DE102015011735B3 - Apparatus for producing a plastic molding and method for producing a plastic molding - Google Patents

Abstract

The invention relates to a device for producing a plastic molded part, comprising a tool cavity (5) delimited by at least two tool halves (1, 3) with an injection unit (37), by means of which in a injection step (ΔtI) under pressure and heat a liquid plastic Starting component (45) in the mold cavity (5) injectable and curable, with a in the mold cavity (5) propagating flow front (47), and with an Evakuiereinheit (11) by means of in an evacuation step (.DELTA.tE) the Werkzeugkavität ( 5) can be evacuated to a negative pressure, which evacuating unit (11) has at least one vacuum valve (9) with a suction opening (23) opening into the tool cavity (5), which vacuum valve (9) in an evacuation step (ΔtE) in an open position the suction opening ( 23) opens, so that a gas stream from the mold cavity (5) can be sucked, and in a closed position, the suction opening (23) closes fluid-tight. According to the Evakuiereinheit (11) is associated with at least one sensor element (27) by means of which in the Injizierschritt (.DELTA.tI) the flow front (47) of the plastic output component (45) is detected immediately before reaching the suction opening (23).

Description

The invention relates to a device for producing a plastic molding according to the preamble of claim 1 and a method for producing the plastic molding according to claim 9.

In vehicle construction, the RTM process (resin transfer molding) can be used for the production of high-performance components made of fiber-reinforced plastics. In the RTM process, a preform made of dry fiber material is first inserted into a mold cavity of an injection tool in a process sequence. Subsequently, the mold cavity is closed with a pressing force and an injection step takes place, in which a liquid starting component of the plastic matrix is injected under pressure and heat into the mold cavity and hardens therein. During the injection step, the liquid plastic output component spreads with a flow front in the mold cavity.

From the DE 1 174 945 A is a generic device for producing a plastic molded part with an Evakuiereinheit known. In this case, a heat sensor is provided in the Evakuierkanal, so that when a contact of the castings with the heat sensor, a shut-off valve is actuated, which closes the Evakuierkanal.

From the DE 10 2013 010 380 A1 a device is known which has an evacuation unit, by means of which the tool cavity can be evacuated to a negative pressure in an evacuation step. The evacuation unit has at least one vacuum valve with a suction opening into the mold cavity. In the evacuation step, the vacuum valve is actuated into an open position, in which the suction opening is open, so that by means of a vacuum source (for example, a vacuum pump), a gas stream from the mold cavity can be sucked. The evacuation step takes place in the DE 10 2013 010 380 A1 prior to the injecting step to prevent penetration of the plastic liquid starting component into the suction opening. After the evacuation step, the vacuum valve is actuated to a closed position, in which the suction opening is closed in a fluid-tight manner.

If the vacuum valve is arranged at a flow path end, the evacuation step and the injection step may optionally be controlled in a partially overlapping manner. This significantly improves evacuation. However, with this process control there is a risk that the vacuum valves, which are still in their open position during the injection step, will be flooded with the liquid plastic starting component.

The object of the invention is to provide a device and a method for producing a plastic molded part, which can be carried out more reliably in a simple manner compared with the prior art.

The object is solved by the features of claim 1 or claim 9. Preferred embodiments of the invention are disclosed in the subclaims.

The invention is based on the problem that in the prior art, the manufacturing process of the plastic molding takes place only by means of a simple machine control without feedback on the current conditions in the injection mold, whereby the quality scattering, especially in the RTM process is great. Such a large dispersion results from the greatly varying composition of the preforms (due to fluctuating weaving, cutting, insertion position). Against this background, according to claim 1, the Evakuiereinheit assigned at least one sensor element by means of which in the Injizierschritt the flow front of the plastic output component is detected immediately before reaching the suction opening. In this way, the vacuum valve can remain in its open state until shortly before an impending entry of plastic into the suction opening and close in time before the plastic enters the suction opening. The vacuum valve is therefore involved in contrast to the above-indicated machine control in a control loop. In this way, the evacuation step can continue in a process-reliable manner until, in the injection step, the sensor element detects the flow front of the plastic starting component directly in front of the suction opening. This significantly improves the evacuation step while ensuring that the vacuum valves are not flooded with the liquid plastic output component.

As mentioned above, according to the invention, the sensor element is integrated in a control loop. For this purpose, the sensor element in a simple system architecture can be in signal connection with a control device, by means of which the evacuation unit for carrying out the evacuation step and / or the injection unit for carrying out the injecting process can be controlled. Upon detection of the flow front of the plastic output component (that is, upon initial contact with the plastic output component), the sensor element can generate a corresponding detection signal and direct it to the control unit. The controller may subsequently actuate the vacuum valve with a closing signal to actuate the vacuum valve to its closed position, that is, to complete the evacuation step.

