基于激光铣削的光内输送微纳粉激光熔覆复合精确成形技术研究

The forming of thin-walled parts by laser cladding results in the development of uneven cladding layers that manifests itself in poor surfaces. Furthermore, it makes it difficult for follow-up forming. In this case, it becomes necessary to conduct auxiliary mechanical milling and polishing. However, laser forming is one quench solidification process that results in high hardness which makes machining of these hardened surfaces impractical. In addition, If the shape of part is complex, the finishing machining operations will require multiple jigs and fixtures setups which are time consuming and highly inefficient, In fact, the finishing machining operations could account for more than 60% of the entire manufacturing cycle. To overcome these difficulties, a new composite precision rapid prototyping technology is proposed. This new technology is based on laser cladding by feeding a mixture of micro-nano powders in hollow laser beam and machining the resulting part by laser milling. The micro-nano powder used in laser cladding will improve the absorption performance of the powder, leading to greatly improved of laser beam. This will allow us to use high-speed CCD to detect and feedback the macroscopic morphology of the cladded layer. The newly proposed high performance and precise approach will result in greatly improved surface quality, as measured by surface morphology, as opposed to the traditional laser cladding forming. Furthermore, it will eliminate the need for the post processing and reduce the processing time and ultimately the processing cost of the part. Finally, it is worth noting that the newly proposed approach will not only be used to form high-performance thin-walled tubular sections, but also can be applied to high value-added thin-walled "obsolete" parts for repair and remanufacturing.

激光熔覆成形高性能薄壁金属零件时，由于熔覆层凹凸不平和挂渣导致成形件表面精度差甚至后续成形困难，往往需要在成形过程中或成形后辅助机械铣削加工和抛光处理。但是成形件因急冷凝固，表面硬度很高，加工非常困难；形状复杂的零件机械加工更需多次装夹，加工时间长，有时要占整个制造周期的60% 以上。为此本申请提出一种基于激光铣削的光内输送微纳粉激光熔覆复合精确快速成形的新技术，拟采用微纳粉作为激光熔覆用粉体，提高粉体对激光的吸收性能，从而可以用光斑更小、光束质量更好的激光成形薄壁件；采用高速CCD实时观测反馈激光熔覆过程中熔覆层的宏观形貌，通过激光振镜三维铣削实现熔覆层精度的闭环控制；从而实现薄壁金属零件的精确成形。该方案克服了传统激光熔覆成形件表面精度低的现状，避免了可能需要的机械精整加工，缩短了加工时间，降低了加工成本，不仅可用于高性能薄壁件的精确成形，也可用于高附加值"废弃"零件的修复和再制造。

金属零件直接快速成形技术是一种基于高能束的逐层堆积直接成形零件的技术，具有周期短、成本低、柔性高、易集成等优点，但仍然存在单工艺成形质量差、复合成形工艺机械加工困难及复合成形工艺材料浪费等问题。本课题在“添加材料”结合“去除材料”加工方式的指导思想下，本项目提出一种基于激光铣削的光内送粉激光熔覆复合精确快速成形技术，主要研究内容及取得成果有：. （1）三维测量系统的设计与研究. 搭建了以电控运动平台、测量系统、电控系统和数据处理系统组成的三维测量系统，并利用VC++语言，结合图像处理技术，自主开发一套测量数据可视化处理软件。该套系统可获得尺寸大小与实物一致且被激光铣削软件直接识别的熔覆件表面及侧面凸点区域文件，真正实现三维精确铣削，提高了激光铣削的效率和精度。. （2）激光铣削整形机理研究. 针对方形薄壁件的三维特性及材料特性，探究激光铣削光整熔覆件的整形机理；建立了单脉冲作用及一定重叠率下激光铣削平整面的排屑模型，在此基础上，针对熔覆件的弧形表层，建立了激光入射弧形表面的排屑模型，此外，针对熔覆件侧面搭接特点，建立了侧面铣削模型。. （3）工艺参数对激光铣削单道三层熔覆件的影响分析 . 用脉冲光纤激光对特定参数的单道三层F313铁基熔覆件表面和侧面分别进行铣削试验，通过单因素试验探究不同激光参数对铣削熔覆件的三维粗糙度、深度及表面形貌的影响规律。通过正交试验探究各工艺参数对三维粗糙度、铣削深度的权重，优化工艺参数。优化后的表面铣削最优参数为：平均功率为100W、点间距为0.1mm、脉宽为4ms、离焦量为-1.5mm，表面粗糙度可达6.293μm，铣削深度为0.12mm；优化后的侧面铣削最优参数为：平均功率135W、点间距0.07mm、脉宽2.4ms、离焦量-1.4mm，侧表面粗糙度可达2.173μm，侧面铣削宽度为0.055mm。. （4）激光复合成形方形薄壁件. 利用三维测量系统获得三层方形熔覆件的表面及侧面凸点区域，根据优化的铣削参数对凸点区域进行铣削，铣削完成后再用激光熔覆三层，然后继续测量、铣削，最终复合成形出9层方形薄壁件。.本项目提出了一种金属零件直接快速成形的新型加工工艺，克服了以往直接成形薄壁件时，表面质量差、尺寸精度不高的问题，实现高性能薄壁金属零件的复合精确成形。