METHOD FOR CONTROLLING THE LOCAL TEMPERATURE OF A PART DURING ITS MANUFACTURING IN A MOLDING PROCESS

Description

Technical field of the invention

[0001] The invention relates to the field of molding, and more specifically to the molding of molten material in a permanent mold. This molten material can be a metal or a polymer. More precisely, the invention relates to the control of the local temperature of the molten material during its introduction and cooling in a metal mold. The invention provides a new method for controlling the local temperature of the material introduced into the mold.

[0002] It applies in particular to injection molding, high pressure or low pressure, and to gravity molding. State of the art

[0003] Molding is a very old metallurgical shaping technique. Today, injection molding in a permanent mold is widely used to mass-produce complex-shaped parts. Parts made of various light alloys for the automotive sector, such as cylinder heads and crankcases, are produced using this method. Complex-shaped parts for the aerospace industry and mechanical engineering are also produced, such as structural components, heat exchangers, and mechanical or fluidic fittings. Besides light alloys (aluminum, aluminum-silicon, magnesium), alloys shaped by injection molding include copper and zinc alloys. In the ferrous metals sector, cast iron molding is a well-known example.

[0004] Permanent molds typically have at least two parts, called shells, which, by closing onto each other, define the external shape of the casting; they may include cores to form openings or depressions in the part. The wall thickness of complex castings can vary significantly from one location to another. Since the latent heat of solidification is extracted by the mold, this implies a variation in the cooling rate. The cooling rate influences the metallurgical structure within the casting, affecting macrosegregation, microsegregation, and precipitation. Consequently, the mechanical properties of the casting material can vary from one location to another, depending on the local cooling rate.This can limit the performance of castings, as the designer cannot fully exploit the capabilities of the alloy used to create the casting. It also complicates the modeling of castings during the design phase. Finally, it increases the risk of defects appearing in critical areas of the part; these defects can include sink marks or porosity.

[0005] To overcome this problem, those skilled in the art have been using localized mold cooling techniques (also called "directed cooling") for decades. These techniques utilize cooled inserts, and in particular cooled cores; for aluminum alloys, this is already described in Aluminium-Taschenbuch, 14th edition, Düsseldorf 1983, p. 419, which is a reference work for those skilled in the art. One such technique is known as "jet cooling." According to this technique, a mold core is formed by a blind tubular body (which those skilled in the art call a "core pin" in English, or, in French, a "broche," and which will be referred to here as a "cooling finger") that is cooled from the inside. This cooling can be continuous or intermittent.The applicant markets jet cooling devices in which a quantity of water is first injected into the tubular body through a first inlet; this water evaporates, at least partially (and it is then primarily the enthalpy of vaporization that causes the cooling), and the water vapor is subsequently expelled by a jet of air injected through a second inlet. This cycle can be repeated several times for each molding cycle. The cooling finger is made of a metal alloy that resists contact with the molten material; however, its lifespan is limited. Given the risk of perforation due to wear, the system's leak-tightness is checked after each cycle; this is one of the functions of the air jet.The other function of the air jet is to expel any traces of water from the tubular body at the end of the molding cycle, before the molten metal enters the mold, given the risk of explosion in case of direct contact between water and molten metal. Several cooling fingers can be deployed within the same mold. This increases the number of degrees of freedom for the part designer but can lead to some congestion around the mold by water and air ducts.

[0006] US patent 2014 / 0008031 (Magna BDW Technologies) shows a typical cooling finger, which has a proximal portion with nozzles for the cooling medium and a distal portion designed to contact the area to be cooled. However, the presence of welded joints in the distal portion may pose a reliability problem in contact with liquid metal.

[0007] Jet cooling has become a standard technique, which has improved the quality of the injection molding process, reduced the scrap rate, extended the life of molded parts and cores, while reducing the molding cycle time.

[0008] However, it is quite difficult to calibrate the cooling process according to the desired result, and according to the local and global parameters of the process.