The sensor element can be a pressure sensor by way of example. In contrast to this, with regard to a simple signal processing and reliable detection of the flow front, the sensor element is preferably a temperature sensor which can detect the temperature in the tool cavity directly at the suction opening of the evacuation unit. Upon initial contact with the flow front of the liquid plastic starting component, the temperature sensor detects a sudden increase in temperature. Upon detection of the erratic temperature rise, the temperature sensor can generate the detection signal and forward it to the control unit.

With regard to process reliability, it must be ensured that the temperature sensor comes into contact with the flow front of the liquid plastic starting component before it reaches the evacuation unit's suction opening. Against this background, it is preferred if measures for a flow behavior are taken, which ensure reliable contact between the temperature sensor and the flow front. Preferably, the flow rate of the liquid plastic starting component can be reduced shortly before reaching the suction opening. In this way, additional time is gained, which is required for a process-reliable detection of the flow front by the temperature sensor.

For such an influencing of the flow behavior, according to the invention, an annular flow channel, which moves the suction opening at a radial distance, is incorporated on a molding surface which faces the suction opening and faces the mold cavity. In the annular flood channel - compared to adjacent Kavitätsabschnitten the cavity height is increased, namely with a corresponding reduction of the flow resistance or an increase in the permeability in the flood channel. Due to the reduced flow resistance, the flood channel is first flooded by the liquid plastic starting component during the injection step, and the liquid plastic starting component only flows with a time delay to the suction opening. Preferably, the temperature detection can take place directly in the flood channel. In this case, the temperature sensor can protrude with its tip into the flood channel.

Alternatively and / or additionally, the flow velocity in the direction of the suction opening can also be reduced by means of a forming threshold. This can also be incorporated at the, adjacent to the suction opening, the mold cavity facing mold surface and extend annularly around the suction opening. The forming threshold protrudes into the mold cavity while reducing the cavity height. Due to the reduced cavity height, an increased flow resistance or a reduced permeability results in the area of the forming threshold, whereby the forming threshold can only be overcome with a time offset from the flow front of the liquid plastic starting component.

Preferably, both the forming threshold and the flood channel can be realized. In this case, the annular forming threshold may preferably be arranged radially inside, in particular concentrically, with respect to the annular flood channel.

The above regulation of the vacuum valve is particularly advantageous in an RTM process in which a fiber-reinforced plastic component is produced. In the RTM process, a preform made of dry fiber material is first inserted into the mold cavity in a process sequence. Subsequently, the mold cavity is closed with a predetermined pressing force and takes place the evacuation step and downstream of the Injizierschritt in which the liquid plastic starting component as a matrix soaks the preform.

The invention and its advantageous embodiments and further developments and their advantages will be explained in more detail by way of example with reference to drawings.

Show it:

1 in a partial schematic representation of an RTM device;

2 in an enlarged detail view of the vacuum valve in its open state during an evacuation step;

3 in a view corresponding to 2 the vacuum valve in a closed position; and

4 a diagram showing a temporal temperature course during the RTM process.

In the 1 an RTM device is shown. The 1 , as well as the 2 and 3 are made with a view to easy understanding of the invention. Therefore, the figures are merely grossly simplified representations that do not reflect a true-to-life structure of the RTM device. Thus, the RTM device in the 1 an upper mold half 1 and a lower tool half 3 on, a tool cavity 5 limit. In the upper mold half is in a mounting recess 7 a vacuum valve 9 used. The vacuum valve 9 is part of an evacuation unit described later 11 , In the 1 is the vacuum valve 9 constructed as a needle valve, with a rotationally symmetrical valve needle 13 in the axial direction in a fixed in the mounting recess 7 mounted valve body 15 is guided. The valve needle 13 is by means of a drive unit 17 between one in the 1 and 3 shown closed position and an open position ( 2 ) adjustable in height. The drive unit 17 can work as an example hydraulically or electromagnetically. In the, in the 1 shown closed position, the valve needle 13 with its cone-shaped tip 19 against a corresponding valve seat 21 of the valve body 15 pressed, causing one in the Werkzeugkavität 5 opening suction opening 23 closed is. The valve body 15 is radially outward by means of a mounting ring 25 in the mounting recess 7 attached.

In addition, it is in close proximity to the vacuum valve 9 a temperature sensor 27 arranged, the evacuation unit 11 assigned. In the 1 the temperature sensor protrudes 27 in the immediate vicinity of the suction opening 23 into the tool cavity 5 one. The temperature-sensing tip of the temperature sensor 23 is directly in a flood channel 29 positioned the suction opening 29 moves annularly at a radial distance.

