| 摘要 |
Steel bit bodies are manufactured with polystyrene patterns in a lost foam casting process. The patterns are machined in complex shapes that cannot be extractable from reusable, two-piece pattern molds. The patterns are machined in a basic, programmed, five-axis machining process to form multiple copies of a complex pattern body. The process is modified to produce multiple copies of a modified design. Multiple bit patterns of variable forms are produced without an intermediate, reusable pattern mold that would require multiple mold pieces, thus eliminating the time and expense in variation of the bit design. The pattern is machined in a single chucking operation in a machine tool adapted for machining plastics in a three-dimensional global process. The plastic composition and density permit it to be machined into a pattern having relatively small, unsupported structural projections and smooth surface features. Bit patterns formed in the process have forward canted blades that are machined from mating planar surfaces to simplify the machining process. The edges of the forward canted blades form a spiral surface for mounting cutter elements. The forward canting makes the blades stronger and permits the blades to be thinner than non-canted blades to increase the clearance between blades, which improves the movement of cuttings. Recesses are machined into the pattern gauge face to produce a recess in the casting for receiving hardfacing. The hardfacing forms a layer that cooperates with the surrounding blade material to form a smooth transition area as the bit wears during usage.
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