EP0809555A1

EP0809555A1 - Process and device for controlling means of dressing in a casting plant

Info

Publication number: EP0809555A1
Application number: EP96901853A
Authority: EP
Inventors: Patrick Hairy; Michel Richard
Original assignee: Centre Technique des Industries de la Fonderie
Current assignee: Centre Technique des Industries de la Fonderie
Priority date: 1995-01-26
Filing date: 1996-01-25
Publication date: 1997-12-03
Anticipated expiration: 2016-01-25
Also published as: FR2729876B1; ATE178821T1; CA2209779A1; JPH10512810A; EP0809555B1; FR2729876A1; WO1996022852A1; US6073676A; DE69602083D1

Abstract

PCT No. PCT/FR96/00126 Sec. 371 Date Jul. 25, 1997 Sec. 102(e) Date Jul. 25, 1997 PCT Filed Jan. 25, 1996 PCT Pub. No. WO96/22852 PCT Pub. Date Aug. 1, 1996An installation has a fixed die portion and a moving die portion, ejector rods under the control of an actuator fed with control fluid, and a spray device for spraying a coating substance. A monitoring apparatus comprises a pressure sensor for continuously measuring the pressure of a control fluid, a device for measuring and recording the pressure as a function of time, a device for comparing the recorded measurement with a reference measurement, and a device for modifying the spraying of the coating substance as a function of the comparison.

Description

Method and device for controlling poteyage means in a molding installation

The subject of the present invention is a method and a device for controlling the poteyage means in an installation for die-casting of metals or metal alloys.

More specifically, the present invention relates, in an installation for die-casting of metals or metal alloys, a device which makes it possible to control, that is to say to optimize, the spreading of the cleaning liquid. on the internal faces of the mold used to carry out the molding operation.

Referring firstly to the appended figures la to ld, there will be described an installation for injection molding of metal alloy parts of known type. The installation essentially comprises a mold 12 consisting of two respectively movable 14 and fixed 16 parts, part of the internal faces respectively 14a and 16a defining the mold cavity or cavity 18. When the mold is closed, the alloy to be molded is introduced into a container 20 and injected under pressure into the cavity 18 by a system of pistons 22. This is what is shown in FIGS. 1a and 1b.

At the end of the molding operation, the movable part 14 of the mold is removed. In order to be able to extract the molded part 24 relative to the part 14 of the mold, it is provided through the part 14 of the extraction rods such as 26 which are slidably mounted in the part 14 of the mold. These rods are controlled simultaneously by a cylinder not shown in the figures.

In addition, in order to avoid adhesion phenomena of the molded part on the two parts 14 and 16 of the mold, before closing the two parts of the mold and carrying out the injection of the metal alloy, an poteyage operation using a potageage ramp 28 which makes it possible to spray on the internal faces 14a and 16a a poteyage liquid forming a film on these faces. The boom can be fixed during the spraying step or be moved back and forth. It has a number of spray nozzles. As is well known, there are various poteyage products, in particular poteyage products based on solvents or water-dilutable cleaners. These poteyage products in themselves are well known. It is understood that the problem is to adapt the content of poteyage product in the solvent, whether it is water or oil, and the quantity of products which must be sprayed before each casting operation. The optimization of the coating operation is decisive because it makes it possible to reduce the force which the ejector 26 must exert in order to demold the part. It is in fact understood that if the stresses are too high, the ejectors or the parts being ejected risk being damaged, which constitutes one of the most important obstacles to the automation of die casting.

We therefore understand that it is very important to be able to constantly monitor the efficiency of the coating process and to be able to intervene quickly as soon as the coating parameters are no longer satisfactory.

Another object of the invention is to provide a control device which automatically makes it possible to modify the composition or the flow rate of the coating product as a function of the actual molding conditions. Yet another object of the invention is to provide a device which makes it possible to trigger an alarm if the conditions for ejecting the molded part go outside of normal operating conditions.

To achieve this goal, the device for controlling the poteyage means in an installation for die-casting of metals or metal alloys, said installation comprising a fixed part of the mold and a movable part of the mold defining an imprint, ejector means for the molded part comprising ejection rods, the displacements of which are controlled by a jack supplied with control liquid and a spraying boom for spraying the coating product on the internal faces of the parts of the mold defining the imprint, and supply means of said ramp in poteyage products, is characterized in that said control device comprises a single pressure sensor for continuously measuring the pressure of the control fluid in said cylinder, means for recording said pressure as a function of time during the cycle of ejection of the part, and means for comparing said recorded curve with a curve of reference including means for detecting in the recorded curve an overpressure level (B) and means for comparing the value of the pressure of said level with a minimum value (Pm) and with a maximum value (Pm) and means for modifying said spraying of poteyage product according to the results of said comparison.

