Drilling tool with internal cavities for chip removal

#The present invention relates to a drilling tool for the chip-breaking machining of metallic materials, especially for so-called ejector drilling. However, it may also advantageously be used for so-called BTA-drilling.

#It is known to use cutting inserts of cemented carbide for drills, which inserts are fastened by mechanical fastening arrangements, the inserts being provided with one or more recesses in the chip surface for chip-breaking purposes. Such drills are, for instance, known from U.S. Pat. No. 4,215,957. However, it has turned out to be difficult to attain an optimal forming of the chips. That is, it has been impossible to attain the desired short, comma-shaped chips, at the same time as it has been impossible to reduce power consumption when running the drill in the desired way. Further, sometimes the chip canals, which conduct the chips to a central discharge hole, have turned out to be too narrow for the created chips, which has resulted in a chip stoppage and jamming.

#Further, in U.S. Pat. No. 5,302,060 drilling tool is described comprising a drill body on which two or more cutting inserts are mounted. The inserts are substantially formed as trapezoids and are axially mounted, i.e., the abutment surfaces of the cutting inserts extend axially, the inserts suitably being fixed by brazing. However, after a certain time of wear, also this drill body has sometimes caused chip jamming in the area where the two chip canals and the central hole meet. Moreover, the drill body consists of two parts which are joined by welding, namely the drill head or crown, and the cylindrical, threaded shaft part. This weld joint in combination with the fact that the drill crown has been cast, has frequently resulted in an imperfect roundness of the final product. This has in turn caused customers to require that a finishing grinding be performed in order to attain a perfect roundness and rotation symmetry around is the central axis, which unnecessarily increases the production cost of the drill. A further drawback of this weld joint has turned out to be that chips occasionally get stuck in the weld joint, since in practice a weld joint leaves a certain gap on the interior side. Sometimes, even if only a single chip gets wedged in that gap, the following chips can pile up and cause chip jamming and, in a worst case, a tool breakdown.

#For illustrative but non-limiting purposes, a preferred embodiment of the invention will now be further described with reference to the appended drawings wherein:

#FIG. 1 shows a drilling tool according to the invention in a perspective view obliquely from above;

#FIG. 2 shows a drill cutting insert according to the invention in a perspective view obliquely from above;

#In FIG. 1, a drilling tool of the ejector type is generally designated by reference numeral 1. Advantageously, the tool may also be generally used for so-called BTA-drilling. The tool comprises a front drilling crown or head 2, an intermediate part 3 and a shaft 4. The shaft 4 is provided with an outer screw thread 5, which is intended, in a way known per se, to be threaded into an outer tube (not shown). An inner tube (not shown) that is concentrical with the outer tube would be inserted in a way known per se into an inner, substantially cylindrical cavity or passage 15 of the drill, extending past a plurality of cooling medium holes 6, whereby formed chips entrained in the cutting medium travel through the inner tube via chip canals 11 and 12.

#According to a previously known technique (for instance, disclosed in U.S. Pat. No. 4,768,901), the drill head 2 per se is formed by casting, while the shaft 4 is formed by turning, whereafter these two parts are joined by welding. A welding always causes deformations due to heat expansion and an uneven contraction during the following cooling. These inconveniences are further accentuated in thin parts. Further, the head may become somewhat unround, in spite of the precision casting. These inconveniences are fully overcome by the present invention by producing the whole drill body in one single piece by turning, thereby avoiding all welding, which in turn brings the advantage that any risk of weld joint gaps being formed on the inside of the drill are avoided, which gaps could snag chips and produce a chip jam.

#As may be seen in FIGS. 3 and 4, the top side of the drill head is provided with three cutting insert seats or pockets 7, 8 and 9 each intended to accommodate a drill cutting insert. Advantageously, the three cutting inserts 10A, 10B, 10C are identical, the only difference being that the central cutting insert 10C is reversed in comparison to the peripheral and intermediate cutting inserts 10A and 10B, respectively. The number of cutting inserts in an ejector drill may be between one and five. However, the disadvantage with only a single cutting insert is that the cutting forces that the support pads have to endure become large since the drill becomes unbalanced.