In the area of the annular flood channel 29 results in the 2 or 3 a cavity height h ₁ , which is increased in comparison to the radially outwardly adjacent cavity height h ₂ . The annular flood channel 29 is in the 1 a profile V-shaped transition joint between the mounting ring 25 and the radially outwardly adjacent molding surface 31 the upper half of the mold 1 ,

In the further course radially inward, the mold surface 31 one the suction opening 23 ring-shaped forming threshold 33 in the area of which - in comparison to a cavity height in the radially outwardly adjacent region of the tool cavity 5 - results in a reduced cavity height h ₃ . The shape threshold 33 is also annular and concentric with the flood channel 29 educated.

Like from the 1 further, is the temperature sensor 27 in signal connection with a control unit 35 with which a vacuum pump 12 as well as the drive unit 17 of the vacuum valve 9 is controllable. There is also an injection unit 37 controllable by means of the injection step Δt _I ( 4 ) a liquid plastic output component under pressure and heat via an injection channel 39 in the upper half of the mold 1 into the tool cavity 5 can be fed.

An RTM process for the production of a fiber-reinforced plastic molding is described below with reference to the figures: Thus, first of all, a preform is produced 41 ( 2 or 3 ) from a still dry fiber material in the still open Werkzeugkavität 5 inserted. Subsequently, the tool cavity 5 closed with a predetermined pressing force and there is an evacuation step .DELTA.t _E ( 4 ), where the vacuum valve 9 in its open position ( 2 ) is adjusted, with the release of the suction opening 23 , allowing a gas flow from the mold cavity 5 over the suction opening 23 as well as a vacuum channel 43 to the vacuum pump 12 is sucked off.

Spaced after the evacuation step .DELTA.t _E , the injection step .DELTA.t _I , in which a liquid starting component 45 the plastic matrix ( 2 or 3 ) under pressure and heat into the mold cavity 5 is injected. During the Injizierschrittes Δt _I , the liquid starting component spreads 45 with a flow front 47 ( 2 and 3 ) in the tool cavity 5 out. The evacuation step Δt _E continues until the temperature sensor 27 in first contact with the flow front 47 the liquid starting component 45 comes. In such a contact recording of the temperature sensor detected 27 a sudden temperature increase ΔT ( 4 ). When the sudden temperature rise ΔT is detected, the temperature sensor generates 27 a flow front signal S _F ( 1 ), to the control unit 35 is directed. The controller then controls 35 the drive unit 17 of the vacuum valve 9 to put it in the closed position ( 3 ). In this way, the suction opening 23 of the vacuum valve 9 just before the imminent entry of plastic into the suction opening 23 closed.

To provide sufficient time for signal processing or temperature detection, the propagation velocity of the flow front 47 towards the suction opening 23 by means of the flood channel 29 and the shape threshold 33 be reduced. In the area of the flood channel 29 there is a reduction of the flow resistance or an increase of the permeability, whereby in the injection step .DELTA.t _I first the flood channel 29 is flooded and only then with time delay, the liquid plastic output component 45 to the suction opening 23 flows. In the area of the radially inner forming threshold 33 on the other hand, the flow resistance is increased, which causes a further delay in the propagation of the flow front 47 towards the suction opening 23 he follows. The above-indicated RTM process with the evacuation step .DELTA.t _E and the injection step .DELTA.t _I is in the diagram of 4 indicated by the temperature sensor 27 measured temporal temperature profile is reproduced. As a result, the evacuation step Δt _E starts before the injection step Δt _I. The evacuation step Δt _E continues until, in the injection step Δt _I, the sudden temperature increase ΔT from the temperature sensor 27 is detected. Upon detection of the temperature rise ΔT, the evacuation step Δt _{E is} ended to flood the vacuum valve 9 with the starting component 45 to avoid.

LIST OF REFERENCE NUMBERS

1

upper mold half

3

lower mold half

5

mold cavity

7

mounting recess

9

vacuum valve

11

evacuation unit

12

vacuum pump

13

valve needle

15

valve body

17

drive unit

19

top

21

valve seat

23

suction

25

mounting ring

27

temperature sensor

29

flood channel

31

form surface

33

shape threshold

35

control unit

37

injection unit

39

injection channel

41

preform

43

vacuum channel

45

starting component

47

flow front

h ₁

Kavitätshöhe

h ₂

Kavitätshöhe

h ₃

Kavitätshöhe

Δt _I

Injizierschritt

Δt _E

the evacuation

.DELTA.T

temperature rise

S _F

Flow front signal

Claims (10)

