Traditional Roughness Parameters Research Articles

Influence of topographical features on the surface appearance measurement of injection moulded components

Adding textures to surfaces is known to improve the external appearance of injection moulded components. However, when high surface quality is required, normally a paint coating is applied on top of the moulded textured surface. In this work, an alternative to painting for obtaining high quality surfaces is proposed, following an environmental-friendly process and having low production cost. Three different surface textures obtained by injection moulding have been characterized and compared with a painted one. Alternative topographical parameters such as the absolute functional height (AFH), the functional height distribution (FHD), texture slope (TS) or texture aperture angle (TAA) besides to the traditional roughness parameters such as the arithmetical mean height (Sa) and the root mean square height (Sq) have been utilized to characterize the random surface textures. The relationships between these parameters and the surface quality appearance represented by gloss and reflectivity contrast have been established using a new total appearance measurement (TAM) apparatus. It was found that by applying secondary operation on the textured mould cavity, such as adding micro roughness features or coatings, equal apparent quality to the ones obtained by painting can be reached.

Research on characterization of anisotropic and isotropic processing surfaces by characteristic roughness

The paper focuses on the analysis of the characteristic roughness (τ*) and surface contour features with respect to anisotropic and isotropic processing surfaces. After measuring 38 specimens made by 9 kinds of manufacturing methods using a two-dimension (2D) profilometer. Then the surface roughness parameter (Ra, arithmetic mean deviation) is easily obtained, as well as the coordinates of the contour curves which will be used to calculate scale coefficient (C) and fractal dimension (FD) by the structure function method (SFM), and then the characteristic roughness (τ*) is acquired. Through analyzing the measurement data and comparing the parameters of the Ra, τ* and FD, the laws among the τ*, Ra, FD and the surface contour features are investigated. The results show that the measurement direction has a great influence on the τ* for anisotropic surfaces; while for isotropic surfaces, the measurement direction has little influence on the τ*. Under the same processing method, whether the surface is anisotropic or isotropic, the relationship between the τ*, FD and Ra are negative proportional. As FD increases, the density of the surface contour adds; as C drops, the amplitude of the contour also decreases; as τ* rises, the surface flatness becomes better, the regularity of the microscopic morphology is more obvious, and the surface quality is better. Under the different processing methods with same Ra, compared to the anisotropic surfaces, the value and difference of τ* are smaller in the cases of isotropic surfaces. The characteristic roughness-τ* does not lose the multiscale characteristic of fractal measurement, but also retains the intuitive characteristics of traditional roughness parameters, and can be used to judge the quality of surfaces and help us to select a suitable processing method for a better cost performance.

Low-coherence interferometry based roughness measurement on turbine blade surfaces using wavelet analysis

In this paper, a non-contact optical system, a low-coherence interferometer (LCI), is introduced for the purpose of measuring the surface roughness of turbine blades. The designed system not only possesses a high vertical resolution and is able to acquire the roughness topography, but also it has a large vertical scanning range compared to other commonly used optical systems. The latter characteristic allows us to measure turbine blades surfaces with large curvature without collisions between the lens and the measurement object. After obtaining the surface topography, wavelet analysis is applied to decompose the original surface into multiple bandwidths to conduct a multiscale analysis. The results show that the developed LCI system proofs a good performance not only in obtaining the surface topography in the roughness scale but also in being able to measure surfaces of objects that possess a complex geometry in a large vertical range. Furthermore, the applied biorthogonal wavelet in this study has performed good amplitude and phase properties in extracting the roughness microstructures from the whole surface. Finally, the traditional roughness parameters, such as the mean surface roughness Sa and the Root Mean Square (RMS) roughness Sq, are evaluated in each decomposed subband and their correlations with the scale of each subband are analyzed.

