镀层表面轮廓曲线分形维数计算方法的评价

镀层表面轮廓曲线具有分形结构,可以用分形维数(D)来定量表征。为了验证现有D值测算方法的准确性,利用W–M分形函数生成了具有不同D值的标准表面轮廓曲线,并用垂直截面法、尺码法、盒维数法、方差法、结构函数法、协方差加权法、功率谱法、均方根法共8种方法计算了其D值。研究表明,尺码法的相对误差范围在6.20%~22.77%之间,平均相对误差最大,为16.76%;其次是协方差加权法,其相对误差范围为2.17%~21.35%,平均相对误差为11.73%;盒维法、功率谱法和方差法的平均相对误差分别为8.61%、6.92%和5.25%;均方根法和垂直截面法的相对误差范围分别为0.51%~9.84%和0.19%~3.97%;结构函数法的最大相对误差仅为1.21%,最小相对误差低至0.01%,平均相对误差仅为0.45%。因此,结构函数法最准确,是计算分形维数的最佳方法。

Technological requirements of profile machining

The term ‘profile machining’ is used to refer to the milling of vertical surfaces described by profile curves. Profile machining requires higher precision (1/1000 mm) than regular 3D machining (1/100 mm) with the erosion of sharp vertices should being especially avoided. Although, profile machining is very essential for making trimming and flange dies, it seldom brought into focus. This paper addresses the technological requirements of profile machining including machining width and depth control, minimizing toolware, and protecting sharp vertices. Issues of controller alarms are also addressed.