CN114850444A

CN114850444A - Hydraulic control mechanism for casting unit of injection molding machine

Info

Publication number: CN114850444A
Application number: CN202210107563.5A
Authority: CN
Inventors: D-W·赫罗德; H·恩格特
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2021-02-03
Filing date: 2022-01-28
Publication date: 2022-08-05
Also published as: DE102021200958A1; JP2022119208A

Abstract

The invention discloses a hydraulic control mechanism for a casting unit of a prototype, comprising: a casting cylinder having a rod-side actuating space and a base-side actuating space, which are separated by a piston, in which a base-side actuating surface and a rod-side smaller actuating surface are formed; and a hydraulically actuable valve device via which the piston force and the piston speed can be controlled in the casting phase by selectively connecting the actuating space to a pressure medium source, a pressure medium sink and/or to one another, wherein at least one pressure-increasing control pressure medium reservoir is provided, via which control pressure medium is stored for hydraulically actuating the valve device.

Description

Hydraulic control mechanism for casting unit of injection molding machine

Technical Field

The present invention relates to a hydraulic control mechanism for a casting unit of an injection molding machine according to the preamble of claim 1.

Background

The term "injection molding machine" shall include in particular the fields of application: die casting machines, thixoforming machines, and plastic injection molding machines.

The basic structure of such a hydraulic control is disclosed, for example, in DE 102017220836 a1 from the present applicant. Accordingly, the control mechanism has a double-acting casting cylinder, the piston surface of which delimits the actuating space on the piston base side (bottom space) and the piston rod-side annular surface of which delimits the actuating space on the piston rod side (annular space). In the known solution, the bottom space is connected to the low-pressure reservoir during the pre-charging phase and the model-charging phase by means of, for example, an 2/2-way valve, which is embodied as an active logic device, wherein the annular space is connected to the bottom space by means of a control valve, so that the pressure medium which is displaced from the smaller annular space in the pre-charging phase is supplied to the larger bottom space by means of said control valve in the differential or regeneration line.

In the mold filling phase, the pressure medium connection to the tank can be opened for firing by a tank-side control valve and the control valve between the piston space and the annular space is closed. In the pressure holding phase, the bottom space is connected via a further control valve to the high-pressure reservoir, wherein the pressure medium connection to the low-pressure reservoir is blocked by the active logic device. This pressure increase can also be accomplished by a pressure transducer. In this pressure holding phase, the pressure medium connection between the annular space and the tank is kept open by the aforementioned tank-side regulating valve, so that the melt in the mold cavity is compressed with high pressure and possible material losses are compensated.

The basic structure of such active logic devices is known from DE 102005035170B 4.

The actuation dynamics and the actuation accuracy of the valve are very important here, since only with high-quality control, the force and speed control of the casting process leads to high product quality.

If the valve can be hydraulically actuated or pre-controlled, the greater the actuation dynamics and the actuation accuracy of the valve, the higher the available control pressure. A control pressure as high as possible is therefore desirable. On the other hand, the pressure medium source provided for this purpose, for example a hydraulic pump, must provide a correspondingly high nominal pressure, which makes such a device expensive.

Disclosure of Invention

In contrast, the object of the present invention is to provide a hydraulic control of a casting unit, by means of which a high control pressure can be achieved for a pressure medium source provided for this purpose with little effort.

This object is achieved by a hydraulic control unit having the features of claim 1.

Advantageous embodiments of the control device are specified in claims 2 to 10.

A hydraulic control mechanism for a casting unit of an injection molding machine, in particular for an injection molding machine, a die casting machine or a thixomolding machine, has a casting cylinder with a rod, with which a casting piston of the casting unit can be coupled. The rod-side actuating space and the bottom-side actuating space of the casting cylinder are separated by a piston of the casting cylinder. In this case, a pressure-loadable bottom-side actuating surface and a pressure-loadable lever-side smaller actuating surface are formed on the piston. In order to control the piston force and the piston speed during the casting phase, a hydraulically actuatable valve device is provided, by means of which the actuating space can be selectively, phase-specifically, fluidically connected to the pressure medium source, the pressure medium sink and/or to each other. At least one pressure-increasing control pressure medium reservoir is provided, in which a control pressure medium is stored for hydraulically actuating the valve device. According to the invention, a pressure-increasing path is provided, via which the actuating space on the lever side can be brought into fluid communication with at least one control pressure medium reservoir for pressure increase.

The advantageous ratio of the piston of the casting cylinder and the control surface of the piston can thus be used to advantage for pressurizing the at least one control pressure medium reservoir. By this ratio, the piston functions appropriately for the pressure transducer. A high control pressure can thus be achieved with little effort for the pressure medium source provided for this purpose.

