Gear Tooth Surface Roughness of Helical Gears Manufactured by a Form Milling Cutter

Manufacturing involute gears using form grinding or form milling wheels are beneficial to hobs in some special cases, such as small scale production and, the obvious, manufacture of internal gears. To manufacture involute gears correctly the form wheel must be purpose designed, and in this paper the geometry of the form wheel is determined through inverse calculation. A mathematical model is presented where it is possible to determine the machined gear tooth surface in three-dimensions manufactured by this tool, taking the finite number of cutting edges into account. The model is validated by comparing calculated results with observed results of a gear manufactured by an indexable insert milling cutter

Prediction and experimental verification of the cutting forces in gear form milling

In this paper, a mathematical model is presented by which the cutting forces in gear form milling process are predicted using the mechanistic approach. To use this approach, a detailed description of the chip geometry is needed. Eccentricity and run-out tool errors are considered, which is of great importance as the chip thickness will by these errors vary for the subsequent cuts. The chip geometry is determined by comparing the path of the cutting edge with already removed material. The boundary of the chips is determinable from the cutting edge geometry, which is here derived in parametric form so spur and helical gears are manufactured correctly. Locally on the cutting edge, the cutting forces are resolved from orthogonal cutting data and on the basis that these forces are proportional to the instantaneous chip thickness. The load each individual cutting tooth experience in operation, as well as the complete load on the tool, are resolved by summing the forces along the cutting edge. In the model, all cut chips are determined for each machined gear tooth gap, with the gear blank boundaries considered. The paper ends with experimental validation using indexable insert milling cutters. It is shown that the model predicts the force shape well and the peak force levels within 12 %

The Management of Defective Resin Composite Restorations: Current Trends in Dental School Teaching in Japan

AIM: The aim of this article is to investigate the contemporary teaching of the management of defective direct resin composite restorations in dental schools in Japan. METHODS: A questionnaire relating to the teaching of the management of defective resin composite restorations was developed and e-mailed to 29 dental schools in Japan in 2010. RESULTS: Completed responses were received from 19 of the 29 invited schools (response rate = 66%). Eighteen schools (95%) report that they included the teaching of repair of direct defective resin composite restorations in their dental school programs. Thirteen schools reported that they included both clinical and didactic instruction on the repair of direct resin composite restorations. Fourteen schools did not teach any mechanical roughening of the exposed resin composite restoration surface before undertaking a repair. The most commonly reported treatment was acid etching with phosphoric acid (12 schools). The most commonly taught material for completing repairs was a flowable resin composite (16 schools). CONCLUSION: The teaching of repair of defective resin composite restorations is well established within many Japanese dental schools, to a greater extent than in some other regions of the world. The impact of this teaching on subsequent clinical practices in Japan should be investigated. Furthermore, it is concluded that there is a need for much stronger leadership in operative and conservative dentistry, ideally at the global level, to resolve differences in key aspects of operative procedures such as repairs