WO2021079379A1

WO2021079379A1 - Compact pressure die casting injector assembly

Info

Publication number: WO2021079379A1
Application number: PCT/IN2020/050895
Authority: WO
Inventors: Mangesh PATWARDHAN
Original assignee: Patwardhan Mangesh
Priority date: 2020-10-20
Filing date: 2020-10-20
Publication date: 2021-04-29
Also published as: WO2021079379A8

Abstract

An injector mechanism for Pressure Die Casting machine, comprising an auxiliary cylinder 11, interconnected in between accumulator and shot cylinder of the machine. The auxiliary cylinder 11 performs a dual function; to feed the shot cylinder 51 with low pressurized hydraulic fluid during first two 5 phases, to act as a pressure intensifier and to feed the shot cylinder 51 with high pressurized fluid for the third phase. The auxiliary cylinder 11 is adapted to drive the first two phases of injection with low volume consumption of the accumulator discharge, which provides: an enhanced ability to provide higher plunger velocity, an ensured high degree of utilization of hydraulic potential 10 energy produced by the system and the scope for reduction of overall size of injector assembly.

Description

Compact Pressure Die-casting injector assembly

FIELD OF THE INVENTION:

The present invention relates to an injector assembly of Cold Chamber High Pressure Die Casting [HPDC] machine. More specifically it relates to an improvement in injector assembly of the machines of the present day. This present invention injector assembly comprising an auxiliary hydraulic cylinder has reduced overall size of an injector assembly. The present invention injector assembly has an enhanced ability to provide higher plunger velocity with the high degree of utilization of hydraulic potential energy produced by the system. This present invention may be adapted for conventional High Pressure Die Casting Machines of the day.

BACKGROUND OF THE INVENTION:

As known HPDC machine mainly consist of Die closing-opening mechanism, Injector mechanism and Ejector mechanism.

Die closing-opening mechanism [Lock End] has the function of closing die halves together and to form die cavity(s) and to open apart die halves.

As shown in the Fig.2, injection mechanism [Shot End] has the function of filling the die cavity 82 with molten light metal like Aluminum alloy and to squeeze it further.

Function of Ejector mechanism is to eject out the casted part.

Conventional HPDC machine injection process is operated with potential hydraulic energy discharged from accumulator(s) 35. This energy transmission is through the set of hydraulic mechanisms.

Injection process [shot operation] broadly comprises of three phases.

During first slow phase molten metal is carried up to the cavity in-gate or just cavity pre-filling. During second phase of high velocity molten metal is injected in to the cavity within some milliseconds.

During first two [cavity filling] phases injector velocities are principally monitored as per given manner of shot setting. As shown in the Fig.2, this segment of first two phases 88 covers most part of the actual shot stroke 87 and pressure built up in shot cylinder 51 happens to be low.

The present day Die casting process designs demands the high plunger velocity during cavity filling. This demand of high plunger velocities sometime may as high as 8 m/s. The level of maximum plunger velocity achieved depends on the achieved rate of accumulator discharge. To meet the demand the present day injector mechanisms have got complex with bulky accumulator and associated Nitrogen gas bottles.

In the existing injector assemblies of the day, during cavity filling phase pressurized fluid discharged for the accumulator 35 is directly fed through flow controlling devices, to the shot cylinder piston side chamber 53. High amount of high pressurized hydraulic fluid discharged from accumulator gets down- pressurized and high amount of potential energy discharged from accumulator is wasted.

When first two injection phases are finished, then third phase of pressure intensification is initiated to squeeze the casting in formation. This phase is also called as squeezing stroke 89.

During intensification phase by virtue of high intensified pressure in shot cylinder high force is exerted on the molten metal injected into the die cavity. This high pressurization of incompressible fluid is carried by activation of hydraulic pressure intensifier 93 [Multiplicator]

OBJECT:

The aim of the present invention is to provide a compact injector assembly for Pressure die-casting machine that overcomes the drawbacks of cited prior art. An object of the present invention is to provide an injection assembly having an enhanced ability to produce higher plunger velocities and higher intensification force.

Another object of the present invention is to ensure the high degree of utilization of hydraulic potential energy produced by the system.

SUMMARY OF THE INVENTION: Object to provide a solution to overcome the drawbacks of cited prior art, a modification is incorporated in the injector assembly of the present invention. The modified injector assembly comprises an auxiliary hydraulic cylinder 11 , which is interconnected in between accumulator 35 and shot cylinder 51.