[0009] From a thermal perspective, the injection molding cycle does not lead to a steady state: it comprises a phase of injecting molten material, followed by a solidification phase of the injected material, during which significant heat transfer occurs from the material to the mold shell, and finally a mold opening phase to unload the part and possibly clean the mold surface. After cleaning, a surface treatment can be applied by spraying with a release agent (coating). It is important to emphasize that the solidification of the molten material is a phase transition accompanied by a significant enthalpy flux.Taking all these parameters into account, it becomes clear that the mold's thermal performance can be affected by changes in overall parameters, such as the mold cycle time, the liquid metal temperature, the ambient temperature in the workshop, and the temperature of the water injected into the nozzle. Furthermore, the calibration of the jet cooling process can vary depending on the part shape and location within the part, and it is highly dependent on the alloy used. Numerical models exist to simulate the temperature distribution within the molded part; these models can assist the process designer in determining the jet cooling sequence.

[0010] The applicant realized that it would be desirable to have an optimized jet cooling process that better reflects the thermal reality within the shell and the molten material injected into the mold during its cooling. Unfortunately, this reality is not accessible in real time. The temperature of the shell's external surface can be easily measured, or temperature probes can be integrated into the shell as described in documents DE 102 015 105 097 (J. Pfleghar), JP 2004-25260 (Honda), EP 1 950 020 (Mitsubishi), US 2003 / 015308 (Howmet Research), WO 2000 / 23244 (Gellert), and JP S62 204915 (Daiwa Kogyo Co.).

[0011] EP 3 315 226 A1 (Nissan Motor Co) describes a cooled casting core used for cylinders in a cylinder head mold. This core is made of two interlocking parts, the outer part having a blind hole for a temperature probe. The two-part design allows a spiral channel to be machined on the outer surface of the inner part. This spiral shape is necessary to ensure satisfactory thermal homogeneity but is quite difficult to manufacture. However, in such a large core, a temperature measurement at a point in the outer part may not be representative. Furthermore, assembling the multi-part core requires labor in the mold shop, and there is a residual risk of fluid leakage, with potentially serious consequences.

[0012] WO 2007 / 026987 (Kang) describes an injection mold equipped with heating elements and a temperature probe near the surface in contact with the molten material. US 2004 / 0213321 (ICIPC) describes a plastic injection mold comprising two plates defining a cavity for receiving the molten material, said plate possibly including a channel for circulating a cooling medium; a metal plate including a temperature probe is inserted between the two plates in contact with said cavity.

[0013] However, these systems provide a rather indirect temperature reading, given the various heat fluxes and temperature gradients that develop within the mold cavity and the cooling casting. The publication "Heat fluxes at metal-mold interface during casting solidification" by A. Sabau, published in Light Metals 2006, pp. 827-832, describes an experimental setup in which a thin-film thermal probe was placed on the internal surface of a mold cavity, leaving a visible trace on the casting. This method certainly provides a particularly representative value for the temperature of the solidifying metal, but the device is far too fragile to be considered for use in a mold used in an industrial setting.

[0014] The applicant noted that the prior art does not describe a method for adjusting the cooling process to the instantaneous reality of the mold. One problem that the present invention seeks to solve is to provide a forced cooling method for an injection mold that best takes into account the actual local temperature of the molten material introduced into the mold, that is easy to use, that does not require significant modification of the mold shells, that is adaptable to a large number of injection mold types, that allows the use of known jet cooling devices, and whose installation and use do not disrupt the industrial process in any way, which must meet high productivity constraints, including during mold changes. Objects of the invention

[0015] According to the invention, the problem is solved by a method which uses a new type of cooling finger directly incorporating the temperature probe in a blind orifice provided in the outer casing of the finger, between the outer surface and the cooling channel, according to claim 1.

[0016] The invention offers numerous advantages over the prior art described above. First, it integrates the cooling and temperature measurement functions within a single mechanical component. This integration allows for the precise and virtually immediate acquisition of a representative temperature value for the metal, namely the molten metal, the metal during solidification, and the metal during cooling. Furthermore, the solution proposed by the invention does not disrupt the industrial molding process, since the mechanical elements dedicated to temperature measurement are integrated into the cooling finger, which is already conventionally used.

[0017] Furthermore, the invention allows for simplified information processing compared to the prior art. Indeed, according to the invention, the blind hole for receiving the temperature probe opens on the outside of the mold, i.e., opposite the molten metal. Consequently, the connection between the temperature probe and the central processing unit can be easily established, notably via wired communication, without having to penetrate the mold walls.

[0018] The solution proposed by the invention will be compared with one involving a cooling plate interposed between two walls of the mold. In this case, the connection between this plate and the processing means is significantly more complex. Indeed, in the case of wired communication, the connecting means must necessarily pass through the walls of the mold.

