Research On Circular Disk Cutter Envelop Milling Theory For Turbine Blade

With the economy transforming and upgrading, and in the pursuit of higher productperformance, there are more and more components with complex curved surface in industrialproducts, which are widely used in aerospace, automobile, energy, chemical, shipbuilding andother fields.Steam turbine is a rotary machinery which can convert the steam heat tomechanical energy, and it is one of the main equipments of thermal power and nuclearpower.The most widely used components in the steam turbine is turbine blade, whose surfaceis complex surface with multiple blending surface. Blade machining efficiency directly affectsthe turbine manufacturing enterprises,responding speed to the market. In the pursuit of highersteam turbine set performance, the blade surface becomes increasingly complex. Under thepremise of guaranteeing the accuracy of blade, how to improve the processing efficiency ofthe steam turbine blade is a needed topic for continuing research.Based on the summary of the current complex surface processing technology and curvesurface forming theory, this paper starts research from the circular disccutter envelopemachining theory, builds a circular disc cutter geometric model, analyzes the relative motionrelations between toroidal surface and processed surface in the process of envelope machining,affirms that the processed surface is shaped by disc milling rotary cutter point toroidal surface,and after discussing the factors influencing the maximum effective cutting radius, and drewsthat in order to avoid over cutting or undercutting, disc milling cutter radius should be lessthan the minimum radius of curvature of intersection line between processed surface andcutting circle.According to the design of the tool path ofcircular disc milling cutter, in the caseof a given residual height, the tool path calculation model spacing can be deduced, andthispaper illustrates the location parameter selection of cutting tools and the linked axisnumber of the circular disc milling cutter and processed surface.As for the turbine blade, this paper puts forward the new processing method with circulardisc milling cutter and builds the circular disc cutter machining turbine blade shaft envelopemodel and milling path model, and through comparison between the radial axial envelope andprocessing effect, and then determines the circular disc cutter axial envelope machiningturbine blade. In order to ensure the tool path line in correct order and keep good machiningefficiency, and get tool path which is in line with the blade surface trend, this paper establishes the residual height calculation model, and analyze the shortage of the residual height method,finally puts forward the maximum residual height control method. The method is in keepingthe tool path and blade surface distortion under the premise of the same direction, equal themaximum residual height control between adjacent tool path and design the tool path. In viewof the circular disc milling cutter in the process of machining turbine blade, toroidal surfaceand the contact point of the blade surface processed in the doughnut an area is easily changeand difficult to determine.In order to solve the problem of calculating tool locus, on the basisof the distance model between the two surfaces, the directional minimum distance algorithm isproposed, and after some research on the solution condition, distance calculation model, theconcavo-convex surface judgment, initial point selection and processing surface algorithm ofmeshes in the algorithm, the algorithm converts cutter points incremental calculation to solvethe toroidal surface with the orientation of the blade surface processed minimum distance, thusindirectly get the cutter point path.In the calculation of directional minimum distance, surfacesdiscrete as grids in vertical and horizontal directions, the discrete space in two directions isrelating to the blade surface.Combining the original data of a given twisted blade, using the cubic spline interpolationto establish fitting equation of radial section lines, and to solve the problem of maximumcurvature calculation at a section, and do the piecewise cubic spline fitting out function withartificial intervention treatment, by comparing the maximum curvature of the specified rangeand concluding the maximum curvature of cross section contour line, then carries on thecomparison to different section, finally find the global maximum curvature to determine themaximum effective cutting of circular disc milling cutter radius value range.Blade longitudinalcross section and horizontal section lines formed curve wed in space, for establishing bladesurface equation, and evaluate the tangent plane and normal vector of grid line intersectionpoint, the introduction of the concept of curve transformation is cited.Circular disc millingcutter residual height calculation is the basis of maximum residual height control applications,the calculating process can be simplified to solve two circular intersection distance and sectioncontour line.The calculation of distance need to be judged from the position of the intersection,afteradjacent inter-row maximum residual height radial cross section corresponding points isdetermined, in accordance with the axial line fitting equations, determined the different axialcorresponding points on the cross section.The simulation of axial corresponding points of different section can form a group with the same direction of blade bending and twisting ofspace curve. In order to use the trajectory of directional minimum distance algorithm for cuttertools, the space curves are used as the control line of tool motion trajectory calculation duringresearch process, and according to the setting step for the interpolation of discrete processingtool path control point, to determine the circular disc cutter trajectory point of envelopemachining turbine blade step by step.In the process of turbine blade machining with circular disc cutter, the establishment ofenvelope processing model is the basis of applying this method to the blade processing, andthe establishment of the relevant mathematical model for the solution provides a tool pathcalculation method. In the tool path designing, if the basin or back transition arc tangent isobtained, it can be used as a starting line in trajectory calculation. Axial section envelopemethod mentions in this paper can not only conforms to the principle of curvature match butalso reduce the empty cut and optimize the tool path. According to the results of using thecircular disc cutter envelope machining turbine blade, the cutting tool path length is greatlyshortened, numerical control program is significantly reduced.This research results can provide certain theoretical basis for turbine CNC machine toolfor blade machining design, blade polishing machine design and so on.