DE202005005475U1 - Thermoformable sandwich composite workpiece for molding three-dimensional products comprises core, fiber reinforced resin and film facing layers enclosed in porous evacuation layers and covering films - Google Patents

Abstract

The sandwich construction comprises a preform stack with a core layer(5), fiber reinforced unreacted resin layers(2) and film facing layers(3). The sandwich is enclosed by porous evacuation layers(4) and sealed from the outer atmosphere by covering layers(1). Air is evacuated from the sandwich preform before pressing so that it forms more easily on the molding tool and the resin is cured while the preform is in contact with the tool surface. The closed cell core material(5) stiffens the sandwich construction before it is formed onto the tool. Use of an open pored fleece or fabric with suitable extension for air evacuation of the sandwich allows good drapability over the molding tool. Forming is performed at an elevated temperature which permits easy forming of the thermoplastic parts, but does not initiate premature gelation of the resin. An independent claim is included for the heating and forming equipment which also has the capability to form the workpiece against a molding tool face using positive pressure on the outside of the workpiece.

Description

The Invention relates to a workpiece and device for providing this with the features of the preamble of the main claim and an apparatus for carrying out the Process.

to Forming of composite materials (sandwiches or composites) is designed the sandwich gravure process. It allows shaping in one Step.

The Processing of composites based on reactive resins as a matrix and a structural material since the 50s known in the 20th century. It will be a structural material with filled a reaction resin and hardened. The resulting composite material combines the material properties both materials. To have a structure, mostly in fiber form. Only fiber materials will be considered below. The matrix takes over in this composite the function of connecting the fibers in brings with it its mechanical properties in the composite material one. Often fulfilled the matrix the function, the toughness of the composite material.

to Production of components made of composite materials is the material applied in layers in a mold. There are several possibilities for that. The The easiest way is to apply the layers by hand and with a roller another push and air pockets to remove.

Of Furthermore, the structure can be vacuum-tightly closed with a film / non-woven construction become. Upon application of a vacuum, the conditions of compression and evacuating.

industrial However, methods with forms consisting of matrix are more likely to be used and Patritze, where in a press the necessary contact pressure is generated. Especially for large volume components Autoclave technology is a common method in which the construction in a pressure vessel in addition to the vacuum with an external pressure is charged.

Alles comply with these procedures but not all applications, solved with fiber composites can be. So you put in a monetary Considering that all hand laminating while low investment require, but require high personnel expenses. In addition, many and expensive disposable materials used to be a plane Concern of the vacuum and a separation of the resin from the vacuum structure to ensure.

Machinery Procedures require very high investments and are inflexible. For special use cases it is always necessary to produce small quantities of a component, with a reproducible quality and low investment costs. If this component still stiffened by a laminated core material should be, and is contoured, none of the said manufacturing processes be applied.

The Task is for to create a method for this purpose. Doe solution according to the invention exists in the method mentioned in claim 1. The dependent claims give advantageous embodiments again.

The Sandwich deep-drawing method according to the invention Fulfills the quality claim, because the laminate - a Thermoforming foil equal - per Vacuum over one Form is pulled. It is inexpensive, since the machine Effort "in Holds boundaries ".

It keeps coming out with very little disposable material and as a shape only one mold half required. In the sandwich gravure process, the laminate buildup becomes on the visual and non-viewing side with a thermoplastic Slide complements. Adhesion problems are not eliminated in this case, they are wanted. To form the laminate, it is between two laid elastic films, evacuated and deep-drawn like a film. Alternatively, the laminate can also by means of pressure chamber to the mold be pressed.

embodiments The invention are illustrated in the drawings and are in following closer described. Showing:

1 the schematic structure of the layers of a sandwich according to the invention,

2 the compacted sandwich,

3 a contoured mold used for the manufacture (by way of example),

4 the manufacturing plant (side view, schematic),

5 the manufacturing plant before forming (front view, schematic),

6 the manufacturing plant after forming (front view, schematic), and

7 the finished component (by way of example).

The sandwich ( 1 ) consists of the core 5 , the cover laminates 4 and the cover sheet 3 , As a core 5 a thermoplastic Airex rigid foam serves it however, tests were also carried out with other foams and honeycomb cores made of phenolic resin-reinforced aramid fiber paper. Depending on the desired degree of deformation, all cores used in composite construction can be used. As a cover laminate 4 serves a glass fiber / epoxy laminate with a body bond. The use of other fibers, such as aramid or carbon fiber, other resins, such as polyester or phenolic resins or other types of tissue, jelly or tapes is feasible and partially also tested.

The sandwich is made of a preferably very open-pored nonwoven 2 enclosed or at least at the points covered with fleece, where it may be manufacturing problems to problems during vacuum build-up. On the connection of the fleece inserts is to be respected. The complete structure is now on top and bottom with a permanently elastic film 1 completed against the environment. It is advisable to use a silicone film as restoring forces, adhesion behavior and heat resistance are unequaled for such a film.

