Electric heating – Metal heating – By arc
Patent
1995-08-16
1997-12-09
Paschall, Mark H.
Electric heating
Metal heating
By arc
21912139, 21912154, 21912159, 21912421, B23K 1000
Patent
active
056956630
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a plasma cutting method and an NC plasma cutting apparatus. More particularly, the invention relates to a plasma cutting method and an NC plasma cutting apparatus best suited to cutting a workpiece by generating a transferred plasma arc.
BACKGROUND ART
Hitherto, a plasma cutting method has been widely employed as a processing method for cutting plate workpieces, such as iron, stainless steel, aluminum and the like, at high speed. Plasma cutting apparatuses used for this method are classified into a transferred type and a non-transferred type, depending on the method of generating a high-temperature plasma arc. A typical non-transferred plasma cutting apparatus, as schematically shown in FIG. 6, comprises an electrode 11 disposed at the center of a plasma torch and a funnel-shaped nozzle 12 which is placed to surround the forward end of the electrode 11 across a plasma gas passage and which has an opening at the forward end thereof. Both the electrode 11 and the nozzle 12 are connected to the output terminal of a power supply source 16. With this construction, during a cutting operation, an arc discharge is generated between the electrode 11 and the nozzle 12 while a plasma gas is allowed to flow therebetween. The plasma gas is thus transformed into the state of high-temperature plasma, and at the same time, a non-transferred plasma jet 13 is ejected through the opening formed at the forward end of the nozzle 12 toward a workpiece 14 to be cut, thereby melting and cutting the workpiece 14. This non-transferred plasma cutting apparatus is advantageous in that the workpiece 14 can be cut by this apparatus whether it is formed of an electrically-conductive material or a non-conductive material. However, the apparatus presents a problem in that it incurs a greater loss of the nozzle and has a heat efficiency as low as approximately 20%.
On the other hand, a typical transferred plasma cutting apparatus, as schematically shown in FIG. 7, is basically constructed in a manner similar to the non-transferred plasma cutting apparatus. That is, the transferred plasma cutting apparatus comprises an electrode 11 and a nozzle 12, with each of the electrode 11, the nozzle 12, and the workpiece 14 to be cut being connected to an output terminal of the power supply source 16.
A description will now be given of a cutting operation of the apparatuses constructed as described above. At the start of the operation, as illustrated in FIG. 6, arc discharge is effected between the electrode 11 and the nozzle 12 so that a non-transferred plasma jet 13 is ejected from the opening of the nozzle, thus generating a pilot arc. When this plasma jet 13 reaches the workpiece 14, electrical conductivity can be obtained between the electrode 11 within the torch and the workpiece 14. Subsequently, as illustrated in FIG. 7, a current flows between the electrode 11 and the workpiece 14, and simultaneously, the nozzle 12 and the power supply source 16 are disconnected so that the pilot arc can be extinguished, and a transferred plasma jet 15 can be formed. The starting operation of the transferred plasma arc is thus completed.
Upon completion of the starting operation, the transferred plasma jet 15 starts to cut the workpiece 14. For achieving high performance of cutting, the plasma arc current applied during the cutting operation is set as the optimum value in consideration of various conditions, such as the shape of the plasma torch, the type of plasma gas, the type and the thickness of the workpiece to be cut, cutting speed and other conditions. The power supply source 16 is controlled so that this optimum current value can be maintained. In general, this plasma arc current is set to be constant without being changed until the cutting operation is completed. In contrast, when a cutting operation is performed on a workpiece having the shape of a small circular arc or an acute angle in cross-section, it is required that the speed of a torch moving device be decreased for preventing vibration of
REFERENCES:
patent: 5043554 (1991-08-01), Kohsaka et al.
patent: 5225658 (1993-07-01), Yamaguchi et al.
Japan Welding Association "Basis and Practise of Plasma Arc Cutting" 1st edit, Dec. 1, 1983, Kosaido Co., Ltd.
Nakau Yutaka
Shintani Toshiya
Kabushiki Kaisha Komatsu Seisakusho
Paschall Mark H.
LandOfFree
Plasma cutting method and NC plasma cutting apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Plasma cutting method and NC plasma cutting apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Plasma cutting method and NC plasma cutting apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1604818