PRESS AND METHOD FOR MANUFACTURING THE MOLDED PART

Description

Technical field

[0001] The invention relates to a press frame comprising an upper beam and a lower beam, an upper die, and a lower die provided on the lower beam for producing a molded part, and at least one press cylinder provided on the upper beam with a piston which is articulated to the upper die via a bearing and designed to exert a pressing force on the molded part. The invention further relates to a method for producing the molded part by means of the upper die and the lower die provided on the lower beam of the press, wherein the press frame of the press comprises the upper beam and the lower beam as well as the at least one press cylinder provided on the upper beam with the piston which is articulated to the upper die via the bearing and designed to exert the pressing force on the molded part. Background of the invention

[0002] Presses are known from the prior art and are used to manufacture molded parts from fiber-reinforced composites using injection molding, also known as resin transfer molding (RTM). In this process, fibers, for example, a fiber semi-finished product, are first placed in a mold, which is generally formed from an upper and lower mold. After the mold is closed, a molding compound, often consisting of a resin and a hardener, is injected into a cavity of the mold. The molding compound surrounds the fibers as a matrix and hardens, forming the molded part. Applying a vacuum and / or pressure to the mold accelerates the curing process. Advantageously, the pressure is generated by clamping the upper and lower molds of the press against each other.

[0003] DE 10 2013 109490 A1 describes a hydraulic rotary press for the production of molded parts made of plastic, in particular of fiber-reinforced plastic, comprising a press tool consisting of an upper tool and a lower tool, a press frame with an upper beam and a lower beam, and several press cylinders attached between the upper beam and the upper tool, wherein the press cylinders are equipped for opening and closing as well as for applying the pressing force.

[0004] FR 1 378 183 A describes a system for attaching a slide to a drive element in machines such as guillotine shears, presses, press brakes or others.

[0005] Presses of this type, used for manufacturing molded parts from fiber-reinforced composites, often operate in cycle mode. To apply the high pressing forces required for manufacturing these parts, plunger cylinders are typically used as press cylinders, along with complex closing and retraction devices in the form of retraction cylinders. This makes the press design relatively complex. To still achieve sufficiently high pressing accuracy and speed, it is known in the art to compensate for play in the connection between the press cylinder and the tooling using a compensating cylinder. However, such compensating cylinders, usually located at the midpoint of the force between the press cylinders, require a corresponding amount of installation space, which is not always available. Description of the invention

[0006] Starting from this situation, it is an object of the present invention to provide a press and a method for producing a molded part which, with a simple press design, enables particularly economical and precise production of the molded part, especially made of plastic.

[0007] The object of the invention is achieved by the features of the independent claims. Advantageous embodiments are specified in the dependent claims.

[0008] Accordingly, the problem is solved by a press with a press frame having an upper beam and a lower beam, an upper tool and a lower tool provided on the lower beam for producing a molded part, at least one press cylinder provided on the upper beam with a piston which is articulated to the upper tool via a bearing and designed to exert a pressing force on the molded part, and a compensating means provided on the bearing which is designed to exert a compensating force on the piston and the upper tool which acts opposite to the pressing force and is variably adjustable in order to compensate for at least a play between the piston and the upper tool caused by a weight force of the upper tool.

[0009] A key aspect of the invention lies in the fact that the play or backlash is eliminated directly in the connection of the press cylinder in the bearing between the upper beam and the upper tool. Since the compensating force is variably adjustable, this compensating force can be switched on and off, in particular in individual discrete steps, for example on a scale from 0 to 100%, and / or controlled via the pressing force and / or the position of the upper tool as the executed stroke. Compared to presses known from the prior art with a compensating cylinder located at the force center between the press cylinders, which requires a corresponding amount of installation space, the proposed compensating device can be arranged on the press in a significantly more space-saving manner and even under confined space conditions.

[0010] Within the scope of the invention, the term "compensating means provided at the bearing" is not to be understood as referring to a compensating cylinder located, in particular, at the force center between the press cylinders. Instead, the term is to be interpreted such that the compensating means is preferably provided only at the connection between the press cylinder and the upper tool, and in particular only between the piston and a guide bar or upper tool carrier holding the upper tool. Most preferably, the compensating cylinder(s) are arranged exclusively in or within the bearing, the connection between the press cylinder and the upper tool, and / or the connection between the piston and the guide bar or upper tool carrier holding the upper tool.

