Method for operating a plasma torch

Abstract

A method for piercing and cutting a workpiece using a plasma torch having an electrode and a nozzle spaced apart from and surrounding a distal portion of the electrode to form a process gas flow passage. According to one embodiment, the method includes delivering a plasma gas through the process gas flow passage of the torch at a first pressure while ionizing the plasma gas to generate a plasma arc extending between the electrode and the workpiece. The piercing operation is performed by using the plasma arc to create a perforation in the workpiece while the plasma gas is delivered at the first pressure. The cutting operation is performed after the piercing operation by delivering the plasma gas through the process gas flow passage at a second pressure that is lower than the first pressure, and a kerf is formed in the workpiece with the plasma gas delivered at the second pressure, the kerf originating at and extending away from a boundary of the perforation.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Patent Application No. 16 / 731,455, filed December 31, 2019, entitled “Method for Operating a Plasma Torch,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to a method for operating a plasma torch during piercing and cutting of a workpiece. Background Technology

[0004] Cutting workpieces with enhanced thickness typically involves forming a piercing in the workpiece, followed by cutting along a designated path to produce the desired work product. There remains a need in the art for a method of operating a plasma torch that prevents arc extinction during piercing formation, providing an efficient transition between piercing and cutting operations without compromising the lifespan of torch consumables and minimizing waste production. Summary of the Invention

[0005] A method for piercing and cutting metal workpieces has been disclosed.

[0006] According to one embodiment, a method for piercing and cutting a workpiece is provided, the method comprising supplying plasma gas at a first pressure through a process gas flow channel of a plasma torch, while ionizing the plasma gas to generate a plasma arc extending between an electrode and the workpiece. With the plasma gas supplied at the first pressure, a piercing operation is performed to create a perforation in the workpiece extending between opposing surfaces of the workpiece. After the piercing operation, a cutting operation is performed by supplying plasma gas at a second pressure lower than the first pressure through the process gas flow channel of the torch. The cutting operation is initiated by forming a slit in the workpiece, the slit originating at the boundary of the perforation and extending away from the boundary of the perforation. According to some embodiments, the first pressure is 10% to 50% greater than the second pressure.

[0007] Compared to the plasma gas pressure during cutting, the increased pressure of the plasma gas supplied during piercing results in an overall increase in the power and momentum of the arc. Therefore, during piercing, at a given current level supplied to the electrodes of the plasma torch, the voltage applied to the electrodes must increase due to the increased arc chamber pressure in order to achieve plasma gas ionization. This increased voltage results in a plasma arc operating at higher power (P = V*I) to generate a higher plasma arc enthalpy. This facilitates more efficient melting of metal during piercing, particularly in workpieces with enhanced thickness (e.g., >1.0 inch). The higher pressure also increases the momentum of the plasma jet, causing it to impact the workpiece with greater force. This advantageously results in a larger amount of molten metal being expelled from the piercing site during perforation, making way for the plasma arc as the piercing depth increases. Furthermore, due to the higher impact force coupling and the strategic arrangement of the side exit holes in the protective shield, the molten metal is dispersed over a larger area, thereby reducing the formation of a large molten pool around the periphery of the resulting perforation. This offers the following advantages: it reduces the lead-in length between the piercing and the starting position of the workpiece's cutting pattern, due to the lack of operation around the large piercing pool. The reduced lead-in length decreases cutting time and also results in less scrap metal generated during the cutting process. It also reduces the risk of the torch colliding with the molten and / or solidified piercing pool.

[0008] According to some embodiments, plasma gas is delivered into the process gas flow channel at different pressures during the puncture operation. According to one embodiment, during the first portion of the puncture process, the plasma gas is delivered at a first pressure, and thereafter at a second pressure greater than the first pressure. According to some embodiments, the plasma gas pressure gradually increases with the depth of puncture. According to one embodiment, the gradual increase in plasma gas pressure occurs linearly, while according to another embodiment, the gradual increase in plasma gas pressure occurs exponentially.

[0009] According to some embodiments, plasma gas is delivered into the process gas flow channel at different pressures in an alternating / pulsed manner during the puncture operation, causing changes in the momentum of the plasma jet. According to some embodiments, the changes occur at a given frequency, while in other embodiments, the changes occur in a non-uniform manner. According to some embodiments, the amplitude of the plasma pressure change remains constant during the puncture operation, while in other embodiments, the amplitude of the pressure change varies over time. According to some embodiments, the main cutting current delivered to the plasma torch electrode is also varied / pulsed during the puncture phase. According to one such embodiment, the main cutting current and the plasma gas pressure are pulsed uniformly, such that the plasma gas pressure and the main cutting current reach their peak values ​​substantially simultaneously.

