激光直接金属沉积熔池温度控制作用研究

Study on Temperature Control of Molten Pool for Laser Direct Metal deposition

激光直接金属沉积(Direct Metal Deposition,DMD)作为一种典型的增材制造方式通过利用激光作为热源逐层沉积金属粉末来制造三维零件。然而成型过程中的不稳定因素较多尤其是熔池温度、冷却速率等,这些最终将导致成形件较低的宏观尺寸精度以及不均一的微观显微组织等进而严重影响零件使用性能。通过选用薄厚特殊基板,利用比色高温计实时监测熔池温度作为闭环反馈信号,通过建立基于PID控制算法的在线控制系统实时调节激光功率使得沉积过程中的熔池温度控制稳定,并利用另外两台比色高温计定点逐层监测沉积层两端热历史并计算冷却速率。开闭环实验对比表明熔池温度稳定条件下层厚标准差降低了62%,各位置晶粒表征参数标准差均得到降低。

Direct Metal Deposition(DMD)is a typical additive manufacturing method that produces three-dimensional parts by depositing metal powder layer by layer using a laser as a heat source.However,many unstable factors in the molding process,especially the molten pool temperature,cooling rate,etc.,will eventually lead to lower macroscopic dimensional accuracy of the formed part,along with uneven microscopic microstructure,which in turn seriously affects the use performance of the part.In this paper,by using a special thin and thick plate as the substrate,the pyrometer is used to monitor the molten pool temperature as a closed-loop feedback signal.The online control system based on the PID control algorithm is used to adjust the laser power in real time to make the temperature control of the molten pool in the deposition process stable.At mean time,another two pyrometers were used to monitor the thermal history at both ends of the sediment layer and calculate the cooling rate.The comparison of the open-loop experiments and closed loop experiment shows that the standard deviation of the layer thickness is reduced by 62%under the condition of stable temperature of the molten pool,and the standard deviation of the grain characterization parameters at each position is reduced.