AT505341A2 - METHOD AND DEVICE FOR INJECTION MOLDING - Google Patents

Description

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The invention relates to a method for injection molding an injection-moldable mass in an injection molding machine having a plasticizing unit provided with a screw, an injection unit, a machine control and a tool having a cavity, wherein injection-moldable mass can be injected into the cavity, and wherein the injection-moldable mass consists of at least one powder component and at least one binder component. Furthermore, the invention relates to an injection molding machine.

In the injection molding of molded parts made of powdery material, the so-called feedstock is melted in a plasticizing unit with a screw by heat conduction from the outside via heating bands attached to the plasticizing cylinder and dissipation in the melt during mixing in the screw cylinder. The feedstock consists of a defined volume fraction of powder and a volume fraction of binder component. The ratio of powder to binder content influences the flow properties and determines the shrinkage of the component during sintering.

The binder component becomes molten in the plasticizing cylinder while the powder component remains in the solid state. After this

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Injection molding process, the sprayed parts are sintered. The feedstock is homogenized in compounding equipment on the injection molding machine prior to processing.

FIG. 2 schematically shows a mixture of a powder and a binder. In this figure, a good homogenization of the powder particles can be seen. This can lead to batch fluctuations in the homogeneity of the mixture. Likewise, due to the admixture of recycled material or regenerated material in the funnel of the injection molding machine, inhomogeneities may occur in the melt and furthermore in the molded part being molded.

FIG. 3 schematically shows a partially segregated mixture of a powder and a binder. The figure thus shows an inhomogeneous distribution of the powder particles. These inhomogeneities, ie the spatially different distribution of powder and binder, lead to voids or cracks during sintering, since the regions with a higher binder concentration do not optimally interact internally.

The invention has for its object to provide a method for injection molding an injection-moldable mass of at least one powder component and at least one binder component and an associated injection molding machine, with or with which it is possible to detect the quality of the mixture and by appropriate measures during Spritzgießproduktion to maintain a good mixture quality. This is intended to increase the quality of the molded part to be produced.

The solution of this problem by the invention is characterized in that the method comprises the steps of: a) determining the injection work for a defined portion of the injection molding cycle of a molded part, in particular for a complete injection molding cycle; b) determination of the metering work for a defined section of the injection molding cycle of a molded part, in particular for a complete injection molding cycle; c) In the event of an increase or decrease in the injection work determined according to step a) from a predetermined tolerance range stored in the machine control and the dosing work determined according to step b) remains within a predetermined tolerance range stored in the machine control: no action for influencing the mixture homogeneity of the injection moldable compound; d) In the event of an increase or decrease in the injection work determined according to step a) from a predefined tolerance range stored in the machine control and an increase or decrease in the dosing work determined according to step b), from a predetermined tolerance range stored in the machine control: initiating a measure for Influencing the mixture homogeneity of the injection-moldable mass. ······································································································ · 0 · · ·· 0 «♦« 0 ··· ··· 4

The injection work and the dosing work are preferably related to reference values which are stored in the machine control system, in which case the determined ratios (quotients) are taken as the basis for the further processing of the data.

If there is another condition than in step c) and step d), no measure is taken to influence the mixture homogeneity of the injection-moldable mass.

Thus, the invention is based on the basic idea that, on the one hand, the injection work and, on the other hand, the dosing work are calculated. Then, the respective results can be normalized by being shared by a stored reference value.

If the injection work or the ratio of injection work out of a predetermined tolerance range, but the Dosierarbeit or the ratio of Dosierarbeiten remains within a tolerance range, it is assumed that a size has changed in the process that does not affect the flowability and thus the mixing quality of Feedstocks concerns. Accordingly, no measures for improving the homogeneity of the melt are initiated (above step c).

If, on the other hand, it turns out that both jobs or both normalized quantities - ie the injection work and the dosing work - increase at the same time, this indicates a change in the feedstock. Accordingly, measures for homogenizing the melt are initiated in this case (step d above). · ♦ ··································································································· .

