Abstract: A system for controlling a plasma arc torch circuit uses two different current thresholds to control pilot current, thereby reducing nozzle wear while maintaining a reliable arc and an adequate transfer height. Specifically, by using a Hall effect current sensor to monitor low levels of current in the lead that normally carries high current, it is possible to determine more accurately (1) when there is a low level of pilot arc current that can be ramped to a higher level, and (2) when the level of transferred current is capable of reliably sustaining a transferred arc such that the pilot arc can be extinguished. Thus, the current can be removed from the nozzle, at the precise moment in time that the torch can reliably sustain the transferred arc, thereby saving wear on the nozzle. In addition, the system of the present invention can save nozzle wear when used in combination with circuits that compensate for discontinuities in the workpiece by decreasing the current to the workpiece to a pilot arc level.

Abstract: An electrode for use in a plasma arc torch has an insert designed to improve the service life of the electrode, particularly for high current processes. The electrode comprises an elongated electrode body formed of a high thermal conductivity material and having a bore disposed in a bottom end of the electrode body. The bore can be cylindrical or ring-shaped. An insert comprising a high thermionic emissivity material, and in some embodiments, a high thermal conductivity material, is disposed in the bore. The insert can be ringed-shaped or cylindrical.

Abstract: A flow of ionizable gas is provided to a shielded plasma arc torch which includes an electrode, a translatable nozzle, a nozzle retainer, and a shield. After passing through a heat exchanger to cool the electrode, the gas flow enters an annular chamber where the flow is divided into three subflows. A first subflow enters a plasma chamber formed by the electrode, the nozzle, and a swirl ring to pressurize the plasma chamber and support a plasma arc. The second subflow passes serially through apertures in the nozzle retainer and the shield to shield the plasma arc. The remaining flow is vented to ambient. Accordingly, a single gas flow may be employed to independently support multiple torch operating requirements.

Abstract: Disclosed is a novel method and structure for contact starting a plasma arc torch. A translatable, electrically conductive component such as a nozzle or swirl ring is biased into contact with an electrode by a compliant spring element. A pilot arc is formed by first passing current through the electrode/component interface. Thereafter, the component is translated under the influence of gas pressure in a plasma chamber formed between the electrode and component, compressing the compliant element and initiating the pilot arc. The spring element may be a separate element or may be maintained integrally with the nozzle, swirl ring, or a retaining cap, facilitating removal and replacement of the spring element with consumable components of the torch.

Abstract: A plasma arc torch includes a torch body and a nozzle mounted relative to an electrode at a first end of the torch body to define a plasma chamber. The torch body includes a plasma gas flow path for directing a plasma gas from a plasma gas inlet to a plasma chamber in which a plasma arc is formed. The nozzle includes a hollow, body portion defining a cavity and a substantially solid, head portion formed integrally with the body portion defining an exit orifice extending from the chamber. The exit orifice has a converging inlet and an outlet, where the inlet has a radius of curvature, and the exit orifice has a length to diameter ratio of greater than 2.5.

Abstract: A safety circuit is utilized in a blow forward contact start plasma arc torch to extinguish the current to the torch upon determination of an unsafe operating condition. The torch includes a torch body, an electrode and a translatable conductive nozzle biased into contact with the electrode. The safety circuit receives a reference signal a signal indicative of the arc voltage and a mode status signal. The torch current is extinguished when the signal indicative of the arc voltage is less than the reference signal and the mode status signal indicates the torch is operating in the transferred arc mode.

Abstract: Disclosed is a novel method and structure for contact starting a plasma arc torch. A translatable, electrically conductive component such as a nozzle or swirl ring is biased into contact with an electrode by a compliant spring element. A pilot arc is formed by first passing current through the electrode/component interface. Thereafter, the component is translated under the influence of gas pressure in a plasma chamber formed between the electrode and component, compressing the compliant element and initiating the pilot arc. The spring element may be maintained integrally with the nozzle, swirl ring, or a retaining cap, facilitating removal and replacement of the spring element with consumable components of the torch. Exemplary spring elements include wave spring washers, finger spring washers, curved spring washers, helical compression springs, flat wire compression springs, and slotted conical discs.

