Modeling of Surface Geometric Structure State After Integratedformed Milling and Finish Burnishing

Abstract

Abstract The article deals with computer-based modeling of burnishing a surface previously milled with a spherical cutter. This method of milling leaves traces, mainly asperities caused by the cutting crossfeed and cutter diameter. The burnishing process - surface plastic treatment - is accompanied by phenomena that take place right in the burnishing ball-milled surface contact zone. The authors present the method for preparing a finite element model and the methodology of tests for the assessment of height parameters of a surface geometrical structure (SGS). In the physical model the workpieces had a cuboidal shape and these dimensions: (width × height × length) 2×1×4.5 mm. As in the process of burnishing a cuboidal workpiece is affected by plastic deformations, the nonlinearities of the milled item were taken into account. The physical model of the process assumed that the burnishing ball would be rolled perpendicularly to milling cutter linear traces. The model tests included the application of three different burnishing forces: 250 N, 500 N and 1000 N. The process modeling featured the contact and pressing of a ball into the workpiece surface till the desired force was attained, then the burnishing ball was rolled along the surface section of 2 mm, and the burnishing force was gradually reduced till the ball left the contact zone. While rolling, the burnishing ball turned by a 23° angle. The cumulative diagrams depict plastic deformations of the modeled surfaces after milling and burnishing with defined force values. The roughness of idealized milled surface was calculated for the physical model under consideration, i.e. in an elementary section between profile peaks spaced at intervals of crossfeed passes, where the milling feed fwm = 0.5 mm. Also, asperities after burnishing were calculated for the same section. The differences of the obtained values fall below 20% of mean values recorded during empirical experiments. The adopted simplification in after-milling SGS modeling enables substantial acceleration of the computing process. There is a visible reduction of the Ra parameter value for milled and burnished surfaces as the burnishing force rises. The tests determined an optimal burnishing force at a level of 500 N (lowest Ra = 0.24 μm). Further increase in the value of burnishing force turned out not to affect the surface roughness, which is consistent with the results obtained from experimental studies.