[0010] According to some embodiments, a protective gas is provided during the piercing and cutting operations to provide a protective gas around the plasma arc and to protect the nozzle from the blowback of the molten spray. According to some embodiments, the protective gas is delivered to the protective gas flow channel of the plasma torch at a first pressure during the piercing operation, and then provided at a second pressure less than the first pressure during the cutting operation.

[0011] These and other advantages and features will become apparent from the accompanying drawings and detailed description. Attached Figure Description

[0012] Figure 1 This is a cross-sectional view of the end portion of the plasma torch.

[0013] Figure 2 It is a graph showing the change of plasma torch operating parameters over time according to the prior art.

[0014] Figure 3 The graph shows the changes in plasma torch operating parameters over time, where an increased plasma gas pressure is provided during the puncture operation.

[0015] Figure 4 It is a graph showing the changes in plasma torch operating parameters over time, where increased plasma gas pressure and increased protective gas pressure are provided during the puncture operation.

[0016] Figure 5 It is similar to Figure 4 The graph shows that the plasma gas pressure changes during the puncture phase.

[0017] Figure 6 yes Figure 5 A variation of the curve, in which the plasma gas pressure increases non-linearly from the first pressure to the second pressure during the puncture phase.

[0018] Figure 7 yes Figure 6 A variation of the curve, in which the plasma gas pressure decreases non-linearly to the cutting stage pressure when the puncture stage is completed.

[0019] Figure 8 yes Figure 7 A variation of the curve, in which there is a linear increase in plasma gas pressure during the first part of the puncture phase.

[0020] Figure 9 yes Figure 7 A variation of the curve, in which the protective gas pressure increases during the puncture phase.

[0021] Figure 10 yes Figure 9A variation of the curve, in which the plasma gas pressure is pulsed during the puncture phase.

[0022] Figure 11 yes Figure 3 A variation of the curve, in which the rise time of the main cutting current is extended to occur over a longer period of time.

[0023] Figure 12 yes Figure 3 A variation of the curve, in which the main cutting current is delivered to the electrodes of the plasma torch in a stepped manner.

[0024] Figure 13 yes Figure 3 A variation of the curve, wherein the plasma gas pressure is maintained at an elevated pressure after the puncture phase ends and during the first part of the cutting phase.

[0025] Figure 14 yes Figure 13 A variation of the curve, in which the rise time of the main cutting current is extended to occur over a longer period of time.

[0026] Figure 15 It is similar to Figure 3 The graph further illustrates that at the end of the puncture phase, the plasma torch begins to move away from the puncture.

[0027] Figure 16 It is similar to Figure 3 The graph further illustrates that after the puncture phase ends, the plasma torch begins to move away from the puncture at regular intervals.

[0028] Figure 17 It is similar to Figure 13 The graph further illustrates that after the puncture phase ends, the plasma torch begins to move away from the puncture at regular intervals. Detailed Implementation

[0029] Figure 1 This is a simplified diagram of the distal portion of a plasma torch 20 according to one embodiment. Figure 1 A plasma torch was demonstrated that does not possess the various components or parts typically included in plasma cutting torches, such as electrical or gas transfer components. Instead, Figure 1Only selected components or parts are shown to allow for a clear and concise explanation of the technology provided herein. In the depicted embodiment, the torch includes multiple consumable parts, such as electrode 23, nozzle 24, and protective cover 25. The emitter 29 is located in the distal portion of electrode 23. Electrode 23 can be mounted into the torch body and torch nozzle 24 can be mounted thereon. Alternatively, electrode 23 and nozzle 24 can be mounted as a single component to the torch body (e.g., these components can be joined together to form a cylinder and mounted as a cylinder on / inside the torch body).

