Composites Textile

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Schmalz Inc.
5850 Oak Forest Drive
Raleigh NC 27616
United States of America

Tel. +1 919 713-0880
Fax +1 919 713-0883
schmalz@schmalz.us
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Glass fibers and carbon fibers are the main fiber materials used for reinforced polymers. Carbon fiber reinforced polymer (CFRP) materials have an even better ratio between strength and weight. This material is primarily used in the automotive, airline and wind energy industries, but is also used in sporting goods, construction and other sectors.

The manufacturing processes for fiber composite workpieces place high demands on the vacuum technology. The alignment of the individual fibers affects the mechanical properties (stability and stiffness) of the workpieces, so it’s very important that the semi-finished products are handled gently to avoid affecting the fiber orientation.

Documentation

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Manufacturing Processes

RTM process

In the RTM (resin transfer molding) manufacturing process, the dry textiles are cut into the desired shapes by means of a CNC cutting machine. A gripper removes the sensitive workpieces from the cutter table and places them on a table or in a depot. Depending on the process, the cut pieces are either manually or automatically draped to create a preform whose shape resembles the final product.

After preforming, the still porous, unstable, three-dimensional preform is removed from the mold. Then, the preform is infused and cured in the actual RTM press. For this purpose, liquid resin is injected into the mold, and pressure and heat are applied to cure the workpiece. Once the workpiece is removed from the press, a finishing process gives it its final shape. Finishing is usually performed by water jet cutting or in a CNC machining center.

Besides the RTM process there are numerous other manufacturing processes for FRP materials e.g. hot-pressing. Some of them are using semi-finished products like prepregs or organo sheets. Depending on the specific process this requires the handling of material that has been heated up to the melting point of up to 300C which can be very challenging not only due to the temperature but also because of the material changing its properties like losing the inherent stability or increasing tackiness.

Requirements and Vacuum Solutions in the Composite Textile Sector

Requirements for Vacuum Technology

Securely gripping porous textiles
The textiles are extremely fragile; it is essential that the fiber orientation is not affected by handling. Schmalz recommends using the composite gripper SCG or the needle gripper SNG for this step in handling. The composite gripper is a ready-to-connect gripping unit with integrated vacuum generation, and ensures gentle gripping of sensitive workpieces. The needle gripper SNG penetrates the workpiece with up to 24 needles. The needles are arranged to move in opposite directions to generate the necessary clamping force to hold the cloth securely.

Handling heated semi-finished products, e.g. organo sheets
The needle gripper SNG-V-HT or suction cups are used to load the presses with semi-finished products with temperatures of up to 200°C. It is essential that the suction cups be heat-resistant. Schmalz offers special suction cup material like HT1, HT2 or FPM to meet this requirement. The type SGPN flat suction cup has a flat, elongated sealing lip and a support installed in the suction cup. This design prevents the suction cup from “drawing in” the material or deforming the material.

Clamping hardened components
The last steps in processing give the workpiece its final shape. The workpieces must be held securely for processing in CNC machining centers or water jet cutting systems. These free-form surfaces are more difficult to process and present new challenges for clamping technology in particular. Schmalz’ newly developed vacuum clamping systems, basic holding fixture and advanced holding fixture, are used to clamp complex components for CNC machining in a simple way. Depending on the design, the component is clamped either manually or automatically.

Removing and stacking hardened components
The hardened, often still hot components have to be gripped securely during removal from the RTM mold, without leaving marks. Suction cups made of HT1 are ideal for this process. These suction cups are heat-resistant and free of substances that contain silicone or could impair surface wetting. If CFRP components are to be coated at a later stage, this rules out the possibility of surface imperfections.