The new claims: supercharging may also be done as a combination. The basic charge (grundmount) to the low pressure (ND) is done by a pump and the boost to the high pressure (HD) is done by a patented scheme.

In an embodiment, which achieves high control dynamics, control accuracy and control diversity, the valve arrangement is divided into valves which can be actuated independently of one another, each of which can be connected to one or more pressure media of the actuation space controlled independently of the one or more other valves.

The actuating space on the rod side can be connected in particular via a first valve of the disassembled valve device to the actuating space on the base side via a first flow path. A regenerative pressure medium flow path can thus be formed by the first valve, which makes it possible to design and provide a primary hydraulic pump for adjusting the casting cylinders with a low nominal volume flow. Furthermore, the first valve and the first pressure medium flow path provide an intervention possibility for speed control.

The actuating space on the rod side is in particular in fluid communication with the pressure medium tank via a second flow path via a second valve of the valve device. In this way the movement of the casting piston can be controlled in a controlled outlet manner by means of the second valve.

In order to be able to realize the holding pressure phase during casting, the control device has, in a further embodiment, a hydraulic pressure intensifier unit which is designed to increase the pressure in the actuating space on the bottom side during the holding pressure phase.

The hydraulic pressure intensifier unit can be designed as an additional high-pressure accumulator or as a pressure converter, in particular as a differential cylinder, the larger actuating surface of which can be acted upon by pressure.

In a further embodiment, in which the pressure intensifier unit is designed as a pressure transducer, in particular as a differential cylinder, a third valve of the valve arrangement is provided for activating the pressure transducer, by means of which a third pressure medium flow path leading into the pressure space or into the actuating space of the pressure transducer can be conducted or can be designed. Depending on the actuating space into which the third pressure medium flow path opens, the pressure converter is controlled in the inlet or in the outlet.

In a further embodiment of the reinforcing unit in the form of a high-pressure accumulator, a third reversing valve which can be actuated in proportion is provided between the high-pressure accumulator and the actuating space on the bottom side of the casting cylinder. The pressure build-up in the bottom-side actuating space can be regulated by this third directional control valve.

In a further embodiment, the fourth valve of the valve device is designed as an active logic valve for a rapid and reproducible connection of the bottom-side actuating space of the casting cylinder to the pressure medium source and for a correspondingly rapid and reproducible disconnection. The bottom-side actuating space can thus be in particular fluidically connected to the pressure medium reservoir and independently of the hydraulic pump.

In one embodiment, at least two control pressure medium reservoirs are provided, wherein a first control pressure medium reservoir can supply control pressure medium to the first, second and third valves and a further second control pressure medium reservoir can supply control pressure medium to the fourth valve.

In one embodiment, the pressure supply path branches off for this purpose to a plurality of control pressure medium accumulators. Alternatively, only one control pressure medium reservoir may be provided.

Different distribution schemes of the valves to the control pressure medium reservoir are of course also possible. The distribution scheme is defined in particular as a function of the respectively required control pressure level of the respective valve and/or the spatial proximity of the control pressure medium reservoir to the respective valve. Here, it is very closely advantageous, since in this way the damping and elasticity are minimized both when loading the accumulator and when removing the control pressure medium. It is thus ensured that the control pressure always remains stable during sudden signal changes of the valve piston, for example during the firing of the casting cylinder, and that the valve piston opens to the desired setpoint value with maximum acceleration.

In order to ensure a safe pressurization of the control pressure medium reservoir or reservoirs and to ensure a safe blocking of the control pressure medium reservoir relative to the casting cylinder, in one embodiment a shut-off valve, in particular an 2/2 selector valve, is provided in the pressurization path.

In order to be able to influence the charge control pressure medium volume flow, in one embodiment, an adjustable throttle device, in particular a flap, is provided in the charge path.

In a further embodiment, a pressure control valve is assigned to the control pressure medium reservoir or to at least one of the control pressure medium reservoirs, by means of which pressure control valve the pressure in the control pressure medium reservoir can be regulated. This is in particular a pressure reducing valve, at the inlet of which the pressure of the actuating space on the rod side or a pressure associated therewith is present and the outlet of which is connected to a control pressure medium reservoir.

In one possible variant, a separate pressurization path is associated with each control pressure medium reservoir.

Correspondingly, in the case of a plurality of charging paths, the last-mentioned shut-off valves, in particular 2/2 directional switching valves, can be provided in each case, and alternatively or additionally the last-mentioned adjustable throttle devices, in particular dampers, can be provided.

The control pressure of the one or more control pressure medium accumulators may alternatively or additionally be determined by the setpoint pressure in the bottom-side actuating space and the area ratio at the piston of the casting cylinder.