In this case, the injection work is preferably calculated as the integral of the injection pressure via the volume of melt injected into the cavity for an injection-molded part.

The metering work is preferably calculated as the integral of the screw torque over the rotation angle of the screw for a predetermined time

The above steps a) to c) or the steps a), b) and d) are preferably carried out periodically repeating.

Following the execution of the above step d), the dosing parameters can be reduced back to the original values.

The measure initiated after the above step d) may be an additional mixing of the injection-moldable mass during the metering process. A mixing of the injection-moldable mass can be carried out at an increased screw speed. Also, a change in the dynamic pressure during dosing can be made. Furthermore, a change in the screw retraction speed can be made during dosing.

The temperature in the plasticizing unit can be kept according to the training by a regulation within a predetermined tolerance range. For controlling the temperature in the plasticizing unit, the heating energy supplied to the plasticizing unit can be used.

The injection molding machine according to the invention is characterized in that sensors are provided for determining the screw speed, the screw torque, the injection pressure and the axial ······························································································· 9 · 999 ··· 6

Worm motion, wherein the machine control is designed to determine the injection work for a defined portion of the injection molding cycle of a molding and for determining the dosing for a defined portion of the injection molding of a molding, wherein the machine control is further formed - for non-output of a signal on rise or fall the determined injection work out of a predetermined stored tolerance range and the remaining dosing work within a stored tolerance range and - to output a signal at increase or decrease the determined injection work from a predetermined stored tolerance range and the rise or fall of the determined dosing from a predetermined stored Tolerance range addition.

If appropriate, it can also be provided here again that the injection or metering work itself is not processed but data normalized to reference values.

The plasticizing unit and the injection unit are preferably designed as a combined shear screw plasticizing and injection unit.

Finally, a further development provides that the screw has mixing, shearing and / or kneading elements

The invention thus relates to a method for injection molding of filled plastics, in which, by measuring the energy consumption during the process of ······················································································. •···········································································································································

Dosing and injection process a control of the mixing quality is performed.

In the drawing, an embodiment of the invention is shown. Show it:

1 is a schematic side view of an injection molding machine,

2 schematically shows a homogeneous mixture of a powder and a binder,

Fig. 3 shows schematically a partially unmixed mixture of a powder and a binder and

4 shows the injection integral normalized to a reference variable (injection work) and the dosing work normalized to a reference variable for two different temperatures of a feedstock.

In Fig. 1, an injection molding machine 1 is shown schematically, which has the usual components. The plasticizing unit 3 and the injection unit 4 are formed as a combined screw extruder plasticizing and injecting unit, i. H. Within a worm cylinder, a worm 2 is arranged, which rotate both with a screw speed ns than can also move axially for the injection of melt by an amount s. The plasticized melt is injected in a known manner into the cavity 7 of a tool 6, the method being controlled by a machine controller 5. ···················································································································································································································· · · 99 99 9 " " · · " 8th

In the present case, a mixture of a powder component 8 and a binder component 9 is used as the injection-moldable mass, see FIG. Fig. 2 and Fig. 3.

The injection molding machine 1 is further provided with sensors to detect the relevant Spritzgießparameter.

The sensor 10 detects the screw speed ns. Another sensor 11 detects the worm torque Ms. The sensor 12 measures the injection pressure pe. Finally, the sensor 13 detects the axial worm displacement s.

Thus, all information is available to determine the injection work We and the dosing work Wd.

The injection work We results as the integral of the injection pressure ps over the injected melt volume; the latter in turn is the product of cross-sectional area and the axial worm movement s with a constant worm cylinder cross-sectional area.

The metering work Wd is the integral of the screw torque Ms over the rotation angle | |> s of the screw. The relation of the rotation angle < j > s with the screw speed ns and the angular velocity ω of the screw 2 is known

In the procedure according to the invention, first of all the injection work We is determined for a defined section of the injection molding cycle of a molded part, ie. H. Computes the corresponding integral ······································································································. ····· ··· 9

At the same time the dosing work Wd is determined in a similar manner, d. H. Again, the integral is determined for a defined section of the injection molding cycle of a molded part.