[0030] Once electrode 23 and nozzle 24 are mounted on the torch body, a protective cover 25 is mounted around the mounting flange of nozzle 24 to secure nozzle 24 and electrode 23 in a suitable position at the operating end of the torch body (and axially aligned with the operating end of the torch body). Alternatively or additionally, nozzle 24 and / or electrode 23 can be secured or attached to the torch body in any desired manner, such as by mating threaded portions included on the torch body with corresponding threads included on the component. For example, in some embodiments, electrode 23, nozzle 24, protective cover 25, and any other components (e.g., locking rings, spacers, auxiliary covers, etc.) can be assembled together in a cylinder that can be selectively coupled to the torch body. For example, these various components can be coupled to a cylinder body or coupled to each other to form a cylinder.

[0031] In use, the plasma torch 20 is configured to emit a plasma arc 34 between the electrode 23 and the workpiece 40, and a working lead associated with a power source is attached to the workpiece 40. For example... Figure 1 As shown, the nozzle 24 is spaced a certain distance from the electrode 23, and a process gas flow channel 30 is provided between them. When the torch is operated, the process gas 32 flows through the process gas flow channel 30. The protective cover 25 is also spaced a certain distance from the nozzle 24, and a protective gas flow channel 31 is provided between them. When the torch is operated, the protective gas 33 flows through the protective gas flow channel 31.

[0032] Figure 2 A timeline is depicted, illustrating how the ignition current C is controlled during plasma torch cutting operations according to existing technology. pThe main cutting current, ignition gas, plasma gas, and protective gas are supplied to the plasma torch. During the initial period at time t0, a high voltage and high-frequency signal are applied between electrode 23 and nozzle 24 to generate an electric arc between them, which extends through the process gas flow channel supplying the ignition gas. As the ignition gas flows through channel 30 during arc initiation, it is ionized to form a conductive plasma arc, which is then guided away from nozzle 24 toward a conductive workpiece 40 (e.g., a metal workpiece). When the plasma arc transfers to workpiece 40 at time t1, the main cutting current then operates at the full cutting current C. f A plasma gas 32 is supplied to electrode 23, establishing a circuit between the power source and the workpiece. At time t1, plasma gas 32 is also supplied through the process gas flow channel. Thus, a plasma arc 34, establishing a closed circuit between electrode 23 and the workpiece, is sufficient to cut through the workpiece by locally melting the material forming the workpiece. Figure 2 As shown, when the main cutting current is supplied to electrode 23, the ignition current to nozzle 24 terminates, and the supply of ignition gas stops as the supply of plasma gas begins. According to some embodiments, the ignition gas is the same as the plasma gas. In such cases, switching from ignition gas to plasma gas may only involve increasing the gas pressure. Figure 2 As further shown, the protective gas is typically allowed to flow through the protective gas flow channel 31 starting at time t0.

[0033] exist Figure 2 In existing technology examples, during the piercing phase (where a puncture is formed through the workpiece) between times t1 and t3 (where a cut is made through the workpiece) and the cutting phase (where the workpiece is cut to form the desired work product) between times t3 and t4, each of the plasma gas pressure and the protective gas pressure is maintained constant. According to a standard operating procedure, the plasma gas pressure is maintained at approximately 60 psi during the piercing and cutting phases, while the protective gas pressure is maintained at approximately 80 psi during this period. Figure 2 Other notable features of the timeline are the main cutting current increase phase at time t1-t2 (where the main cutting current increases from an ignition current level of 10-50 amps to, for example, 150 amps) and the main cutting current and plasma pressure decrease phase at time t4-t5 (where the main cutting current decreases to 0 amps and the plasma pressure decreases to 0 psi or close to 0 psi).

[0034] Figure 3 The graph shows the changes in plasma torch operating parameters over time, where an increased plasma gas pressure is provided during the piercing operation. When the plasma torch starts at time t0, the initial ignition current C... pAn electric arc (e.g., 10 to 50 amperes) is supplied to nozzle 24 to generate an arc across process gas flow channel 30 between nozzle 24 and electrode 23, through which ignition gas is supplied. As the ignition gas flows through channel 30 during arc initiation, it is ionized to form a conductive plasma, which is then directed away from the nozzle toward a conductive workpiece (e.g., a metal workpiece). When the arc is transferred to the workpiece at time t1, a full current C is applied. f The main cutting current is supplied to electrode 23, and a circuit is established between the power supply and the workpiece. According to some embodiments, when the plasma arc is transferred to the workpiece, the current change is detected by the power supply, and the current begins to rise from the ignition current C. p To the main cutting current C f The switching occurs during the process. During this switching, the power supply is disconnected from nozzle 24 and the main cutting current ramps up to the full cutting current C. f At time t1, plasma gas is supplied through the process gas flow channel under pressure P2, and the piercing stage begins. Therefore, a closed-circuit plasma arc is established between electrode 23 and the workpiece, sufficient to cut through the workpiece by locally melting the material formed within the workpiece. Figure 3 As shown, when the main cutting current is supplied to electrode 23, the ignition current to nozzle 24 terminates, and the supply of ignition gas stops as the supply of plasma gas begins. According to some embodiments, the ignition gas is the same as the plasma gas. In such cases, switching from ignition gas to plasma gas may only involve increasing the process gas pressure. For example... Figure 3 As further shown, the protective gas 33 is typically allowed to flow through the protective gas flow channel 31 starting at time t0.

