激光熔覆加工头聚焦性能及成形工艺研究进展

Research Progress on Focusing Performance of Laser Cladding Machining Head and Forming Technology

激光熔覆作为一种十分有前途的制造技术,已在工业中广泛用于部件修复、表面改性以及增材制造等领域。在激光熔覆系统中,激光熔覆加工头是其关键核心部件,可以在基材表面实现激光束、熔覆材料和熔池之间的精准耦合并形成连续熔覆层。激光熔覆加工头内置有光学镜组,主要用于激光束的传输、变换和聚焦,可以根据不同的加工需求对光束进行处理。主要从分析激光熔覆加工头聚焦性能对熔覆成形工艺影响的角度出发,综述了加工头的设计及其成形工艺的发展,具体包括光斑尺寸、光斑形状、光斑能量分布、激光功率、光源特性等对材料沉积速度、材料利用效率、熔覆层质量等的影响。首先按照激光熔覆的材料类型和材料与激光束的耦合形式,对激光熔覆光料耦合方式及加工头进行了简要概述,并对成形工艺造成的影响进行了总结。其次分别讨论了连续高斯光束和平顶光束以及脉冲激光的聚焦性能对熔覆层的影响,同时概述了3种不同形状光斑(圆形、矩形、环形)的能量分布特性和光斑尺寸对成形工艺的影响;接着研究了激光能量密度对熔覆层质量的影响;基于超高速激光熔覆技术分析提出透镜长焦深聚焦特性能够大幅提升激光熔覆的加工效率。最后展望了激光熔覆加工头聚焦性能在成形工艺上的发展趋势和应用前景。

As a promising manufacturing technology,laser cladding has been widely used in industry for component repair,surface modification,and additive manufacturing.In a laser cladding system,the laser cladding machining head is its key component,which can realize the precise coupling between the laser beam,the cladding material and the molten pool on the surface of the substrate and continuously form the cladding layer.The laser cladding machining head has a built-in optical lens group,which is mainly used for transmission,transformation,and focusing of the laser beam,and the beam can be processed according to different processing requirements.The processed beam develops specific focusing properties such as spot size,spot shape,energy distribution and depth-of-focus characteristics.In general,the focusing characteristics of different light sources vary greatly,and the focusing characteristics directly affect the quality of the cladding layer and the formed part through optical material coupling.This requires matching process parameters,including laser power,scanning speed,feed rate and overlap rate.This article mainly analyzes the influence of the laser cladding machining head's focusing performance on the cladding forming process,and reviews the design of the machining head and the development of its forming process.Specifically,it includes the influence of spot shape,spot size,spot energy distribution,laser power,light source characteristics,etc.on material deposition speed,cladding material utilization efficiency,and cladding layer quality.Firstly,according to the type of laser cladding material and the coupling form of the material and the laser beam,a brief overview of the laser cladding optical material coupling method and machining head is given,and the influence of the forming technology is summarized.Coaxial feed cladding heads offer significant advantages over side axis feed cladding heads and are widely used.Secondly,the effects of the focusing properties of continuous Gaussian and flat-top beams and pulsed lasers on the cladding layer are discussed separately,while the energy distribution characteristics and the influence of the spot size on the cladding process for three different spot shapes(circular,rectangular and toroidal)are outlined.In addition to the properties of the cladding material and the substrate,the properties of the cladding layer also depend on the microscopic particle activity under temperature control during the cladding process.The pulsed laser has higher peak power,faster instantaneous heating speed,and the stirring effect on the melt pool can increase the convection circulation of the melt pool,enhance the cooling rate,reduce the temperature gradient,and greatly improve the mechanical properties and microstructure of the cladding layer.Thirdly,the effect of laser energy density on the quality of cladding layer is studied.Laser energy density is a reliable way to describe quantitative heat input.For different materials,there is an optimal combination of parameters for the energy density of laser cladding.Based on the analysis of ultra-high-speed laser cladding technology,it is proposed that the long focal depth focusing characteristics of the lens can greatly improve the processing efficiency of laser cladding,reduce the heat accumulation and improve the material utilization.Finally,the development trend and application prospect of focusing performance of laser cladding machining head are outlooked.