STANDARDIZATION - A MITIGATING OR A CONFUSING CIRCUMSTANCE IN SURFACE ROUGHNESS MEASURING IN THE METAL PROCESSING INDUSTRY

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1 International Journal of Industrial Engineering & Technology (IJIET) ISSN Vol. 3, Issue, Mar 3, 37-4 TJPRC Pvt. Ltd. STANDARDIZATION - A MITIGATING OR A CONFUSING CIRCUMSTANCE IN SURFACE ROUGHNESS MEASURING IN THE METAL PROCESSING INDUSTRY MIKOLAJ KUZINOVSKI & MITE TOMOV Ss. Cyril and Methodius University in Skopje, Faculty of Mechanical Engineering-Skopje, Skopje, Karpos II. BB, Macedonia ABSTRACT As a result of a detailed analysis of several International standards, this paper suggests several dilemmas arising from the recommendations in the standards referring to surface roughness measurement. These dilemmas can lead to confusion among users and can have a significant impact on the accuracy of the roughness parameters values, especially when using contact skidded or skidless instruments. Such inconsistencies in the International standards are contrary to the objectives of standardization, where the main principle is the unequivocalness of measuring procedures. KEYWORDS: International Standards, Roughness Parameter, Profile Filter, Skidded Instruments, Skidless Instruments INTRODUCTION In order to make the results from the measurement of any value measured at different locations, comparable and repeatability, usually the prescribed measurement methodology is in accordance with the recommendations of specific National or International standards. This also applies to surface roughness measurements. However, one must bear in mind that the prescribed recommendations contained in the International standards are general and applicable to a wider scope of measuring instruments and devices. There are various kinds of measuring instruments, with different features, used to measure surface roughness. This leads to equivocality when defining the measuring procedures for determining surface roughness. This paper stipulates certain ambiguities (dilemmas) present in the International standards for surface roughness measurement. Here, they will be considered systematically in two groups: instrumentation and software filtration. INSTRUMENTATION According to (ASME B46.-9) all instruments that measure surface texture can be grouped into six groups of instruments (first: profiling contact skidless instruments, second: profiling non-contact instruments, third: scanned probe microscopy, fourth: profiling contact skidded instruments, fifth: skidded instruments parameters only, and sixth: area averaging instruments). The most commonly used instruments in the metal processing industry are the contact skidded or skidless instruments. Figure, according to (Mite et al., 3) and based on the recommendations of several International standards, shows a measuring procedure for obtaining the primary profile, the roughness profile and the waviness using contact skidless instruments. The role of the skid is well known. In addition to the role of a mechanical reference used to register the vertical movement of the measuring stylus, the skid also has a role of a mechanical separator (a mechanical filter) of the roughness profile from the surface (total) profile, Figure.

2 38 Mikolaj Kuzinovski & Mite Tomov Real surface ISO 487:997 z y x Surface profile ISO 488:996 ISO 374:996 and other. Measurement process 3 4 Traced profile ISO 374:996 ISO 374: Total profile Nominal form (removed) ISO 374:996 ISO 487: mm mm ISO 374:996 µ m - - ISO 487:997; ISO 374:996; ISO 56:996; ISO 66 series. ISO 487:997 Mean line for the primary profile mm Application of the profil filter λc Primary profile Roughness profile Mean line for the roughness profile Application of the profil filter λs Noise mm Application of the profil filter λf Waviness profile ISO 487:997; ISO 374:996; ISO 56:996; ISO 66 series. ISO 487:997; ISO 374:996; ISO 56:996; ISO 66 series mm Roughness paremeter Ra, Rq, Rt, Rp, Rv.. Figure : Procedure for Obtaining the Primary Profile, the Roughness Profile and the Waviness using Contact Skidless Instruments (Mite et al., 3) z Total profile a) x z Roughness profile? b) x Figure : The Role of the Skid, a) Skidless Instruments, b) Skidded Instruments