[0035] exist Figure 3 In one embodiment, the plasma gas pressure initially reaches an increased pressure P2 at time t1 at the start of the puncture phase and remains elevated throughout the duration of the puncture phase. At the end of the puncture phase, at time t3, the plasma gas pressure subsequently decreases to a reduced pressure P1 during the cutting phase between times t3 and t4. According to some embodiments, pressure P2 is 10% to 50% greater than pressure P1. Figure 3 Other notable features of the timeline are the main cutting current rising phase t1-t2 (where the main cutting current rises to, for example, 400 amperes) and the main cutting current and plasma gas pressure falling phase t4-t5 (where the main cutting current falls to 0 amperes and the plasma gas pressure falls to 0 psi or close to 0 psi).

[0036] As described above, the increased pressure of the plasma gas supplied during the piercing phase, compared to the pressure during the cutting phase, results in an overall increase in the power and momentum of the arc. Therefore, during piercing, at a given current level supplied to the electrodes of the plasma torch, the voltage applied to the plasma torch electrode 23 will increase due to the increased arc chamber pressure in order to cause ionization of the plasma gas. This increased voltage results in a plasma arc operating at higher power (P = V*I) to generate a higher plasma enthalpy. This facilitates more efficient melting of metal during piercing, particularly in workpieces with enhanced thickness (e.g., >1.0 inch). The higher pressure also increases the momentum of the plasma jet, causing it to impact the workpiece with greater force. This advantageously results in a larger amount of molten metal present in the piercing being expelled from the piercing during perforation, making way for the plasma arc as the piercing depth increases. Furthermore, due to the high impact force of the plasma arc on the molten metal and the strategic arrangement of the exit orifice within the protective shield 25, the molten metal is dispersed away from the workpiece or over a larger area, thereby reducing the formation of a large pool of molten and / or solidified metal around the circumference of the resulting perforation. This has the advantages of reducing the lead-in length between the perforation and the starting position of the workpiece's cutting pattern, due to the absence of operations around the large molten pool. The reduced lead-in length decreases cutting time and also results in less scrap metal generated during the cutting process. It also reduces the risk of the torch colliding with the pool of molten and / or solidified metal located around the perforation.

[0037] According to one embodiment, the full main cutting current C delivered to electrode 23 is... f The pressure is 400 amps, and the plasma gas is delivered to plasma gas flow channel 30 at 80 ± 5 psi during the puncture phase and then reduced to 60 ± 5 psi during the cutting phase. Figure 3 In this implementation, during the ignition, puncture, and cutting phases, the protective gas pressure P3 is maintained constant between 80 psi and 95 psi in high-ampere applications. However, as... Figure 4 As shown, according to some embodiments, the protective gas pressure is increased from pressure P3 to pressure P4 during the puncture phase. According to one such embodiment, P3 is maintained at 80 ± 5 psi and P4 is maintained at 95 ± 5 psi. Increasing the protective gas pressure while the plasma gas pressure is rising as the puncture is cut provides a greater total impact pressure applied inside the puncture. As mentioned above, this has the advantage of more effectively removing and moving molten metal generated inside the puncture away from it, reducing or completely eliminating large molten and / or solidified metal pits formed around the puncture when the puncture operation is completed. Maintaining the protective gas pressure at the increased level P4 during the puncture phase also provides additional protection to the torch by deflecting the melt backflush caused by the increased plasma gas pressure P2.

[0038] In the methods disclosed herein, each of the plasma gas and protective gas can be, for example, compressed air, oxygen, nitrogen, H₂O, etc. 35 (35% hydrogen / 65% argon). The protective gas can also be a mist of H2O. The plasma and protective gas used in a specific situation depend primarily on the composition and thickness of the workpiece being cut.