Fig.1 illustrates the schematic hydraulic diagram of the present invention. During injection shot operation shot cylinder 51 is driven by hydraulic fluid discharged from auxiliary hydraulic cylinder 11 and pressurized hydraulic fluid is supplied to the auxiliary cylinder 11 by the Accumulator 35.

Auxiliary cylinder 11 performs a dual function; to feed the shot cylinder 51 with low pressurized fluid during first two phases, to act as a pressure intensifier while feeding to the shot cylinder with high pressurized fluid for the third phase [intensification phase].

Therefore after incorporation of auxiliary cylinder 11 in the injector assembly of the present invention, the separate pressure intensifier 93 of the existing injector assembly is eliminated.

During first two phases of injection, pressurized hydraulic fluid discharged from the accumulator 35 is charged into the annular chamber 12 of the auxiliary cylinder 11 ; this moves the piston 20 and discharges fluid from piston side chamber 14. This discharge of fluid into the connected shot cylinder 51 drives its piston rod 55.

The surface area of the piston at annular side 28 is much lesser than the surface area of full bore side piston 29 [Cap side]. Very less volume of pressurized hydraulic fluid discharged from the accumulator 35 drives the shot cylinder’s piston rod 55 during first two phases of injection. This less volume is corresponding to ratio of surface areas of opposite sides of the piston 20. Of course there will be corresponding pressure drop, but the resulting achievable pressure level is well above the actual and normal pressure built in the shot cylinder 51.

As this segment of first two phases covers most part of the actual shot stroke and are carried out with the much less volume of pressurized hydraulic fluid discharged from the accumulator 35; According the similar discharge rate and lesser consumption of discharge volume the present invention provide an enhanced ability to provide higher plunger velocities; also the required accumulator discharge capacity is much lesser. In the present invention instead of allowing the wastage of potential [Pressure] energy discharged from the accumulator in the form of down-pressurizing, it is used to multiply the movement of the piston 56 during down-pressurizing. Thus high degree of utilization of hydraulic potential energy produced by the system is ensured. Also as compared to the existing injector assembly, according the present invention larger portion of the accumulator discharge volume capacity is left for the subsequent third phase, which is advantageous for the achievable speed of intensification [third phase].

During third phase of pressure intensification, pressurized hydraulic fluid discharged from the accumulator is supplied to the auxiliary cylinder’s piston side chamber 14; whereas the shot cylinder is fed by the discharge from the auxiliary cylinder’s annular side chamber 12. As the surface area of the piston 20 at annular side 28 is much lesser than the surface area of full bore side piston 29 results in the corresponding pressure multiplication in the annular chamber 12, thus the auxiliary cylinder 11 acts as pressure intensifier; high pressurized fluid from annular chamber 12 is fed to the shot cylinder 51 . Depending on this multiplication factor injection assembly has an enhanced ability to provide higher intensification force.

Reduction of accumulator capacity with associated reduction of volume of Nitrogen gas bottles and elimination of separate pressure intensifier makes the overall injector assembly compact. If the intensifier has separate accumulator, it also is eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS:

Fig.1 illustrates the schematic hydraulic diagram of the present invention. The auxiliary hydraulic cylinder 11 is interconnected in between accumulator 35 and shot cylinder 51 . The auxiliary cylinder 11 is connected to the accumulator 35 through directional control valve 15. The auxiliary cylinder 11 is connected to the shot cylinder 51 through the directional control valve 25. FIG. 2 is a sectional view showing basic structure of the conventional die casting machine’s injector assembly and illustrates the associated details of injector stroke; cavity filling stroke 88, intensification stroke 89 and actual injection stroke 87.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT:

A preferred embodiment of the present invention will be described below with reference to drawings.

As illustrated in Fig.1.

The present embodiment comprises an auxiliary cylinder 11 , which is interconnected in between the accumulator 35 and Shot cylinder 51 of the machine.

Since the present embodiment does not require any change in the existing shot control system, it can be adapted hereinafter only the preferred new controls associated with the incorporation of the auxiliary cylinder are described appropriately. These preferred controls are non limited and various alternate controls may be adapted.

