We report a study of the correlation between three optical methods for characterizing surface roughness: a laboratory scatterometer measuring the bi-directional reflection distribution function (BRDF instrument), a simple commercial scatterometer (rBRDF instrument), and a confocal optical profiler. For each instrument, the effective range of spatial surface wavelengths is determined, and the common bandwidth used when comparing the evaluated roughness parameters. The compared roughness parameters are: the root-mean-square (RMS) profile deviation (Rq), the RMS profile slope (Rdq), and the variance of the scattering angle distribution (Aq). The twenty-two investigated samples were manufactured with several methods in order to obtain a suitable diversity of roughness patterns. Our study shows a one-to-one correlation of both the Rq and the Rdq roughness values when obtained with the BRDF and the confocal instruments, if the common bandwidth is applied. Likewise, a correlation is observed when determining the Aq value with the BRDF and the rBRDF instruments. Furthermore, we show that it is possible to determine the Rq value from the Aq value, by applying a simple transfer function derived from the instrument comparisons. The presented method is validated for surfaces with predominantly 1D roughness, i.e. consisting of parallel grooves of various periods, and a reflectance similar to stainless steel. The Rq values are predicted with an accuracy of 38% at the 95% confidence interval.

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The generation of fine machined surfaces with high gloss is an important topic in mould manufacturing. The surface gloss can be characterized by means of scattered light sensors and a representative parameter such asAq. In this paper, in-line measurements of scattered light distribution are compared with roughness parameters calculated using a confocal microscope, in order to assess surface aesthetic quality. Several surfaces have been machined by means of high precision milling, producing different surface topographies. Surface characterization has been performed on a machine using a scattered light sensor, and using a confocal microscope in laboratory conditions. The calculatedAqparameter is compared with the amplitude roughness parametersSaandSq, and with hybrid parametersSdqandRdqrepresenting the average slope of the surface features. Scanning electron microscope (SEM) images are used as visual benchmarks to identify the parameters’ correlation with the visual appearance. A different linear trend of the relationship betweenAq,Rdq, andSdqis observed. The description of the surface quality throughSaorSqinstead is found to be insufficient. This is explained by means of SEM pictures showing a dramatic influence of the smeared material over the machined surface.

Abstract:The reproducibility of a reaming test was analysed to document its applicability as a performance test for cutting fluids. Reaming tests were carried out on a drilling machine using HSS reamers. Workpiece material was an austenitic stainless steel, machined using 4.75 m·min -1 cutting speed and 0.3 mm·rev -1 feed. A mineral straight oil and a water-based lubricant at two different oil concentrations were compared with respect to hole quality, evaluated in terms of surface finish (conventional arithmetic mean roughness Ra and roughness profiles), and hole geometry (hole diameter and roundness). Process reproducibility was assessed as the ability of different operators to ensure a consistent rating of individual lubricants. Absolute average values as well as experimental standard deviations of the evaluation parameters were calculated, and uncertainty budgeting was performed. Results document a built-up edge occurrence hindering a robust evaluation of cutting fluid performance, if the data evaluation is based on surface finish only. Measurements of hole geometry provide documentation to recognise systematic error distorting the performance test.[ He is an internationally recognised expert in manufacturing and metrology, having published over 200 technical papers in international journals and conference proceedings. His theoretical models quantifying the role of friction and lubrication in metal cutting are described in textbooks worldwide. He has been the Supervisor of more than 100 MSc students and over 20 PhD students. He has been initiator and coordinator of major framework programmes, and created and directed since its formation the Centre for Geometrical Metrology (CGM). Moreover, he has established a transnational virtual institute for geometrical metrology between DTU and Padova University. He is a Fellow of the International Academy for Production Engineering (CIRP) and panel member of the Foundation Committee of the European Society for Precision Engineering and Nanotechnologies (Euspen).

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