WO2013050026A1

WO2013050026A1 - Method and device for producing plastic moulded parts

Info

Publication number: WO2013050026A1
Application number: PCT/DE2012/100282
Authority: WO
Inventors: Michael Klemt
Original assignee: Universität Stuttgart
Priority date: 2011-10-07
Filing date: 2012-09-14
Publication date: 2013-04-11
Also published as: DE102011054287B4; DE102011054287A1

Abstract

The invention relates to a method and a device (1) for producing a plastic moulded part from a planar semi-finished product (2) by means of a thermal reshaping method, in which the semi-finished product (2) is conveyed, by a gripper, from a stocking point into a pressing tool (3) that comprises pressing tool parts (4, 5) which form a mould for said plastic moulded part, the semi-finished product being fixed to said pressing tool (3) and shaped, by heating, using a pressing tool (3) pressing process, said product (2) being provided with electrically-conductive additives during its production as a polymer material and, prior to the pressing process, being regulated to a predefinable temperature by resistively heating these electrically-conductive additives. In order to shorten the production time and achieve continuous heating of said semi-finished product (2), the product is heated as it is being conveyed in the gripper (26).

Description

Method and device for producing plastic molded parts

The invention relates to a method and an apparatus for producing a

Plastic molding from a flat semi-finished by means of a hot forming process, in which the semi-finished transported by a gripper from a storage location in a pressing tool with a shape of the plastic molding forming pressing tool parts, fixed to the pressing tool and is brought under heating by a pressing operation of the pressing tool in the form, said Semi-finished product during its production as a polymer material provided with electrically conductive additives and is controlled to a predetermined temperature before the pressing process by resistance heating of the electrically conductive additives.

In particular, in the motor vehicle due to their low weight increasingly three-dimensionally shaped plastic moldings are used, which are made of flat, planar semi-finished products, so-called organo sheets. The shaping takes place in, for example, divisible in two halves pressing tools with complementary inner surfaces, in which the semi-finished inserted and brought under plastic deformation in the desired shape. The semi-finished product is heated in a heat chamber, for example by means of radiant heat such as infrared radiation or recirculation heating, contact heating or the like to a temperature at which a plastic hot forming is possible, for example, heated over glass temperature and inserted by a gripper in the pressing tool. In this case, not only the semifinished product but also corresponding receiving frames, parts of the gripper and the like are heated, so that this process is energy-consuming. As a result of cooling of the semi-finished product during transport, a higher, the quality of the semi-finished product temperature must be provided. Furthermore, the integration of a heat chamber in the production process is time-consuming and costly and requires a higher staging area of the production plant. In DE 2009 016 215 A1 a process for the production of plastic moldings is described, in which the pressing tool is heated to a temperature sufficient for plastic deformation of the semifinished product itself. Due to the high heat capacity of the pressing tool heating of the pressing tool is energy-consuming.

From DE 103 51 178 A1 a process for the production of carbon fiber composite materials is further known, in which the semi-finished product is heated to a predetermined temperature by means of an electrical resistance heater after being placed in the tool mold and then pressed by means of the mold The heating process of the semifinished product takes place in the Form, so that the heating process requires correspondingly long cycle times in production.

The object of the invention is therefore to propose a method and a device in which made of semi-finished plastic moldings can be produced energy-saving, fast and with low production space requirements.

The object is achieved by a method for producing a plastic molded part from a flat semi-finished by means of a hot forming process, wherein the semi-finished transported by a gripper from a storage location in a pressing tool with a shape of the plastic molding forming pressing tool parts, fixed to the pressing tool and under heating by a pressing operation the semifinished product during manufacture as a polymer material with electrically conductive additives, for example, to form a fiber composite material, provided and before the pressing process during transport from the storage location to the pressing tool by resistance heating of the electrically conductive additives to a predetermined temperature is regulated. In the same sense, the object is achieved by a device for carrying out the method, which has a power generating device waiving a heat chamber for resistance heating of the semifinished product.