[0019] One means of the invention is a cooling finger for controlling the local temperature of a part during its molding by introducing molten material into a permanent mold. The cooling finger comprises an elongated body having an outer peripheral wall designed to penetrate a wall of the mold, and a longitudinal end designed to be in contact with, or in the immediate vicinity of, the molten material. The body comprises at least one channel for circulating a heat transfer fluid. The cooling finger is characterized in that the body further comprises at least one blind hole, separate from the circulating channel. The blind hole is adapted to receive temperature measurement means. The circulating channel for the heat transfer fluid is straight. Its diameter is advantageously between 1.5 mm and 6 mm.

[0020] The elongated body is very advantageously formed as a single piece; this saves assembly time and also minimizes the risk of leaks at assembly points in an environment marked by thermal gradients.

[0021] The blind hole takes the form of a channel of small diameter, typically between approximately 0.3 mm and approximately 3 mm; this diameter is advantageously substantially constant. The blind channel may be straight, and / or it may include at least one curved portion, in particular a curved portion separating two straight sections. It advantageously opens at the end of the body opposite the mold. The smallest distance separating, in operation, the blind hole and the peripheral wall of the body is advantageously between 2.0 mm and 7.0 mm.

[0022] Said cooling finger includes two blind holes, in particular arranged symmetrically with respect to the main axis of the body, viewed from the end.

[0023] Another means of the invention is a control assembly comprising at least one cooling finger according to the invention, as well as at least one temperature measuring element, said temperature measuring element being received in a blind hole of said cooling finger, said assembly further comprising a central unit including a microprocessor, as well as means for transmission between said central unit and said at least one temperature measuring element. Said temperature measuring element may, in particular, be a thermocouple or a platinum probe. It may be inserted into said blind hole, preferably to the bottom so that the measurement is representative of the temperature of the material injected into the mold. Advantageously, said control unit is capable of controlling an auxiliary cooling element, adapted to direct a heat transfer fluid in the circulation channel of said cooling finger.

[0024] Another means of the invention is a method for controlling the local temperature of a part during its molding by introducing molten material into a permanent mold, using a control assembly according to the invention, a method in which: molten material is introduced into said mold, at least one cooling-evacuation sequence is carried out, during which a heat transfer fluid is first admitted into the main channel of the cooling finger, in order to cool the material injected into the mold, then the residual fraction of said heat transfer fluid is evacuated by means of an evacuation fluid, at least one measurement of the value of a parameter representative of the temperature is carried out, by means of said measuring means.

[0025] Several point measurements of the value of this temperature-representative parameter can be taken, particularly at a predetermined frequency. A recording of the value of this temperature-representative parameter can also be made, particularly for tracing purposes.

[0026] Advantageously, the measured value of said parameter is compared with a predetermined maximum or minimum value, and if this measured value is higher than said maximum or lower than said minimum, the execution of at least one cooling-evacuation sequence is modified. This modification may include, in particular, a change in at least one of the control parameters for the injection of the heat transfer fluid, these parameters being at least the flow rate, pressure, and duration of the heat transfer fluid injection. Alternatively, or in addition, the modification may also be made by performing at least one additional cooling-evacuation sequence. It may also concern the temperature of said injected heat transfer fluid.

[0027] The object of the invention is a method for controlling the local temperature of a part during its molding by introducing molten material into a permanent mold, by means of a control assembly comprising at least one cooling finger for controlling the local temperature of a part during its molding by introducing molten material into a permanent mold, as well as at least one temperature measuring element, said temperature measuring element being received in a blind hole of said cooling finger, said assembly further comprising a central unit including a microprocessor, as well as means for transmission between said central unit and said at least one temperature measuring element, said cooling finger comprising an elongated body, preferably forming a single piece, said elongated body having an outer peripheral wall intended to penetrate through a wall of said mold, as well as a longitudinal end intended to be in contact with said molten material, or in the immediate vicinity of said molten material, the body comprising at least one circulation channel for a heat transfer fluid, said circulation channel being straight, and said body further comprising at least one blind hole, separate from said circulation channel, said blind hole being suitable for receiving temperature measuring means, and at least one of said cooling fingers having two blind holes, a temperature measuring means being received in each of the two blind holes, said process being characterized in that: molten material is introduced into said mold, at least one cooling-evacuation sequence is carried out,during which a heat transfer fluid is first admitted into the main channel of the cooling finger to cool the material injected into the mold, then the residual fraction of said heat transfer fluid is evacuated by means of a evacuation fluid, at least one measurement of the value of a temperature parameter is carried out, by means of said measuring means, the temperature values ​​deduced from said temperature representative values ​​(or directly said temperature representative values) provided at the same instant by each of said two temperature measuring means are compared for at least one of the cooling fingers having two temperature measuring means, in the event that the absolute value of the difference between these two values ​​exceeds a predefined threshold, an alert is given, and / or the actuation of the cooling-evacuation sequences is interrupted,and / or the molding cycle for a part is interrupted and / or the next molding cycle is not triggered. Brief description of the figures

