尼龙及其复合粉末流动特性的实验研究与数值模拟

发布时间：2018-10-14 15:43

【摘要】：选择性激光烧结(Selective Laser Sintering,SLS)是增材制造技术的一个重要分支,通过逐层铺粉、逐层扫描烧结的方式来直接制造零件。铺粉作为SLS的中间工序,对烧结成形后成型件的质量有着至关重要的影响。铺出均匀、无缺陷且具有高密度的粉末层是进行良好烧结的前提条件之一,即粉体的流动性越好,粉体的铺展性能也就越好,后续的烧结质量也就越好。因此,开展粉体流动性影响因素的研究对粉体铺展性能、烧结质量有着至关重要的影响。本文以SLS的原料——尼龙粉末为研究对象,采用实验和数值仿真相结合的方法来研究尼龙粉末及碳纤维/尼龙复合粉末的流动性,探索环境温度、粉体自身物性参数以及添加剂等对粉末流动性的影响规律。具体内容包括以下几个方面:(1)通过超景深显微镜和激光粒度分析仪观测尼龙粉末的微观形貌与粒径分布,采用粉体综合测试仪和直剪仪测定表征尼龙粉末流动性的各项物理指标。实验研究并分析了粉末样本容量、粉末温度及添加剂对尼龙粉末流动性的影响。同时,通过实验研究了碳纤维含量、温度等对碳纤维/尼龙复合粉末流动性的影响规律。(2)在离散元软件PFC5.0中建立了粉体颗粒模型,选取滚动阻尼模型作为尼龙粉末颗粒间以及碳纤维/尼龙复合粉末颗粒间的接触模型,并在此接触模型的基础上,通过编写FISH函数加入范德华力。建立了尼龙粉末及复合粉末的休止角模型与直剪试验模型,并通过数值仿真与实验结果对比,校准了前述接触模型的各个微观参数。(3)通过离散元仿真分析了粒径、粒径分布、温度对尼龙粉末流动性的影响规律。仿真结果表明:单粒径分布与均匀分布的颗粒大小对尼龙粉末的流动性都有一定的影响,而呈高斯分布的尼龙颗粒大小对流动性的影响规律不明显。同时,对不同温度下的尼龙粉末的休止角进行仿真与实验对比,其结果吻合较好,从而进一步验证了选取的接触模型的可行性及接触参数的合理性。(4)根据对SLS铺粉时粉体所受的应力状态进行分析,设计并制作了与铺粉时具备相似应力状态的滚筒实验台,并通过实验研究分析了环境温度、滚筒转速及粉体填充率对尼龙粉末流动性的影响。结果表明,粉体填充率、环境温度以及滚筒转速过高都会不同程度地导致粉体流动性变弱。
[Abstract]:Selective laser sintering (Selective Laser Sintering,SLS) is an important branch of material augmentation technology. It can be directly manufactured by layer powder and layer by layer scanning sintering. As an intermediate process of SLS, powder laying plays an important role in the quality of sintered forming parts. The uniform, non-defective and high-density powder layer is one of the prerequisites for good sintering, that is, the better the fluidity of the powder, the better the spreading performance of the powder, and the better the subsequent sintering quality. Therefore, it is very important to study the influencing factors of powder fluidity on the properties of powder spreading and sintering quality. In this paper, the flow of nylon powder and carbon fiber / nylon composite powder were studied by using the method of experiment and numerical simulation, and the ambient temperature was explored, taking the raw material of SLS, nylon powder, as the research object, and the method of numerical simulation was used to study the fluidity of nylon powder and carbon fiber / nylon composite powder. The effect of physical parameters and additives on the fluidity of powder. The main contents are as follows: (1) the microstructure and particle size distribution of nylon powder were observed by means of hyperfield microscope and laser particle size analyzer. The physical indexes of nylon powder fluidity were measured by powder comprehensive testing instrument and direct shearing instrument. The effects of powder sample size, powder temperature and additives on the fluidity of nylon powder were studied and analyzed experimentally. At the same time, the effects of carbon fiber content and temperature on the fluidity of carbon fiber / nylon composite powder were studied experimentally. (2) the powder particle model was established in discrete element software PFC5.0. The rolling damping model is selected as the contact model between nylon powder particles and carbon fiber / nylon composite powder particles. On the basis of the contact model, the van der Waals force is added by writing the FISH function. The angle of repose model and the direct shear test model of nylon powder and composite powder were established, and the microscopic parameters of the contact model were calibrated by comparing the numerical simulation with the experimental results. (3) the particle size and particle size distribution were analyzed by discrete element simulation. The effect of temperature on the fluidity of nylon powder. The simulation results show that the particle size of single particle size distribution and uniform distribution have some influence on the flowability of nylon powder, while the size of nylon particle distributed by Gao Si has no obvious effect on the flow rate of nylon powder. At the same time, the simulation and experimental comparison of the angle of repose of nylon powder at different temperatures show that the results are in good agreement with each other. The feasibility of the selected contact model and the reasonableness of the contact parameters are further verified. (4) according to the analysis of the stress state of the powder when the powder is laid by SLS, a roller test bench with similar stress state to the powder laying is designed and made. The effects of ambient temperature, drum speed and powder filling ratio on the fluidity of nylon powder were studied. The results show that the fluidity of the powder is weakened to some extent due to the powder filling ratio, ambient temperature and the rotating speed of the roller.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB332

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