Patent Application
20210146468
The present invention relates generally to a contact-start, liquid-cooled plasma arc cutting torch, and, more particularly, to separating various consumables under pressure in such a torch to generate and sustain a plasma arc during cutting operations.
Plasma arc torches are widely used for high temperature processing (e.g., cutting, welding, and marking) of metallic materials. A plasma arc torch generally includes a torch body, an electrode mounted within the body, an emissive insert disposed within a bore of the electrode, a nozzle with a central exit orifice, a shield, electrical connections, passages for cooling and arc control fluids, a swirl ring to control the fluid flow patterns, and a power supply. The plasma arc torch can produce a plasma arc, which is a constricted, ionized jet of plasma gas with high temperature and high momentum. Gases used in the torch can be non-reactive (e.g., argon or nitrogen) or reactive (e.g., oxygen or air).
A plasma arc torch can generate a plasma arc using a contact start method. This involves first operating the torch in a pilot arc mode, which includes establishing physical contact and electrical communication between the electrode and the nozzle, e.g., by using a biasing force from, for example, a spring. A current path and a small pilot arc current flow are established between the electrode and the nozzle while they are biased together. A plasma gas is introduced into a plasma chamber between the nozzle and the electrode, such that gas pressure builds up in the plasma chamber to break the physical contact between the electrode and the nozzle to separate the two components. The separation causes an electrical arc to be created in the gap between the electrode and the nozzle in the plasma chamber. The electrical arc ionizes the flowing plasma gas in the plasma chamber to produce a plasma arc (i.e., a pilot arc). The plasma gas can be passed through a swirl ring to impart a tangential motion to the gas as it passes through the torch, thereby improving torch performance. This plasma gas is adapted to push the plasma arc toward the front of the nozzle. Next, in a transferred arc mode, the torch is moved near a grounded workpiece and the plasma arc makes contact with the workpiece by extending through the nozzle bore. Upon contact, the current return path transfers from the nozzle to the workpiece, which means that the electrical return path from the nozzle is opened (i.e., electrically disconnected) and the current returns from the workpiece back to the power supply. During transferred arc mode, the current flow can be increased to a larger amount such that the arc generated processes (e.g., gouges, pierces or cuts) the workpiece.
Even though the contact start approach for generating a plasma arc can significantly reduce electromagnetic interference and other electrical noises, this approach is typically employed in air-cooled, light industrial (e.g., handheld) plasma cutting torches with limited usage in heavy industrial settings. This is because heavy industrial (e.g., mechanized) plasma cutting torches are often exposed to high heat loads during torch operations, which necessitates a complex coolant path design to accommodate high-pressure, convective liquid cooling. A contact start approach generally cannot overcome the high coolant pressure (e.g., about 160 PSI to about 180 PSI) in heavy industrial plasma cutting torches without jeopardizing torch functions, such as being able to maintain proper alignment of consumable components, minimize leakage potential and maintain cut quality. Instead, a heavy industrial plasma cutting torch typically uses a high voltage, high frequency (HVHF) circuit, such as a Tesla coil ignition circuit, to generate a plasma arc. One disadvantage of this approach is that the HVHF circuit produces very high levels of electromagnetic interference and/or noises during plasma arc initiation, which can cause many unintended harms that lead to customer complaints and delays in project timelines.
The present invention provides contact start techniques and related apparatus for generating plasma arc in liquid-cooled plasma arc torches, such as in heavy industrial plasma cutting torches that can be characterized by an operating current of above about 130 amps, employment of forced convective cooling using a liquid coolant, having complex cooling paths formed by torch and consumable geometries, and used in multiple processes with different gases (not limited to air). In some embodiments, contact start of a plasma arc torch of the present invention is repeatedly and controllably achieved by manipulating two fluids (e.g., one liquid and one gas) to actuate certain torch components, such as drive an electrode to contact and separate from a nozzle. The designs of the present invention can significantly reduce electromagnetic interferences and electrical noises in the torch and system, which in turn produce a number of benefits including reducing the impact of noise on performance of other torch equipment, reducing the need for shielding and/or filtering components, and expanding design space to accommodate new functionalities (e.g., torch, consoles, sensors and radio-frequency identification tags) to enhance automation. Other benefits include reducing cost, weight and size of various torch components (e.g., the consoles and leads), reducing spacing between power and control harness at the system level, and reducing product development timelines and costs. These benefits ultimately facilitate operation and integration, thus improving customer satisfaction. In some embodiments, certain aspects of the present contact start techniques and apparatus described herein can be adapted to air-cooled (e.g., light industrial) plasma cutting systems.
