Gear cutting – milling – or planing – Milling – Thread or helix generating
Reexamination Certificate
1998-08-19
2001-07-10
Briggs, William (Department: 3722)
Gear cutting, milling, or planing
Milling
Thread or helix generating
C409S074000
Reexamination Certificate
active
06257810
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a milling tool for thread-milling and boring of high-strength materials. The tool includes a holding shaft and a lateral cutting region with cutters for milling threads into a workpiece. The cutters are disposed on thread-milling teeth on the lateral periphery of the tool, which teeth are not configured with a pitch, and a front face region in which bore-milling cutters are disposed. The regions of the tool forming the cutters are comprised of hard material, and the thread-milling cutters each have a rake angle.
BACKGROUND OF THE INVENTION
In a known milling tool for thread-milling and boring of this type as exemplified by Ger. Gbm. 88 03 565, the configuration of the rake angle and the configuration of the tool surface are not specified. The tool is intended for the machining of aluminum workpieces. Hard tool materials are used if the tool is to be operated at high cutting speeds. The hard materials are deemed to be, e.g., high-strength materials, such as certain high-strength steels, having as a rule a Rockwell hardness of at least 40, and typically 56-58.
SUMMARY OF THE INVENTION
It is an underlying problem of the present invention to devise a milling tool for thread-milling and boring of the type described initially supra, wherewith even high-strength workpieces can be machined successfully. The inventive milling tool for thread-milling and boring which solves this problem is characterized in that the rake angle of the thread-milling cutters is zero or negative, and in that a coating of hard material is present in the region of the milling cutters.
The combination of features consisting of the use of hard material in the cutting region of the tool, the provision of a coating of hard material in the cutting region, and a zero or negative rake angle, enables use of the milling tool for thread-milling and boring with high-strength workpieces without problems and without experiencing high wear. The rotational speed employed for the tool, and the lateral advance speed used for moving the milling tool translationally in a circular path, are similar to the speeds used customarily in machining of soft materials such as aluminum. The hard material in the region of the cutters is a sintered material.
The cutting tool may be used in a customary counter-machining arrangement wherein the tool is moved in a circular translational path which is counter to the direction in which the tool is rotated around the tool axis; however under these circumstances the cutting tool will experience appreciably more wear.
According to the invention the hard material in the region of the milling cutters, and the hard material of the coating of the milling cutters, for a milling tool for thread-milling and boring, are features which are combined with the feature that the thread-milling cutters have a zero or negative rake angle.
In tools with a positive rake angle, the cutting angle is smaller; however, the cuttings are lifted in the process of cutting. When a negative rake angle is used, the cutting angle is greater, but the material of the cuttings is forced out of the way.
The cutting regions of the milling tool which are comprised of hard material may be comprised of, e.g., cutting plates. However, as a rule the milling tool for thread-milling and boring is of a unitary construction, entirely comprised of hard material. The grooves to accommodate cuttings are present at least in the cutting region; they may have a shape which is, e.g., straight or spiral.
As a rule the sintered material is a hard metal having Vickers hardness (HV) at least 1700. As a rule the hard material coating is an anti-wear coating produced by PVD (physical vapor deposition) or CVD (chemical vapor deposition). The material may be, e.g., titanium nitrite or titanium carbonitrite. The hard material coating may be, e.g., single-layered or multilayered. As a rule the coating has a surface hardness at least 3000 HV.
It is particularly advantageous if the rake angle of the thread-milling cutters is in the range 0 to minus 25°, preferably −10 to −15°. As a rule, the negative rake angle is chosen depending on the material of which the given tool is comprised.
It is also particularly advantageous if the bore-milling cutters have a rake angle in the range +3 to −15°, preferably zero to −10°, particularly preferably −5 to −10°. In this way, the wear experienced on the bore-milling cutters is also low.
Further, it is advantageous if the holding shaft is not coated with the hard material coating. In this way, the cost of fabricating the inventive milling tool for thread-milling and boring is reduced.
It is also advantageous if the tool is provided with coolant channels from the holding shaft to and into the milling and front face regions. The supplying of coolant, which expedient is per se known, improves the performance of the inventive milling tool for thread-milling and boring with high-strength workpieces.
The invention also comprises a method of applying the above-described inventive milling tool for thread-milling and boring, wherein the tool, in the course of machining a thread in a workpiece, simultaneously executes: an advance into the workpiece, a circular translational movement, and a rotation; and the direction of the circular translational movement is opposite to the direction of rotation. In other words, the direction of rotation of the tool is opposite to the direction of the circular translational movement, which circular translational movement is dictated by the intended configuration of the thread. Accordingly the process is according to the principle of downcut milling.
The combination of the described method of applying the milling tool for thread-cutting and boring, and the inventive configuration of the tool, results in improved inside thread-milling of high-strength workpieces, in that the advantages of downcut milling are added to the advantages of the inventive configuration. In downcut milling, the milling cut begins at the thicker end of the comma-shaped cutting which is being cut away, and the cut ends at the thinner end of said cutting. This reduces the frictional wear on the thread-milling cutters, and leads to a reduced tendency of the tool to seize. The use of downcut milling in the thread-milling process enables (or facilitates) the thread-milling of high-strength materials. To produce a right-hand thread, the circular translational movement is clockwise and the rotation is counterclockwise, whereas to produce a left-hand thread the circular translational movement is counterclockwise and the rotation is clockwise.
The inventive milling tool for thread-milling and boring may have truncations and the like on its cutting teeth, or not. Preferably, a truncation occurs for approximately one thread loop. For the hard material coating, one may, e.g., apply an intermediate layer (e.g. of titanium nitrite) on the hard metal, which intermediate layer serves as a binder; then only one other layer, a second layer (e.g. of titanium aluminum nitrite, 2-3 micron thick), is applied to the intermediate layer by means of a PVD process.
In the inventive milling tool for thread-milling and boring, as a rule the outer diameter of the lateral cutting region in which the thread-milling teeth are disposed is greater than the outer diameter of the front end region in which the bore-milling cutters are disposed. This relationship between the outer diameters will be the relationship primarily used in practice, with the described tool configuration and method of application. The mode of operation of the inventive tool will always be such that the core opening and threads are produced simultaneously.
REFERENCES:
patent: 4755399 (1988-07-01), Fujii et al.
patent: 4761844 (1988-08-01), Turchan
patent: 4831674 (1989-05-01), Bergström et al.
patent: 4930949 (1990-06-01), Giessler
patent: 4943191 (1990-07-01), Schmitt
patent: 5429459 (1995-07-01), Palm
patent: 5542177 (1996-08-01), Hillestad
patent: 6012882 (2000-01-01), Turchan
patent: 8803565 (
Briggs William
Jacobson & Holman PLLC
LandOfFree
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