This disclosure relates to electro-hydraulic manufacturing operations including electro-hydraulic forming operations and a trimming operation.
Electro-hydraulic Forming (EHF) is a process in which capacitors provide a high-voltage discharge across two electrodes positioned in a fluid-filled chamber. Electrical energy (typically between 5 and 50 kJ) is stored in a bank of capacitors that are discharged across a gap between two electrodes that are immersed in water (or other conductive and relatively incompressible liquid medium) over a very short period of time (usually less than 1 millisecond).
A typical EHF system consists of electrically isolated electrodes that are inserted through a thick-walled hollow cavity that is filled with water. A sheet metal blank is placed on top of the cavity. A one-sided female die is placed facing downwardly above the blank. Air is evacuated from both sides of the blank. A capacitor bank is charged and is then discharged through the electrodes. About a millisecond after the voltage is applied to the electrodes, a high temperature plasma channel forms, and current from the capacitors drives and expands the plasma channel. The region surrounding the plasma channel is filled with gas in the form of superheated steam which transitions to a steam/water interface. The chamber is filled with relatively incompressible fluid, such as water, and all air is evacuated. A high intensity, high velocity shock wave forms in the liquid causing immense pressure to rapidly build up and the sheet metal blank is explosively driven into the die. Since the liquid transmits the force, only the female die is required.
EHF has several benefits over conventional stamping and other lower strain rate sheet metal manufacturing processes. Due to the single-sided tooling, EHF has a lower capital cost than conventional stamping. EHF also provides significantly increased formability in many sheet metal materials due to the elevated strain rates that result from the discharge. It requires only a single die—potentially, the multiple die sets that are used to form complex parts can be reduced down to a single die (this reduction is achieved by using multiple pulses in specific energy increments to form the blank). Significant residual stress reductions can be achieved by delivering a post forming pulse to the blank to greatly reduce blank distortion caused by stored elastic energy (springback). This process can significantly reduce the die development costs (easily the single greatest production cost, often in the neighborhood of a million dollars for a single large part), because the die can be cut to the part's final geometry rather than requiring additional forming processes to compensate for springback.
The EHF process offers potential advantages as a method of manufacturing automotive and truck components from high-strength steel, stainless steel, and aluminum alloys, but the time required to fill the chamber with water, evacuate the air from the chamber and then drain the chamber results in low production rates. The combination of air/water management cycling times and the maximum rate at which the EHF electrical pulse generator operates means that an entire EHF cycle may take, for example, approximately 36 seconds. Approximately 70% of this time is dedicated to water and air management, and opening and closing of the press. The EHF pulse generator itself is capable of producing a discharge every two seconds at full speed. Trimming presses are capable of trimming a part, for example, every 10-12 seconds, or less. A single EHF forming press associated with a single trimming press may result in the trimming die being idle for two thirds of the time.
Smaller capacity presses may be used for EHF tools because the reciprocating movement of the press is not used to form the part. Instead the press is opened and closed by a hydraulic actuator and the part is formed by the short duration pulse or pulses. The press must have sufficient capacity to resist the force of the intense discharge.
This disclosure is directed to solving the above problems and other problems as summarized below.
According to one aspect of this disclosure, a press is provided for forming a blank in an electro-hydraulic forming (EHF) tool defining a chamber that is filled with a liquid. An electrode is disposed within the chamber that provides a plasma arc in the liquid when connected to a source of stored charge that results in an EHF discharge. A one-sided die is reciprocated by the press relative to the chamber while the blank is disposed on the die. A lock is connected to and operated by the press that holds the die against the chamber during the EHF discharge.
According to other aspects of the disclosure as it relates to the press, the lock may further comprise a mechanical restraining device that selectively connects a movable platen of the EHF machine supporting the die to a portion of frame of the press. The mechanical restraining device may be a pin carried by the frame of the press that is shifted into engagement with the movable plate.
According to further aspects of the disclosure, an alternative press wherein the lock may comprise a clamp that selectively clamps the die against the EHF tool, wherein a hydraulic ram moves the clamp relative to the EHF tool in a direction transverse to the direction that the die is reciprocated. The clamp may include a first stop that engages the die and a second stop that engages the EHF tool.
