A New Evaluation Method for Surface Finish of Composite Automotive Panels Using Waveform Analysis

Abstract

The surface finish of composite plates made using Resin Transfer Molding of glass/polyester is studied. A surface profilometer is used to measure the surface profile and to record raw data. The objective is to develop an objective method (rather than using human judgment) to differentiate the quality of one surface from another. Initially commonly used current techniques are utilized to assess the quality of the surface finish. These include subjective evaluation through a survey of observations from a group of people; the use of the average amplitude of the signals, frequency analysis, and filtering. For surfaces that have approximate quality, human visual observation can differentiate the quality between the surfaces, but the objective methods (average amplitude, frequency spectrum, and filtering) cannot. A new objective technique is found to be able to distinguish surfaces of approximate quality. This uses the comparison between the parameters of a reference good surface to those of the surface under consideration. A comparative index can be obtained to indicate the degree of similarity between the surface under study and the reference (good) surface.

Ranking of fibre-reinforced composite plate surface finish quality by wavelet texture analysis

“…Spearman's rho (ρ) and Kendall's tau (τ) rank correlation coefficients were calculated for each rater pair as a measure of interrater reliability and the results are presented in Table 2. The average variation in plate ranking was only 1.76, which compares favourably to a similar multi-rater rank-based analysis [5] . All inter-rater rank correlation coefficients were positive, large and statistically significant.…”

“…All inter-rater rank correlation coefficients were positive, large and statistically significant. There was a high degree of agreement between the raters, suggesting that a simple mean of the three rank scores for each plate can be used as the basis for an overall combined rank score, which when re-ranked then becomes the reference/benchmark rank, as used in the similar previous analysis noted above [5] .…”

“…Traditionally, the quality of automotive surface finish has been judged by expert human auditors [1] . It has also been the most commonly used and reliable approach for evaluation of the surface quality of composites [5] . While it is possible for an expert rater to make an absolute assessment of surface quality, it is also common for human assessors to undertake visual assessments by ranking a number of samples, either indirectly as a series of pair-wise comparisons or directly into an ordinal sequence [1,5,6] .…”

“…The use of human inspectors in assessing surface quality, while effective, is labour-intensive, does not lend itself to automation and can have problems with subjectivity in rating and inter-rater reliability [7] . However, many available objective instrumental techniques for the measurement of surface finish quality do not always correlate well with human assessment [1] ; it has been suggested that the surface roughness parameters commonly used do not completely characterise the visually-perceived quality [5,8] . So, an objective instrumental technique that can provide comparable results to human experts is desirable [1,5] .…”

“…However, many available objective instrumental techniques for the measurement of surface finish quality do not always correlate well with human assessment [1] ; it has been suggested that the surface roughness parameters commonly used do not completely characterise the visually-perceived quality [5,8] . So, an objective instrumental technique that can provide comparable results to human experts is desirable [1,5] . ASTM E430-11 describes standard test methods for measurement of the gloss of highgloss surfaces by abridged goniophotometry and is used by the automotive industry, however the equipment required (for example a BYK-Gardner GmbH wave-scan Dual) costs more than US$40k.…”