Basic Components & Elements of Surface Topography

Transcription

1 Basic Components & Elements of Surface Topography

2 Skid and Skidless Measuring Equipment

3 Surface Profile Measurement Lengths Sampling Length (l) Assessment (Evaluation) Length (L) Traversing Length

4 Cutoff Selection Effect on Surface Finish Measurement

5 Recommended Cutoffs for Different Surface Finishes

6 Traditional Surface Texture Parameters and Functions Some of these parameters can also be calculated from unfiltered and waviness profiles. (P and W families of parameters)

7 R a = AA = CLA R q = RMS On majority of prints only R a is specified.

8 Roughness Average R a

9 R a Roughness Average Advantages The most commonly used parameter to monitor a production process. Default parameter on a drawing if not otherwise specified. Available even in the least sophisticated instruments. Statistically a very stable, repeatable parameter. Good for random type surfaces, such as grinding. A good parameter where a process is under control and where the conditions are always the same, e.g. cutting tips, speeds, feeds, cutting fluid (lubricant). Disadvantages Not a good discriminator for different types of surfaces (no distinction is made between peaks and valleys). Not very informative on surfaces with R sk outside ±2. Not a good measure of sealed surfaces.

10 Ra, Rq Parameters Roughness average R a is the arithmetic average of the absolute values of the roughness profile ordinates. Root mean square (RMS) roughness R q is the root mean square average of the roughness profile ordinates.

11 R q Root Mean Roughness R q is more sensitive to peaks and valleys then R a, because the amplitudes are squared. Applications Very similar to R a, which practically replaced it for general use. Used to control very fine surfaces in scientific measurements and statistical evaluations.

12 R z, R max Parameter

13 R z Mean Peak-to-Valley Height R max Maximum Peak-to-Valley Height Applications R z is more sensitive than Ra to changes in surface finish as maximum profile heights and not averages are being examined. R max is useful for surfaces where a single defect is not permissible, e.g. a seal with a single scratch. R z and R max are used together to monitor the variations of surface finish in a production process. Similar values of R z and R max indicate a consistent surface finish, while a significant difference indicates a surface defect in an otherwise consistent surface.

14 R p, R pm Parameter The Mean Leveling Depth R pm is the mean of five leveling depths of five successive sample lengths l. R pm = 1/5 (R p1 + R p2 + R p3 + R p4 + R p5 ) The Leveling Depth R p is also the largest of the five leveling depths. The Maximum Roughness Depth R t (peak to valley height) is the vertical distance between the highest peak and the lowest valley of the roughness profile R within the evaluation length L.

15 R p and R pm R p, per ISO 4287, is the max height of any peak to the mean line within one sampling length. R pm, the mean leveling depth - per rules of ISO 4288, is an averaging of R p over 5 cutoffs; according to ASME B , R p calculated over the evaluation length is R pm. Many instruments, e.g., M2 Series, measure R pm but report the result as R p. Applications R pm is useful in predicting bearing characteristics of a surface. A low value of R pm and large value of R z indicates a plateau surface The ratio R pm /R z quantifies the asymmetry of profile. R pm is recommended for bearing and sliding surfaces and surface substrates prior to coating. R v is a good parameter where stress is a major factor. R p is a good parameter to control coating quality.

16 R 3Z, R 3zmax Parameters Per Daimler Benz Corporate Standard N31007:1983 R 3z mean third highest peak-to-valley height over 5 sampling length. R 3zmax maximum third highest peak-to-valley height of the 5 third highest peak-to-valley height. R 3z disregards the 2 highest peaks and deepest valleys that have little effect on the surface performance, with the intent to reduce the instability of peak parameters (such as R z ), by ignoring profile extremes. Applications Sealing Surfaces Porous Surfaces

17 Bearing Length Ratio t p (R mr )

18 Bearing Area Curve (BAC)

19 Different Methods of t p (R mr ) BAC Evaluation Applications Probable run-in behavior and wear resistance of surfaces such as sliding and rolling faces (e.g., cylinder liners). Seals, bearings, electrical and thermal controls, adhesives, coatings, etc.

