Electric heating – Metal heating – By arc
Reexamination Certificate
2002-11-06
2004-11-30
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
By arc
C219S136000, C361S616000
Reexamination Certificate
active
06825441
ABSTRACT:
This invention relates to a power supply apparatus, for example, a power supply apparatus for use with, for example, a welder.
BACKGROUND OF THE INVENTION
There are various welding techniques, such as manual welding and TIG welding. A power supply apparatus suitable for a particular welding technique is selected.
A general description of the basic structure of power supply apparatuses for welders is given hereunder. A commercial AC voltage is converted to a DC voltage by an input-side rectifier and a smoothing capacitor of a power supply apparatus. The DC voltage is converted to a high-frequency voltage in an inverter, which, in turn, is transformed to a desired voltage in a transformer. The resulting voltage is converted back to a DC voltage in an output-side rectifier for application to a load. If necessary, this ultimate DC voltage may be converted to a low-frequency AC voltage before it is applied to a load. By virtue of the use of an inverter for converting a DC voltage to a high-frequency voltage, this type of power supply apparatus can use a small-sized transformer, which results in downsizing of the power supply apparatus itself.
A power supply apparatus for use in manual welding with the above-described basic configuration has a constant-current output characteristic, in which a constant output current is provided even when its output voltage varies. The power supply apparatus is provided with a control panel on which an output current setter for setting the value of the output current is disposed.
In manual welding, when the welding is to be initiated or when, for example, a load including a welding torch and a workpiece is short-circuited, hot-starting of the welder may be employed for generating a desired arc by supplying to the load with current larger than the output current. A hot-start setter for setting the current to be supplied for hot-starting of the power supply apparatus is also disposed on the control panel. Indicators for indicating the magnitudes of the output voltage and current are also disposed on the control panel.
DC TIG welding is suitable for, for example, welding stainless steel, and a power supply apparatus for use in DC TIG welding has a constant-current output characteristic. DC TIG welding sometimes requires hot-starting as in manual welding. When DC TIG welding is employed for welding a flat workpiece, the output current value is held constant. On the other hand, when DC TIG welding is used for welding a workpiece like a pipe, a pulse output current is used. When a pipe, in particular its bottom portion, is welded with a constant output current, melt may drop from the pipe, which may necessitate another welding. Sometimes, melt may adhere to a TIG welding electrode of the torch and damage the electrode. By applying pulse current instead of a constant current, a molten weld pool formed in the bottom portion of the pipe is cooled down while a base portion IB of the pulse current is flowing, to thereby prevent the melt from dropping from the pool or adhering to the torch welding electrode.
There are two methods for initiating arcing in DC TIG welding. One is a touch-starting method in which a small current is supplied to the welding electrode with the electrode and the workpiece short-circuited, and, after that, the electrode is separated from the workpiece to thereby generate an arc between them. The other method is a high-frequency starting method, in which the welding electrode is kept separated from the workpiece, and a high-frequency, high voltage, which may have a frequency of from, for example, 1 MHz to 3 MHz and a magnitude of from, for example, 5 kV to 20 kV, is applied between them to thereby initiate arcing.
The power supply apparatus for DC TIG welding may be provided with a control panel with an output current setter and a hot-start setter disposed thereon. In addition to these setters, disposed on the control panel are up-ramping and down-ramping time setters for use when a pulse current is applied as an output current. The up-ramping time setter is for setting an up-ramping time during which a starting current increases to a maximum pulse current (i.e. a set output current), and the down-ramping time setter is used to set a down-ramping time during which the current decreases from the maximum pulse current value to the value of a crater current which is caused to flow at the end of the welding. Also disposed on the control panel are a pulse frequency setter for setting the frequency of the pulse current, a pulse current switch for switching the current to be supplied to the load between a DC current and a pulse current, an arc-initiating mode switch for switching the arc-initiating mode between the touch-starting mode and the high-frequency starting mode, and indicators for indicating the values of the output voltage and output current.
AC TIG welding is used for welding, for example, an aluminum material. An aluminum workpiece has an oxide film thereon having a high melting point. Therefore, if a DC power supply is used and current is supplied with a workpiece serving as a positive electrode and with a welding electrode serving as a negative electrode, the workpiece cannot be heated to a temperature high enough for welding. Accordingly, the workpiece is made a negative electrode with the welding electrode made to act as a positive electrode, thermoelectrons are emitted from the workpiece when current is supplied, which removes the surface oxide films, enabling the welding. The removal of oxide films is called “cleaning effect”. On the other hand, when the workpiece is used as a positive electrode with the welding electrode made to act as a negative electrode, the electrode can be cooled. Accordingly, when AC TIG welding is used, both the cleaning effect and the cooling effect are available. By adjusting the time periods during which the workpiece is serving as a positive electrode and a negative electrode, the amounts of the cleaning and cooling effects can be adjusted.
An AC/DC TIG welder can be used both for AC TIG welding and DC TIG welding. On a control panel of a power supply apparatus for an AC/DC TIG welder, there are disposed an output current setter, a hot-start setter, an up-ramping and down-ramping time setters, a pulse frequency setter, a pulse current switch for switching supplied current between a DC current and a pulse current, an arc-initiating mode switch for switching the arc-initiating mode between the touch-starting mode and the high-frequency starting mode, and indicators for indicating the values of the output voltage and output current for DC TIG welding. In addition, there are disposed a voltage-frequency setter for setting the frequency of the voltage for the AC welding, a waveform balancer for setting the ratio between positive and negative portions of the pulse current.
Because of various setting devices put on control panels of power supply apparatuses for welders, as described above, various different procedures are required for manufacturing power supply apparatuses for various welding methods. Also, it requires complicated arrangements to manufacture a single power supply apparatus which can be used for various welding modes or techniques because of a number of setting devices. In addition, settings using such various setting devices will be very troublesome.
In Japanese Patent No. 3,231,694 issued on Sep. 14, 2001, or in corresponding U.S. Pat. No. 6,051,806 assigned to the same assignee of the present application, a power supply apparatus is disclosed, which includes a control panel. On the control panel, there are provided a welding mode selection push button with which a welding mode, e.g. manual welding or DC TIG welding, is selected, a parameter setting push button with which a parameter for the selected welding is set, and one setter with which output current, output voltage etc. are set for the selected welding mode. In addition, a welding mode indicator, a parameter indicator, an UP/DOWN push button for changing the set parameter, an output voltage indicator and an output current indica
Danjo Kenzo
Ishii Hideo
Katooka Masao
Morimoto Takeshi
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