Electrohydraulic Ram Velocity Control Circuit

Abstract

An electrohydraulic control circuit for controlling the velocity of a ram driving a fluid into a die cavity is disclosed. In accordance with the control method disclosed, the position of the ram is sensed by a pulse generator and sensed ram positions are used to provide electric signals which vary in accordance with the sensed positions and flow of hydraulic ram drive fluid is varied in accordance with the electric signals provided to vary the velocity of the ram. The electric signals may be further varied in accordance with one or more of the positions of a metering member in a hydraulic valve supplying ram drive fluid, the pressure of the fluid in the shot cylinder, the velocity of the ram and the pressure in the die cavity. Control of the ram may be directly from a large electrohydraulic servo valve or a pilot electrohydraulic servo valve may be used to control a larger hydraulic valve supplying ram drive fluid.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to electrohydraulic servo controls and methods and refers more specifically to a control circuit for and method of controlling the flow of fluid into a die cavity in die casting to provide a most efficient flow rate, using sensors monitoring different parameters of the die casting operation and providing an electric control signal corresponding to the sensed parameters to an electrohydraulic servo valve controlling the actual movement of the ram in accordance with a predetermined velocity program.

2. Description of the Prior Art

In the past, feeding fluid into cavities in die casting operations and the like has been deficient in that in general a single speed of fluid fed into the cavity has been used on application of a single hydraulic pressure to a ram forcing the fluid into the cavity. Such operation, if the ram speed is too fast, wears the die cavity opposite the inlet port and may produce air bubbles in finished castings. If the ram speed is too slow, improper cooling and filling of the cavity will produce unacceptable castings.

SUMMARY OF THE INVENTION

In accordance with the present invention, an electrohydraulic control circuit is provided to control the velocity of the ram forcing casting material such as molten metal out of a cylinder into a die cavity in accordance with the position of the ram to provide most efficient metal flow at all times during casting. In accomplishing this result, the position of the ram is sensed at a plurality of points and an electric signal is supplied to hydraulic servo means corresponding to each position of the ram for varying the hydraulic drive for the ram in accordance with the position of the ram.

The electric signal may also be changed in accordance with a plurality of other parameters including the position of the hydraulic valve metering fluid to drive the ram, the pressure in the shot cylinder from which the molten metal is forced, the velocity of the ram, and the pressure of the metal in the casting cavity. Control of the ram velocity may be either from a single large electrohydraulic servo valve or a large hydraulic main valve may be controlled by a smaller pilot electrohydraulic servo valve.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a partly block, partly diagrammatic illustration of the electrohydraulic control circuit of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The electrohydraulic control circuit 10 illustrated in the FIGURE includes a multiple slidewire resistance circuit 12, a switching circuit 14, a first comparator 16, a first amplifier 18, a second comparator 20, a second amplifier 22, an electrohydraulic servo valve 24, a main hydraulic valve 26, a ram cylinder 25, a ram 27 and a shot cylinder 28 for forcing molten aluminum into a die 30 having a die cavity 32 therein.

Control circuit 10 further includes a ram position electric pulse generator 34, a die cavity pressure to electric signal transducer 36, a ram velocity to electric signal transducer 38, a shot cylinder pressure to electric signal transducer 40 and a main hydraulic valve position to electric signal transducer 42.

More specifically, the multiple slidewire resistance circuit 12 which is a purchased item of commerce includes a resistance network 44 connected across a power source, and a plurality of separate slides 46 associated with different output conductors 48. The slides 46 may be moved vertically as indicated in the FIGURE to tap off a greater or lesser signal from the resistance network 44 which will appear at the output terminal 48 associated with the particular slide.

Thus, in use a plurality of selected voltages may be provided at the output terminals 48 of the multiple slidewire resistance circuit 12 which are selected in accordance with a predetermined velocity program for the ram 27 in the shot cylinder 28. Further, the velocity program for the ram 27 will be graphically indicated on the multiple slidewire resistance circuit 12 by the position of the slides thereon. Thus, a slide position closer to the power source indicated in the FIGURE would provide a greater output signal from the multiple slidewire resistance circuit on the output conductor associated therewith and thus produce a greater hydraulic fluid flow and more rapid movement of the ram 27, as will be seen subsequently.

The selection of a signal from a particular output terminal of the multiple slidewire resistance circuit 12 by the switching circuit 14 may be by any convenient means such as a rotary stepping switch responsive to each count of a counter, if desired. In practice, the switching circuit 14 has included a binary counter in conjunction with a plurality of separate amplifiers and appropriate logic circuitry to actuate a different field effect transistor associated with each of the output signals and thus pass each of the output signals represented by the positions of the slides on the multiple slidewire resistance circuit in response to a corresponding position of the ram 27. Other switching circuits are possible actuated by the pulse generator 34 and operable to pass the output signals from the switching circuit 14 in accordance with the program of the multiple slidewire resistance network in response to pulses from the pulse generator 34 indicating the position of the ram 27.

The signals from the switching circuit 14 are passed to a conventional comparator 16 where they are changed in accordance with the pressure in the shot cylinder 28, the velocity of the ram 27 and the pressure in the die cavity 32, if desired. Control in accordance with these additional parameters is not essential to the operation of the control circuit 10. Control in accordance with these additional parameters is, however, useful wherein control of the velocity of the ram in accordance with the position of the ram does not optimize the other indicated parameters.

The signal from the amplifier 18 is then passed into an additional comparator wherein the signal is altered in accordance with the velocity of the spool of the main hydraulic valve 26. The final control signal from the comparator 20 is fed through the amplifier 22 and in the embodiment of the invention illustrated is used to control an electrohydraulic servo valve 24.

