 220 at the exact location where the mold base 220 has the dome-shaped surface curvature 224, which deviates from the smooth base surface 222. For this purpose, the mold base 220 is provided with the bore 330 locally at the location of the dome-shaped surface curvature 224. The bore 330 is arranged centrally with respect to the surface curvature 224. It opens with one end into the mold cavity 250 and with its second end into the interior of the block-shaped mold base 220. The course of the bore 330 in the mold base 220 is essentially perpendicular to the base surface 222. In the drilling direction, the bore 330 has an upper, a middle, and a lower section, which differ in terms of their drilling radii. The upper section 331 facing the mold cavity 250 is provided for guiding the displaceable plunger 310.The upper section 331 has a bore radius that is only slightly larger than the radius of the guided plunger 310. The middle section 332 has a larger bore radius relative to the upper section 331 in order to accommodate the spring device 320. The third section 333, following the second section 332, has an even larger bore radius than the second section 332. The third section 333 functions as the cylinder of a cylinder-piston device of the pneumatic or hydraulic actuation device, as will be described in more detail below.

[0050] The ram 310 is rod-shaped. At its end facing the mold cavity 250, the ram 310 has a front side 312 that locally replicates the surface curvature of the mold base 222. In other words, the front side 312 of the ram 310 received in the mold base 220 locally replicates the shape of the mold base 220 at the receiving position. In the present case, the tip of the dome-shaped surface curvature 224 is replicated by the ram front side 312. Furthermore, at its end facing away from the mold cavity 250, the ram 310 has a cylindrical section 314 (piston) with a larger cross-sectional area than the first end. Section 314 is arranged in the drilling section 333 and, together with the lower drilling section 333, forms a cylinder-piston device of the pneumatic or hydraulic actuation device.

[0051] The spring device 320 is implemented as a helical spring. In the assembled state, the helical spring 320 is wound around the plunger 310 and received in the central section 332 of the bore 330. The helical spring 320 is clamped between a shoulder 334 formed at the transition between the upper bore section 331 and the central bore section 332 and a surface 315 of the piston 314, which act as support surfaces for the opposite ends of the helical spring 320. The helical spring 320 is designed to hold the plunger 310 in the molding position or to move it back.

[0052] The third drilling section 333 is coupled on its underside 316 to a channel 360, which couples the drilling section 333 to a hydraulic fluid source or compressed air source. The channel 360 can be formed entirely or partially as a bore in the block-shaped mold base 220. Compressed air or hydraulic fluid can thus be supplied to or discharged from the drilling section 333 via the channel 360. By supplying compressed air or hydraulic fluid, a pressure is built up on the underside 316 of the piston 314. If the pressure is so high that the pressure force acting on the piston 314 exceeds the spring force of the coil spring 320, the plunger 310 is displaced in the direction of the mold cavity 250 (in Fig. 3a upwards). By moving the plunger 310 towards the molding chamber 250, the coil spring 320 is compressed. The plunger 310 projects with its first end 312 into the molding chamber 250. This plunger position is in Fig. 3b and corresponds to the demolding position. If the pressure built up in the drilling section 333 is released by returning the compressed air or hydraulic fluid (via channel 360), the plunger 310 is moved back to its original position by the pre-tensioned coil spring 320. This configuration corresponds to the molding position and is shown in Fig. 3a.

[0053] By hydraulic or pneumatic pressure build-up in the drilling section 333, the ram 310 can be moved between the molding position (original position of the ram 310 without actuation) and the demolding position (extended ram 310 by hydraulic or pneumatic actuation). Because the ram 310, in the demolding position, projects beyond the dome-shaped base region 224 into the molding chamber 250 (see Fig. 3b), the demolding of the cup 1000 is locally assisted by the dome-shaped bottom surface 224. This is because the movement of the ram 310 toward the mold cavity 250 mechanically pushes the cup bottom 1020 adhering to the dome-shaped bottom surface 224 away from the bottom surface. The impact impulse imparted by the ram 310 releases the cup bottom 1020 from the dome, thus assisting the demolding of the cup 1000.

[0054] It is understood that the plunger 310 remains in the demolding position during the molding of the cup 1000 in order not to disturb the molding process. The plunger 310 is only actuated after the molding is complete and has cooled down during an ejection process. Fig. In the thermoforming tool with ejection device 140 shown in Figure 2a, the plunger 310 can be actuated synchronously with the ejection rod 142. Alternatively, it is also conceivable that the actuation of the plunger 310 occurs with a time delay relative to the actuation of the ejection rod 142. For example, it is conceivable that the plunger 310 is only actuated towards the end of the ejection process. In both actuation variants, the mold base 220 is brought into the ejection position by the ejection device, and the plunger 310 is additionally brought into the demolding position. This configuration is shown in Fig. 2b.

