You can see it…but you can’t seem to quantify it with your surface finish measurements, and thus you don’t know how to fix it! Many times component appearance such as refrigerator doors, car hoods, sink bowls, faucets, knee implants and even food may affect the success of the product in the market. Being able to quantify and relate the surface finish to the appearance is challenging, requiring the need to understand the various spatial components that comprise the texture and the many surface finish parameters that may ultimately correlate to the intended appearance. When attacking an appearance problem, the first task is to determine which spatial wavelengths that comprise the texture are critical to the appearance desired. For example, if an “orange peel” type of appearance is needed, the spatial wavelengths of 1 millimeter to 5 millimeters may be of importance. On the other hand, if the texture needs to look like “satin,” spatial wavelengths between 0.010 millimeters and 0.1 millimeters might be preferred. Bruker’s 3D optical profilers employ various lenses and computer-controlled image stitching to enable the measurement of surface finish over spatial wavelengths from 5 microns to hundreds of millimeters. Coupled with advanced 3D surface texture analysis software, the surface finish within the various spatial wavelength bandwidths can be analyzed. Once the spatial wavelengths are determined, the next step in relating surface finish to appearance is to establish a set of texture parameters. For example, the overall roughness (Sa) within the specified spatial bandwidth may be sufficient. More advanced consideration might suggest the measurement of the surface slope (Sdq) or surface area (Sdr) to be of more importance. Note that the chosen surface texture parameters are evaluated only within the determined spatial wavelength bandwidth. For many applications the various spatial wavelengths that comprise the texture may affect different aspects of the component. For example, when working with sheet steel, the shorter wavelength components (<0.5 mm) may affect the lubricating properties and friction during forming. However, once the steel surface is treated and painted, the longer spatial wavelengths (>0.25 mm) may be critical to final appearance. Thus the ability to measure the original surface before forming and painting may be advantageous in predicting the final component performance and in avoiding the production of an unacceptable finished product. Advances in 3D optical surface profiling providing high lateral resolution, large field of view measurements and selectable bandwidth filtering software are now allowing the industry to better predict, control and optimize the production of critical aesthetic features comprising products from washing machines to chocolate bars!
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