[0011] The devices known from the prior art for compensating the play between the press cylinder and the upper tool disadvantageously require the press to be designed and dimensioned to compensate for both the weight forces of the guide rail and upper tool, as well as the tool tear-out forces that occur during the production of molded plastic parts. Accordingly, the compensating force must always be greater than the maximum tensile force occurring during a press cycle to ensure that the play in the connection remains closed. However, in these known devices, the compensating force acts as a normal force on the sliding surfaces of the joint in the connection between the press cylinder and the upper tool, thus acting as a frictional force that permanently opposes the desired mobility of these joints.Since the compensation force is variably adjustable, the proposed press is not characterized by this disadvantage, but rather allows for a corresponding mobility of these joints.

[0012] The press is preferably designed as a hydraulic rotary press for producing a molded part in an "open-die mode" and / or by injection molding, in particular using a resin transfer molding (RTM) process and / or by extrusion, in particular using a sheet molding compound (SMC) process, especially with subsequent coating in the upper and / or lower mold using an in-mold coating (IMC) process. When producing molded parts in "open-die mode," particularly precise positioning of the upper mold relative to the lower mold is necessary. Play or backlash within the connection of the press cylinders can reduce this accuracy or decrease the speed of the manufacturing process, since this backlash can only be eliminated during the actual pressing process and consequently only after the molding compound has been injected.Accordingly, the invention is based on the understanding that the pressing process can be optimized before the pressing force is applied by "removing" the backlash using the proposed compensation device. The compensation force is preferably greater by a predetermined amount than the weight of the upper tool, and optionally the upper tool carrier and optionally also the weight of the pistons of the press cylinders.

[0013] The press is designed to produce the molded part from a plastic, in particular a thermosetting plastic, for example comprising a resin, epoxy resin, polyester resin and / or polyurethane resin, which is initially liquid, viscous or powdery and hardens under the influence of a hardener, pressure and / or heat. The invention also includes the production of molded parts from thermoplastic materials, which are, for example, heated, introduced into the mold as a melt, and harden by cooling. Particularly preferably, "plastic" refers to a fiber-reinforced plastic and consequently a fiber composite material in which fibers are embedded in a plastic matrix.

[0014] The fibers can be glass fibers and / or carbon fibers, but also ceramic fibers, metal fibers and / or natural fibers, as well as corresponding combinations. The fibers can be loose, preferably in the form of semi-finished products, for example as fiber mats or the like. For the purposes of this invention, molded parts are understood to be, for example, molded parts for the automotive industry, such as body parts, or molded parts for aerospace engineering, such as fuselages, wing parts, or the like for aircraft construction. Furthermore, they can be components for mechanical engineering, such as components for power plant construction, plant engineering, and in particular wind turbines or the like.

[0015] The press has a control and / or regulating device designed to control and / or regulate the compensation force as a function of the pressing force. Preferably, the control and / or regulating device is designed to control, switch, and / or regulate the compensation force via the position of the upper tool as a stroke. The control and / or regulating device is preferably microprocessor-based and / or designed to adapt the compensation force to the force requirement of the respective pressing phase, for example, weight compensation or compensation of tool tearing forces, in a variable and / or adjustable manner. Furthermore, the press cylinders or their control valves can be connected to the control and regulating device to provide pressure and / or stroke control for the press cylinders. Likewise, the prevailing pressures in individual cylinder chambers can be controlled.Determine the resulting pressing forces of the press cylinders and feed them into the control and / or regulating device. From the determined pressures / forces, and taking into account the structural data of the press stored in the control and / or regulating device, continuously determine deformations of the press frame. The determined deformations can be compensated for by applying correspondingly modified pressing forces to the press cylinders.

[0016] In principle, the compensating device can be designed in various ways. It can be designed to generate a hydraulic and / or pneumatic compensating force and / or as an annular piston cylinder. Preferably, the compensating device is designed to generate a mechanical compensating force. Particularly in a press with spherical bearings between the press cylinder and the running beam or upper tool holder, the compensating device is preferably designed to introduce a switchable, hydraulically generated compensating force to compensate for the play. A particularly preferred solution is an annular piston cylinder as the compensating device, located in, within, or directly adjacent to the bearing, to introduce the hydraulically generated compensating force. Likewise, depending on the required compensating force and the available installation space at the connection between the piston and the upper tool holder, a pneumatic solution of the same type is also possible.

[0017] According to an alternative preferred embodiment, the compensation means is designed to generate the compensation force by rotating a cam disk and / or translating a wedge geometry. In this way, a mechanical clamping between the piston and the upper tool can be achieved, in which the compensation force is generated by a relative movement of corresponding geometries of the cam disk and / or the wedge geometry to compensate for the clearance.