[0028] Other advantages of the invention will become apparent upon reading the description of four embodiments of the invention, given below by way of example only and not limitation, with reference to the attached drawings in which: There figure 1 is a front view, illustrating a temperature control device usable in the process according to the invention. figure 2 is a front view, analogous to the figure 1 illustrating another temperature control device usable in the process according to the invention. figure 3 is a front view, analogous to the figure 1 illustrating a first embodiment of a temperature control device used in the process according to the invention. figure 4is an end view, illustrating the temperature control device of the figure 3 . There figure 5 is a front view, analogous to the figure 1 illustrating a second embodiment of a temperature control device used in the process according to the invention. figure 6 is an end view, illustrating the temperature control device of the figure 5 . There figure 7 is derived from the figure 1 and shows a variant of this device.

[0029] The following reference symbols are used in the figures and in the detailed description that follows: 1 Cooling finger 2 Body 11 Auxiliary organ 12,13 Tips 15 Threaded end 20 Inner longitudinal end of 2 21 Outer longitudinal end of 2 30 Base 35 Main barrel 40 Terminal col 41 Free end 42,44 Shoulders 50 Main Channel 51,52 Sections of 50 53 Tapping 55 Tube 56 Central unit 57 Command line 60 Hole 62 End of 60 (bottom of the hole) 63 60mm end (hole opening) 64 Transmission line 72, 74 Solenoid valves 73 Connector 82,83 Liquid and air supply 84 Purge 85 Inlet duct Detailed description

[0030] There figure 1illustrates a first embodiment of a temperature control device usable in the process according to the invention. This device comprises, firstly, a cooling finger, which is designated as a whole by reference numeral 1. Note A1 the main longitudinal axis of the finger, which is vertical on this figure 1 Once the finger is installed in a mold part, not shown in the figure 1 This main axis extends transversely with respect to this part of the mold. In other words, the finger extends through this part of the mold, between its inner and outer faces respectively.

[0031] This cooling finger first comprises a body 2, made of a heat-conducting material, such as, in particular, highly alloyed carbon steels based on chromium, molybdenum and vanadium, and preferably alloys suitable for use at high temperature.

[0032] This body 2 is fixed, by its outer peripheral face, to the aforementioned mold part. This fixing, which is of a type known per se, is notably achieved by screwing. For this purpose, the aforementioned outer face may be equipped with suitable means, not shown. With reference to the axis A1, the body comprises two longitudinal extremities, one of which 20 is called internal, because it is adjacent to the molten metal in use, and of which the other 21 It is said to be external because it is opposite to that metal.

[0033] In a conventional manner, the body comprises different concentric regions, the cross-section of which decreases from the outermost end. 21 towards the inner end 20. As shown on this figure 1 the body 2 includes a base 30, a main barrel 35, as well as a terminal neck 40.These constituent elements are separated in pairs by their respective shoulders. 42 And 44. The geometry of the body is not an essential feature of the invention, so it will not be described in further detail. However, it should be noted that the invention applies particularly to cooling fingers having an outside diameter at the terminal neck 40 which does not exceed 12 mm.

[0034] The free end 41 The neck, which is rounded in shape, is designed to be in contact with the molten material or in its immediate vicinity. On the figure 1 Two typical positions of the inner face of the mold section, corresponding to the interface with the molten metal, have been marked in dashed lines. The line P1 illustrates an internal face located above the end 41, so that the latter is not in immediate contact with the molten metal. On the other hand, the line P2illustrates an internal face located below the end 41, so that the latter is immersed in this molten metal. In any case, this end is positioned so that the finger 1 is capable of cooling molten material, as we will see below.

