Tungsten Carbide Micro Drills and Micro Drilling Ⅳ

In part 3 we know that A tungsten carbide spade-type micro drill has a large thrust force compared to the diameter of the drill during micro drilling process and the drill point angles vary according to its work piece materials. Here we talk about the mechanism of micro drilling process.

A micro drilling spindle uses a vee-block bearing arrangement. The tungsten carbide micro drill is mounted in the mandrel and is fabricated integral with the mandrel. The mandrel rides against four convex diamond surfaces which are the only points of contact. So long as the tungsten carbide micro drill was ground with the mandrel supported in a similar manner, the drill will be concentric about an axis. That axis may not coincide with the mandrel axis but that is not significant as long as the offset is not sufficient to cause excessive vibration, and it normally is not. A small pulley is fastened to the drill mandrel and a drive belt passes around the pulley and drives the drill from an external motor. The belt tension is the only force holding the mandrel against the diamond pads and a slight upward component of the belt tension is used to retract the drill. The upper end of the mandrel rides against a ceramic material which provides the drill thrust force. This disk may also rest against a force sensor to measure drill thrust force which is often used to indicate the extent of drill wear.

(To be continued. This article is divided into several parts and this is part 4, for part 3 please refer to http://news.chinatungsten.com/en/tungsten-information/80042-ti-10262)

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