EP1113892A1

EP1113892A1 - Injection unit for a pressure die casting machine

Info

Publication number: EP1113892A1
Application number: EP00943750A
Authority: EP
Inventors: Roland Fink; Norbert Erhard; Herbert Noschilla; Bruno Stillhard; Ronald Siegrist
Original assignee: Oskar Frech GmbH and Co KG
Current assignee: Oskar Frech GmbH and Co KG
Priority date: 1999-06-01
Filing date: 2000-05-31
Publication date: 2001-07-11
Anticipated expiration: 2020-05-31
Also published as: ES2267548T3; JP4558954B2; DE50013156D1; PL345746A1; WO2000072998A1; CZ2001418A3; EP1113892B1; CZ300224B6; ATE332778T1; JP2003500219A; PL193801B1; US6581670B1; HK1035343A1; EP1057560A1

Abstract

Disclosed is an injection unit for a hot-chamber pressure die casting machine, providing an electromechanical drive for the plunger. A spring element (16) in the form of a plastic component or a hydraulic spring is inserted in between the plunger and the connecting rod (9) in order to absorb the moments of inertia which occur when the plunger drive mechanism is shifted from the phase in which the mould is filled to a pressure dwelling phase. Said spring element is compressed by the additional travel of the connecting rod after the motor is decelerated. The extent of said compression can be selected in such a way that the resulting axial force which is exerted upon the plastic component or hydraulic spring suffices to create the desired pressure dwell in the melt.

Description

Press-in unit for a die casting machine

The invention relates to a press-in unit for a die casting machine, in particular for a hot chamber die casting machine for processing metal melts with a casting piston for pressing the casting material into a mold, which can be acted upon via a push rod which is connected to a linear drive driven by an electric motor, which after the filling phase the mold to achieve a pressure in the casting material is held in a pressure phase, a spring element being connected between the casting piston and the push rod.

A press-in unit is known from EP 0 430 616 A1, in which a spindle for driving a nut is provided as the linear drive. The casting piston connected to the linear drive is driven by a belt driven by an electric motor. The belt drive acts on the spindle via an electromagnetically controllable disc clutch, so that in this way the feed speed of the casting piston and, after filling the mold, the pressure to be held in the casting material can be controlled. It serves for. Control a speed-dependent signal, which is emitted by a tachometer connected to the spindle drive. A drive of this Type for the press-in unit is relatively complex. The control and regulation of the disc clutch harbors disadvantages mainly because of the susceptibility to wear of such clutches.

From the patent abstract of Japanese patent 0 7155 925, a press-in unit of the type mentioned at the outset for a die casting machine is known, in which an elastic spring element is connected between the casting piston and the push rod, which avoids undesirable pressure peaks caused by the inertia forces inherent in the drive when stopping the system Drive and arise in the transition to pressure control. While such problems do not occur in plastic injection molding machines because of the elastic behavior of liquid plastics, the conditions in die casting machines for processing metal melts are different insofar as the metal melts are practically incompressible.

It is also known to control the extruder spindles there intended for extrusion in the case of injection molding machines for processing liquid plastic masses with the aid of electronic controllers so that in the critical phases of the dynamic pressure build-up during plastification and the maintenance of the pressure in the holding pressure phase, the desired propulsion speeds or torques for the Compliance with the pressure can be exercised (DE 43 45 034 AI). There is also an indication that a similar drive principle can also be used in die casting machines if a spring element is connected between the drive and the movable injection elements.

The present invention has for its object to construct a press-in unit of the type mentioned in the simplest possible way. To obtain a simple construction, according to the invention it is provided in a press-in unit of the type mentioned at the outset that the spring element is designed as an elastic plastic component or as a liquid spring and is designed in such a way that the reaction force on the casting piston resulting from its prestress is large enough to apply the axial force required to achieve the necessary pressure in the casting material on the casting piston. Such a spring element can absorb the moment of inertia that occurs when the drive is braked. The spring travel caused by this prevents further displacement of the casting piston and thus also the occurrence of pressure peaks without the need for complicated control measures.

The invention thus achieves two things in a press-in unit of the type mentioned at the outset. On the one hand, the moments of inertia caused by the masses of the electric motor and the transmission when braking the drive can be absorbed. The casting piston is therefore no longer moved from the time of switching from mold filling to pressure. The additional path that occurs due to the moments of inertia is also used to preload the spring element and the preload that is then generated is used to apply an axial force to the casting piston that is large enough to maintain the desired holding pressure in the casting material.