Abstract: A translatable nozzle is supported in a contact start plasma arc torch at an aft end by a swirl ring and at a longitudinally spaced forward end by an insulative bearing member of a nozzle retainer. The nozzle is biased into contact with an electrode by a compliant spring element. A pilot arc is formed by first passing current through the electrode and nozzle. Upon pressurization of a plasma chamber formed therebetween, the nozzle is translated forward, compressing the spring element and initiating the pilot arc. The spring element may be maintained integrally with the nozzle to facilitate removal and replacement of the spring element with the consumable nozzle.

Abstract: A plasma arc torch system includes a plasma arc torch and a positioning apparatus for automated processing of workpieces. In order to maintain consistent cut quality, a controller maintains arc voltage at a predetermined reference value by controlling a standoff between the torch and the workpiece. To prevent contact between the torch and workpiece during kerf crossings and to maintain an optimum standoff during acceleration and deceleration, standoff control override algorithms are implemented in the controller. Additionally, a contact sensing apparatus is provided to automatically retract the torch in the event of contact with the workpiece during processing.

Abstract: Disclosed is a method and structure for improving alignment of a plasma arc with an axial centerline of a plasma arc torch. At least one of an electrode and nozzle are mounted in respective bores of a cathode block and torch body using a radial spring element. By concentrically machining the bores along an axial centerline of the torch and centering the consumable components within the bores using the spring elements, an insert disposed in a tip of the electrode is axially aligned with an orifice formed in a tip of the nozzle. Asymmetric wear of the nozzle orifice due to a skewed arc path is markedly reduced or eliminated. The torch may be employed in computer controlled cutting and marking systems to produce components or workpieces with reduced dimensional and angular errors.

Abstract: A method of operating a plasma arc torch for marking a metallic workpiece spaced a stand-off distance from the torch utilizes a torch that includes a body, an electrode, and a nozzle mounted in the body so as to define a plasma chamber. The nozzle has a central passage and an exit orifice through which the transferred arc passes to the workpiece. The method also utilizes a plasma gas flow through the body to form a pilot arc in the plasma chamber and then to form a transferred arc between the electrode and the workpiece. The method includes forming the plasma gas flow with a selected mixture of hydrogen and an inert gas. The percentage of hydrogen in the selected mixture is between 0% and 35%. The percentage of inert gas in the selected mixture is between 100% and 65%. The inert gas may be argon.

Abstract: A plasma arc torch apparatus and method for cutting or marking a workpiece includes a torch having an electrode and a nozzle coupled to a power supply, and a plasma gas source coupled to a fluid line for delivering plasma gas to the torch. A flow restriction member is disposed in the fluid line adjacent the torch and causes the pressure of the plasma gas in the torch to gradually increase during start up thus creating a stable plasma arc. A three-way valve is disposed in the fluid line downstream of the flow restriction member and has an inlet, a torch outlet, and a vent outlet. The inlet is in fluid communication with the torch outlet for delivering plasma gas to the torch when the valve is in the open position, and the torch outlet is in fluid communication with the vent outlet when the valve is in the vent position, for rapidly dissipating the gas in the plasma chamber of the torch to atmosphere after the arc has been extinguished.

Abstract: A coolant tube for a liquid-cooled electrode disposed a plasma arc torch does not become damaged during an electrode blow-out condition. The coolant tube includes a hollow member and a substantially solid member. The hollow member has a first end, a second end and a coolant passage extending between the first and second ends. The first end can be secured within the torch such that the coolant tube is disposed adjacent the interior surface of the electrode and such that the coolant passage is in fluid communication with a coolant supply. The substantially solid member extends from the second end of the hollow member and has at least one flow restriction orifice extending therethrough. Each flow restriction orifice is fluid communication with the coolant passage for providing at least one high velocity jet of coolant to the interior surface of the electrode.

Abstract: A plasma arc torch has a secondary gas flow that is extremely large during piercing of a workpiece to keep splattered molten metal away from the torch and thereby prevent "double arcing". The secondary flow exits the torch immediately adjacent the transferred plasma arc and is an extremely uniform, swirling flow. A swirl ring is located in the secondary gas flow path at the exit point. A prechamber feeds gas to the swirl ring, which is in turn fed through a flow restricting orifice. For certain applications the secondary gas is a mixture of an oxidizing gas, preferably oxygen, and a non-oxidizing gas, preferably nitrogen, in a flow ratio of oxygen to nitrogen in the range of 2:3 to 9:1. Preferably the flow ratio is about 2:1. A network of conduits and solenoid valves operated under the control of a central microprocessor regulates the flows of plasma gas and secondary gas and mixes the secondary gas.

