EP1072340B1 - Method of process control of injection molding or semiliquid die casting of metals - Google Patents

Abstract

Process for monitoring die casting or thixoforming of metals (14) in a die casting or thixoforming device containing a casting chamber (10), a plunger (12) and a mold with cavities (16, 18) comprises measuring the periodic course of the pressure and determining the time-dependent speed of the plunger, calculating energy introduced through the plunger as a function of the process time and the total energy introduced during die casting and/or thixoforming through the plunger based on the time-dependent course of the pressure and the plunger speed, and using the total energy as a parameter for the monitoring of the process.

Description

The invention relates to a method for process monitoring in die casting or thixoforms of metals according to the preamble of claim 1. The invention further relates to a die casting or thixoforming device accordingly the preamble of claim 12.

The automotive industry in particular is making ever increasing demands the tolerances and the mechanical properties of die casting and Provided thixiform parts. To achieve these high quality requirements the most complete possible monitoring of the process parameters and their Reproducibility is of great importance.

For the control of a die casting or thixoforming process are on the one hand Condition of the metal inserted in the casting chamber and on the other hand the parameters of the die casting or thixoforming process. To the die casting or to optimize the thixoform process or any, for process stability and to evaluate reproducibility critical parameters, all must if possible Parameters are recorded which can influence the process.

An essential factor for achieving high reproducibility and Process stability is the condition of the thixotropic metal bolt or the die-casting alloy when inserted into the casting chamber, the temperature of the thixotropic bolt or die casting alloy is a very important size.

To control and monitor the die casting or thixoform process Temperature measurements in the alloy melt or inside the thixotropic metal studs are made during the heating process, the temperature distribution, for example by means of thermocouples at different Melt or bolt positions (inside the bolt and on Bolt edge) is determined. It is usually for the individual Relevant heating curve, i.e. Temperature as a function of heating time, determined.

While for the monitoring of alloy melts for die casting in Essentially the temperature measurement is used, the measurement forms during electrical heating energy supplied to the preheating is another possibility for monitoring the stud condition during thixoforming.

For monitoring a thixoforming process, you can also use the thixotropic Bolt metallographic tests to determine the distribution of the liquid content be carried out, for example by the bolt on different Cut longitudinal positions transverse to its longitudinal axis and the liquid portion in the cross section of the bolt, for example as a function of the distance from the center of the bolt, is determined. The aim of such investigations is to optimize the heating curves in such a way that a predetermined proportion of liquid is as short as possible is achieved homogeneously throughout the thixotropic bolt. Furthermore, you can calorimetric measurements were carried out to determine the average liquid fraction become.

Regarding the parameters of the die casting or thixoforming process usually the temperatures of the casting chamber, the sprue and the Mold cavity measured, as well as the pressure and humidity in the evacuated Form cavity determined.

The previously usual determination of the parameters with regard to the die casting or Thixoform materials and the die casting or thixoforming process are complex and are not suitable for monitoring the die casting or thixoforming process under production conditions.

The invention has for its object a method for process monitoring in die casting or thixoforming of metals with which to manufacture of die cast or thixiform parts reliably under production conditions can be monitored.

The solution to this object according to the invention is that the time profile of the pressing pressure p (t) is measured and the time-dependent speed of the casting piston v (t) is determined, and the energy E (t) supplied by the casting piston as a function of the process time t, and the during the pressure casting or thixoforming process, total energy E _tot supplied by the casting piston is calculated on the basis of the time-dependent course of the pressing pressure p (t) and the casting piston speed v (t), and the total energy E _{tot is used} as a characteristic value for monitoring the pressure casting or thixoforming process becomes.

Further embodiments of the method according to the invention are in the dependent Claims 2 to 10 described. The method according to the invention is particularly suitable for die casting or thixoforming of aluminum, Aluminum alloys or magnesium alloys.

The method according to the invention is particularly suitable for horizontal thixoforming devices and horizontal die casting systems, i.e. Devices, at which the casting chamber is horizontal.

The method according to the invention is based on the knowledge that the Total energy supplied to the plunger is a very relevant control parameter the entire die casting or thixoforming process. The inventive Method for determining the energy supplied by the casting piston and the use in particular of the total energy value as a parameter for Process monitoring is also called RTIM (Real Time Injection Monitoring).

