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Vacuum casting (VC) of reactive polymer resins in silicone molds is one of the oldest rapid tooling methods. It is widely used in the industry for prototype and small‐series production of thermoset plastic parts. Despite its widespread use, its scientific exploration is still scarce compared to other prototyping methods, such as three‐dimensional (3D) printing. Compared to conventional 3D printing methods, a wide range of excellent material properties can be achieved, making it well suited for the production of functional prototypes and even final products. The properties of the thermosets are comparable to those of injection molding in terms of viable shapes, mold fidelity, and material properties. However, due to the high cycle time and limited service life of the molds, VC is rarely utilized for mid‐ or large‐series production. Here, we provide a comprehensive overview of the state of the art and recent advances in the field. The review also provides a detailed technical introduction to the mold production, the process flow, and the materials used. A particular focus is on the key challenges facing industrial‐scale VC today—how to reduce cycle time, and how to increase mold service life? [ABSTRACT FROM AUTHOR]

Vacuum casting of polyurethane (PUR) in silicone molds is used industrially for the production of prototypes and small series as well as in various noncommercial research areas. This includes the reproduction of archeological findings, biological samples or electronic devices. In this study, the authors investigate the molding accuracy of different commercial silicones and PUR casting resins both on microscopic and macroscopic scales. For this, they used a variety of master models to generate silicone rubber casting molds. The resulting PUR castings are investigated by helium ion microscopy, confocal laser scanning microscopy, and optical 3D‐scanning. [ABSTRACT FROM AUTHOR]

Vacuum casting of polyurethane in silicone molds is a widely used method for prototype replication and holds great potential for application in small batch production. Products produced in this way offer extremely good shape accuracy even in the nanometer range and high surface quality, as well as flexible material properties that are convenient for serial production. In this work, we present a new method for increasing the feasible output of silicone casting molds in vacuum casting processes. By supplementation of polyamide 12 powder, which is a waste product of the selective laser sintering process, to the silicone rubber the maximum output of the casting molds could be increased by up to 38.5% while the amount of new silicone used has been substituted by up to 20%. Both generic silicone samples and representative silicone molds have shown that with increasing polyamide content, aging characteristics decrease as the output increases. The improvement was quantified by comparative weight, hardness and thermogravimetric measurements. As surface energy and roughness measurements as well as extensive casting experiments have shown, the silicone surface and thus the product surface remains unimpaired. [ABSTRACT FROM AUTHOR]

We present an in-depth investigation of the aging effects in silicone molds for vacuum casting processes. Their lifetime is limited to a few production cycles due to contamination with the diisocyanate component of polyurethane casting materials. Using thermogravimetric analysis measurements, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and helium-ion-microscopy the chemical and physical mechanisms of the aging process have been identified. It has been shown that a diffusion process of diisocyanate into the cavity surface leads to the formation of interpenetrating polymer networks of polyurea derivatives in silicone rubber. This has been proven by extracting and analyzing polyurea of low molecular weights from the silicone. [ABSTRACT FROM AUTHOR]