Drawings

Preferred embodiments of the invention are explained in more detail below with the aid of schematic drawings. In the figure:

FIG. 1 is a schematic view of a casting unit; and is provided with

Fig. 2 shows a simplified hydraulic circuit diagram of the casting unit according to fig. 1 with a hydraulic control according to an exemplary embodiment.

Detailed Description

Fig. 1 shows the main mechanical components of a hydraulic casting unit 1 according to the invention of a die casting machine. The casting unit 1 has a casting cylinder 10, which is designed as a differential cylinder and whose piston 11 is correspondingly designed with a piston rod 12. The piston 11 and the housing 13 of the casting cylinder together delimit a bottom space 14 on the bottom side and an annular space 15 which is traversed by the piston rod 12. At the end section of the piston rod 12 projecting from the housing 13, a cast piston 16 is fixed, which is inserted into a firing chamber 18 of a cast bush 17. In this shot chamber, a charging opening 19 for liquid or pasty forming material, referred to below as melt, is located from which the workpiece to be formed is to be produced. The casting liner 17 is attached to a pattern 20, which is typically made up of movable and stationary pattern halves. The two mould halves delimit a mould cavity 21, also called mould cavity, which is designed according to the geometry of the workpiece to be formed. The launching chamber 18 opens into the mould cavity 21 via a casting channel 22.

Such a casting unit 1 serves for introducing a melt into a mold 20, wherein, due to the rapid solidification process, a high speed and subsequently a high pressure are required for the charging in order to completely fill the mold 20 and to compress and to compensate for the shrinkage of the material during solidification.

In the embodiment according to the invention shown in fig. 2, the casting unit 1 has a hydraulic control. For simplicity, the cast piston 16, cast liner 17 and mold 20 are not shown.

A pressure converter 24, also referred to as a multiplier cylinder, is assigned to the casting cylinder 10 as a booster unit, which is designed, for example, as a differential cylinder. The primary piston 26 delimits with the bottom surface a pressure converter pressure space 28 and the piston rod 30 penetrates a pressure converter counter-pressure space in the form of an annular space 32. The construction of such a pressure transducer 24 is known and need not be explained further. Other boosting units without a pressure converter, such as a high-pressure accumulator which can be switched on, are of course also possible.

The basic pressure medium supply of the illustrated casting unit 1 is effected by a hydraulic pump 34, which in the illustrated embodiment is designed as a constant hydraulic machine and is driven by a speed-regulated electric motor 36, which is designed, for example, as a servomotor with a servo converter or as an ac motor with a frequency converter. The pressure connection of the hydraulic pump 34 is connected via a pump line to a pretension valve (vorspan valve) 42 which is designed as an 4/3 directional valve. This pretension valve, in its illustrated spring-pre-centered base or intermediate position, blocks the hydraulic pump 34 from the casting cylinder 10 and the pressure booster 24 and instead connects at least the bottom space 14 to the tank T via a non-return valve 72, which can be unblocked, and to the annular space 32 of the pressure booster 24 via the pump line 40 and the non-return valve 70. The pretension valve 42 can be switched by means of two switching magnets and hydraulic pretension control into two passage positions a, b, in which it can fulfill the function of a device for pretensioning the casting cylinder 10 and the pressure transducer 24 together with the hydraulic pump 34, as explained further below.

The annular space 15 of the casting cylinder 10 can be connected to the bottom space 14 of the casting cylinder 10 via a first pressure medium flow path 23 and a first reversing proportional valve 27 arranged in the first pressure medium flow path. The last-mentioned first reversing proportional valve 27 is designed in the exemplary embodiment shown as an electrohydraulic pilot-controlled 2/2 reversing proportional valve with a spring-biased base position or blocking position, which is known from the series by the applicant as 2WRCE-4X and is designed as a flow control valve. By actuating the electrohydraulic pilot control, the opening cross section of the valve 27 is increased as a function of the actuating signal and the annular space 15 for regenerative operation (Verfahren) is connected to the bottom space 14.

The annular space 15 of the casting cylinder 10 can furthermore be connected to the tank T via a second pressure medium flow path 44 in which a second reversing proportional valve 46 is arranged. The second directional control proportional valve 46 is of the same construction as the first directional control proportional valve 27 with regard to valve type and actuation, but has a greater setpoint variable than this first directional control proportional valve, since the pressure medium volume flow through the second directional control proportional valve 46 is greater than the pressure medium volume flow through the first directional control proportional valve 27 in regenerative mode. The second directional proportional valve is designed as an electrohydraulic pilot-controlled 2/2 flow control valve, which 2/2 flow control valve in its basic position blocks the pressure medium connection to the tank T and, as a function of the actuating signal, increases the opening cross section to the tank T by actuating the electrohydraulic pilot control.

