Cutting tool

Details Cutting tool Cutting tool

1997-12-04

2001-04-10

Howell, Daniel W. (Department: 3722)

Cutting by use of rotating axially moving tool

Tool of specific diverse material

C408S223000, C408S230000

Reexamination Certificate

active

06213692

ABSTRACT:

The invention relates to a cutting tool such as a drill, milling cutter, screw tap, reamer or core drill in accordance with the preamble of claim
1
.
The use of numerically controlled machine tools has been a substantial contribution to increasing the productivity, flexibility, manufacturing quality and efficiency of modern production apparatuses. The versatile possibilities of control technique and information processing have been responsible for machine designs suited for use in automatic manufacturing systems. Systems of this kind are usually equipped with tool and workpiece storage means, automatic changing means and integrated measuring stations so that the steps to be manually taken by the machine operator are minimized. Sensors for monitoring machine functions and process states, such as wear and breakage of tools, ensure the automatic manufacturing sequence. In order to be able to exploit the full capacity of such machine tools, in parallel with the development of machine tools also appropriate tools have to be provided which permit a prolonged tool life as well as an increase in the cutting speeds so that the manufacturing times can be reduced to a minimum. However, in the case of modern machining processes the increase in the cutting speed need not necessarily be of major importance, but with particular applications, such as the machining of light metals, for instance, it may be endeavored to dispense with coolants and lubricants or at least to reduce the use thereof and, on the other hand, to accept a reduced cutting speed.
In the case of tools having geometrically defined cutting edges, such as, e.g., drills, milling cutters, reamers, screw taps, core drills etc., preferably high-alloy tool steels, hard metals, i.e. sintered materials of metallic hard materials such as, for instance, cermet, ceramic insert, monocrystalline diamond, polycrystalline diamond, polycrystalline boron nitride etc. are employed as cutting materials.
Moreover, there are known tools in which the wear resistance of the tools is further increased by coating them with hard material layers, such as, e.g., titanium nitride, titanium carbide and aluminium oxide.
In DE-OS 23 57 134 a cutting tool is disclosed in which a coating film of precious metal is applied by an ion-plating method. DE-AS 12 71 495 relates to a method of manufacturing a cutting tool in which a cover layer of copper or brass is applied to the portions not to be hardened prior to a hardening operation.
The cutting tools known from the two a.m. publications have the common drawback that, on the one hand, the cover layers consist of comparatively expensive materials and the tool lives are improvable, especially when light metals are processed.
The continuous development of the machine tools and the use of novel methods, such as dry machining, for instance, where the workpieces are machined without using coolants/lubricants or machining with reduced amounts of coolant, and the endeavor to obtain more and more reduced manufacturing tires make requirements to the tools as regards the tool lives and the maximum obtainable cutting speeds which cannot be fully met by conventional tools.
The object underlying the invention is to provide a cutting tool which has a simple design and permits an improved tool life while, at the same time, the cutting speed is increased or the amount of coolant is reduced.
This object is achieved by the features of claim
1
.
The tool wear can be considerably reduced by the measure to apply a soft slide layer containing sulphides, selenides, tellurides, such as, e.g., MoS
2
, NbS
2
, TaS
2
, WS
2
, MoSe
2
, NbSe
2
, TaSe
2
, WSe
2
, MoTe
2
, NbTe
2
, WTe
2
or mixed compounds, to the cutting tool, because the chip slides off the soft slide layer and thus the face wear is reduced and the formation of a built-up edge is prevented. Moreover, the friction between the tool and the open face is minimized so that the wear of the open face is reduced, too. Thus the tool life can be considerably improved by the slide layer according to the invention compared to conventional solutions. There are already known some coating methods for applying wearing coats to cutting tools so that a respective description is dispensed with. A method of the co-applicant VILAB AG/Switzerland has turned out to be especially suited.
It is of particular advantage to apply the soft slide layer to a wear-resisting base layer which, in turn, has been applied to the base body of the cutting tool so that the latter is provided with two layers.
In order to ensure an optimum machining operation, the soft slide layer is not applied in the area of the cutting edge.
It is especially advantageous when the base body of the cutting tool is made of HSS, hard metal, cermet or ceramic material and the wear-resisting layer consists of TiN, TiAlN, TiCN, diamond or the like.
Depending on the application, it is preferred to apply the base layer in a thickness of 1-10 &mgr;, while the hardness of the base layer should be between 2000-10000 UV and the slide layer should have a Mohs' hardness of 1-2.
The measure to form one or a plurality of grooves, especially in grooved shape, in the flute promotes breakage of chips so that the formation of long flowing chips, which interfere with the operating cycle, e.g. in automatic machine tools, and impede the chip removal, is prevented. With the short discontinuous chips a high surface quality is guaranteed, while the chips can easily be removed. Moreover, in the case of wet machining the groove facilitates the supply of coolants and lubricants to the cutting portion of the tool so that the stability thereof is increased and the carrying-off of the chip is further facilitated.
Preferably a plurality of grooves extending along the flute at parallel distance is formed in the face.
The chip formation and the chip discharge can be further improved by providing also the open space with groove-like recesses extending away from the cutting edge. The supply of coolant and lubricant, too, can be further improved by such recesses compared to the above-described embodiment.
The chip capacity and the tool times of such a tool are superior to those of conventional tools, even if the workpieces are machined in a dry state or with reduced supply of coolant.
In case that the cutting edge is formed at the front of the cutting member, such as, e.g., in drills, face mills, core drills etc., the recesses are advantageously formed as segments of a circle or spiral on the open face which are positioned approximately concentrically with respect to the axis of the cutting tool.
The chip formation and the supply of coolant and lubricant can be further improved by the fact that a recess is associated with each groove so that the recess is practically arranged in extension of a groove.
In special cases of application it may be advantageous to form the grooves or recesses only over a partial area of the flute and the open space, respectively.
It has proved especially advantageous when the width and the depth of the grooves and/or the recesses is between 0.02-2 mm, preferably 0.02-0.5 mm.
Further advantageous developments of the invention are described in the subclaims.


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