The invention, in one aspect, features a contact start liquid-cooled plasma arc cutting torch. The torch includes a translatable liquid-cooled electrode having an electrode body defining a proximal end and a distal end along a longitudinal axis of the electrode body. The electrode body includes a coolant cavity with a distal internal coolant surface disposed at the distal end of the electrode body. The coolant cavity is configured to receive at least a portion of a coolant tube of the torch for directing a liquid coolant flow distally through the coolant tube within the coolant cavity and toward the distal internal coolant surface of the electrode. The distal internal coolant surface is shaped to substantially redirect the liquid coolant flow proximally over an exterior surface of the coolant tube within the coolant cavity. The torch also includes a nozzle disposed about the distal end of the electrode body. The torch further includes a multi-piece cathode disposed about the proximal end of the electrode body. The cathode comprising a first body shaped to matingly engage the electrode and a second body shaped to matingly engage the torch. The first body slidingly engages the second body such that the first body and the electrode are axially translatable relative to the second body along the longitudinal axis.
In another aspect, the present invention features a multi-piece torch cathode for a contact start liquid-cooled plasma arc torch. The multi-piece torch cathode comprises a first body including a cavity configured to receive and matingly engage an electrode. The multi-piece torch cathode also comprises a second body disposed within the torch. The first body slidingly engages the first body and axially translates relative to the second body during an operation of the plasma arc torch.
Any of the above aspects can include one or more of the following features. In some embodiments, the axial translation of the electrode relative to the second body biases the electrode relative to the nozzle at the distal end of the electrode. In some embodiments, the torch includes a gas input port for receiving and supplying a biasing gas to the torch. The biasing gas is adapted to create a blowback pressure on the first body of the cathode to axially translate the first body into an abutting position with the second body, thereby axially translating the electrode away from the nozzle. In some embodiments, the axial translation of the electrode is independent of a plasma gas flow through the torch.
In some embodiments, the liquid coolant flow in the coolant cavity of the electrode body is adapted to create a forward biasing pressure on the electrode to axially translate the electrode toward the nozzle, thereby axially translating the first body away from the second body of the cathode. In some embodiments, the forward biasing pressure is greater than the blowback pressure. In some embodiments, a lateral surface of the first body directly exposed to the blow-back pressure has a surface area that is greater than a surface area of the internal coolant surface of the electrode directly exposed to the forward biasing pressure. The lateral surface of the first body and the internal coolant surface of the electrode are substantially orthogonal to the longitudinal axis.
In some embodiments, the torch includes a sealed pressurization chamber having a first portion defined by a blowback flange of the first body of the cathode. In some embodiments, the blowback flange includes a first surface exposed to a biasing gas flow for urging the first body into an abutting position relative to the second body. In some embodiments, the sealed pressurization chamber is pressurized by the biasing gas received from a gas port disposed in the torch. In some embodiments, a pressure of the liquid coolant flow against the distal internal coolant surface of the electrode is greater than a pressure of the biasing gas flow. For example, the pressure of the liquid coolant flow is about 40% great that the pressure of the biasing gas flow. In some embodiments, a surface area of the first surface of the blowback flange is greater than a surface area of the distal internal coolant surface.
In some embodiments, the sealed pressurization chamber has a second portion defined by one of a swirl ring or a plasma chamber cover. In some embodiments, the plasma chamber cover and the swirl ring form a unitary structure.
In some embodiments, the cathode includes a set of one or more anti-rotation features located between the first and second bodies to prevent a radial movement of the first and second bodies relative to each other. In some embodiments, the set of one or more anti-rotation features comprises a set of one or more male shoulder sections of the first body and a set of one or more female shoulder sections of the second body. The male shoulder sections are configured to matingly engage the corresponding female shoulder sections.
In some embodiments, the first body of the cathode includes a set of one or more threads to matingly engage the electrode. In some embodiments, the torch includes an electrical contact disposed between the first and second bodies of the cathode. In some embodiments, the electrical contact comprises a canted coil spring. In some embodiments, the electrical contact is configured to pass substantially all of a pilot arc current between the first and second bodies during a pilot arc mode of torch operation.