The second pressure medium flow path 44 can be in fluid communication with a pre-tensioned line 50 that can be fed by the hydraulic pump 34 via a check valve 48 that opens into the second pressure medium flow path 44. The pretensioning line 50 is blocked in the spring-pretensioned basic position of the check valve 48.

The pump line 40 opens into the third pressure medium flow path 25 between the third directional proportional valve 29 and the pressure converter annular space 32. In the pump line 40, a check valve 70 which opens into the pressure converter annular space 32 is arranged between the branch of the pretension line 50 from the pump line 40 and the opening. The two

non-return valves

48, 70 open at a sufficient pressure in the pump line 40 and the pretension line 50, so that the

annular spaces

15, 32 of the casting cylinder 10 and of the pressure transducer 24 are supplied with pressure medium. The casting cylinder 10 and the pressure transducer 24 can be moved back in this way and the required counter pressure can be built up in the respective

annular space

15, 32 for their pretensioning.

For this purpose, the pretension valve 42 has a first switching position a in which the pressure connection P of the hydraulic pump 34 is connected to the pump line 40 and the pretension line 50, and in which the first pressure medium flow path 23 and the bottom space 14 can be connected to the pressure medium reservoir T via a non-return valve 72, which can be unblocked.

The pressure at the outlet of the hydraulic pump 34 can be limited in a manner known per se by a pressure limiting valve opening towards the tank T.

The pressure transducer 24 and the casting cylinder 10 are assigned a valve arrangement which is subdivided into three

flow control valves

27, 46 and 29 which can be actuated independently of one another and which are each designed as a valve with two connections which can always be adjusted and which is controlled by an electrohydraulic actuator. The hydraulic actuation or pilot control is carried out here with the control pressure medium stored in the control pressure medium storages SD1 and SD2, which are explained in greater detail below.

The pilot-controlled 2/2-way-operated built-in seat valve is designed as an active logic device (Aktivlogik) 41. The pre-control of the active logic device is accomplished by a switching pilot valve 52 designed as an 3/2 reversing valve. The inlet connection a of the active logic device 41 is connected to a low-pressure accumulator 56 via a low-pressure accumulator line 54. The output connection B of the active logic device 41 is connected to the bottom space 14 of the casting cylinder 10.

Possible configurations of the active logic device 41 are sufficiently known from the documents DE 102017220836 a1 and DE 102005035170B 4 cited in the introduction to the description, so that only the structural elements required for understanding the invention are explained here and reference is additionally made to these prior art. Accordingly, the active logic device 41 has a stepped main piston 60 which is prestressed against the valve seat 58 by pressure from the control pressure medium reservoir SD1 by switching the pilot valve 52 on to the surface a5 and which blocks the pressure medium connection between the connections A, B of the active logic device 41 and thus between the low pressure reservoir line 54 and the pressure line 59. The pressure line 59 opens into the bottom space 14 of the casting cylinder 10. The main piston 60 has a bore from its rear side a5 into the end side A3, thereby ensuring a pressure equalization between the closed surface a5 and the open surface A3. The active logic device 41 can be opened and closed in a targeted manner by the action of the switching pilot valve 52 via the control surface a 4. In this case, the area a4 can be selected to be greater than the difference a5-A3 or the control pressure of the control pressure medium reservoir SD1 can be set correspondingly higher in order to safely open the active logic device 41.

The tank line 62 is connected to the tank connection of the switching pilot valve 52 and the inlet connection of the switching pilot valve 52 is connected to a control pressure medium reservoir SD1 via a line 64. By energizing the switch magnet of the switch pilot valve 52, this switch pilot valve can be adjusted against the force of a spring into a switching position in which the annular control space of the active logic device 41, which is delimited by the surface a4, is connected to the low-pressure reservoir ND1 via the line 64, so that the main piston 60 is lifted from the valve seat 58 and the fluid connection between the connections A, B is opened as a result of the pressure acting on the annular end surface a 4.

The active logic device 41 is designed such that it can be flowed through with minimal pressure loss and, when actuated accordingly, is closed by the switching pilot valve 52 with minimal switching time and with high repetition accuracy. The stroke of the active logic device 41 may also be limited in order to optimize the subsequent closing behavior. With this design of the active logic device 41, only a small control oil flow is required even at large nominal values in order to open and close the active logic device 41 quickly and with high repetition accuracy.