Device for producing a plastic molding, with one of at least two mold halves ( 1 . 3 ) limited tool cavity ( 5 ), with an injection unit ( 37 ), by means of which in a Injizierschritt (At _I ) under pressure and heat, a liquid plastic starting component ( 45 ) into the tool cavity ( 5 ) is injectable and curable, with one in the Werkzeugkavität ( 5 ) spreading flow front ( 47 ), and with an Evakuiereinheit ( 11 ) by means of the in an evacuation step (.DELTA.t _E ) the Werkzeugkavität ( 5 ) is evacuable to a vacuum, which Evakuiereinheit ( 11 ) at least one vacuum valve ( 9 ) with one in the Werkzeugkavität ( 5 ) opening suction opening ( 23 ), which vacuum valve ( 9 ) in the evacuation step (Δt _E ) in an open position, the suction opening ( 23 ), so that a gas flow from the mold cavity ( 5 ) is sucked, and in a closed position, the suction opening ( 23 ) closes fluid-tight, wherein the Evakuiereinheit ( 11 ) at least one sensor element is assigned, by means of which in the injection step (Δt _I ) the flow front ( 47 ) of the plastic starting component ( 45 ) immediately before reaching the suction opening ( 23 ) is detectable, characterized in that at one of the suction opening ( 23 ), the tool cavity ( 5 ) facing surface ( 31 ) an annular flood channel ( 29 ) is incorporated, which the suction opening ( 23 ) moves with distance, and that the cavity height (h ₁ ) in the annular flood channel ( 29 ), while reducing the flow resistance or increasing the permeability in the flood channel ( 29 ). Apparatus according to claim 1, characterized in that the sensor element with a control device ( 35 ) is in signal connection, by means of which the Evakuiereinheit ( 11 ) for carrying out the evacuation step (Δt _E ) and / or the injection unit ( 37 ) are controllable for carrying out the injection step (Δt _I ), and in that the sensor element is detected when the flow front ( 47 ) of the plastic starting component ( 45 ) a corresponding flow front signal (S _F ) to the control unit ( 35 ), whereupon the control unit ( 35 ) the vacuum valve ( 9 ) with a closing signal to terminate the evacuation step (Δt _E ). Device according to one of claims 1 or 2, characterized in that the sensor element is a temperature sensor ( 27 ), which determines the temperature in the mold cavity ( 5 ) and that the temperature sensor ( 27 ) at one until just before the suction ( 23 ) expanded flow front ( 47 ) detects a sudden increase in temperature (ΔT), and in particular that the temperature sensor ( 27 ) upon detection of the sudden temperature rise (ΔT), the flow front signal (S _F ) is generated and sent to the control unit ( 35 ). Device according to one of the preceding claims, characterized in that the sensor element in the annular flood channel ( 29 protrudes and it detects the temperature. Device according to one of the preceding claims, characterized in that the annular flood channel ( 29 ) a transition joint between a mounting ring ( 25 ) of the vacuum valve ( 9 ) and a radially outwardly adjacent molding surface ( 31 ) of the upper mold half ( 1 ). Device according to one of the preceding claims, characterized in that on to the suction opening ( 23 ), the tool cavity ( 5 ) facing surface ( 31 ) an annular, in the Werkzeugkavität ( 5 ) protruding threshold ( 33 ), in particular a survey, is incorporated, which the suction opening ( 23 ) moves at a distance, and that the cavity height (h ₃ ) at the annular shape threshold ( 33 ), while increasing the flow resistance or reducing the permeability at the forming threshold ( 33 ). Apparatus according to claim 6, characterized in that the annular shape threshold ( 33 ) radially inside, in particular concentrically, to the annular flood channel ( 29 ) is arranged. Device according to one of the preceding claims, characterized in that by means of the device in a RTM process, a fiber-reinforced plastic component can be produced, in which RTM process in a process sequence a preform ( 41 ) from still dry fiber material into the mold cavity ( 5 ), the tool cavity ( 5 ) and the evacuation step (Δt _E ) takes place and then the injection step (Δt _I ) is feasible, in which the liquid plastic starting component ( 45 ) as a matrix the preform ( 41 ). Process for the production of a plastics molding by means of a device according to one of the preceding claims, in which process the evacuation step (Δt _E ) and the injection step (Δt _I ) are carried out partially overlapping in time. Method according to Claim 9, characterized in that the evacuation step (Δt _E ) begins before the injection step (Δt _I ), and that the evacuation step (Δt _E ) continues until, in the injection step (Δt _I ), the sensor element blocks the flow front (Δt _I ). 47 ) of the plastic starting component ( 45 ) detected.

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