Research On Path Planning And Material Removal Optimization In Deterministic Polishing

With the development of science and technology,the demand for ultra-precision parts with aspherical surfaces,freeform surfaces and other complex curved surfaces,and their manufacturing molds in the fields of national defense,aviation,aerospace,medical,and automotive is becoming more and more common and demanding.These ultra-precision surfaces are usually produced by precision polishing after grinding,which not only requires high surface form accuracy and low surface roughness,but also requires strict control of midspatial frequency and subsurface damage.In addition,the existing polishing processes are diverse,the process parameters are numerous and interacting,and the material removal mechanism is complex,which also poses severe challenges to improve the quality and certainty of ultra-precision polishingThe improvement of polishing quality and its certainty cannot be separated from basic research on polishing removal optimization models,path generation strategies,material removal theory,and deterministic schedulding models.Aiming at the application of polishing in uniform material removal and surface form correction,this thesis has carried out a series of related research including physical uniform coverage path planning theory for achieving uniform material removal,residual error optimization based on adaptive path in surface form correction,analytical model of material convolution removal process in polishing,direct feed rate schedulding model,and machine tool dynamic performance based on path adaptivity.The research in this thesis has formed a relatively complete theoretical system,which has important academic theoretical value and industrial application value for deep understanding of polishing removal process and improving its certainty.The main research contents and research results of the thesis are as follows:(1)Controlling the uniformity of material removal is critical in polishing applications that do not compromise surface form accuracy,improve surface quality,or remove machining marks left by previous processes.Given the current polishing path planning methods for contact polishing,most of them are based on the uniformity of geometric coverage,and lack of consideration of the physical contact between the polishing tool and the workpiece.In this thesis,the method of physical uniform coverage polishing path planning considering physical contact is studied in depth.The concepts of polishing ribbon circle and polishing ribbon are proposed.And we respectively give the physically uniform planning algorithms for scanning path and spiral path,which can easily and efficiently realize the active control of the overlap between the polishing ribbons corresponding to adjacent polishing paths.According to the proposed path planning theory and method,given a polishing path,a threedimensional contact area map between the polishing tool and workpiece can be obtained.Based on this,the pros and cons of the path can be evaluated from the perspective of the contact distribution.Comparative polishing experiments are carried out,and the experimental results confirmed the feasibility and effectiveness of the proposed path in promoting uniform material removal.(2)In form correction polishing,the form error distribution determines the difference in material removal depth,and its distribution feature often seriously affect the effect of surface form iterative correction and the convergence speed.For this reason,we deeply study the influence of path spacing and material removal depth on the residual errors obtained after correction polishing.Based on the rootmeansquare(RMS)and peaktovalue(PV)maps,the relationship model of the key evaluation parameters such as the RMS and PV of residual error,the path interval,and the material removal depth was established.This paper proposes a path planning strategy based on the adaptability of form error distribution.In the proposed strategy,the path spacing is finetuned according to the proposed model to compensate for the effect of different material removal depths on the residual error due to the form error distribution.Simulation experiments show that the proposed strategy can significantly optimize the overall residual error distribution without affecting the convergence accuracy and efficiency.It can greatly reduce the influence of the initial surface form error distribution on the residual error distribution after correction,and the consistency and uniformity of the residual error in each region of the polished surface can be significantly improved(3)The convolution removal process based on discrete simulation limits the intuitively obtained the relationship between polishing process parameters(path spacing,tool influence function,polishing speed,removal depth,etc.)and process results(material removal profile,waviness contour,and its PV value,RMS value and PSD curve).The analytical model of the material convolution removal process is proposed and deduced for the first time in this thesis,which intuitively reveals their inherent relationship.The proposition of these analytical models provides new insights for deterministic polishing and opens new doors for more intuitive and efficient solutions to related forward and inverse problems.Through fluid jet polishing(FJP)experiment,the correctness of the proposed model was confirmed In addition,we propose to use Monte Carlo method to model TIF fluctuations in FJP,and studied the influence of TIF fluctuations on the polishing results,and effectively predicted the profile of the waviness resulted from fluctuation(4)Deterministic polishing cannot be separated from feed rate scheduling The existing feed rate scheduling depends on the solution of dwell time,which makes it difficult to optimize the dynamic performance of the machine tool.This thesis proposes to use a Gauss mixture model to model the general shape of tool influence function(TIF)and express it as a linear superposition of a series of single Gaussian functions.Based on the derived theoretical model of single Gaussian convolution removal,a theoretical analytical model corresponding to the general TIF is obtained.This model gives a direct feed rate scheduling method that can be used in correcting polishing.This method is suitable for many types of TIFs including Gaussian and Wshaped.Given the influence of form error distribution characteristics on the accuracy of the model,an iterative compensation strategy was proposed to obtain the best feed rate scheduling accuracy.At the same time,an adaptive path theory model with controllable path spacing is proposed to optimize the gradient of the feed rate for reducing the dynamic stress on the machine tool during the polishing process.Simulation and experiments show that the direct feed rate scheduling method proposed in this paper can effectively achieve deterministic surface form correction,and can reduce the dynamic stress on the machine tool during the polishing process.