The preheating temperature and the corresponding temperature distribution are particularly relevant in the metal bolt as well as the amount of that supplied by the casting piston Energy in thixoforming because it has a certain range of variation liquid content in the thixotropic material got to. For example, in the case of thixoforming from a large one, through the casting piston total energy supplied can be concluded that the viscosity of the thixotropic material is too deep, which is either due to a too deep liquid portion or too little shear during the thixoforming process.

The method according to the invention allows better process stability, one Optimizing process parameters, improving product quality and a reduction in the reject rate.

The method according to the invention is particularly preferred for thixoforming Application. It is used in particular to determine the optimal liquid content of the thixotropic metal bolt under production conditions. The optimal the average liquid content in the thixotropic metal bolt is 40-55% by weight. If the liquid content is too high, thixoforming of thixotropic material occurs almost under the same conditions as the die-casting of liquid Metal alloys, so for example the advantage of low shrinkage of thixotropic material is lost in the mold cavity when cooling, or that Shear the oxide skin surrounding the thixotropic metal bolt difficult or is impossible. In addition, the dimensionally stable insertion of a thixotropic bolt into the casting chamber with a high liquid content difficult and mostly not reproducible.

Another important factor in thixoforming is the homogeneity of the thixotropic Condition, i.e. the distribution of the liquid portion over the bolt length and Bolt cross section, this homogeneity is generally better the slower the preheating process is carried out; on the other hand, it becomes business As short a heating-up time as possible.

As part of the inventive step it has now been found for thixoforming, that by determining the feed through the casting piston to the thixoform material Total energy during a thixoforming process after preheating present liquid content and its homogeneity in the thixotropic bolt can be monitored indirectly.

Furthermore, the method according to the invention is particularly suitable for monitoring the preheating furnaces, i.e. by determining the total energy for everyone Shot, i.e. for every complete die casting or thixoforming process, with thixotropic bolts or die-cast material from a specific preheating furnace the regularity of this furnace can be determined and checked. moreover can by determining the total energy for each shot with thixotropic Bolts or die-cast material from various preheating furnaces ensure regularity the heating output of the respective stoves compared and monitored become.

The determination of the total energy for each shot also enables Control of solidifications. Pre-solidification, i.e. early solidification of material, can, for example, due to a too low casting chamber and / or mold temperature be conditional and are the resultant, usually bad ones Mold properties due to undesirable. Due to the possibility of investigation The temperatures of the casting chamber can also be indirectly affected by pre-solidification and check the mold. In addition, statements can also be made indirectly do the design of the mold cavity.

Furthermore, the determination of the total energy for each shot also enables Investigations of pressure losses during the shot as a result, for example tribological properties and thus enables the receipt of information about the friction of the casting piston, the mechanical condition of the casting piston and / or the casting chamber, the piston lubrication and the release agent influence. Accordingly, the determination of those fed into the system by the casting piston serves Total energy during a shot also to monitor the tribological Relationship with the casting piston and casting chamber.

According to the process time-dependent speed v (t) of the casting piston either measured directly or by measuring the process time-dependent Casting piston position s (t) can be determined.

Based on the time-dependent position measurement s (t) of the casting piston, the time-dependent speed v (t) of the casting piston can be determined according to the function v (t) = ds (t) / dt calculate, ie by deriving the time-dependent casting piston position s (t) after the time t. The calculation of the speed of the casting piston based on the position measurement s (t) is expediently carried out at discrete, for example equidistant, times. The speed is expediently calculated at 50 to 800, preferably at 180 to 500 and in particular at 250 to 400 discrete process times. The discrete speed values determined in this way are preferably filtered by numerical methods. In addition, a continuous speed curve v (t) is preferably calculated using numerical interpolation methods.

berechnet werden, wobei A die gegen das Strangguss- oder Thixoformmaterial gerichtete Fläche des Giesskolbens bezeichnet. The time-dependent energy E _{x, y} (t) supplied by the casting piston during two process times t _x and ty, where t _x <t _y, can then according to the integral function

can be calculated, where A denotes the surface of the casting piston directed against the continuous casting or thixoform material.