By saving a heating chamber, the entire production process can be simplified and streamlined. The integrated in the semi-finished electrical Conductive additives form the heat source through their internal resistance. It has proven to be advantageous if these additives mechanically reinforce the plastic material used, for example a thermoplastic. For example, carbon particles such as carbon fibers can be used for this purpose. Fiber composite materials, for example so-called continuous carbon fiber reinforced thermoplastic semi-finished products (CFRP) have proved to be particularly advantageous. Alternatively, intrinsically electrically conductive polymers such as polyimides can be provided, in particular for lower mechanical stress. In addition, the plastic molded parts can be formed as single-layered or as sandwich components with at least one layer with electrically conductive additives. It is understood that in order to achieve an electrical resistance heating, the semi-finished products are designed to be resilient with correspondingly high currents and voltages of the power supply device. The resistance heating essentially selectively and exclusively heats the semifinished product to the required forming temperature, so that energy-efficient heating is achieved. Due to the low heat radiation of the semi-finished products, this remains low until the pressing process. Hot forging process is to be understood as meaning a process in which the semifinished products, after or with appropriate heating, are capable of being given a predetermined temperature, plastic deformation, for example at or above the glass transition temperature, softening temperature and the like of the single-layer semifinished product or of all layers a multi-layer semifinished product in a multi-part, preferably two-part pressing tool can be brought from the sheet shape into a three-dimensional shape. In this case, the pressing tool parts, which are moved toward one another and are provided with complementary surface portions, in the closed state form the limiting volume for the plastic molded part to be molded. After the pressing process, the triggered plastic molded part can be brought into final form by finishing, for example, removal of excess edges, surface treatment and the like. The pressing tool is advantageously formed with a lower electrical conductivity so with a higher electrical resistance than the semifinished product, so that no further measures of electrical insulation of the pressing tool must be made against the semifinished product. For this purpose, the surfaces of the press tool parts, for example, greased, be be coated or otherwise treated, so that the selection of the material of the pressing tool can be adapted to the specifications of the pressing process substantially independent of its electrical conductivity.

Under gripper is a device to be understood, which per pressing tool cyclically a substantially planar part of the semifinished product on the storage device, for example, a vertical or horizontal stratification of semi-finished parts, a feed belt and or the like receives and in a preferred manner, the molded plastic part again in a storage device or a conveyor belt or the like stores. The semifinished product in the form of prefabricated flat sheets may be accommodated in frames, for example made of ceramic or other temperature-resistant materials above the softening point of the semifinished product, which have corresponding fixing points at which the semifinished product is positioned at counter points such as pins in the pressing tool. Alternatively, the semifinished product itself can have corresponding fixing points such as openings.

[00010] The power generating device can be provided as a transformer with a current, voltage or power regulating device which preferably provides electrical energy as high current and low voltage. Here, empirically and / or by simulation, a relationship between the electrical energy to be expended and the temperature of the semifinished product can be determined and the supply of electrical energy can be controlled accordingly. The power supply device can be arranged stationary, wherein the energy can be supplied to the semifinished product during transport in the gripper and optionally after its insertion into the pressing tool. Alternatively or additionally, the power supply device or at least its the electrical energy in the semifinished product electrodes may be provided on the gripper or the said frame, so that the electrical energy already initiated when receiving the semifinished product by the gripper and thereby the clock rate can be increased. In this case, the gripper can remain on the pressing tool during the pressing process and at least temporarily maintain the resistance heating during the pressing process. [0001] In an advantageous embodiment of the method, the semifinished product can already be elastically deformed by the pressing tool before reaching a plastic state, so that the cycle rates can be additionally reduced. In this case, the closing of the pressing tool can be effected as a function of the variables applied to the power supply device such as voltage, power, current or a temperature determined by means of these variables or a resistance of the semi-finished product determined in another way. The temperature of the semifinished product can be predefinably distributed in an improved manner over the entire semifinished product by providing more than two contact electrodes which feed the electrical energy. Depending on the lateral shape, bellies and the like to be shaped, the contact electrodes can be distributed over the circumference of the semifinished product, so that essentially the same temperatures can be controlled in particular during the pressing process over the surface of the semifinished product or the forming plastic molded part. For this purpose, the contact electrodes can be arranged laterally and / or on the front side of the semifinished product and be biased for example by means of pressure sensors with respect to this. The current transmission from the contact electrodes to the semifinished product can be controlled inter alia by their area and their contact pressure. The contact electrodes can be pressurized accordingly by the pressure transmitters.

Furthermore, the detection of the resistance of the quality assurance of

Semi-finished product and / or serve the plastic molding. For example, the resistance measurements, in particular via a plurality of contact electrodes for quality assurance, for example, the mechanical strength of the plastic molded part can be used. For this purpose, for example, during the heating, pressing and / or Abwärmprozesses the introduced electrical energy, the resistance in the de-energized state or similar electrical measurement method, the distribution of a gain of the semifinished product and / or the plastic molding providing, electrically conductive distribution, which on the plastic molding acting temperature and other parameters relevant to quality from the reception of the semifinished product to the storage of the finished plastic molded part are determined, evaluated and archived, so that at any time and for each individual a quality assessment can be provided. [00013] The method is also suitable for plastic components to be additionally attached to the plastic molded part, which, for example, is molded onto the semifinished product or the finished, preferably still energized, plastic molded part by means of an injection molding tool during a stay of the semifinished product. In this way, plastic moldings can be provided as composite parts of different materials. For example, in an injection molding process, a further, reinforced or unreinforced thermoplastic or in a correspondingly modified injection molding a thermoset can be molded. By means of the resistance heating, it is possible, if appropriate, to provide selectively at the location of the plastic components to be sprayed, temperatures of the semifinished product or of the plastic molded part which are changed as a function of the remainder.