In yet another aspect, the present invention features a method for contact starting a liquid-cooled plasma arc torch that comprises an electrode, a nozzle disposed about a distal end of the electrode, and a multi-piece cathode disposed about a proximal end of the electrode. The method includes supplying a coolant flow to the electrode, where the coolant flow is adapted to exert a first pressure on a surface of the electrode thereby biasing the electrode into physical contact with the nozzle. The method also includes establishing a torch current flow between the electrode and the nozzle that is a pilot current flow and supplying a plasma cutting gas to a plenum of the torch. The method additionally includes supplying a biasing gas to a sealed pressurization chamber of the torch. The biasing gas is adapted to create a second pressure in the sealed pressurization chamber that biases the electrode away from the nozzle thereby initiating a plasma arc using the plasma cutting gas in the plenum. The method further includes transferring the torch current flow from the nozzle to the workpiece while cutting the workpiece with the plasma arc.
In some embodiments, the biasing of the electrode into physical contact with or away from the nozzle is independent of the plasma cutting gas flow through the torch. In some embodiments, the coolant flow is supplied to the electrode via a coolant tube inserted into a cavity of the electrode, where the cavity comprises a distal coolant surface adapted to be directly exposed to the first pressure.
In some embodiments, the sealed pressurization chamber is located proximal to the plenum. In some embodiments, a portion of the sealed pressurization chamber is defined by a biasing flange of a first body of the multi-piece cathode. The first body is fixedly attached to the electrode and translatable relative to a stationary second body of the cathode. The first body is disposed distal to the second body.
In some embodiments, the method further includes exerting the second pressure against a biasing surface of the biasing flange of the first body to translate the first body proximally into physical contact with the first body, thereby translating the electrode proximally away from the nozzle. In some embodiments, a first area of the distal coolant surface is smaller than a second area of the biasing surface of the biasing flange. In some embodiments, the first pressure of the coolant flow against the distal coolant surface is greater than the second pressure of the biasing gas against the biasing surface.
In some embodiments, the method further includes ramping down the supply of the biasing gas for operating the torch to enable the first pressure exerted on the electrode to translate the first body away from the second body of the cathode and allow the electrode to physically contact the nozzle in preparation for a next start of the torch. In some embodiments, the method further includes passing substantially all of the pilot current flow via a dynamic electrical contact located between the first and second bodies of the cathode.
In yet another aspect, the present invention features a contact start liquid-cooled plasma arc cutting torch comprising a consumable torch head including a nozzle, an electrode, a coolant tube and a cathode. The torch also includes a receptacle connected to a proximal end of the torch head. The receptacle is configured to controllably supply a liquid coolant and one or more gases to the cutting head. The receptacle includes a coolant valve interface for providing a supply of the liquid coolant to the coolant tube, where the liquid coolant is configured to cool the torch head while exerting a forward pressure configured to bias the electrode toward the nozzle. The receptacle also includes a first gas valve for regulating a supply of a plasma cutting gas to a plenum located between the electrode and the nozzle of the torch head, the plasma cutting gas adapted to create a plasma arc for cutting a workpiece. The receptacle further includes a second gas valve for regulating a supply of a biasing gas to a pressurization chamber located adjacent to the cathode of the torch head. The biasing gas is adapted to create a backward pressure in the pressurization chamber to bias the electrode away from the nozzle.
In some embodiments, the coolant valve interface is adapted to supply the liquid coolant to the coolant tube during both a transferred arc mode and a pilot arc mode for operating the torch. In some embodiments, the second gas valve for regulating the biasing gas supply is adapted to be closed or ramped down for at least a portion of a time duration when operating the torch.
In some embodiments, the torch further includes a volume disposed in the receptacle for storing a radio-frequency identification (RFID) tag. The RFID tag is configured to store at least one of consumable identification information, consumable usage history or process parameters.
In some embodiments, the biasing gas comprises a nitrogen gas.
The advantages of the invention described above, together with further advantages, may be better understood by referring to the following description taken in conjunction with the accompanying drawings. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention.
