| 摘要 |
Steel bit bodies are manufactured in a production process that employs polystyrene patterns in a lost foam casting process. The patterns are machined to permit the formation of complex shapes that cannot be reproduced in simple patterns that are extractable from reusable, two-piece pattern molds or dies. The patterns are machined from a billet material according to a basic, programmed, five-axis machining process to form multiple copies of a reproducible complex pattern body. The process is modified to produce multiple copies of a modified design. Machining the complex patterns and producing variations by changing the machine program permit multiple bit patterns of variable forms to be produced without need for building an intermediate, reusable pattern mold that would require multiple mold pieces, thus eliminating the associated time and expense required in the creation of a new pattern mold for each 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 has a composition and a density that 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 thus permits the blades to be thinner than non-canted blades to increase the clearance between blades, which improves the movement of cuttings past the bit. Recesses are machined into the gauge face of the patterns to produce a recess in the casting for receiving hardfacing. The hardfacing in the recess forms a layer that cooperates with the surrounding blade material to form a smooth transition area as the bit wears during usage. |
