DE102015122376B4 - Method for producing a fiber composite component - Google Patents

Abstract

Method for producing a fiber composite component by means of an injection method, in which a matrix material (14) is injected into a fiber material and the injected matrix material (14) is cured, with the steps:
a) introducing a fiber material into an injection region (12) of a molding tool (11) and providing a matrix material (14) outside of the injection region (12) in a reservoir communicating with the injection region (12), and
b) generating a pressure difference between the matrix material (14) and the injection region (12) so that an injection pressure acts on the matrix material (14) and the matrix material (14) is injected from the reservoir into the fiber material introduced into the injection region (12), marked by
c) measuring the cavity pressure within the injection area (12) by one or more pressure sensors (S ₁ to S ₈ ) during and / or after the injection of the matrix material (14), so that for each pressure sensor (S ₁ to S ₈ ) a plurality of Measured values are determined
d) forming time-pressure curves of the cavity pressure for each pressure sensor (S ₁ to S ₈ ) as a function of the measured values of the respective pressure sensor (S ₁ to S ₈ ) by an evaluation unit (16), and
e) detecting at least one characteristic deviation in at least one formed time-pressure curve and determining a pore movement of one or more pores within the matrix material as a function of a detected deviation in at least one formed time-pressure curve by the evaluation unit.

Description

The invention relates to a method for producing a fiber composite component by means of an injection method, in which a matrix material is injected into a fiber material and the injected matrix material is cured, according to the preamble of patent claim 1.

Fiber composite materials are an indispensable part of the aerospace industry today. But also in the automotive sector, the use of such materials is becoming more and more popular, which is not least due to the fact that fiber composite components produced from a fiber composite material have a very high weight-specific strength and rigidity. In the process, it is increasingly being used to produce structure-critical components made of fiber composite materials.

However, fiber composites have some disadvantages compared to conventional materials such as aluminum, especially in the production. Thus, even today, in many areas in the production of fiber composite components, manual work steps and process monitoring are required, which makes the production of such components cost-intensive.

An essential quality feature of fiber composite components produced by means of an injection process is the complete impregnation or infiltration of the matrix material into the fiber material. In classical injection methods, a dry or slightly preimpregnated fiber material is used, which is brought into the appropriate shape and then infiltrated using a corresponding injection pressure with a matrix material. The matrix material, which may be, for example, a thermosetting plastic and forms an integral unit with the infiltrated fiber material after curing, is generally provided in a reservoir, which communicates with the fiber material via injection lines.

When injecting the matrix material into the fiber material, however, it must be ensured that no gas inclusions form in the fiber material or that the pore content in the component is too large, since such a quality defect leads outside of the tolerable limit to the reject of the component. The causes of such gas pockets, also called dry spots or dry spots, are, for example, in the lead of the matrix material or matrix system, which leads to flow front mergers, which then lead to the gas inclusions and thus to defects. The poor interaction of various sprues and vents or the variation of the impregnation properties of the fiber material can also be the cause of such gas inclusions.

There is therefore great interest in preventing such gas inclusions. However, since this can not be ensured as a rule 100 percent, it is particularly for mass production of great interest to be able to determine such gas inclusions during the injection process, so if necessary to take countermeasures in good time or remove the component early from the production process to be able to. As a result, the manufacturing cost can be reduced and the quality can be increased.

From the DE 10 2013 100 092 A1 is a method for impregnation testing of fiber composites known, with the aid of ultrasonic transmitters and ultrasonic receivers, the component is illuminated and then closed by ultrasound reflection to a degree of impregnation.

From the DE 10 2007 060 739 A1 For example, a method and an apparatus for producing fiber composite components is known in which a lower temperature is set in edge regions of the molding tool than in the remainder of the component so as to avoid leading the matrix resin at these edge regions. It can be concluded by means of pressure sensors on the shape of the flow front.

From the EP 2 105 285 A2 a method and an apparatus for producing a fiber composite component is known in which pressure sensors, for example, are integrated into the vacuum film in order to be able to measure the internal pressure. Based on the pressure measurement can be concluded that a possible leakage in the vacuum structure.

From the WO 2014/006131 A2 a method and an apparatus for producing a fiber composite component is known, wherein by means of pressure sensors also pressure measurements during the injection of the matrix resin are performed and based on the pressure values then the injection pressure is adjusted so as to realize an optimum flow rate of the matrix resin can.

From the US 5 219 498 A Finally, a method is known in which dielectric properties of the fiber material are measured by means of a dielectric sensor.