und die während dem Druckgiess- bzw. Thixoformprozess durch den Giesskolben zugeführte Gesamtenergie E_tot durch die Integral-Funktion

berechnen, wobei A die gegen das Druckguss- oder Thixoformmaterial gerichtete Fläche des Giesskolbens, t₀ den Anfangszeitpunkt t=0 des Druckgiess- oder Thixoformverfahrens und t₄ den Zeitpunkt bezeichnet, an dem der Giesskolben zum ersten Mal nach t₀ die Geschwindigkeit v(t)=0 annimmt. Zum Zeitpunkt t₄ ist der eigentliche Druckgiess- bzw. Thixoformprozess abgeschlossen und die Formkavität ist gefüllt. Um während dem Abkühlen des Formteils in der Formkavität eine Materialschrumpfung auszugleichen und eine entsprechende, unvollständige Formfüllung zu vermeiden, wird der Druck auf die Druckguss- bzw. Thixoformmasse üblicherweise auch nach t₄ noch für eine Weile aufrechterhalten, so dass der Giesskolben eine weitere translatorische Bewegung ausführen kann, wobei dann die Giesskolbengeschwindigkeit ein weiteres Mal auf Null fallen kann.The energy E (t) supplied by the casting piston as a function of the process time t can be determined according to the integral function

and the total energy E _tot supplied by the casting piston during the die casting or thixoforming process through the integral function

calculate, where A is the area of the plunger directed against the die casting or thixoform material, t _{0 is} the starting point in time t = 0 of the die casting or thixoforming process, and t _{4 is} the point in time at which the plunger for the first time after t _{0 is} the velocity v (t ) = 0 assumes. At time t ₄ the actual die casting or thixoforming process is completed and the mold cavity is filled. In order to compensate for material shrinkage in the mold cavity during the cooling of the molded part and to avoid a corresponding, incomplete mold filling, the pressure on the die casting or thixoform compound is usually maintained for a while even after t ₄ , so that the casting piston undergoes a further translational movement can perform, then the plunger speed can drop to zero again.

Instead of measuring the time-dependent casting piston position s (t), the time-dependent speed profile v (t) can be measured directly and used to calculate the energy E (t) supplied by the casting piston or the total energy E _tot .

The piston position s (t) or the piston speed v (t) and are preferred the course of the pressing pressure p (t) during the entire die casting or thixoforming process measured continuously.

It is also essential to the invention that the measurements s (t) and p (t), or v (t) and p (t), and the calculation of v (t), E (t) and E _tot on-line during the process sequence be carried out so that the parameters are available immediately after the shot for corresponding corrective measures, ie the measurements of s (t) or v (t) and p (t), and the determination of v (t) and E (t) takes place in real time. A process window is available between two shots, which allows intervention by taking corrective measures, because immediately after the shot the molded part must be cooled further, the mold opened, the molded part removed from the die casting or thixoforming device and the casting chamber re-die-casted - or loaded with thixoform material. Loading the casting chamber with a thixotropic metal bolt is preferably done by a robot. The casting chamber is loaded with a liquid metal alloy for die casting, for example by opening a valve or stopper in a casting trough, so that the liquid metal can flow into the casting chamber.

• beim Thixoformen die durch den Giesskolben während der Dauer vom Zeitpunkt to bis zum Zeitpunkt t₁ zugeführte partielle Energie E₁ für die Verschiebung des thixotropen Metallbolzens in der Giesskammer bis zum Anschlag des Matallbolzens am formseitigen Ende der Giesskammer, wobei t₁ den Zeitpunkt bezeichnet, an dem der Metallbolzen am Ende der Giesskammer auftrifft; für einen Druckgiessprozess beträgt die partielle Energie E₁ stets Null;
• beim Druckgiessen oder Thixoformen die durch den Giesskolben während der Dauer vom Zeitpunkt t₁ bis zum Zeitpunkt t₂ zugeführte partielle Energie E₂ für die Verformung des thixotropen Metallbolzens bzw. der Druckgussmaterials, wobei t₂ den Zeitpunkt bezeichnet, an dem das Druckguss- oder Thixoformmaterial auf seiner ganzen Länge den ganzen Giesskammerquerschnitt ausfüllt;
• beim Druckgiessen oder Thixoformen die durch den Giesskolben während der Dauer vom Zeitpunkt t₂ bis zum Zeitpunkt t₃ zugeführte partielle Energie E₃ für die Füllung der Eingusskanäle, wobei t₃ den Zeitpunkt bezeichnet, an dem die zwischen der Giesskammer und der Formkavität befindlichen Eingusskanäle allesamt vollständig gefüllt sind;
• beim Druckgiessen oder Thixoformen die durch den Giesskolben während der Dauer vom Zeitpunkt t₃ bis zum Zeitpunkt t₄ zugeführte partielle Energie E₄ für die Füllung der Formkavität, wobei t₄ den Zeitpunkt bezeichnet, an dem alle Teile der Formkavität vollständig gefüllt sind und die Geschwindigkeit des Giesskolbens auf Null gesunken ist, d.h. v(t₄)=0.

