A model to predict the three-dimensional cutting force system for drilling with arbitrary point geometry.

摘要

Drilling is a widely used hole generation process in industry today. The quality of the hole produced includes characteristics such as roundness and cylindricity errors, surface finish, burrs, delamination in drilling composites, etc. Most of these parameters are related to the cutting forces generated in the process. Modeling the cutting forces in drilling, in terms of the tool geometry and machining conditions, is an important step in developing a simulation-based platform for the design and evaluation of new drill point geometry to improve quality and productivity.; A model is first developed to predict the three-dimensional cutting force system in drilling with the conical drill. Separate models are developed for the cutting lips and chisel edge of the drill. The cutting lips model is based on a fundamental mechanistic oblique cutting model. A calibration algorithm is developed to determine the model coefficients for a tool and workpiece material combination from just four drilling experiments. The drilling force model is validated for a wide range of drill point geometry parameters and machining conditions. The model coefficients determined from drilling tests are also used to predict the forces in end milling to show these coefficients are process independent.; The model is then extended to predict the forces for arbitrary drill point geometry. A method is developed to parametrically describe the geometry and to determine the required cutting angles and chip thickness at elements along the cutting lips. Four commercially available drill points--Racon, Helical, Bickford and Double angle points, are mathematically parameterized and the model simulations are in good agreement with thrust and torque data from experiments over a range of machining conditions.; In this study, some common problems encountered in drilling and their effect on the cutting forces are also modeled. These include errors in grinding the drill point, errors in locating the drill in a tool holder, and the case of drill penetration into a workpiece surface inclined to the drill axis. These cases create an unequal chip load on each lip and result in a net radial force. The radial forces are the primary cause for drill deflection and wandering, and result in higher roundness and cylindricity errors. Experiment are conducted for drilling into workpiece surfaces inclined to the drill axis at 10{dollar}spcirc{dollar} and 20{dollar}spcirc{dollar} and the thrust, torque and radial forces simulated match the experimental data.