JP2008068532A - Molding method of preform made of fiber-reinforced plastic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To mold a fiber-reinforced plastic containing continuous fibers. <P>SOLUTION: Raw materials 6 and 7 made of a continuous fiber-reinforced plastic are used as a work W. First, the work W and a mold 1 are preheated and the peripheral edge part of the work W is grasped by work holders 10. Then, the pressing of the work W by the mold 1 is started in a stage that the viscosity of the work W lowers to a moldable value. At this time, the work W is pressed while drawn in the mold 1 from the work holders 10. Finally, a molded preform P is heated to be solidified. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for molding a fiber-reinforced plastic preform containing continuous fibers.

In recent years, lightweight and strong fiber reinforced plastics are used in various fields. As an application to automobiles, for example, there is a vehicle body panel in which front and back layers are formed of fiber reinforced plastic and foam is filled between these layers (see Patent Document 1).
JP 2002-264846 A

  Fiber reinforced plastics include those containing continuous fibers and those containing discontinuous fibers. Those containing discontinuous fibers are extensible and can be molded with a mold. On the other hand, those containing continuous fibers do not have extensibility. Therefore, if this is forced to mold, the product will be damaged. This is because the fiber itself does not have extensibility, and the fiber is broken by receiving a forming load.

  In view of such circumstances, an object of the present invention is to provide a method capable of molding a fiber-reinforced plastic containing continuous fibers.

  The present invention for solving the above-mentioned problems is a method of molding a fiber reinforced plastic containing continuous fibers, using a sheet made of continuous fiber reinforced plastic as a work, and preheating the work and the mold. , The process of clamping the peripheral part of the work with the work holder, the process of starting the work pressing with the mold when the work viscosity is lowered to a moldable value, and drawing the work from the work holder to the mold side It is characterized by comprising a step of pressing while solidifying or semi-solidifying a molded workpiece by heating or cooling.

  According to this configuration, when the workpiece is preheated, the viscosity of the workpiece (the viscosity of the matrix resin) is decreased, the internal fibers are gradually scattered, the fibers are easily slipped, and the workpiece can be extended. The work extensibility gradually increases as the work viscosity decreases. And when the viscosity of a workpiece | work falls to the value which can be shape-molded, the press of the workpiece | work by a metal mold | die will be started. The work is pressed while being drawn from the work holder to the mold side. That is, since the peripheral part of the work is held in a semi-constrained state by the work holder, the dispersion of the fibers accompanying the decrease in the viscosity of the work is not hindered. In short, since the workpiece is pressed in a state where sufficient elongation is possible due to the dispersion of the fibers, the molding can be performed without causing the product to be damaged due to the breaking of the fibers.

  Prior to the preliminary heating of the workpiece, it is preferable to attach a film having heat resistance and stretchability to both surfaces of the workpiece.

  According to such a configuration, the friction of the workpiece against the mold surface is reduced, the product can be prevented from being damaged or wrinkled, and the workpiece is less likely to be in close contact with the mold surface. , Also helps prevent dust deposits.

  According to the present invention, the work pre-heating reduces the work viscosity (matrix resin viscosity), the internal fibers are scattered, and the fibers are easily slipped, so that the work can be stretched. And since the press by the mold is started when the viscosity of the work is reduced to a value that can be molded, even if the work includes continuous fibers, the mold does not cause damage to the product due to fiber breakage. Molding can be performed.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 10 shows the outline of the manufacturing process of the fiber reinforced plastic automobile panel.
In the previous step, a fiber reinforced plastic original fabric (prepreg) containing continuous fibers is cut, and a plurality of original fabrics are overlapped so that the fiber directions cross each other, and these are pressed and integrated. In addition, the detailed example of the lamination method of an original fabric is described in Japanese Patent Application No. 2005-1266.

  Next, preheating is performed by blowing warm air on the laminated original fabric. Instead of blowing warm air, the work may be sandwiched between hot plates or irradiated with infrared rays. In the case of a thermosetting resin at the same time as the preheating, the mold 1 is also preheated to the same temperature, and in the case of a thermoplastic resin, the temperature is adjusted to the preheating temperature or lower. Then, the preheated raw fabric is pressed with a mold 1 to form a preform. The molded preform is trimmed and then sent to the main process.

In the main process, in the case of a thermosetting resin, it is press-molded with a mold whose temperature is controlled to a temperature above the preform temperature, while in the case of a thermoplastic resin, the mold is re-preheated and the temperature is It is press-molded with a temperature-controlled mold below.
Although the post-process varies depending on the type of panel, it is finished into a final product after trimming and painting.

