Patent Application
20160121457
The present invention relates to a system and method for low pressure piercing using a waterjet cutter.
Precision cutting for industrial and commercial purposes is often accomplished through the use of a waterjet system that directs a high speed stream of water at a workpiece. Waterjet cutting uses ultra-high pressure water, typically over 15,000 psi, produced on-site with special equipment, to produce a high velocity stream of water traveling at speeds in excess of Mach 2. This high-velocity stream, often mixed with abrasives, is capable of cutting hard materials such as metal and granite with thicknesses of more than a foot. Among other benefits, waterjet cutting eliminates the adverse effects of high temperature zones and material deformation generated during traditional cutting methods.
In one embodiment of a high-pressure waterjet cutting system, the system includes a pump operable to produce a flow of pressurized hydraulic fluid, a piston receiving the flow of pressurized hydraulic fluid and reciprocating in response to a pressure differential produced by the flow of pressurized hydraulic fluid, and an intensifier connected to the piston and operable to produce a high-pressure flow of water in response to reciprocation of the piston. A valve is positioned to receive the flow of hydraulic fluid and is movable between a first position in which the pressure differential is a first value and a second position in which the pressure differential is a second value less than the first value.
Another embodiment provides a method of operating a high-pressure waterjet cutting system for a piercing operation on a workpiece to be cut. The method includes operating a hydraulic pump at a non-zero minimum speed to produce a flow of hydraulic fluid, directing the flow of hydraulic fluid to a piston to define a first pressure differential and to produce reciprocation of the piston, and operating an intensifier in response to reciprocation of the piston to produce a flow of high-pressure water at a first pressure. The method also includes moving a valve from a first position toward a second position to reduce the pressure differential to a second pressure differential and to produce a flow of high-pressure water at a second pressure that is lower than the first pressure and directing the flow of high-pressure water at the second pressure to a waterjet cutting head to pierce the workpiece. The method further includes moving the valve to the first position and increasing the speed of the hydraulic pump to a normal speed to produce a third pressure differential that is greater than the first pressure differential and the second pressure differential to produce a flow of high-pressure water at a third pressure that is greater than the first pressure and the second pressure, and performing a cutting operation on the workpiece.
Another embodiment of a high-pressure waterjet cutting system includes a pump operable at a normal speed to produce a flow of hydraulic fluid having a pressure, and a hydraulic drive including a piston that reciprocates within a space that defines a first chamber and a second chamber, the hydraulic drive defining a first pressure differential having a first value when the pump operates at the normal speed. A directional control valve is operable to cyclically deliver the flow of hydraulic fluid to one of the first chamber and the second chamber and to direct a flow of drained hydraulic fluid from the other of the first chamber and the second chamber to produce a back-and-forth reciprocation of the piston, and a valve is positioned to vary one of the flow of hydraulic fluid and the flow of drained hydraulic fluid to produce a second pressure differential having a value below the first pressure differential.
Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.
Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations herein are meant to encompass the items listed thereafter and equivalents thereof as well as additional items.
One of ordinary skill in the art will realize that unique problems occur at ultra-high pressures. Thus, solutions common to lower pressure pumps are not necessarily applicable to systems operating at pressures in excess of 15,000 psi and, in fact, can produce results contrary to those seen in low pressure operation. Thus, for the purposes of this application, the terms “high pressure” or any modifications of high-pressure will be referring to pressures that typically exceed 15,000 psi.
The hydraulic system 20 includes a motor 24, a hydraulic pump 28, a flow control valve 32, a hydraulic drive 36, a pressure control valve in the form of an unloader valve 40, a hydraulic oil sump 44 for collecting low pressure hydraulic fluid, and a series of pipes and other hardware that interconnect the various components. The pipes include first and second chamber pipes 48, 52 between the flow control valve 32 and the hydraulic drive 36. The motor 24 can include an electrical motor, a gas-powered motor, or any other suitable prime mover, and operates to drive the hydraulic pump 28. The hydraulic pump 28 operates in response to operation of the motor 24 to discharge a flow of pressurized hydraulic fluid (oil, butanal, esters, etc.) through the pipes of the hydraulic system 20. While any suitable pump can be employed (e.g., reciprocating, centrifugal, scroll, etc.) preferred constructions employ a rotary screw pump.
