DE102004058058A1 - Manufacturing textile-covered plastic injection molding with non-linear hollow channel for use in automobile industry, employs water injection technology with tangential removal - Google Patents

Abstract

Plastic melt is introduced into the injection molding cavity (100) and pressurized fluid is injected into the melt via a first section (14) of the injection mold, forming a hollow channel (16). A novel feature is removal of surplus melt and fluid from the cavity via a second section (20), in a tangential direction, into a connected secondary cavity. Removal is tangential with respect to the original flow direction of melt and fluid occurring during formation of the hollow channel. Residual fluid is removed from the cavity. The melt solidifies and the molding is removed. Injection of melt and fluid are effected at opposite ends of the hollow channel under formation. The fluid is water and its pressure is 20-30 bar. The injection and removal stage is used twice; the second time, the water pressure is higher, exceeding 30 bar. During or before injection, the plastic is expanded to foam. Before melt introduction into the mold, a textile layer is laid into its cavity. To increase rigidity of the molding, ridges are formed at suitable locations. An independent claim is included for the corresponding molding with a non-linear hollow channel.

Description

The The invention relates to a process for the production of plastic moldings with a hollow channel according to the preamble of claim 1.

It is known to produce molded plastic parts, in which Hollow chambers or hollow channels to increase the mechanical rigidity are provided. The use is known Gas injection technique, in which for producing a hollow body via a integrated injector gas (typically nitrogen) in the tool in the already filled with plastic melt cavity of an injection mold is injected. The gas pushes the still flowable plastic Plastic core inside the molding out of the tool, so that a cavity is created. The so-called blowing out forced out Plastic core can be removed in overflow cavities or in the injection cylinder to be led back. Thereafter, the resulting plastic molding is removed from the mold.

In recently, Time, however, wins the use of water injection technology in importance, which compared to the above gas injection technique has decisive advantages. Because water has a much higher specific Heat capacity and thermal conductivity has as for example nitrogen, by its use the cooling effect of the Injection medium greatly improved. The molding will not only through the tool wall from the outside, but also effectively cooled by the water from the inside. Thereby can On the one hand, drastic cycle time reductions are achieved. on the other hand can thinner walls Components are generated. Another advantage is that Water is almost incompressible, so you can work with stronger pressures. Lastly, the use of water is also much cheaper as that of technical gases like nitrogen.

Now is the application of an injection technique based on gas or Water standing on geometrically simple, rectilinear parts of the technique. For more complicated components that have a three-dimensional Have contour with non-rectilinear hollow channels or hollow chambers, the geometric complications which the Expelling a plastic melt due to the geometry of the tool, in particular at curved Course, complicate. When using an injection technique from the The state of the art is the plastic core for elongated hollow channels cooled quickly, making an undesirable thick residual wall thickness persists.

Regarding the increase The stiffness of plastic moldings comes in more complicated structures aggravating that the insertion of Ribs in the contour is made more difficult because the contour is so undercut and three-dimensionally deformed is that no favorable Entformungsrichtung can be found. In addition, it is often of increased interest to the design from ribs altogether, if the component has a relatively large visible surface. By the construction of thin-walled Components with hollow chambers can be omitted on the setting of ribs be, or it can the still necessary ribs at least less high become.

task The invention is relatively strong three-dimensionally deformed, long Components using the water injection technique with a thin-walled Hollow channel equip and thereby using suitable constructive measures the removal of the plastic core from the hollow channel during the To facilitate production.

• (a) Injektion einer Kunststoffschmelze in eine eine Kontur des herzustellenden Kunststoffformteils zumindest teilweise abbildenden Kavität des Spritzgießwerkzeugs;
• (b) Injektion einer druckbeaufschlagten Flüssigkeit über einen ersten Anschnitt des Spritzgießwerkzeugs in die eingebrachte Kunststoffschmelze, so dass durch die eindringende Flüssigkeit ein Hohlkanal innerhalb der Schmelze geformt und die überschüssige Kunststoffschmelze zusammen mit der Flüssigkeit über einen zweiten Anschnitt aus der Kavität in eine mit dieser verbundenen Nebenkavität abgeführt wird;
• (c) Ausbringung der Restflüssigkeit aus der Kavität;
• (d) Verfestigenlassen der Kunststoffschmelze bis zur Bildung eines festen Formteils;
• (e) Entformen des Formteils aus der Kavität des Spritzgießwerkzeugs.

According to the invention, this object is achieved by means of a method with the features mentioned in claim 1 and by means of a plastic molding with the features mentioned in claim 9. The inventive method comprises the following steps:

• (A) injection of a plastic melt in a contour of the molded plastic part at least partially imaging cavity of the injection mold;
• (B) injection of a pressurized liquid via a first gate of the injection molding in the introduced plastic melt, so that formed by the penetrating liquid, a hollow channel within the melt and the excess plastic melt together with the liquid via a second gate from the cavity into a connected thereto Nebenkavität is discharged;
• (c) applying the residual liquid from the cavity;
• (d) allowing the plastic melt to solidify until a solid molding is formed;
• (E) removal of the molding from the cavity of the injection mold.

