| For the past few years, structure design and motion control of precision machine tool in our country has developed rapidly, but most of the base components are still made of cast iron or steel welding structure, the preparation period is longer, vibration attenuation property is close to the limit and the environmental pollution in production process is serious. Research and development of materials with excellent damping performance has important theoretical and engineering practical significance in promoting technical progress of the engineering industry.Resin mineral composite (RMC) is composed of granite aggregate, organic resin system and some other auxiliary components that it can be casting at room temperature in conjunction with precision mold and embedded part designing technology. RMC is suitable to produce the base components of precision machine tool, such as bed, base and so on. There is no high temperature sintering in its productive process, which is basically no pollution to the environment.Compared with cast iron, RMC has better damping and vibration attenuation property. However, the strength of RMC is lower and the thermal expansion property is worse that its application is restricted to some extent, In this article, carbon fiber is used in cooperate with the gradation optimization of aggregate to reinforce RMC. How to improve the strength and thermal expansion performance on the basis of high damping property is the main research emphasis. The contents include the following:①Component and preparation optimization of RMC;②Fractal aggregate gradation and fiber reinforcing mechanism of RMC;③Energy loss mechanism and damping characterization of RMC;④Carbon fiber’s block expansion mechanism and thermal expansion property of RMC;⑤Structure optimization of RMC precision lathe bed.Based on the property of components and their reaction mechanism, resin system, aggregate and auxiliary components are optimized, the basic ratio of each component is obtained combined with the macroscopic characterization of RMC. Negative pressure cylinder model of bubble in RMC is established, the preparation and curing process is optimized according to the long-term behavior analysis, which can effectively reduce the preparation period. The compressive strength in the seventh day is already reached149.92MPa.Statistical analysis and simplification are used, dispersion and stacking sequence of aggregates with different size are overall considered, the final dimension of screen holes are proposed based on the particle filling theory. Fractal theory is used to get a more accurate formula and gradation evaluation parameter. Particle flow simulation and image process method are used to identify the tendency of porosity, the simulation results are basically identical with the actually measured value that it can be used as a verification element in the follow-up gradation design. Stress transfer model of contiguous aggregates is established and compressive strength test is used to validate the aforementioned assumptions. Experimental results show that with the increase of the maximum aggregate size, skeleton strength increases and resin consumption reduced, internal defecs and micro cracks in single aggregate have more influence to the strength of RMC. Stress transmission mechanism of carbon fiber is systematically researched based on the shear lag theory, stress redistribution model under the fiber breakage or interface debonding condition are established respectively too, the optimal dosage of carbon fiber is acquired combined with the experimental research.Effective intrinsic and interfacial damping factor is obtained based on the energy dissipation mechanism of viscoelastic materials, the fiber’s direction coefficient is introduced and the model of energy loss mechanism is established. Mechanism of damping production between resin, aggregate, reinforcing fiber and their interfaces are analyzed detailedly, the energy dissipation formula of micro interface slip is deduced, which has important influence to the damping property. Single factor experiments are used to get the influence of component, aggregate gradation and fiber’s parameter to the damping ratio. Compared to the other factors, intrinsic damping of resin plays the most important role in vibration attenuation. The maximum damping ratio is about ten times the HT200cast iron, reasonable fiber dosage and interface control can further improve the damping performance of RMC, but there also need to avoid the fibers’winding cluster phenomenon.For the characteristic that carbon fibers have negative thermal expansion property in room temperature condition, its block-expansion model in RMC is established. In the warming process, carbon fiber is under tensile stress and RMC is under compressive stress, interface mismatch stress is generated, which can restrict the thermal expansion of RMC. The basic principle of damage mechanics is used to research the crack production and extension between aggregate, carbon fiber and resin, reasonable explanation is conducted to the destruction phenomenon under heat effect. Combined with the glass state temperature of resin, average thermal expansion coefficient in80℃is used as an evaluation parameter. Finally, the influence of each component is researched by experimental method, the optimal expansion coefficient of RMC is about9.627x10-6/℃.Simplified three-dimensional model of typical precision lathe bed is established in Pro/E and imported into FEA software. The corresponding model definition is proceeded according to the parameter of cast iron and RMC. All the bed stress distribution under static and dynamic condition are analyzed and calculated according to their actual working conditions, their final deformations are acquired too. According to the results, the deformation of RMC precision machining tool in X, Y and Z direction are all about3.5～3.6times that of cast iron, two corresponding structure optimization schemes are proposed and the corresponding deformation analysis and thermal-mechanical analysis are conducted in order to satisfy the stiffness requirement of the machine tool. Natural frequency of optimized RMC in each order are all higher than cast iron, the first and second order have a more obvious influence to the guide rail surface, which needs to cooperate with local reinforcement technology in practical application. |
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