It is therefore an object of the present invention to provide an improved method, with the component quality can be increased with respect to gas inclusions and pore formation.

The object is achieved by the method according to claim 1 according to the invention.

According to claim 1, a method for producing a fiber composite component by means of an injection method is proposed in which a matrix material is injected into a fiber material and the injected matrix material is cured. Matrix material and fiber material are parts of a fiber composite material for producing a fiber composite component. The fiber material may be dry or (lightly) preimpregnated prior to injection.

According to the known injection method, the fiber material is introduced into an injection area of a molding tool and the matrix material is provided outside the injection area in a reservoir communicating with the injection area. The injection area is the part of the tool in which the fiber material is introduced and subsequently injected with the matrix material. In the classic open-mold process, the injection area is limited by a shaping tool surface on the one hand and the vacuum structure on the other hand, which in particular contains a corresponding vacuum film. In the classic closed-mold process, the injection area is enclosed by two or more mold halves and usually sealed vacuum-tight.

After introduction of the fiber material and provision of the matrix material, an injection pressure acting on the matrix material is now generated, so that the matrix material is injected from the reservoir via a corresponding injection line into the fiber material introduced into the injection area. The injection pressure can be generated, for example, by evacuating the injection area, whereby a vacuum / fine vacuum is set here. Due to the atmospheric external pressure and the concomitant pressure difference, an injection pressure is generated on the matrix material, which was provided outside the injection area, which acts in the direction of the injection area. As an alternative or in addition to this, it is also possible to exert on the matrix material, which is provided outside the injection area, a higher pressure on the matrix material than the pressure conditions of the injection area, which pressure is, for example, greater than the atmospheric pressure, as a result of which alternatively or additionally a further injection pressure ( or portion thereof) is generated.

According to the invention, it is now provided that the cavity pressure is continuously determined during or after the injection of the matrix material with the aid of pressure sensors arranged within the injection area, so that a large number of measured values are determined for each pressure sensor. In this case, a pressure sensor is already sufficient if it is arranged, for example, in the vicinity of the venting port. Under Ventingport usually means the last filled area of a tool or a line which leads into a resin trap in front of the vacuum pump.

Subsequently, from the measured values of the individual pressure sensors, corresponding time-pressure profiles of the cavity pressure are formed for each pressure sensor, so that a pressure curve of the cavity pressure at the position of the pressure sensor is generated over time for each pressure sensor. This can be detected, for example, online, wherein a time-pressure curve can also consist of discrete measured values.

According to the invention, it is then proposed that at least one characteristic deviation is detected in at least one formed time-pressure curve and then determined as a function of a recognized characteristic deviation in at least one formed time-pressure curve, whether a pore movement of one or more pores within the Matrix material takes place. The pores are formed, for example, upon dissolution of a substantially stationary gas inclusion within the matrix material or pass through leaks in the tool or in the injection system into the fiber material to be impregnated.

The inventors have recognized that it can be determined by means of the cavity pressure, whether a pore movement takes place, as reflected such pore movements, for example in the form of vibrations, noise, pressure minima and / or pressure maxima in the respective time-pressure curve of a sensor. A characteristic deviation of a time-pressure curve is always present when significant parameters of the time-pressure curve, which as a rule can be regarded as a kind of curve, change significantly, ie the changes in the parameters of the time-pressure curve. Curve are greater than a tolerable limit. A pressure minimum or a maximum pressure of more than 0.1 bar within a few seconds, for example within less than 10 seconds, is, for example, such a characteristic deviation which, for example, suggests the onset of pore movement of pores within the matrix material. However, this value is only to be understood as an example and may depend on the size of the component and the injection pressure used. If necessary, it would be necessary to determine experimentally which characteristic deviations at existing injection pressure and component geometry / Component size would arise in artificially induced gas inclusions and pores or pore movements. Stationary gas inclusions in the sense of the present invention are understood to mean the inclusion of a gaseous material, for example outside air or outgassings of the materials used, which are formed within the fiber material by an enclosed flow front of the matrix material. The stationary gas pockets are essentially stationary, ie there is no significant change in the local positions with respect to the position of the fiber material. Such gas inclusions are also called "dry spots" or dry spots.

A pore or gas pore in the sense of the present invention is understood to mean a small hollow space within the matrix material which forms, for example, by dissolution of a gas inclusion. Such pores can arise during the dissolution of a stationary gas inclusion in the form of bleeding of the stationary gas inclusion, wherein the pores are usually in the direction of the pressure-grading, i. opposite to the pressure connection or the pressure source, move. In this case, a narrow ramification of the pores is often observed. However, pores can also be caused by tool leaks or leaks in the injection system. A pore is thus a very small gas inclusion in relation to the component, which often has an elongated structure.

