Cutting by use of rotating axially moving tool – Tool or tool with support – Having stepped cutting edges
Patent
1995-03-16
1997-11-18
Rachuba, M.
Cutting by use of rotating axially moving tool
Tool or tool with support
Having stepped cutting edges
408713, 407113, B23B 5100
Patent
active
056880839
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a metal cutting tool having one or more indexable cutting inserts and particularly designed for use in drilling, boring, sinking, hole formation or enlarging and similar rotary cutting operations. Such a tool is hereinafter generically referred to as a drilling tool.
BACKGROUND OF THE INVENTION
It is well known, in particular in drilling holes having a large depth-to-diameter ratio, that the drilling efficiency in terms of output, chip flow and tool life is significantly influenced by the efficiency of chip evacuation. In order to ensure efficient drilling and to have the chips readily removed from a cutting zone a width-to-thickness ratio of the chip produced by a cutting edge of a drill should be kept within a certain optimum range, and to this end it has been proposed to split the chip into relatively narrow strips.
Among such prior proposals is that disclosed in GB 20311487. Here there are disclosed square inserts having cutting edges in which are respectively formed pairs of chip splitting notches. Each notch has radially innermost and outermost edges such that, when the insert is mounted in the drill in a position slightly slanted with respect to an axis of the drill, the radially innermost edge of the outermost notch of the indexed cutting edge extends substantially parallel to the axis of the drill. The disclosure asserts that in this way chip splitting is ensured. However, even if such chip splitting is achieved it is very energy consuming seeing that the workpiece is in continuous contact with the notch. Besides, the construction of the cutting edge cannot provide for chip splitting over the entire length of the cutting edge as only one of the notches can be so positioned as to meet the requirements of the disclosure.
JP-59-196107 proposes a chip splitting solution similar to the one described above. Here a cutting edge of an insert is formed with chip splitting steps slightly projecting in a cutting direction. As these steps are also in a continuous contact with a machined workpiece, the chip separation provided by this drill is extremely energy consuming. Furthermore, in view of the fact that it is designed for drilling deep holes, the drill is provided with guide pads, making the whole construction more complicated and expensive.
With drilling holes of large depth-to-diameter ratios, it is not practical to provide indexable-insert drills with such guide pads, and as such drills are not guided by the holes it is important to ensure that the cutting forces acting on the drill, especially radial components of such cutting forces, are substantially balanced and in this way to minimize size loads leading to tool deflection and consequent inaccuracies in hole size.
SUMMARY OF THE INVENTION
In the further description and claims the term "center of the insert" means a center of a circle inscribed in the insert and the term "median line" means a line drawn from the center of the insert to the center of a line connecting two outermost cutting edge extremities.
It is the object of the present invention to provide an improved metal drilling tool and an indexable insert for use therein, in which the above referred-to disadvantages are substantially reduced and with which a more effective chip splitting is ensured along the cutting edge.
According to the present invention, there is provided a metal drilling tool having an elongated body with a longitudinal axis and provided with at least one pocket at its working end, at least one indexable cutting insert mounted in the or each pocket for performing drilling action the said insert comprising: a rake face, relief flank face a base, a plurality of cutting edges, each defined between the rake face and adjacent relief flank face and included between two adjacent cutting corners, at least one of said cutting edges comprising at least one set of component cutting edges, each set consisting of two pairs of component cutting edges, each pair consisting of a first and a second component cutting edge, the
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Iscar Ltd.
Rachuba M.
Tsai Henry W.H.
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