Considerations on the Built-up Edges in Drilling Aluminium Alloys

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  • Zaima Shigeo
    Department of Mechanical Science, Faculty of Engineering, Shizuoka University

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In the drilling of aluminium alloys, as built-up edges are frequently formed and fallen off, the behavior of built-up edges in the drill margin especially affects the condition of the drilled surface. In this paper, in the drilling of wrought aluminium such as 1100, 2024, 5052 and 6061 types, the behavior of built-up edges produced at the drill cutting edge and the effect of built-up edges on the drilled surface condition have been studied by use of a quick-stopping device built as a trial, in order to clarify to the drilling mechanism and to improve the finished surface in drilling. The results obtained are as follows.<BR>The rake angle of a twist drill greatly changes from the margin part to the chisel part and from positive to negative values, and, in dry drilling, built-up edges are often formed and stuck all over the region of the drill cutting edge. Under this experimental condition, the formation of large built-up edges, especially 5052–F, was found in all the region of cutting edge and the formation of built-up edges for 2024–T4 and 6061–T6 is not much in the margin part and the formation of built-up edges for 1100–F was very little. The sticking condition of the built-up edges depended on the materials, but a constant equivalent rake angle due to the built-up edge of about 35° was found in all the cutting edge region even in different sticking conditions. In each specimen, the shape, size and hardness of the built-up edges in drilling were almost the same as those obtained in orthogonal cutting using the plain tool with the corresponding rake angle under the same condition as drilling. In drilling with cutting liquid in dripping method, built-up edges disappeared, but, in the drilling cooled by dry ice without cutting liquid, the formation of built-up edges was found in all the region of cutting edge, so is seems that the lubricating effect is more effective to decrease the formation of built-up edges than the cooling effect. And, the built-up edges formed and stuck near the margin part had a marked effect on the drilled surface, especially the cylindrical surface in drilling.

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