The invention will be explained in more detail with reference to the embodiments illustrated in Figures 1 to 5. Showing:

1 shows a detail of a device for the production of

Plastic moldings from plan semi-finished products before a pressing and spraying process on average,

FIG. 2 shows the device of FIG. 1 during the pressing and injection process, FIG. 3 shows the device of FIGS. 1 and 2 after the pressing and injection process,

FIG. 4 is a sectional view of a power supply device modified relative to the power supply device of FIGS. 1 to 3;

Figure 5 is a systematically illustrated gripper with integrated power supply device.

The device 1 shown in Figure 1 is used to carry out the method for

Manufacture of plastic moldings from plan as plates as organo sheets shaped semifinished products 2, wherein only the core of the device 1 shown with the pressing tool 3 and omitted other components of the device 1 as the storage location of the semifinished product 2 and this in the pressing tool and the plastic moldings wegtransporting gripper are. The sectional pressing tool 3 is formed from several - here two - pressing tool parts 4, 5, the surfaces 6, 7 are formed to each other three-dimensionally and complementary to each other while maintaining a mold volume.

The semifinished product 2 is heated by displacement of the pressing tool parts

4, 5 against each other in the corresponding three-dimensional shape and consists of one or more layers of one or more types of thermoplastic polymer, wherein at least one layer contains electrically conductive additives such as fibers, such as carbon fibers or particles, which also as a mechanical reinforcement of the semifinished product 2 and the plastic molded part produced below is used. The semifinished product 2 is heated by means of a supply of electrical energy by means of the power supply device 8 with the current source 9 and the contact electrodes 10, 1 1, wherein the internal resistance of the electrically conductive additives ohmic heat develops.

The supply of electrical energy is controlled by means of the control device of the size and time after so that the semifinished product 2 uniformly heated to a predetermined temperature, for example in the range of glass or softening temperature and the semi-finished 2 hot formed in the pressing tool 3 becomes. In addition to controlling the power supply in the form of a high current application with preferably low voltages by means of the power supply device 8, the semifinished product 2 can be selectively heated by the position and number of at least two contact electrodes 10, 1 1 is selected accordingly. Furthermore, by the bias of the contact electrodes 10, 1 1 by means of the pressure transducer 13, 14 against the semifinished product 2, a contact resistance can be set or optimized.

As shown, the contact electrodes 10, 1 1 connected to the frame 15 or be added to this. The frame 15 takes on the semifinished product 2 and allows by means not shown Aufsteckpins a positioned arrangement on the pressing tool 3 - here on the pressing tool part 5. The frame is made of electrically insulating material, for example made of ceramic or provided by an insulating conductive layer. Additional wise at least the surfaces 6, 7 compared to the conductivity of the semifinished product 2, a lower conductivity in order to reduce leakage currents through the pressing tool 3 or prevent. For this purpose, the surfaces 6, 7 by appropriate treatment such as coating, passivation and the like have a low electrical conductivity and / or the material of the pressing tool 3 have reduced conductive properties.

To save the production time or an increase in the clock rate, the semifinished product 2 can be heated before being introduced. For this purpose, the contact electrodes can be provided with the frame mobile, so that semi-finished 2 and frame 15 together with contact electrodes 10, 1 1 can be moved from the storage location in the pressing tool 3.

In addition to the hot forming of the semifinished product 2, it is provided in the pressing tool 3 shown to inject a further plastic component onto the semifinished product 2 by means of the injection molding unit 16, which is only partially shown. For this purpose, the liquefied plastic component 17 is held in the injection molding unit 16 and filled after appropriate conditioning of the semifinished product 2 on the surface 6, the injection mold 18 and made a plastic connection with the semifinished product 2.

Figure 2 shows the device 1 during the pressing process with already formed form of the semifinished product 2 and molded plastic component 17. It has been found to be advantageous to maintain the temperature of the semifinished product 2 at least partially up to a better connection of plastic component 17 and semi-finished 2 to achieve.

