Electric heating – Metal heating – By arc
Patent
1984-11-26
1986-06-17
Paschall, M. H.
Electric heating
Metal heating
By arc
219121PB, 219121PM, 148 9R, B23K 900
Patent
active
045958173
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates generally to machine engineering, and more particularly to thermomechanical machining with plasma arc preheating of the surface to be cut.
BACKGROUND OF THE INVENTION
There is known the "Cutfast" high-speed method of thermomechanical machining developed by the PERA Company of Great Britain. In this method the surface being removed is preheated by a plasma arc with the anode spot located in advance of the cutting tool.
This method resides in localized preheating of the surface to be cut by a plasma arc and substantially simultaneous chip removal. Heat resistant tools are employed, since cutting is effected in the heat-affected zone.
However, the process is costly and its application is inherently limited because of the employment of pure argon as a plasma-forming gas.
Machining efficiency in this method is improved by increasing the cutting speed at invariable or even reduced tool feed compared with machining without heating. In turn, this increase in the cutting speed makes it impossible to machine heavy unbalanced workpieces having an eccentricity, since such an increase in the cutting speed leads to greater impact loads and results in premature wear and failure of the tool. Also, increased workpiece rotation speed and the accompanying impact loads entail faster wear of the equipment.
The above method fails to provide for machining many active metals, such as titanium and its alloys, because the thin chip heated to a very high temperature becomes self-inflammable as a result of the exothermic reaction when the chip is oxidized by the air. Further, in the "Cutfast" process tool life is reduced because it is in continuous contact with the alpha-layer in the zone of the anode spot.
In view of the foregoing, this known method is intended for machining by a single-edged cutting tool with small depth and width of cut.
SUMMARY OF THE INVENTION
The invention is directed toward the provision of a thermomechanical machining method with such a selection of operating conditions in terms of heating by plasma arc of the surface to be removed and chip removing which would be characterized by a greater depth of cut to enable machining with a higher efficiency and longer tool life, of unbalanced workpieces of heavy weight having a certain amount of eccentricity including workpieces of such active metals as titanium and its alloys.
This has been attained in that in a method of thermomechanical machining whereby the surface to be removed by a cutting tool is preheated by a plasma arc with the anodic spot localization in advance of the cutting tool, and whereby, according to the invention, the parameters of heating and positioning of the anodic spot are selected depending on the desired conditions and depth of cutting, having in view the fact that greater depth of heating improves machinability.
The selection of preheating and cutting conditions provides for uniform heating of the workpiece surface to be removed to a required temperature, which in turn enables an increase in the depth of cut. This eventually makes it possible to machine unbalanced heavy workpieces having a certain amount of eccentricity with a higher efficiency without resorting to increased cutting speeds.
Such an increase in the depth of cut also makes it possible to machine workpieces of such active metals as titanium and titanium alloys without chip self-inflammation.
The thus preselected conditions of preheating and cutting enable the reduction of the effect of impact loads acting on the cutting tool as well as to obviate the effect of the alpha-layer formed in the region of the anodic spot on the tool to result in a longer life of the tool.
In the ease of using a plasma arc with a stationary anodic spot, it is preferable that the anodic spot size in terms of the width of cut be less than the width of cut by a value of from 1.2 to 2.5 the selected depth of cut, the cutting tool being preferably spaced from the anodic spot at a distance substantially equal to a product of the speed of cutting by the ti
REFERENCES:
patent: 4139757 (1979-02-01), Sipek
Bobrov Alexandr V.
Gaponenko Olga S.
Ivchenko Nikolai S.
Litvinov Lev P.
Papov Jury A.
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