Furthermore, the operational safety is increased by actively opening and closing the active logic device 41 by means of the switching pilot valve 52 and by safely locking (Zuhalten) the active logic device 41 by means of the accumulator pressure. It is possible here to freely select the conditions for the shutdown by actively shutting down the active logic device 41. Such closing can be done, for example, as a function of pressure, load force, operating stroke, operating speed, etc.

As shown in fig. 2, in addition to the low-pressure accumulator 56, a further low-pressure accumulator 57 is provided, which can be connected to the pressure converter pressure space 28 via an 2/2 directional seat valve, which is referred to below as an accumulator shut-off valve 66 and is controlled by a pilot control valve 68. The two low-

voltage accumulators

56 and 57 can alternatively and depending on the customer requirements be combined into one. In this case, in the prestressed basic position of the pilot valve 68, the pressure of the low-pressure accumulator 56 acts on the rear space of the accumulator shut-off valve 66, which acts in the closed position, with the tank pressure in the switching position, and the accumulator shut-off valve 66 thus connects the low-pressure accumulator 57 to the pressure converter pressure space 28. In the switching position, the pressure transducer is therefore tensioned in the support direction.

In the following, the operation of the casting unit 1 shown in fig. 2 during the phases I to III described at the outset is explained before the components for providing the control pressure medium required for this purpose are discussed.

In order to prevent a pressure wave in the direction of the casting cylinder 10 during the pre-charging phase (which pressure wave generates the starting pressure) during the start-up of the casting cylinder 10, the piston 11 of the casting cylinder 10 is prestressed in the direction of the diminishing bottom space 14 before the start of the pre-charging phase I before the active logic device 41, also referred to as an accumulator shut-off valve, is opened. It is thus prevented that such a starting pressure could mix the melt, air and the melt skin, which could lead to porosity and impurities of the casting and to poor quality or defective products in unfavorable cases.

The pretensioning can be done in different ways depending on the available pressure medium source. In the exemplary embodiment shown, when the casting cylinder 10 is moved back and the pressure converter 24 is moved back, the annular space 15 of the casting cylinder 10 and the pressure converter annular space 32 of the pressure converter 24 can be prestressed to the maximum pump pressure by means of the hydraulic pump 34 and the prestressing valve 42 which is actuated into its first switching position a and by means of the open

non-return valves

48 and 70. In doing so, the first directional proportional valve 27, the second directional proportional valve 46, and the third directional proportional valve 29 are closed, thus preventing a short circuit to the tank. The shut-off and pretension valve 42 is preferably designed with a non-return function.

For the pre-tensioning task of the hydraulic pump, the hydraulic pump 34 can be designed as a high-pressure pump up to, for example, 420 bar.

Alternatively or additionally, a pressure transducer can be provided for preloading the

annular space

15, 32, which results in a less high-pressure hydraulic pump. At low pretension pressures, there is usually the possibility of setting a low-pressure hydraulic pump or a low-pressure booster pump.

In the next step, the melt is introduced into the casting chamber 18 of the casting insert 17 through the charging opening 19 according to fig. 1 and the pre-charging phase I is started. For this purpose, the hydraulic pump 34 is actuated by means of a ramp function and now loads the bottom space 14 of the casting cylinder 10 by means of the second switching position b of the shut-off and pretension valve 42 to the value of the reservoir pressure of the low-pressure reservoir 56. The casting cylinder 10 is thus moved out slowly and without starting pressure slightly against the prestress in the annular space 15 until the fluid contained in the annular space 15 is compressed and there is a force equilibrium at the piston 11. It is important here that a smooth adaptation of the pressure in the bottom space 14 of the casting cylinder 10 to the pressure in the low-pressure accumulator 56 is achieved by this control. The low-pressure accumulator 56 can then be connected to the bottom space 14 via the active logic device 41 (accumulator shut-off valve) and the low-pressure accumulator 56 is connected to the pressure converter pressure space 28 via the accumulator shut-off valve 66.

This is not necessary provided that pump 34 can generate a sufficiently high pressure. In the correspondingly highly prestressed annular space 15, the low-pressure accumulator 56 can also be connected to the piston space 14 via the active logic device 41.

The first reversing proportional valve 27 is then actuated by the pilot control in such a way that the pressure medium emerging from the annular space 15 is supplied directly to the bottom space 14 in the manner of a regenerative circuit. This allows the casting cylinder 10 to start and operate gently (smoothly, regeneratively, and regulated). The melt is thereby accelerated and moved in the direction of the mold cavity 21 in fig. 1. This is done until the melt has reached the mold gate (formanschitt) and the precharge phase I has ended.