The torch body 102 can include a torch insulator 108 configured to support a multi-piece cathode 110 and a coolant tube 112 with a portion of which disposed in the torch insulator 108. The cathode 110 and coolant tube 112 may or may not be consumables of the plasma arc torch 100. In some embodiments, the torch insulator 108 of the torch body 102 is made from an electrically insulating material and includes a central main channel 114 that extends along and substantially disposed about the central longitudinal axis A. The main channel 114 can be configured to house at least a portion of the multi-piece cathode 110. As shown, the cathode 110 can extend within the main channel 114 along a portion of the length of the torch insulator 108. The cathode 110 can include two distinct bodies comprising a proximal cathode body 110a and a distal cathode body 110b. The proximal cathode body 110a is shaped and configured to matingly engage the torch body 102, such as to fixedly engage a surface of the main channel 114 in the torch insulator 108 of the torch body 102. One or more torch locking components (e.g., threads or O-ring seals) can be used to secure an external surface of the proximal cathode body 110a of the cathode 110 to the main channel 114 inside of the torch insulator 108. The distal cathode body 110b is shaped and configured to matingly engage the electrode 104. For example, one or more electrode locking components (e.g., threads or O-rings) can be used to fixedly engage an interior surface of the distal cathode body 110b to an exterior surface of the proximal end of the electrode 104. In some embodiments, the proximal and distal cathode bodies 110a, 110b are made from an electrically conductive material, such as brass and/or copper. Further, the distal cathode body 110b can slidingly engage the proximal cathode body 110a such that the distal body 110b and the electrode 104 are axially translatable relative to the proximal body 110a along the longitudinal axis A. In some embodiments, the multi-piece cathode 110 further includes a resilient element 116 (e.g., a canted coil spring) that is disposed and connected between the proximal and distal bodies 110a, 110b of the cathode 110 to minimize friction during the axial translation of these bodies relative to each other. In addition, the resilient element 116 can be conductive to provide a consistent electrical contact between the two bodies 110a, 110b during their relative movement. Details regarding the connections among the cathode bodies 110a and 110b, the torch insulator 108 and the electrode 104 are explained below with reference to
In some embodiments, the interconnection of the distal cathode body 110b of the cathode 110, the proximal cathode body 110a of the cathode 110, and the electrode 110 defines a housing within which the coolant tube 112 is encased. Specifically, as shown in
In some embodiments, the coolant tube 112 is a multi-piece telescoping coolant tube. As shown, the coolant tube 112 comprises at least two pieces, a proximal piece 112a and a distal piece 112b. The distal coolant tube piece 112b is adapted to translate axially within the hollow boy of the proximal piece 112a in a telescoping fashion, while the proximal piece 112a is fixedly engaged to the torch insulator 108. For example, the proximal piece 112a of the coolant tube 112 can be fixedly engaged to the main channel 114 of the torch insulator 108 via a threaded connection comprising the one or more threads 118 disposed on an exterior surface of the proximal piece 112a of the coolant tube 112. An advantage of using the multi-piece telescoping coolant tube 112 is that it improves consumable alignment, where the close tolerance of the proximal piece 112a acts as a guide post for the electrode 104 during torch operations.
In some embodiments, the nozzle 106 is disposed about the distal end of the electrode body 104 and is circumferentially spaced from the electrode body 104 to define a plenum region 124 therebetween. The nozzle 106 can include a central nozzle exit orifice 126 for expelling a plasma arc, such a as an ionized gas jet, for processing (e.g., cutting) a workpiece or for allowing pre-flow gases to expel from the plenum region 124 prior to electrode nozzle separation (e.g., pilot arc formation). In some embodiments, the nozzle 106 is a two-piece nozzle that includes an inner nozzle liner 106a substantially surrounded by a nozzle body 106b. Thus, in this configuration, physical contact between the electrode 104 and the nozzle 106 occurs at an interface 105 between the electrode 104 and the inner nozzle liner 106a. Alternatively, in embodiments where the inner nozzle liner 106a is absent (i.e., the nozzle 106 is a one-piece structure), the physical interface occurs between the electrode 104 and the nozzle body 106b. In some embodiments, the torch tip 103 includes an inner retaining cap 128 securely connected (e.g., threaded) to the torch body 102 to retain the nozzle 106 to the torch body 102 as well as radially and/or axially position the nozzle 106 with respect to the longitudinal axis A. In some embodiments, the torch tip 103 includes a shield 130 that is secured (e.g., threaded) to the torch body 102 via an outer retaining cap 132. The shield 130 includes a shield exit orifice 134, which in combination with the nozzle exit orifice 126, define a plasma arc exit orifice through which a plasma arc is delivered to a workpiece during torch operation.