[0039] Table 1 below includes plasma torch operation data and puncture time related to conventional puncture operations. Table 2 below includes plasma torch operation data and puncture time related to a process performed according to one aspect of the invention. Tables 1 and 2 show that by increasing the plasma gas pressure and the protective gas pressure during the puncture phase, the time required to create a puncture in a flat carbon steel workpiece is significantly reduced. In each puncture operation in Tables 1 and 2, the plasma gas is oxygen, and the protective gas is compressed air.

[0040] Table 1

[0041]

[0042] Table 2

[0043]

[0044] Figure 5 It is similar to Figure 4 The process involves variations in plasma gas pressure during the puncture phase. Figure 5 In one embodiment, plasma gas is delivered to the plasma torch at a first pressure P1 at time t1, and increases to a second pressure P2 after a specified time period t2. Therefore, as the penetration depth increases over time, the plasma gas pressure also increases. According to one embodiment, the plasma gas pressure is maintained at the first pressure P1 between times t1 and t2, during which time the main cutting current increases from the ignition current (e.g., 10 to 50 amperes) to, for example, 400 amperes. Figure 5 In one embodiment, the first pressure P1 corresponds to the plasma gas pressure supplied to the plasma torch during the cutting phase. According to other embodiments, the first pressure P1 may be higher or lower than the plasma gas pressure supplied to the plasma torch during the cutting phase.

[0045] Continue to refer to Figure 5The advantage of delivering plasma gas at a lower first pressure P1 during the first part of the piercing phase (time t1-t2) and then increasing it to a second pressure P2 during the second part of the piercing phase (time t2-t3) is that it provides a more energy-efficient piercing process. Because the molten metal remains closer to the workpiece surface during the first part of the piercing phase, and because the vertical distance between the torch tip and the workpiece is generally minimal, delivering plasma gas at a lower pressure P1 is sufficient to effectively melt the workpiece at the piercing location and effectively remove molten metal from shallow piercings.

[0046] exist Figure 5 In this implementation, during the puncture phase, the plasma gas pressure transitions from P1 to P2 in a stepwise manner at time t2. This sudden change in plasma gas pressure can more effectively induce the discharge of molten metal accumulated during the first part of the puncture phase. However, as... Figures 6-10 As shown, the plasma gas pressure can also increase from the first pressure P1 to the second pressure P2 in a non-linear (e.g., exponential) or linear manner. Figure 5 In this implementation, when the puncture phase is completed at time t3, the second pressure P2 decreases stepwise to the first pressure P1. However, as... Figures 7-10 As shown, the plasma gas pressure can also be gradually reduced from the second pressure P2 to the first pressure P1. Figures 7-10 In one embodiment, the plasma gas pressure decreases linearly in a non-linear manner, but alternatively, it decreases linearly.

[0047] Figure 6 yes Figure 5 A variation of the process in which the plasma gas pressure increases nonlinearly from a first pressure P1 to a second pressure P2 during the puncture stage.

[0048] Figure 7 yes Figure 6 A variation of the process, in which, when the piercing stage is completed, the plasma gas pressure P2 decreases obliquely and non-linearly to the cutting stage pressure P1 during the cutting stage.

[0049] Figure 8 yes Figure 7 A variation of the process, wherein a linear increase in plasma gas pressure occurs during at least the first portion of the puncture phase in the time period t1-t2. Figure 8 In the example, between times t1 and t2, the plasma gas pressure increases from the ignition pressure to, for example, 80 psi in a continuous linear manner.

[0050] Figure 9 yes Figure 7 Variations in the process. In Figure 7In this implementation, during the ignition, puncture, and cutting phases, the protective gas pressure P3 is maintained constant between 80 psi and 95 psi. However, as... Figure 9 As shown, according to some embodiments, the protective gas pressure is increased from a first pressure P3 to a second pressure P4 during the puncture phase. According to one such embodiment, P3 is maintained at 80 ± 5 psi and P4 is maintained at 95 ± 5 psi. Increasing the protective gas pressure while the plasma gas pressure is rising as the puncture is cut provides a greater total impact pressure applied inside the puncture. As mentioned above, this has the advantages of more effectively removing and moving molten metal generated inside the puncture away from it, minimizing or completely eliminating large pools of molten and / or solidified metal formed around the puncture during the puncture phase. Maintaining the protective gas pressure at the increased level P4 during the puncture phase also provides additional protection to the torch through deflecting melt backflush.

