Tungsten Carbide Micro Drills and Micro Drilling Ⅲ

In part 2 we know that the first character of tungsten carbide spade-type micro drills during micro drilling is that it has no point at the tip and is easy to make an eccentric motion. Here we talk about the cutting energy distribution when micro drilling and the point angle characters.

A second consequence of the chisel edge of a tungsten carbide spade-type micro drill is its relatively long length compared to the drill diameter. This results in a relatively high thrust force along the drill axis. While the sloped cutting edges are increasing the diameter of the hole machined by the chisel edge, the specific cutting energy along the cutting edge is normally lower than at the chisel edge. The result is a large thrust force compared to the diameter of the drill. Again, this size effect works against the micro drilling process similar to the size effect in micro milling.

Micro drills are typically made of either cobalt steel or micro grain tungsten carbide. The steel drills are less expensive and easier to grind but are not as hard or strong as the tungsten carbide drills. The drill point angle is based on the material to be drilled. The normal point angle is 118 degrees and 135 degrees is used for hard materials. The larger included point angle provides more strength at the drill point.

 (To be continued. This article is divided into several parts and this is part 3, for part 2 please refer to http://news.chinatungsten.com/en/tungsten-information/79982-ti-10251; for part 4 please refer to  http://news.chinatungsten.com/en/tungsten-information/80043-ti-10264)

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