Recursive Subspace Identification Based Adaptive Predictive Control Design For Melt Pool Temperature During Laser Additive Manufacturing

Laser addictive manufacturing utilizes a high-power laser beam to create a melt pool and melt the delivered metallic powders onto a substrate to form components layer by layer.Compared with the traditional manufacturing technology,this technology has many advantages,such as high flexibility,no limitation of parts structure,short cycle and so on.It has been widely used in aerospace,rapid prototyping and medical supplies and other fields.The quality of laser beam forming is affected by various factors such as such as process parameters,external environment and the melt pool temperature.Among these factors,the melt pool temperature is the most important factor affecting the forming quality of parts.It is important to monitor and control the melt pool temperature during the laser addictive manufacturing process.However,it is hard to establish the model of melt pool temperature and the model of melt pool temperature in laser additive manufacturing process will change.Currently,there is no suitable algorithm for to control melt pool temperature.In this thesis,in order to achieve precise control of melt pool temperature in laser additive manufacturing process.A recursive subspace identification based adaptive predictive control algorithm was improved,and the melt pool temperature system based on the improved algorithm was designed.Finally,the control effect of melt pool temperature was verified by experiments.The main work and achievements of this thesis were as follows:(1)On the basis of laser material manufacturing equipment,a temperature control platform for laser addictive manufacturing was established.It was provides the basis for the design and test of the melt pool temperature control system.(2)Combined with the actual situation of the laser addictive manufacturing,the recursive subspace identification based adaptive predictive control algorithm was improved.In contrast to the MATLAB/Simulink simulation,the results showed that the improved algorithm successfully solved the problem that the initial control effect was shock,made the algorithm more applicable to melt pool temperature.(3)The characteristics of the melt temperature system was analyzed,and the temperature control strategy and basic requirements of the bath was determined.Then the melt pool temperature control system was designed based on the improved algorithm.The system uses the dual-color pyrometer to monitor the melt pool temperature during the process.And control the melt pool temperature by varying the laser power.The basic parameters of the controller was determined by off-line simulation and experiment.The simulation results verified the theoretical control effect of the system when the melt temperature changes rapidly and changes slowly.(4)Two contrast experiments was designed to verify the effect of the melt pool temperature control system in the situation of the complex path and using the complex substrate.The experimental results showed that the melt pool temperature control system can realize the temperature control in complex conditions,and improve the stability of laser addictive manufacturing processing.