By the regenerative operation of the casting cylinder 10 in the pre-charging phase I, less pressure medium is drawn off from the low-pressure accumulator 56, so that this casting cylinder can be designed with a smaller volume than in conventional solutions without regenerative operation. Furthermore, a better solution of the casting cylinder speed is achieved on the basis of a smaller pressure drop caused by the differential line and a smaller nominal value or values of the first directional proportional valve 27, so that the casting cylinder 10 can be operated at a lower speed and with better repetition accuracy.

A further advantage of the regeneration operation is that, on account of the small pressure losses at the first reversing proportional valve 27 and on account of the fact that the pressure medium from the annular space 15 flows out not against the tank pressure (0 bar) but against the pressure in the low-pressure reservoir 56, fewer cavitation and therefore less wear occur at the valve 46, at the piston 11 and at the housing 13 of the casting cylinder 10 and at the associated control block.

By actuating the first directional control valve 27 and the second directional control valve 46 connected in series therewith, the pressure in the bottom space 14 can be actively influenced in the sense of a pressure reduction or decompression. For example, pressure overshoots in the bottom space 14 can be eliminated in this way in a simple manner.

Furthermore, the pressure in the bottom space 14 may also be influenced by a third direction-changing proportional valve 29 which can be actuated completely independently of the first and second direction-changing proportional valves 27, 46. Based on the described independent pressure

medium flow paths

23, 44, 25 and

valves

27, 46, 29, an accurate and dynamic regulation of the pressure in the bottom space 14 is produced.

As soon as the melt has reached the mold gate, the actual mold charging process begins (phase II). In the case where the mold charge (injection) is performed at a low mold charge force, the regenerative operation is also performed. Correspondingly, at the time point when the melt reaches the mold gate, the first directional control valve 27 is set, for example, in a step function into a position in which the pressure medium connection between the annular space 14 and the bottom space 15 is opened further, so that the melt is injected into the mold 20 at a high injection speed (up to 10 m/s). In this case, the pressure medium which is pressed out of the annular space 15 is also regeneratively supplied to the enlarged bottom space 14.

This practice with regeneration has the advantage that, in phase II, too, less pressure medium must be removed from the low-pressure accumulator 56 than in conventional solutions.

In the case of injection at high mold loading forces, at the point in time when the melt reaches the mold gate, the first directional control proportional valve 27 is brought into its closed position, for example, in a step function, so that the pressure medium connection between the annular space 15 and the bottom space 14 is interrupted. The second reversing proportional valve 46 opens in the outlet, for example in parallel, with a step function to a predetermined opening cross section towards the tank T. This results in the melt being ejected into the mold cavity 21 at a very high ejection speed, but in this case, unlike in the case of low mold filling forces, no recuperation operation takes place and the maximum force of the casting cylinder 10 can therefore be used.

In principle, a mixed mode can also be considered, in which the first reversing proportional valve 27 is adjusted into its shut-off position only during phase II as a function of the load force.

Stage II can also be run entirely regeneratively. However, this presupposes that the required load force can also be achieved in the regeneration circuit in phase II. In this case, the second reversing proportional valve 46 may be replaced by a fast switching valve for relieving the annular space 15 in phase III.

After the mold cavity 21 has been completely filled, a transition is made to stage III, i.e. a dwell pressure (Nachdrucken). For this purpose, at the end of the mold filling phase II, the third directional proportional valve 29 is actuated by a pilot control in the direction of opening the connection of the pressure booster annular space 32 to the tank T. The second reversing proportional valve 46 is simultaneously opened. The resulting pressure relief of the pressure transducer annular space 32 accelerates the primary piston 26 and accordingly builds up a high pressure in the bottom space 14, so that the piston 11 is charged with high pressure and the melt is recompressed. When the desired holding pressure is reached, the second reversing proportional valve 29 is reset again in the closing direction by the pressure regulator. Without closing the second reversing proportional valve 29 sufficiently quickly, the pressure overshoot in the bottom space 14 can be eliminated by conducting the pressure relief path, i.e. the reversing proportional valves 27 and 46, towards the tank T.

The active logic device 41 may also be replaced by a shut-off valve and an external check valve.

The previous explanation shows that for high quality of the cast product, the force control and speed control of the

pistons

11 and 26 must have a high precision and dynamics. The valves that are important for such control are, in particular, the

hydraulically actuatable valves

27, 29, 41 and 46, to which the control pressure medium reservoirs SD1 and SD2 are provided for supplying control pressure medium. The function and operation of the

valves

27, 29, 41 and 46 has been elucidated here.

The

respective control surfaces

74, 76 and 78 of the

valves

27, 29 and 46 can be connected to a control pressure medium reservoir SD2 via respective control pressure

medium lines

80, 82 and 84. The face a4 can be connected to a control pressure medium reservoir SD1 via the line 64 and the switching pilot valve 52 as explained above.