It has been found that such a pore movement can be detected in the time-pressure curve of the sensors arranged on the tool, since the time-pressure curve has characteristic deviation characteristics which can be clearly associated with the pore movement.

The recognition of a characteristic deviation can, for example, also arise from the fact that the time-pressure curve is compared with an idealized time-pressure curve which is defined by a time-pressure curve of the respective pressure sensor without pore movement in the matrix material. A deviation from such an idealized pressure curve lying above a respective critical limit value can be recognized as a characteristic deviation which suggests a pore movement.

Advantageously, the characteristic deviation is detected in at least one formed time-pressure curve by curve vibrations, curve noise, pressure minima and / or pressure maxima within the respective time-pressure curve. Pressure minima and / or pressure maxima would have to be outside a tolerable limit value in order to be recognized as a characteristic deviation, since smaller deviations within the time-pressure curve do not undoubtedly indicate pore movement. Curve oscillations are understood as meaning in particular mutual amplitude changes above a tolerable limit value, the amplitudes in this case representing the pressure parameter of the time-pressure curve. Under a curve noise is understood in particular the superposition of many harmonic curve oscillations, in which case the amplitude represents the cavity pressure. In other words, in the case of the curve oscillations or the curve noise, changes in the cavity pressure are regarded as the amplitude of an oscillation outside a tolerable limit value, wherein a pore movement within the matrix material can be clearly concluded due to a mutual change in the cavity pressure.

In a further advantageous embodiment, an end of a recognized characteristic deviation is detected in at least one formed time-pressure curve in which it is no longer detectable characteristic deviations in the time-pressure curve, in which case depending on the detected end of a detected characteristic deviation the termination of the detected pore movement is detected. This makes it possible to read off the beginning and end of a pore movement from the characteristic deviation within the time-pressure curve, wherein the termination of a pore movement can also mean the dissolution of the one or more pores.

Advantageously, such information is stored in a data memory for later logging and detection purposes.

In a further advantageous embodiment, a direction of movement of the pore movement is determined in dependence on the position of the pressure sensors with respect to the fiber material and the characteristic deviations of a plurality of time-pressure curves, so that not only the pore movement can be determined per se, but also their concrete direction. Due to the fact that the pressure sensors are arranged spaced apart within the injection area, information about the direction of movement of the pore movement can be derived.

Advantageously, the process parameters of the injection process can now be adjusted or adjusted when recognizing a pore movement and possibly also at the end of the pore movement in order to be able to react to the particular conditions with regard to the gas inclusion and the pores formed therefrom. Thus, it is conceivable, for example, that if the pore movement is detected, the injection pressure is continuously raised for so long, until the completion of the pore movement is detected, so that, for example, an increased injection pressure is reduced again to a preset standard value. This can increase the quality of components and reduce waste.

This makes it possible for the first time to be able to detect a pore movement and to be able to adjust and adjust the process parameters of the injection process in the production of the fiber composite component accordingly, in order to increase the component quality and to reduce a possible production spread.

• 1 schematische Darstellung einer Anlage zur Durchführung des erfindungsgemäßen Verfahrens;
• 2 Diagramm von mehreren Zeit-Druck-Verläufen und deren jeweiligen charakteristischen Abweichungen.

The invention will be explained in more detail by way of example with reference to the attached figures. Show it:

• 1 schematic representation of a plant for carrying out the method according to the invention;
• 2 Diagram of several time-pressure curves and their respective characteristic deviations.

1 shows schematically the structure of a plant 10 , which is designed for producing a fiber composite component by means of an injection method. The attachment 10 has a mold for this purpose 11 on top of that, an injection area 12 in which the fiber material (not shown) is introduced. The injection area 12 is usually covered by a vacuum film (also not shown) and thus sealed vacuum-tight.

In the injection area 12 are several pressure sensors S ₁ to S ₈ arranged to measure the cavity pressure within the injection area 12 are formed.

A gate opening 13 that the tool 11 is provided with one outside the injection area 12 provided matrix material 14 communicatively connected.

The attachment 10 further includes a plant controller 15 which, among other things, can control the injection pressure and other process parameters.

Furthermore, the attachment points 10 an evaluation unit 16 on that with the sensors S ₁ to S ₈ signal technically in conjunction to form according to the present invention from the measured over the time measured values of the individual sensors each a time-pressure curve to investigate these time-pressure curves with respect to characteristic deviations and determine whether a pore movement takes place.