[0018] According to a preferred embodiment, the compensating means is designed as a split clamping ring with a clamping piston. If spherical bearing between the press cylinder and the guide rail or upper tool carrier is not required, for example, because only a slight tilting between the upper and lower tools is expected due to the process, the compensating means can be designed as a switchable clamping device on a plate joint between the piston and the upper tool. Alternatively, the compensating means can be formed by split clamping rings between the piston and the upper tool, which have a number of hydraulically interconnected clamping pistons to compensate for the clearance between the piston and the upper tool.

[0019] In another preferred embodiment, the piston is articulated to the upper tool via a spherical bearing, a gimbal bearing, or a plate joint, and / or the bearing is designed to withstand compression and tension. In a preferred embodiment, the press has an upper tool carrier to which the upper tool is attached and to which the piston is articulated. The press cylinder is preferably pivotably mounted on the upper beam, and / or the piston of the press cylinder is particularly preferably pivotably mounted on the upper tool or the upper tool carrier, especially by means of a spherical bearing capable of withstanding tension and compression, or alternatively by means of the gimbal bearing. To ensure a reliable articulated connection, such bearings are generally equipped with a certain degree of play. This play is compensated for by means of the compensating element.The upper tool can therefore be moved into a backlash-free position with the help of the press cylinder and the compensating means, and thus immediately "on point", without any play that may be present having to be corrected during the subsequent pressing process.

[0020] In a further preferred embodiment, the press cylinder is designed as a double-acting differential cylinder, through which the piston can be subjected to both pressure and tension. Advantageously, the differential cylinders can be used to apply the pressing force as well as to open and close the press, without the need for separate retraction cylinders, rapid-stroke drives, or the like. Likewise, by providing differential cylinders, positioning of the press cylinders themselves, for example by separate spindle drives or the like, can be dispensed with. Complex locking devices are also unnecessary. Preferably, the press has a plurality of press cylinders.

[0021] According to another preferred embodiment, the compensating means is designed to exert the compensating force before and / or when the pressing force is applied. As already mentioned, this allows any play to be eliminated in a particularly advantageous way even before the pressing process begins, and the upper tool to be brought into a play-free position. It can be useful to first partially close the press to a gap width of, for example, 0.4 mm between the upper and lower tools. The molding compound can then be injected, and the upper tool can be pressed down by the press cylinder to the desired gap of, for example, 0.2 mm, in order to close any pores within the molded part. This pore closure is of great importance for the strength of the molded part being produced.The proposed compensation device allows the target position required for optimal pore closure to be precisely reached for different pressing forces and different molding compounds, without the need for complex adjustment of the pressing force, which significantly speeds up the pressing process.

[0022] The object of the invention is further achieved by a method for producing a molded part by means of an upper tool and a lower tool provided on a lower beam of a press, wherein a press frame of the press has an upper beam and the lower beam and at least one press cylinder provided on the upper beam with a piston which is articulated to the upper tool via a bearing and is designed to exert a pressing force on the molded part, with the steps; Applying a compensating force at the bearing on the piston and the upper tool, acting in the opposite direction to the pressing force and variably adjustable, in order to compensate for at least any play between the piston and the upper tool caused by a weight force of the upper tool, and applying the pressing force to produce the molded part.

[0023] The proposed method enables the precise and rapid production of molded parts in a particularly economical manner, using a very simple press design. Double-acting differential cylinders, acting as press cylinders, allow for fast and precise opening and closing, as well as the application of even the highest pressing forces, despite relatively large oil volumes. The variably adjustable compensation force allows the pressing process to be flexibly adapted to different molding compounds while simultaneously optimizing speed and accuracy.

[0024] Preferably, the press is designed as a hydraulic intermittent press for producing the molded part from a fiber-reinforced composite material by injection molding, particularly using a resin transfer molding (RTM) process. More preferably, the fibers, for example, a fiber semi-finished product, are first placed into a mold, which typically consists of an upper and a lower mold. After the mold is closed, the molding compound, for example, a two-component compound of a resin and a hardener, is injected into the mold cavity, so that the compound surrounds the fibers as a matrix and cures, forming the molded part. The mold can be pressurized with a vacuum or reduced pressure before and / or during the injection of the molding compound.

