A new process, called thermoset in-mold forming, for combining thermoset master forming and thermoset forming in one mold is in development. A pre-impregnated continuous-fiber reinforced sheet based on epoxy (prepreg) is formed in the injection molding machine, followed by instantaneous overmolding of a short-fiber reinforced epoxy compound in one step. Compared with conventional processes in which thermoset injection molding, prepreg compression molding, and hence curing of the materials are separated, the new process allows for the combination in one step and simultaneous curing of both components. The result is a hybrid component, which features a continuous-fiber reinforced part for higher mechanical performance and a short-fiber reinforced part with high design freedom for integration of additional functions. For a successful combination of both materials in one process, it is essential to investigate the bond strength between them in relation to the processing parameters and their influence on the degree of cure. This paper analyzes the influence of the mold temperature in this process on curing degree, bond strength, and the processing viscosity.
Integrative manufacturing of thermoset injection molding components with continuous fiber-reinforcement A new process for the manufacturing of thermoset injection molding components with local continuous fiber-reinforcement in one shot has been developed. "Dry" textiles or continuous fibers are inserted into the cavity of an injection mold. Subsequently, the continuous fibers are impregnated and embedded into a short-fiber-reinforced thermoset molding compound by the following injection molding process. In this paper, the technical feasibility of the process is proven by the analyses of the wettability and impregnability of dry carbon-rovings depending on the mold temperature. Furthermore, mechanical tests show that by this new process the integration of continuous fibers into injection molded components improves the mechanical properties if they are impregnated completely. Integrative Herstellung von endlosfaserverstärkten Duroplastbauteilen im Spritzguss Es wird ein neuer Prozess zur Herstellung von duroplastischen Spritzgussteilen mit lokaler Endlosfaserverstärkung in einem Spritzgießzyklus entwickelt. Hierfür werden "trockene" Textilien oder Endlosfasern in die Kavität eines Spritzgießwerkzeuges eingelegt. Anschließend werden die Endlosfasern mittels einer kurzfaserverstärkten duroplastischen Formmasse imprägniert und eingebettet. In dieser Veröffentlichung wird die technische Machbarkeit des Verfahrens durch die Analyse der Benetzbarkeit und Imprägnierbarkeit von trockenen Carbon-Rovings in Abhängigkeit der Werkzeugtemperatur nachgewiesen. Darüber hinaus zeigen mechanische Tests, dass durch dieses neue Verfahren, dass die Integration von Endlosfasern in Spritzgussteilen deren mechanische Eigenschaften verbessern, sofern diese vollständig imprägniert sind.
In this study, epoxy molding compounds are combined with fast-curing epoxy prepregs in thermoset injection molding using a new integrative process. The combination is carried out under the varied parameters of mold temperatures and curing times, which are dominant factors in thermoset processing. The focus of the investigations is the bond strength in the interface resulting from these parameters, as the interface is known as the weak point of hybrid components. To identify causes for possible increases and decreases of the bond strength, additional rheological and thermoanalytical analyses are done under near-process conditions. The influence of prepreg pre-crosslinking, a function of the mold temperature, is also described by means of additional tests in which specific pre-crosslinking of the prepreg is adjusted by the temperature storage and then functionalized in integrative process combination. The aim of the study is to identify and understand initial process limits for the integrative process combination for a potential process window.
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