In addition to the total energy E _tot , the partial energies E ₁ to E ₄ supplied by the casting piston are preferably determined for the following process steps:

• in thixoforming, the to by the casting piston during the period from time to to time t ₁ supplied partial energy E ₁ for the displacement of the thixotropic metal bolt in the casting chamber until the stop of the Matallbolzens at the mold-side end of the casting chamber, where t ₁ is the time at where the metal bolt hits the end of the casting chamber; for a die casting process, the partial energy E _{1 is} always zero;
• in diecasting or thixotropic molding by the casting piston during the period from time t ₁ to time t ₂ supplied partial energy E ₂ for the deformation of the thixotropic metal bolt or the die casting material, where t ₂ represents the time at which the diecasting or Thixoformmaterial Fills the entire cross-section of the casting chamber along its entire length;
• in diecasting or thixotropic molding, the t by the casting piston during the period from the time ₂ to time t ₃ supplied partial energy E ₃ for filling the sprues, where t ₃ indicates the time at which the sprue channels located between the casting chamber and the mold cavity are all are completely filled;
• in diecasting or thixotropic molding by the casting piston during the period from time t ₃ to time t ₄ supplied partial energy E ₄ for the filling of the mold cavity, where t ₄ designates the time, are completely filled in which all parts of the mold cavity and the speed of the casting piston has dropped to zero, ie v (t ₄ ) = 0.

In particular, the determination of the partial energy E ₁ allows the determination of pre-solidifications of die casting or thixoform material in the casting chamber. In addition, E1 in particular also provides information about the general tribological conditions, e.g. pressure losses due to friction, wear and tear and lubrication, and thus serves, for example, to assess the influence of separating agents and lubricants and also provides information about the friction of the casting piston and its lubrication.

The casting piston of pressure die casting or thixoforming devices is usually driven by hydraulic means. In the case of die casting or thixoforming devices designed in this way, the time-dependent pressure profile p (t) is particularly advantageous by simultaneously measuring the time-dependent pressure profile p _GK (t) on the casting piston surface directed against the die casting or thixoform material and by measuring the pressure _profile p _hyd (t) in the Hydraulic fluid is determined, wherein the pressure pressure curve p _GK (t) is preferably used to calculate the energy supplied to the die-casting or thixoform material by the casting piston.

Since it is not the absolute energy quantities E (t), E _tot , E ₁ to E ₄ that are important for the monitoring of the die casting or thixoforming process and the corresponding process control, but essentially the corresponding energy values for different thixoform bolts or die casting material quantities from the same preheating furnace or from different preheating furnaces, the pressure pressure _curve p _hyd (t) can also be used to calculate the energy values E (t), E ₁ to E ₄ and E _tot .

p _hyd (t) describes the total pressure exerted on the casting piston. However, this does not correspond to the pressure exerted on the die-casting or thixoform material, since the casting piston itself is exposed to a certain amount of friction in the casting chamber.

Therefore, the simultaneous measurement of p _hyd (t) and p _GK (t) allows the determination of the pressure drop Δp = p _hyd (t) -p _GK (t) due to the friction of the casting piston and therefore allows a statement about the mechanical condition of the casting chamber or the casting piston and the lubrication of the casting piston.

While E _tot allows global control of the entire thixoforming or die casting process, the partial energy values E ₁ to E _{4 provide} information about certain process parameters, as was described in the case of E1 for example for the above-described tribological conditions or for the determination of solidifications. E ₂ is suitable, for example, for obtaining information regarding the required deformation energy and, in the case of thixoforming, provides information, for example, about the state of the stud, ie whether the thixotropic stud is too hard or too soft, or whether the liquid content is too high or too deep. E ₃ and E _4, on the other hand, are suitable, for example, for monitoring the filling behavior of the pouring channels or the mold cavity and thus, for example, provide information about the influence of the release agent and, in the case of thixoforming, also about the shear forces acting on the thixotropic material.