[0025] Alternatively, a Sheet Molding Compound (SMC) process can be used, in which sheet-shaped, dough-like molding compounds made of thermosetting resins and usually glass fibers are used to produce fiber-reinforced plastics. In this process, all necessary components are preferably premixed and ready for processing, with polyester or vinyl ester resins typically being used. The SMC semi-finished products are preferably further processed into a finished molded part by means of extrusion. In the In-Mold Molding (IMC) process, plastic parts, especially molded parts made of fiber-reinforced composites, are coated immediately after molding, still within the mold, by injecting coating into a defined space between the mold and the molded part.

[0026] Since the molding compound often hardens not only through hardener or heat but also through pressure, it is advantageous to clamp the mold halves—the upper and lower molds—against each other using a press with a predetermined pressing force. Ideally, the mold halves are mounted in the press so that the molding compound can be injected into the closed mold after the fibers have been inserted and the mold has been closed.

[0027] According to a preferred further development, the procedure includes the step of controlling, switching and / or regulating the compensation force depending on the pressing force, in particular such that the compensation force is greater than the pressing force.

[0028] Further embodiments and advantages of the method become apparent to the person skilled in the art by analogy to the press described above. Brief description of the drawings

[0029] The invention is explained in more detail below with reference to the attached drawing and by means of preferred embodiments.

[0030] The drawing shows Fig. 1 a hydraulic rotary press for producing a molded part according to a preferred embodiment of the invention in a schematic view, Fig. 2 a connection between the upper tool carrier and the press cylinder of the Fig. 1 The press shown according to the preferred embodiment of the invention in a schematic detail view, and Fig. 3 a connection between the upper tool carrier and the press cylinder of the in Fig. 1 The press shown according to a further preferred embodiment of the invention in a schematic detail view. Detailed description of the implementation examples

[0031] Fig. 1Figure 1 shows a hydraulic press for producing a molded part from a plastic material in a press tool consisting of an upper tool 1a and a lower tool 1b. The press tool is loaded with a fiber semi-finished product and closed. The resulting mold cavity is filled with the molding compound, a resin, and a hardener. The molding compound hardens under the pressure applied by the press and, if necessary, heat.

[0032] The press comprises a press frame 2 with an upper beam 3 and a lower beam 4, as well as side panels 5. The press can be of frame construction and have a plurality of closed press frames arranged one behind the other. Alternatively, the press can be of column construction, so that the side panels are formed by press columns or the like. The press has an upper tool carrier 7 that is movable in the vertical direction, to which the upper tool 1a is attached. The lower tool 1b usually rests stationary on the lower beam 4 or on a press table arranged on the lower beam 4, or on a lower tool carrier 4'. Several press cylinders 8 are attached to the upper beam 3 of the press frame 2, the pistons of which act on the upper tool carrier 7 to exert a pressing force on the molded part.

[0033] The press cylinders 8 are designed as double-acting differential cylinders, whose pistons 9 are directly connected to the upper tool carrier 7 by means of tension / compression links, so that not only the pressing force is applied, but also the opening and closing of the press is effected by the differential cylinders. The stroke of the press cylinders 8 is sufficiently large to allow for tool changes and adaptation to different tool geometries and, in particular, tool heights.

[0034] In the front view of the press, only two press cylinders 8 arranged side by side are visible. However, it is advantageous to provide several such rows of cylinders side by side, so that, for example, four or six press cylinders 8 can be used. For the precise and variable positioning of the upper tool 1a relative to the lower tool 1b, the pistons 9 of the press cylinders 8 are pivotably connected to the upper tool carrier 7 via a spherical articulated bearing 10 capable of withstanding both tensile and compressive loads. A similar spherical articulated bearing 6 is provided between the cylinders 8 and the upper beam 3. Furthermore, the press cylinders 8 are equipped with control valves 11 in a known manner.

[0035] Fig. 2 shows a connection between the upper tool carrier 7 and the piston 9 of the press cylinder 8 of the press according to Fig. 1In a schematic detail view, the previously described spherical articulated bearing 10 is shown. A compensating element 12 is integrally integrated with the articulated bearing 10, through which a compensating force can be exerted on the piston 9 and the upper tool 1a, acting in the opposite direction to the pressing force. The compensating force is variably adjustable to compensate for any play between the piston 9 and the upper tool 1a caused by the weight of the upper tool 1a. In other words, the play is eliminated directly at the connection between the press cylinder 8 and the upper tool 1a.

[0036] A microprocessor-based control and / or regulating device 13 is provided for variably adjusting the compensation force, schematically shown in Fig. 1The diagram shows how the compensation force can be controlled and / or regulated depending on the pressing force. In this way, the compensation force can be adapted to a specific pressing phase, such as weight compensation or compensation of tool opening forces. The control and / or regulating device 13 allows the compensation force to be controlled so that it is applied before and when the pressing force is applied.