[0051] exist Figure 4 In this implementation, the protective gas pressure increases from P3 to P4 in a stepwise manner and decreases from P4 to P3 in a stepwise manner. However, as... Figure 9 As shown, according to other embodiments, P3 rises to P4, and P4 then slopes down to P3 at the beginning and end of the piercing process. The rise and slope descent can occur linearly or non-linearly. Figure 9 In this implementation, the increase from P3 to P4 is linear, and the sloping decrease from P4 to P3 is non-linear.

[0052] Figure 4 , Figure 9 and Figure 10 The process provides increased protective gas pressure during the puncture phase. However, it is important to note that... Figures 5-8 and Figures 11-1 The process of 8 can also be modified to incorporate such features.

[0053] Figure 10 yes Figure 9 A variation of the process is used where the plasma gas pressure pulsates between pressures P1 and P2 during the piercing phase. This pulsation causes the ionized plasma jet to impact the workpiece with alternating high and low forces, similar to a jackhammer. Figure 10 In this implementation, the plasma gas pressure variation includes two waves 10 and 12, but may include any number of waves. (See reference...) Figure 10 The first wave 10 includes a linear rise from P3 to P4 and a linear descent from P4 back to P3, and the second wave 12 includes a linear rise from P3 to P4 and a non-linear descent from P4 back to P3. According to other embodiments, the alternation between P3 and P4 occurs in a stepwise manner.

[0054] exist Figure 10 In the process, during the cutting stage, a similar Figure 8 and Figure 9 The process occurs by descending from P4 to P3 via a final slope.

[0055] Figure 11 yes Figure 3 A variation of the process in which the rise time of the main cutting current is extended to occur over a longer period of time. Figure 3 Faster ramp rates are better suited for cutting metals such as stainless steel and aluminum, where oxygen-free plasma and protective gases are used during the piercing and cutting phases. Examples of non-oxidizing gases are nitrogen and H₂O. 35 (35% hydrogen / 65% argon mixture). Figure 11 Lower ramp rates are more suitable for ferrous metals, such as low-carbon steel, where oxygen-containing plasma and protective gases are appropriately used during the piercing and cutting phases. Examples of oxidizing gases are air and oxygen. The type of emitter 29 used in the plasma torch also affects the selection of the appropriate rise time. For example, when the emitter 29 is tungsten, it does not tend to wear significantly when using a nitrogen plasma jet to cut, for example, stainless steel workpieces. Therefore, higher ramp rates or even a stepwise increase in the main cutting current (see...) Figure 12 This is suitable because it does not significantly affect the lifetime of electrode 23. However, when the emitter is hafnium, hafnium craters typically exist at the electrode tip at the end of the ignition phase. In this case, if the main cutting current increases too rapidly, the hafnium crater may be blown away from the plasma torch nozzle. If this occurs, the electrode lifetime will be significantly reduced.

[0056] Figure 12 yes Figure 3 A variation of the process in which the main cutting current is delivered to the electrodes of the plasma torch in a stepped manner.

[0057] Figure 13 yes Figure 3 A variation of the process, wherein the piercing stage ends at t3 and the first part of the cutting stage (time t3-t4) occurs after t3. xDuring this phase, the plasma gas pressure is maintained at the elevated pressure P2. As mentioned above, in some cases, slag may accumulate around the perforation during its formation. This effectively increases the thickness of the metal to be cut in the region surrounding the perforation. By maintaining the plasma gas pressure at the elevated pressure P2 after the piercing phase ends and during the first part of the cutting phase, the ionized plasma jet (i.e., the plasma arc) is maintained at a higher temperature and impacts the workpiece with greater force. Therefore, as the plasma torch moves away from the perforation, the plasma arc more easily cuts through any metal pits surrounding the perforation. This has the advantage of reducing the total cutting time by eliminating the need to operate around the metal pool. It also reduces the risk of the torch contacting the metal pit, which can cause double arc discharge and damage to torch consumables.

[0058] Figure 14 yes Figure 13 A variation of the process in which the rise time of the main cutting current is extended to occur over a longer period of time.