Abstract: Plasma arc or laser cutting uses a mix of reactive and reducing gas flows to cut sheets of stainless steel, aluminum and other non-ferrous metals. The reducing gas flow to the cut varies as a percentage of the total gas flow to maintain a reducing atmosphere down through the cut, but to leave a predominantly oxidizing atmosphere at the intersection of the cut and the bottom surface of the sheet being cut. In plasma arc cutting these flows can also be characterized as either a plasma gas flow, one that forms the arc, or a shield gas flow that surrounds the arc. The reactive gas is preferably a flow of air, oxygen, nitrogen, carbon dioxide or a combination of these gases. The reducing gas is preferably hydrogen, hydrogen 35, methane, or a mixture of these gases. For aluminum, the reactive gas is preferably air or nitrogen and the reducing gas is preferably methane or a mixture of methane and air. In laser cutting the reducing gases such as methane can be used by mixing them with reactive assist gases.

Abstract: A liquid cooled plasma arc cutting torch system includes a plasma arc torch, a torch receptacle and a cooling system. The torch is removably mounted to the receptacle. The cooling system includes a liquid storage tank, supply and return lines providing fluid communication paths between the tank and the receptacle and a pump for pumping the cooling liquid from the tank through the supply line, the receptacle, the torch and the return line. A valve coupled to the return line includes a nozzle that directs liquid toward an inside top surface of the tank. A flow restriction member may be provided to equalize pressure in the supply with atmospheric pressure when the pump is not operating. A pressurized gas source may be utilized to substantially clear the receptacle, torch and return line of liquid when the pump is not operating.

Abstract: An alignment device and method for a plasma arc torch system which corrects the position of a torch in relation to the receptacle for a successful union. The device and method mechanically align in situ electrical contacts, gas, and water conduits of the torch during a torch change. The time expended for a torch charge is reduced because the torch is self aligning to the receptacle. Minimal human interaction is required to change a torch.

Abstract: An arc control circuit in a plasma arc torch, having an electrode and a nozzle, maintains a plasma arc during operation of the torch. The circuit includes a power supply electrically coupled to the electrode, nozzle and a workpiece. A logic device opens a power switch electrically coupling the nozzle to the power supply, disconnecting the nozzle from the supply, when a transferred arc is formed between the electrode and the workpiece. An amplifier is electrically connected to the power supply. The amplifier compares a sensed current to an operating current. The amplifier increases the output voltage of a power supply to maintain the operating current in coordination with an increasing distance between the workpiece and the torch. A comparator is electrically connected to a logic device and compares the output voltage of the power supply to a maximum voltage. When the output voltage of the power supply exceeds the maximum voltage, the comparator sets the logic device.

Abstract: An insert securely disposed in a bottom end of an electrode has an exposed emission surface shaped to define a recess in the insert, wherein the recess is initially dimensioned as a function of the operating current level of the torch, the diameter of the insert, and the plasma gas flow pattern in the torch. The electrode has an elongated body formed of a high thermal conductivity material such as copper, and a bore disposed in the bottom end of the body along a central axis. The insert is formed of a high thermionic emissivity material, such as hafnium, and securely disposed in the bore with the emission surface exposed. The emission surface may be initially shaped by removing a predetermined amount of the high thermionic emissivity material from the insert to define a generally concave recess, a generally cylindrical recess or other shapes. When used in a torch, the electrode provides for reduced deposition of the high thermionic emissivity material on the nozzle, thereby reducing nozzle wear in the torch.

Abstract: A switch mechanism with a safety member for operating a tool or a weapon which reduces the probability of inadvertent operation. The switch mechanism comprises a trigger and a safety member disposed adjacent to the trigger for preventing the trigger from contacting an actuation switch. The safety member is shaped such that when it is positioned in a first position, it prevents the trigger from contacting the switch. In addition, the safety member is shaped such that when the safety member is positioned in a second position, it allows the trigger to contact the actuation switch.