1
Background In an alloy, the percent-
age of silicon and the shape and distribution of the particles play an important
role in determining machinability. An aluminum matrix contain- ing eutectic silicon comprises the microstructure of an aluminum-sil- icon alloy. This silicon can appear as needle-like crystals and plates or a refined fibrous structure, depend- ing on the level of chemical modi- fication and the casting’s cooling rate. The machining characteristics of aluminum-silicon alloys depend on microstructural features such as shape, size and morphology of the eutectic silicon particles, the den- drite morphology of α-aluminum, and the morphology and amount of other intermetallics. Measuring thrust force (i.e., the
force component in the cutting direc- tion) and torque (i.e., the moment of force about the tool’s axis of rotation) is a common technique for moni- toring tool wear. Previously, using a microcomputer-based feedback control system, experiments were carried out under diff erent cutting conditions to test the eff ectiveness of
ture of thermal softening in the tool. Drastically increasing cutting speeds would lead to signifi cant gains in productivity in the automotive and aerospace industries. T e overall condition of the work
Fig. 1. Each completed test block had 144 holes on four of its fi ve ribs.
the thrust force gradient in predict- ing failure. T e workpiece material is the most signifi cant factor dictating which type of cutting tool should be employed. High speed machining techniques permit high rates of ma- terial removal, which in turn reduces machining cycle times. One advan- tage of high speed machining with aluminum alloys is that the melting points fall well below the tempera-
piece can infl uence the drilling outcome considerably, which is why certain metallurgical factors must be taken into account. T ese factors include alloying elements, micro- structural features and porosity, cast- ing methods, heat treatment, grain refi nement and modifi cation, 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 cop- per and silicon signifi cantly increased the material work hardenability and drastically reduced the tendency toward built-up edge formation on the cutting tool. Magnesium hardens the alloy matrix, reduces the fric- tion between tool and work piece and produces a better surface fi nish. Magnesium hardens the alloy but does not increase abrasiveness be- cause, in small amounts, it does not contribute to the formation of hard intermetallic phases.
Table 1. Chemical Composition of the Alloys Used in the Present Machinability Study Element (wt%)
Alloy Alloy Code Si G2 G3
396 B319.2 G12 Fe 10.82 0.53 0.35
10.84 0.88 2.42 7.533
Cu Mn Mg Zn Sn 2.23 0.55 0.26 0.70
3.59 0.29
Table 2. Summary of Four Drills Used in Testing Drill
Solid Type Material
Diameter (mm) Point Type
Overall Length (mm) Flute Length (mm) Point Angle
Drill Profi le
Carbide Drill Solid Carbide
6.5
Standard 90 53
120°
0.29 0.24
0.04 Ti
0.04 0.19 0.13
0.22
0.06 0.18
0.26 0.24
Bi 0.01 Sr 0.009
0.03 0.009 0.00 0.009
Bal
Bal 0.82 Bal 0.83
Al Mn/Fe S.F. 1.04 1.65 2.35 0.93
Special Solid Carbide Drill
Solid Carbide 6.5
Cobalt Grade Drill
Solid Carbide 6.5
Self-Centering Point Self-Centering Point 106 66
91 53 140° 130°
Solid Carbide High Precision Drill
Solid Carbide High Precision 6.5
Self-Centering Point 91
53 140°
40 | METAL CASTING DESIGN & PURCHASING | Sept/Oct 2013
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60