[0055] The demolding device 300 described here is particularly simple and space-saving, allowing it to be integrated into any mold base. The described spring device 320 and cylinder-piston device create a durable, cost-effective, and easy-to-control actuation device for the ram 310.

[0056] Fig. 4 shows a further embodiment of a molding device 200a for producing the Fig. 1 shown cup 1000. Components of the molding device 200a, which are structurally and functionally identical to corresponding components of the molding device 200 in the Fig. 2a and Fig. 3a or differ only insignificantly (e.g., in their horizontal and vertical dimensions), are designated by the same reference numerals. To avoid unnecessary repetition, identical components will not be described in detail again. Instead, reference should be made to the above description in connection with the Fig. 2a, Fig. 2b, Fig. 3a and Fig. 3b.

[0057] The molding device 200a differs from that in the Fig. 3a and Fig. 3b in the implementation of the actuating device. Instead of the Fig. A further channel 362 now emerges from the spring device 320 shown in Figure 3a, one end of which opens into an upper side of the bore section 333 and the other end of which opens into a hydraulic fluid source or compressed air source. The piston 314 is arranged in the bore section 333 between the inlets of the two channels 360 and 362. In other words, the piston 314 divides the bore section 333 into an upper and lower chamber section for receiving compressed air or hydraulic fluid.

[0058] By supplying compressed air or hydraulic fluid via channel 360 into the lower chamber section, pressure is built up on the underside 316 of the piston 314. The plunger 310 then moves upwards (towards the molding chamber 250), thereby achieving the demolding position. The plunger 310 can be moved back from the demolding position into the molding position by diverting the hydraulic fluid or compressed air present on the underside 316 of the piston 314 via channel 360 and, at the same time, directing compressed air or hydraulic fluid into the upper chamber section via channel 362. This applies pressure to the top side 315 of the piston 314. The pressure applied to the top side 315 of the piston, which is greater than the pressure applied to the bottom side 316 of the piston, causes the plunger 310 to be moved back into the molding position (i.e., downwards).In the present implementation, the ram 310 is moved back and forth hydraulically or pneumatically between the molding position and the demolding position.

[0059] It should be noted that in the present implementation, the channel 362 opens laterally into the cylinder. To ensure that the piston 314 does not block the channel opening to the upper chamber section in the demolding position, the piston 314 has a cutout or chamfer at the appropriate location (in Fig. 4 not shown). It should also be noted that both chamber sections must be fluidically or pneumatically isolated from each other. This can be achieved by a sealing device arranged in the piston 314 (in Fig. 4 is also not shown).

[0060] Fig. 5 shows a further embodiment of a molding device 200b for producing the Fig. 1 shown cup 1000. Components of the molding device 200b, which are structurally and functionally identical to corresponding components of the molding device 200 in the Fig. 2a and Fig. 3a or differ only insignificantly (e.g., in their horizontal and vertical dimensions), are designated by the same reference numerals. To avoid unnecessary repetition, identical components will not be described in detail again. Instead, reference should be made to the above description in connection with the Fig. 2a, Fig. 2b, Fig. 3a and Fig. 3b.

[0061] The molding device 200b in turn comprises a demolding device 300b with at least one plunger 310b, at least one bore 330b receiving the at least one plunger 310b, and an actuating device 300b. A difference between the molding device 200b and the one shown in the Fig. 2a and Fig. 3a consists in the design of the ram 310b. As can be seen from Fig. 4, the plunger 310b has a larger cross-section, with the local dome-shaped surface curvature 224 being completely reproduced by the plunger end 312b facing the molding space 250. In contrast, the Fig. 2a and Fig. 3b has a narrower cross-section compared to the surface area of ​​the dome-shaped surface area 224, so that the plunger 310 with its plunger end 312 only reproduces a part of the dome-shaped surface area 224.