In some embodiments, the torch tip 103 includes a swirl ring 135 mounted around the electrode 104. The swirl ring 135 can have a set of radially and/or axially offset (or canted) gas distribution holes configured to impart a tangential and/or parallel velocity component to a plasma gas flow, thereby causing the plasma gas flow to swirl. This swirl creates a vortex that constricts the arc and stabilizes the position of the arc on the electrode 104. In some embodiments, the torch tip 103 includes a chamber cover 138 configured to provide a substantially fluid proof seal of the plenum region 124 by bridging the gap between the cathode 110 and the swirl ring 135. For example, as shown in
In general, a contact start approach can be used to generate a plasma arc in the torch 100 for heavy industrial plasma cutting, while the torch 100 is being liquid cooled to remove excess heat from the torch consumables. In operation, the liquid coolant flow 140 is provided from the torch body 102 to the coolant tube 112 connected thereto. Exemplary liquid coolant includes water, propylene glycol, ethylene glycol, or any number of commercially available coolants designed for plasma cutting systems. For example, a liquid coolant can comprise about 30% propylene glycol and about 70% water. The coolant tube 112 conducts the coolant flow 140 to the electrode 104 to cool the torch tip 103. A typical pressure exerted by the coolant flow 140 on entry to the coolant tube 112 in the distal direction is about 160 pounds per square inch (PSI) to about 180 PSI. While flowing through the coolant tube 112 within the coolant cavity 120 of the electrode body 104, the coolant flow 140 is adapted to exert a forward biasing force on a biasing surface of the electrode 104, such as on the distal internal coolant surface 122 of the electrode 104 as the coolant flow 140 exits from the coolant tube 112 within the cavity 120. In the absence of an equal or greater counter blowback force, this forward biasing force associated with the coolant flow 140 axially translates the electrode 104 in the distal direction toward the nozzle 106 until the electrode 104 physically contacts the nozzle 106 in the plenum region 124, at which position the distal movement of the electrode 104 is restrained by the nozzle 106.
In some embodiments, the axial translation and biasing of the electrode 104 relative to the nozzle 106 at the distal end of the electrode 104 causes axial translation of the distal cathode body 110b relative to the proximal cathode body 110a at least because the distal cathode body 110b is coupled to the proximal end of the electrode 104. Specifically, in the pilot arc mode when the forward biasing force associated with the coolant flow 140 is greater than any counter blowback force (and the electrode 104 is being biased into physical contact with the nozzle 106), the distal body 110b of the cathode 110 is adapted to translate distally away from the relative stationary proximal body 110a of the cathode 110 to create an axial gap 141 between the two bodies, as illustrated in
In the pilot arc mode where the electrode 104 is biased forward by the coolant flow 140 to physically contact the nozzle 106, a current flow path of a small pilot arc current is established between the nozzle 106 and the electrode 104. The pilot arc current can be between about 9 amps to about 60 amps. A flow of plasma gas 150 is also introduced to the plenum region 124 of the torch 100 between the electrode 104 and the nozzle 106. After establishing the pilot arc current, a blowback force is applied to a blowback surface of the torch 100 to break the physical contact between the electrode 104 and the nozzle 106 in the plenum region 124, at which point the pilot arc current induces a spark discharge in the plasma gas flow 150 in the resulting gap 107 in the plenum region 124. In some embodiments, the plasma gas flow 150 supplied to the plenum region 124 is also used to generate the blowback force to separate the contact between the electrode 104 from the nozzle 106, in which case the blowback surface is the distal end face of the electrode 104. Alternatively, in the plasma arc torch 100 of
In some embodiments, the biasing fluid is routed within the torch 100 along the fluid flow path 142 to pressurize a substantially sealed pressurization chamber 146 of the torch 100. The pressure exerted by the biasing fluid flow 142 in the sealed pressurization chamber 146 can be modulated to generate a blowback force that creates a non-equilibrium condition for separating the electrode 104 from the nozzle 106 in the plenum region 126. As shown in