The evaluation unit 16 is further with the plant control 15 connected, so for example, on the process parameters during the injection of the matrix material 14 to be able to influence depending on a detected pore movement.

In the embodiment of 1 is further at the opposite end of the gate 13 a suction opening 17 that with a vacuum pump 18 communicates. This can be done before the injection of the matrix material 14 as well as possibly creating and maintaining a vacuum during the injection.

2 shows an example of a diagram of time-pressure curves V ₁ to V ₃ of three sensors. Initially, a negative pressure of less than 0.1 bar was set in the injection area.

It can be seen that first up to about 50 seconds, the time-pressure curves V ₁ to V ₃ almost congruent and the pressure in the injection area increases continuously.

From about 50 seconds, however, characteristic deviations arise 20 within the time-pressure curves V ₁ to V ₃ , which is particularly due to vibrations and noise in the time-pressure curves V ₁ to V ₃ outside a tolerable limit range.

This characteristic deviation 20 shows, according to the invention, that a pore movement has formed in the matrix material, ie the pores which have formed at a dissolution of a substantially stationary gas inclusion have begun to move at about 50 seconds. From about 100 seconds, this pore movement is completed, which can happen, for example, by the resolution of the pores or the "dry spots".

The characteristic deviations 20 in the time-pressure curves V ₁ to V ₃ as well as their characteristic features may depend inter alia on the component geometry, the injection pressure and on the fiber and matrix material used. It has proved to be expedient, first in a test run under the same boundary conditions of the later production with an artificially induced gas inclusion the characteristic features of the characteristic deviations 20 to determine and then transfer to the later series production.

LIST OF REFERENCE NUMBERS

10

investment

11

Tool

12

injection area

13

gate

14

matrix material

15

system control

16

evaluation

17

suction

18

vacuum pump

20

characteristic deviation

S ₁ -S ₈

pressure sensors

V ₁ to V ₃

Time-pressure curves

Claims (7)

Method for producing a fiber composite component by means of an injection method, in which a matrix material (14) is injected into a fiber material and the injected matrix material (14) is hardened, with the steps: a) introduction of a fiber material into an injection region (12) of a molding tool (11) and providing a matrix material (14) outside of the injection area (12) in a reservoir communicating with the injection area (12), and b) creating a pressure differential between the matrix material (14) and the injection area (12) such that an injection pressure is applied to the matrix material (14) acts and the matrix material (14) is injected from the storage container into the fiber material introduced into the injection area (12), characterized by c) measuring the cavity pressure within the injection area (12) by one or more pressure sensors (S ₁ to S ₈ ) during and / or after the injection of the matrix material (14), a plurality of measured values are determined for each pressure sensor (S ₁ to S ₈ ), d) forming time-pressure profiles of the cavity pressure for each pressure sensor (S ₁ to S ₈ ) as a function of the measured values of the respective pressure sensor (S ₁ to S ₈ ) by an evaluation unit (16), and e) detecting at least one characteristic deviation in at least one formed time-pressure curve and determining a pore movement of one or more pores within the matrix material in response to a detected deviation in at least one formed time -Druck-course through the evaluation unit. Method according to Claim 1 , characterized in that the characteristic deviation is detected in at least one formed time-pressure curve with respect to an idealized pressure curve, wherein the idealized pressure curve formed by a time-pressure curve of the respective pressure sensor (S ₁ to S ₈ ) without pore movement in the matrix material is. Method according to Claim 1 or 2 , characterized in that the characteristic deviation is detected in at least one formed time-pressure curve by curve oscillations, curve noise, pressure minima and / or pressure maxima within the respective time-pressure curve. Method according to one of the preceding claims, characterized in that one end of a detected characteristic deviation detected in at least one formed time-pressure curve and in response to the detected end of a detected characteristic deviation, the termination of the detected pore movement is detected. Method according to one of the preceding claims, characterized in that a direction of movement of the pore movement is determined by the evaluation unit in dependence on the position of the pressure sensors (S ₁ to S ₈ ) with respect to the fiber material and the characteristic deviations of a plurality of time-pressure curves. Method according to one of the preceding claims, characterized in that, depending on at least one detected characteristic deviation, the formation or the dissolution of a gas inclusion is detected by the evaluation unit. Method according to one of the preceding claims, characterized in that depending on the determination of a pore movement or the determination of the completion of the pore movement, the process parameters of the injection process by the evaluation unit (16) are adjusted or adjusted.

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