Sa Parameter Research Articles

On the Application of Replica Molding Technology for the Indirect Measurement of Surface and Geometry of Micromilled Components

The evaluation of micromilled parts quality requires detailed assessments of both geometry and surface topography. However, in many cases, the reduced accessibility caused by the complex geometry of the part makes it impossible to perform direct measurements. This problem can be solved by adopting the replica molding technology. The method consists of obtaining a replica of the feature that is inaccessible for standard measurement devices and performing its indirect measurement. This paper examines the performance of a commercial replication media applied to the indirect measurement of micromilled components. Two specifically designed micromilled benchmark samples were used to assess the accuracy in replicating both surface texture and geometry. A 3D confocal microscope and a focus variation instrument were employed and the associated uncertainties were evaluated. The replication method proved to be suitable for characterizing micromilled surface texture even though an average overestimation in the nano-metric level of the Sa parameter was observed. On the other hand, the replicated geometry generally underestimated that of the master, often leading to a different measurement output considering the micrometric uncertainty.

EFFECTS OF SURFACE PREPARATION ON FRICTION AND WEAR IN DRY SLIDING CONDITIONS

Wear tests were conducted using a ball-on-disc tester T-11. In the experiment, a 42CrMo4 rotating steel disc with a hardness of 40±2 HRC was placed in contact with a 100Cr6 steel ball with a diameter of 6.35 [mm]. The hardness of the ball was set to 62±2 HRC. Finishing treatment applied to the surfaces was sand blasting. Disc samples were prepared to obtain surfaces in similar range of the Sa parameter (arithmetical mean height of the surface) but other surface topography parameters vary. Dry sliding tests were conducted at sliding speeds of v1 = 0.16; v2 = 0.24 i v3 = 0.32 [m/s]. The sliding distance was set to 282.6 [m], and the normal load was set to 9.81 [N]. During the tests, the friction force was monitored as a function of time. Disc and ball wear was measured after the tests using a white light interferometer Talysurf CCI Lite. Profiles were taken in four positions (900 apart) perpendicular to the wear track. Then, using an interferometer software program TalyMap Gold 6.0, they were computed and averaged. It was found that the initial surface topography has a significant influence on friction and wear levels under dry sliding conditions. It was also identified the correlation between several surface topography parameters and wear volume.

Characteristics of geometric structure of the surface after grinding

This paper presents the technological and functional capabilities of surface textures produced by cutting and grinding operations on hardened steel of about 54 HRC hardness. Special focus was placed on surface textures generated by hard turning and grinding operations which are characterized by the Sz roughness parameter of about 3 - 4 μm and distinctly similar values of the Sa parameter. A set of 3D surface roughness parameters was used to characterize the superficial effects of precision grinding operations and their influence on the parts functionality.

Analysis of the stability of 3Y-TZP zirconia abutments after thermocycling and mechanical loading

ObjectivesAlthough implant abutments made of yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) show great predictability, some issues related to its aging require further study. The objective of this in vitro study is to assess the stability of 3Y-TZP zirconia implant abutments with two different implant connections when subjected to aging simulation through thermocycling and mechanical loading (TCML). MethodsTen 3Y-TZP zirconia abutments were selected and equally divided into two groups (n=5): CEZr, abutments for externally hexed implants; and CIZr, abutments for implants with an internal conical connection. The samples were subjected to thermocycling (5000 cycles; 5–55°C) and mechanical loading (1.2×106 cycles; 88.8N; 4Hz). Before and after the aging procedures, X-ray diffraction (XRD) analysis was conducted to observe tetragonal-monoclinic (t-m) phase transformation, and topographic surface analysis was performed by 3D profilometry, and data were analyzed using Mann-Witney test (p<0.05). ResultsXRD measurements revealed no monoclinic phase in any of the abutments after aging. The comparative analysis regarding roughness (using the Sa parameter) at the abutments’ seating platforms (using 3D profilometry) revealed a slight increase in roughness in both connections after TCML. Statistically significant differences (test U=57.0, p=0.161>0.05), before and after TCML, and between implants connections (test U=57.0, p=0.053>0.05) were not detected. ConclusionsAfter a 5-year simulation of its clinical use, the analyzed 3Y-TZP zirconia abutments did not show signs of aging. The connection's geometry does not interfere in aging.

Influence of Steel Surface Preparation Method on Topography and Tribological Behaviour in Dry Sliding Conditions

Tribological tests were conducted using a pin-on-disc tester. In the experiment, a steel disc of hardness 40 HRC was put in contact with a steel ball of hardness 62 HRC. Disc samples were prepared in order to obtain very similar values of the Sa parameter, smaller than 0.5 μm. Different methods of preparing smooth surfaces were used. Dry tests using similar contact conditions were carried out. During tests, the friction force was monitored as a function of time. Wear of discs and balls was measured after the test using white light interferometer. In order to decrease variation of the experimental results, during tests the wear debris was continuously removed from the disc surface. It was shown that type of treatment play a role on tribological behavior of sliding pairs.

