DE102007030637A1 - Injection molding method comprises determining compressibility and flowability of molding composition and calculating content of binder in composition or homogeneity of the binder-filler mixture from this data - Google Patents

Abstract

The injection molding method comprises determining the compressibility and/or flowability of the molding composition from time to time. The content of binder in the composition or the homogeneity of the binder/filler mixture can then be calculated from this data. An independent claim is included for an injection molding for use in the method.

Description

The The invention relates to a method for injection molding of an injection moldable composition in an injection molding machine, a plasticizing unit, an injection unit, a machine control and an injection mold with a cavity wherein injection-moldable mass via a extending from the injection unit into the cavity of the injection mold melt flow in the injection mold is injected and wherein the injection-moldable mass of at least one first component, in particular a powder component, and at least a second component, in particular a binder component consists. Furthermore, the invention relates to an injection molding machine.

At the injection molding filled Moldings, especially of powdery material, the so called Feedstock in a plasticizing unit by heat conduction from the outside over here Heating bands attached to the plasticizing cylinder as well as due to dissipation in the melt during mixing by means of a screw in the plasticizing cylinder melted.

Of the Feedstock consists of a defined volume fraction of powder and from a defined volume fraction binder or binder components (eg plastic). This ratio from powder to binder content influences the flow properties and determined the shrinkage of the component during sintering.

The Binder components are in the plasticizing completely or to a very large extent molten, while the powder components remain in the solid state. After the injection molding process the sprayed parts are debinded and sintered. The feedstock is applied to the injection molding machine in compounding equipment prior to processing homogenized.

1 schematically shows a feedstock consisting of a first component 8th namely, a powder component, and a second component 9 namely a binder component. It is not only the correct mixing ratio between the components 8th and 9 before, it is also given a good homogenization of the powder particles in the binder.

Deviating from the ideal state according to 1 There may be batch fluctuations in the mixture homogeneity. In addition, fluctuations in the volume fractions of binder and filler due to uneven dosage of both components during mixing are possible. Likewise, by adding recycle or regrind to the funnel of the injection molding machine, inhomogeneities in the melt may occur.

2 shows an inhomogeneous distribution of the powder particles, although the mixing ratio of the components 8th and 9 correct is. These inhomogeneities, ie the spatially different distribution of fillers and binders, lead to voids or cracks during sintering, since the areas with a higher binder concentration do not optimally sinter together.

Farther to lead inhomogeneities in the proportions of powder and binder or binder components different shrinkages during sintering and thus to rejects.

These inhomogeneities can on differences in spatial Distribution of fillers or on different filler proportions be due.

• 1. Die Volumenanteile Pulver zu Binder sind korrekt, die räumliche Verteilung von Pulver und Binder ist jedoch ungleichmäßig. Dies ist in 2 skizziert.
• 2. Die Volumenanteile Pulver zu Binder sind falsch, die räumliche Verteilung von Pulver und Binder ist gleichmäßig,
• 3. Die Volumenanteile Pulver zu Binder sind falsch, außerdem die räumliche Verteilung von Pulver und Binder ist ungleichmäßig. Dies ist schematisch in 3 skizziert.

Generally speaking, there are the following variants of inhomogeneities, the deviations from the in 1 represent optimal mixture shown:

• 1. The volume fractions of powder to binder are correct, but the spatial distribution of powder and binder is uneven. This is in 2 outlined.
• 2. The proportions by volume of powder to binder are wrong, the spatial distribution of powder and binder is uniform,
• 3. The volume fractions of powder to binder are wrong, also the spatial distribution of powder and binder is uneven. This is schematically in 3 outlined.

Of the Invention is based on the object, a method for injection molding a injection-moldable mass from at least two components, in particular from a powder component and at least one binder component, and an associated injection molding machine to create, with or with which it is possible, the filler content the melt and a nonuniform component distribution, in particular Powder / binder distribution, detect. This should be inhomogeneities in the processed Feedstock are determined on their cause, as they are at the above three variants can occur. It should be distinguished can be which variant of inhomogeneity is present.

The solution of this object by the invention according to the method is characterized in that the method comprises the at least temporary measurement of the compressibility and / or the flowability of the injection-moldable mass in the injection molding machine from the measured values for the compressibility and / or the flowability of the Content of the second component, in particular binder component, in the injection-moldable mas and / or to be able to conclude the homogeneity of the injection-moldable composition consisting of the first component, in particular powder component, and second component, in particular binder component.

specially can be provided that the measurement of the compressibility of the injection-moldable mass done by first the melt flow path between injection unit and cavity is closed and then a piston or a screw of the injection unit to a defined Amount is shifted and the case occurring pressure increase in the melt is measured. Correspondingly vice versa can also To proceed so that the measurement of the compressibility of the injection-moldable mass done by first the melt flow path between injection unit and cavity is closed and then a displacement of a piston or a screw of the injection unit is measured, which is required to a defined pressure increase to reach in the melt.

