| Additive manufacturing technology is a rapid prototyping technology based on layer-bylayer stacking and accumulation principle.With the advantages of fast forming,less restriction on workpiece shape and high material utilization rate,Additive manufacturing has been widely used in aerospace,automobile,heavy machinery and other fields.The additive manufacturing forming process still can be divided into two steps,melting process and forming process,The material melting into liquid state with the active of energy sources,then cooling into solidification state.The liquid molten pool is affected by tension,gravity,adhesion and other forces,during the melting and condensation process,So the forming process always with great uncertainty.The workpiece surface shape always be influenced during the process of multi-track and multi-layer deposition,by temperature gradient,acceleration of the laser cladding head and energy source fluctuation.Because of the principle of layer by layer addictive,deformation has a tendency to increase with the growth of the workpiece.Therefore,early detecting of deformation and corresponding adjustment can significantly improve the workpiece forming accuracy and passing rate.To monitoring surface deformation of additive manufacturing workpiece,constructed an online measuring system.The measuring system include communication unit,PLC unit and storage unit,and the core part of the system is laser displacement sensor.During the additive manufacturing process the workpiece adjacent area always with the conditions of high temperature,high light and dust,To prevent the laser displacement sensor and avoid interference and fouling to the sensor camera designed a kind of protective system to guarantee the environment near the sensor is always in a relatively constant condition.Due to the deformation of the workpiece’s upper surface is easily occur,The deformation degree is always obvious,at the same time,the workpiece is easily elongate,the amount of workpiece point clouds and digital-mode point clouds always can not be match,a point cloud registration method based on the joint constraint of curvature and Z-value deviation was proposed.In the process of workpiece surface deformation repair.During the repairing process,as the workpiece upper surface deformed into hook face,and depositing at hook face will induce different mechanical property between repair area and additive manufacture area,so to avoid that proposed the best repairing angle for the substrate plate.In addition,a regional repair method is proposed for the deformed region.Finally,by the steps of on-line scanning,locating the deformation area,deviation calculating and deviation repairing,A closed-loop manufacturing mode include deposition manufacturing,on-line measurement and on-line repair for laser powder feeding additive manufacturing system was realized.The experiment shows that the X-direction and Y-direction uncertainty of the constructed online measurement system is less than 0.1mm,the Z-direction uncertainty is less than 0.05 mm,and the measurement error rate is less than 0.1%.The proposed point cloud registration method can realize the registration under the condition of workpiece surface deformation and the amount of point clouds of the workpiece is different from the digital modular point clouds.Comparing with the results of before repair and after repair workpiece measurement,the z-coordinate of the workpiece after repair are all in the setting tolerance,and the expected effect is achieved. |
