ROUGHNESS VARIATION CAUSED BY GRINDING ERRORS OF CUTTING EDGES IN SIDE MILLING

Abstract

A numerical model was developed to predict the roughness profile along a line in the feed direction, in contour milling operations with cylindrical milling tools. From the model, average roughness R_a and maximum peak-to-valley roughness R_t were calculated for families of tools defined by 100,000 random combinations of radius values. Radii were selected by means of the Monte Carlo Method. Each family is defined by an average radius and a standard deviation of radius, assuming normal behavior. Histograms, roughness variation intervals, medians and modes, were calculated at different feeds. The model was validated through experimental tests. Effect of standard deviation of radius, number of teeth and tool diameter were studied. Although radius values were randomly selected according to a normal law, roughness values did not follow a normal distribution. At low standard deviations, intervals of roughness values, medians and modes vary only slightly with feed, except at very low feeds where intervals are narrow. On the contrary, at higher standard deviations, median, mode and width of roughness intervals rise as feed increases. Use of a lower number of teeth and higher tool diameter leads to narrower intervals and asymmetrical roughness frequency distributions even at high feeds, with modes near upper reference values.

Keywords:

• grinding errors
• Monte Carlo
• runout
• side milling
• surface roughness

ACKNOWLEDGMENT

The authors thank the Spanish Ministry of Education and Science for funding project (DPI2007-66546). Mr. Alejandro Domínguez-Fernández and Mr. Ramón Casado-López are also acknowledged for their contributions to machining, roughness measurements and simulations.