It is understood that the principle of the invention is to detect the force which the cylinder must exert to carry out the operation of ejecting the molded part. In fact, the inventors have shown that the quality and the efficiency of the coating operation are inversely proportional to the effort that the ejection rods had to exert to eject the part from the mold imprint. It will be understood that it is thus possible, with the aid of this reading of variations in pressure, to act on the supply of the mixing boom to optimize the effect of the mixing. According to a preferred embodiment, the control device further comprises means for comparing the pressure curve measured with a maximum pressure and means for triggering an alarm if the pressure measured is greater than the maximum pressure. It is understood that in this way it is possible to operate the molding installation without permanent human supervision since the alarm system informs the attendant of unacceptable operating conditions. It goes without saying that, as a variant, the alarm signal can automatically control the stopping of the injection molding installation.

Preferably also, the device further comprises means for modifying the supply of the ramp with poteyage product as a function of the comparison between the measured pressure curve and the reference curve. In this improved embodiment, it is understood that the adaptation of the coating parameters is done automatically as a function of the difference which exists between the measured curve of the pressure in the control cylinder of the ejector and an optimal pressure curve. .

The invention also relates to a method for controlling the coating means which is characterized in that the pressure of the control fluid is measured, throughout the duration of an ejection cycle. of the ejector cylinder, said measurements are recorded and action is taken on the coating parameters to optimize the measurement curve of said pressure.

Other characteristics and advantages of the present invention will appear better on reading the following description of several embodiments of the invention given by way of nonlimiting examples. The description refers to the appended figures in which:

- Figures la to ld, already described, illustrate an injection molding installation of known type; - Figure 2a shows a molding installation provided with the device for controlling the poteyage means according to a first embodiment of the invention;

- Figure 2b shows an example of a variation curve of the pressure of the control fluid in the control cylinder of the ejector; and

- Figure 3 shows a second embodiment of the control device for automatic adaptation of the coating parameters.

Referring first to Figure 2a, we will describe a first embodiment of the control device of the coating system. This figure shows the two parts 14 and 16 of the mold as well as a molded part 24. The ejector rods 26 are also shown, which are mechanically connected to the rod 30 of a control jack 32. The jack 32 is supplied with control fluid by the inputs 34 and 36. According to the invention, a pressure sensor 38 is permanently mounted on the jack 32 to measure the pressure prevailing in the control cylinder. The sensor 38 which can be of any suitable type delivers an analog signal which is converted into digital information possibly by the converter 40. A processing circuit 42 makes it possible to record and memorize the different pressure values as a function of time during all an ejection cycle. The corresponding curve can be displayed on a control monitor such as 44. The processing circuit 42 also includes comparison means which will be explained later. Also shown in Figure 2a, the movable poteyage ramp 28 which is supplied from a reservoir of poteyage liquid 46 via one or more control valves 48.

In Figure 2b, there is shown as a function of time t the pressure P measured by the sensor 38. The pressure curve has a first pressure peak A which corresponds to the arrival of the control oil in the jack. This peak is not significant of the ejection efforts.

Then there is a rise in pressure with a bearing B which effectively corresponds to the output of the part from the movable part of the mold under the effect of the ejector. This stage B of very short duration (30 to 50 milliseconds) corresponds to the rupture of the coating film and of the micro-bonds between the internal face of the mold and the molded part. The curve comprises a third bearing C at constant pressure and of lower value which corresponds to the end of the ejection stroke. It has been established that the most significant parameter and the most sensitive to variations in the coating condition is the maximum value of the pressure on the bearing B. According to an important characteristic of the invention, it is therefore the value of the pressure corresponding to level B which is retained and used as the only significant parameter of the ejection force and which is therefore used to optimize the conditions for cleaning.

It should be remembered that the parameters for poteyage are numerous. The effectiveness of the coating phase and in particular the quality of the film of lubricant deposited on the internal faces of the mold is sensitive to many parameters which vary from one production to another within a fairly wide range depending on the alloy considered and the shape of the part to be produced. Among these parameters, we can cite:

- mold temperature (170'C to 350 * Q

- the type of product (ratio of wax to silicone, mineral or synthetic oil) - the duration of spraying using the spraying boom (2 to

20 seconds)

- the concentration of pure product (0.5% to 5%)

- the air pressure used to carry out the spraying (3 to 6 bars) - the product pressure (3 to 6 bars)

- spraying distance (100 to 400 mm) - the product flow rate per spray nozzle (10 to 30 cm ^ per second)

- the number of nozzles (4 to 20 nozzles or even more) and

- the spraying mode (fixed boom or with a back-and-forth movement).

