In-Process Electrical Dressing of Metal-Bonded Diamond Grinding Wheels
A new development of hybrid in-process electrical dressing of metal-bonded diamond grinding wheels is proposed in this paper. The electrical dressing method is used for overcoming the limitations of the conventional dressing methods available in relation to a super-abrasive wheel because of the hardness of its abrasive grains and the durability of its bonding material. The proposed hybrid in-process electrical dressing method consists of electro-discharge and electro-chemical processes and is implemented with twin copper electrodes and alternating power supplies. The results show that with properly maintained process conditions, a better surface finish is produced by the proposed method compared with traditional rotating SiC wheel dressing.
In-process wire electrical discharge dressing (IWEDD) of metal bonded diamond wheels
Abstract Electrical discharge dressing has been established as alternative for conditioning metal bonded diamond wheels, which will be exploited to develop in-process wire electrical discharge dressing (IWEDD). The main requirements for its successful implementation are first presented in this work. Small depth of dressing cuts was found to be feasible and high material removal rates were achieved without damaging diamonds. Dulled grains are finally removed by mechanical contact with the work piece. It was found that grinding forces can be kept constant over time while non-productive time is reduced, showing that IWEDD is a suitable conditioning method with great potential for future industrial applications.
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.