[0035] The body 2 is dug with a main canal 50, in this case, a straight line, extending parallel to the longitudinal axis A1. This channel opens onto the outer end 21, but not on the inner end 20. This channel 50 consists of two successive sections, one of which 51 is provided both in the neck, the shaft, and part of the base. In contrast, the other section 52, of larger diameter, is only found in the base. Near its opening, the walls of this section 50 form a tapping 53, intended to cooperate with an auxiliary body11, of a type known in itself.

[0036] As shown schematically on the figure 1 (but not on the figures 2 , 3 And 5 ), this auxiliary organ 11 is connected to a cylindrical tube 55 which, when the device is in operation, is housed in the main channel 50 and extends along most of its length, almost to its end. It is through this tube 55 which is injected into the channel 50 a quantity of heat transfer fluid for cooling the finger, and it is through this tube 55 Air is then injected to evacuate this fluid from the channel 50 These two fluid flow directions are marked by arrows on the figure 1 This cycle is referred to here as the cooling-evacuation cycle.

[0037] The auxiliary organ 11 It has two nozzles 12 And 13, mon 12connected to a supply of a cooling fluid 82 (also called heat transfer fluid here, typically water), the other 13 connected to a compressed air supply 83, suitable for injection into the tube 55 successively these two fluids, namely water (which, by evaporating, cools the body) 2 and in particular its terminal neck 40 ) and air. Each of these two power supplies 82,83 is equipped with a solenoid valve 72,74 ; These are controlled by a microprocessor, according to a sequence that can be programmed by a technician for each type of molded part. The component 11 It is also equipped, in the conventional manner, with a threaded end. 15, suitable for being mounted in a removable and watertight manner on the threaded hole 53 cooling finger 1. Solenoid valves 72,74 are advantageously located in a single connector 73which can be mounted directly onto the nozzles 11,12 or which may be located at a certain distance from said nozzles.

[0038] According to an essential aspect of the invention, the body 2 is also equipped with a blind hole 60, separate from the main channel 50. This hole 60 opens onto the outer longitudinal end 21, but not on the inner end 20. This hole 60 is achieved by any suitable process. For example, a mechanical process, such as drilling or boring, may be used.

[0039] The hole 60, which extends here in a straight line, is slightly offset from the longitudinal axis A1. The offset angle relative to the axis of the main channel 50 allows this hole 60 to be globally equidistant from the outer walls of the body, as well as from its inner walls bordering the canal50.

[0040] We will now give, as non-limiting examples, different dimensional values ​​of the cooling finger 1 described above: total height H1 between 50 mm and 500 mm; diameter D51 of the canal at the level of its main section 51, between 1.5 mm and 6 mm; diameter D60 of the hole between 0.3 mm and 3.0 mm; distance d between the hole and the channel, taken perpendicular to the axis of this hole, between 3 mm and 10 mm; distance D between the hole 60 and the external surface of the cooling finger, measured perpendicularly to the axis of this hole, between 3 mm and 10 mm; external diameter at the terminal neck 40 not exceeding 12 mm.

[0041] The hole 60 receives temperature measurement means, which are formed by a thread-like probe 61.This probe, of a type known per se, is for example a thermocouple or a platinum probe. The probe is fixed relative to the walls of the hole 60, by all appropriate means, including screwing. This probe 61 presents longitudinal dimensions greater than those of the hole 60. Therefore, a first extremity 62 one end of the probe extends near the bottom of the hole, while the other end 63 protrudes beyond the opening of this hole. This end 63 is connected, via a transmission line 64, to a central unit 56 control and command unit, which includes a microprocessor. This unit is also connected via a command line 57, to the solenoid valves 72,74 described above.

[0042] The implementation of the temperature control device, described above, will now be explained in the following.

[0043] When molten material is poured into the mold, equipped with the cooling finger 1, solenoid valves 72,74 are activated to perform successive cooling and then evacuation sequences, as described above. These sequences can be performed in a predefined manner, in particular at a predetermined frequency and / or with a predetermined cycling.

[0044] Furthermore, measurements are taken of the value of a parameter representative of the temperature, using the probe 61.As mentioned above, the temperature measured by the probe is representative of the actual temperature of the molten material, given the close proximity between the probe and the molten material. Therefore, a preliminary calibration can be performed to determine the correlation between these two temperatures, knowing that the temperature of the molten material is also known. These measurements of the temperature parameter can be taken continuously or intermittently, particularly at a predefined frequency. For example, the temperature can be measured after the molten material has been injected into the mold and after each cooling and mold removal cycle.

