基于功能参数的渐进成形件表面质量表征研究

Quality Characterization of Surfaces Formed by Single Point Incremental Forming Based on Functional Parameters

目的以圆锥台成形件为例,基于粗糙表面的区域支承率曲线,进行了用功能参数表征表面几何形貌的研究,以全面、准确、定量地表征渐进成形件的表面质量,预测表面性能。方法用渐进成形工艺加工成形角分别为35、45和55的圆锥台件,将各圆锥台的成形面分为顶部、中部和底部三个区域,并使用三维表面轮廓仪,在上述三个区域中随机测量各4个样本。根据ISO 25178-2:2012,将各样本表面的区域支承率曲线分为峰区、核心区和谷区,选用部分功能参数——核心区高度Sk、峰区材料体积Vmp、核心区材料体积Vmc和谷区空隙体积Vvv表征表面,并与常用的高度表征参数——Sa、Sq、Ssk和Sku进行比较。结果成形件表面的Ssk和Sku的计算值极不稳定,变异系数(标准偏差与均值之比)最高值分别可达127.67%和39.11%,Sa、Sq的最大变异系数分别为4.41%和4.26%,虽然它们的参数计算值较为稳定,但常无法体现表面形貌的实际差异。功能参数独立表征不同功能区,Sk和Vmc的最大变异系数分别为9.32%和7.73%,说明同一表面各处,在长期工作阶段具有较为一致的表面性能,Vmp和Vvv的最大变异系数分别为60.53%和31.25%,说明表面各处峰、谷区的形貌有所不同,因而在磨合时间、磨粒存储等方面会有不同的表现。结论粗糙表面的三维本质要求用三维表征参数才能全面表征其几何形貌。高度参数虽然计算简单,但常难以解读它们的物理意义,无法定量评价表面性能;功能参数具有明确的物理意义,可为表征表面质量、预测表面性能提供定量、实用的方法。

The work aims to characterize the quality of surfaces formed by single point incremental forming(SPIF)comprehensively,accurately and quantitatively,and predict the surface properties and then carry out study on the characterization of geometrical morphology by functional parameters based on the material ratio curve in rough surface with conical frustums as examples.Conical frustums with forming angles of 35,45 and 55 were processed respectively by SPIF.The formed surface of each frustum was divided into top,middle and bottom regions,and 4 samples were randomly measured in each region by three-dimensional surface profile.According to ISO 25178-2:2012,the material ratio curve of each measured rough surface was divided into three regions:peak,core and dale.Some functional parameters,such as core height Sk,peak material volume Vmp,core material volume Vmc and dale void volume Vvv were selected and compared with commonly used height characterization parameters including Sa,Sq,Ssk and Sku.The values of Ssk and Sku of the formed surfaces were extremely unstable,and the maximum variation coefficients(ratio of standard deviation to mean value)were 127.67%and 39.11%respectively.The maximum variation coefficients of Sa and Sq were 4.41%and 4.26%respectively,which were relatively stable,but often failed to reflect the actual differences in morphology.Since functional parameters characterized functional regions independently,the maximum variation coefficients of Sk and Vmc were 9.32%and 7.735 respectively,which indicated consistent surface properties in long-term working stages.Meanwhile,the maximum variation coefficients of Vmp and Vvv were 60.53%and 31.25%respectively,which indicated different appearance in peak and dale regions,and different performance in running-in stage and wear particle storage.Therefore,the three dimensional nature of rough surfaces requires three dimensional parameters to fully characterize their geometries.The calculation of height parameters is simple,but it is often difficult to interpret the physical meaning,and evaluate the surface properties quantitatively.The functional parameters have clear physical meaning,which provides a quantitative and practical way for surface quality characterization and performance prediction.