Study On Helical Drill Point With Nonlinear Pitch Based On The Biglide Parallel Machine

Twist drill is a type of hole-machining tool with extremely complicated structure.Different flank surfaces of drill point should be ground corresponding to different grinding methods,of which the conical drill grinding is widely-used.In spite of simple grinding motions in conical method,the micro-drilling manufacture increasingly springs up with the rapid development of production industries ranging from precise mechanics to advanced electronics.Main problems considered in micro-drilling process are unsteady self-alignment and larger thrust force which lead to worse drilling performances including lower hole quality and more severe drill wear.To explore solutions to these problems,the thesis presents in-depth research on the geometric structure and grinding technology for the helical drill point with nonlinear helical pitch based on kinematic characteristics of biglide parallel machine.The thesis mainly includes the following four aspects:(1)The first step is to conduct the basic theoretical research on twist drill.On the foundation of summaries for existing grinding methods,mathematical models for drill point are established using the vector method which combines the nonlinear deceleration in Z-axis direction of the biglide parallel grinder.Furthermore,determine four geometrical parameters,four grinding parameters and establish relevant theoretical models and relational equations between them.In virtue of the optimization algorithm,nonlinear equations about grinding parameters can be solved successfully.The last step of theoretical work is to analyze the error relationship between two types of parameters to guide practical grinding process.(2)In order to settle the uniqueness of solutions to grinding parameters,the thesis introduces the heel clearance angle as the fourth complementary geometrical parameter.Deeply analyze the attribution of heel clearance angle on flank surface with nonlinear helical pitch and discuss its advantages,On condition that the length of parallel link has influence on the movement locus of moving platform,the paper establishes the relationship between geometry of drill point and link length and finally optimize the structure of machine tool.(3)This thesis presents numerical and three-dimensional simulations on the chisel edge based on the mathematical models.Develop convenient human-computer interfaces including GUI interface for solution to grinding parameters and VB interface for optimizing programs to improve grinding efficiency.(4)In order to verify the validity of theoretical models for drill point and geometrical parameters,grinding experiments and examinations are performed to compare the design parameters required and actual parameters measured.To verify that the helical twist drill has better drill performances than conical drill,drilling experiments on composite material are conducted to measure the drilling thrust force and torque.Research indicates that:with the consideration of the nonlinear deceleration in Z-axis direction of the biglide parallel grinder,theoretical models established above are better aligned with actual grinding movements.Simulations demonstrate that the chisel edge presents S-shape in end-view plane perpendicular to drill axis.Drilling experiments validate that compared to conical twist drill,helical drill can cut more smoothly with more stable self-alignment and lower thrust force,improve hole quality when drilling materials and finally prolong life-span of drill point.