Research On Key Techniques In High-speed Milling Of Pre-sintered Zirconia Denture And Digital Oral Equipment

With the development of science and technology, CAD/CAM technologies are graduallyapplied to dental medical treatment, which has greatly improved the quality and efficiency ofdental restoration. The high speed machining (HSM) technology is a key component of dentalrestoration CAD/CAM system for manufacturing denture, which directly related to the quality ofthe workpieces. Due to the complex morphology of denture and hard to machining raw materials(metalic alloy, ceramic), the machining process is complex and the quality is hard to achieved.Considering the demands of dental clinic, the relevant theories and key technologies of HSMused in manufacturing denture are deeply studied in this dissertation based on the experiments.The focuses of the study are the milling performance and machining parameters setting onmilling pre-sintered zirconia ceramics, and designing a digital oral equipment which with twospindles.The main contents and achievements are shown as follows:1. Researching on the phenomenon of exit chipping during in the denture milling on thepre-sintered zirconia ceramics, a new milling method which can dramatically reducing exitchipping has been introduced. The factors leading to phenomenon of exit chipping in millingpre-sintered zirconia has been analysed and verified in several experiments. It's shown thatdifferent milling and the corresponding performance parameters (rigidity, fracture toughness,micro particle size) of material have effects on exit chipping. The width of exit chipping can bedecreased by optimizing milling parameters.2. Considering the wearing of cutter, milling pre-sintered zirconia has great effect onmachining denture quality; a prediction model of cutter wear has been introduced based on thegray system theory after analyzing the tool wear data collected by the same time interval. Thewearing capacity and lifetime of tool can be forecasted based on this model. The model's wasverified after analyzing and comparing the measured value in an experiment3. Studying on the geometric model of ball end mill and the high speed cutting parameters,the theory model of high speed milling force in micro-diameter cutter has been established on thebasis ofinfinitesimal of body force. The effets such as radial width of cut, feed rate, cuttingmethods and shape of the workpiece in the milling on cutting force of milling have been studiedsystematically. The empirical prediction model of milling force on machining pre-sinteredzirconia ceramics has been introduced by means of the method of multivariate orthogonalregression to analyse the data of plane milling experiment. The model's veracity was verifiedaccording to the result of milling experiment about simulate curvature changes in morphology ofdenture.4. On the basis of fixed-effect model, the factorial experiment on surface roughness ofmilling pre-sintered zirconia has been designed, then the effects of milling parameters such as spindle speed, radial width of cut and axial depth of cut have on the surface quality of workpiece.Using quadratic regression orthogonal experiment, an optimizing model has been established tooptimize the milling parameters when machining pre-sintered zirconiao to obtain the bestminimum surface roughness. The model provides reliable guarantees for denture's machiningusing pre-sintered zirconia.5. Using JDPaint software to generate and analyze milling tool path for machining dentureon the basis ofthe milling experiments and result of optimizing analysis, then selecting therational machining parameters and modes to milling a pre-sintered zirconia denture. Itsmorphology and surface roughness have been observed. The results show good quality for needsof dental restoration in oral medicine. The rationality and feasibility of the aforementioned modelalso been verified by the experiment.6. Designing CNC equipment dedicated for prosthetic dentistry, the characteristics ofdenture processing have been analyzed using functional analysis approach. The mechanicalstructure of the processing system has been set up. The structure of equipment is four-axis withtwo spindles. With a view to compact its structure, the system's structure also been analysed andoptimized to realized the concept of "the processing next to chair". On the basis of the theory ofMulti-body system and the actual situation of machine tool been studied, the model ofVolumetric error has been deduced and the main resources and affects were analyzed whichprovide the theoretical basis of accuracy.