Research On Close-loop Control Of Molten Pool Temperature During Laser Cladding Process Based On Color CCD

Laser Cladding Metal Additive Manufacturing is a new manufacturing technology developed based on laser cladding and rapid prototyping technology,this technology has the advantages of being able to produce complex strcuctural parts,high material utilization,and short manufacturing cycles.However,during the laser cladding process,due to changes in the cooling conditions of the substrate and changes in the dimensional structure of the formed parts,the fluctuation range of the molten pool temperature is large.The thermal effect may lead to imbalance of the thermal action of the molten layer,uneven structure,and irregularities in the forming surface.Uneven,even collapsed.Therefore,it is necessary to carry out real-time monitoring and close-loop control of the molten pool temperature in order to improve stability of the molten pool temperature and improve quality of the formed parts.At present,most researches at home and abroad adopt the scheme of adjusting process parameters based on the pyrometry measurement results to control the molten pool temperature.The cost of the system scheme is high,and due to the molten pool temperature mechanism model is more complex,there are many algorithms that are applicable to the closed-loop control of the temperature of the molten pool,which are not common or have low control accuracy.In this paper,in order to solve the above problems,combined with colorimetric thermometry and fuzzy PID control priciple to carry out a systematic study of the detection and control of the molten pool temperture,a color-CCD-based molten pool temperature measurement and control system is constructed,and a specific experiment is designed to verify the system.Have achieved more satisfactory results.A laser molten pool temperature measurement and control system is constructed based on an optical feed powder cladding nozzle and a color CCD.The system can stably collect the thermmal radiation image of the hollow ring laser molten pool.The selected optical feed powder cladding nozzle has uniform scanning energy distribution,powder beam straight and other advantages.A laser molten pool temperature detection model was established based on the Planck radiation law and the principle of colorimetric temperature measurement.A measurement plan foe the dual channel structure was established.The spectral response curve and temperature measurement range of the CCD were comprehensively considered,and a suitable colorimetric temperature measurement wave length was selected to establish.The relationship between gray ration and temperature is linear,and the formula foe the calculation of the molten pool temperature is duduced.With the infrared camera as the temperature calibration device,the maximum error between the temperature detection result and the calibration result is 2.3%,and the source of the error caused by the temperature measurement is analyzed.Based on the joint programming of the Visual C# language and the machine vision software Halcon,a dedicated system software for the melten pool temperature was developed.The modular interface was used to design the software interface.The image acquision,image processing,and data input/output module implementation methods were described in detail.Socket communication is used to realize the feedback of the temperature value signal between the industrial controller and the robot controller,which provides the basis for the next close-loop control.The influence of the laser cladding basic process on the quality of the cladding layer was studied.After the measurement and analysis of the pool temperature in the single-channel cladding process,the laser power was determined as the parameter of the close-loop control.Designing temperature controller algorithe combined with the fuzzy PID control principle.The control effect of temperature measurement and control system was verified by stacking experiments of thin-walled cylinders on the substrate,and the influence of temperature of the molten pool on the quality of the formed parts was analyzed from the perspective of dimensional accuracy,microstructure and hardness.The results show that the temperature measurement and control system of the molten pool can effectively control the molten pool temperature,the absolute error between the actual temperature of the molten pool and the set temperature does not exceed 46°C and the relative error is controlled within 2.7%.and further improve the mechanical properties of the formed part by controlling the diffiences in microstructure.The outer diameter of the bottom of the formed part is only 0.9 mm from the top outer diameter,and the dimensional accuracy is significantly improved.The microstructural differences of the formed parts were small,the microstructure was dense and uniform,and the mechanical properties were further improved.