In the case of thixoform or die casting processes with RTIM process monitoring according to the invention, a protocol is preferably printed out per working shift, which is usually of the order of 8 hours, the number of cast or thixoform parts manufactured, ie the number of shots n, the partial energies E1 to preferably E4 and the total energy E _{tot are} calculated for each shot and shown on the log printout. The average total energy E _{tot, m} and the standard deviation σ _n for all n shots with die-cast or thixoform material from the same preheating furnace are more preferably determined and printed out.

The average total energy E _{tot, m} for a number n of shots with thixoform or die-cast material from the same furnace k is calculated, for example, as an arithmetic mean:

berechnet werden.The standard deviation can then be too

be calculated.

The relative measure of scatter according to σ rel = 100% σ n 2 / E dead, m be calculated.

On the basis of an assessment of the resulting molded parts and the corresponding comparison of the energy values E _tot and E ₁ to E ₄ , as well as the mean value and the standard deviation, it can then be concluded which energy range is permissible for maintaining a sufficient molded part quality. Thus, with respect to the energy values E _tot and E ₁ to E ₄ , a setpoint range can be defined for the thixoform or die casting process, which can be used as a parameter for a process interruption, a change of a preheating furnace, a calibration of the heating output of a preheating furnace, a correction of the casting curve or the triggering of a monitoring alarm can be used.

With regard to the device, the present invention is based on the object to provide a thixoform or die casting device for monitoring of the manufacturing process under production conditions allowed.

According to the invention, this is achieved by a device with the features according to Claim 12 reached. Preferred developments of the device according to the invention are described in dependent claims 13 and 14.

In particular, a die casting or thixoforming device according to the invention is preferred, where the measuring devices have a continuous detection the time-dependent pressing pressure p (t) and a continuous position measurement Allow s (t).

bestimmt wird.The measuring device for determining the position s (t) can further preferably also have a device for measuring the time-dependent speed v (t) of the casting piston, the position of the casting piston s (t _x ) increasing at time t _x

is determined.

The device according to the invention is particularly suitable for thixoforming or die casting using the method according to the invention for Process monitoring.

• Fig.1 bis 5 den zeitlichen Verfahrensablauf beim Thixoformen in einer Horizontal-Thixoformanlage;
• Fig. 6 und 7 Protokollausdrucke einer erfindungsgemässen RTIM-Prozessüberwachung;
• Fig. 8 eine graphische Protokolldarstellung der gemessenen und berechneten Werte für das erfindungsgemässe RTIM-Verfahren.

Further advantages, features and details of the invention emerge from the following description of FIGS. 1 to 8 using the example of thixoforming, and with reference to the drawings; these show schematically in

• 1 to 5 the temporal process sequence for thixoforming in a horizontal thixoforming system;
• FIGS. 6 and 7 log printouts of an RTIM process monitoring according to the invention;
• 8 shows a graphical log representation of the measured and calculated values for the RTIM method according to the invention.

Figures 1 to 5 show a vertical longitudinal section along the longitudinal axis through the casting chamber of a horizontal thixoforming device. The cylindrical one The casting chamber 10 is arranged horizontally and contains a casting piston 12, a radially symmetrical oxide pocket 22, a sprue opening 24, two sprue channels 26 and 28 as well as two mold cavities 16 and 18th

FIG. 1 shows the thixoforming device at the time t ₀ = 0, a thixotropic metal bolt 14 brought to the required temperature in a preheating furnace (not shown) being inserted into the horizontally lying casting chamber and the casting piston 12 being brought up to the bolt. FIG. 1 shows an example of a pressure sensor 30 attached to the casting piston surface directed against the thixotropic metal pin 14. FIG. 1 also shows a position or speed measuring device 32.

FIG. 2 shows the thixoforming device at the time t ₁ , at which the thixotropic metal bolt 14 hits the mold-side end 11 of the casting chamber 10. Since the cross-sectional area of the cylindrical, thixotropic metal pin 14 is smaller than the cross-sectional area of the casting chamber 10, the thixotropic pin 14 does not yet fill the entire casting chamber cross section at the time t ₁ .

FIG. 3 shows the thixoforming device at time t ₂ . At this point, the thixotropic metal bolt has lost its geometric shape and is now in the form of a thixoform compound 15. The point in time t ₂ thus denotes the point in time at which the thixoforming compound or the thixoforming material 15 fills the entire cross-section of the casting chamber over its entire length, that is to say the thixoforming compound 15 fills the entire space between the casting piston 12 and the mold-side end 11 of the casting chamber 10, at the point in time t ₂ essentially no thixotropic material has flowed through the pouring opening 24 or oxidic edge material into the oxide pocket 22.