Figure 3 shows the device 1 with open after the pressing and injection process

Pressing tool 3 with the plastic molding 19 formed from the semifinished product 2 and the plastic component 17. This is removed from the contact electrodes 10, 1 1 and the frame 15 and transported away individually or in other embodiments, including frame and contact electrodes. Figure 4 shows a section through a clock against the con tacts 10, 1 1 of Figure 1 modified contact electrode 10a with two laterally and opposite semi-finished only 2 contacting electrodes 20, 21 and the semifinished product 2 frontally contacting electrode 22nd In the illustration shown, the electrodes 20, 21, 22 are shown not contacting at a distance from the semifinished product 2. By means of the presettable pressure transmitters 13a, 13b, 13c, the electrodes 20, 21, 22 displaceably received in the frame 15a can be biased against the semifinished product 2 with a predetermined biasing force. Each electrode 20, 21, 22 has its own power connection 23, 24, 25, so that they can be controlled separately, wherein different current paths in conjunction with further contact electrodes, which are arranged at a distance from the contact electrode 10 a on the semifinished product 2, can be provided , which allow a uniform or predetermined surface areas selectively variable heating of the semifinished product 2.

Figure 5 systematically shows the gripper 26, which the frame 15b with the

Semifinished product 2 at the storage location 27 receives and inserts into the pressing tool, not shown. The frame 15b contains the contact electrodes 10b, 11b. The supply lines 28, 29 supply them with electrical energy, so that the semifinished product 2 can already be preheated during transport to the pressing tool. The power source is housed in a manner not shown in the gripper or stationary in a supply unit.

LIST OF REFERENCES

contraption

Workpiece

press tool

Pressing tool part

surface

Power supply means

power source

contact electrode

a contact electrode

b contact electrode

contact electrode

b contact electrode

control unit

thruster

a pressure transducer

b Pressure transducer

c Pressure transducer

thruster

frame

a frame

b frame

injection molding unit

Plastic component

injection mold

Plastics molding

electrode

power connection Power connection Power connection Gripper

Supply point supply line

supply

Claims

claims

1 . Method for producing a plastic molded part (19) from a flat semifinished product (2) by means of a hot forming method, in which the semifinished product (2) is moved by means of a gripper (26) from a storage point (27) into a pressing tool (3) having a shape of the plastic molded part (3). 19) forming pressing tool parts (4, 5), fixed to the pressing tool (3) and brought under heating by a pressing operation of the pressing tool (3) in the form, the semifinished product (2) provided during its preparation as a polymer material with electrically conductive additives and before the pressing operation is controlled by resistance heating of the electrically conductive additives to a predeterminable temperature, characterized in that the resistance heating during the transport of the semifinished product (2) from the storage location (27) in the pressing tool (3) is operated.

2. The method according to claim 1, characterized in that the resistance heating by means of a in the gripper (26) integrated power supply device (8) is operated.

3. The method according to claim 1 or 2, characterized in that the resistance heating of the semifinished product (2) in the pressing tool (3) is operated.

4. The method according to any one of claims 1 to 3, characterized in that the semifinished product (2) before reaching a plastic state by the pressing tool (3) is elastically deformed.

5. The method according to any one of claims 1 to 4, characterized in that during a residence of the semifinished product (2) in the pressing tool by means of an injection molding unit (16), a further plastic component (17) is injection-molded onto the semifinished product (2).

6. The method according to any one of claims 1 to 5, characterized in that a monitoring of a power consumption of the semifinished product (2) and / or plastic molding (19) is evaluated over at least a portion of the process as a quality variable.

7. The method according to any one of claims 1 to 6, characterized in that at least one circuit through the semifinished product (2) on more than two laterally and / or frontally arranged electrodes (20, 21, 22) is closed.

8. The method according to claim 7, characterized in that a plurality of circuits are controlled and regulated independently of each other.

9. Device (1) for carrying out the method according to one of claims 1 to 8 comprising a semifinished product (2) in a divisible pressing tool (3) inserting gripper (26) and a power supply device (8) for resistance heating of the semifinished product (2).

10. Device (1) according to claim 9, characterized in that the power supply device (8) a plurality of, against the semi-finished product (2) biased contact electrodes (10, 10a, 10b, 1 1, 1 1 b).

1 1. Apparatus according to claim 10, characterized in that the bias of the contact electrodes (10, 10a, 10b, 1 1, 1 1 b) relative to the semifinished product (2) by means of a pressure transducer (13, 13a, 13b, 13c, 14) is controllable.

12. Device (1) according to one of claims 9 to 1 1, characterized in that a conductivity of the pressing tool (3) is less than a conductivity of the semifinished product (2).