The electrohydraulic servo valve 24 is a pilot valve and is used to control the position of the spool in the main hydraulic valve 26. The main hydraulic valve 26 in turn controls the flow of hydraulic fluid to the ram cylinder 25 and thus the velocity of the ram 27 in accordance with the signal received by the electrohydraulic servo valve 24 from the switching circuit 14 through the comparators 16 and 20 and associated amplifiers 18 and 22.

The pulse generator 34 which may be, for example, an electromagnetic structure positioned adjacent ram 27 for determining the position thereof or may be a photoelectric cell 35 operable in conjunction with mechanical means 37 carried by the ram to provide pulses of energy representing the position of the ram is effective to provide an output signal to the switching circuit 14 in accordance with the position of the ram 27. Thus, if for example, the ram 27 has a 48-inch travel and it is desired to change the velocity of the ram every 2 inches, 24 mechanical actuating means 37 may be positioned every 2 inches along the path of the ram operable in conjunction with one photoelectric cell to produce an electric pulse each time the ram moves 2 inches.

In overall operation, the ram 27 is backed up past the inlet gate 52 of the shot cylinder 28 and liquid metal such as aluminum is placed in the shot cylinder. When the shot cylinder has the required charge therein, the ram 27 is caused to move toward the die 30. Movement of the ram is slow past the inlet gate 52. The velocity of the ram is controlled in accordance with the settings of the slides on the multiple slidewire resistance circuit 12 and is changed with each pulse from generator 34 since the pulses from generator 34 change the effective output conductor from the multiple slidewire resistance circuit 12 through switching circuit 14 to provide a single electric output signal to the comparator 16 which varies in accordance with the position of the ram 27.

The single output signal from switching circuit 14 modified by the signals from the main hydraulic valve spool position to electric signal transducer 42, the shot cylinder pressure to electric signal transducer 40, the ram velocity to electric signal transducer 38 and the die cavity pressure to electric signal transducer 36 through comparators 16 and 20 and amplifiers 18 and 22 actuates the electrohydraulic servo valve 24 to position the main hydraulic valve 26, thus providing the desired control of the velocity of ram 27.

While one modification of the invention has been considered in detail, it will be understood that modifications and other embodiments of the invention are contemplated. Thus, for example, other structures may be used for the multiple slidewire resistance circuit 12 to establish a program for the velocity of the ram 27 and other switching circuits than those disclosed may be substituted for the switching circuit 14. It is the intention to include all embodiments and modifications suggested by the above disclosure within the scope of the appended claims.

Claims

What we claim as our invention is:

1. In conjunction with a die having a cavity therein, a shot cylinder, means for feeding fluid into the shot cylinder and for passing fluid out of the shot cylinder into the die cavity, a ram for forcing the fluid from the shot cylinder into the die cavity and means for driving the ram into the shot cylinder, the improvement comprising means for sensing the position of the ram in the shot cylinder over substantially the entire length of the shot cylinder and means operable in response to the sensed position of the ram for controlling the movement of the ram into the shot cylinder over substantially the entire length of the shot cylinder to provide optimum fluid flow from the shot cylinder into the die cavity during filling of the die cavity.

2. Structure as set forth in claim 1 wherein the means for sensing the position of the ram comprises a pulse generator for producing a separate pulse in response to arrival of the ram at a plurality of predetermined positions within the shot cylinder which positions are spaced apart over substantially the entire length of the shot cylinder.

3. Structure as set forth in claim 1 wherein the means for controlling the driving of the ram comprises a multiple slidewire resistance circuit for providing different electric output signals and a switching circuit connected to the multiple slidewire resistance circuit for passing separate ones of the different electric output signals in response to different sensed positions of the ram.

4. Structure as set forth in claim 3 wherein the means for controlling the driving of the ram further includes a main hydraulic valve controlling flow of hydraulic fluid to the ram.

5. Structure as set forth in claim 4 and further including means for controlling the driving of the ram into the cylinder in accordance with at least one of the additional parameters velocity of a portion of the main hydraulic valve, the pressure of the fluid in the shot cylinder, the velocity of the ram, and the pressure of the fluid in the die cavity.

6. Structure as set forth in claim 5 wherein the means for controlling the driving of the ram further includes a pilot electrohydraulic servo valve positioned between the switching circuit and main hydraulic valve for controlling fluid flow through the main hydraulic valve.

7. In combination, a die cavity, a shot cylinder into which molten metal is placed for movement into the die cavity positioned adjacent to the die cavity, a reciprocally movable ram positioned within the shot cylinder for moving the molten metal from the shot cylinder into the die cavity in accordance with the movement of the ram into the shot cylinder, a ram cylinder in which the ram is mounted for reciprocal movement, a main hydraulic valve connected to the ram cylinder operable to produce movement of the ram within the ram cylinder and shot cylinder, an electrohydraulic servo valve connected to the main hydraulic valve for metering hydraulic fluid through the main hydraulic valve in accordance with an electric signal applied to the servo valve, a source of electrical energy, a multiple slidewire resistance circuit connected to the source of electrical energy for providing a plurality of different output electrical signals, a switching circuit connected to the multiple slidewire resistance circuit for providing an output from the switching circuit in accordance with one of the output signals of the multiple slidewire resistance circuit in accordance with programming of the switching circuit, means for sensing the position of the ram and programming the switching circuit in accordance with the position of the ram whereby the output signal from the switching circuit reflects the position of the ram, means connected to the switching circuit for modifying the output signal from the switching circuit in accordance with at least one of the pressure in the shot cylinder, the velocity of the ram, and the pressure in the die cavity to provide a modified output signal, means for further modifying the modified output signal in accordance with the position of the main hydraulic valve and means for actuating the electrohydraulic servo valve with the further modified output signal whereby the placing of the molten metal in the die cavity is accomplished under optimum conditions.