The requirements for controlling the pressure medium supply are: in order to open the active logic device 41 as described above by applying the surface 4, a control pressure of at least 20 bar, in the exemplary embodiment shown 30 bar, above the pressure in the low-

pressure accumulator

56 or 57 is required, by means of which the phases II and III of the casting process are controlled.

It should be added that the higher the control pressure supplied to the

valves

27, 29 and 46, the better the dynamics (step response time) that can be achieved in phases I, II, III when opening and closing these valves.

In conventional solutions, the control pressure medium reservoir is pressurized by a hydraulic pump 34 or other suitable hydraulic pump. The maximum achievable control pressure then depends on the maximum pressure that these hydraulic pumps can generate. Since high accuracy and dynamics of force control and speed control can be achieved with high control pressures, these hydraulic pumps must be able to just meet such high pressures, which is energy-consuming and cost-intensive.

The control pressure medium reservoirs SD1 and SD2 can therefore be pressurized in other ways according to the invention. To this end, according to the invention, a pressure charging path 86 is provided, via which the annular space 15 of the casting cylinder 10 can be brought into fluid communication with a branch 88 towards the control pressure medium reservoir SD1 and with a branch 90 towards the control pressure medium reservoir SD 2. In the boost path 86, a two-way selector valve 92 and an adjustable throttle 94 are also fluidly connected in series before branching occurs. Each

branch

88 and 90 has a respective

pressure relief valve

96, 98, by means of which the current pressure can be regulated and thus limited to the required control pressure in the respective control pressure medium reservoir SD1, SD 2. Alternatively, it is of course possible to provide each control pressure medium reservoir SD1, SD2 with a corresponding two-way directional switching valve and a series-connected adjustable throttle device.

If the same control pressure is required in both control pressure medium storages SD1, SD2, then alternatively only one pressure reducing valve may be provided in the pressure buildup path 86. When it is provided that the control pressure medium can be taken separately from each of the control pressure medium storages SD1, SD2, one check valve per

branch

88, 90 can be provided. Such a non-return valve is not absolutely necessary when the two control pressure medium reservoirs SD1, SD2 are always simultaneously removed.

The pressurization of the pressure medium reservoirs SD1, SD2 can thus be controlled according to the invention by the annular space 15 of the casting cylinder. The area ratio of the control surfaces on the base side of the piston 11 to the control surfaces on the rod side of the piston acts in a manner adapted to the pressure transducer, so that a higher pressure in the annular space 15 and thus also the control pressure in the respective control pressure medium reservoir SD1, SD2 can be achieved by a lower pressure in the bottom space 14. This area ratio is, for example, between 1.5 and 2.5 and 3, as a result of which a corresponding pressure change can take place. In other words, a high control pressure can be reached with the less high pressure hydraulic pump 34 (the pressure in the bottom space depends indirectly on this hydraulic pump), which is then supplied to the

valves

27, 29, 41 and 46 or other valves for the control required for high dynamics and high accuracy.

The control pressure medium storage SD1, SD2 can be pressurized with the casting cycle. Several variants of the method for supercharging are available here, individually or in combination:

the first possibility is: after the aforementioned preloading of the casting cylinder 10 and the pressure transducer 24, the bottom space 14 is charged with pressure medium and pressurized to a pressure that can be provided by the hydraulic pump 34. For this purpose, the hydraulic pump 34 feeds pressure medium through the pretension valve 42, which is actuated into the switching position b, and through the non-return valve 72 into the bottom space 14. The result is that the piston 11 is slowly moved out and the pressure medium flows from the annular space 15 of the casting cylinder via the pressure-reducing

valves

96, 98 into the control pressure medium reservoirs SD1, SD2 when the directional switching valve 92 of the pressure-increasing path 86 is open and the throttle device 94 is open. The control pressure which can be achieved in this way is above the pressure which can be provided by the hydraulic pump 34 in the bottom space 14 in accordance with the area ratio at the piston 11 (piston surface to annular surface ratio) and can be reduced, if desired, by the

pressure reducing valves

96, 98.

Another possibility is to control the pressurization of the pressure medium reservoirs SD1, SD2 via the pressurization path 86 during the above-described regenerative operation of the casting cylinder 10 (pre-charging phase). For this purpose, the two-way selector valve 92 is opened and, during regenerative operation of the piston 11, the control pressure medium reservoirs SD1, SD2 are pressurized by means of an adjustable throttle device 94 and

pressure reducing valves

96, 98.

