Roughness evaluation of machined Ti-6Al-4V alloys with a study of surface topography measurement noise

• Various machined Ti-6Al-4V surface topographies were investigated. • The surface roughness was studied with a contactless WLI instrument. • The surface topography vibrational noise was reduced with a newly introduced method. • The methodology used was validated against a regular, repetitive measuring technique. • Variations and influences on ISO 25178 texture parameters were presented in detail. The Ti-6Al-4V alloys are widely used materials in plenty of engineering solutions since they provide many industry-required properties. Accuracy in analysing this type of alloy depends on numerous factors that can be studied extensively. Except for the encouraging material strength characteristics, a thorough evaluation of their topographies can be crucial in a profound understanding of many mechanical behaviours. Therefore, a comprehensive and precise analysis of surface layers depends on a proper assessment of topography. Recently, very modern and popular contactless measuring techniques against the stylus have been fast but burdened with various external disturbances. Those disruptions can cause a measurement noise occurrence in the data collected during the measurement process. A typical example of the topography measurement error is high-frequency noise, which originates from vibration of the measuring system. This type of disturbance can cause a serious distortion in the values of surface texture parameters. The most common method for reducing this type of roughness measurement noise is to repeat the surface measurements and average the received results, as defined in the international noise definition of ISO 25178 (part 600). In this study, an alternative measurement noise extraction method was proposed for the analysis of various types of machined Ti-6Al-4V materials. An extensive study of noisy data supported this methodology, with a proper application of functions widely used in surface metrology. The proposed method presented that the usage of general functions with a suitable order can allow for a proper definition of the measurement noise and reduce its destructive influence on the results of topography measurements. Finally, comparing the results to the international noise ( N M ) definitions and general method with measurement repetitions, this procedure was encouraged and validated for regular use, allowing for a selection of suitable digital filters for minimisation of the effect of surface topography measurement noise.