Automatic gas control for a plasma arc torch

Abstract

A method and apparatus for controlling a gas supply to a plasma arc torch uses a proportional control solenoid valve positioned adjacent the torch to manipulate the gas flow to the torch, thereby extending electrode life during arc transfer and shutdown. Swirl ring design can be simplified and gas supply and distribution systems become less complicated. The invention also allows manipulation of shield gas flow to reduce divot formation when making interior cuts. The system can be controlled with a digital signal processor utilizing a feedback loop from a sensor.

1 . A method for extending the life of a torch consumable comprising: 
 providing a first fluid line for supplying a plasma gas to the torch;    positioning a programmable control valve in the first fluid line adjacent the torch to control a flow of the plasma gas; and    manipulating the programmable control valve thereby 
 a) controlling the flow of the plasma gas to the torch during operation of the torch; and  
 b) compensating for a volume in the first fluid line between the proportional solenoid control valve and the torch.  
   
   
   
       2 . The method of  claim 1  wherein the positioning step further comprises: 
 disposing the programmable control valve near the torch; and    adjusting an opening of the programmable control valve to change the flow of the plasma gas a plurality of times during a ramp cycle of the plasma gas.    
   
   
       3 . The method of  claim 2  wherein the ramp cycle is at least one of a plasma gas ramp up flow and a plasma gas ramp down flow.  
   
   
       4 . The method of  claim 1  wherein a control output from a digital signal processor is used to adjust the programmable control valve to perform at least one of the controlling and the compensating steps.  
   
   
       5 . The method of  claim 1  wherein the programmable control valve is a proportional solenoid control valve.  
   
   
       7 . The method of  claim 4  further comprising a sensor disposed between the torch and the programmable control valve, such that the digital signal processor uses a signal from the sensor to adjust the control output to the programmable control valve.  
   
   
       7 . The method of claim  6  wherein the sensor is at least one of a pressure sensor or a flow sensor.  
   
   
       8 . The method of  claim 1  further comprising the steps of: 
 positioning a sensor in the first fluid line between the programmable control valve and the torch;    sensing a parameter in the first fluid line;    using the sensed parameter to adjust the programmable control valve during the controlling step.    
   
   
       9 . The method of  claim 1  further comprising the step of: 
 controlling a ramp-up flow of the plasma gas during start-up of the torch using the programmable control valve.    
   
   
       10 . The method of  claim 1  further comprising the step of: 
 controlling a ramp-down flow of the plasma gas during shut-down of the torch using the programmable control valve.    
   
   
       11 . The method of  claim 1  wherein operation of the torch comprises the step of: 
 controlling a ramp-up flow of the plasma gas and a ramp-down flow of the plasma gas using the programmable control valve, to reduce a cycle time of workpiece cuts by the torch.    
   
   
       12 . The method of  claim 1  wherein the torch consumable includes an electrode and operation of the torch includes: 
 controlling at least one of a ramp-up or a ramp-down of a flow of the plasma gas based on a type of the electrode installed in the torch.    
   
   
       13 . A method for control of a gas flow to a plasma arc torch including a plasma chamber disposed within a torch body comprising: 
 providing a first fluid line for supplying a first gas to the torch;    positioning a programmable control valve in the first fluid line adjacent the torch to control a flow of the first gas; and    manipulating the programmable control valve thereby 
 a) controlling the flow of the first gas to the torch during operation of the torch; and  
 b) compensating for a volume in the first fluid line between the programmable control valve and the torch.  
   
   
   
       14 . The method of  claim 13  wherein the positioning step further comprises: 
 disposing the programmable control valve near the torch; and    adjusting an opening of the programmable control valve to change the flow of the first gas a plurality of times during a ramp cycle of the first gas.    
   
   
       15 . The method of  claim 14  wherein the ramp cycle is at least one of a first gas ramp up flow and a first gas ramp down flow.  
   
   
       16 . The method of  claim 13  wherein the programmable control valve is a proportional solenoid control valve.  
   
   
       17 . The method of  claim 13  wherein the first gas is a plasma gas that supplies the plasma chamber.  
   
   
       18 . The method of  claim 17  further comprising the steps of: 
 positioning a second programmable control valve in a second fluid line for supplying a second gas to the torch; and    controlling a flow of the second gas to cool and protect from splatter a shield that surrounds a nozzle and is mounted on the torch body.    
   
   
       19 . The method of  claim 18  further comprising the steps of: 
 diverting at least a portion of the flow of the second gas through a third fluid line to join with the flow of the plasma gas to the torch;    positioning a third programmable control valve in the third fluid line adjacent the torch to control the diverted gas flow;    manipulating the third programmable control valve thereby 
 a) controlling the flow of the diverted portion of the second gas; and  
 b) compensating for a volume in the third fluid line between the third programmable control valve and the torch.  
   
   
   
       20 . (canceled)  
   
   
       21 . The method of  claim 17  wherein the second programmable control valve is a proportional solenoid control valve.  
   
   
       22 . The method of  claim 13  wherein a control output from a digital signal processor is used to adjust the programmable control valve to perform at least one of the controlling and the compensating steps.  
   
