A cutter-workpiece engagement (CWE) calculation approach for multi-axis milling of spur gears based on surface trimming was proposed.Firstly, to accurately describe the relative motion relationship between the milling cutter and the workpiece, a gear milling motion model was established.Secondly, based on the established precise mathematical model of the involute gear tooth profile, the constant scallop-height method was applied for tool path planning, with precise calculation of the coordinate positions for each cutter location point.Thirdly, the cutter sweep surface was approximated using a hemispherical surface, and the CWE was defined as a partial sphere constrained by three boundary curves.The hemispherical surface was trimmed using the surface where the boundary curves are located to accurately extract the CWE.Finally, the engagement angles were calculated through an intersection operation between the CWE and a plane perpendicular to the tool axis.A comparative analysis of the simulated and experimentally measured CWE demonstrates the high computational accuracy of the proposed method.Furthermore, compared with solid modeling-based method adopted in the literature, this method has a higher computational efficiency.
图7g中切触区域CWE k 可表示为上述3个可能切触区域的相交区域;可能切触区域是由曲面分割代表刀具回转面的半球面SS k 形成的.因此,CWE k 可通过渐开面等距面IS、辅助平面FS k 和半圆柱面HCS k-1依次修剪半球面SS k 来获取,如图7h所示.
通过曲面修剪构造切触区域CWE k 的过程如图8所示.首先建立刀具回转面,即初始可能切触区域SS k 和渐开面等距面IS,通过IS修剪SS k,得到更新的切触区域FCWE1;其次,构造刀路k-1的刀具扫掠面HCS k-1,通过HCS k-1修剪FCWE1得到更新的切触区域,即部分FCWE2;然后,在Lk,i 处构造辅助平面FS k,通过其修剪部分FCWE2,得到最终的结果切触区域CWE k;最后,沿着刀具轴线建立垂直于刀轴的辅助平面SP i,通过其与CWE k 求交得到表示切触区域的圆弧曲线,进而确定切入角和切出角.
仿真与试验所采用的加工参数如表1所示.仿真采用NX 1953实体建模软件,结合NX/Open二次开发模块和Visual Studio 2019编程环境实现直齿轮铣削切触区域的计算.齿轮铣削加工采用五轴加工中心DMU 50,如图10a所示;切触区域边界曲线测量采用19JPC-V数显万能工具显微镜,如图10b所示.
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