Turning – Process of turning
Reexamination Certificate
1999-09-15
2001-12-25
Tsai, Henry (Department: 3722)
Turning
Process of turning
C082S047000, C407S107000, C407S119000
Reexamination Certificate
active
06332385
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of turning a rotating metallic workpiece.
PRIOR ART
Polycrystalline cubic boron nitride (PCBN), is next to diamond, the hardest material. PCBN is, contrary to diamond, stable at high temperatures, which means that the turning of hardened components, such as hardened steel having a hardness of 45-65 HRC, becomes possible also with economically advantageous cutting characteristics. This is utilized within today's modern machining industry by turning the hardened components that earlier used to be ground. Efficient CNC lathes enable quick and flexible machining to an equivalent quality as with grinding in the sense of surface roughness and tolerances but at a lower cost and with shorter machining times. Martensitic transformations, so called white layers, just as residual strains in the machined surface, can occur during both grinding and hard turning. These phenomena depend on the generation of heat and the mechanical strain in the cutting process and they are influenced by cutting characteristics, tool shape as well as the choice of tool paths.
The hard turning methods currently used for machining try to have as little contact between the cutting insert and workpiece surface as possible in order to meet the quality requirements for the finished component. This means that machining is made with small cutting depth and feed and relatively pointed cutting corners. The cutting corner, which is in little engagement, is brought from the beginning of the machined surface to its end, by using typical cutting characteristics in the order of cutting depth ap=0.1 mm, feed f=0.1 mm/r and cutting speed =150 m/min.
OBJECTS OF THE INVENTION
One object of the present invention is to provide a method for hard turning, which obtains the advantages of the prior art.
Another object of the present invention is to provide a method for hard turning in order to drastically reduce the machining time for the fine turning of hardened components.
Another object of the present invention is to provide a method for hard turning in order to improve the surface quality during the fine turning of hardened components.
Another object of the present invention is to provide a method for hard turning in order to minimize the existence of white layers and residual strains in the machined surface.
SUMMARY OF THE INVENTION
The invention pertains to a method of turning a metallic workpiece having a hardness in the range of 45-65 HRC, to generate a surface having a surface finish Ra no greater than 0.2 &mgr;m, the method comprising the steps of:
A. mounting a cutting insert in a toolholder, the cutting insert comprising a cutting edge formed of cubic boron nitride; and
B. establishing relative movement between the insert and the workpiece in a feed direction, whereby the insert engages the workpiece and cuts in the feed direction for a distance which is shorter than an effective length of the cutting edge oriented perpendicular to the feed direction, the cutting edge including opposite ends disposed out of contact with the workpiece during the feeding of the insert.
REFERENCES:
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patent: 5129767 (1992-07-01), Satran et al.
patent: 5246315 (1993-09-01), Hansson et al.
patent: 5256008 (1993-10-01), Hansson et al.
patent: 5503913 (1996-04-01), Konig et al.
patent: 5722803 (1998-03-01), Battaglia et al.
patent: 5876160 (1999-03-01), Johnson
Kautto Eilert
Konig Norbert
Burns Doane Swecker & Mathis L.L.P.
Seco Tools AB
Tsai Henry
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