Next, the preform molding method in the previous step will be described in detail.
As shown in FIG. 5, two original fabrics 6 and 7 are bonded in advance through a resin sheet 8 (which may be a liquid resin) as an intermediate layer. As will be described later, the resin sheet 8 (or liquid resin) is faster in solidification (thermosetting in the case of a thermosetting resin and cooling in the case of a thermoplastic resin) than the matrix resin of the original fabric 6,7. There is. A film 9 having heat resistance and stretchability is attached to both surfaces of the bonded original fabrics 6 and 7, and preheating is performed by blowing warm air for a predetermined time. Instead of blowing warm air, the work may be sandwiched between hot plates or irradiated with infrared rays. The preheating of the workpiece is performed until the viscosity of the workpiece W is lowered to a value that enables mold forming as will be described later.

In the case of a thermosetting resin, the mold 1 is preheated to a temperature similar to the preheating temperature of the work W, and in the case of a thermoplastic resin, the mold 1 is not higher than the preheating temperature of the work W. Then, the workpiece W is set on the mold 1 (see FIG. 1). Next, the peripheral portion of the workpiece W is clamped by the workpiece holder 10 (see FIG. 2).
The work holder 10 has a spring action by compressed gas or the like, and holds the peripheral portion of the work W in a semi-constrained state (slidable state). Note that the preheating of the workpiece W may be performed in a state of being set in the mold 1. Alternatively, the entire mold may be placed in an atmosphere at a temperature to be preheated.

  And the workpiece | work W which reached the viscosity which can be shape-molded by preheating is pressed with the metal mold | die 1 (refer FIG. 3). That is, the workpiece W is pressed against the die 12 by the punch 11. Since the work W is held in a semi-constrained state by the work holder 10, the work W is pressed while being drawn from the work holder 9 to the mold 1 side. The workpiece W is demolded after being pressed by the mold 1 for a predetermined time. FIG. 4 shows an example of the preform P formed in this way.

FIG. 6 shows an example of thermosetting characteristics of the matrix resin (thermosetting resin) of the original fabrics 6 and 7 and the resin sheet 8 (or liquid resin) interposed between the original fabrics 6 and 7. In the figure, the matrix resins of the original fabrics 6 and 7 are indicated by solid lines, and the resin sheet 8 (or liquid resin) is indicated by dotted lines. In the figure, the time point when the material having the temperature T ₀ ° C is placed in the atmosphere of T ₁ ° C is used as the base point of the heating time. At that time, the temperature of the workpiece W changes as indicated by the alternate long and short dash line. Here, the preheating temperature of the workpiece W and the mold 1 is indicated as T ₁ ° C.

That is, since the resin sheet 8 (or liquid resin) is thermally cured faster than the matrix resin of the original fabrics 6 and 7, the time t _b when the viscosity of the resin sheet 8 (or liquid resin) is minimum is the original fabric. It becomes earlier than the time t _Mb when the viscosity of the matrix resin Nos. 6 and 7 becomes the lowest. Press work W by the die 1, considering productivity, will be performed at time t _Mb earlier at time t _a later reaches moldable viscosity without risk of damage.

That is, when the workpiece W is preheated, the viscosity of the workpiece W is decreased, the internal fibers are gradually scattered, the fibers are easily slipped, and the workpiece W can be extended. The extensibility of the workpiece W gradually increases as the viscosity of the workpiece W decreases, and decreases to a value that enables mold forming. Note that the viscosity η _{c of the} workpiece W that can be molded is different depending on the density of the fibers of the raw fabrics 6 and 7, the molding shape, and the like, but is approximately 5 × 10 ⁴ Poise or less. On the other hand, after the elapse of time t _Mb , thermosetting starts, and the viscosity of the workpiece W increases. That is, in consideration of productivity, it is preferable that the press of the workpiece W is started before the time t _Mb .

  Since the workpiece W is pressed while being pulled from the workpiece holder 10 to the mold 1 side, that is, the peripheral portion of the workpiece W is held in a semi-constrained state by the workpiece holder 10, the viscosity of the workpiece W decreases. The fiber dispersion is not hindered. In short, since the workpiece W is pressed in a state where sufficient elongation is possible due to the dispersion of the fibers, the molding can be performed without causing the product to be damaged due to the breaking of the fibers.

The workpiece W can be removed from the mold 1 at time t _c when the resin sheet 8 (or liquid resin) reaches a viscosity η _r that does not cause the shape of the workpiece W to be deformed. On the other hand, when the resin sheet 8 (or liquid resin) is not used, _demolding is not performed until time t _Mc .

FIG. 7 shows an example of the viscosity change characteristic of the thermoplastic resin. In the figure, the characteristics of the resin sheet 8 (or liquid resin) are omitted, but other than that, it is the same as FIG. 6 including values on the vertical axis and the horizontal axis. Also in this figure, although the time of placing the temperature T ₀ ° C. material in an atmosphere of T ₁ ° C. and a base point of the heating time depends on the mold 1 at time t _Mb viscosity of the workpiece W is minimized Since the press is started, the temperature of the workpiece W changes as shown by a dashed line.

