DE2406528C2 - Control device for a die-casting machine that works according to the multiphase principle - Google Patents

Description

The invention relates to e ^; .ne control device for a die-casting machine operating according to the multiphase principle with a plunger that can be displaced in a press cylinder and a multiplier piston that can be displaced in a multiplier cylinder and which can be set under pretension, the pressure medium supply line that opens into the working chamber of the press cylinder and the pressure medium supply line that opens into the pressure chamber of the multiplier cylinder are adjustable via an adjusting element.

It is found time and again on die casting machines that that after setting the machines at the start of production, flawless die-cast parts were poured that, however, with increasing production time, rejects arise, although at the machine setting no change was made.

To reverse the deterioration in quality, the die casting machine used to be done by hand

ίο been adjusted. It depended on the experience of the The adjuster determines whether the correct valve has been adjusted and thus the desired casting quality can be quickly obtained again became.

For some years now, electronic measuring technology has been developed to such an extent that the die caster has the Measure and measure the most important influencing factors involved in the casting process with sufficient accuracy can evaluate. It has been shown that the setting values on the press-in unit are particularly strong

2 "fluctuations, which is particularly disadvantageous affects the quality of the cast parts. The reason for this is primarily the change in viscosity, friction, the Leakage losses, etc., which are mainly due to the changing temperature of the hydraulic medium Die casting machine, adjust. .

Monitoring of the setting values for the pressed part was sometimes very complex in some factories Messanlag-jn used. So will the eligible ones Parameters in the case of insufficient casting quality with

ω checked suitable transducers. By Compare the measured values with the optimal setting values known from previous measurements there are indications as to where or in which area there are deviations, so that the die caster

J 5 by manually adjusting the corresponding valves Can help. Such a procedure requires continuous casting in order to maintain constant casting quality Control measurements. However, the financial and human effort that is necessary for this is so great that

that there is practically no ongoing monitoring.

The invention is based on the object of designing a control device of the type mentioned at the outset for maintaining the pressure medium supply required during the individual press-in phases in such a way that the most important setting values are recorded during the press-in process and, if necessary, automatically corrected. To solve this problem, the control device according to the invention comprises at least one setpoint generator (SE) for specifying the duration (X _K ) of a press-in phase, at least one actual value meter (M) for determining the actual duration (X) of a press-in phase, at least one comparator (VC) for Comparison of the respective time setpoint (Xk) and the actual time value (X) and for generating an actuating signal (Y) as a function of a difference between the setpoint time value (Xk) and actual time value (X) and an adjusting device for actuating the respective setting element as a function of the actuating signal (Y) . "

A time counter is advantageously assigned to the control device for each press-in phase, at which the desired pressing time (target time) can be set and which is the actual duration (actual time) of the individual Press-fit phases and the deviation of the actual time from the target time.

It is also beneficial if each time counter is behind depending on a certain pressure the plunger is pulse controlled.

It is also of particular advantage if the control device adjusts to the desired setpoint has adjustable device with which the pressure during the first press-in phase behind the plunger is monitored. If the set target value is exceeded, a display shows the corresponding Note for existing unwanted friction.

When the preload pressure is achieved using a flow control block with several actuators via an input element, in particular a step switch, is adjustable, then it is further recommended to use a separate controller for the production and Maintaining the multiplier pressure to provide, which controller primarily to a structural unit is combined with the rest of the control system.

The invention is explained below with reference to the drawing. It shows

1 shows the press-fit part of a die-casting machine, schematically with a pressure-medium supply that can be regulated.

Fi g. 2 a selector switch with three levels, diagrammatically,

3 shows the pressure curve in the press cylinder of a die casting machine,

F i g. 4 shows a block diagram of a pressure medium quantity regulator, as it is in the regulating device according to the invention is used,

F i g. 5 an adjustment panel for the operating and control elements.

In the press cylinder 1, a press piston 2 is axially displaceable. A piston rod 3 is with a Not shown shooting piston connected, by means of which the metal in a likewise not shown Die casting mold is printed. The press cylinder 1 is followed by a multiplier cylinder 4 in which a Multiplier piston 5 is guided axially displaceably. The piston rod 6 of the multiplier piston 5 passes through it a preload space 7 and a wall 8. The piston rod 6 has a continuous longitudinal bore 9 on. In addition, a check valve 10 is provided in the multiplier piston 5.

The injection pressure on the plunger 2 is supplied by an accumulator 11 to which a line 12 is connected, to which parallel orifices 13 to 17 are connected. The cross-sections of these diaphragms are dimensioned differently. Their gradations are in particular chosen so that, starting from the smallest diaphragm, the diaphragm openings of the respective following diaphragm allow twice the amount of pressure medium to flow through the previous diaphragm per unit of time. The diaphragms 13 to 17 are combined with their associated magnetically operated directional control valves 18 to 22 to form a structural unit in the form of a hydraulic block. The directional control valves 18 to 22 are switched by an electrical rotary switch 23, as shown in FIG. 2 is illustrated. However, in contrast to the switch shown, the rotary switch has five levels. The rotary switch has 2 " detent positions, where π indicates the number of diaphragms. In the hydraulic ^{block labeled 24 there are 2 5} = 32 detent positions.