Analogous it is also possible that measuring the compressibility of the injection-moldable mass done by first the flow of melt through the melt flow path into the cavity is prevented, then between the cavity and a piston or screw a defined volume of injection moldable mass is precompressed and that then the precompressed injection-moldable mass of a defined initial pressure to a defined final pressure withdrawal the piston or the screw is relieved, with the required for this Displacement of the piston or the screw is measured. Corresponding conversely, it is also possible to proceed in such a way that the measurement the compressibility the injection-moldable compound done by first prevents melt flow through the melt flow path into the cavity is, then between the cavity and a piston or screw a defined volume of injection moldable mass is precompressed and that then the pre-compressed injection-moldable compound by retreating the piston or the screw to a defined displacement is relieved, taking place in the injection-moldable mass thereby Pressure drop is measured.

If here from preventing melt flow through the melt flow path in the cavity the Speaking, this can be actively activated by a closure in the melt flow path cavity be accomplished. An alternative and preferred option However, this is that the (further) melt flow prevents this that is the injection-moldable mass for a Molding in the cavity is injected and then for a certain time the emphasis is applied; then comes it also no longer flows through the melt flow path. Of the Advantage of this way of preventing further melt flow exists in that then it can be provided that the measurement of compressibility during mining of reprinting during an injection molding cycle he follows.

In The machine control can then from the measured or predetermined Values for calculated the displacement and the pressure increase or pressure drop, the compressibility become.

on the other hand can measure the flowability the injection-moldable compound take place by a lot of melt from the injection unit over a Messfließweg is applied, which is fluidly coupled to the melt flow path is, where needed Spout pressure is measured, to achieve a defined Volume flow required becomes. Again, it is possible conversely possible that the measurement of flowability the injection-moldable compound takes place by a lot of melt from the injection unit over a Messfließweg is applied, which is fluidly coupled to the melt flow path is measured, wherein the volume flow is measured, which is when applying a defined ejection pressure results. Again, again be provided that in the machine control from the measured or predetermined values for the flow rate and the ejection pressure the fluidity is calculated.

The Measurement of flowability the injection-moldable compound can also be done by measuring the work required to carry out the injection process for a injection mold is needed. In this case, in the machine control from the measured Value for the work for the injection process the fluidity be calculated.

The Determination of compressibility and / or the fluidity can do this at defined time intervals or in certain process stages be repeated.

The determined values for the compressibility and / or the fluidity the injection-moldable compound can continue to be used by the machine control to the amount of admixture of the second component, in particular the Binder component, and / or on the intensity of the mixing of the first Component, in particular the powder component, and second component, especially the binder component, so to influence that the Values for the compressibility and / or the fluidity the injection-moldable compound within a given range of values.

In the proposed Spritzgießmaschi ne is inventively provided that in the melt flow path in the region between the injection unit and the cavity, a valve element is arranged, which selectively releases the Schmelzefließweg in a first position and blocks the Schmelzefließweg in a second position.

The Valve element preferably further has a measuring flow path, the in a third position fluidly to that of the injection unit upcoming melt flow path is coupled.

The Thus, the invention is based on the basic idea that the filler content in the consisting of at least two components feedstock Measurement of compressibility and / or the mixture homogeneity of the feedstock by measuring the flowability of the melt during injection molding and especially during an injection molding cycle be determined.

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

1 schematically a homogeneous mixture of a powder and a binder at the correct ratio of powder to binder,

2 schematically an inhomogeneous mixture of a powder and a binder with the correct ratio of powder to binder,

3 schematically an inhomogeneous mixture of a powder and a binder with improper ratio of powder to binder,

4 schematically an injection molding machine in side view,

5 an example of the relative volume change (compressibility) of a polypropylene melt as a function of the pressure and the filler content,

6 an example of a viscosity curve of a feedstock with optimum powder / binder ratio and with a higher binder content,

7 a valve element disposed between a plasticizing and injection unit and an injection molding tool in a first, open position,

8th the valve element in a second, closed position and

9 the valve element in a third position in which a Meßfließweg is fluidly coupled to the plasticizing and injection unit.