[0062] A further difference lies in the actuation of the ram 310b. Although the actuating device of the demoulding device 300b again has a spring device in the form of a helical spring 320b and a cylinder-piston device realized by the bore section 333 and ram section 314 for the hydraulic or pneumatic actuation of the ram 310b, there are nevertheless significant differences to the Fig. 3a and Fig. 3b. This is because, according to the present implementation, the molding position is achieved with the ram 310b extended. Thus, during a molding process, a sufficiently high pressure must be built up in the drilling section 333 to hold the ram 310b in the extended position against the spring force of the coil spring 320. Only for the purpose of demolding (and after completion of the molding process) is the pressure in the drilling section 333 reduced by discharging the compressed air or hydraulic fluid via the channel 360. The ram 310b is then moved downward (i.e., out of the mold cavity 250) by the preloaded coil spring 320b. The dome-shaped region 224 is thus at least partially retracted into the mold base in the demolding position.

[0063] By retracting the entire dome-shaped area as described, the demolding process can be carried out particularly gently. The present demolding device 300b is therefore particularly suitable for molded parts with thin walls.

[0064] In connection with Fig. 6, a further molding device 200c is described. Components of the molding device 200c, which are structurally and functionally identical to the components of the molding device 200 in the Fig. 2a and Fig. 3a or differ only insignificantly are again designated by the same reference numerals. Reference is made to the above description.

[0065] The molding device 200c differs from the molding device 200 in the design of the demolding device. The ram 310c of the demolding device 300c has a widened section 314c arranged centrally in the longitudinal direction of the ram, which in turn functions as the piston of a cylinder-piston arrangement. Accordingly, the bore 330c, which accommodates the ram 310c, also has a widened portion in its central section 332c to accommodate the piston 314. Section 332c thus functions as the cylinder of the cylinder-piston arrangement. A spring device 320c is accommodated in the lower section 333c of the bore. The spring device 320c can in turn be designed as a helical spring which surrounds the plunger 310c at its lowermost section and which is clamped between a lower surface 316c of the piston 314c and an end of the bore 330c facing away from the mold space 250.

[0066] At the upper end of the bore section 332c, a channel 360c opens, which is at least partially formed as a bore in the mold base 220. It connects the bore section 332c to the compressed air source or hydraulic fluid source of the thermoforming machine, so that compressed air or hydraulic fluid can be displaced into the cylinder 332c.

[0067] According to the present implementation, hydraulic fluid or compressed air is displaced into the upper end of the bore section 332c to achieve the molding position. This pressurizes the surface 315c of the piston 314c. The plunger 310c is pressed downward (i.e., away from the mold cavity 250c), compressing the coil spring 320c. If the plunger 310c is to be moved into the demolding position, the hydraulic fluid or compressed air displaced into the bore section 332c is discharged again via the channel 360c. The compressed coil spring 320c relaxes, and the plunger 310c is moved toward the mold cavity 250 by the coil spring 310. Here, too, the piston 314c has a chamfer or lateral recess so as not to block the laterally opening channel 360 in the demolding position (in Fig. 6 not shown).

[0068] The demolding devices described here can actively support the demolding of a molded part at the mold base. Due to their compact design, the demolding devices described can be integrated into the mold base in any desired position (e.g., in areas with strong base curvature). It is understood that the block-shaped mold base described above does not have to be a single piece, but can be assembled from two or more blocks to facilitate the installation of the demolding devices. In particular, the demolding devices can be combined with an ejection device or even used in thermoforming tools without an ejection device.