According to another aspect of the disclosure, a method is disclosed for manufacturing an article on a production line that includes a plurality of electro-hydraulic forming (EHF) tools and a plurality of one-sided dies that are each operated by a press. The production line also includes a trim press. The method comprises clamping a blank onto each of the plurality of the EHF tools and the one-sided dies in a progressive sequence. Discharging each of the EHF tools in the progressive sequence to form a part shape in the blank and trimming the blanks that are formed to include the part shape in the trim press.
According to other aspects of the method, the plurality of EHF tools and one-sided dies may include three EHF tools and three one-sided dies that are operated by three presses and wherein the progressive sequence further comprises operating the presses in a repeating order. The cycle time for the trim press may be about one-third of the cycle time for each press. Alternatively, the cycle time for the trim press may be about equal to the reciprocal of the number of the plurality of presses.
According to other aspects of the method, the method may further comprise filling a chamber defined by the EHF tool with water. Evacuating air from the EHF tool prior to the discharging step and draining the water from the EHF tool. The time required for the clamping step, the filling step, the evacuating step, the discharging step and the draining step is a multiple of the time required for trimming the blanks formed to include the part shape in the trim press. The multiple corresponds to the number of EHF tools. The discharging step may further comprise multiple discharges of the EHF tool to complete forming the part shape.
According to another aspect of the disclosure, an alternative method of manufacturing an article on a production line is disclosed that includes an electro-hydraulic forming (EHF) tool and a one-sided die that are operated by a press. The production line also includes an EHF trim press. The alternative method may comprise clamping a blank onto the EHF tool and the one-sided die. Discharging the EHF tool to form a part shape in the blank. The blank with the part shape may be trimmed in an electro-hydraulic (EH) trim press.
According to other aspects of the alternative method, the method may further comprise filling a chamber defined by the EHF tool with water. Evacuating air from the EHF tool prior to the discharging step and draining the water from the EHF tool.
These and other aspects of the disclosure will be described with reference to the attached drawings in the following detailed description of the illustrated embodiments.
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the disclosed apparatus and method. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure as claimed. The features of various implementing embodiments may be combined to form further embodiments of the disclosed concepts.
Referring to
A one-sided die 30 defines a die cavity 32. The blank 16 is formed into the die cavity 32 during the EHF forming process. The press 12 includes a movable platen 34. The one-sided die 30 is secured to the movable platen 34 that moves the one-sided die 30 into and out of engagement with the EHF vessel 18. A pair of locking pins 36, or wedges, are provided to lock the movable platen 34 to the press 12. A hydraulic ram 38 is provided to move the movable platen 34 in a reciprocating manner relative to the EHF vessel 18. The locking pins 36 lock the one-sided die 30 to the press 12 when the ram 38 has moved the movable platen 34 carrying the one-sided die 30 into position to clamp the blank 16 to the EHF vessel 18. The locking pins 36 hold the one-sided die 30 against the EHF vessel 18 during the EHF pulses.
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In the next phase of the cycle, the EHF press 1 forms a part by discharging five EHF pulses in the chamber 20 of the EHF vessel 18. EHF press 2 is loaded with blank 2, the tool is clamped and the chamber is filled with liquid. EHF press 3 is drained, the tool is unclamped and part 3 is unloaded to the blank post 70. The trimming press trims part 2.
In the third phase of the cycle, EHF press 1 is in the process of draining the chamber, clamping the tool and unloading part 1. EHF press 2 is connected to the source of stored charge and five EHF pulses are used to form part 2. During this time period, blank 3 is loaded into EHF press 3, the tool is clamped and the chamber is filled with liquid. The trimming press in this time period trims part 3 that was previously received from EHF press 3.
The timing of the press cycle is divided into 12 second periods and the total elapsed cycle time is shown at the bottom of
Referring to
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the disclosed apparatus and method. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure as claimed. The features of various implementing embodiments may be combined to form further embodiments of the disclosed concepts.
This application is a division of U.S. application Ser. No. 13/590,506 filed Aug. 21, 2012, the disclosure of which is hereby incorporated in its entirety by reference herein.
The invention was made with Government support under Contract No. DE-FG36-08G01828. The Government has certain rights to the invention.
Number | Date | Country | |
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Parent | 13590506 | Aug 2012 | US |
Child | 14859955 | US |