In 4 is schematically an injection molding machine 1 shown, which has the usual components. The plasticizing unit 2 and the injection unit 3 are as a combined shear screw plasticizing and injection unit 2 . 3 formed, ie within a worm cylinder is a worm 10 arranged, which rotate both with a screw speed as well as for the injection of melt can move axially by a defined amount. The plasticized melt is in a known manner in the cavity 6 an injection mold 5 injected, the method of a machine control 4 is controlled or regulated. During injection, the melt flows from the antechamber 13 along a melt flow path 7 into the cavity 6 , The end of the plasticizing and injection unit 2 . 3 has a melt nozzle 14 (S. 7 to 9 ) on the injection mold 5 is scheduled to melt into the cavity 6 inject.

In the present case, the injection-moldable composition is a mixture of a powder component 8th and a binder component 9 used, s. 1 to 3 ,

The injection molding machine 1 is further provided with sensors, not shown, to capture the relevant Spritzgießparameter. A sensor can detect the screw speed. Another sensor may be provided to measure the worm torque. Furthermore, a pressure sensor can be provided to the pressure p in the area of the screw antechamber 13 capture. Another sensor detects the axial worm displacement s. By means of these sensors, all information is available to determine the injection work W _E. The injection work W _E results as the integral of the injection pressure p 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.

To determine if the composition of the feedstock - both in terms of the volume fractions of the components 8th and 9 as well as with respect to the homogeneity of the melt - is OK, proceed as follows.

For example, after a certain number of shots, a measurement of the compressibility κ and the flowability η of the injection-moldable mass in the injection molding machine is carried out in each case. From the measured values for the compressibility κ and the flowability η is based on the content of binder component 9 in the injection-moldable mass as well as on the homogeneity of the components 8th and 9 closed melt.

For measuring the compressibility κ of the melt, first the melt flow path is determined 7 between injection unit 3 and cavity 6 closed and then the snail 10 the injection unit 3 shifted by a defined amount Δs. The resulting pressure increase .DELTA.p in the melt is measured, in the screw antechamber 13 ,

To measure the flowability η of the melt is a lot of melt from the injection unit 3 over a measuring flow path 11 , s. 9 , the measuring flow path, as will be explained in more detail, fluidly to the melt flow path 7 is coupled. In this case, the required ejection pressure p is measured, which is needed to achieve a defined volume flow dV / dt.

In the machine control 4 is then calculated from the measured or predetermined values for the displacement Δs and the pressure increase Δp the compressibility κ and from the measured or predetermined values for the volume flow dV / dt and the ejection pressure p, the flowability η, for which in the machine control 4 corresponding data are stored.

by name is based on the following concept:

5 shows the relative volume change, ie the compressibility, of a polypropylene melt, depending on the content of the powder component 8th (Filler) and the pressure p. As usually the filler 8th one to the binder 9 has different compressibility, results at different Füllstoffgehalten the front of the screw 10 melt volume also a different compressibility of the melt in the screw antechamber 13 , One can conclude either an absolute value of the filler content (although the compressibilities of filler and binder are known) or a relative (batch to batch) value of the filler content (if the compressibilities of filler and binder are not known).

The corresponding families of curves are in the machine control 4 so that they can rely on it in the calculation of compressibility and flowability.

If one opposite a standard different powder / binder distribution is present, can by measuring the flowability the melt can be determined. The greater the inhomogeneity, the worse flows the melt.

For this purpose, the said ejection of a previously metered amount of melt takes place via a measuring flow path 11 (By-pass nozzle) with defined channel dimensions (s. 9 ). The ejection volume flow dV / dt is specified and the resulting pressure requirement p is measured (or vice versa, a pressure p in the antechamber 13 specified and the adjusting volumetric flow dV / dt detected). From the relationship between pressure requirement p and volume flow dV / dt, which in turn is proportional to the screw feed rate, results in a parameter which indicates the flowability η and in a broader sense the viscosity.

In 6 is a viscosity curve for a feedstock with optimal powder / binder ratio (designation "316L standard") and a viscosity curve of a feedstock containing a higher binder content, but otherwise the same starting materials (powder and binder components) has (designation "316L + 5% As can be seen, the flowability also changes with variable binder content.

The means that usually only by measuring the flowability the feedstock no statement possible is whether the binder content has changed or if there is another mixture homogeneity. Only through additional Measurement of compressibility can be recognized, whether the altered flowability attributable to another binder content.

The determination of fluidity can also be done by measuring the injection energy W _E required for injection.