These measures make the control of the casting piston drive very easy. In this way, the regulation of the holding pressure can be reduced to a secondary speed regulation in a regulator cascade with primary force regulation.

In a further development of the invention, a sensor which is connected to the control of the drive and which detects the axial force exerted by the spring element can be assigned to the spring element. and controls the drive control accordingly. As a result, the electric drive can be controllable in such a way that the spring element is not compressed to a predetermined extent.

In a further development of the invention, an elastic plastic ring can be provided as the spring element, which is held between two flanges, one of which is held on the push rod and the other is fixedly connected to a sleeve which is guided telescopically on the push rod. The relative movement between the push rod and the sleeve compresses the plastic ring, to an extent that corresponds to the adjustment path of the push rod, which is caused by the overrun of the drive after the braking process. It has been shown that such a plastic ring, in particular if it consists of a tempered polyurethane rubber, can exert the high forces that occur in die casting machines for the compression of the molten metal. This plastic ring can also be constructed from two or more parts which can be deformed one after the other, so that different spring characteristics can also be realized for absorbing the moment of inertia and then for applying the axial compressive force.

In a structurally simple manner, the push rod can have an extension of smaller diameter penetrating the plastic ring, on which the sleeve is also guided. The shoulder provided between the extension and the push rod can then serve as an attachment for the disk held on the push rod or for a pressure sensor assigned to it. It is also possible for the spring element and the arrangement of the sleeve to be coordinated with one another in such a way that the extension can only be adjusted a certain distance relative to the sleeve. In a simple manner, as in the prior art, a threaded drive consisting of a spindle and a nut guided thereon can be provided as the linear drive. However, it is also possible to provide a rack and pinion drive as a linear drive, which enables a robust construction and also has a low noise level. The rack and pinion drive can take place via a gear mechanism that engages the rack on both sides, so that there is no one-sided load on the rack. With such a construction, two motors can also be provided for driving the transmission, so that a power adjustment with a higher dynamic range as well as a higher acceleration and deceleration is possible. The gear unit can be completely encapsulated so that oil cannot escape in the direction of the weld pool.

Finally, the linear drive can also be a slide guide driven by a connecting rod of a crank drive, wherein, if a certain height adjustment is provided, an optimal adaptation of the force curve to the mold filling stroke is possible.

However, a liquid spring known per se can also be provided as the spring element (LUEGER Lexikon der Technik, Volume 12 - Vehicle Technology - Edition 1967, Verlag DVA Stuttgart, page 223). Such cylinder / piston units, which are usually filled with oil, can provide the necessary spring travel in the case of the press-in forces of around several tons which occur in the case of die casting machines, the spring force then also being able to be used to act upon the casting piston.

In a practical embodiment, the liquid spring can be provided with an immersion piston which is pressed into the interior of the cylinder under the force of a spring in order to pre-tension the liquid even before it is acted upon by the push rod to put. In a further development of the invention, the cylinder of the liquid spring can also be provided with an opening to which an overpressure limiting valve and a pump for the possible return of leaked liquid are connected. In this case, a pressure-voltage converter can be connected to the connecting line to the pressure-limiting valve, which in turn can be connected to the control of the electromotive drive.

However, additional liquid volumes can also be advantageously connected to the connecting line, the controllable connection of which contributes to changing the suspension characteristics. In this way, even when using a liquid spring, an adaptation of the spring characteristic can be achieved in a similar way as is the case with a multi-part plastic ring in the manner described above.

The invention is illustrated in the drawing using exemplary embodiments and is explained below. Show it:

1 is a press-in unit for a hot chamber die casting machine for processing molten metal,

2 shows a press-in unit similar to FIG. 1, but with a rack and pinion drive instead of a threaded spindle drive,

Fig. 3 is a schematic representation of a section through the unit of Fig. 2 in the direction of the Schnittli never III-III ^¬,

4 shows a representation similar to FIG. 3, but with a different gear arrangement for loading the rack, 5 shows a press-in unit for a hot chamber die casting machine similar to FIG. 1, but with a crank drive for the push rods,

6 shows a schematic illustration of the plastic spring used in FIGS. 1, 2 and 5,

7 shows a modified design of the plastic spring according to FIG. 6,

8 shows the course of the force path caused by the plastic spring according to FIG. 6,

9 shows the course of the force path when using a plastic spring according to FIG. 7, and

Fig. 10 shows an embodiment of a liquid spring which can be used instead of the plastic spring according to Fig. 6 or 7 between the push rod and the casting piston of the press-in units.