[0045] The parameter representing the temperature can be, depending on the type of probe, for example a voltage, a current, or a resistance. The measured values ​​of this parameter are transmitted to the central processing unit. 56, or to a unit dedicated to the processing and recording of these signals (not shown in the figures), where they may be subjected to at least one processing step, among those mentioned below.

[0046] These values ​​can first be stored to allow for tracing the manufacturing process of the cast part. This tracing can, in particular, be part of a quality assurance approach.

[0047] These values ​​can also be used to initiate a feedback step via the central processing unit. In particular, if at least one value measured by the probe 61is greater than a predetermined threshold value, the central unit controls the auxiliary device, via the line 57. This control operation can lead to a modification of at least one cooling-evacuation sequence. This modification may include, in particular, a change to at least one of the control parameters for the injection of the heat transfer fluid; these parameters being at least the flow rate, pressure, and duration of the heat transfer fluid injection. For example, at least one additional cooling-evacuation sequence can be implemented using this auxiliary device. 11, in order to lower the temperature of the molten material introduced into the mold.

[0048] There figure 2 illustrates a second embodiment of a cooling finger usable in the process according to the present invention. On this figure 2 , the mechanical elements analogous to those of the figure 1They are assigned the same reference numbers, increased by the number 100.

[0049] The cooling finger, shown on this figure 2 differs from that 1 of the figure 1 essentially in that it presents a body 102 whose geometry is different. More precisely, the main shaft 135 is made up of two elements 136 And 137 of different cross-sections, connected by an additional shoulder 138. Furthermore, the pass 140 is equipped with a terminal nipple 146. Finally, the neck and the shaft are connected by a ramp 140, whose axial dimension is greater than that of the shoulder 40 of the first embodiment. The circulation channel 150 is rectilinear, and the same remark applies to the blind hole 160.

[0050] The differences that exist between the respective fingers 1 And101 are not related to temperature measurement, nor to the processing of the measured values. Indeed, as in the first embodiment, the finger 101 is equipped with a single straight blind hole 160 allowing the reception of a single probe 161 temperature measurement.

[0051] THE figures 3 and 4 illustrate a first embodiment of a cooling finger used in the process according to the present invention. On these figures 3 and 4 , the mechanical elements analogous to those of the figure 1 They are assigned the same reference numbers, increased by the number 200.

[0052] The cooling finger 201, represented on these figures 3 and 4 differs from that 1 of the figure 1 firstly, in that it includes two blind holes 260 And 270, extending symmetrically with respect to the longitudinal axis A201.Furthermore, each hole 260, 270 comprises two straight sections 265, 275 And 266, 276, mutually connected by a central section 267, 277 curved in shape.

[0053] It should be noted that, in this third embodiment, the cross-section of the main shaft 235 is significantly lower than that of the base 230. Under these conditions, the presence of this curved section 267, 277 allows blind holes to be located approximately equidistant from the inner and outer walls of the body, respectively.

[0054] It should also be noted that, in this embodiment, each blind hole does not extend into the terminal neck 240. Indeed, this neck is intended to be fully immersed in the molten material, and the wall thickness is too thin at this point to allow for the creation of a blind hole.

[0055] As in previous embodiments, each blind hole receives a respective threaded probe 261, 271, which must be flexible enough to adapt to the curved section 267, 277 and rigid enough to be threaded all the way through the blind hole. The ends of each probe, protruding outside the receiving holes, are typically connected to a single control unit not shown.

[0056] THE figures 5 and 6 illustrate a second embodiment of a cooling finger that is used in the process according to the present invention. On these figures 5 and 6 , the mechanical elements analogous to those of the figure 1 They are assigned the same reference numbers, increased by the number 300.

[0057] The cooling finger 301, represented on these figures 5 and 6 differs from that 1 of the figure 1 in that it has four blind holes 360, 370, 380 And 390.As shown on the figure 6 These holes are straight and are regularly spaced at an angle around the main axis. A301. Each blind hole receives a respective thread-like probe 361, 371, 381, 391. The ends of each probe, protruding outside the receiving holes, are typically connected to a single control unit not shown.