The determined values for the compressibility κ and the flowability η of the injection-moldable mass can be determined by the machine control 4 then also be used to the amount of admixing the binder component 9 and on the intensity of the mixing of the two components 8th . 9 to influence in the closed loop such that the values for the compressibility κ and for the flowability η of the melt lie within a predetermined value range.

The equipment of the proposed injection molding machine is on the 7 to 9 pointed. By means of the device outlined there and in particular with the illustrated valve element 12 Located between the end of the screw cylinder and the injection mold, both the compressibility and the flowability of the plasticized melt can be determined.

For normal injection molding operation, the valve element rotatable about the vertical axis with a cylindrical basic contour is in the first position I , in the 7 is shown. So there is an "open position on "before, in the melt flow path 7 between the snail's anteroom 13 and cavity 6 is open.

To determine changes in the homogeneity of the melt, a defined volume of melt in the screw antechamber 13 brought and the injection unit moved to a position in which the following measurements are performed. By turning the valve element 12 around the vertical axis to a second position II , s. 8th , So in a "closing position", the melt flow path 7 through the valve element 12 completely blocked. The snail 10 with preferably closed backflow lock (analogous, a piston can be used) compressed by an axial movement s of the screw in the direction of the nozzle tip in the screw antechamber 13 located melt. The compressibility is calculated according to a mathematical model of compressed volume and the pressure required for compression and compared with a specification. After completion of the data recording, a pressure relief takes place in the antechamber.

So the snail drives in the direction of the snail's anteroom 13 until the pressure p rises there. This can be done in two ways. On the one hand, the screw can travel a defined path Δs and there is a measurement of the associated pressure difference Δp or, on the other hand, the pressure difference Δp can be preset and the screw advances until this pressure difference is reached. Measured here is the distance traveled by the worm Δs. The compressibility of the melt volume located upstream of the screw can now be calculated from the associated values .DELTA.s and .DELTA.p according to a mathematical model. If it is a piston injection unit, the injection piston takes over the task of pressure build-up instead of the screw. The compressibility κ can be calculated from the volume before the beginning of the compression and the change in volume when the pressure changes.

By turning the valve element 12 in a third position III , s. 9 , ie in a position "By-pass", now the melt flow path 7 to a measuring flow path 11 diverted.

The geometry of the measuring flow path 11 is designed so that at the on the machine control 4 to be given ejection speeds a shear rate profile in the measuring flow path 11 adjusts, in which no appreciable temperature increases of the melt occur because they can lead to an influence on the measurement result. The snail 10 moves forward at a defined and preferably constant speed in the direction of the antechamber 13 and pushes the melt through the measuring flow path 11 from, whereby a certain volume flow dV / dt sets in it. Due to the necessary pressure p, the flowability can be calculated according to a mathematical model.

The information about the compressibility and the fluidity serve as a continuation of the quality documentation and - as already mentioned above - the scheme the quality the melt.

Becomes For example, in the course of spraying, it is found that the mixture homogeneity is worse is, as a previously set reference value, so may by an adjustment the plasticizing conditions achieved a better homogenization become. This usually happens by increasing of Back pressure and / or screw speed during the metering phase of the injection molding process.

If facing each other a previously set reference value ("ideal feedstock") has changed the filler content, Thus, by adjusting the injection conditions, the shrinkage the moldings are influenced so that it is the same again as at the ideal feedstock. This is usually done by increasing the Injection pressure and / or the emphasis.

It can therefore also be provided that the measured compressibility, which a measure of the filler content is, and the fluidity, which is a measure of the mixture homogeneity, as Input variables for a control strategy at the plasticizing and injection conditions in the way in which the molding quality is made with regard to Shrinkage and homogeneity even with fluctuating quality the starting material (feedstock) is kept as equal as possible.

The execution The above measurements can be either automatic or manual in defined intervals (ongoing or random).

Of the determined filler content and the determined mixture homogeneity may be specially for regulation the plasticizing process and / or the injection process used become. It can also be provided that the determined filler content and a value of injection work for regulation (and also for quality documentation) be used.