High-precision Finishing Hard Steel Surfaces Using Cutting, Abrasive and Burnishing Operations

This paper presents the technological and functional capabilities of surface textures produced by high-precision cutting, abrasive and ball burnishing operations on hardened steel parts of about 60 HRC hardness. Special focus was placed on surface textures generated by hard turning, belt grinding and ball burnishing operations which are characterized by the Sz roughness parameter of about 1.3μm and distinctly different values of the Sa parameter. Apart from the standard 2D and 3D roughness parameters, the fractal and motif parameters were analyzed.

A non-contact 3D method to characterize the surface roughness of castings

A non-contact technique using a 3D optical system was used to measure the surface roughness of two selected standard surface roughness comparators used in the foundry industry. Profile and areal analyses were performed using scanning probe image processor (SPIP) software. The results show that the surface quality of the standard comparators was successfully evaluated and it was established that the areal parameters are the most informative for cast components. The results from the surface comparators were compared with the results from a stylus instrument. Sand cast components were also evaluated and the surface roughness parameter (Sa) values were compared with those of the standards. Sa parameter suffices for the evaluation of casting surface texture. The S series comparators showed a better description of the surface of castings after shot blasting than the A series.

Uncertainties and optimized sampling in surface roughness characterization

Usage of 3D roughness parameters measurements requires knowledge of uncertainty causes in order to design proper measurement procedures. Even on apparently homogeneous machined surfaces, large local variations in 3D roughness parameters have previously been reported. This paper introduces and tests a concept for optimized sampling based on local-, and global topography analysis, using measurements of the Sa parameter on a large machined component as a practical example. It is shown that more than 40 measurements of Sa may be needed to attain a stable value, but that choice of an appropriate sampling strategy may reduce this requirement considerably. The results point to a possible route to minimize required measurements and contribute to the development of the best-practice when using 3D surface structure metrology.

Characterisation of Titanium Dental Implants I: Critical Assessment of Surface Roughness Parameters

Titanium is commonly used for dental implants because of its unique ability to get incorporated into living bone. There is an ongoing development to obtain better anchorage and surface properties such as roughness and chemical composition are modified to reach this. In this study titanium dental implant surfaces were characterised by recording the topographical changes induced by each individual processing step such as cleaning, blasting, and HF etching. To fully describe the different surfaces, the same point was analysed before and after each step using Atomic Force Microscopy (AFM) and 3D-Scanning Electron Microscopy (3D-SEM). A set of 3D surface parameters were calculated as a function of filter size to describe the topographic features at different levels. The chemical treatment introduces nano-sized features while blasting changes the topography at the micrometer level and by combining AFM and 3D-SEM the entire range can be assessed. The results show that the chemically induced changes in the topography can only be revealed by AFM while 3D-SEM gives a clear description of the topography of blasted surfaces. The fractal dimension for the chemically treated surface was the same as for the blasted surfaces but crossover size was much smaller. Besides the commonly used Sa parameter it is suggested that the root-mean-square of the surface slope (Sdq) and the void volume (Vvc) parameters are included in the characterisation of rough surfaces. These parameters can be used for correlation with in vivo performance.

An in vitro and in vivo evaluation of bioactive titanium implants following sodium removal treatment

Objective The aim of this study was to evaluate the effect of dilute HCl as a sodium removal treatment of grit blasted/NaOH/heat treated cp titanium implants on the in vitro bioactivity and the in vivo interface shear resistance at different healing periods. Methods Cylindrical implants were machined from cp titanium bars. Half of the implants were blasted by AL 2O 3 particles followed NaOH/heat treatment. The other half received similar treatment except, dilute HCl was additionally used as a sodium removal treatment. Implants surfaces topography was characterized by AFM before and after immersion in simulated body fluid (SBF) for 3 and 7 days. The implants resistance to interfacial shear force was evaluated at 2, 4, and 8 weeks implantation periods in experimental rabbits. Results Sodium removal treatment significantly increased surface roughness (Sa parameter), valley fluid retention index and surface area before and after immersion in SBF, however, it significantly decreased core fluid retention index. Calcium and phosphorus containing surface deposits, of larger surface area, were precipitated on implants received the sodium removal treatment after 3 and 7 days in SBF. The implant–bone interface resistance to shear force was significantly increased at 2 weeks healing period after the use of the sodium removal treatment. Significance The sodium removal treatment showed to be effective in improving the early bone–implant interface resistance to shear force. Topographical changes, after dilute HCl etching, seem to contribute to the different in vitro and/or in vivo responses observed.