EP0576795B2 - Method and apparatus to controle the process of a die casting machine - Google Patents

Description

The invention relates to a method and an apparatus to carry out the process control process a die casting machine.

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

Three-phase system is therefore understood the course of the casting process, especially in the horizontal Cold chamber die casting machine with a pre-filling phase the casting chamber (first phase), one Mold filling phase of the mold (second phase) and one Postpress phase of the mold (third phase).

The known device according to DE-PS 20 21st 182 is also used as a two-circuit casting unit referred to as in the first circle during the first and second phase of the plunger and in the second Circle during the third working phase of the multiplier pistons with pressure medium from different piston accumulators be charged. Here, the known device of the multiplier piston with a Piston rod provided on both sides of the piston executed so that for the pressurization of the multiplier piston a front ring surface on Multiplier piston itself and another circular area on the rear piston rod. This has the advantage that separate regulation of the annular Pressure chamber on the multiplier piston and the additional one rear cylinder space behind the piston rod is made possible. To regulate these pressure rooms are Pass valves provided by position transducers the piston rod of the plunger or on this connected piston rod of the casting piston attached are. This is done via the valve control first the rear cylinder space behind the rear Piston rod of the multiplier piston with pressure medium acted upon, which via the central bore to the cylinder space of the press cylinder and thus to Press plunger arrives (first and second working phase). During the third work phase (reprint phase) is by a displacement sensor or by pressure-dependent Switch another passage valve to act on of the annular cylinder space of the Multiplier piston and the rear cylinder space opened with pressure medium, the center hole in Multiplier pistons automatically when the pressure rises closes.

In this known device, the pressure medium in front of the plunger during the first and second working phase via an outlet hole in an oil tank without special regulation and pressure control pushed out and when resetting of the plunger again. The Pressure medium in front of the multiplier piston in the cylinder chamber of the multiplier as it moves forward in the third work phase (reprint phase) also via a throttle valve in an oil tank promoted and when resetting the multiplier piston pumped back in accordingly. The regulation and control of plungers and multiplier pistons therefore happens exclusively in the known device about the time the Print medium to the individual print rooms in the Press cylinder and in the multiplier cylinder or rear cylinder space, with additional throttle valves a certain amount regulation through a pressure drop enable. Another influence in the Control is due to the lack of control options not provided.

From the Ernst Brunnhuber reference: "Praxis der Druckgußfertigung ", 3rd edition, 1980, are also Multiplier arrangements known on pages 70 to 78 are explained in more detail. In particular are on pages 73, 75 multiplier arrangements a casting drive shown, by means of which also in Three-phase system can be worked. there the pressure accumulator is activated for the Reprint phase also via an impulse from Pouring plunger by opening a shot valve. In the Presentation on page 75 of this reference is about additional regulation of the multiplier pressure by a back pressure by means of a proposed further pressure accumulator, by means of which the forward movement of the multiplier piston slowed down and pressure peaks avoided. To some extent, this can result in regulation the pressure build-up time in the third work phase be made possible. According to the literature Pressure rise times through the pressure accumulator of approx. 10 ms or less achieved. A corresponding one Pressure-time diagram is on page 77 of the literature reference Brunnhuber stated for explanation.

In one embodiment as shown in the Brunnhuber reference, page 78, refers to a Through hole in the multiplier piston omitted and the pressurization of the plunger immediately made in the cylinder room behind. In this case, a first pressure accumulator works directly on the cylinder space of the plunger, also called drive piston. A second pressure accumulator acts on the Multiplier piston.

In addition to the cited references, there is a Numerous literature references become known with process control both when injection molding also deal with die casting. In particular from the literature reference Klein: "Automatic casting process monitoring die casting ", foundry 68, (1981), No. 18, page 531 ff., Is such a casting process monitoring became known in which a variety of parameters, such as mold filling time, Pressure build-up time, pressure of the melt, degree of mold filling, Temperature of the melt etc., as actual values recorded and compared with predetermined target values become.

If the quality of the product is poor the actual values and possibly also the target values are corrected, for an improvement in subsequent casting processes to achieve the casting result. The Pouring conditions are accordingly during the Die casting process monitored and in subsequent Casting processes corrected if necessary.

All known casting process monitoring methods have the disadvantage that during the casting process determined casting parameters not immediately can influence the casting process currently taking place, since a feedback of determined casting parameters is not provided.

From DE-3142811 A1 is still a method and a device for regulation the piston movement during the Press-in process on a die casting machine became known in which the Movements as well as the plunger as also of the multiplier piston an associated proportional valve is controlled or regulated. About one additional plunger exhaust valve can the braking of the casting piston at the end of the mold filling phase can be controlled.

The invention has for its object an improved Processes for casting process monitoring and especially for process control of a die casting machine and a corresponding device for Propose implementation of the procedure.