[0058] It is noted that in the embodiments with several blind holes which are shown, respectively, on the figures 3 and 4 and on the figures 5 and 6 , the smallest distance separating the blind hole and the peripheral wall of the body is the same for each of the blind holes.

[0059] Using multiple temperature probes, each housed in a separate blind hole, can offer specific advantages. This allows for the simultaneous acquisition of several independent temperature measurements. Under these conditions, the central processing unit typically calculates an average, for example, an arithmetic or geometric average, of these measurements. The resulting averaged measurement is more accurate than any individual measurement. Alternatively, each measurement can be used individually. This can be particularly useful in two situations. The first involves a mold whose shape near the cooling finger is asymmetrical, which can lead to temperature differences in the molten material introduced into the mold during its cooling process.

[0060] The presence of several temperature measurement probes on the same cooling finger also facilitates the detection of a local perforation of a blind hole following wear of its metal wall; in an extreme case the blind hole will be invaded by material in a molten state, which leads, on this probe, to a statistically aberrant temperature value.

[0061] More specifically, in the method according to the invention, the representative temperature values ​​provided at the same instant by each of the two temperature measurement means are compared for at least one of the cooling fingers comprising two temperature measurement means. If the absolute value of the difference between these two values ​​exceeds a predefined threshold, an alert is triggered, and / or the activation of the cooling-evacuation sequences is interrupted, and / or the molding cycle of a part is interrupted, and / or the next part molding cycle is not initiated. In this last case, the casting machine stops.

[0062] We can also foresee two successive thresholds for said absolute value: after exceeding the first threshold an alert is given, and after exceeding the second threshold, higher than the first, the current molding cycle is interrupted and / or the next molding cycle of parts is not triggered.

[0063] Obviously, instead of comparing the representative temperature values ​​measured by each of the two probes, and determining the absolute value of the difference between these values, one can also determine the temperature represented by these measured values, and determine the absolute value of the difference between these two temperatures; this variant requires additional data processing steps to calculate the temperature from the representative value of this temperature which is measured by said probes, which is typically done by applying the calibration curve specific to each probe.

[0064] As a variant compared to the methods of implementation of figures 3 to 6It can be expected that the blind holes will have different diameters. This offers specific advantages, notably in that it allows for the use of different types of temperature probes (for example, a thermocouple and a platinum probe). Generally, the diameter of the blind holes is constant and typically ranges from 0.3 mm to 3 mm. It is undesirable to have too much play between the probe and the wall of the blind hole: the correct hole diameter (for a given probe) is the smallest diameter that allows the probe to be fully inserted; similarly, the correct probe diameter (for a given hole) is the largest diameter that allows the probe to be fully inserted. Even when the blind holes have different diameters, it is advantageous for the smallest distance between the blind hole and the peripheral wall of the body to be the same for each of the blind holes.

[0065] THE figure 7 shows an advantageous variant of the embodiment of the figure 1 The difference lies in the auxiliary organ. 11 which is connected, on the one hand, to an inlet duct 85, and on the other hand to an outlet duct 84, also called "purge". The inlet duct 85 is alternately supplied with the cooling fluid (typically water) which arrives via the cooling fluid supply 82, and with compressed air coming in through the air supply 83. The purge pipe 84 can be opened and closed using a solenoid valve 72. The system leak test mentioned above can be performed by injecting air through the duct. 83, the solenoid valve 72 being closed.

[0066] As explained above, the cooling finger 1according to the invention, equipped with its temperature probe inserted into the blind hole 60, can be integrated into a control system, which also includes a central processing unit 56 including a microprocessor, as well as transmission means 64 between said central unit and said at least one temperature measuring device. Said control unit is capable of controlling an auxiliary cooling device, adapted to direct a heat transfer fluid in the circulation channel of said cooling finger.

[0067] We describe here a typical embodiment of an injection molding process that uses this control system. In this process Molten material is introduced into said mold, for example by high-pressure injection, low-pressure injection, or casting; at least one cooling-evacuation sequence is carried out, during which a heat transfer fluid is first admitted into the main channel of the cooling finger in order to cool the material introduced into the mold; then the residual fraction of said heat transfer fluid is evacuated by means of an evacuation fluid; at least one measurement of the value of a parameter representative of the temperature is carried out by means of said measuring means.

[0068] Temperature measurement can be carried out when the metal introduced into the mold is still liquid, and / or when it is cooling, and / or during the cooling of the solidified metal.