The pressure in the prestressing space 7 can also be selected using a flow control block. This hydraulic block, which is designated by 27, has four actuators, namely orifices 28 to 31. In this case 2 ⁴ , i.e. 16 different amounts can be set. The setting is again made using a selector switch as shown in FIG. 2, which here, however, must have four levels and is used to switch directional control valves 32 to 35. An associated pressure accumulator is denoted by 36.

The die-casting machine explained works on the three-phase principle, whereby the accumulator is charged the pressure compensator, not shown, is locked. Of the

The pressure curve in the press cylinder 1 of such a cold chamber machine is shown in FIG. 3 reproduced. In the first press-in phase, which extends over the period of time t 1 , the plunger moves relatively slowly, the liquid metal being pushed towards the die-casting mold. The pressure Pj behind the plunger 2 during the first press-in phase is negligibly small under perfect conditions. In the second press-in phase, which extends over the time f2, the plunger 2 is accelerated to a higher speed.

2Ii The liquid metal is pressed into the die casting mold. The pressure behind the plunger 2 rises to the value Pi after the coal filling has ended. In the third injection phase, which extends over the period r ₃ , the liquid metal is in the mold cavity

2ϊ redensified. The pressure behind the plunger 2 rises from Pi via P% and Pi . Pj is a few bar below Pt. Pi is the pressure at which the timer switches off for h.

For cast parts to be produced in series,

jo determine the most favorable times t \, ti and h as well as the associated pressures easily by means of test casts. If it is assumed that the relationship between the path 5 of the plunger 2 and its speed ν and the time t is s = vxi, then

π results arithmetically for the time periods ti,! 2 and fj

a value according to the relation t = -. Accordingly, ii = - applies to the first press-in phase. The speed

speed of the plunger 2 (Fig. 1) depends on the amount of pressure oil through the line 26 after Press-fit part 25 arrive. The amounts of pressure medium which are sent to the line 26 from the accumulator 11 arrive are determined by the respectively selected locking positions of the directional control valves 18 bib 22 associated selector switch according to FIG. 2 with five levels. Since the selector switch is 2 ", ie 32 detent positions can take the different amounts of pressure medium that reach the line 26 belong to, belongs to each detent position of the selected selector switch a clearly determined speed of the Plunger 2.

It is assumed that the speed of the plunger 2 in the first press-in phase is 0.15 m / sec should be. In an experimental version, this ram speed was then reached, when the selector switch is in the detent position »8«. If it is now assumed that the plunger 2 covers a distance of 240 mm in the first press-in phase, then the relation fi = -

for ii the value 1.6 seconds.

If the target times ι for /, h, and tz are known, then, may by reference to a control device, such as b5 it is generally shown in Figure 4, be ensured that the times t \, tz, h prepared for the individual Druckgießvorgängen and is maintained.

The control device according to FIG. 4 has a setpoint adjuster Sf, which is used to set UsOu (Xk) in the first injection phase. In addition, there is a measuring device M, for example a line counter, which measures the time actually required iu ,, l'Xj. The control device also includes a comparator VG , which forms the control deviation and converts it into the corresponding manipulated variable and delivers it to the actuator. This actuator causes a rotation of the selector switch corresponding to the manipulated variable, whereby larger or smaller amounts of pressure medium ■ reach the plunger 2 and influence its speed in such a way that the time fi; _s , which is aligned with the time of Usoii.

The setting and monitoring of the automatic control is particularly easy if the operating and control elements are combined on a common setting panel. Such a setting table is shown in FIG. 5 reproduced. On the left, it has an option for setting the target times of the plunger 2 in the respective press-in phases. On the right outside a display for the respectively measured actual time of the plunger 2 in the respective press-in phases is provided. In addition, the permissible deviations from the target times can be set on the setting panel, and finally four selector switches are provided, and in the field for the first press-in phase a setting option 49 for the maximum permissible pressure P \ and an indicator lamp 50 are connected of the permitted pressure P \ lights up.

Before the start of die casting, the selector switches 37 to 40 (FIG. 5) are set to the desired locking positions. In addition, the target times U, t ₂ and Γ3 are set at 41, 42, 43 and the permissible deviations at 44 to 46 and the permissible pressure P \ at 49. After the die-casting mold is closed. the metal loading device triggers the command for the first press-in phase via a contact (not shown). According to the setting of the selector switch 37, pressure medium is called up from the volume control block (not shown) for the machine movements and arrives via line L to the press cylinder 2. With the command for the first press-in phase, the time counter for fi is also started. Should the pressure Pi exceed the pressure set at 49 , then the lamp 50 lights up. what causes the operator to determine the cause and eliminate it.