By using values stored in the machine control 5, the work is normalized (which is not mandatory, but only optional), ie. H. There is a division by fixed values for the injection and the Dosierarbeit. The ratio of the injection work VE results from the calculated injection work We divided by the stored standard value Weo. Accordingly, the ratio Vd results as a quotient of dosing work WD and stored standard value Wdo.

Depending on the calculated results, the determination is made on the further procedure:

If the ratio VE increases or decreases beyond a predetermined tolerance range stored in the machine controller 5 and the ratio Vd remains within a predetermined tolerance range stored in the machine controller 5, no further action is taken.

However, when the ratio VE increases or decreases beyond a predetermined tolerance range and the ratio Vd increases or decreases beyond a predetermined tolerance range, a measure for influencing the mixture homogeneity of the injection moldable mass is made.

Namely, it has been found in the production of moldings using powder that the mixing quality of powder and binder is the same as that of powder and binder 9 999 999 999 999 999 10

Flowability of the melt influenced The more irregular the powder particles are distributed in the binder, the more difficult the melt is usually.

This relationship is used in the characterization of feedstocks in rheometers.

The flowability and thus the viscosity of the melt have an influence on the pressure required for mold filling. An integral quantity for detecting fluidity is the injection integral (injection work), d. H. the integral of the injection pressure over the injected volume. This size is used as a quality control feature.

However, the injection integral has the disadvantage that, in addition to the viscosity of the feedstock, it is also influenced by the tool temperature.

Another way to monitor melt flowability is to record dosing work Dosing work is the integral of the product of worm torque and worm angular velocity over dosing time. This value is also called MFQ (monitoring of feedstock quality) because it is used to monitor the feedstock Quality is used

The dosing work is not affected by the mold temperature. This relationship is illustrated in Figure 4 where the injection integral normalized to a datum and the dosing work normalized to a datum are shown for two different temperatures. ··· During the relative dosing work, i. H. the dosing work based on a nominal value, practically independent of temperature, this does not apply to the injection integral, d. H. for the injection work. Here it can be seen that at a lower temperature (45 ° C) a lower normalized value results than at a higher temperature (65 ° C). The dosing work is therefore usually better suited for characterizing batch fluctuations of feedstocks than the injection integral.

In the proposed method, both the injection integral (injection work) and the dosing work are monitored or taken into account. The control of the mixing quality takes place directly in the injection molding machine.

If the injection integral changes in such a way that its value is outside a limit set in the machine control and if the dosing work remains the same, a variable has changed in the process which does not affect the flowability and thus the quality of the mixture of the feedstock.

By contrast, if both quantities, ie the injection integral and the dosing work, increase to the same extent, this indicates a change in the feedstock.

In order to increase the quality of mixing again in such a case, an additional mixing of the melt must be carried out in the plasticizing screw during dosing. The metering parameters dynamic pressure and speed are therefore changed in this case so that in conjunction with the screw geometry used (advantageously provided with mixing, shearing and kneading elements) again a homogeneous mixture in the melt is achieved. ···· ···· ························································································ * ··· · # ··· ··· 12

It is advantageous, instead of the parameters dynamic pressure and screw speed, to directly change those parameters which influence the flow of the melt in the screw, namely the screw peripheral speed in connection with the screw return speed.

Dismantled areas and thus errors in the molded part can therefore not occur. The injection work then drops back to its original value, while the dosing work has risen due to the change in dosing parameters. From now on, both the injection integral and the metering work will be monitored again.

If the mixture quality and thus the viscosity of the next batch are back to the original value, the injection integral and the dosing work decrease in the same way. The dosing parameters are now to be reduced again to values, so that the injection integral also remains constant. If the dosing parameters were not adjusted, there could be an excessive load on the feedstock during plasticization. This would cause the risk that a mechanical or thermal damage of the binder component takes place

In the case of particularly high-viscosity feedstocks, changing the metering parameters may also result in a change in the melt temperature. This change can be compensated by adjusting the cylinder temperature profile or by controlling the heat energy supplied.

