Prevention of Chatter Vibration in Ball End-Milling Operation of Curved Surfaces with Cutting Edge of Reduced Tool-Chip Contact Length

本文对减小刀屑接触长度的球头立铣刀在凹模加工中防止颤振的效果进行了试验研究。对于具有圆形部分、倾斜部分和平底的模具横截面，以具有y轴拾取进给的x-z轴控制的方式执行操作。经验证，无论使用何种切削条件、圆形零件的半径、斜面的倾斜度以及立铣刀的上或下走刀，减少接触刃总是有效的。本文提出了一个分析系统，使我们能够仅用正交切削数据作为数据库，预测在任何切削条件下，端铣时切削力的三个分量（无颤振）。预测的切削力分量与实验结果吻合较好，进一步发展了该系统，使其适用于含颤振的动态切削过程，并实现了颤振发生的计算机模拟。仿真结果表明，当切屑厚度存在扰动时，减小接触长度可以抑制切削力的变化，从而减小振动系统的激振力。但是，目前的仿真系统还存在一些不足，不能预测与实验结果一致的稳定阈值。改进试验仍在进行中。

The etrects of ball end-mill with cutting edge of reduced tool-chip contact length upon prevention of chatter vibration are examined experimentally in die sinking operation. The operation is performed in the manner of x - z axs control with y axis pick feed for a die cross-section having circular parts, slant parts and flat bottom. It is verified that the reduced contact edge is always effective, regardless of cutting conditions used, radius of the circular part, inclination of the slant, and up or down pass of the end-mill. The threshold depth of cut for chatter occurrence is made 1.5-3 times as much as conventional cutting edge.An analytical system is developed, which enables us to predict three components of cutting force (without chatter) during the end-milling of any cutting conditions by only using orthogonal cutting data as data-base. The predicted force components are proved to be in good agreement with experimental results.This system is further developed to be adapted for dynamic cutting process with chatter vibration, and computer simulation of chatter occurrence is made possible. Through the simulation, it is revealed that the reduced contact length suppresses the cutting force variation when some disturbance is introduced in undeformed chip thickness, hence it would reduce excitation of the vibration system. The simulation system, however, has some deficiencies at present and is not able to predict the stability threshold which agrees with experimental results. The improving trials are still going on.