[0059] Figure 15 It is similar to Figure 3 The graph further illustrates that at the end of the piercing phase, the plasma torch begins to move away from the piercing hole. Figures 15-17 In the diagram, this movement of the plasma torch is represented by lines labeled "torch movement." Line M1 indicates a plasma torch at rest relative to its movement along the length and / or width of the workpiece. Line M2 indicates horizontal movement of the plasma torch above the top surface of the workpiece. Figure 15 In this implementation, the plasma torch remains stationary during the piercing phase and is then positioned at time t3, coinciding with the end of the piercing phase and the start of the cutting phase, to move away from the piercing in the longitudinal and / or transverse directions of the workpiece. It is important to note that the torch height and / or torch angle can be varied during the stationary state of M1. For example, when producing a piercing, the torch height can be varied as the piercing depth increases, and / or the torch angle can be varied to achieve a bevel cut. Despite the above examples, in the case of workpieces comprising cylindrical forms (e.g., pipes), line M2 represents the plasma torch moving around the circumference of the pipe.

[0060] Figure 16 It is similar to Figure 3 The graph further illustrates that after the puncture phase ends, the plasma torch begins to move away from the puncture at regular time intervals. Figure 16 In the implementation method, the puncture phase includes time t1-t x The first part and at time t x The second part of -t3 occurs at time t1-t xDuring this period, plasma gas is supplied at an increased pressure P2, at time t x During -t3, plasma gas is supplied at a cutting pressure P1. The plasma gas pressure is reduced from P2 to P1 while the torch remains above the perforation, allowing the plasma arc to be stabilized at the new cutting pressure before the torch begins to move away from the perforation. The delay in moving the torch away from the perforation also provides time to reposition the torch height and / or tilt angle before the cutting phase begins.

[0061] Figure 17 It is similar to Figure 13 The graph further illustrates that after the puncture phase ends and when plasma gas is supplied to the plasma torch at an increased pressure P2, the plasma torch begins to move away from the puncture at regular intervals. (The above is combined with...) Figure 13 The description discusses the advantages of the process.

[0062] In each of the embodiments disclosed herein, the height of the plasma torch tip above the piercing location can vary with increasing piercing depth. For example, the height of the plasma torch tip above the top surface of the workpiece can be reduced between times t1 and t3 to minimize plasma arc extension during the piercing process. Excessive extension of the plasma arc reduces its cutting capability and may cause arc extinguishing.

[0063] As mentioned above, Figure 1 This is a simplified diagram sufficient to represent the distal portion of a plasma torch with the operating characteristics disclosed herein. U.S. Patent No. 9,131,596 discloses a plasma torch that can also be used to perform the processes disclosed herein, and is incorporated herein by reference in its entirety.

[0064] The foregoing examples are not intended to limit other variations. This disclosure is merely exemplary in nature, and therefore, variations that do not depart from the spirit of this disclosure should fall within its scope.

Claims

1. A method for piercing and cutting a workpiece using a plasma torch, the plasma torch comprising an electrode and a nozzle, the nozzle being spaced apart from and surrounding a distal portion of the electrode to form a process gas flow channel, the plasma torch comprising a protective shield being spaced apart from and surrounding a distal portion of the nozzle to form a protective gas flow channel, the method comprising: Plasma gas is delivered through the process gas flow channel at a first pressure, while the plasma gas is ionized to generate a plasma arc extending between the electrode and the workpiece. The puncture operation is performed by creating a perforation in the workpiece using the plasma arc. During the puncture operation, a protective gas is delivered through the protective gas flow channel at a third pressure, and the protective gas is maintained at the third pressure throughout the puncture operation. After the puncture operation Adjusting the pressure of the plasma gas from a first pressure to a second pressure lower than the first pressure, wherein the first pressure is 10% to 50% greater than the second pressure, involves adjusting the pressure of the plasma gas so that the pressure decreases linearly from the first pressure to the second pressure; and The plasma gas is delivered at the second pressure through the process gas flow channel to perform a cutting operation, and a cut is formed in the workpiece while the plasma gas is delivered at the second pressure. The cut originates at the boundary of the perforation and extends away from the boundary of the perforation. During the cutting operation, the protective gas is delivered at a fourth pressure through the protective gas flow channel, and the third pressure is greater than the fourth pressure.

2. The method according to claim 1, wherein, During the puncture operation, the plasma gas is increased in pressure from a pressure lower than the first pressure to the first pressure.