To bias the electrode 104 away from being in contact with the nozzle 106, the blowback force created by the biasing fluid flow 142 on the blowback surface 148a of the pressurization chamber 146 is larger than and in substantially opposite direction from the forward biasing force associated with the liquid coolant flow 140, which is defined as a non-equilibrium condition for operating the torch 100. To achieve this non equilibrium condition, the sealed pressurization chamber 146 is pressurized by the biasing fluid received from the fluid input port 144. Within the pressurization chamber 146, the surfaces of the pressurization chamber 146, including the lateral surface 148a of the blowback flange 148 of the distal cathode body 110b, are exposed to the biasing fluid flow 142 and the resulting pressure. As the fluid pressure in the pressurization chamber 146 builds, a distal blowback force is exerted on the blowback flange 148 of the slideable distal cathode body 110b to urge the distal cathode body 110b to translate into an abutting position with the proximal cathode body 110a. In some embodiments, the axial translation and biasing of the distal cathode body 110b causes an axial translation of the electrode 104 relative to the nozzle 106 in the plenum region 124 at least because the proximal end of the electrode 104 is coupled to the distal cathode body 110b. Specifically, when the blowback force is greater than the forward biasing force associated with the coolant flow 140 (and the distal cathode body 110b is biased into physical contact with the proximal cathode body 110a), the electrode 104 is adapted to translate proximally away from the relative stationary nozzle 106 to create the air gap 107 in the plenum region 124, as illustrated in
In some embodiments, even though the blowback force generated by the biasing gas flow 142 against a blowback surface is greater than the forward biasing force generated by the coolant flow 140 against a forward biasing surface, the pressure of the biasing gas flow 142 supplied to the torch 100 is less than the pressure of the coolant flow 140 supplied to the torch 100. For example, the pressure of the biasing gas flow 142 can be less than about 160 PSI, such as about 80 PSI to about 90 PSI, while the pressure of the coolant flow 140 is greater, such as about 160 PSI to about 180 PSI. In some embodiments, the blowback surface exposed to the biasing gas flow 142 is a surface of the distal cathode body 110b, such as the lateral surface 148a of the blowback flange 148 of the distal cathode body 110b. In some embodiments, the forward biasing surface exposed to the coolant flow 140 is a surface of the electrode 104, such as the distal internal coolant surface 122 of the electrode. The lower biasing fluid pressure can be achieved by configuring the surface area of the lateral surface 148a of the blowback flange 148 to be greater than the surface area of the distal internal coolant surface 122, where both surfaces 148a, 122 are substantially orthogonal to the longitudinal axis A. Since pressure is inversely proportional to the available surface area on which the pressure is applied, a larger surface area means a smaller pressure is required to achieve a desired force. In some embodiments, the pressure of the liquid coolant flow 140 is about 40% greater than the pressure of the biasing gas flow 142. In some embodiments, the surface area of the lateral surface 148a of the blowback flange 148 is about 40% greater than the surface area of the distal internal coolant surface 122.
In some embodiments, the dynamic electrical contact 116 is disposed between the proximal body 110a and the distal body 110b of the cathode 110. The electrical contact 116 can be in the form of a ring-shaped, canted coil spring located between an exterior circumferential surface of the distal cathode body 110b and an interior circumferential surface of the proximal cathode body 110a. In some embodiments, the dynamic electrical contact 116 is configured to pass substantially all of a pilot arc current between the proximal and distal cathode bodies during a pilot arc mode of torch operation, as will be described below in detail.
In general, the plasma arc cutting torch 100 of
To start a pilot arc in the pilot arc mode, a pilot arc current is coupled to a power line from a power supply (not shown) to the plasma arc torch 100, where a pilot current flow is established between the electrode 104 and the nozzle 106 due to their physical contact with each other (step 804). In an exemplary pilot current flow path, the pilot arc current flow can be passed from the power supply to the proximal body 110a of the cathode 110. In some embodiments, at least a portion of the pilot arc current is passed from the proximal cathode body 110a to the distal cathode body 110b via the dynamic electrical contact 116 therebetween. For example, the electrical contact 116 can be suitably configured to pass substantially all of the pilot arc current between the two cathode bodies 110a, 110b. In some other embodiments, all or substantially all of the pilot arc current passes directly between the two cathode bodies 110a and 110b themselves. The distal cathode body 110b can in turn pass the pilot arc current to the electrode 104 to which the distal cathode body 110b is physically connected. Due to the physical contact between the electrode 104 and the nozzle 106 (caused by the forward biasing force provided by the coolant flow 140), the pilot arc current is adapted to flow to the nozzle 106. In some embodiments, because the electrical contact 116 is sandwiched between the two cathode bodies 110a, 110b, and both of which are liquid cooled by the coolant flow 140, this enables effective heat removal from the electrical contact 116, thereby allowing the electrical contact 116 to carry full process current (e.g., up to 300 Amps in case of a fault condition) without damaging torch components.
