EP0576795B1 - Method and apparatus to controle the process of a die casting machine - Google Patents

Description

The invention relates to a method and a device for carrying out the method for process control of a die casting machine according to the preamble of claim 1 and claim 11,

From DE-PS 20 21 182 of the applicant, a device for adjusting the ram speeds and pressures in die casting machines has become known, which operates according to the so-called three-phase system in cold chamber die casting machines. This operating mode is used to set the different plunger speeds and pressures required for die casting, with only the plunger of the press cylinder acting on the plunger being acted upon via pressure medium lines in the first and second working phases, and a multiplier piston designed as a stepped piston being acted upon during the third working phase. In this known device, the plunger is in the first and second working phase via a bore with a check valve in the multiplier piston with pressure medium acted upon. Due to the increasing pressure in the cylinder space of the press cylinder, the bore in the multiplier piston closes, so that during the third phase (holding pressure phase) the multiplier piston, with its piston surface ratio, acts on the press piston and thus on the casting piston.

The three-phase system is understood to mean the sequence of the casting process, particularly in the case of a horizontal cold chamber die casting machine, with a pre-filling phase of the casting chamber (first phase), a mold filling phase of the casting mold (second phase) and a holding pressure phase of the casting mold (third phase).

The known device according to DE-PS 20 21 182 is also referred to as a two-circuit casting unit, since in the first circuit during the first and second working phases of the plunger and in the second circuit during the third working phase of the multiplier piston with pressure medium from different piston accumulators. In the known device, the multiplier piston is designed with a piston rod provided on both sides of the piston, so that there is a front annular surface on the multiplier piston itself and a further circular surface on the rear piston rod for pressurizing the multiplier piston. This has the advantage that a separate regulation of the annular pressure space on the multiplier piston and the additional rear cylinder space behind the piston rod is made possible. To regulate these pressure chambers, passage valves are provided, which are attached to the piston rod of the plunger or to the piston rod of the casting piston connected to it by displacement sensors. Via the valve control, pressure is first applied to the rear cylinder space behind the rear piston rod of the multiplier piston, which medium passes through the central bore to the cylinder space of the press cylinder and thus to the press piston (first and second Work phase). During the third working phase (holding pressure phase), a passage valve for pressurizing the annular cylinder chamber of the multiplier piston and the rear cylinder chamber with pressure medium is opened by a displacement sensor or by pressure-dependent switching, the center bore in the multiplier piston automatically closing when the pressure rises.

In this known device, the pressure medium is pushed out in front of the plunger during the first and second working phases via an outlet bore into an oil container without special regulation and pressure control and is admitted again when the plunger is reset. The pressure medium in front of the multiplier piston in the cylinder chamber of the multiplier is also conveyed into an oil tank via a throttle valve when it moves forward in the third working phase (holding pressure phase) and is pumped in again when the multiplier piston is reset. The regulation and control of plunger and multiplier piston is therefore done in the known device only via the time the pressure medium is connected to the individual pressure chambers in the press cylinder and in the multiplier cylinder or to the rear cylinder chamber, additional throttle valves allowing a certain amount regulation by a pressure drop. There is no other influence in the control system due to the lack of control options.

Multiplier arrangements have also become known from the literature reference Ernst Brunnhuber: "Praxis der Druckgußfertigung", 3rd edition, 1980, which are explained in more detail on pages 70 to 78. In particular, pages 73, 75 show multiplier arrangements on a casting drive, by means of which it is also possible to work in a three-phase system. The Activation of the pressure accumulator for the holding pressure phase also via an impulse from the casting piston by opening a shot valve. In the illustration on page 75 of this literature reference, additional regulation of the multiplier pressure by means of a counterpressure by means of a further pressure accumulator is proposed, by means of which the forward movement of the multiplier piston is braked and pressure peaks are thus avoided. To a certain extent, this allows regulation of the pressure build-up time in the third work phase. According to the literature, pressure rise times of about 10 ms or less are achieved by the pressure accumulator. A corresponding pressure-time diagram is given on page 77 of the Brunnhuber reference for explanation.

In one embodiment, as shown in the Brunnhuber literature, page 78, there is no through hole in the multiplier piston and the pressurization of the plunger is carried out directly in the cylinder space behind it. In this case, a first pressure accumulator acts directly on the cylinder space of the plunger, also called the drive piston. A second pressure accumulator acts on the multiplier piston through the corresponding pulse.

