This paper presents in-time motion adjustment in laser cladding manufacturing process as a means to improve dimensional accuracy and surface (nish of the built part. Defects occurring during laser cladding degrade the part quality such as dimensional accuracy and surface (nish. In this paper, in-time motion adjustment strategy was presented to remedy and eliminate defects occurring during laser cladding to improve the dimensional accuracy and surface (nish. Based on the relationship between the motion of laser head relative to the growing part and other parameters in e4ects on clad pro(le, the laser traverse speed, stand-o4 distance and laser approach orientation to the existing clad layer were adjusted by instructions from a close-loop control system in real time to remedy and eliminate defects. The results of the experiments veri(ed the e4ects of in-time motion adjustment on dimensional accuracy and surface (nish.

In this paper, model of effects of powder concentration distribution on fabrication of thin-wall parts in coaxial laser cladding was developed. There exists relationship between powder concentration distribution and power density distribution, which affects fabrication of thin-wall parts in coaxial laser cladding. Changes in powder concentration distribution lead to changes in wall thickness and wall growing rate. Fluctuation of powder feed rate deteriorates the growing wall in laser cladding. Deviation of the powder flow stream makes the powder concentration distribution, the thermal flux density and consequently the molten pool not symmetrical against the x-axis, resulting in irregular upper faces of the formedwall. This was verifiedby the results of experiment.

In this paper, a model of cross-section clad profile on the substrate in coaxial single-pass cladding with a low-power laser was studied. The static model of powder mass concentration distribution at cold-stream conditions was defined as a Gaussian function. In coaxial single-pass cladding with a low-power laser, since the influence of surface tension, gravity and gas flow on the clad bead could be neglected, the cross-section profile of the clad bead deposited by a low-power laser on the substrate was dominated by the powder concentration at each point on the pool and the time when the material was liquid at this point. The height of each point on the cross-section clad profile was defined as a definite integration of a Gaussian function from the moment at which the melt pool was just arriving at the point to the moment at which the point left the melt pool. In the presented experiment, powder of Steel 63 (at 0.63 wt%C) was deposited on a substrate of Steel 20 (at 0.20wt%C) at the laser power of 135 W. The experimental results testified the model.

试验研究了较低功率的激光熔覆成形金属薄壁结构及其影响因素。成形金属薄壁结构的能力对零件薄壁部位的成形和小型零件的制造十分重要。由于传统的激光表面处理工艺观念的影响、对激光单道熔覆成形薄壁结构过程及其规律的认识不够，目前成形薄壁结构的能力较差。试验研究了用与表面处理工艺不同的、功率和光斑尺寸较小的C02激光进行单道熔覆成形薄壁试样，试验结果表明较低功率、较小光斑的激光与适当的扫描速度、送粉速度等配合可以得到壁厚最小为0.4 mm的薄壁结构。激光单道熔覆的壁厚与工艺参数和工件高度有关，粉末流与激光束之间的同轴度和送粉速度的稳定性等因素也影响薄壁结构的成形。

A low-power C02 laser is used to deposit Fe powder and mixture of Fe and carbon powder on substrates respectively, and the macro and micro-structure of the formed samples are investigated. It is demonstrated that most grains of these samples are equi-axed. This is derived from the high nucleation velocity in the shallow melt pool besides rapid solidification of the liquid-state alloy or metal. Bainitic structure, combination of pearlite and ferrite structure and ferrite structure are seen respectively in the samples involving various amounts ofcarbon owing to no martensitic transforma-tion in these small samples.

The power of a focused laser beam with a Gaussian intensity profile attenuated by powder in coaxial laser cladding is investigated experimentally and theoretically, and its resolution model is developed. With some assumptions, it is concluded that the attenuation of laser power is an exponential function and is determined by the powder feed rate, particle moving speed, spraying angles and waist positions and diameters of the laser beam and powder flow, grain diameter and run of the laser beam through the powder flow. The attenuation of laser power increases with powder feed rate or run of laser beam through the powder flow. In the experiment presented, 300W laser power from a focused Gaussian beam is attenuated by a coaxial powder flow. The experimental results agree well with the values calculated with the developed model.

In this paper, effects of process variables on wall thickness, powder primary efficiency and speed of forming a thin metallic wall in single-pass coaxial laser cladding are investigated, and some resolution models are established and testified experimentally. With some assumptions, each of wall thickness, powder primary efficiency and formation speed can be defined as a function of the process variables. Wall thickness is equal to width of the molten pool created in single-pass laser cladding and determined by laser absorptivity, laser power, initial temperature, scanning speed and thermo-physical properties of clad material. Powder primary efficiency and formation speed are both dependent on an exponential function involving the ratio of melt pool width, which is decided by the process variables, to powder flow diameter. In addition, formation speed is influenced by powder feed rate. In present experiment, a 500W continual-wave (CW) CO2 laser is used to produce thin-wall samples by single-pass coaxial laser cladding. The experimental results agree well with the calculation values despite some errors.

Direct fabrication of thin-wall metallic parts by low-power laser cladding is developed. With some assumptions for fabrication of thin-wall metallic parts with a focused Gaussian laser beam, theoretic models of the minimum laser power and of wall thickness are established, and effects of process parameters on the minimum laser power and wall thickness are analyzed. In the presented experiment, a CO2 laser with low power and a small light spot on the interacting area are applied in single-pass cladding. The experimental results demonstrate that if the scanning velocity, powder flow rate, and other process parameters are matched suitably with the laser, a thin wall with thickness down to 0.4 mm can be formed and that the thickness of the wall formed by single-pass cladding is dependent on the process parameters and the wall height.

In order to determine a cross-sectional profile of a clad bead in coaxial laser cladding, its formation mechanism is investigated theoretically and experimentally. In laser cladding, every point at the back edge of a melt pool is contributed to a cross-sectional profile of the clad bead to be formed, and points at the same pool edge but on different cross sections are located at different cross-sectional profiles of the clad bead. A cross-sectional profile of a clad bead is composed of points of intersection between the cross section and a series of pool edges. Model of the cross-sectional clad profile in single-pass coaxial laser cladding is developed. A 500W CO2 laser is used in the experiment. The experimental result agrees well with the calculated cross-sectional clad profile.

为掌握激光熔覆成形壁厚的变化规律，提高成形薄壁结构能力，对激光单道熔覆成形的金属零件壁厚进行了研究，提出并验证了激光单道熔覆成形金属零件壁厚的理论模型．研究表明，在一定简化条件下，根据能量平衡和物质守恒定律，推导出较低功率、较小光斑的激光单道熔覆成形的金属零件壁厚的理论模型，该模型显示单道熔覆成形的零件壁厚是各工艺参数和材料热物理特性的函数．采用500W功率连续输出的CO，激光以较小光斑进行单道熔覆成形，实验得到了最小壁厚为0.4 mm 的薄壁试样，试样壁厚与理论模型计算的壁厚比较一致．