   
       23 . The method of  claim 22  further comprising a sensor disposed between the torch and the programmable control valve, such that the digital signal processor uses a signal from the sensor to adjust the control output to the programmable control valve.  
   
   
       24 . The method of  claim 13  wherein the first gas comprises at least one of oxygen, nitrogen, hydrogen, methane, or argon.  
   
   
       25 . The method of  claim 13  wherein the plasma chamber is defined by an electrode and a nozzle, and the first gas is a shield gas that cools and protects from splatter a shield surrounding the nozzle and mounted on the torch body.  
   
   
       26 . The method of  claim 25  further comprising the step of: 
 adjusting the flow of the first gas to reduce formation of a divot in an interior cut of a workpiece.    
   
   
       27 . The method of  claim 25  further comprising the step of: 
 controlling the flow of the shield gas to be a piercing flow during a piercing operation of the torch or to be a cutting flow during a cutting operation of the torch.    
   
   
       28 . A method for control of a shield gas flow to a shield surrounding a nozzle and mounted on a torch body of a plasma arc torch comprising: 
 providing a first fluid line for supplying a shield gas to the torch;    positioning a programmable control valve in the first fluid line adjacent the torch to control the flow of the shield gas;    manipulating the programmable control valve thereby 
 a) controlling the flow of the shield gas to the torch during operation of the torch; and  
 b) compensating for a volume in the first fluid line between the proportional solenoid control valve and the torch; and  
 c) adjusting the flow of the shield gas to reduce formation of a divot in an interior cut of a workpiece.  
   
   
   
       29 . The method of  claim 28  wherein the positioning step further comprises: 
 disposing the programmable control valve near the torch; and    adjusting an opening of the programmable control valve to change the flow of the shield gas a plurality of times during a ramp cycle of the shield gas.    
   
   
       30 . The method of  claim 29  wherein the ramp cycle is at least one of a shield gas ramp up flow and a shield gas ramp down flow.  
   
   
       31 . The method of  claim 28  wherein the programmable control valve is a proportional solenoid control valve.  
   
   
       32 . A plasma arc torch for cutting a workpiece, the plasma torch having a plasma gas source to supply a plasma chamber such that an electrical current passing between an electrode and a nozzle produces a plasma arc that exits the torch through a nozzle exit orifice, the plasma torch comprising: 
 a means for sensing a parameter in a first fluid line that supplies a plasma gas from the plasma gas source; and    a means for controlling a flow of the plasma gas to the plasma chamber based on the sensed parameter using a programmable control valve disposed in the first fluid line adjacent the plasma torch.    
   
   
       33 . The plasma arc torch of  claim 32  wherein the programmable control valve is a proportional solenoid control valve.  
   
   
       34 . The plasma torch of  claim 32  wherein the sensed parameter is a pressure or a flow of the plasma gas.  
   
   
       35 . The plasma torch of  claim 32  further comprising: 
 a means for controlling a flow of a shield gas from a shield gas source to the torch through a second fluid line, the means comprising a second programmable control valve disposed in the second fluid line adjacent the plasma torch.    
   
   
       36 . The plasma torch of  claim 35  wherein the second programmable control valve is a proportional solenoid control valve.  
   
   
       37 . The plasma torch of  claim 35  further comprising a swirl ring that imparts a swirling motion to at least one of the plasma gas or the shield gas.  
   
   
       38 . The plasma torch of  claim 32  wherein a control output from a digital signal processor is used to manipulate at least one of the programmable control valve or the second programmable control valve.  
   
   
       39 . The plasma torch of  claim 38  wherein the output of the digital signal processor is adjusted based on the type or thickness of the workpiece to be cut.  
   
   
       40 . The plasma torch of  claim 32  wherein the plasma gas comprises at least one of oxygen, nitrogen, hydrogen, methane, or argon.  
   
   
       41 . The plasma torch of  claim 32  wherein the nozzle is surrounded by a shield mounted to a retaining cap and having an exit port that aligns with the exit orifice of the nozzle.  
   
   
       42 . A plasma cutting system comprising: 
 a power supply; and    a plasma arc torch for cutting a workpiece, the plasma torch having a plasma gas source to supply a plasma chamber such that an electrical current passing between an electrode and a nozzle produces a plasma arc that exits the torch through a nozzle exit orifice, the plasma torch comprising:    a means for sensing a parameter in a first fluid line that supplies a plasma gas from the plasma gas source; and    a means for controlling a flow of the plasma gas to the plasma chamber based on the sensed parameter using a programmable control valve disposed in the first fluid line adjacent the plasma torch.    
   
   
       43 . The plasma cutting system of  claim 42  wherein the programmable control valve is a proportional solenoid control valve.  
   
   
       44 . The method of  claim 17  wherein at least a portion of the plasma gas is vented to the atmosphere through a vent valve.  
   
   
       45 . The method of  claim 44  wherein the vent valve is a programmable control valve.  
   
   
       46 . The method of  claim 19  wherein the third programmable control valve is a proportional solenoid control valve.