In the RTM (resin transfer molding) manufacturing process, the required shapes (1) are cut from the dry FRP textiles on CNC cutting tables. A gripper picks the sensitive workpieces from the cutter and sets them on a table or in a magazine. In some cases, the cut textiles are stored temporarily before further processing and doing the “lay-up”. In doing so, different layers are placed on top of each other in a defined order to create a specific layer structure (2). Depending on the process, the cut pieces are then heated and manually or automatically draped to create a preform whose shape resembles the final product (3-5).
After preforming, the still porous, unstable, three-dimensional preform is taken out of the mold (6). Then, the preform is inserted into the RTM press. A mixture of resin and hardener is injected into the tool, and pressure and heat are applied to cure the workpiece (7). Once the workpiece is removed from the press (8), a finishing process (9) gives it its final shape. This usually takes place in a CNC milling machine or through water jet cutting.
As well as the RTM process, there are other similar manufacturing processes, such as wet pressing. Unlike the RTM procedure, the resin is applied before the actual pressing process, which means that the stack is pressed and cured in a wet state.
Securely gripping porous textiles
The textiles are extremely sensitive; it is essential that the fiber orientation is not influence by the handling. Schmalz recommends using the composite gripper SCG or the needle gripper SNG for this handling step. 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 on both sides of the grippers move in opposite directions for generating the necessary tension to hold the textile securely.
Removing and stacking cured workpieces
The cured, often still hot workpieces have to be gripped securely during removal from the RTM tool, 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 painting processes. If FRP components are to be coated at a later stage, this eliminates possible surface imperfections.