3 Standardization a Mitigating or a Confusing Circumstance in 39 Surface Roughness Measuring in the Metal Processing Industry However, as we all know, one pick-up can contain several skids. It is recommended to place the skid in close proximity to the measuring stylus, before or after the stylus, or the measuring stylus can pass through the middle of the skid. Each of these positioning combinations (before or after the measuring stylus) influences the shape of the measured profile. Usually the shape and the position of the skid (skids) depend on the type of the pick-up (pick-up for the deep groove, pick-up for the curved surface etc.). Each construction will have a different impact on the shape of the measured profile. In this context, the International standards lack recommendations about the metrological characteristics of the geometry of the contact segment of the skid. Simply, according to (ISO 374:996), if the skid is employed, its radius in the direction of the trace should be no less than 5 times the nominal cut-off wavelength used. If we want to establish a measuring procedure using skidded instruments, based on the recommendations contained in the International standards (similar to the one shown in Figure ) we will face the following ambiguities. According to (ISO 374:996), instruments using skids can be used for measuring roughness parameters only. On the other hand, the calculation of the values of the roughness parameters requires the determination of a mean reference line using a λc profile-filter, which means that the measured profile should undergo software filtration using a λc profile filter. How do we call the profile through which we draw the mean reference line using a λc profile filter? Is this the primary profile shown on Figure? Also, having in mind that it is not possible to isolate the noise from the signal during the measurement, again there is a need for software filtration using a λs profile filter. If we add the noise to the primary profile, do we get the total profile from Figure? Every measuring instrument has a λs profile-filter, and usually, in the case of portable instruments, this filter turns on automatically, without any activation by the metrologist. If, on top of this, we also add the software leveling of the measured profile (using the least squares method) which is the same as removing the nominal linear shape, then we get the total profile using the procedure shown on Figure. Therefore, the question is: What kind of an initial profile is obtained when the using an instrument that uses a skid as a mechanical reference? SOFTWARE FILTRATION In order to obtain the roughness profile, regardless of the measuring instrument used, it is necessary to use a λc profile filter. Today there are several λc profile filters that can be used for surface roughness measurements. Their number increased when the ISO/TS 66 standard series appeared. The new profile filters introduces with the ISO/TS 66 standard series include: Gaussian filters (ISO 66-:), Gaussian regression filters (ISO/TS 66-3:), Spline filters (ISO/TS 66-3:9; ISO/TS 66-:6), Spline wavelets (ISO/TS 66-9:6), Disk and horizontal line-segment filters (ISO/TS 66-4:6), Scale space techniques (ISO/TS 66-49:6) and Motif filters (under preparation). All of these profile filters were developed to overcome the disadvantages of the Gaussian filter. In step 9 of the procedure presented in Figure, the metrologist should select one of these profile filters in order to obtain the roughness profile (separate it from the primary profile). The logical question here would be: Which profile filter to select? The metrologist makes this decision on the basis of the shape of the primary profile (or measured profile using skidded instruments). However, what will the metrologist do if he/she uses an instrument which does not provide a graphical presentation of the measured profile? To remove the disadvantages (the end distortions of the filter mean line obtained using the standard Gaussian filter) (ISO/TS 66-8:) recommends several methods of increasing the length of the primary profile. Here we especially consider the following methods: Zero padding, Linear extrapolation, Line symmetrical profile reflection and

4 4 Mikolaj Kuzinovski & Mite Tomov Point symmetrical profile reflection. In these methods particularly stand out and graphically represent the profiles with slope, Figure 3, 4, 5 and 6. Figure 3 : Zero Padding Using Standardized Gaussian Filter and Profile with Slope (ISO/TS 66-8:) Figure 4 : Linear Extrapolation Using Standardized Gaussian Filter and Profile with Slope (ISO/TS 66-8:) Figure 5 : Line Symmetrical Profile Reflection Using Standardized Gaussian Filter and Profile with Slope (ISO/TS 66-8:) Figure 6 : Point Symmetrical Profile Reflection Using Standardized Gaussian Filter and Profile with Slope (ISO/TS 66-8:) According to (ISO 374:996) the nominal forms are removed before the primary profile is obtained, which means that, when performing software filtration using a λc profile filter, the primary profile cannot have a slope. This begs the question: Why does the ISO/TS 66-8: standard include sloped profiles? The mean lines of the profile shapes shown on Figures 3, 4, 5 and 6 will not feature end distortions even if their lengths are zero padded and a standardized Gaussian filter used, of the nominal shape is removed before the filtration. CONCLUSIONS The dilemmas stated above, arising from the recommendations of the International standards, clearly show inconsistencies with the standardization objective which refers to unequivocalness of the measuring procedure definitions. These dilemmas can have a significant impact on the measured values of the roughness parameters, i.e. the values of the measured values depends on the experience and the knowledge of the metrologist. The authors of this paper, having in mind that the ISO standards are general and have to apply in multiple countries think that the standards need to be revised in the future in order to overcome these dilemmas. Further research is required in order to quantitatively determine what would be the impact of the dilemmas discussed above, especially when using skidded versus skidless instruments. REFERENCES. ASME B Surface texture (surface roughness, waviness, and lay). The American Society of Mechanical Engineers.. Mite Tomov, Mikolaj Kuzinovski, Pavel Kovać (3). A new approach in measuring of the roughness for surface constituted with machining process by material removal. International Journal of Mechanical and Production Engineering Research and Development (IJMPERD), ISSN , Vol. 3, Issue, Mar 3, 4-5.

5 Standardization a Mitigating or a Confusing Circumstance in 4 Surface Roughness Measuring in the Metal Processing Industry 3. ISO 374:996; Geometrical Product Specifications (GPS) - Surface texture: Profile method - Nominal characteristics of contact stylus instruments. 4. ISO 66-:; Geometrical product specifications (GPS)-Filtration: Linear profile filters: Gaussian filters. 5. ISO/TS 66-3:; Geometrical product specifications (GPS)-Filtration: Robust profile filters: Gaussian regression filters. 6. ISO/TS 66-3:9; Geometrical product specifications (GPS)-Filtration: Robust profile filters: Spline filters. 7. ISO/TS 66-:6; Geometrical product specifications (GPS)-Filtration: Linear profile filters: Spline filters. 8. ISO/TS 66-9:6; Geometrical product specifications (GPS)-Filtration: Linear profile filters: Spline wavelets. 9. ISO/TS 66-4:6; Geometrical product specifications (GPS)-Filtration: Morphological profile filters: Disk and horizontal line-segment filters.. ISO/TS 66-49:6; Geometrical product specifications (GPS)-Filtration: Morphological profile filters: Scale space techniques.. ISO/TS 66-8:; Geometrical product specifications (GPS) - Filtration - Part 8: Profile filters: End effects.

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