In Fig. 1, an electric motor 1, for example an asynchronous motor or other variants of servomotors, is provided with a gear (not shown in detail) and with a coupling part 2 which drives a threaded spindle 3 for a rotary movement. The threaded spindle 3 is sealed in a protective housing 5. On it a nut 4 cooperating with the thread of the spindle 3 is guided, which engages with a guide cam 6 in a groove 7 within the housing 5 and is thereby guided in the housing 5 so that it cannot rotate. The nut 4 is connected via an extension 8, which extends over the free end of the spindle 3, to a push rod 9, which in turn leads out of the housing 5 in a sealed manner and is provided with an extension 10 with a smaller diameter. A first disk 11 is movably guided on the extension 10 and bears against a pressure sensor 12, which can be designed, for example, in the manner of a piezoelectric element. This pressure sensor 12 is above a Signal line 13 with a not shown, because known multi-parameter controller in connection, which controls the motor 1.

In addition, a sleeve 14 with an end plate 15 is slidably mounted on the extension 10, a spring element in the form of a plastic ring 16 being arranged between the end plate 15 and the disc 11 resting on the pressure sensor 12 and also penetrated by the extension 10. The sleeve 14 is provided at the end facing away from the disc 15 with a connecting end 17 for connection to the casting piston, not shown, the free end of the extension 10 being provided with a shoulder 18 of larger diameter which holds the sleeve on the extension 10 and also can serve for a certain preload of the plastic ring 16. This shoulder 18 is a distance a away from an inner end surface 18 of the sleeve 14. This press-in unit is now put into operation in order to press a molten metal out of the crucible of a hot-chamber die casting machine through the casting cylinder and a riser pipe into the mold in a known manner, then the electric drive 1 is excited to rotate the spindle 3 via the multi-parameter controller (not shown), which leads to the nut 4 running downward from the position shown along the spindle 3 and thereby also pushing the push rod 9 downward, specifically at the speed required for the filling process of the casting mold.

If the mold is filled, the rotary drive of the spindle 3 must be switched from speed control to torque control and for this purpose the motor 1 is braked. Since both the engine and the gearbox not shown in detail and all displaced by the drive in rotary parts adhering a weight conditional moment of inertia, it is not possible, the further rotation of the spindle 3 from the order ^¬ switching timing immediately to stop. To avoid in this case that the casting piston, not shown, continues to press on the incompressible melt in the mold and thereby undesirable pressure peaks in the melt or force peaks occur in the drive mechanism, which could lead to damage, the spring element 16 is provided, which in this case compresses and takes up the path that the casting piston would otherwise have had to travel in addition. Due to the incompressibility of the molten metal in the mold, the pouring plunger, so to speak, stands still after the mold has been filled, while the push rod 9 and its extension 10 are still moved a certain distance, but which is absorbed by the spring element 16 due to the relative displacement between the sleeve 14 and extension 10 can be.

The arrangement is such that the distance still traveled by the drive is smaller than dimension a. The spring element 16 therefore compresses by an amount slightly less than a and is therefore put under tension. The design can take place in such a way that with the set spring travel - which is therefore less than a - a reaction force exerted by the spring element 16 acts on the sleeve 14 and thus on the casting piston, which is sufficiently large to provide the required pressure in the melt due to a force in the order of 7-8 tons (70-80 KN), for example. The plastic ring used in the exemplary embodiment can apply these forces without building too large. It would also be possible to use a liquid spring, in which the compressibility of liquids, in particular oil, is exploited at high pressures. The motor 1 can be adjusted to a holding torque, so that no complicated measures are required to maintain the holding pressure in the melt.

In order to keep the force exerted by the spring element 16 so large that the required pressure is generated in the melt, the pressure sensor 12 is provided, which emits a measure of the force that is exerted by the spring 16 onto the sleeve 14 and thus the casting piston is exercised. As previously explained, the disk 11 is slidably attached to the extension 10. arranges. The disks 11 and 15 are therefore subjected to the same axial force. This force can be adjusted to a very specific size via the previously mentioned multi-parameter controller and the drive motor 1, as long as it is ensured that the deflection path for the spring element 16 does not exceed the dimension a.

FIG. 2 shows the schematic illustration of a press-in unit similar to FIG. 1. The same reference numbers have therefore been retained for the same parts.

