Design Of Rheological Properties Of Liquid Silicone Rubber For 3D Printing And Its Application Research

Liquid silicone rubber(LSR)is a kind of silicone elastomer whose main chain is composed of alternating silicon and oxygen atoms,and organic functional groups are attached to its side chains.Its molecular chain structure is characterized by organic and inorganic hybridization,which gives it excellent high and low temperature resistance,aging resistance and biocompatibility.They are widely used in aerospace,automotive manufacturing,electronic devices and biomedical applications.However,when faced with complex use environments,great demands are placed on the material properties and molding methods.Traditional LSR molding technologies including molding,extrusion,and injection have the advantages of good molding quality and high efficiency,but also have the disadvantages of high mold manufacturing cost and difficulty in manufacturing complex hollow structure parts.Therefore,it is of great importance to use advanced molding technology to effectively solve the difficult problems of traditional molding methods for high precision,complex structure and customized design.3D printing technology,as one of the core technologies of the 3rd industrial revolution,can meet the requirements of the future manufacturing industry for rapid,personalized and integrated.Compared with traditional molding methods,3D printing has the advantages of high precision and customizable molding of complex structures.Material is the material basis of 3D printing,and it is also the technical bottleneck that limits the further development of 3D printing.Direct ink writing(DIW)is one of the 3D printing methods,which requires the printing material to have suitable rheological properties.These include significant shear thinning,rapid viscosity recovery,high yield stress,and other rheological properties.However,LSR,as a Newtonian fluid,has rheological properties that do not meet the printing requirements.Therefore,most of the current liquid silicone rubbers cannot be directly used for direct ink writing.Therefore,based on the methyl vinyl polysiloxane system,this thesis intends to make the liquid silicone rubber meet the rheological requirements of DIW through rheological property design.On this basis,silicone rubber foam with different structures was constructed by DIW technology,and its micromorphology,friction properties,friction mechanism,mechanical properties,etc.were studied.The main research content includes the following three parts:(1)Design of rheological properties of liquid silicone rubber ink for 3D printing and its printability study.The silicone inks were prepared by using methyl vinyl polysiloxane as the matrix and hydrophilic nano-silica with different mass fractions as thixotropic agents.The variation patterns of viscosity,modulus and yield stress of silicone inks with different ratios were investigated using a rotational rheometer.The curing parameters of the inks were determined by IR and DSC: 150℃ and 1 h.The rheological properties,printability and mechanical properties of several formulations were comprehensively compared,and the ink with 3 wt% of hydrophilic nano-silica was selected as the basis for subsequent experiments and verified to have excellent printability.(2)3D printing of silicone rubber foams with different surface structures and their static friction properties were investigated.Silicone rubber foams with different surface structures were constructed by direct ink writing using the above-designed ink.The effects of normal load FN,microstructure orientation,and contact area on the frictional properties of 3D printed silicone rubber foams were investigated.The results show that the contact area of the samples is affected by the microstructure orientation of the surface,which affects the maximum static friction of the samples.Moreover,the maximum static friction increases with the increase of normal load for the same sample under different normal loads.The friction coefficient decreases with the increase of normal load.In addition,the effect of temperature on friction was also investigated.The results showed that the lower the temperature,the higher the coefficient of friction of silicone rubber foam.Finally,the friction mechanism was further investigated by equation derivation and curve fitting.The results show that for elastomer foam,the friction properties show obvious bulk effects in addition to surface effects.(3)Preparation and mechanical properties of 3D printed sandwich-structured silicone rubber foams.The sandwich structure silicone rubber foams with different densities were constructed by direct ink writing.The results show that for the sandwich foam with the same structure,the strain under the same stress gradually decreases and the stress plateau gradually disappears when the internal line spacing decreases.And the maximum strain value of the non-cored structure is larger than that of the sandwich structure at the same internal line pitch.The stress relaxation results show that the stress relaxation rate of SC structure basically fluctuates around 23% and does not change with the change of internal line distance;the stress relaxation rate of FCT structure decreases from 24% to 16% with the increase of internal line distance of sandwich structure.