The flow control valve 32 is preferably a four way valve with other types of valves being possible. The flow control valve 32 includes an inlet that is connected via piping to the outlet of the hydraulic pump 28 to receive the flow of pressurized fluid. The flow control valve 32 also includes two high-pressure outlets and a low pressure outlet. The flow control valve 32 is movable between a first position and a second position in response to either a mechanical or electrical control signal. In the first position, the flow control valve 32 defines a first flow path between the inlet and a first of the two high-pressure outlets and a second flow path between the second of the two high-pressure outlets and the low pressure outlet. In this position, the flow of pressurized hydraulic fluid passes through the flow control valve 32, out through the first high-pressure outlet, and through the first chamber pipe 48. In the second position, the flow control valve 32 defines a third flow path between the inlet and the second of the two high-pressure outlets and a fourth flow path between the first of the two high-pressure outlets and the low pressure outlet. In this position, the flow of pressurized hydraulic fluid passes through the flow control valve 32, out through the second high-pressure outlet, and into the second chamber pipe 52.
The hydraulic drive 36 includes a piston 72 disposed within a cylinder 76. The cylinder 76 includes a first end and a second end with a cylindrical wall extending between the ends to define a cylinder volume. A first fluid connection is positioned adjacent the first end and is fluidly coupled to the first chamber pipe 48. A second fluid connection is positioned adjacent the second end and is fluidly coupled to the second chamber pipe 52. The piston 72 is positioned within the cylinder 76 such that it divides the cylinder 76 into a first chamber 80 and a second chamber 84. A first shaft 88 extends from the piston 72 and out the first end of the cylinder 76 and a second shaft 92 extends from the piston 72 and out the second end of the cylinder 76. Thus, the first fluid connection is in fluid communication with the first chamber 80 and the second fluid connection provides for fluid communication with the second chamber 84.
As illustrated in
With continued reference to
The first intensifier 112 is virtually identical to the second intensifier 116, with each intensifier coupled to one of the first shaft 88 or the second shaft 92 of the piston 72. Because the intensifiers 112, 116 are similar, only the first intensifier 112 will be described in detail. The first intensifier 112 includes a cylindrical body, a seal head, and an intensifier piston. The cylindrical body includes a first end, a second end, and a cylindrical space that extends between the first end and the second end. A water inlet is formed in the cylindrical body and is positioned to direct a flow of water into the cylindrical space. In preferred constructions, an inlet check valve is positioned at the water inlet to control the flow of water into the cylindrical body and to inhibit the flow of water out of the cylindrical body via the inlet.
The intensifier piston is positioned within the cylindrical body to occupy a portion of the cylindrical space. The intensifier piston is coupled to one of the shafts 88, 92 such that the intensifier piston reciprocates within the cylindrical body in response to reciprocating movement of the piston 72. The seal head is connected to the cylindrical body to seal the second end of the cylindrical body and enclose the cylindrical space between the second end and the first end of the intensifier piston. In preferred constructions, the seal head includes a discharge flow path and a discharge check valve 120, 124 arranged to open and discharge the high-pressure water produced by the intensifiers 112, 116. The design and arrangement of the intensifier is not critical to the operation of the system described herein. As such, other arrangements and designs are possible.
With continued reference to
The pressure sensor 148 measures the pressure of the flow of water at the cutting head 144 and provides the measured value to the controller 152. The pressure sensor 148 may alternatively be configured to take pressure measurements at the exits of the check valves 120, 124 or at a location in the pipes of the system 10 between the check valves 120, 124 and the cutting head 144.
The controller 152 is preferably a microprocessor-based controller that includes some form of memory or data storage, a processor, and an input/output device. In the illustrated construction, the controller 152 uses the measured pressure data provided by the pressure sensor 148, along with user inputs, to determine and set the desired position of the unloader valve 40, as will be discussed in greater detail with the operation of the device. As one of ordinary skill will realize, other controllers including mechanical, electrical, PLC-based, and manual controllers are possible.