[0037] Fig. 3Figure 1 shows an embodiment in which the compensating element 12 is designed as an annular piston cylinder for applying a switchable, hydraulically generated compensating force and circumferentially surrounds the piston 9. This annular piston is designed in particular such that the degree of freedom of the spherical bearing 10 is not restricted. Alternatively or additionally, depending on the available installation space on the press, the compensating element 12 can be configured to generate a pneumatic and / or mechanical compensating force at the articulated bearing 10. In the case of mechanical clamping, the compensating force can be generated by a relative movement of corresponding geometries, for example, by rotation of a cam disk and / or translation of a wedge geometry.

[0038] If a spherical bearing between press cylinder 8 and tool carrier 7 is not required because a very small tilting between upper tool 1a and lower tool 1b is to be expected due to the process, a switchable clamping can be designed on the plate joint. Fig. 2 Figure 1 shows a corresponding embodiment as a section, wherein the compensation means 12 is designed by split clamping rings which contain a number of hydraulically interconnected clamping pistons.

[0039] The described embodiments are merely examples that can be modified and / or supplemented in various ways within the scope of the claims. Each feature described for a specific embodiment can be used independently or in combination with other features in any other embodiment. Each feature described for an embodiment of a particular category can also be used accordingly in an embodiment of another category. Reference symbol list Upper tool 1a Subtool 1b Press frame 2 Oberholm 3 Lower rail 4 side panels 5 Joint bearing 6 Upper tool carrier 7 Press cylinder 8 Pistons 9 Joint bearing 10 Control valve 11 Compensation means 12 Control and / or regulating device 13

Claims

1. A press for producing a molded part made of a plastics material, comprising a press frame (2) having an upper beam (3) and a lower beam (4), an upper die (1a) and a lower die (1b) provided on the lower beam (4) for producing a molded part, at least one pressing cylinder (8) provided on the upper beam (3) and comprising a piston (9), which is articulated to the upper die (1a) by a bearing (10) and is configured to exert a pressing force on the molded part, and a compensation means (12) provided on the bearing (10), which means is configured to exert a variably adjustable compensation force acting counter to the pressing force on the piston (9) and the upper die (1a), in order to compensate for at least one clearance generated by a weight force of the upper die (1a) between the piston (9) and the upper die (1a), characterized by a control and / or regulating device (13), which is configured to control and / or regulate the compensation force on the basis of the pressing force, wherein the compensation means (12) is configured to generate a hydraulic and / or pneumatic compensation force and / or is configured as a rotary piston cylinder.

2. The press according to claim 1, wherein the compensation means (12) is configured to generate the compensation force by rotation of a cam disk and / or translation of a wedge geometry.

3. The press according to any one of the preceding claims, wherein the compensation means (12) is configured as an in particular split clamping ring comprising a clamping piston.

4. The press according to any one of the preceding claims, wherein the piston (9) is articulated to the upper die (1a) and / or the bearing can be subjected to compression and tension by means of a spherical bearing (6), a gimballed spherical plain bearing, or a planar joint.

5. The press according to any one of the preceding claims, comprising an upper die carrier (7), on which the upper die (1a) is provided and to which the piston (9) is articulated.

6. The press according to any one of the preceding claims, wherein the pressing cylinder (8) is configured as a double-acting differential cylinder, by means of which the piston (9) can be subjected to compression and tension.

7. The press according to any one of the preceding claims, wherein the compensation means (12) is configured to exert the compensation force before applying the pressing force and / or when the pressing force is being applied.

8. A method for producing a molded part from a plastics material by means of an upper die (1a) and a lower die (1b) provided on a lower beam (4) of a press, wherein a press frame (2) of the press comprises an upper beam (3) and the lower beam (4), and at least one pressing cylinder (8) provided on the upper beam (3) and comprising a piston (9), which is articulated to the upper die (1a) by a bearing (10) and is configured to exert a pressing force on the molded part, comprising the steps of: exerting a variably adjustable hydraulic and / or pneumatic compensation force, which acts counter to the pressing force and is controlled and / or regulated on the basis of the pressing force, at the bearing (10) on the piston (9) and the upper die (1a), in order to compensate for at least one clearance generated by a weight force of the upper die (1a) between the piston (9) and the upper die (1a), and exerting the pressing force to produce the molded part.

9. The method according to the preceding claim, comprising the step of: controlling, switching, and / or regulating the compensation force on the basis of the pressing force, in particular such that the compensation force is greater than the pressing force.