Thereby, that the exhaustion the plastic melt and the liquid is substantially tangential to the flow direction the plastic melt and the liquid in the forming hollow channel takes place, is advantageously a low-deflection, smooth movement the fluids reached in continuation of the flow direction. The Creation of flow resistances Turbulence is suppressed. Under a substantially tangential discharge here is a diversion the flow direction around 30 °, preferably at 10 °, and / or under a radius of curvature of 10 cm, preferably 50 cm, understood.

By the use of a liquid, in particular of water, as the injection medium, those already mentioned above Advantages over the Use of gas can be used. Especially to be highlighted the increased cooling effect of the medium that increased melt displacement in the cavity, which is ensured by the incompressibility of the water as well as the lower process costs due to the low Provisioning costs for Water.

In A preferred embodiment of the invention is provided that the Injection of the plastic melt and injection of the pressurized fluid essentially at opposite ends of the forming hollow channel respectively. By this countercurrent principle is an advantageous Pressure distribution generated in the hollow channel to be formed.

Especially It is preferred that pressurized liquid is water at a pressure of 20 to 30 bar is used. In particular, it is preferred that the Step (b) is applied twice, with the liquid is applied at the second application with a higher pressure than at the first application (when using water as injection fluid a pressure of more than 30 bar is used). Through this rinsing of the Hollow channels will be a smoothing the inner surface of the hollow channel reaches.

In a further preferred embodiment of the invention is provided that the plastic while or expelled to foam before the injection. By such measure will be the filling the plastic in deeper, narrower areas of the cavity of the injection mold, which for example for the formation of ribs are facilitated, since the viscosity of the plastic on the one hand is lowered, so that the plastic lighter on the other hand, no complete filling of the Tool with plastic is required because existing in the plastic Gas particles expand and the plastic in the cavities of the Driven tools.

Further preferred embodiments of the invention will become apparent from the others, in the subclaims mentioned features.

The Invention will be described below in embodiments with reference to FIG associated Drawings closer explained. Show it:

1 schematically the flow directions of water and plastic / polymer in the application of the method according to the invention to a non-rectilinear component;

2 a perspective view of a window frame in the tailgate of a motor vehicle;

3 a center piece of the window frame according to 2 ;

4 a section through a side legs of the window frame (sectional plane S in 2 );

5 a section through a roof trim strip of the form of a motor vehicle.

1 shows schematically the flow direction of water and plastic when applying the method according to the invention to a non-linear component 100 , One, the contour of a plastic molding to be produced at least partially imaging, cavity 100 is arranged in an injection mold such that the largest part of the hollow channel to be formed is substantially vertical. The produced plastic molding may have a length of up to 2 m. Plastic, typically a rheologically suitable polymer, is injected into the cavity at a lower region of the injection molding tool with the aid of an injection unit, not shown, so that the plastic melt in the cavity from below parallel to the flow direction 12 rises.

In a second process step is over a first gate 14 that is in the upper part of the cavity 100 injected, injected with a pressure of 20 to 30 bar of pressurized water. The still molten polymer mass in the core of the cavity 100 is made with the help of water through a forming flushing channel 16 along the flow direction 18 , which of the flow direction 12 is opposite, expelled. In the lower part of the cavity is a second cut 20 provided, through which the water runs out together with the excess polymer in a Nebenkavität not shown. As in 1 illustrated, it is provided that the application of the water and the polymer is substantially tangential, that is, without significant change in direction to the forming or already formed hollow channel occurs. After carrying out the method step described, the water injection process is repeated at a higher pressure (30 bar) in order to increase the rinsing action. With the described method, reductions of the molded part by about 10% and reductions in the residual wall thickness in the hollow chamber area to less than 4 mm can be achieved. Compared with the gas injection technique, the cycle time in production can be reduced by 10 to 15%. In cavities, which has a more complicated three-dimensional structure than the schematic model in 1 have, becomes the channel 16 used before the injection with water as a cold channel for filling the cavity with plastic in order to avoid the problem of long flow paths in such moldings.

2 shows a perspective view of a window frame in the tailgate of a motor vehicle 200 which is a center piece 22 and two side legs 24 and in which the method according to the invention can be successfully used to increase the rigidity. In such a complicated structure, which is deformed undercut and three-dimensional, the insertion of ribs to increase the rigidity is difficult because it is difficult to find an ideal Entformungsrichtung for separating the plastic molded part of injection molding.