20 Pc (RPc) Peak Count Nr Normalized Peak Count The peak count is the number of local roughness peaks which project through a selectable band centered about the mean line. The count is determined over the evaluation length and is reported in peaks per cm or inch. HSC (RHSC) High Spot Count The number of roughness peaks, reported in peaks per cm, projecting through the mean line, or a line parallel to it, at a selected distance above or below the mean line.

21 Pc (RPc), Nr HSC (RHSC) Applications Sheet metal industry to measure quality of surfaces subjected to bending, forming and painting and where appearance is critical. General adhesion and coating applications.

22 R k Family of Parameters A 1 A 2 R k R pk R vk M r1 M r2 R pkx (R pk *) R vkx (R vk *) Material filled profile peak area Lubricant filled profile valley area Core roughness depth Reduced peak height Reduced valley depth Material component relative to peaks Material component relative to valleys Total Peak Height Total Valley Depth Applications Multiprocessed, multipurpose surfaces, such as plateau honed Sintered, porous surfaces

23 Waviness Height - W t Sum of the largest peak height and the largest valley depth of waviness profile within evaluation length L Applications To monitor processes where in addition to roughness, waviness, possibly caused by vibrations (both within the machine and external), is also critical. e.g. cylinder head waviness of the sealing surface produced on a vertical mill largely depends on the alignment of the cutting tips in the milling head.

24 Corresponding Parameters in Parameters Defined in ASME B ISO R a Arithmetic Average Deviation of the Assessed Profile R a R q Root Mean Square Deviation of the Assessed Profile R q R p Maximum Profile Peak Height R p R v Maximum Profile Valley Depth R v R t Maximum Height of the Profile R t R pm Average Maximum Profile Peak Height ---- R z Average Maximum Height of the Profile R y R max Maximum Roughness Depth ---- S m Mean Spacing of Profile Irregularities R sm P c Peak Density ----

25 Corresponding Parameters in Parameters Defined in ASME B ISO t p Profile Bearing Ratio R mr(c) H tp Difference in the Heights for Two t p Ratios R δc R sk Skewness R sk W t Waviness Height W t R ku Kurtosis R ku a Average Absolute Slope ---- q Root Mean Square Slope R dq

26 ISO Standards on Surface Finish ISO ISO ISO ISO ISO ISO ISO ISO ISO ISO ISO Part 1 Part 2 Part 3 Indication of Surface Texture Nominal Characteristics of Contact (Stylus) Instruments Terms, Definition and Surface Texture Parameters Rules and Procedures for Assessment of Surface Texture Calibration, Measurement Standards Calibration, Soft Gages Surface Imperfections - Terms, Definitions and Parameters Metrological Characteristics of Phase Correct Filters Motif Parameters Calibration of Contact (Stylus) Instruments Characterization of Surfaces Having Stratified Functional Properties Filtering and General Measurement Conditions Height Characterization using the Linear Ratio Curve Conditions Height Characterization using the Material Probability Curve of Surfaces Consisting of Two Vertical Random Components

27 R z to R a Conversion BS 1134/ Siemens Recommendations R z = x4 - x7 R a R z = x4 - x10 R a Actual ratio depends upon the shape of the profile.

28 Surface Texture Symbols ASME Y14.36M-1996 ISO ISO b c a x c f a b e d e d a = roughness value Ra a = one single parameter and sampling b = production method, treatment, length or cutoff coating, other text, or note callout b = other parameters c = roughness cutoff or sampling length c = production method, treatment,coating d = direction of lay d = direction of lay e = minimum material removal requirement e = material removal allowance f = roughness value other than Ra preceded x = not to be used by its parameter symbol (e.g. Rz 0.4) = material removal symbol = material removal symbol

29 Different Methods of Designating R a 32 Symbol Standard 32 AA ANSI B CLA 32 AARH RNR a 0.8 N6 CH Ra BS Rare US Designation Old US MIL Specifications JIS B JIS B DIN JIS B ISO Charmilles VDI 3400 ASME Y14.36M-1996 ISO ISO Common US Designation

30 WHERE DO WE GO WRONG IN SURFACE FINISH GAGING? Including Flaws and Defects into the Measurements Inattention to Leveling Not Taking Into Consideration Environmental Conditions Not Understanding Calibration Procedures and Limitations Ignoring Advanced Gage Functions