Claims

[1] Forming device (200, 200a-200c) for a thermoforming tool for producing a molded part (1000) from heated thermoplastic film, comprising: a mold insert (210) and a mold base (220) which together form a mold space (250), wherein the mold base (220) is movable relative to the mold insert (210); and a demoulding device (300, 300a-300c) provided for the local demoulding of a moulded part (1000) formed in the moulding space (250); wherein the demoulding device (300, 300a-300c) comprises at least one actuatable ram which is displaceably mounted in the mould base (220) and is displaceable back and forth relative to the mould base (220) between a moulding position and demoulding position, and wherein the demoulding device (300, 300a-300c) is arranged in the interior of the mould base (220) such that the at least one ram is arranged in or near a mould base region (224) which has a local surface curvature relative to the base surface (222) of the mould base (220). [2] Molding device (200, 200a-200c) according to claim 1, wherein the demolding device (300, 300a-300c) is arranged in the interior of the mold base (220) such that the displacement of the at least one ram takes place substantially perpendicular to the mold base surface (222). [3] Molding device (200, 200a-200c) according to one of the preceding claims, wherein the demolding device (300, 300a-300c) is designed such that the at least one ram can be moved into the mold space (250) during a demolding process. [4] Molding device (200, 200a-200c) according to one of the preceding claims 1 to 2, wherein the demolding device (300, 300a-300c) is designed such that the at least one ram can be moved out of the mold space (250) during a demolding process. [5] Molding device (200, 200a-200c) according to one of the preceding claims, wherein the demolding device (300, 300a-300c) comprises at least one bore (330, 330c) formed in the mold base (220) for displaceably receiving the at least one plunger. [6] Molding device (200, 200a-200c) according to one of the preceding claims, wherein the demolding device (300, 300a-300c) comprises an actuating device for actuating the at least one plunger. [7] Molding device (200, 200a-200c) according to claim 6, wherein the actuating device for actuating the at least one ram is realized as a hydraulic, pneumatic, electromagnetic and / or electromechanical actuating device. [8] Molding device (200, 200a-200c) according to one of the preceding claims, wherein the demolding device (300) comprises a spring device (320, 320c) which is designed to prestress the at least one ram in the molding position or demolding position. [9] Molding device (200, 200a-200c) according to one of the preceding claims, wherein the demolding device (300) comprises: a spring device (320, 320c) designed to hold the at least one plunger in the forming position; and a pneumatic or hydraulic actuating device (314, 333; 314c, 333c) which is designed to move the at least one plunger from the molding position into the demolding position against a restoring force of the spring (320, 320c). [10] Molding device (200, 200a-200c) according to one of the preceding claims, wherein the demolding device (300) comprises: a spring device (320, 320c) designed to hold the at least one plunger in the demolding position; and a pneumatic or hydraulic actuating device (314, 333; 314c, 333c) which is designed to move the ram from the demoulding position into the moulding position against a restoring force of the spring (320, 320c). [11] Forming device (200, 200a-200c) according to one of the preceding claims, wherein the at least one plunger is rod-shaped or ring-shaped. [12] Molding device (200, 200a-200c) according to one of the preceding claims, wherein an end of the at least one plunger facing the molding space (250) is shaped such that the plunger locally replicates the mold base (220) in the molding position. [13] Thermoforming tool (100) for producing a molded part (1000) from heated thermoplastic film, comprising: an upper and a lower tool part (110, 120) which are movable relative to each other; at least one molding device (200, 200a-200c), wherein the at least one molding device (200, 200a-200c) is arranged in the lower tool part (120) or upper tool part (110) and comprises the following: a mold insert (210) and a mold base (220) which together form a mold space (250), wherein the mold base (220) is movable relative to the mold insert (210); and a demoulding device (300, 300a-300c) provided for the local demoulding of a moulded part (1000) formed in the moulding space (250); wherein the demoulding device (300, 300a-300c) comprises at least one actuatable plunger which is displaceably mounted in the mould base (220) and is displaceable back and forth relative to the mould base (220) between a moulding position and demoulding position, and wherein the demoulding device (300, 300a-300c) is arranged in the interior of the mould base (220) such that the at least one plunger is arranged in or near a mould base region (224) which has a local surface curvature relative to the base surface (222) of the mould base (220); and an ejection device (140) comprising an ejection rod (142) which is movable relative to the tool parts (110, 120), wherein the ejection rod is coupled to the mold bottom (220) of the mold device (200, 200a-200c) in order to move the mold bottom (220) relative to the mold insert (210) during an ejection process. [14] Thermoforming tool (100) according to claim 13, further comprising: a pre-stretching device (150) with a pre-stretcher (156) which is displaceable back and forth between a rest position and a stretched position, wherein the pre-stretcher (156) is received within a cavity (135) of the hold-down device (130) in the rest position, and wherein the pre-stretcher is moved into the molding space (250) of the molding device (200, 200a-200c) in the stretched position. [15] Thermoforming tool according to claim 13 or 14, further comprising: at least one recess (135) formed coaxially with the corresponding forming device (200, 200a-200c) in the upper tool part (110) or lower tool part (120) and open towards the lower or upper tool part (120, 110), in which a hold-down device (130) is displaceably arranged. [16] Thermoforming machine comprising: the thermoforming tool (100) according to any one of claims 13-15; and a control unit configured to activate an actuating device of the molding device (200, 200a-200c) after forming a molded part (1000) in order to actuate the at least one ram and to release the molded part (1000) from the molding device (200, 200a-200c), wherein the control unit is further configured to activate the ejection device of the thermoforming tool in order to move the mold base (220) relative to the mold insert (210) and thus eject the molded part (1000). [17] Thermoforming machine according to claim 16, wherein the control unit is designed to carry out the activation of the ejection device (140) and the actuating device substantially simultaneously or to delay it by a predetermined time interval. [18] Thermoforming machine according to any one of claims 15-17, further comprising: a pneumatic or hydraulic pressure source for actuating the actuating device.

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