control system, experiments were carried out under different cutting conditions to test the effectiveness of the thrust force gradient in predicting failure. Te workpiece material is the most


significant factor dictating which type of cutting tool should be employed. High speed machining techniques permit high rates of material removal,


which in turn reduces machining cycle times. One advantage of high speed machining with aluminum alloys is the melting points fall well below the temperature of thermal softening in the tool. Drastically increasing cutting speeds would lead to significant gains in productivity in the automotive and aerospace industries.


Te overall condition of the


work piece can influence the drill- ing outcome considerably, which is why certain metallurgical factors must be taken into account. Tese factors include alloying elements, microstructural features and poros- ity, casting methods, heat treatment, grain refinement and modification, and the physical and mechanical proper- ties of the work material. A previous study found that a small magnesium addition (about 0.3% of total weight) in aluminum alloys containing copper and silicon significantly increased the material work hardenability and dras- tically reduced the tendency toward built-up edge formation on the cutting tool. Magnesium hardens the alloy matrix, reduces the friction between tool and work piece and produces a better surface finish. Magnesium hardens the alloy but does not increase abrasiveness because, in small amounts, it does not contribute to the formation of hard intermetallic phases.


the required alloys. Table 1 provides the chemical composition for the 396 alloys


2 48 | MODERN CASTING January 2014


Procedure Te ingots were cut into


smaller pieces, cleaned, dried and melted in 220.5-lb. (100-kg) charges to prepare


Fig. 1. Each completed test block had 144 holes drilled on four of its five ribs.


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