等离子弧增材制造钛合金热质传递行为数值模拟研究

增材制造技术(Additive Manufacturing，AM)，又被普遍称为3D打印(3D printing)，是一种基于离散-堆积原理，利用计算机辅助加工的新型制造技术。增材制造技术面向航空航天、汽车、微电子、生物医疗等领域，具有应用面广、技术灵活和一体化成型等特点。金属增材制造受到了更加广泛的青睐和应用，与传统的铸造、锻造和焊接等传统工艺相比，金属增材制造技术具有成形速度快、制造复杂结构材料一体化、自动化程度高、节约材料等优势。金属增材制造主要是分为粉床式增材制造和送丝式增材制造，粉床式增材制造的热源主要是激光和电子束，送丝式增材制造的热源绝大部分是电弧。基于电弧堆焊的理论基础和成熟工艺，电弧增材制造已经发展了多种电弧增材制造的技术手段，相对于钨极氩弧焊、热喷涂等金属成型技术，等离子弧增材制造具备沉积效率高、可打印大型部件、能量密度高等优点，在多层打印过程中熔池形貌、小孔演变、熔池流动形态和热场演变仍然未能系统性的探究和揭示，未能揭示复杂打印路径的熔池的具体形貌、流动方向的机制。在利用红外热成像对熔池进行测量，未能反映熔池的温度峰值和温度演变，采用高速摄像机对熔池的轮廓进行拍摄，未能检测到熔池的流动方向和流动速度以及小孔的形貌。因此，有必要利用数值模拟技术对等离子弧增材制造的熔池形貌演变、流动方式、小孔尺寸和热场进行系统性地探究，数值模拟的结果可有效支撑实际实验的数据和验证在不同工况的金属成形。

深入分析等离子弧增材制造熔池内液态金属的流动行为、热变换和质量传输，建立起完善的等离子弧增材制造在热力作用下的熔池和小孔演变数值分析模型。综合考虑电磁力、浮力、电弧剪切力、电弧压力和自由界面对流散热和辐射等问题，将不定期的熔滴下落设置为周期性的熔滴过渡模式。对Fluent流体软件进行二次开发，以能量源项、动量源项、质量源项的形式对增材制造过程中的热力行为进行描述，使其符合等离子弧增材制造的加工过程。通过对等离子弧增材的单道多层打印的研究，能够发现熔池形态、小孔演变和熔池温度变化的机制。

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