In addition to the cited references, a large number of references have become known which deal with process control both in injection molding and in die casting. Such a casting process monitoring has become known in particular from the literature reference Klein: "Automatic casting process monitoring during die casting", Gießerei 68, (1981), No. 18, page 531 ff., In which a large number of parameters, such as mold filling time, pressure build-up time, pressure of the Melt, degree of mold filling, temperature of the melt, etc., recorded as actual values and compared with predetermined target values.

If the quality of the product is poor, the actual values and possibly also the target values are corrected in order to improve the casting result in subsequent casting processes. The casting conditions are therefore monitored during the die casting process and corrected if necessary in subsequent casting processes.

All known casting process monitoring methods have the disadvantage that the casting parameters determined during the casting process cannot act directly on the casting process that is currently taking place, since a feedback of the determined casting parameters is not provided.

The invention is based on the object of proposing an improved method for monitoring the casting process and in particular for regulating the process of a die casting machine and a corresponding device for carrying out the method.

This task is solved on the basis of the generic concept of the respective process or device main claim by the characterizing features of the respective property right claims.

Advantageous and expedient developments of the invention are specified in the subclaims.

The method according to the invention or the corresponding device for carrying out the method has the advantage over the known prior art that a so-called real-time controlled two-circuit casting unit is created, with which a direct influence on the casting parameters is made possible during the casting process. This happens in particular in that the movement of the plunger or drive piston for the casting piston can be controlled and regulated in every phase of its movement. The same applies to the movement of the multiplier piston during its movement in the third working phase. The plunger or drive piston is quasi "clamped" in the associated press cylinder and the multiplier piston in the associated multiplier cylinder space between a front and a rear adjustable pressure cushion, so that during the three-phase movement the respective pistons move forward or backward in both their speed as well as their acceleration behavior can be regulated separately and in a coordinated manner. The cylinder space in front of the plunger and in front of the multiplier piston is accordingly used as a controllable pressure chamber, the regulation known in this regard being improved in the case of multiplier pistons in such a way that the control values can be fed back directly.

This regulation is possible through the use of extremely fast reacting so-called servo-proportional control valves in the respective control circuits, which are also referred to as so-called "continuous valves".

With this control option, pressure peaks at the end of the mold filling phase can be reduced or prevented both by braking the plunger and by possibly reversing the multiplier piston depending on these movements. The third working phase with the build-up of holding pressure can also be carried out in an optimally short time by coordinating the movement of the two pistons, the control times taking less than 5 ms.

Any change in the speed of the casting plunger can therefore be achieved by controlling the plunger in the first and second working phases alone and the multiplier plunger in the third working phase by coordinating the hydraulic quantity flowing to these two cylinder spaces, with higher accelerations are possible than is possible with a hydraulic medium supply from only one hydraulic medium reservoir.

Figur 1

eine schematische Darstellung einer Vorrichtung zur Durchführung des Verfahrens zur erfindungsgemäßen Prozeßsteuerung,

Figur 2

weitere Einzelheiten aus Figur 1,

Figur 3

eine weitere Ausführungsvariante und

Figur 4

einen zentralen Rechner mit Regelfunktion für die zu verarbeitenden Daten.

Further details and advantages of the invention are given in the following description of an embodiment of the invention. In detail shows

Figure 1

1 shows a schematic representation of a device for carrying out the method for process control according to the invention,

Figure 2

further details from FIG. 1,

Figure 3

a further embodiment variant and

Figure 4

a central computer with control function for the data to be processed.

Description of the invention:

The casting drive 1 shown in FIG. 1 is used to actuate a casting set 2, consisting of a casting chamber 3 with the molten metal 4 contained therein and a casting piston 5 for inserting the molten metal 4 into a mold cavity, not shown in any more detail. The casting piston 5 is connected to the casting drive 1 via a casting piston rod 6. The casting drive 1 consists of a front press cylinder 7, with a press piston 8 guided therein, which serves as a drive piston 8 for the associated piston rod 9. The piston rod 9 is connected to the casting piston rod 6. The press cylinder 7 has a front cylinder chamber 10 and a rear cylinder chamber 11, which are separated by the press piston 8. The front cylinder space 10 is connected to a pressure medium connection 14 via a radial and subsequently axial bore 12 in the cylinder head 13.