FIG. 4 shows the thixoforming device at time t ₃ . The time t ₃ denotes the time at which the sprue opening 24 and the sprue channels 26 and 28 are completely filled with thixoform material 15. The oxide pocket 22, which receives the oxide material located in the edge layer of the thxotropic metal bolt 14, is already largely filled.

FIG. 5 shows the thixoforming device at time t ₄ . The time t ₄ denotes the final state of the actual thixoforming process, ie the time before the mold is opened. At time t ₄ , the mold cavities 16 and 18 are completely filled with thixoform 15 and the speed of the casting piston 12 has dropped to zero. During the subsequent cooling and solidification phase of the thixiform part, the casting piston pressure can be maintained for a short time in order to compensate for shrinkage during the cooling process by replenishing thixotropic material, so that the casting piston can carry out an additional movement after time t ₄ . At time t ₄ in the present example, the radially symmetrical oxide pocket 22 is also completely filled with oxidic components of the original edge layer of the thixotropic bolt 14.

FIG. 6 shows, by way of example, the calculated total energy values of thixoforming processes of individual thixotropic metal bolts from the same preheating furnace, ie the total energy values of individual shots, in such a way that the respective total energy is plotted on the ordinate and the shot number in the form of the corresponding shot times on the abscissa ; the shot number of a shot corresponds to a specific point in time t _x , so that the ordinate corresponds to a time axis. The specific point in time t _x can be predefined as desired, ie it can be defined, for example, as the starting point in time at which the casting piston for the thixoforming process is started. Any other, precisely definable point in time during a thixoforming process can also be defined as a specific point in time t _x . For the values shown in FIG. 6, the start of the casting piston at the beginning of each thixoforming process was chosen.

The partial figures a to h of FIG. 6 each give the total energy values determined for a number of shots again, the values for the thixotropic Metal studs of a particular preheater are shown separately, i.e. the Representations a to h give the values for thixotropic metal bolts from the same Preheat again.

FIG. 6 a shows the total energies of 32 shots with thixotropic bolts which were heated in a No. 1 oven. The start of the casting piston at the beginning of each thixoforming process was selected as the specific point in time t _x . The display includes shots from 7.47 p.m. until 2.37 p.m. the following day. The total energy averaged over all 32 shots is 26.01 kJ with a relative spread of ± 16%.

6b shows the total energies of 46 shots with thixotropic bolts, which were heated in a No. 5 oven. The illustration includes Shots in a period from 7:06 p.m. to 2:21 p.m. the following Day. The total energy averaged over all 46 shots is 31.97 kJ a relative spread of ± 10%.

6 c shows the total energies of 47 shots with thixotropic bolts, which were heated in a No. 6 oven. The illustration includes Shots in a period from 6:59 p.m. to 2:34 p.m. the following Day. The total energy averaged over all 47 shots is 23.91 kJ a relative measure of scatter of ± 9%.

6d shows the total energies of 48 shots with thixotropic bolts, which were heated in a No. 7 oven. The illustration includes Shots from 7:00 p.m. to 2:36 p.m. the following Day. The total energy averaged over all 48 shots is 30.58 kJ a relative spread of ± 15%.

6e shows the total energies of 42 shots with thixotropic bolts, which were heated in a No. 9 oven. The illustration includes Shots in a period from 7:01 p.m. to 2:28 a.m. the following Day. The total energy averaged over all 42 shots is 23.53 kJ a relative spread of ± 16%.

6 f shows the total energies of 49 shots with thixotropic bolts, which were heated in a No. 10 oven. The illustration includes Shots in a period from 7:00 p.m. to 2:47 p.m. the following Day. The total energy averaged over all 49 shots is 23.03 kJ with a relative spread of ± 12%.

6 g shows the total energies of 47 shots with thixotropic bolts, which were heated in a No. 11 oven. The illustration includes Shots in a period from 7:04 p.m. to 2:39 a.m. the following Day. The total energy averaged over all 47 shots is 20.38 kJ with a relative spread of ± 8%.

6 h shows the total energies of 51 shots with thixotropic bolts, which were heated in a No. 12 oven. The illustration includes Shots in a period from 7:05 p.m. to 2:32 p.m. the following Day. The total energy averaged over all 51 shots is 46.15 kJ with a relative spread of ± 7%.