As a quality feature for the quality of mixing, the flowability of the filled molding composition is used. By means of the energy for the injection and the energy for the metering at the injection molding machine, the relative

Flowability of the filled Fonmnasse determined. Changes in energy for injection are detected by the controller due to tool temperature changes such that, in such a case, the energy for dosing remains unchanged. The dosing parameters are varied depending on the measured energies for injection and dosing such that the dosing parameters vary Mix quality remains constant. The metering parameters dynamic pressure and screw speed are preferably used here. The dosing parameters, worm peripheral speed and worm retraction speed can also be used. In addition, the cylinder temperature T can be monitored and regulated. In particular, the heat energy supplied to the plasticizing cylinder can be monitored and regulated. As filled molding compounds, feedstocks are used for powder injection molding. I # · ···· ···· I # · ···· ····

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List of Reference Numerals: 1 2 3 4 5 6 7 8 9 10 11 12 13

injection molding machine

slug

plasticizing

Injection unit

machine control

Tool

cavity

Powder component binder component sensor (screw speed)

Sensor (worm torque)

Sensor (injection pressure)

Sensor (axial screw displacement) WE Injection work Weo stored value for injection work Wd Dosing work Wdo stored value for dosing work Ve ratio We / Weo Vd ratio Wd / Wdo Pe injection pressure Ms screw torque • · ·· 9 9 9 9 9 9999 ···· φβ t ns ω T s

angle of rotation

Time

Screw speed

Snails angular velocity

Temperature axial screw movement

Claims (17)

