Tungsten Carbide Micro Drills and Micro DrillingⅤ

In part 4 we know that the micro drilling process is a series of precisely linked connection and motion of the tungsten carbide micro drill, mandrel, pulley, drive belt, and external motor, etc. Here we talk about the usage of fluid and removal way of a drill from the hole in a peck cycle to reduce chips affection on hole quality.

Tungsten carbide micro drills must be used in a peck cycle wherein the drill is repeatedly withdrawn and reinserted into the hole being drilled. This is necessary to help clear chips from within the hole. A thin cutting fluid is also recommended to aid in chip clearing. The fluid should be moving, as in an air-oil mist rather than stagnant. Stagnant fluid will allow chips to reenter the hole along with the drill. The effect of not using a fluid is clearly shown. The hole has more, large chips, on the order of 5 micrometers in size, and the drilling thrust force under such a condition is typically higher than if the chips are cleared from the hole. With no fluid to help clear chips, two hole is packed with chip debris and the axial force on the drill is typically several times (2-3) higher than with fluid.

In very soft materials, complete removal of the tungsten carbide micro drill from the hole each peck cycle can cause a slight taper near the hole entrance. This can be avoided by incomplete removal of the drill. For softer materials, chip removal is not as severe a problem since the machining forces for such materials is normally lower than for hard materials but chips left in the hole can cause the drill to wander from an axial path and can result in a drilled hole with a center which does not lie along a line.

(To be continued. This article is divided into several parts and this is part 5, for part 4 please refer to http://news.chinatungsten.com/en/tungsten-information/80043-ti-10264; for part 6 please refer to http://news.chinatungsten.com/en/tungsten-information/80077-ti-10281)

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