It is well known that the greater the ratio of length to diameter of a drill is, the greater its bending tendency is. Reducing the length to diameter ratio can reduce the flexural force, thus avoiding bit breaking and increasing the aperture error. The deeper hole requires larger ratio of length to diameter of the bit. Usually, the hole depth is more than 3 times the diameter is “deep hole”, and the hole depth of micro drill usually exceeds this limit.
Generally speaking, high-speed steel drill allowed a deflection and bending force, but the corresponding, the elastic deformation ability and high speed steel has low hardness, the wear resistance is reduced, thus limiting the tool life. The hard alloy has high rigidity and high hardness, so it can make the tool life longer and the machining precision higher.
The high wear resistance of cemented carbide makes it reach 3 times the speed of high speed steel after micro drilling, and the life can also be improved. At the same time, the high rigidity of cemented carbide is helpful to correct positioning and maintain the size of the hole.
Though the tools are manufactured in the material and geometrical parameters precision drilling completed a lot of development, do not need all of the scratch test, but many factors during drilling are well controlled, is not an easy task.
So, as the diameter of the drill bit decreases and the brittleness increases, the deflection becomes the root of many problems. To control the brittleness of the drill bit, it is necessary to weigh the hardness and toughness of the tool matrix.

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