EP0809555B1 - Process and device for controlling means of dressing in a casting plant - Google Patents

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

The subject of the present invention is a method and a device for control of poteyage means in an under molding installation pressure of metals or metal alloys.

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

By first referring to the appended figures 1a to 1d, we will describe an injection molding installation for alloy parts metallic of known type. The installation essentially comprises a mold 12 consisting of two parts respectively mobile 14 and fixed 16, including part of the internal faces 14a and 16a respectively define 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 in the cavity 18 by a piston system 22. This is what which is shown in Figures 1a and 1b.

At the end of the molding operation, the movable part 14 of the mold is discarded. To be able to extract the molded part 24 relative to the part 14 of the mold, it is provided through part 14 of the rods such as 26 which are slidably mounted in 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 part molded on the two parts 14 and 16 of the mold, before closing the two parts of the mold and proceed to inject the alloy metal, we perform a poteyage operation using a ramp poteyage 28 which allows spraying on the internal faces 14a and 16a a coating liquid forming a film on these faces. The ramp can be stationary during the spraying stage or be animated by back and forth movement. It has a number of nozzles spray. As is well known, there are different poteyage products, in particular poteyage products based on solvents or water-dilutable cleaners. These products of poteyage in themselves are well known. We understand that the problem is to adapt the content of poteyage product in the solvent, be it water or oil, and the amount of product that needs to be sprayed before each casting operation. Optimization of the poteyage operation is decisive because it reduces the force which the ejector 26 must exert to demold the room. We understand that if the constraints are too high, the ejectors or parts being ejected may be damaged, which is one of the biggest barriers to automation of die casting.

We therefore understand that it is very important to be able to control the effectiveness of the poteyage and power operation intervene quickly as soon as the coating parameters are no longer satisfactory.

The Glesserei-Paxis document n ° 5, March 10, 1973 Berlin DE Pages 79-84, XP002001 757 H Tosa et al. ; "Ein Flussgrössen auf die Druckguss-Auswerfung "describes the study of force of ejection of a metal part molded under pressure in particular in depending on the type of potting agent used. However, this document does not not allow for installation for automatic control of the poteyage.

Another object of the invention is to provide a device for control that automatically changes the composition or the flow rate of the cleaning product as a function of the actual conditions of molding.

Yet another object of the invention is to provide a device which allows an alarm to be triggered if the conditions for ejecting the molded part come out of normal operating conditions.

To achieve this goal, the means of control of coating in a metal die casting installation or of metal alloys, said installation comprising a fixed part of mold and a movable part of a mold defining an imprint, means for ejecting the molded part comprising ejection rods whose movements are controlled by a cylinder supplied with liquid and a spray bar for spraying the product on the internal faces of the parts of the mold defining the imprint, and means for supplying said ramp with poteyage products, characterized in that said control device comprises a single pressure sensor to continuously measure fluid pressure control means in said cylinder, means for recording said pressure as a function of time during the part ejection cycle, and means for comparing said recorded curve with a curve of reference including means for detecting in the recorded curve an overpressure bearing (B) and means for comparing the value of the pressure of said bearing at a minimum value (Pm) and at a value maximum (Pm) and means for modifying said spraying of poteyage product based on the results of said comparison.

It is understood that the principle of the invention is to detect the force that the cylinder must exert to carry out the ejection operation the molded part. Indeed, the inventors have demonstrated that the quality and efficiency of the poteyage operation were inversely proportional to the effort that the ejection rods had to exert to eject the part from the mold imprint. We understand that it is so possible using this pressure variation report to act on feeding the potage ramp to optimize the effect of poteyage.

According to a preferred embodiment, the device for control further comprises means for comparing the curve of pressure measured at maximum pressure and means for trigger an alarm if the pressure measured is greater than the maximum pressure.

We understand that in this way it is possible to operate the molding installation without permanent human supervision since the alarm system informs the condition monitoring officer unacceptable operating conditions. It goes without saying that as a variant the signal can automatically stop the installation of injection molding.

Also preferably, the device further comprises means for modifying the supply of the ramp with product of poteyage according to the comparison between the pressure curve measured and the reference curve.

In this improved embodiment, it is understood that the adaptation of the coating parameters is done automatically by function of the difference between the measured pressure curve in the ejector control cylinder and an optimal pressure curve.