The press cylinder 7 is followed by a multiplier device 15, consisting of a closed multiplier cylinder housing 16 with a multiplier piston 17 axially displaceable therein, which separates the multiplier cylinder chamber into a front closed cylinder chamber 18 and a rear closed cylinder chamber 19. The multiplier piston 17 points forward in a manner known per se, i. H. towards the casting set 2, pointing first piston rod 20, which extends through the cylinder wall of the multiplier cylinder housing into the rear cylinder space 11 of the press cylinder 7. The multiplier piston 17 also has a rear piston rod 21, which likewise extends laterally via the multiplier cylinder housing into a rear cylinder chamber 22 of an additional connection housing 23. The multiplier piston 17 with the front piston rod 20 and the rear piston rod 21 is penetrated by a central longitudinal bore 24, in which a check valve 25 is arranged. In the rearmost position of the multiplier piston 17, the check valve 25 is pressed away from the valve seat by means of a rod 26 projecting through the longitudinal bore 24 and thus opened.

The rear cylinder space 19 of the multiplier cylinder can be acted upon by the pressure medium connection 28, the rear cylinder space 22 of the additional connection housing 23 via the pressure medium connection 29.

Each position of the casting piston rod 6 or the piston rod 9 is detected by means of a displacement / speed / acceleration measuring device 30. The same applies to the measuring device 31 for detecting any position and the path, the speed, the acceleration of the multiplier piston 17. A displaceable protrudes for this Measuring rod 32 from the multiplier piston 17 parallel to the longitudinal axis to the corresponding measuring device 30. The measuring device can be carried out, for example, as described in DE 32 09 834 A1.

The basic structure of the casting drive for the casting set is also described in the aforementioned patent specification PS 20 21 182 by the applicant. As far as it is relevant for the present invention, reference is hereby expressly made to the entire content of this patent specification.

According to the invention, a series of quickly controllable servo-proportional valves, also called continuous valves, is used to produce a real-time controlled two-circuit casting unit. By using at least two continuous valve assemblies 33, 34 and by matching the corresponding piston surfaces A _{1 of} the plunger 8 and the annular surface A _{2 of} the multiplier piston 17 and the circular surfaces A _{2.1 of} the front piston rod 20 and A _{2.2 of} the rear piston rod 21 the motion sequence of the casting drive coordinates. In Figure 2, the basic structure or the arrangement of the casting drive is shown again.

The pressure in the pressure chambers 10, 11 or 18, 19 or 22 can be detected by means of p / U transducer and evaluated as a control signal.

The servo-proportional valve 33 accordingly regulates the pressure conditions in the front cylinder chamber 10 (pressure p ₂ at the transducer 44) of the press cylinder 7 and causes the press piston 8 to be clamped between the pressure chamber 10 (pressure p ₂ ) and the pressure chamber 11 (pressure p ₁ ). The latter can be detected by means of the p / U converter 45 and can therefore be regulated. The movement of the plunger 8 can thus be controlled.

Similarly, the servo-proportional valve 34 regulates the rear pressure chamber 19 of the multiplier piston 17, the front pressure chamber 18 of the multiplier piston preferably also being regulated via a further servo-proportional valve 35. These continuous valves can also be assigned p / U transducers, which are shown in more detail in FIG. 1, in order to detect and thus regulate the pressure conditions in the pressure chambers 18, 19.

Finally, for the regulation of the rear cylinder chamber 22, the regulation of a fast-switching servo-proportional valve 36 at the pressure medium connection 29 is also used, so that the application of pressure chamber 22 via a first pressure accumulator 37 and the application of pressure chamber 19 via a second pressure accumulator 38 via one fast switching proportional valve control can take place. Additional p / U transducers can also be used here.