3. The method according to claim 2, wherein, The plasma gas increases in pressure linearly.

4. The method according to claim 2, wherein, The plasma gas increases in pressure in a non-linear manner.

5. A method for piercing and cutting a workpiece using a plasma torch, the plasma torch comprising an electrode and a nozzle, the nozzle being spaced apart from and surrounding a distal portion of the electrode to form a process gas flow channel, the method comprising: Plasma gas is delivered through the process gas flow channel at a first pressure at the first moment; The plasma gas is delivered through the process gas flow channel at a second pressure at a second time, and the second pressure is different from the first pressure. The plasma gas is ionized to generate a plasma arc extending between the electrode and the workpiece; as well as By using the plasma arc, while delivering the plasma gas at the first pressure and the second pressure, a puncture operation is performed by creating a perforation in the workpiece. After the piercing operation, a cutting operation is performed by delivering the plasma gas through the process gas flow channel at a third pressure lower than at least one of the first and second pressures, and a cut is formed in the workpiece when the plasma gas is delivered at the third pressure, the cut starting at the boundary of the piercing and extending away from the boundary of the piercing.

6. The method according to claim 5, wherein, The first pressure is greater than the second pressure, and the first time is before the second time.

7. The method according to claim 5, wherein, The first pressure is greater than the second pressure, and the second time occurs before the first time.

8. The method according to claim 6, wherein, Each of the first pressure and the second pressure is greater than the third pressure.

9. The method according to claim 7, wherein, Each of the first pressure and the second pressure is greater than the third pressure.

10. The method according to claim 6, wherein, The first pressure is greater than the third pressure, and the second pressure is substantially the same as the third pressure.

11. The method according to claim 7, wherein, The first pressure is greater than the third pressure, and the second pressure is substantially the same as the third pressure.

12. The method according to claim 5, wherein, The first pressure is greater than the second pressure, and during the puncture operation, the plasma gas is delivered to the process gas flow channel at alternating pressures of the first and second pressures.

13. The method according to claim 5, wherein, The plasma torch includes a protective shroud spaced from and surrounding the distal portion of the nozzle to form a protective gas flow channel. The method further includes delivering protective gas through the protective gas flow channel at a fourth pressure during the puncture operation and subsequently delivering the protective gas through the protective gas flow channel at a fifth pressure during the cutting operation, the fourth pressure being greater than the fifth pressure.

14. The method according to claim 5, wherein, The first pressure is 10% to 50% greater than the second pressure.

15. A method for piercing and cutting a workpiece using a plasma torch, the plasma torch comprising an electrode and a nozzle, the nozzle being spaced apart from and surrounding a distal portion of the electrode to form a process gas flow channel, the method comprising: Plasma gas is delivered through the process gas flow channel at a first pressure, while the plasma gas is ionized to generate a plasma arc extending between the electrode and the workpiece. While delivering the plasma gas at the first pressure, a puncture operation is performed by using the plasma arc to create a perforation in the workpiece. After the piercing operation, the plasma gas is delivered at the first pressure through the process gas flow channel to perform a first cutting operation to form a first incision in the workpiece, the first incision starting at the boundary of the perforation and extending away from the boundary of the perforation. After the first cutting operation, a second cutting operation is performed at a second pressure lower than the first pressure to form a second slit in the workpiece, the second slit starting at the end of the first slit and continuous with the first slit.

16. A method for piercing and cutting a workpiece using a plasma torch, the plasma torch comprising an electrode and a nozzle, the nozzle being spaced apart from and surrounding a distal portion of the electrode to form a process gas flow channel, the method comprising: During the first time period, plasma gas is delivered through the process gas flow channel at a first pressure; During a second time period, the plasma gas is delivered through the process gas flow channel at a second pressure, the second time period being after the first time period, and the second pressure being less than the first pressure; The plasma gas is ionized to generate a plasma arc extending between the electrode and the workpiece; By using the plasma arc, a puncture operation is performed by creating a perforation in the workpiece during the first time period and the first part of the second time period, while the plasma gas is delivered first at the first pressure and then at the second pressure. Following the piercing operation, during the second portion of the second time period, the plasma gas is delivered at the second pressure through the process gas flow channel to perform a cutting operation to form a slit in the workpiece, the slit originating at the boundary of the perforation and extending away from the boundary of the perforation, the first portion of the second time period preceding the second portion of the second time period.

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