The invention also relates to a method for controlling poteyage means which is characterized in that one measures during all the duration of an ejection cycle for different values of the same setting parameter the maximum pressure of the control fluid said actuator, the variations are recorded using a single sensor of the fluid pressure in the cylinder as a function of time and we retain as maximum pressure that which corresponds to a level (B) of maximum pressure in the curve representative of the variations of pressure as a function of time and in that the value of the parameter corresponding to the lowest maximum pressure value.

• les figures 1a à 1d, déjà décrites, illustrent une installation de moulage par injection de type connu ;
• la figure 2a montre une installation de moulage munie du dispositif de contrôle des moyens de poteyage selon un premier mode de mise en oeuvre de l'invention ;
• la figure 2b montre un exemple de courbe de variation de la pression du fluide de commande dans le vérin de commande de l'éjecteur ; et
• la figure 3 montre un deuxième mode de mise en oeuvre du dispositif de contrôle permettant une adaptation automatique des paramètres de poteyage.

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 1a to 1d, already described, illustrate an injection molding installation of known type;
• FIG. 2a shows a molding installation provided with the device for controlling the coating means according to a first embodiment of the invention;
• FIG. 2b shows an example of a variation curve of the pressure of the control fluid in the control cylinder of the ejector; and
• FIG. 3 shows a second mode of implementation of the control device allowing automatic adaptation of the coating parameters.

Referring first to Figure 2a, we will describe a first embodiment of the system control device poteyage. In this figure, the two parts 14 and 16 of the mold as well as a molded part 24. We have also shown the ejector rods 26 which are mechanically connected to rod 30 of a control cylinder 32. The cylinder 32 is supplied with control fluid via inputs 34 and 36. According to the invention, a pressure sensor 38 is permanently mounted on the cylinder 32 to measure the prevailing pressure in the control cylinder. The sensor 38 which can be of any type suitable provides an analog signal which is converted into a 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 a whole ejection cycle. The corresponding curve can be displayed on a control monitor such as 44. The processing circuit 42 comprises also means of comparison which will be explained later. We have also shown in Figure 2a, the ramp mobile poteyage 28 which is supplied from a reservoir of poteyage liquid 46 via one or more control valves 48.

In FIG. 2b, the time t represents the pressure P measured by the sensor 38. The pressure curve presents a first pressure peak A which corresponds to the arrival of oil from control in the cylinder. This peak is not significant of the efforts ejection.

Then there is a rise in pressure with a bearing B which actually corresponds to the exit of the part from the moving part of the mold under the effect of the ejector. This level B of very short duration (30 to 50 milliseconds) corresponds to the rupture of the coating film and micro-links between the internal face of the mold and the molded part. The curve has a third bearing C at constant pressure and value lower which corresponds to the end of the ejection stroke. It was established that the most significant parameter and the most sensitive to variations in condition of poteyage 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 the bearing B which is retained and used as the only significant parameter of the ejection effort and which is therefore used to optimize poteyage conditions.

• le type de produit (ratio cire sur silicone, huile minérale ou synthétique)
• la durée de pulvérisation à l'aide de la rampe de poteyage (2 à 20 secondes)
• la concentration en produit pur (0,5% à 5%)
• la pression de l'air servant à réaliser la pulvérisation (3 à 6 bars)
• la pression du produit (3 à 6 bars)
• la distance de pulvérisation (100 à 400 mm)
• le débit de produit par buse de pulvérisation (10 à 30 cm³ par seconde)
• le nombre de buses (4 à 20 buses ou même davantage) et
• le mode de pulvérisation (rampe fixe ou animée d'un mouvement de va-et-vient).

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:

• 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 for spraying (3 to 6 bars)
• product pressure (3 to 6 bars)
• spraying distance (100 to 400 mm)
• the product flow rate per spray nozzle (10 to 30 cm ³ per second)
• the number of nozzles (4 to 20 nozzles or even more) and
• spraying mode (fixed boom or moving back and forth).

In addition, there are many synergies between the different parameters defined above which make a priori difficult settings to optimize the poteyage phase. According to prior techniques, any launch of a new production therefore requires a phase of more or less long preliminary development where all or part of the parameters below will have to be adjusted to get a mold release correct. We understand that, thanks to the control device, optimization of the various parameters can be obtained by performing, before putting the pieces into production, various tests. For each parameter which is varied, it is possible thanks to the invention to determine a optimal parameter value by selecting the parameter value which has been determined to correspond to the lowest pressure P possible at level B.