, $\text{p = f(t)}$

in Figur 4 prinzipiell dargestellt ist. Als Meßgröße dient weiterhin der Druck in den einzelnen Druckräumen. Die zugehörigen Meßdaten aus den Meßeinrichtungen 30, 31 bzw. den p/U-Meßwertumformern 44, 45 usw. führen über Meßleitungen 39, 40 zu einem Rechner 41 (siehe Figur 1 und 4), in welchem die übrigen erforderlichen Gießparameter ebenfalls erfaßt und ausgewertet werden. Die Stetig-Ventil-Baugruppen bzw. Servo-Proportional-Ventile 33 bis 36 werden dann vom Rechner 41 angesteuert, so daß der Bewegungsablauf des Gießantriebs in jeder Phase während des Gießprozesses kontrolliert und geregelt werden kann. Beispielsweise können durch entsprechende zusätzliche Drucksensoren im Formenhohlraum der dortige Druck P_F oder durch entsprechende Temperatursensoren die dortige Temperatur T_F der Schmelze erfaßt und über die Steuerleitungen 42, 43 dem Rechner 41 zugeführt werden. Druckspitzen am Ende der Formfüllphase können dann sowohl durch Abbremsen des Preßkolbens 8 als auch durch ein eventuelles Rückwärtssteuern des Multiplikatorkolbens 17 in jeweils gegenseitiger Abhängigkeit dieser Bewegungen abgebaut oder ganz vermieden werden. Auch der Nachdruckaufbau kann durch Abstimmung der Bewegungen dieser beiden Kolben in optimal kurzer Zeit erfolgen, wobei die Regelung der Proportional-Ventile 33 bis 36 in einer Zeit unterhalb von 5 ms erfolgt.As a result of these measures, both the plunger 8 and the multiplier piston 17 are “clamped” on both sides, so that a sensitive movement can take place in all axial directions, ie forwards and backwards. The control or regulation of the casting drive is carried out by continuously determining the position "s", the speed "v" or the acceleration of both the casting piston rod 6 and the multiplier piston 17 during the casting process, as is also the case in the two diagrams $\text{v = f (s)}$

, $\text{p = f (t)}$

is shown in principle in Figure 4. The pressure in the individual pressure rooms continues to serve as the measured variable. The associated measurement data from the measurement devices 30, 31 or the p / U transducers 44, 45 etc. lead via measurement lines 39, 40 to a computer 41 (see FIGS. 1 and 4), in which the other required casting parameters are also recorded and evaluated will. The continuous valve assemblies or servo proportional valves 33 to 36 are then controlled by the computer 41 so that the movement sequence of the casting drive can be checked and regulated in every phase during the casting process. For example, the corresponding pressure P _F in the mold cavity or the corresponding temperature sensors T _{F in} the melt can be detected by corresponding additional pressure sensors in the mold cavity and fed to the computer 41 via the control lines 42, 43. Pressure peaks at the end of the mold filling phase can then be reduced or avoided altogether by braking the plunger 8 as well as by possibly reversing the multiplier piston 17 depending on these movements. The build-up of the holding pressure can also take place in an optimally short time by coordinating the movements of these two pistons, the regulation of the proportional valves 33 to 36 taking place in a time of less than 5 ms.

The speed changes of the plunger 8 and thus the casting piston 5 to influence the casting speed can be influenced by tuning the amount of hydraulic medium flowing to the press cylinder 7 to act on the plunger 8 and to the multiplier cylinder to act on the multiplier piston 17, with higher accelerations of the two pistons being possible than this with the hydraulic medium supply from only one hydraulic medium reservoir. Appropriate clamping of the two pistons controls and influences any movement of the casting drive.

In particular, the piston surfaces A _2.1 and A _2.2 are to be designed so that, for. B. during the forward movement of the multiplier piston, the amount of the medium flowing in at A _2.2 , ie the rear piston rod of the multiplier piston, for movement to the amount of the medium displaced at A _2.1 in the range of the ratio 0.8 to 1.2: 1. The behaves Circular cylinder area A _{1 of} the plunger 8 to the sum of the areas from A ₂ + A _2.2 in a ratio of 1: 2.5 to 4. This coordination of the surfaces enables optimal operation of the casting drive.

In a simplified, alternative exemplary embodiment according to FIG. 3, only the front pressure chamber 10 of the press cylinder 7 and the rear pressure chamber 19 of the multiplier device 15 are regulated via the continuous valves 33, 34 shown. Here again, the measured value is recorded for "clamping" the drive piston 8 via the two p / U transducers 44, 45 with the detected actual value signals p ₁ , p ₂ , which result in control value signals y ₁ , y ₂ at the output of the computer 41 to lead. The corresponding control functions are shown in Fig. 4.