The system of
The reciprocating motion of the piston 72 provides a similar reciprocating movement of the intensifier pistons of the intensifiers 112, 116. In preferred arrangements, the intensifiers 112, 116 are arranged such that while one intensifier is compressing water, the other intensifier is drawing water into the intensifier. In this way, ultra high-pressure water is provided for each stroke of the piston 72.
The high pressure mode of operation is identical to the ultra high-pressure mode of operation except that the movable element of the unloader valve 40 is moved toward or into its second position. In this position, a portion of the pressurized hydraulic fluid exits the unloader valve 40 through the second outlet and is directly returned to the sump 44. Thus, a smaller quantity of hydraulic fluid is provided to the flow control valve 32, thereby reducing the quantity of water that can be pumped by the intensifiers 112, 116. In this mode, the pressure difference between the first chamber 80 and the second chamber 84 is less than the maximum pressure difference.
The water from the intensifiers 112, 116 flows through the cutting head 144, where the pressure is converted to velocity and the water is discharged to cut a workpiece as is known in the art. In the high-pressure mode of operation, less water (or water at a lower pressure) is available at the cutting head 144, thereby producing a lower velocity stream of water for cutting.
The flowchart of
The water pressure is then measured by the pressure sensor 148 (see block 204). If the pressure of the water determined by the pressure sensor 148 is above the desired low piercing pressure, the unloader valve 40 may be moved toward the second position to divert hydraulic fluid away from the hydraulic drive 40 and to the sump 44 in order to lower the pressure of the flow of water (see blocks 212, 216). Alternatively, if the pressure measurement is lower than desired, the unloader valve 40 may be moved toward the first position to increase the flow of hydraulic fluid to the hydraulic drive 40.
In one construction, the unloader valve 40 may divert between 0 and 40 percent of the total amount of hydraulic fluid produced by the hydraulic pump 28. The unloader valve 40 may further be adjusted until the pressure reaches the desired low pressure suitable for piercing, for example, 15,000 psi or less. Of course, other constructions divert a larger percentage of the hydraulic fluid to produce even lower pressures as may be required.
During operation of the construction illustrated in
During periods when a lower water pressure is desired, the pump pressure is first reduced, typically by reducing the speed of the pump. The reduction in pump output pressure lowers the pressure applied at the pilot pressure sensing port 235, thereby allowing the biasing member 240 to move the counterbalance valve 220 toward the closed position. As the counterbalance valve 220 moves toward the closed position, the drain path between the inlet port 225 and the outlet port 230 becomes restricted, thereby producing a backpressure in the chamber 80, 84 being drained. This backpressure reduces the pressure differential between the chambers 80, 84 and results in a corresponding reduction in the water pressure produced by the intensifiers 112, 116 and the waterjet cutter.
Once the water pressure is at the desired pressure for piercing, the waterjet cutting head 144 can direct the flow of water to pierce a workpiece until the workpiece is pierced (see blocks 220, 224). The piercing operation allows for the waterjet cutter 140 to pierce through the workpiece without fracturing or otherwise damaging the workpiece. Once pierced, the unloader valve 40 is closed to allow for a higher pressure flow of water to be emitted from the waterjet cutting head 144, for example, 30,000 psi or more (see blocks 228). The speed of the motor 24 and the hydraulic pump 28 may also be increased to increase the pressure of the flow of water. The unloader valve 40 may be further adjusted as described above until the water pressure reaches the desired pressure for cutting (see blocks 232, 236). Once the pressure is at the desired level, the workpiece may be cut (see block 240). In the construction of
It should be noted that the embodiments illustrated herein utilize variable speed pumps and motors to vary the pressure of the hydraulic fluid. However, other methods such as pressure reducing valves and the like could be employed to control the pressure of the flow of hydraulic fluid.
Various features and advantages of the invention are set forth in the following claims.
