Research On Technology Of Geometry Repairing For Parts With Complex Shapes Based On Non-rigid Registration

In aerospace,vehicle,energy equipment and other important engineering fields,many key parts such as aircraft turbine blades are restrained by developed countries and rely heavily on import due to the limitations of materials preparation and machining technology etc.Usually,these parts are made of high-performance and expensive high-temperature alloys.They easily suffer from bending deformation and surface damage due to long-term extreme working environments with high temperature,high speed and high pressure.This leads to the early retirement before their lives.The direct replacement for these damaged parts would cause high operating costs,which is a great waste of money.Hence,how to repair the damaged parts so as to extend their working lives is a research focus in academia and industry.For this,this paper focuses on discussions of the repairing technique with respect to complex parts,and put emphasis on studying the model reconstruction technique of these damaged parts as well as the related processing methods when repairing them in efficient CNC machining operations.Firstly,recognition processes of damaged areas and repairing finishing areas are studied in detail,and the corresponding recognition algorithm is proposed.A boundary data extracting method is proposed based on rotation angle.Using this method,the damaged boundary and machining region pan be recognized quickly.In order to acquire the section data in order,a fast algorithm based on the section reconstruction method is proposed using the minimum relating point.When the target point is far away from the nominal curve,the shape mutation may occur.In order to avoid this drawback,based on curvilinear constraint deformation and smoothing method,curve smoothing deformation is transformed into deformation energy minimization problem.On this base,the control point of the curve is calculated.The curve after construction not only goes through the target point but also meets the requirement of smoothing.Rigid registration process between the measure data and nominal model is discussed in next step.The mathematical description is given for this rigid registration.Quaternion algorithm,singular value decomposition method and iterating method are employed to compute this mathematical problem.On this base,the corresponding relationship between measure data and section profile is built using the curvature information.Furthermore,the translation transformation table is obtained using the tri-point rotation and translation method.The right 3D coordinate translation is acquired by using the minimum distance function.Then,the initial registration is realized.To obtain accurate registration between the measure data and nominal curve,with the help of Bernstein polynomial arithmetic operations and the convex principle of Bezier curve,a method for calculating the recursive partition based point to the closest point of B-spline curve is proposed.This registration method can be extended to surface rigid registration process.Next,for the complexity of the damaged part and the uncertainty of the damaged section,the non-rigid registration ideology is introduced to reconstruct the model of the damaged part.First of all,the non-rigid registration mathematical model between measure data and nominal model is built.Though analyzing the transformational matrix of the non-rigid registration,the non-rigid registration model is divided into rigid motion,and then the space posture transform between measured data and nominal model can be obtained and flexible transform is used to change profile.Then a computing method is proposed to obtain these two transforms.On this base,the non-rigid registration reconstruction method for section profile in which only deformation exists is proposed.And then the constraint conditions of the damaged section or non-rigid registration is discussed.Further,the damaged part is reconstructed by using skinning algorithm.Afterwards,the self-adaptive method for feedrate scheduling is analized to repair the failure part after the bead weld operation.First,the toolpath surface is evaluated by bi-NURBS curves,and five-axis machine kinematic model is given Then,the formulas of the chord error,tool tip and acceleration,angular velocity and acceleration of the axis,driving axis's velocity and acceleration and constrict condition are deduced.Utilizing these formulas,the feedrate optimizing strategy is introduced based on the equal proportion adjustment and curve smoothing deformation.And the feedrate scheduling method is deduced.This method has ability to self-adjust the control point of the feedrate B-spline curves.Finally,a classical Wiggle surface and a blade are taken as examples,the theory mentioned above,including damaged part's data measuring and processing,damaged part's reconstruction,damaged section's recognition and additional materials removal,are verified.The results show that the theory in this paper can avoid data ordering and simplify model surface's reconstruction process.And the feedrate optimization method can make the repairing area to be machined smoothly.