Evolution of roughness parameters along polishing tests of previously ground surfaces
In polishing tests, precise determination of polishing time needed is difficult, since representation of 
surface roughness against polishing time leads to an asymptotic curve. In the present work, results of 
the polishing tests of previously ground surfaces are presented. Different roughness parameters were 
considered. Grinding wheels of 100 and 150 Norton grain size respectively were used. Cutting speed 
was 25 m s-1 and depth of cut was 0.02 mm. Two different feeds were considered: 9 m min-1 and 15 m 
min-1. A polishing test was performed by means of corundum polishing pads of grain size 2500. 
Results show that, the higher the initial grain size of the grinding wheel, the higher initial roughness is 
as expected. Amplitude roughness parameters such as Ra and Rq decrease with polishing time. 
Regarding material percentage parameters, Rk and Rpk decrease more sharply than amplitude 
roughness parameters in the first 20 s of the polishing test, and afterwards decrease slightly. Rvk 
decreases more slowly than amplitude roughness parameters along the polishing test. 
Keywords: grinding, polishing, roughness parameters
A neuro-fuzzy approach to generating mold/die polishing sequences
A neuro-fuzzy approach to generating polishing sequences is presented. The measured initial surface roughness of the EDMed mold or die and the desired final polished surface roughness are the major inputs fed to the system. After receiving this input, the system consults its database for the polishing efficiency curves of the abrasive stone grain sizes available to it. With the outputs of this system being optimized for minimum polishing time, there is a selected sequence of grain sizes from among an available set, with each grain size used for each polishing step. There was a series of initial polishing experiments which were conducted for the different available grain sizes and workpiece roughness at different pressures and RPM's, with a change in roughness measured for polishing duration. From this, the database is constructed for designing the fuzzy logic rules. For constructing the exact membership function of the fuzzy interface, the neuro-fuzzy technique is combined with learning ability of neural network and the inferring ability of fuzzy logic system. Finally, while considering the stone-changing time, the actual experimental results from suggested polishing sequences are compared with the predicted value in order to establish the proposed approach.
Microstructure of the solder-casting zone in bridges of dental gold alloys.
The composition and structure were studied in the cast and in the solder of bridges which had failed clinically. Both materials were gold alloys but with different contents of Pt, Ag and Zn. The metallographic investigation revealed defects mostly in the solder, situated in the subsurface layer. SEM studied of the fracture surface revealed large porosites and a structure of dense parallel lines--striations--, indicating that the material had failed from fatigue. The materials in the fractured bridges were identified by micro-probe measurements. It was stated that cast material and solder material used together, were of different composition.