That is, the viscosity of the workpiece W gradually decreases due to the preheating, the viscosity becomes minimum at time t _Mb , and thereafter, cooling and solidification proceeds in the mold 1 at the temperature T ₂ . For this reason, the workpiece W may be set in the mold 1 at any time as long as it is after the time t _{Ma when} the viscosity of the workpiece W is reduced to a mold-forming value η _c (approximately 5 × 10 ⁴ Poise). It is necessary to start pressing the workpiece W before the temperature of the workpiece decreases and the viscosity becomes η _c or more. The workpiece W is demolded after being cooled and solidified in a pressed state.

  In addition, since the film 9 having heat resistance and stretchability is attached to both surfaces of the workpiece W and molding is performed, the friction of the workpiece W against the mold surface is reduced, preventing product damage and wrinkles. In addition, the work W becomes difficult to adhere to the mold surface, which is useful for preventing the occurrence of demolding defects such as resin deficiencies and dust adhesion. The film 9 is preferably removed immediately before main molding. FIG. 8 shows the height of the ridge generated in the flange portion f of the preform P in FIG.

  By the way, the preform P molded in the previous process may be deformed by the spring back action after demolding, which may hinder the hot press in the molds 3 and 4 in the main process. Therefore, as shown in FIG. 5, by performing mold molding with the resin sheet 8 (or liquid resin) interposed between the raw fabrics 6 and 7, the deformation of the preform P is suppressed by suppressing the springback action. It is preventing.

  That is, as shown in FIG. 6, the resin sheet 8 is rapidly cured as compared with the matrix resins 6 and 7, and when the workpiece W is removed, the resin sheet 8 (or liquid resin) is formed. The cured resin layer has progressed considerably. For this reason, the cured resin layer suppresses the shrinkage of the matrix resin layers of the original fabrics 6 and 7, and the spring back action generated in the preform P after demolding is suppressed. The resin sheet 8 (or liquid resin) is a material that quickly cures even at a low heating temperature. However, such a material has a relatively low strength particularly at high temperatures, and is used as a matrix resin of raw fabrics 6 and 7. There are many cases that cannot be used.

  FIG. 9 shows a state in which the shape of the preform P changes after demolding.

  In the figure, A shows the case where the work W interposing the resin sheet 8 is pre-heated (80 ° C. warm air is blown for 5 minutes), the shape change does not occur in the preform P, and the shape retention ratio is 1. I keep it. B shows the case where the work W in which the resin sheet 8 is not interposed is preheated (80 ° C. warm air is blown for 5 minutes), and the shape retention ratio gradually decreases. C shows the case where the workpiece W in which the resin sheet 8 is not interposed is molded without preheating, and the decrease in the shape retention ratio is steeper than that of B. The shape retention ratio refers to a value obtained by dividing the height h of the convex portion in the preform P in FIG. 4 by its initial value.

〔Example〕
In order to confirm the effect of the present invention, the following experiment was conducted.
1. Fabrication of work The fibers of the original fabrics 6 and 7 were carbon fibers, and the matrix resin was epoxy (in the case of a thermosetting resin) or polypropylene (in the case of a thermoplastic resin). The weight ratio of carbon fiber was 40-60%. In addition, four types (low density polyethylene film, high density polyethylene film, polypropylene film, nylon film) of liquid epoxy that hardens quickly even at a low heating temperature and a film for adhering to both surfaces of the work were prepared.

  The raw fabrics 6 and 7 were cut into a size of 300 × 300 mm, and then superposed and pressed to obtain a laminated workpiece W. When the fiber pattern of the raw fabric is unidirectional, the laminated pattern has four patterns of 0 °, 90 °, + 45 °, and −45 ° in the fiber direction, and a total of 8 layers so as to be symmetrical with the center of the layer as a boundary. did. In the case of cloth, two patterns of 0 ° / 90 ° and + 45 ° / −45 ° were used, and a total of four layers were formed so as to be symmetrical with the center of the layer as a boundary. In the middle layer of each workpiece (4 to 5 days in the case of one direction, 2 to 3 layers in the case of cloth), epoxy is applied at a coating rate of 0.1 to 0. It was applied at 5 g / 100 cm2.