From the piston rod 3 (FIG. 1), after leaving the intended path of the plunger 2 during the first press-in phase, the switchover to the second press-in phase is effected. As soon as the plunger 2 is accelerated in the second press-in phase after pressing the switch, a specially provided pulse pick-up connected to the plunger 2 gives the time counter for fi the switch-off pulse and at the same time the start pulse for the time counter of t2 - the measured actual time fi is at 51 displayed - If the measured actual time ti in the first press-in phase exceeds the maximum permissible target time, for example three times in a row in the same direction, then the manipulated variable Y, for example via an adjusting motor, causes the selector switch 37 to be adjusted by one step in the desired Direction. The training is so done

that the adjustment of the selector switch 37 is only carried out if Pi does not have the permitted value has exceeded.

For the following shot, by moving the selector switch 37, the amount of oil fed into the line 26 and thus to the plunger 2 has been changed in accordance with the increment made, which changes the speed of the plunger 2 and thus changes fi ", in Direction iu ,, // leads. This control process by one step is repeated if ii, ₍ , should still be outside the tolerance of;, ",,; even after the following shot.

In the second press-in phase, the selector switch 38 is for the quantities of pressure medium supplied to the press-in part 25 responsible. As soon as the switch from the first to the second phase takes place, the am Selector switch 38 retrieved the set amount of hydraulic medium, whereby the speed of the Plunger 2 is increased.

If the actually measured time t2 exceeds or falls below the set target time by the permitted deviation three times in a row in the same direction during the ongoing die-casting production, the manipulated variable of the control device (FIG. 4) causes the selector switch 38 to be adjusted by one each time Switching stage until i2, «is again within the desired tolerance range of hsoii. Again, the design has been made in such a way that readjustment of / 2 "is not carried out if the permissible pressure Pi has been exceeded during the first press-in phase.

The timer for h switches off when the pressure P _{2 is} applied to the pressure sensor in the press-fit cylinder. At the same time, the time _{counter for r 3} receives its start pulse. He receives the switch-off pulse when the pressure Pi is present in the press-fit cylinder. As soon as the pressure P _{2 is} reached, the check valve 10 also closes (FIG. 1). In addition, the pressure medium in the prestressing space 7 is given the opportunity to escape into the tank 36. The amount of pressure medium flowing out of the prestressing space 7 via the line 51 is determined by means of the selector switch 39 (FIG. 5), which is assigned to the directional control valves 32 to 35. As soon as the pressure in the prestressing space 7 is below the value on the right in FIG. 1 acting on the multiplier piston 5 is the multiplier piston 5 is shifted to the left, so that on the plunger 2, the multiplied pressure comes into effect

As soon as the measured value tus is not within the tolerance range of t3 _SO n , an actuator based on the manipulated variable of the control device according to FIG. 4, the selector switch 39 to respectively adjusted one step, and as long, is to fe, "back in the desired range hsoii

The multiplier pressure is set on the selector switch 40 (FIG. 5), the associated boost pressure for the memory 36 and thus the preload space 7 _{being called up in each case according to the multiplied final pressure P 4 set on the switch 40 from the pressure control block (not shown) for the machine movements.} Such a control block to be set digitally has already been proposed.

For this purpose 3 sheets of drawing uncertainty

Claims (6)

Patent claims: 1. Control device for a die-casting machine operating on the multiphase principle with a plunger which can be displaced in a press cylinder and a multiplier piston which can be displaced in a multiplier cylinder and which can be placed under pretension, the pressure medium supply line opening into the working chamber of the pressing cylinder and the pressure medium supply line being assigned to the pressure chamber of the multiplier cylinder which can be set using a setting element, characterized by at least one setpoint generator (SE) for specifying the duration (Xk) of a press-in phase, at least one actual value meter (M) for determining the actual duration (X) of a press-in phase, at least one comparator (VG ) to compare the respective time setpoint (Xk) and the time actual value (X) and to generate an actuating signal (Y) depending on a difference between time setpoint (Xk) and time actual value (K) and an adjusting device for actuating the respective setting element in Dependency of the control signal (Y). 2. Control device according to claim 1, characterized in that at least one of the actual value meters (M) can be controlled by the pressure in the working space of the press cylinder (1). 3. Control device according to claim 1 or 2, characterized in that at least one of the actual value meters (M) can be controlled by a pulse pickup connected to the plunger (3). 4. Control device according to one of claims 1 to 3, characterized in that the control device a displacement transducer for measuring the distance covered by the plunger (2) during each pressing phase Has way. 5. Control device according to claim 4, characterized in that the switching from the first is controlled by the displacement transducer on the second press-in phase. 6. Control device according to one of claims 1 to 5, characterized in that the control device has a setpoint generator for specifying the pressure in the working space during the first press-fit phase, a pressure sensor for measuring the actual pressure, a comparator for comparing the set pressure and the actual pressure and a Display device (50) comprises which displays the exceeding of the set pressure (Pt).