The diagrams shown in FIG. 4 relate to target value specifications for controlling the casting process.

dargestellten Kurven 1 bis 4 stellen Beispiele für Soll-Wert-Vorgaben dar und zwar den Soll-Wert vom Druckverlauf p über die Zeit t. Diese Druckverläufe $\text{p = f(t)}$

können während des Betriebs geregelt gefahren werden.The ones in the diagram $\text{p = f (t)}$

Curves 1 to 4 shown are examples of target value specifications, namely the target value of the pressure curve p over time t. These pressure curves $\text{p = f (t)}$

can be driven in a controlled manner during operation.

als Soll-Wert-Vorgabe der Geschwindigkeit des Gießkolbens über den Gießkolbenweg. Die Werte s₁ bis s₄ stellen bestimmte Wegpunkte des Gießkolbens dar, wobei zu jedem Wegpunkt eine bestimmte Geschwindigkeit zugeordnet werden kann. Beispielsweise wird im Punkt s₄ die Gießkolbengeschwindigkeit kurz vor Formfüllende auf eine Restgeschwindigkeit abgebremst. Diese Vorgänge werden ebenfalls geregelt gefahren.The same applies to the diagram $\text{v = f (s)}$

as target value specification of the speed of the casting piston via the casting piston path. The values s ₁ to s ₄ represent certain waypoints of the casting piston, and a certain speed can be assigned to each waypoint. For example, in point s _4, the casting piston speed is braked to a residual speed shortly before the mold filling end. These processes are also carried out in a regulated manner.

Claims (14)