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

During normal use of the mold, the control device allows for each operation to check whether the pressure value maximum does not increase from the defined optimal value previously. In this case, a modification of the coating parameters as indicated previously.

In addition, according to a preferred embodiment, the device can continuously compare the maximum pressure corresponding to stage B at a minimum pressure Pm value permissible and at a maximum permissible pressure value PM. If the maximum measured pressure value exceeds the pressure range between Pm and PM, the processing circuit 42 triggers a circuit alarm 50 which can feed a visual alarm on the monitor 44 or an audible alarm 52. It is understood that, in this mode of embodiment, the control device also allows monitoring of the effective functioning of the mold ejection system.

Referring now to Figure 3, we will describe a second embodiment of the control device in which is provided a servo system for adjusting the liquid parameters of poteyage according to the indications provided by the sensor of pressure. According to this embodiment, the processing circuit 42 includes means for comparing the maximum pressure of the control liquid corresponding to tray B with a value of instructions. If a deviation greater than a predetermined value is detected, the processing circuit 42 activates a control circuit 60 which allows order the modification of certain spraying parameters poteyage liquid. For example, the control circuit 60 controls the ramp control valve 48 for the ramp 28 of poteyage and for example a supply line 62 in solvent for poteyage product in container 46. When ordering automatically thus the modification of the flow rate of the poteyage liquid and spray time as well as the concentrated product content of solvent coating, we can automatically modify the parameters to find optimal conditions of poteyage without manual intervention is required. We thus realize a enslavement of the poteyage phase.

Claims (5)

1. Device for controlling dressing means in a diecasting plant for metals or metal alloys, said plant comprising a fixed mould part (16) and a movable mould part (14) defining an impression (18), ejector means for the moulded part comprising ejector pins (26), the displacements of which are operated by a cylinder (32) supplied with operating fluid and a ramp (28) for crushing dressing product on the internal faces of the parts of the mould defining the impression, and means (46, 48) for supplying said ramp with dressing products, characterised in that said control device comprises a single pressure sensor (38) for permanent measurement of the pressure of the operating fluid in said cylinder (32), means (42) for recording said pressure as a function of time during the ejection cycle of the part, and means for comparing said recorded curve with a reference curve including means for detecting a stage (B) of overpressure in the recorded curve and means for comparing the value of the pressure of said stage with a minimum value (Pm) and with a maximum value (PM) and means (46, 48) for modifying said crushing of the dressing product as a function of the results of said comparison.
2. Device for controlling dressing means according to Claim 1, characterised in that they moreover comprise means (50) responding to said comparison to trigger an alarm (52) if the measured pressure is not within the range of values (Pm) and (PM).
3. Device for controlling dressing means according to any one of Claims 1 and 2, characterised in that they comprise means (42, 60) for modifying the supply of the crushing ramp (28) with dressing product as a function of the comparison between the measured pressure curve and the reference pressure curve.
4. Process for controlling dressing means in a diecasting plant for metals or metal alloys, said plant comprising a fixed mould part (16) and a mobile mould part (14) defining an impression (18), ejector means for the moulded part comprising ejector pins (26), the displacements of which are operated by a cylinder (32) supplied with operating fluid and a ramp (28) for crushing dressing product on the internal faces of the parts of the mould defining the impression, and means (46, 48) for supply said ramp with dressing products, characterised in that during the entire duration of an ejection cycle, the maximum pressure of the operating fluid of said cylinder is measured for different values of the same dressing parameter, the variations in the pressure of the fluid in the cylinder as a function of time are recorded by means of a single sensor, and the value retained as maximum pressure is that which corresponds to a stage (B) of maximum pressure in the curve representing the variations in pressure as a function of time, and in that the value of the parameter corresponding to the lowest maximum pressure value is selected.
5. Process according to Claim 4, characterised in that in order to detect the maximum pressure of the operating fluid of the cylinder, the variations in the pressure of the fluid in the cylinder is recorded as a function of time by means of a single sensor, and the value retained as maximum pressure is that which corresponds to a stage (B) of maximum pressure in the curve representing the variations in pressure as a function of time.

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