Another possibility is to control the pressurization of the pressure medium reservoirs SD1, SD2 via the pressurization path 86 in the model charging phase or the firing phase. In this case, these control pressure medium reservoirs can be pressurized to the control pressure which is generated in the annular space 15 during the firing.

A phase in which the piston 11 is braked before reaching the final position at the time of "firing" in such a way that the (outlet) valve 46 is blocked has proved to be suitable as another possibility. The pressure in the annular space 15 is thereby increased and the control pressure medium reservoir SD1, SD2 can be pressurized via the pressurization path 86.

A combination can also be selected from these possibilities.

The applicant reserves the right to: the patent application or the independent claims are used for such a method for pressurizing at least one control pressure medium reservoir and/or for controlling a casting unit having such a pressurization.

By means of the valve 27, the speed of the piston 11 can be adjusted in the pre-charging phase and the volume flow can be adjusted when the control pressure medium reservoirs SD1, SD2 are pressurized.

A hydraulic control mechanism for a casting unit of a prototype is disclosed, the casting cylinders of which can be controlled in terms of force and speed in a time-dependent manner during the casting phase by means of hydraulically actuatable valve devices. The supply of pressure medium is controlled by a pressurizable pressure medium reservoir or a pressurizable pressure medium reservoir. According to the invention, a pressurization path is provided from the annular space of the casting unit to the pressure medium reservoir or the pressure medium reservoir, whereby the pressure of the piston of the casting cylinder is converted sufficiently for pressurization and the pressure medium source provided for pressurization can have a lower pressure level.

Claims

1. A control mechanism for the hydraulic pressure of a casting unit (1) of an injection molding machine, with: a casting cylinder (10) having a rod-side actuating space (15) and a base-side actuating space (14), which are separated by a piston, at which a base-side actuating surface and a rod-side smaller actuating surface are formed; and a hydraulically actuatable valve device (27, 29, 41, 46) via which the piston force and piston speed can be controlled in the casting phases (I, II, III) by selectively connecting the actuating space (14, 15) to a pressure medium source (34), a pressure medium tank (T) and/or to one another, wherein at least one pressurizable control pressure medium reservoir (SD 1, SD 2) is provided, via which control pressure medium is stored for hydraulically actuating the valve device (27, 29, 41, 46), characterized by a pressurization path (23, 86, 88, 90) via which the rod-side actuating space (15) can be brought into fluid communication with the at least one control pressure medium reservoir (SD 1, SD 2) for pressurization.

2. Control mechanism according to claim 1, wherein the lever-side actuating space (15) can be connected to the base-side actuating space (14) via a first flow path (23) by means of a first valve (27) of the valve device (27, 29, 41, 46).

3. A control mechanism according to claim 1 or 2, wherein the rod-side operating space (15) can be brought into fluid communication with the pressure medium tank (T) via a second flow path (44) by means of a second valve (46) of the valve arrangement (27, 29, 41, 46).

4. A control device according to one of claims 1 to 3, having a hydraulic pressure transducer (24) which is designed to increase the pressure in the bottom-side actuating space (14) during a pressure holding phase, wherein a third pressure medium flow path (25) leading into the pressure space (32) of the pressure transducer (24) can be switched on or can be formed by a third valve (29) of the valve arrangement (27, 29, 41, 46) in order to activate the pressure transducer (24).

5. The control mechanism according to any one of claims 1 to 4, wherein the fourth valve (41) of the valve arrangement (27, 29, 41, 46) is configured as an active logic valve (41), by means of which the bottom-side actuating space (14) can be brought into fluid communication with a pressure medium reservoir (56) independently of the hydraulic pump (34).

6. A control mechanism according to any one of claims 2 to 5, with at least two control pressure medium reservoirs (SD 1, SD 2), wherein control pressure medium can be supplied from one control pressure medium reservoir (SD 1) to the first, second and/or third valve (27, 46, 29) and from the other control pressure medium reservoir (SD 2) to the fourth valve (41).

7. The control mechanism according to any one of the preceding claims, wherein a shut-off valve (92) is provided in the boost path (86).

8. A control mechanism according to any one of the preceding claims, wherein an adjustable throttle device (94) is provided in the boost path (86).

9. The control mechanism according to any one of the preceding claims, wherein the pressure charging path (86) branches (88, 90) to a plurality of control pressure medium accumulators (SD 1, SD 2).

10. The control mechanism according to any one of the preceding claims, wherein a pressure regulating valve (96, 98) is assigned to at least one of the control pressure medium reservoirs (SD 1, SD 2), and/or wherein the control pressure of the one or more control pressure medium reservoirs can be determined by a nominal pressure in the bottom-side actuating space and an area ratio at the piston of the casting cylinder.