A pre-flow of the plasma gas flow 150 can be introduced into the plenum region 124 between the nozzle 106 and the electrode 104 before, during and/or after the pilot arc current in the plenum region 124 is established (step 806). In the prior art gas cooled systems, the pressure exerted by the plasma gas flow 150 is used to overcome the mechanical (e.g., spring based) based forward biasing force to move the electrode 104 proximally away from the nozzle 106, thereby creating an air gap between the two components. However, for the plasma arc torch 100, the biasing fluid flow 142 supplied to the sealed pressurization chamber 146 is turned on or ramped up to create a blowback force against the lateral surface 148a of the biasing flange 148 of the distal cathode body 110b (step 808). The blowback force is adapted to be greater than the forward biasing force of the coolant flow 140 on the electrode 104 in order to urge the distal cathode body 110b to axially translate in the distal direction until the biasing flange 148 is in physical contact with the proximal cathode body 110a, as illustrated in
To generate a plasma arc, a potential difference develops between the electrode 104 and the nozzle 106 as the gap 107 between them increases. The pilot arc current ionizes the pre-flow of plasm gas flow 150 in the resulting gap 107 and initiates a pilot arc in that region. Thus, in the plasma arc torch 100, the biasing of the electrode 104 relative to the nozzle 106 (either into contact or away from each other) is independent of the plasma gas flow 150. For example, the electrode 104 can be actuated to bias away from the nozzle 106 after the plasma gas flow 150 is supplied to the plenum region and the appropriate plasma gas pressure is reached. In some embodiments, the lateral blowback surface 148a of the blowback flange 148 has a larger surface area than the distal internal coolant surface 122 of the electrode 104 such that the biasing fluid flow 142 is able to create a sufficiently large blowback force to overcome the forward biasing force to separate the electrode 104 from the nozzle 106, even though the pressure of the biasing fluid flow 142 is less than the pressure of the coolant flow 140. In general, the separation of the blowback pressure (created by the biasing fluid flow 142) from the plasma gas pressure (of the plasma gas flow 150) results in better cut quality by the plasma arc torch 100 at least because the plasma gas flow 150 no longer needs to establish a sufficiently high pressure to bias the electrode 104 away from the nozzle 106; thus a lower plasma gas pressure can be used that provides better control over torch operations. In addition, depleting plasma gas pressures during ramp down and/or supplying different plasma pressures for different processes no longer negatively impact electrode movement in the plasma arc torch 100 (in contrast to prior art torches), thus improving consumable life and quality. Further, as described above, a pre-flow of the plasma gas can be supplied to the plenum region 124 prior to and/or during physical contact between the electrode 104 and the nozzle 106, thereby establishing sufficient pressure in the plenum region 124 that drives rapid arc transfer immediately/shortly after physical contact breaks between the electrode 104 and the nozzle 106, without having to wait for optimal transfer conditions to be established.
In a transferred arc mode of torch operation for cutting a workpiece, the workpiece is grounded and brought close to the distal end of the torch 100. A voltage higher than the voltage used to initiate the pilot arc can be applied across the electrode 104 and the workpiece to induce the arc to transfer to the workpiece after the gap is ionized. This arc between the electrode 104 and the workpiece is a transferred arc that can be used to cut the workpiece (step 810). To maintain the transferred arc, a transferred arc current, which supplies the higher voltage from the power supply, is passed from the proximal cathode body 110a to the distal cathode body 110b to the electrode 104. In some embodiments, the electric contact 116 passes at least a portion of the transferred arc current. Another portion of the transferred arc current can be passed via the physical contact/interface between the proximal and distal cathode bodies 110a, 110b. To complete the transferred arc circuit, the transferred arc current is returned from the workpiece to the power supply through separate wirings (not shown).
In some embodiments, because torch cooling is needed during both pilot arc initiation and plasma cutting by transferred arc, the coolant flow 140 is supplied during both modes of operation. In some embodiments, the coolant flow 140 is supplied into the torch 100 with a relatively constant pressure during both modes of torch operation. Thus a relatively constant forward biasing force can be present during both modes of torch operation. In contrast, prior art plasma arc torches and systems do not control the pressure of the coolant flow to ensure forward biasing of the electrode relative to the nozzle. In some embodiments, the pressure supplied by the biasing fluid flow 142 is suitably modulated to either (i) ramp up or be turned on to create a blowback force greater than the forward biasing force to bias the electrode 104 away from the nozzle 106 or (ii) ramp down or be turned off such that the forward biasing force dominates, thereby biasing the electrode 104 into the nozzle 106.