The preferred swept volumes of the auxiliary cylinder 11 and Shot cylinder 51 are same. Preferred surface area of the piston rod of the auxiliary cylinder is sixty percent of the piston surface area 29 at full bore side. That is surface area of the piston 20 at the annular side 28 is forty percent of the surface area at full bore side 29, so the ratio of their surface areas is 1 :2.5.This may be changed suitably.

The auxiliary cylinder 11 is connected to the accumulator 35 through directional control valve 15; annular chamber 12 is connected to the port 17 and Piston side chamber 14 is connected to the port 18, through the existing flow and pressure control devices the accumulator 35 is connected to the directional control valve port 16.

The auxiliary cylinder 11 is connected to the shot cylinder 51 through the directional control valve 25; annular chamber 12 is connected to the port 22, Piston side chamber 14 is connected to the port 24 and Shot cylinder piston side chamber 53 is connected to the port 26.

When the injector shot is initiated, during first two phases, the pressurized hydraulic fluid discharged from the accumulator 35 is charged into the annular chamber 12 through the port 17 of directional control valve 15. This charging displaces the piston 20 and discharges hydraulic fluid through valve port 24. This discharged fluid is charged into the shot cylinder’s piston side chamber 53, this process drives the shot piston rod 55.

As the shot cylinder 51 and the auxiliary cylinder 11 have same swept volumes and the preferred surface area of the auxiliary cylinder’s piston 20 at the annular side 28 is forty percent of the surface area 29 at full bore side; during the first two phases of injection, the volumetric displacement of the auxiliary cylinder’s piston 20 in the annular chamber 12 is only forty percent of the actual volumetric displacement of shot cylinder piston 56 in the piston side chamber 53.

During this process, corresponding to ratio of surface areas of opposite sides of the piston 20, less charging volume of hydraulic fluid in to auxiliary cylinder 11 discharges out high volume of hydraulic fluid. Said discharged fluid is charged into the shot cylinder’s piston side chamber 53 and the shot cylinder piston rod 55 is driven.

Of course during the said process corresponding down-pressurizing of the hydraulic fluid happens; the fluid pressure in the shot cylinder’s piston side chamber 53 is nearly forty percent (Considering marginal pressure drop in the system) of the fluid pressure in auxiliary cylinder’s annular chamber 12, but said achievable pressure level is well above the actual and normal pressure built in the shot cylinder, which happens to be low during first two phases of injection.

As this segment of first two phases covering the most part of the actual shot stroke is carried out with the involved multiplication of the volumetric displacement done during the down-pressuring, by the much less volume of pressurized hydraulic fluid discharged from the accumulator 35; accordingly the velocity of driven shot piston rod 55 which is dependent on the accumulator discharge rate, gets multiplied. Thus the present invention provides an enhanced ability to provide higher plunger velocities.

According to the present invention instead of allowing the wastage of potential [Pressure] energy discharged from the accumulator 35 in the form of down- pressurizing, the available pressure energy has been explicitly used to multiply the volumetric displacement and the velocity of the shot cylinder piston rod 55. Thus high degree of utilization of hydraulic potential energy produced by the system is ensured.

At the end of cavity filling phase, when the metal flow is restricted, then counter force of metal pressure starts increasing rapidly. This counterforce causes pressure building in shot cylinder piston side chamber 53 and in the connected auxiliary cylinder’s piston side chamber 14. On reaching the first set pressure, directional control valve 15 is actuated and discharge flow from the accumulator 35 is directed through the port 18, to the auxiliary cylinder’s piston side chamber 14. Said pressurized fluid flow increases the pressure in the piston side chamber 14 and continues the flow with increased fluid pressure through port 24, into the shot cylinder’s piston side chamber 53.

On reaching the second set pressure in the piston side chamber 53, directional control valve 25 is actuated, which shifts the connection of shot cylinder 51 , now the auxiliary cylinder’s annular chamber 12 is connected to the shot cylinder’s Piston side chamber 53 through the port 22.

At this time the auxiliary cylinder starts to act as pressure intensifier, corresponding to the ratio of surface areas of opposite sides of the piston 20, the pressure of fluid in the auxiliary cylinder’s annular chamber 12 is multiplied. The movement of piston 20 of the auxiliary cylinder towards rod end side discharges fluid of boosted pressure into the shot cylinder’s piston side chamber 53 through the valve port 22.