FIG. 7 shows a bar diagram of the averaged total energies E _{tot, i} (i = 1 ... 12, where i denotes the furnace number) for the thixoform tests shown in FIG. 6 during a working shift of approx. 8 hours, in each case the Standard deviations are entered. Each bar in FIG. 7 thus represents the total energy E _{tot, i} averaged over all shots of a working shift for thixotropic metal bolts from furnace no. i represents.

On the basis of the assessment of the resulting molded parts and the corresponding comparison with the average total energy E _{tot, i} or E _{tot, it} can then be concluded which energy range is permissible for sufficient molded part quality. The resulting molded parts can be assessed, for example, by optical or microscopic assessment, or by material testing, material-specific examinations using, for example, micrographs, material analyzes, structural examinations, etc. Based on the assessment of the molded parts and the total energy values E _tot known for their production, as well as the values for the partial energies E ₁ to E ₄ , an overall energy setpoint range can be defined, for example, with respect to E _tot as a parameter for the thixoform or die casting process. The setpoint range can then be used as a further parameter, whereby if the total energy value of a shot or a number of shots falls below or falls below, for example, a process interruption, a change in a preheating oven or a recalibration of the heating output of a preheating oven can be carried out.

The assessment of the molded parts using the thixofom method relating to FIG shows that in this case the total energy per Shot must be between 35 kJ ≥ Etot ≥ 10 kJ so that the required molding quality can be achieved. Near the energy thresholds determined in this way can both molded parts with the required molded part properties as well Molded parts with inadequate molded part properties result. Is the Total energy value of a shot outside the determined energy band, the risk of producing a non-conforming molded part increases, i.e. a molded part that does not meet the required molded part properties Structure, dimensions, etc. having. Accordingly, the determination of the Total energy for a shot is a measure of the probability of one good or bad molding production, i.e. a measure of the reject probability.

FIG. 8 shows an example of a graphical protocol representation of the measured and calculated values for the inventive RTIM method, on the one hand the measured path s (t) traveled by the casting piston 12 and on the other hand the measured, time-dependent pressing pressure exerted by the casting piston 12 p (t) during a thixoform process, i.e. during a shot are, as well as determined by points, determined at discrete times Velocity values v (t) = ds (t) / dt of the casting piston 12 are entered. The log display shown in FIG. 8 also contains a speed curve v (t), which is obtained by numerical filtering and smoothing of the discrete Velocity values ds (t) / dt is calculated.

Claims (14)

1. Method for process monitoring during the die casting or thixoforming of metals (14, 15) in a die casting or thixoforming device containing a shot chamber (10), an injection piston (12) and a mould with a mould cavity (16, 18), characterised in that the variation of the injection pressure with time p(t) is measured, the time-dependent speed of the injection piston v(t) is determined, the energy E(t) supplied by the injection piston as a function of the process time t and the total energy E_tot supplied by the injection piston (12) during the die casting or thixoforming process are calculated on the basis of the variation of the injection pressure with time p(t) and of the speed of the injection piston with time v(t) and the total energy E_tot is used as a parameter for monitoring the die casting or thixoforming process.
2. Method for the process monitoring of a die casting or thixoforming device according to claim 1, characterised in that the variation of the injection pressure p(t) is determined by measuring the pressure p_GK(t) at the surface of the injection piston directed towards the die casting or thixoforming material (14, 15).
3. Method for the process monitoring of a die casting or thixoforming device according to claim, 1, in which the injection piston (12) is driven hydraulically, characterised in that the variation of the injection pressure p(t) is determined by measuring the pressure p_hyd(t) in the hydraulic fluid.
4. Method according to one of claims 1 to 3, characterised in that the energy E(t) supplied by the injection piston (12) as a function of the process time t is calculated according to the integral function

   

   and the total energy E_tot supplied by the injection piston (12) during the die casting or thixoforming process is calculated by the integral function