As described above, in both torch 100 of
In some embodiments, the receptacle 902 includes a gas channel 910 disposed in the receptacle body 902, where the gas channel 910 extends along the length of the receptacle body 902. The gas channel 910 can be located radially offset from and non-concentric relative to the central longitudinal axis A. The gas channel 910 is configured to receive at least a portion of a plasma gas valve 912 adapted to regulate and deliver the plasma cutting gas flow 150 to the plenum region 124 of the torch 100. In some embodiments, the receptacle 902 includes a fluid channel 914 disposed in the receptacle body 902, where the fluid channel 914 extends along the length of the receptacle body 902. The fluid channel 914 can be radially offset from and non-concentric relative to the central longitudinal axis A. In some embodiments, the fluid channel 914 is configured to receive at least a portion of a biasing fluid valve 916 adapted to regulate and deliver a supply of the biasing fluid (e.g., gas) flow 142 to the pressurization chamber 146 of the torch 100. The biasing fluid valve 916 can controllably adjust the pressure of the biasing fluid flow 142, such as increase (or turn on) the fluid pressure to create a blowback force against a blowback flange 148 of the pressurization chamber 146 to bias the electrode 104 away from the nozzle 106 or decrease (or turn off) the fluid pressure to allow the forward biasing force of the coolant flow dominate (e.g., bias) the electrode 104 into contact with the nozzle 106. In some embodiments, the biasing fluid valve 916 is a three-way valve, as described below in detail with respect to
One advantage of locating the biasing fluid valve 916 in the receptacle 900 adjacent to the torch 100 is that this enables faster actuation of the electrode 104 relative to the nozzle 106, which minimizes energy dissipation and/or heat buildup at the nozzle 106, thus positively impacting consumable life.
In some embodiments, the receptacle 900 is configured to support wireless communication with the plasma arc cutting torch 100, such as facilitate radio-frequency identification (RFID)-based communication with the torch 100. In such an RFID enabled system, an RFID tag can be disposed in the torch 100, while an RFID reader (not shown) can be disposed in the receptacle 900. The RFID tag can be configured to store data related to operating the torch 100, such as at least one of consumable identification information, consumable/torch usage history, process parameters, or operating data related to at least one of the liquid coolant flow, plasma cutting gas flow and/or biasing fluid flow.
In addition, the insulator 108 includes several non-concentric channels that are offset from the central longitudinal axis A for conducting various liquids and/or gases to the consumables attached thereto. For example, the insulator 108 includes a plasma gas channel 1504 extending along the longitudinal axis A for receiving a plasma gas flow (e.g., the plasma gas flow 150 of
As described above, systems and methods of the present invention can utilize two fluid flows to actuate torch components, such as a liquid coolant flow to enable contact between the nozzle and the electrode and a biasing gas flow from a separate chamber to break this contact. An advantage of using fluids for component actuation is that they offer reliable and consistent motive force, which is free from common spring problems such as stiffness variability, aging, fatigue, wear, cracking and distortion. Another advantage is that these fluids enable component actuation independent of process gas (e.g., plasma cutting gas) type and pressure. This allows greater freedom in terms of process design, such as gas types, pressure set points, ramp up and/or down curves etc. Yet another advantage is that the electrode movement can be initiated after desired fluid flows and pressures are established in the plenum region. For example, the electrode 104 can be actuated to bias away from the nozzle 106 after the plasma gas flow 150 is supplied to the plenum region and the appropriate plasma gas pressure is reached. Other advantages include elimination of the need for high frequency starting using a HVHF circuit, enhanced cooling of pilot current carrying elements that improves robustness and range, and extended consumable life and consistent cut quality.
It should be understood that various aspects and embodiments of the invention can be combined in various ways. Based on the teachings of this specification, a person of ordinary skill in the art can readily determine how to combine these various embodiments. Modifications may also occur to those skilled in the art upon reading the specification.
This application claims the benefit of and priority to U.S. Provisional Patent Application Nos. 62/937,537, filed on Nov. 19, 2019, and 62/940,039, filed on Nov. 25, 2019, the entire content of both of which are owned by the assignee of the instant application and incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62937537 | Nov 2019 | US | |
| 62940039 | Nov 2019 | US |