3 shows a centerpiece of the in 2 window frame shown. In order to increase the rigidity of the component and to stop the delay during the cooling of the molding, ribs are set. For relatively tall ribs 26 is disadvantageous that the distortion increases in a direction perpendicular to the ribs and a kind of garland formation 28 leads. Thus, it is attempted to provide as few ribs as possible in the construction of the plastic molding to the ripple generated by them 28 to suppress. By the insertion of a hollow channel produced using the method according to the invention 16 becomes an essential part of the delay in the direction of the hollow channel 16 braked and the additional necessary ribs can be designed less high.

4 shows a section through a side legs of the window frame (sectional plane S in 2 ). On one side of the side leg 24 is an additional rib supporting the stiffness 30 provided, wherein the rib height expires against the edge of the component, so that the resistance of the rib decreases towards the edge. On the opposite side of the side leg of the hollow channel runs 16 , In 4 For comparison, the wall thicknesses are shown, which result from the use of the gas injection technique according to the prior art 32 and by the use of the water injection technique using the method of the invention 34 let produce. By using the method according to the invention thinner-walled parts are obtained, which produce less distortion in the manufactured component according to the principle of constant wall thicknesses. In addition, because of the thinner wall thickness, the injected water can dissipate heat more quickly, allowing the plastic to cool faster, resulting in a shorter cycle time.

In a complicated component such as the illustrated window frame of a tailgate 200 will fill the entire cavity 100 greatly facilitated to the required deep, narrow cavities when the polymer is foamed or provided with propellant, since it has a lower viscosity on the one hand, on the other hand by the expansion of the trapped gas particles in different directions of the cavity 100 is urged. In the filling section for the polymer while nitrogen, CO ₂ or a blowing agent is added. Typically, the gas is injected into the screw channel or into the area in front of the screw tip.

In the interior of a motor vehicle, the equipment of plastic parts with a textile surface is becoming increasingly important. The cheapest method for producing such components is to inject the textile decor directly with plastic. Even with such components ribbing and stiffening is often necessary. Since the plastic and the textile-reinforced layer of the view contract differently when cooling, here is also discussed above garland formation 28 observed. By creating a hollow channel 16 using the method according to the invention also this problem is avoided.

5 shows schematically the section through one with a felt insert 40 provided Dachabschlussleiste the form of a motor vehicle, in which a circumferential rib 38 using the method according to the invention as a hollow channel 16 is trained. The rigidity of the component is ensured by the use of polymers such as ABS / PC, PBTP or PP with or without filler. In addition, if the polymer can be processed foamed, a weight reduction and a lower compressive stress of the textile can be achieved.

100

Cavity of the injection mold

200

window frame in the tailgate of a motor vehicle

10

injection of the plastic / polymer

12

flow direction Plastic / polymer

14

first Bleed / water injection

16

hollow channel

18

flow direction water

20

second Gating / spreading water and plastic

22

centerpiece

24

side leg

26

height rib

28

Garlands Education / wave formation

30

rib

32

Wall thickness GIT

34

Wall thickness WIT

36

Entformrichtung

38

rib

40

Filzeinlage

S

cutting plane

Claims (10)

Process for the production of plastic moldings with at least one hollow channel by the injection molding process, with the following process steps: (a) introduction of a plastic melt into a cavity which at least partially depicts a contour of the plastic molding to be produced ( 100 ) of an injection mold; (b) injecting a pressurized fluid over a first gate ( 14 ) of the injection mold in the introduced plastic melt, so that by the penetrating liquid a hollow channel ( 16 ) formed within the melt and the excess plastic melt together with the liquid via a second gate ( 20 ) is discharged from the cavity into a secondary cavity connected thereto; (c) applying the residual liquid from the cavity; (d) allowing the plastic melt to solidify until a solid molding is formed; (E) demolding of the molded part from the cavity of the injection mold, characterized in that the discharge of the plastic melt and the liquid substantially tangentially to the flow direction of the plastic melt and the liquid in the forming hollow channel ( 16 ) he follows. A method according to claim 1, characterized in that the injection of the plastic melt and the injection of the pressurized liquid substantially at opposite ends of the forming hollow channel ( 16 ) respectively. Method according to one of the preceding claims, characterized in that water is used as the pressurized fluid. Method according to one of the preceding claims, characterized characterized in that a fluid pressure from 20 to 30 bar is applied. Method according to one of the preceding claims, characterized characterized in that step (b) is applied twice, wherein the liquid is applied at the second application with a higher pressure than at the first application. Method according to claim 5, characterized in that that in the second application a fluid pressure of more than 30 bar is applied. Method according to one of the preceding claims, characterized characterized in that the plastic during or before the injection is raised to foam. Method according to one of the preceding claims, characterized in that prior to the application of step (a) a textile layer into the cavity of the injection mold ( 100 ) is inserted. Plastic molding with a non-linear hollow channel, manufactured according to a method according to one of the preceding claims. Plastic molding according to claim 9, characterized that to increase the stiffness ribs in appropriate areas of the plastic molding are provided.