In addition, there are many synergies between the various parameters defined above, which make it difficult to adjust a priori to optimize the coating phase. According to the prior techniques, any launching of a new production therefore requires a more or less long phase of preliminary development where all or part of the parameters below will have to be adjusted to obtain a correct release. It is understood that, thanks to the control device, the optimization of the various parameters can be obtained by carrying out, before the production of the parts, various tests. For each parameter that is varied, it is possible, thanks to the invention, to determine an optimal parameter value by selecting the parameter value which has been determined to correspond to the lowest possible pressure P at the level B.

In this preliminary phase, it is therefore possible with the aid of the device to adjust the various parameters which thus correspond to an optimal pressure curve or more precisely to a maximum pressure value of the bearing B as low as possible.

During normal use of the mold, the control device makes it possible, for each operation, to check whether the maximum pressure value does not increase compared to the optimal value defined previously. In this case, it would then be necessary to modify the coating parameters as indicated above.

In addition, according to a preferred embodiment, the treatment device can permanently compare the maximum pressure corresponding to the bearing B with a minimum value Pm of admissible pressure and with a maximum value PM of admissible pressure. If the maximum measured pressure value exceeds the pressure range between Pm and PM, the processing circuit 42 triggers an alarm circuit 50 which can supply a visual alarm on the monitor 44 or an audible alarm 52. We understand that in this mode of embodiment, the control device also allows monitoring of the effective operation of the mold ejection system.

Referring now to FIG. 3, a second embodiment of the control device will be described, in which a system for controlling the adjustment of the parameters of the coating liquid is provided as a function of the indications provided by the pressure sensor. According to this embodiment, the processing circuit 42 comprises means for comparing the maximum pressure of the control liquid corresponding to the plate B with a set value. If a deviation greater than a predetermined value is detected, the processing circuit 42 activates a control circuit 60 which makes it possible to control the modification of certain spraying parameters for the spraying liquid. For example, the control circuit 60 controls the valve 48 for regulating the supply of the spraying boom 28 and for example a supply line 62 with solvent for the spraying product in the container 46. By automatically controlling the modification of the flow rate of the spraying liquid and the spraying time as well as the content of concentrated spraying product in the solvent, the parameters can be automatically modified to find optimal spraying conditions without manual intervention being necessary. We thus enslave the poteyage phase.

Claims

1. Device for controlling the poteyage means in an installation for die-casting of metals or metal alloys, said installation comprising a fixed part (16) of the mold and a movable part (14) of the mold defining an imprint (18) , means for ejecting the molded part comprising ejection rods (26), the movements of which are controlled by a jack (32) supplied with control liquid and a boom (28) for spraying the coating product on the internal faces of the parts of the mold defining the imprint, and means of supply (46, 48) of said ramp with poteyage products, characterized in that said control device comprises a single pressure sensor (38) for permanently measuring the pressure control fluid in said cylinder (32), means (42) for recording said pressure as a function of time during the part ejection cycle, and means for comparing said recorded curve with u a reference curve including means for detecting in the recorded curve an overpressure level (B) and means for comparing the value of the pressure of said level with a minimum value (Pm) and with a maximum value (Pm) and means (46, 48) for modifying said spraying of plaster product according to the results of said comparison.

2. Device for controlling the poteyage means according to claim 1, characterized in that they further comprise means (50) in response to said comparison to trigger an alarm (52) if the pressure measured is not between the values (Pm) and (PM).

3. Device for controlling the poteyage means according to any one of claims 1 and 2, characterized in that it comprises means (42, 60) for modifying the supply of the boom (28) for spraying product mixing according to the comparison between the measured pressure curve and the reference pressure curve.

4. Method for controlling the poteyage means in an installation for die-casting of metals or metal alloys, said installation comprising a fixed mold part (16) and a movable part (14) of the mold defining an imprint (18), means for ejecting the molded part comprising ejection rods (26) whose movements are controlled by a jack (32) supplied with control liquid and at at least one ramp (28) for spraying the coating product onto the internal faces of the parts of the mold defining the imprint, and means for supplying (46, 48) of said ramp with coating products, characterized in that measure for different values of the same poteyage parameter the maximum pressure of the control fluid of said jack and in that the value of the parameter corresponding to the lowest maximum pressure value is selected.

5. Method according to claim 4, characterized in that, to detect the maximum pressure of the actuator control fluid, the variations of the fluid pressure in the actuator are recorded as a function of time using a single sensor and one retains as maximum pressure that which corresponds to a plateau (B) of maximum pressure in the curve representative of the variations in pressure as a function of time.