Other permanently elastic films can used when e.g. the stretching of the silicone is not sufficient is. The strenght the film is in the present case 1 mm. Lower film thicknesses have the advantage of lower restoring force, the durability suffers. For stronger ones Slides behave the other way around.

The complete layer structure is in 1 shown schematically.

Form 6 ( 3 ) must fulfill the following tasks. It must withstand the working pressure, the processing temperature of the sandwich and, as it is in the evacuated space, it must be either porous or with vacuum holes 7 be provided.

To form and harden the sandwich is a production plant ( 4 . 5 and 6 ) on the one hand a film thermoforming according to the sandwich pressed or sucked on the mold, on the other hand acts as a curing oven and the sandwich after molding under the influence of temperature and maintaining the vacuum is allowed to harden. The production plant ( 4 ) consists of a heating chamber 8th and a molding chamber 9 , Both are using heaters 10 heated. Both chambers are thermally separated from each other and the temperatures can be controlled separately.

The clamping frame 11 , which picks up the sandwich and clamps it vacuum-tight, is on roller rails between both chambers 8th . 9 to move. The tool 6 will be on the tool table 13 attached. This one is with a vacuum hole 18 provided to the tool and with the vacuum unit 17 connected. The tool table is framed with a sealing lip 15 , This is intended to seal the tool table to the clamping frame.

The execution the sealing lip is variable. Advisable is an inflatable silicone tube seal an approximate Reach vacuum. The tool table is vertically movable 19 and dives into the tenter with the tool. He seals that Vacuum space by being driven against the clamping frame.

By applying the vacuum 17 the sandwich is sucked to the mold. In this position, it is hardened and then demolded. Alternatively, or for better shaping in difficult contours, the sandwich can also be pre-blown, ie it is pre-expanded either from below by air pressure, or from above by negative pressure. In this case can also be formed by pressure reversal.

In order for the sandwich to behave like a foil, it is evacuated before the process. This is about the vacuum connection 12 possible. Crucial for the whole process is the right choice of pressure in the sandwich. At ambient pressure (1 bar) no adhesion of the sandwich is achieved, but the individual layers slide very well on each other. With vacuum (0 bar) no more gliding is possible, since the problem of this layer structure is that not all materials behave the same way.

Some Form very well (the laminate), others hardly (the core, depending on the thick). As a result, wrinkles may form on the surface. The right attitude must be tested become. In tests, absolute pressures between 0.2 and 0.9 bar as applicable, depending on the shape and laminate construction.

Further essential to the process is the right choice of temperatures and times. The heating chamber 8th serves to preheat the sandwich. In it, the sandwich is heated to a temperature at which the cover films 3 and the core 5 mold, the reaction resin laminate 4 but does not begin to respond. For the right temperature - time ratio, the choice of materials is crucial.

In the preferred materials used (ABS film, epoxy resin (cold curing) and Airex foam), the range of temperatures for preheating between 130 and 180 ° C for 50 to 120 sec moves. A longer residence time leads to better heating of the sandwich, but also leads rather to a coling of the foam core. The forming furnace is less heated. Here is the Temperature accelerate the reaction of the resin.

The choice of the right temperature is also dependent on the resin used. For the cold-curing epoxy resin used, a temperature above 90 ° C is not recommended to avoid blistering. The lower the temperature, the longer the curing process. At set 70 ° C, the reaction resin is cured after 90 minutes as far as possible and the component ( 7 ) can be removed from the mold.

Claims (7)

workpiece from a three-dimensional under pressure profiled plastic sandwich and / or plastic laminates characterized by a sandwich construction from a stack of unreacted fleece / plastic, core and foil layers with two cover sheets that seal the stack to the atmosphere, with under the Cover sheets lying evacuation layers for forwarding a uniform negative pressure in the interior of the while pressing the sandwich construction on a mold until the hardening of the Workpiece. Workpiece according to claim 1, characterized in that the sandwich construction with a closed-pored core material ( 5 ) is stiffened prior to application to the mold. workpiece according to claim 1 or 2, characterized in that as a cover sheet a thermoplastic film is provided. workpiece according to one of the preceding claims, characterized by a for evacuation of the stack of layers interposed open-pored Fleece or fabric, which is a for the shaping has the necessary form of stretching required form. workpiece according to one of the preceding claims, characterized that the Layer structure at such an elevated Temperature is shaped that the thermoplastic parts are thermoplastic molded without the reaction resin over the Gelpunkt to have brought. Device for creating the workpiece with a Device for forming by overpressure from outside the sealing film of the layer structure pressure exerting against a mold. Apparatus according to claim 6, characterized by a means of air pressure equalization on the mold.