The difference is that a rack 20 is fixedly connected to the push rod 9. 1 is therefore not available. The rack 20, like the spindle 3 of FIG. 1, is sealed in the housing 5 and guided in the rack housing 25 which is tightly connected to the latter. Gear oil can therefore not escape and possibly penetrate the molten metal.

As shown in FIG. 3, the rack 20 is provided with a toothing on both sides and is in contact with a pinion 23 or 24, which is supported on a shaft 21 or 22, respectively. In this embodiment, the shaft 21 is driven by two motors 26 and 27, each of which is in drive connection with the shaft 21 via a coupling 28. In this case, power can be adjusted in each case by controlling the clutches 28 to the extent that the toothed rack is driven only via one of the electric motors or via both electric motors 26 and 27. With this configuration, higher dynamics and also higher acceleration and deceleration can be exerted on the rack 20. The adjustment speeds for the rack and push rod 9 can be kept relatively high.

FIG. 4 shows a rack and pinion arrangement similar to FIG. 3, except that here the rack 20 'is driven by pinions 29 and 30, which in turn is part of a gear consisting of further pinions 31, 32, 33 and of the gear wheels 34 and 35. is driven, in which the gear 35, which is fixed on the shaft 36, is in turn optionally driven by one or both of the electric motors 26, 27. With such a gear arrangement, gear ratios can be achieved which ensure that the pressing unit functions particularly well.

Fig. 5, in which reference numerals are also retained, which relate to the same parts as are already used in Fig. 1, now shows a deviation in the construction in that the push rods 9 are acted upon by a carriage 37 which in a straight guide 38 is guided in the direction of the axis of the push rods 9. This slide 37 is acted upon by a connecting rod 39, which is actuated by a crank disk, which in turn can be moved by an electric motor 41 via a gear, not shown, or two.

FIG. 6 shows the plastic ring 16 as it is used in all the exemplary embodiments shown in FIGS. 1, 2 or 5 as a spring element between the push rod 9 and the casting piston. This plastic ring 16 consists of a hardened polyurethane rubber, and when it is compressed in the direction of the arrow s it can produce the force path characteristic shown in FIG. 8. 8, the force F and s the deformation path of the plastic ring 16 are designated in FIG. 8.

Fig. 7 shows an embodiment in which the plastic ring 16 is replaced by two concentrically arranged ring parts 16a and 16b, which may also consist of tempered polyurethane rubber and, according to FIG. 9, can produce a different displacement / force characteristic. If the plastic ring 16a is compressed by the amount sl, the force F exerted by it increases to a certain amount, which is shown schematically in FIG. 9 when the distance sl is reached. However, the two plastic rings 16a and 16b continue to travel over the distance sl Compressed along the distance s2, then they act together as a much stronger spring, so that the increase in force per path unit is significantly larger. This configuration can be used to increase the pressure force exerted on the melt without the need for complex control measures for the drive.

Finally, FIG. 10 shows a liquid spring 42, as it can also be switched on between the push rod and the casting piston instead of a plastic spring element. This liquid spring 42 consists of a stable cylinder 43, which is equipped with a connection bore 44 for attaching a part provided with the connecting part 17 (FIG. 1), which in turn receives the casting piston, not shown. A piston rod 46, which is guided in a sealed manner in the cover 45, projects into the interior of the cylinder 43, which is closed by a cover 45 and is filled with a volume Vi of pressure oil. This piston rod is provided at its lower end with a plate-shaped extension 47, on which a compression spring 48 acts, which is supported on the cover 45. This compression spring 48 therefore presses the piston rod 46 into the volume Vi by a certain amount, so that the pressure of the liquid contained in the cylinder 43 is increased by the piston rod 46 acting as a displacer.

With this liquid spring arrangement, the compressibility of liquids at very high pressures is used, as already indicated at the beginning. Liquid springs, like the previously mentioned plastic spring bodies, are therefore suitable for absorbing the high forces that occur in die casting machines.

In the embodiment shown, the cylinder 43 has an opening 49 which is connected to a pressure relief valve 51 via a connecting line 50. Any liquid that escapes via the pressure relief valve 51 is collected in a schematically indicated container 52. gene and fed back via a pump 53 to the interior of the cylinder 43. Connected to the connecting line 50 is a pressure-voltage converter 54, which in turn can be connected to the control of the electric drive motors. In this way, the desired press-in force on the molten metal can be set and maintained properly via the drive.