1. Method for controlling the process of a die casting machine, with a casting chamber (3) for the molten metal (4) and a casting piston (5), with a pressing cylinder (7) following the casting chamber (3), with a pressing piston (8) for driving the casting piston (5) and with a multiplier device (15) following the pressing cylinder (7), with a multiplier piston (17) guided therein, the casting drive (1) being constructed as a two-circuit casting unit and a pressure medium acting by means of a first valve control mechanism (36) directly on the pressing piston (8) and by means of a further valve control mechanism (34) on the multiplier piston (17), characterised in that the two-circuit casting drive is controlled by means of quickly adjustable servo-proportional valves (33 to 36) (continuous valves), the control taking place by means of at least one servo-proportional valve (33, 34) located in the inlet or outlet (14) to the pressure chamber (10) in front of the pressing piston (8) as well as in the inlet or outlet (28) of the pressure chamber (19) behind the multiplier piston (17), that the entire movements of the pressing piston (8) and thus of the casting piston (5) as well as the movements of the multiplier piston (17) are ascertained by way of distance/speed measuring devices (30, 31) as well as the pressures in the pressure chambers of the pressing cylinder (7) and/or multiplier device (15), that the control or regulation of the servo-proportional valves (33, 34) takes place depending on each other and depending on the movements of the pressing piston (8) or of the multiplier piston (17) as well as on the pressures and possibly further casting parameters in the moulding cavity by means of a computer (41), so that the current injection process during the pre-filling phase and/or the mould-filling phase and/or the subsequent pressure phase takes place by a controlled movement of the pressing piston (8) in conjunction with the movement of the multiplier piston (17) at the required reference values.
2. Method according to Claim 1, characterised in that the multiplier device (15) comprises a multiplier piston (17) with an effective rear pressing surface A₂ in the shape of a circular ring, in a closed multiplier cylinder housing (16), in which case a first front piston rod (20) of the multiplier piston (17) with an effective front pressure surface A_2.1 opens into the pressure chamber (11) of the pressing cylinder (7) and a second, rear piston rod (21) of the multiplier piston (17) with an effective pressure surface A_2.2 opens into a further, rear pressure chamber (22) and the multiplier piston (17) with its two piston rods (20, 21) comprising a common longitudinal axis, having a longitudinal bore (24) with a non-return valve (25).
3. Method according to Claim 1 or 2, characterised in that provided in the inlet or outlet of the pressure chamber (18) located in front of the multiplier piston (17) is a further rapidly adjustable servo-proportional valve (35) and/or provided in the inlet or outlet of the rear pressure chamber (22) for the rear piston rod (21) is a further rapidly adjustable servo-proportional valve (36).
4. Method according to one of Claims 1 to 3, characterised in that by means of the servo-proportional valve control arrangement on the pressing cylinder (7) and on the multiplier device (15), at the end of the mould-filling phase, a deceleration of the pressing piston (8) by a counter pressure actuation of the pressing piston (8) takes place in the pressure chamber (10), in order to minimize pressure peaks in the casting mould.
5. Method according to one of Claims 1 to 4, characterised in that by means of the servo-proportional valve control arrangement on the multiplier device (15), a deceleration or a reverse control of the multiplier piston (17) takes place, in order to minimize pressure peaks in the casting mould.
6. Method according to one or more of the preceding Claims, characterised in that by means of the servo-proportional valve control arrangement, the movement of the pressing piston (8) with respect to the movement of the multiplier piston is coordinated within optimum short times of t≤ 0.5 ms with each other so that optimum subsequent pressure values can be achieved in the third working phase.
7. Method according to one or more of the preceding Claims, characterised in that the pressing piston (8) and/or the multiplier piston (17) is "clamped" during its movement constantly between two pressure cushions, in which case preferably the bilateral pressure cushions of the pressure chambers (10, 11) or (18, 19) and thus the movements of the pistons (8, 17) being adjustable by means of a servo-proportional valve control arrangement of the valves (33 to 36) within a regulating time of preferably t≤ 5 ms.
8. Method according to one or more of the preceding Claims, characterised in that the pressing piston (8) and/or the multiplier piston (17) is variable in its speed within a time interval of t≤ 5 ms.
9. Method according to Claim 2, characterised in that the ratio of the piston surface A_2.1 of the front piston rod (20) to the piston surface A_2.2 of the rear piston rod (21) is measured such that at the time of the forwards movement of the multiplier piston (17), the quantity m₁ of the pressure medium flowing towards the rear piston rod (21) with respect to the quantity m₂ of the pressure medium compressed in the pressure chamber (11) at the front piston rod (20) has a ratio of m₁:m₂ = 0.8 to 1.2:1.
10. Method according to one or more of the preceding Claims, characterised in that the effective pressure surface A₁ of the pressing piston (8) in the pressure chamber (11) with respect to the surface difference of the multiplier circular ring surface A₂ in the annular chamber (19) plus the effective pressure surface A_2.2 of the rear piston rod (21) in the pressure chamber (22) has a ratio of A₁:(A₂ + A_2.2) = 1:(2.5 to 4).
11. Apparatus for carrying out the method according to one or more of the preceding Claims, with a casting lining (2), a subsequent casting drive (1), consisting of a pressing cylinder (7) with pressing piston (8) and a multiplier device (15) with multiplier piston (17), the casting drive being constructed as a two-circuit casting unit, characterised in that a valve control arrangement for the two-circuit casting drive is provided, which consists of rapidly adjustable servo-proportional valves (33 to 36) with an adjusting time t≤ 5 ms, in which case at least the inlet or outlet of the pressing cylinder (7) as well as the inlet or outlet of the multiplier device (15) is provided with rapidly adjustable servo-proportional valves (33, 34) and in which case the entire movements of the casting piston rod (6) and of the multiplier piston (17) can be monitored by way of distance/speed measuring devices (30, 31), and a computer being provided for controlling or regulating the servo-proportional valves depending on the movements of the casting piston rod (6) and of the multiplier piston (17).
12. Apparatus according to Claim 11, characterised in that the multiplier device (15) is provided with a multiplier piston (17) and a front piston rod (20) connected thereto and a rear piston rod (21) as well as a central longitudinal bore (24) with a non-return valve (25), the front pressure chamber (18) and the rear pressure chamber (19) being adjustable by means of servo-proportional valves (34, 35) for clamping the multiplier piston (17).
13. Apparatus according to Claim 10 or 11, characterised in that the pressure chamber (22) lying behind the rear piston rod (21) of the multiplier piston can be regulated by means of a servo-proportional valve control arrangement (36) as a pressure chamber.
14. Apparatus according to Claim 10 or 11, characterised in that the pressure in the pressure chambers (10, 11) or (18, 19) for "clamping" the pressing piston (8) or the multiplier piston (17) can be monitored by means of signal modulators (44, 45 etc.) and can be supplied as an actual value to the computer (41).

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