[0069] These measurements can be performed periodically, particularly at a predetermined frequency. The value of the temperature parameter can be recorded, notably for tracing purposes. In one embodiment, the measured value of the parameter is compared with a predetermined maximum value, and if the measured value exceeds this maximum value, at least one additional cooling-evacuation sequence is performed. The invention also allows monitoring of the local temperature evolution of the metal introduced into the mold; this cooling curve can be critical for certain alloys, as it is known that the metal structure can evolve even after solidification through diffusion and precipitation processes.

[0070] The invention can be applied in particular to the molding of metal parts made of light alloys (magnesium alloys, aluminum alloys), to the molding of parts made of zinc alloys, or to the molding of polymer parts. It can be applied to injection molding (in particular high-pressure and low-pressure) and to gravity molding.

Claims

1. A method for controlling the local temperature of a part during its molding by introducing molten material into a permanent mold, using a control assembly comprising at least one cooling finger for controlling the local temperature of a part during its molding by introducing molten material into a permanent mold, and comprising at least one temperature measuring element, said temperature measuring element being received in a blind hole (60) of said cooling finger (1), said assembly further comprising a central unit (56) comprising a microprocessor, and means for transmission between said central unit and said at least one temperature measuring element, said cooling finger comprising an elongated body (2), preferably forming a single piece, said elongated body (2) having an outer peripheral wall intended to penetrate through a wall of said mold, and a longitudinal end intended to be in contact with said molten material, or in the immediate vicinity of said molten material, the body comprising at least one circulation channel (50) for a heat transfer fluid, said circulation channel (50) being straight, and said body (2) further comprising at least one blind hole (60), separate from said circulation channel, said blind hole being suitable for receiving temperature measurement means, and said at least one cooling finger having two blind holes, a temperature measurement means being received in each of said two blind holes, said method being characterized in that : - molten material is introduced into the mold, - at least one so-called cooling-evacuation sequence is carried out, during which a heat transfer fluid is first admitted into the main channel of the cooling finger, in order to cool the material injected into the mold, then the residual fraction of said heat transfer fluid is evacuated by means of an evacuation fluid, - at least one measurement of the value of a parameter representative of the temperature is carried out, by means of said measuring means, - for the at least one cooling finger equipped with two temperature measurement means, the values representative of the temperature provided at the same instant by each of said two temperature measurement means are compared; - in the event that the absolute value of the difference between these two values exceeds a predefined threshold, an alert is given, and / or the activation of the cooling-evacuation sequences is interrupted, and / or the molding cycle of a part is interrupted, and / or the next molding cycle is not triggered.

2. A method according to claim 1, wherein several spot measurements of the value of said parameter representing the temperature are carried out, in particular at a predetermined frequency.

3. A method according to any of claims 1 and 2, wherein a recording is made of the value of said parameter representing the temperature, in particular for tracing purposes.

4. A method according to any of claims 1 to 3, wherein the measured value of said parameter is compared with a predetermined maximum or minimum value and, in the event that this measured value is greater than said maximum value or less than said minimum value, at least one of the control parameters of the injection of the heat transfer fluid is modified, and preferably at least one of the control parameters selected from the group formed by the flow rate, pressure and duration of injection of heat transfer fluid, and / or at least one additional cooling-evacuation sequence is carried out.

5. A method according to any of claims 1 to 4, wherein said circulation channel (50) has at the level of its main section (51) a diameter (D51) between 1.5 mm and 6 mm.

6. A method according to any of claims 1 to 5, wherein the cross-section of said blind holes (60) is between approximately 0.3 mm and approximately 3 mm.

7. A method according to any of claims 1 to 5, wherein the smallest distance separating, in service, the blind holes (60) and the peripheral wall of the body is between 2.0 mm and 7.0 mm.

8. A method according to any of claims 1 to 7, wherein said blind holes are straight or comprise at least one curved portion, in particular a curved portion separating two straight sections.

9. A method according to any of claims 1 to 8, wherein said blind holes open onto the end of the body, opposite the mold.

10. A method according to any of claims 1 to 9, wherein said blind holes are arranged symmetrically with respect to the main axis of the body, viewed from the end.

11. A method according to any of claims 1 to 10, wherein the smallest distance separating, in service, the blind holes (60) and the peripheral wall of the body is the same for each of the blind holes.

12. A method according to any of claims 1 to 11, wherein said molten material is a metal.