However, there is also another line 55 connected to the connecting line 50, which, via a control valve 56, enables the connection of an additional volume V ₂ or - via the connecting line 57 - also the connection of further volumes, which are schematically marked with V _x . This configuration allows the force path characteristic exerted by the liquid spring 52 to be changed in a similar manner and to be adapted to the respective requirements, as has already been explained with reference to FIG. 9 for the two-part plastic ring.

Due to the configuration according to the invention there is therefore always a fixed relationship between the deflection path (which is preferably smaller than a - FIG. 1) of the spring element 16 or 42 and the axial force exerted on the casting piston. The invention therefore enables the drive of a press-in unit for hot chamber die casting machines with electromechanical means and offers the advantage of a relatively simple control and regulation.

Claims

claims

1. Press-in unit for a die casting machine, in particular for a hot chamber die casting machine for processing metal melts with a casting piston for pressing the casting material into a mold, which can be acted upon by a push rod (9) which is connected to a linear drive driven by an electric motor, which according to Filling phase of the mold to achieve a pressure in the casting material is held in a pressure phase, a spring element being connected between the casting piston and the push rod (9), characterized in that the spring element (16, 16 °, 16b as an elastic plastic component or as a Liquid spring (42) is designed and designed so that the reaction force generated by its tension on the casting piston is large enough to apply the axial force required to achieve the necessary pressure in the casting material.

2. Press-in unit according to claim 1, characterized in that the spring element (16, 42) is associated with a sensor (12, 54) connected to the control of the drive (1) which detects the axial force exerted by the spring element.

3. Press-in unit according to claim 1 and 2, characterized in that the electric drive (1, 26, 27) is controllable in such a way that the spring element (16, 42) is not pressed together beyond a predetermined dimension (a).

4. Press-in unit according to one of the preceding claims, characterized in that the spring element is an elastic plastic ring (16) which is held between two disks (11, 15), one of which (11) is held on the push rod (9) and the another (15) is fixedly connected to a sleeve (14) which is guided telescopically on the push rod.

5. Press-in unit according to claim 4, characterized in that the plastic ring is constructed from two or more parts (16a, 16b) which are deformable one after the other.

6. Press-in unit according to claim 1, 4 or 5, characterized in that the plastic component (16, 16a, 16b) consists of a tempered polyurethane rubber.

7. Press-in unit according to claim 4, characterized in that the push rod (9) has a plastic ring (16) penetrating extension (10) of smaller diameter on which the sleeve (14) is guided.

8. Press-in unit according to claim 4, characterized in that the spring element (16) and the arrangement of the sleeve (14) are matched to one another in such a way that the extension (10) can only be adjusted a certain distance (a) relative to the sleeve (14) .

9. Press-in unit according to claim 2, characterized in that the sensor (12) on the between the push rod (9) and the extension (10) formed smaller diameter

Paragraph (20) and on the shoulder (10) guided disc (11) which abuts the spring element (16).

10. Press-in unit according to claim 1, characterized in that a linear drive is provided from a spindle (3) and a nut (4) guided thereon, existing threaded drive.

11. Press-in unit according to claim 1, characterized in that a rack and pinion drive is provided as the linear drive.

12. Press-in unit according to claim 11, characterized in that the drive of the rack (20, 20 ') takes place via a gear which acts on both sides of the rack.

13. Press-in unit according to claim 12, characterized in that two motors (26, 27) are optionally provided for driving the transmission.

14. Press-in unit according to claim 1, characterized in that the linear drive is a slide (37) which is driven by a connecting rod (39) of a crank mechanism (40) and which is held in a straight guide (38).

15. Press-in unit according to claim 1, characterized in that the liquid spring (42) consists of a cylinder (43) with a plunger rod (46), the plunger rod being pressed under the force of a spring (48) into the interior of the cylinder (43) is to put the liquid (Vi) under a certain pre-tension even before it is loaded by the push rod.

16. Press-in unit according to claim 15, characterized in that the cylinder (43) of the liquid spring (42) is provided with an opening (49) to which an overpressure relief valve (51) and a pump (53) are connected for the possible return of leaked liquid .

17. Press-in unit according to claim 16, characterized in that a pressure-voltage converter (54) is connected to the connecting line (50) to the pressure limiting valve (51) and is connected to the control of the electric drive motor (3, 26, 27).

18. Press-in unit according to claim 16, characterized in that additional liquid volumes (V ₂ , V _x ) are connected to the connecting line (50), the controllable connection of which contributes to changing the suspension characteristics.