Evaluating the Roughness According to the Tool Path Strategy When Milling Free Form Surfaces for Mold Application

The mold manufacture has a direct influence on the lead time, costs and quality of plastic products. Milling is the most important machining process in this industry. Due to some limitations on the milling operations, the surface roughness required for a mold is frequently only achieved by hand finishing. Even using updated technologies such as High Speed Milling, which improves the machined surface quality, the hand finishing is still required and it brings some drawbacks such as costs, time and geometrical errors. Today, any CAM software offers some different tool path strategies to milling free form geometries. However, the users must have the know-how to choose the strategies according to geometry complexity, cutting tool geometry and its contact on the machined surface. Choosing an optimum strategy is a rather difficult task to do on the shop floor. This topic is still not very well explored. The current work investigates different tool path strategies for milling a mold cavity during finishing operation. A mold cavity was manufactured and the results show that the tool path strategies have a great influence on the real milling time, surface roughness and hand finishing time and also show that the traditional roughness parameters are not adequate to measure the roughness in such applications.

Fractal analysis of engineering ceramics ground surface

Traditional methods of roughness characterization cannot properly reflect the differences between metal and engineering ceramics surfaces. Therefore, fractal method is introduced to characterize the engineering ceramics ground surface in this paper. This article compares various methods to calculate profile dimension. By comparison, the variation method is suitable for extracting fractal dimension of engineering ceramics ground surface. The precision of variation method is further improved by modifying the error. In view of engineering ceramics ground surface, we have analyzed the relationship between fractal dimension and traditional roughness parameters, surface texture, surface function and material property using modified variation method.

Biologically Inspired Surfaces: Broadening the Scope of Roughness**

AbstractSuperhydrophobicity can be used for many applications that require non‐adhesive and water‐repellent surfaces. A successful design of superhydrophobic surfaces requires a correct assessment of the surface roughness effect on wetting. Roughness is an important property in surface mechanics, physics, chemistry, and biology, and it is critical for many tribological applications. Roughness can be defined in different ways, and the definition should be adequate to the problem under investigation. Our recent studies of biological and biomimetic superhydrophobic surfaces show that traditional roughness parameters, such as the root‐mean‐square, correlation length, or fractal dimension, are not always appropriate for the analysis of wetting. This is, in particular, due to the hierarchical nature of wetting mechanisms and interfaces. We discuss the effect of roughness on wetting mechanisms and relevant roughness parameters and ways to broaden the concept and scope of surface roughness.

Surface texture characterization of injection‐molded pigmented plastics

AbstractAn appropriate description of the surface textures deliberately created on injection‐molded plastic parts of interior car components is presented. A spatial wavelength‐dependent analysis is used as an interesting alternative to the traditional roughness parameters. Auto‐correlation functions and power spectral densities are examples of such spectral functions that include parameters both in amplitude and profile directions. Even fractal concepts can be useful descriptors. As an illustration, it is also shown how the effects on the surface topography of the plastic part of after‐etching the mold can be assessed by suitable descriptors. An experimental evaluation of injection‐molded plaques containing three different surface patterns was carried out using an optical profilometer, supplemented by contact stylus measurements. The ability to assess the topography of these plaques by means of a new fast photometric stereo‐technique, denoted OptiTopo, was also evaluated. In its present form, however, this technique does not provide a detailed description of the topography of a pigmented plastic. Reasons for this and possible improvements are discussed. Polym. Eng. Sci. 44:1615–1626, 2004. © 2004 Society of Plastics Engineers.

The fractal character of processed metal surfaces

The fractal character of lapped and shaped Babbitt alloy surfaces was investigated by using the structure function analysis method, and the fractal parameters D and G of these two typical kinds of engineering surfaces were determined. It is shown that the random lapped surface was fractal and had a bifractal structure within the range of length scale investigated in this paper. Like the traditional roughness parameters of the lapped surface, its fractal parameters in different measuring directions had almost the same value. A periodic shaped surface was also fractal when the length scale was smaller than the mean spacing roughness S m, but its fractal parameters in the direction orthogonal to the machining direction differed greatly from those parallel to the machining direction just as its traditional roughness parameters did. The scale-independence of fractal parameters D and G was studied by changing the sampling spacing Δ t of the computer system, which corresponds to spatial measuring resolution, and sampling length L during surface profilometry. Experimental results show that the sampling spacing Δ t did not affect D and G values. Sampling length L did not effect D and G values when L≫ S m, but too short a sampling length L meant these two fractal parameters changed. The reasons causing this phenomenon are discussed in this paper.