This task will through the characteristics the respective property right claims 1 and 11 solved.

In the subclaims are advantageous and Appropriate developments of the invention are given.

The method according to the invention or the corresponding one Device for performing the method has the compared to the known prior art Advantage that a so-called real-time controlled two-circuit casting unit is created with which one immediate influence on the casting parameters during of the casting process is made possible. This happens especially in that the movement of the plunger or drive piston for the casting piston controlled in every phase of its movement and can run regulated. The same applies to the movement of the multiplier piston during its movement in the third phase of work. The plunger or Drive piston is in the associated press cylinder and the multiplier piston in the associated multiplier cylinder space quasi between a front and a rear adjustable pressure pads practically "clamped", so that during the three-phase movement the respective Piston in their forward movement or too Backward movement both in their speed as well as in their acceleration behavior separately and can be regulated in a coordinated manner. The cylinder space in front of the plunger and in front of the Multiplier piston is therefore used as an adjustable pressure chamber used, the known in this regard Control in multiplier pistons improved accordingly is that an immediate feedback of the Control values can take place.

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

This control option can pressure peaks at the end of the mold filling phase Braking the plunger as well as possible Reverse control of the multiplier piston in interdependence of these movements is reduced or be prevented. The third phase of work with the pressure build-up can by a Coordination of the movement of the two pistons in optimal a short time, the control times under 5 ms is done.

Any change in speed of the casting piston can therefore be controlled and regulated of the plunger alone in the first and second Working phase and the multiplier piston in the third Working phase by coordinating the two Amount of hydraulic fluid flowing into the cylinder chambers, where higher accelerations are possible than this with a hydraulic medium supply from only a hydraulic medium reservoir is possible.

Figur 1

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

Figur 2

weitere Einzelheiten aus Figur 1,

Figur 3

einen zentralen Rechner mit Regelfunktion für 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 central computer with control function for data to be processed.

Description of the invention:

The casting drive 1 shown in FIG. 1 serves for actuating a casting set 2, consisting of a casting chamber 3 with molten metal contained therein 4 and a plunger 5 for inserting the Metal melt 4 in a not shown Mold cavity. The casting piston 5 is via a casting piston rod 6 connected to the casting drive 1. The Casting drive 1 consists of a front press cylinder 7, with a plunger 8 guided therein, which as Drive piston 8 for the associated piston rod 9 serves. The piston rod 9 is with the casting piston rod 6 connected. The press cylinder 7 has a front Cylinder chamber 10 and a rear cylinder chamber 11 on, which are separated by the plunger 8. The front one Cylinder chamber 10 is radial and subsequent axial bore 12 in the cylinder head 13 with a Media port 14 connected.

A multiplier device closes the press cylinder 7 15, consisting of a closed Multiplier cylinder housing 16 with one in it axially displaceable multiplier piston 17, the Multiplier cylinder room in a front closed Cylinder chamber 18 and a rear closed Separates cylinder space 19. The Multiplier piston 17 in a manner known per se forward, d. H. towards the pouring set 2, pointing first piston rod 20, which extends through the cylinder wall of the multiplier cylinder housing in the rear Cylinder chamber 11 of the press cylinder 7 into it extends. The multiplier piston 17 also has a rear piston rod 21, which is also laterally into one via the multiplier cylinder housing rear cylinder space 22 of an additional connection housing 23 extends. The multiplier piston 17 with front piston rod 20 and rear piston rod 21 is penetrated by a central longitudinal bore 24, in which a check valve 25 is arranged is. In the rearmost position of the multiplier piston 17 is the check valve 25 by means of a Longitudinal bore 24 protruding rod 26 from Valve seat pushed away and thus opened.

The rear cylinder space 19 of the multiplier cylinder is via the pressure medium connection 28, the rear Cylinder chamber 22 of the additional connection housing 23 via the pressure medium connection 29 with pressure medium acted upon.

Each position of the casting piston rod 6 or the piston rod 9 is by means of a distance / speed / acceleration measuring device 30 recorded. The same applies to the measuring device 31 for detection any position as well as the way, the speed, the acceleration of the multiplier piston 17. For this purpose, a displaceable measuring rod 32 protrudes from the multiplier piston 17 parallel to the longitudinal axis of the corresponding one Measuring device 30. The measuring device can can be carried out, for example, as in DE 32 09 834 A1 is described.

The basic structure of the casting drive for the Casting set is also in the aforementioned Patent specification PS 20 21 182 described by the applicant. On the entire content of this patent specification, insofar as it is relevant to the present invention, hereby expressly referred.

According to the invention, a series of quickly controllable servo-proportional valves, also called continuous valves, is used to manufacture 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.