Claims 1. A method of injection molding an injection-moldable mass in an injection molding machine (1) comprising: a screw (2); provided plasticizing unit (3), an injection unit (4), a machine control (5) and a tool (6) having a cavity (7), wherein in the cavity (7) injection-moldable mass can be injected and wherein the injection-moldable mass of at least a powder component (8) and at least one binder component (9), characterized in that the method comprises the steps of: a) determining the injection work (We) for a defined portion of the injection molding cycle of a molding, in particular for a complete injection molding cycle; b) determination of the dosing work (Wd) for a defined section of the injection molding cycle of a molded part, in particular for a complete injection molding cycle; ···································································································· C) In the event of an increase or decrease in the injection work (We) determined according to step a), out of a predetermined tolerance range stored in the machine control unit (5) and remaining in step b ) determined dosing work (Wd) within a predetermined and stored in the machine control (5) tolerance range: not causing a measure to influence the mixing homogeneity of the injection-moldable mass; d) In the case of an increase or decrease in the injection work (We) determined according to step a) from a predetermined tolerance range stored in the machine control (5) and during the increase or decrease in the dosing work (Wd) determined according to step b) from a given and in the Machine control (5) stored tolerance range: causing a measure to influence the mixture homogeneity of the injection-moldable mass. 2. The method according to claim 1, characterized in that it comprises the steps of: a) determination of the injection work (We) for a defined portion of the injection molding cycle of a molding; b) determination of the dosing work (WD) for a defined section of the injection molding cycle of a molded part; ····································································································. Forming a ratio (Ve) between the injection work (We) determined according to step a) and a value of an injection work stored in the machine control (5) (Weo); b ') forming a ratio (Vd) between the dosing work (Wd) determined according to step b) and a value of a dosing work (Wdo) stored in the machine control (5); c) In case of increase or decrease of the ratio (Ve) formed according to step a ') beyond a predetermined tolerance range stored in the machine control unit (5) and remaining the ratio (Vd) formed in step (b) within a predetermined ratio and within Machine control (5) stored tolerance range: non-initiation of a measure to influence the mixture homogeneity of the injection moldable mass; d) When the ratio (Ve) formed in step a ') increases or decreases beyond a predetermined tolerance range stored in the machine control unit (5) and when the ratio (Vd) formed in step (b) increases or decreases over a predetermined and in the machine control (5) stored tolerance range addition: initiate a measure to influence the mixture homogeneity of the injection moldable mass. · ··························· · · · ······· 3. The method according to claim 1 or 2, characterized in that the injection work (We) is calculated as the integral of the injection pressure (PSS) on the injected into the cavity volume of melt for an injection molded part. Method according to claim 1 or 2, characterized in that the dosing work (Wd) is calculated as the integral of the worm torque (Ms) over the angle of rotation (<} > s) of the worm (2) for a predetermined time (t) , 5. The method according to claim 1, characterized in that the steps a) to c) or the steps a) and b) and d) are carried out according to claim 1 periodically repeating. 6. The method according to claim 2, characterized in that the steps a) to c) or the steps a) to b ') and d) are carried out according to claim 2 periodically repeating. 7. The method according to any one of claims 1 to 6, characterized in that following the execution of step d) according to claim 1 ····· ···· ···· # • · ······· • ··························································································································································································································· be reduced to the original values. 8. The method according to any one of claims 1 to 7, characterized in that the measure initiated after step d) according to claim 1 or 2 measure an additional mixing of the injection-moldable mass during the dosing process. 9. The method according to claim 8, characterized in that a mixing of the injection-moldable mass at increased screw speed (ns) takes place. 10. The method according to claim 8, characterized in that a change in the back pressure during dosing is made. 11. The method according to claim 8, characterized in that a change in the screw retraction speed is performed during dosing. ···· ···· • · • ·················· · · · ········ 21 12. The method according to any one of claims 1 to 11, characterized in that the temperature (T) in the plasticizing unit (3) is held by a regulation within a predetermined tolerance range. 13. The method according to claim 12, characterized in that for controlling the temperature (T) in the plasticizing unit (3) of the plasticizing unit (3) supplied heating energy is used. 14. Injection molding machine (1) for injection molding of an injection-moldable mass which has a plasticizing unit (3) provided with a screw (2), an injection unit (4), a machine control (5) and a tool (6) with a cavity (7) , in particular for carrying out the method according to one of claims 1 to 13, characterized in that sensors (10, 11, 12, 13) are provided for determining the screw speed (ns), the screw torque (Ms), the injection pressure (pe) and the axial screw movement (s), wherein the machine control (5) for determining the injection work (We) for a defined portion of the injection molding cycle of a molding and for determining the dosing (Wd) is formed for a defined portion of the injection molding cycle of a molding, wherein the Machine control (5) is further configured. For not outputting a signal on rising or falling of the determined injection work (We) from a preset stored tolerance range and at Remaining of the determined dosing (Wd) within a stored tolerance range and - to output a signal for increase or decrease of the determined injection work (We) from a predetermined stored tolerance range and the rise or fall of the determined dosing (Wd) from a predetermined stored tolerance range addition , 15. Injection molding machine (1) according to claim 14, characterized in that the machine control (5) further for forming a ratio (Ve) between the determined injection work (We) and a stored value for the injection work (Weo) and for forming a ratio ( Vd) is formed between the determined dosing work (Wd) and a stored value for the dosing work (Wdo), wherein the machine control (5) is further configured - for non-output of a signal upon increase or decrease of the formed injection work ratio (Ve) beyond a predetermined stored tolerance range and while the dosing work ratio (Vd) formed remains within a stored tolerance range, as well as • ································································································. ···················································································································································································· injection ratio (Ve) beyond a predetermined stored tolerance range and the rise or fall of the dosing ratio formed (Vd) over a predetermined stored tolerance range addition. 16. Injection molding machine according to claim 14 or 15, characterized in that the plasticizing unit (3) and the injection unit (4) as a combined screw extruder plasticizing and injection unit (3,4) are formed. 17. Injection molding machine according to one of claims 14 to 16, characterized in that the screw (2) has mixing, shearing and / or kneading elements.