As in the present invention injector assembly, the shot cylinder 51 and the auxiliary cylinder 11 have same swept volumes; there is no considerable difference as against the existing injector assembly in the required volume of pressurized hydraulic fluid discharge from the accumulator 35 to carry out the third phase injection stroke. There could be marginal difference against the existing injector assembly depending on the difference of respective multiplication factors of intensifiers.

According the high reduction in the required volume of pressurized hydraulic fluid discharge from the accumulator 35 for first two phases, which covers the most part of the actual shot stroke, whereas no change is required for the third phase, there is scope to reduce the capacity of the existing injector assembly’s accumulator, which could be by up to fifty percent. This makes considerable energy saving through the reduction in accumulator charging time.

According to the present invention the characteristic low consumption of hydraulic fluid volume for first two phases, as compared to the existing injector assembly larger portion of the accumulator discharge volume capacity is left for the subsequent third phase, which is advantageous for the achievable speed of intensification [third phase].

During Plunger follow through motion happening at the time of die opening, to feed the shot cylinder’s piston side chamber 53 through the valve port 24, suitably any side charging of the auxiliary cylinder 11 may be used.

During Shot cylinder piston rod 55 returning, that is moving to words full bore end side [Cap end], the hydraulic fluid in the piston side chamber 53 is discharged into the auxiliary cylinder’s piston side chamber 14 through the valve port 24, normally closed directional control vale 41 connected to annular chamber is actuated and with the movement of piston 20 to words rod end side hydraulic fluid in the annular chamber 12 is drained. On reaching it to the home position consequently normally closed directional control valve 42 is actuated and the fluid in the auxiliary cylinder’s piston side chamber 14 is drained until shot cylinder piston 56 is reached to its home position.

Claims

CLAIMS:

1. The present invention injector assembly comprises an auxiliary hydraulic cylinder 11 , which is interconnected in between accumulator 35 and shot cylinder 51 of the machine; said auxiliary cylinder 11 performs a dual function; to feed the shot cylinder 51 with low pressurized fluid during first two phases, to act as a pressure intensifier and to feed the shot cylinder 51 with high pressurized fluid for the third phase [intensification phase];

2. The present invention characterized in that, as the auxiliary cylinder 11 acts as the pressure intensifier also; the pressure intensifier 93 of the existing injector assembly is eliminated in the present invention injector assembly.

3. According the present invention, during the first two phases of the injection which covers the most part of the actual shot stroke, the shot cylinder 51 is fed by the auxiliary cylinder 11 by discharging the hydraulic fluid from its piston side chamber 14, whereas the hydraulic fluid is charged into the annular chamber 12 by the accumulator discharge; the multiplication of volumetric displacement is carried by this activity and the shot cylinder piston rod 55 is driven by the much less volume of fluid received from the accumulator 35.

4. According the present invention during the third phase of injection [intensification phase], the shot cylinder 51 is fed with high pressurized fluid by the auxiliary cylinder 11 ; When hydraulic fluid is charged into the piston side chamber 14 by the accumulator discharge, the high pressurized fluid discharging from its annular chamber 12 is fed into the shot cylinder’s piston side chamber 53; this activity involves pressure multiplication corresponding to the ratio of surface areas of opposite sides of the piston 20.

5. According to claim 3, as the plunger velocity depends on the accumulator fluid discharge rate, by virtue of the characteristic multiplication of the volumetric displacement, according the present invention for the same discharge rate as the existing, the velocity of driven shot piston rod 55 gets multiplied accordingly; thus the present invention has an enhanced ability to provide higher plunger velocities.

6. According to claim 3, unlike the existing injector assembly which allows wastage of potential [Pressure] energy discharged from the accumulator 35 in the form of down-pressurizing, according the present invention the available pressure energy has been explicitly used to multiply the volumetric displacement; thus high degree of utilization of hydraulic potential energy produced by the system is ensured.

7. According to claim 3, the present invention has the characteristic low consumption of hydraulic fluid volume for first two phases, therefore as compared to the existing injector assembly larger portion of the accumulator discharge capacity is left for the subsequent third phase, which is advantageous for the achievable speed of intensification [third phase].

8. According to the present invention reduction of accumulator capacity with associated reduction of volume of Nitrogen gas bottles and according to claim 2, the elimination of separate pressure intensifier reduces the overall size of the injector assembly; if the intensifier has separate accumulator, it also is eliminated; said reduction of the accumulator capacity saves the energy through the reduction in the accumulator charging time duration.