2. Measuring method of resin characteristics (viscosity change by heating and cooling) Both viscosity / viscoelasticity measuring machine and dielectric analysis measuring machine (manufactured by NETZSCH) were used. In the viscosity / viscoelasticity measurement, only the matrix resin used in the raw fabrics 6 and 7 was collected, adjusted to a temperature of 20 ° C., and then put into a stage controlled at 80 ° C. to measure the viscosity. The same measurement was performed on the liquid epoxy for the intermediate layer. In the dielectric analysis measurement, a film-like sensor was inserted between the stacked raw materials, the temperature was adjusted to 20 ° C., and the measurement was performed by pressing with a small press controlled at 80 ° C. The liquid epoxy for the intermediate layer was measured by inserting a film sensor into the liquid epoxy. On the other hand, when the matrix resin is thermoplastic, it is only measured with a viscosity / viscoelasticity measuring instrument, and only the matrix resin used in the original fabric is collected and then made into a thin (0.2 to 0.4 mm) film and heated to 20 ° C It was adjusted. This was put into a stage controlled at 168 ° C. and the viscosity was measured.

3. Molding of preform The temperature T ₀ of the workpiece W before preheating was kept at 20 ± 1.0 ° C. There are three preheating methods: hot air spraying, sandwiching with a hot plate, and infrared irradiation, but the hot plate is the easiest to reproduce the same heating rate as the above-mentioned resin characteristic measurement. It was done by the method of pinching. Immediately after the preheating was performed for a predetermined time, it was transferred to the press. A press machine having a maximum clamping force of 60 tons was used, and the temperature of the mold 1 was controlled to 80 ° C. in the case of a thermosetting resin and 40 ° C. in the case of a thermoplastic resin. Molding was performed at different development ratios of 1.01 to 1.15 by changing the height h of the preform P shown in FIG. The expansion rate is a value obtained by dividing the length of the line connecting the points abcde on the surface of the preform P shown in FIG. 4 by the length of the line connecting the points ae in plan view.

4. Evaluation method The occurrence of tearing of the preform was observed by visually observing the preform after demolding to determine whether the preform was broken. In FIGS. 11 to 13, ◯ indicates no tearing, Δ indicates that tearing occurs only with a high aperture ratio shape, and × indicates that clear tearing occurs (* 1).

  As for the shape retention state of the preform, the change in the height h (see FIG. 4) of the preform immediately after demolding was continuously measured with a laser displacement meter, and the degree of springback was evaluated by the above-described shape retention ratio. 11 to 13, ◯ indicates 0.95 or more, Δ indicates 0.9 to 0.95, and X indicates less than 0.9 (* 2).

The state of resin deficiency due to mold adhesion was evaluated by weight reduction rate% (= 100 × (W ₀ −W ₁ ) / W ₀ ), where W ₀ and W ₁ were workpiece weights before and after forming a preform, respectively. 11 to 13, ◯ indicates less than 1.0%, Δ indicates 1.0 to less than 1.5%, and X indicates 1.5% or more (* 3).

5. Evaluation results
(1) By reducing the viscosity of the matrix resin by preheating, there is an effect of suppressing fiber breakage of the preform.

  (2) By providing the intermediate layer with a resin having a high curing rate, the preform shape after demolding can be maintained, which has the effect of improving productivity.

  (3) The film adhering to both surfaces of the workpiece is effective in suppressing fiber breakage and preventing resin deficiency due to mold adhesion by reducing the coefficient of friction against the mold surface. Highly heat-resistant HDPE and PP are effective. is there.

The figure which shows the 1st process in the case of shape | molding a preform with the method of this invention The figure which shows the 2nd process Diagram showing the third step Perspective view of preform molded by the same method Sectional view of workpiece set in the mold The figure which shows the viscosity change by heating of thermosetting resin The figure which shows the viscosity change by heating of the thermoplastic resin The figure which shows the generation | occurrence | production state of wrinkles in the preform shape | molded by the method of this invention Diagram showing the shape change after preform removal The figure which shows the manufacturing process of the body panel of the car A diagram showing a part of the result of molding a preform with thermosetting resin FIG. 11 shows the remaining part of FIG. The figure which shows the molding result of the preform with the thermoplastic resin

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mold 2 Mold 6 Original fabric 7 Original fabric 8 Resin sheet 9 Film 10 Work holder 11 Die 12 Punch W Work P Preform

Claims (2)

A method of molding a fiber reinforced plastic containing continuous fibers,
Using a continuous fiber reinforced plastic sheet as a work, preheating the work and the mold, and sandwiching the peripheral edge of the work with a work holder;
Starting the pressing of the workpiece with a mold when the viscosity of the workpiece has dropped to a value that can be molded;
Pressing the workpiece while drawing it from the workpiece holder to the mold,
A process of solidifying or semi-solidifying the molded workpiece by heating or cooling;
A method for molding a fiber reinforced plastic preform, comprising:   2. The method for molding a fiber-reinforced plastic preform according to claim 1, wherein films having heat resistance and stretchability are adhered to both surfaces of the work prior to preheating the work.

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