   

   where A is the surface of the injection piston (12) directed towards the die casting or thixoforming material (14, 15) and t₀ is the starting time t = 0 of the die casting or thixoforming process and t₄ is the time at which the injection piston assumes the speed v(t) = 0 for the first time after t₀.
5. Method according to one of claims 1 to 4, characterised in that the time-dependent position of the injection piston s(t) is measured and the speed of the injection piston v(t) is determined as a derivative of the time-dependent position of the injection piston s(t) after the time t at separate times according to the function v(t) = ds(t)/dt, where the speed v(t) is preferably determined at 180 to 500, in particular, at 250 to 400 separate process times during the die casting or thixoforming process.
6. Method according to one of claims 1 to 5, characterised in that the time-dependent energy E_x,y(t) supplied by the injection piston (12) during two process times t_x and t_y, where t_x < t_y, is calculated according to the integral function

   

   where A is the surface of the injection piston (12) directed towards the die casting or thixoforming material (14, 15).
7. Method according to claim 6, characterised in that the partial energies E₁ to E₄ are calculated for the following process stages:

   a) in thixoforming, the partial energy E₁ supplied by the injection piston (12) during the period from the time t₀ to the time t₁ for the displacement of the thixotropic metal bolt (14) in the shot chamber (10) until the metal bolt (14) stops at the mould end (11) of the shot chamber (10), where t₁ is the time at which the thixotropic metal bolt (14) strikes the end (11) of the shot chamber;

   b) in die casting and thixoforming, the partial energy E₂ supplied by the injection piston (12) during the period from the time t₁ to the time t₂ for the deformation of the thixotropic metal bolt (14) or the die casting material (15), where t₂ is the time at which the entire length of the die casting or thixoforming material (15) fills the entire cross section of the shot chamber;

   c) in die casting and thixoforming, the partial energy E₃ supplied by the injection piston (12) during the period from the time t₂ to the time t₃ for filling the sprues (26, 28), where t₃ is the time at which the sprues (26, 28) situated between the shot chamber (10) and the mould cavity (16, 18) are all completely filled, and

   d) in die casting and thixoforming, the partial energy E₄ supplied by the injection piston (12) during the period from the time t₃ to the time t₄ for filling the mould cavity (16, 18), where t₄ is the time at which the mould cavity (16, 18) is completely filled and the speed of the injection piston (12) has fallen to zero, i.e. v(t₄) = 0.
8. Method according to claim 7, characterised in that the total energy E_tot is calculated as E_tot = E₁ + E₂ + E₃ + E₄.
9. Method according to one of claims 1 to 8, in which the injection piston (12) is driven hydraulically, characterised in that the variation of the injection pressure p(t) is determined by measuring the pressure p_hyd(t) in the hydraulic fluid and simultaneously by measuring the pressure p_GK(t) at the surface of the injection piston directed towards the die casting or thixoforming material (14, 15), where the variation of the injection pressure p_GK(t) is used to calculate the energy values supplied by the injection piston (12), and the energy loss as a result of friction up to the time t is determined by calculating the integral function

   

   where A is the surface of the injection piston (12) directed towards the die casting or thixoforming material (14, 15) and t₀ is the starting time of the die casting or thixoforming process.
10. Method according to one of claims 1 to 9, characterised in that the total energy E_tot for a plurality of die casting or thixoforming processes using die casting or thixoforming material (14, 15) from a specific preheating furnace is determined and the corresponding mean value and the standard deviation are calculated therefrom, the mean value and the standard deviation being used as further parameters.
11. Use of the method according to one of claims 1 to 10 for the die casting or thixoforming of aluminium or magnesium alloys.
12. Die casting or thixoforming device, in particular a die casting or thixoforming device for the die casting or thixoforming of aluminium alloys, in which the die casting or thixoforming device contains a shot chamber (10), an injection piston (12) and a mould with at least one mould cavity (16, 18), characterised in that the die casting or thixoforming device either has measuring devices (30, 32) for the simultaneous determination of the process-time-dependent injection pressure p(t) and the process-time-dependent determination of the position s(t) of the injection piston (12) or measuring devices (30, 32) for the simultaneous determination of the process-time-dependent injection pressure p(t) and the process-time-dependent determination of the speed v(t) of the injection piston (12).
13. Die casting or thixoforming device according to claim 12, characterised in that the measuring device for determining the process-time-dependent injection pressure p(t) contains a pressure sensor (30) fitted or fixed to the surface of the injection piston directed towards the die casting or thixoforming material (14, 15).
14. Die casting or thixoforming device according to either of claims 12 or 13, in which the injection piston (12) is driven hydraulically, characterised in that the measuring device for determining the process-time-dependent injection pressure p(t) contains a pressure sensor for determining the pressure in the hydraulic fluid.

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