Using the p / U transducer, the pressure in the pressure rooms 10, 11 and 18, 19 and 22 detected and be 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.

Likewise, the servo proportional valve 34 a regulation of the rear pressure chamber 19 of the multiplier piston 17, preferably the front pressure chamber 18 of the multiplier piston also via a further servo proportional valve 35 is regulated. These continuous valves can also be seen in Fig. 1 assigned p / U transducer shown be the pressure conditions in the pressure chambers 18, 19 to record and thus regulate.

Finally, to regulate the rear cylinder space 22 also the regulation of a quick switching servo-proportional valve 36 at the pressure medium connection 29 used so that the loading the pressure chamber 22 via a first Pressure accumulator 37 and the loading of the pressure chamber 19 via a second pressure accumulator 38 a fast switching proportional valve control can be done. Additional p / U transducers can also be used here be used.

Through 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 v = f (s), p = f (t) is shown in principle in FIG. 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 become. 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 adjusted by tuning the Press cylinder 7 for loading the press piston 8 and to the multiplier cylinder to act upon the Multiplierork 17 inflowing amount of hydraulic medium be influenced, with higher accelerations of the two pistons are possible than with the Hydraulic medium supply from only one hydraulic medium reservoir is possible. By the appropriate Clamping the two pistons becomes any Controlled and influenced 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, to the amount of the medium displaced at A _{2.1 are} in the range of the ratio 0.8 to 1.2: 1. The circular cylinder area A _{1 of} the plunger 8 relates 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 areas enables optimal operation of the casting drive

The diagrams shown in FIG. 3 relate to Soil value requirements for controlling a casting process.

The curves shown in the diagram p = f (t) 1 to 4 represent examples of target value specifications and the setpoint of the pressure curve p over time t. These pressure curves p = f (t) can during the Operated controlled.

The same applies to the diagram v = f (s) as the target value specification of the speed of the casting piston over 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 (13)

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) downstream of the casting chamber (3), with a pressing piston (8) for driving the casting piston (5) and with a multiplier device (15) downstream of the pressing cylinder (7), with a multiplier piston (17) guided therein, wherein the casting drive (1) is constructed as a two-circuit casting unit and a pressure medium acts by means of a first valve control arrangement (36) directly on the pressing piston (8) and by means of a further valve control arrangement (34) on the multiplier piston (17), the two-circuit casting drive being controlled by means of quickly adjustable servo-proportional valves (33 to 36) (continuous valves), the control taking place by means of at least one respective servo-proportional valve (33, 34) located in the inlet or outlet (14) to the pressure chamber (10) upstream of the pressing piston (8) as well as in the inlet or outlet (28) of the pressure chamber (19) downstream of the multiplier piston (17), 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) being detected by 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), the control or regulation of the servo-proportional valves (33, 34) taking place as a function of each other and as a function of the movements of the pressing piston (8) or the multiplier piston (17) as well as of the pressures and optionally further casting parameters in the moulding cavity by means of a computer (41), so the current injection process during the pre-filling phase and the mould-filling phase and 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), a first front piston rod (20) of the multiplier piston (17) with an effective front pressure surface A_2.1 opening 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 opening 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 upstream 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 loading 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 of the multiplier device (15), a deceleration or a reverse control of the multiplier piston (17) takes place, in order to minimise 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 arrangements, 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 in such a way that optimum subsequent pressures 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, the bilateral pressure cushions of the pressure chambers (10, 11) or (18, 19) and thus the movements of the pistons (8, 17) being preferably adjustable by means of a servo-proportional value 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 during 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 downstream casting drive (1), consisting of a pressing cylinder (7) with a pressing piston (8) and a multiplier device (15) with a multiplier piston (17), wherein the casting drive is constructed as a two-circuit casting unit, a valve control arrangement for the two-circuit casting drive being provided, which consists of rapidly adjustable servo-proportional valves (continuous valves) (33 to 36) with an adjusting time t ≤ 5 ms, at least the inlet or outlet of the pressing cylinder (7) as well as the inlet or outlet of the multiplier device (15) being provided with rapidly adjustable servo-proportional valves (33, 34) and the entire movements of the casting piston rod (6) and of the multiplier piston (17) being detectable by distance/speed measuring devices (30, 31), and a computer being provided for controlling or regulating the servo-proportional valves as a function of the movements of the casting piston rod (6) and of the multiplier piston (17) and the pressure in the pressure chambers (10, 11) or (18, 19) for "clamping" the pressing piston (8) or the multiplier piston (17) being detectable by means of signal modulators (44, 45 etc.) and being capable of being supplied as an actual value to the computer (41).
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 11, characterised in that the pressure chamber (22) lying behind the rear piston rod (21) of the multiplier piston can be adjusted by means of a servo-proportional valve control arrangement (36) as a pressure chamber.

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