1

injection molding machine

2

plasticizing

3

Injection unit

2, 3

Reciprocating screw plasticizer and injection unit

4

machine control

5

injection mold

6

cavity

7

melt flow

8th

first Component (powder component)

9

second Component (binder component)

10

slug

11

Messfließweg

12

valve element

13

the screw

14

molten material

κ

compressibility

η

flowability

.DELTA.s

displacement

Ap

pressure rise

dV / dt

flow

p

ejection pressure

W _E

Injection work

I

first position

II

second position

III

third position

Claims (17)

Method for injection molding an injection-moldable mass in an injection molding machine ( 1 ) comprising a plasticizing unit ( 2 ), an injection unit ( 3 ), a machine control ( 4 ) and an injection molding tool ( 5 ) with a cavity ( 6 ), wherein injection-moldable mass via a from the injection unit ( 3 ) into the cavity ( 6 ) of the injection molding tool ( 5 ) extending melt flow path ( 7 ) in the injection mold ( 5 ) and wherein the injection-moldable composition comprises at least one first component ( 8th ), in particular a powder component, and at least one second component ( 9 ), in particular a binder component, characterized in that the method comprises the at least temporary measurement of the compressibility (κ) and / or the flowability (η) of the injection-moldable mass in the injection molding machine ( 1 ) from the measured values for the compressibility (κ) and / or for the fluidity (η) on the content of the second component ( 9 ), in particular binder component, in the injection-moldable mass and / or on the homogeneity of the first component ( 8th ), in particular powder component, and second component ( 9 ), in particular binder component, to be able to close existing injection-moldable mass. A method according to claim 1, characterized in that the measurement of the compressibility (κ) of the injection-moldable mass is carried out by first the melt flow path ( 7 ) between injection unit ( 3 ) and cavity ( 6 ) is closed and then a piston or a screw ( 10 ) of the injection unit ( 3 ) is displaced by a defined amount (Δs) and the pressure increase (Δp) taking place in the melt is measured. A method according to claim 1, characterized in that the measurement of the compressibility (κ) of the injection-moldable mass is carried out by first the melt flow path ( 7 ) between injection unit ( 3 ) and cavity ( 6 ) and then a displacement (Δs) of a piston or a screw ( 10 ) of the injection unit ( 3 ), which is required to achieve a defined pressure increase (Δp) in the melt. A method according to claim 1, characterized in that the measurement of the compressibility (κ) of the injection-moldable mass is carried out by first the melt flow through the melt flow path ( 7 ) into the cavity ( 6 ), then between the cavity ( 6 ) and a piston or a screw ( 10 ) is precompressed a defined volume of injection-moldable mass and that then the precompressed injection-moldable mass of a defined initial pressure to a defined final pressure by retraction of the piston or the screw ( 10 ) is relieved (.DELTA.p), wherein the required displacement path (.DELTA.s) of the piston or the screw ( 10 ) is measured. A method according to claim 1, characterized in that the measurement of the compressibility (κ) of the injection-moldable mass is carried out by first the melt flow through the melt flow path ( 7 ) into the cavity ( 6 ), then between the cavity ( 6 ) and a piston or a screw ( 10 ) is precompressed a defined volume of injection-moldable mass and that then the precompressed injection-moldable mass by retraction of the piston or the screw ( 10 ) is relieved by a defined displacement (.DELTA.s), wherein the taking place in the injection-moldable mass pressure drop (.DELTA.p) is measured. Method according to claim 4 or 5, characterized that the measurement of compressibility (κ) in the reduction of the emphasis while an injection molding cycle he follows. Method according to one of claims 2 to 6, characterized in that in the machine control ( 4 ) from the measured or predetermined values for the displacement (.DELTA.s) and the pressure increase or decrease (.DELTA.p), the compressibility (κ) is calculated. A method according to claim 1, characterized gekenn characterized in that the measurement of the flowability (η) of the injection-moldable mass takes place by applying a quantity of melt from the injection unit ( 3 ) via a measuring flow path ( 11 ) is applied, the fluidically to the melt flow path ( 7 ) is coupled, whereby the required ejection pressure (p) is required, which is needed to reach a defined volume flow (dV / dt) is measured. A method according to claim 1, characterized in that the measurement of the flowability (η) of the injection-moldable mass is carried out by a lot of melt from the injection unit ( 3 ) via a measuring flow path ( 11 ) is applied, the fluidically to the melt flow path ( 7 ), whereby the volume flow (dV / dt) which results when a defined discharge pressure (p) is applied is measured. Method according to claim 8 or 9, characterized in that in the machine control ( 4 ) is calculated from the measured or predetermined values for the volume flow (dV / dt) and the ejection pressure (p) the flowability (η). A method according to claim 1, characterized in that the measurement of the flowability (η) of the injection-moldable mass is carried out by the work (W _E ) is measured, which is required for carrying out the injection process for an injection molded part. Method according to claim 11, characterized in that in the machine control ( 4 ) from the measured value for the work (W _E ) for the injection process, the flowability (η) is calculated. Method according to one of claims 1 to 12, characterized that the determination of the compressibility (κ) and / or the fluidity (η) in defined intervals or repeated at certain stages of the process. Method according to one of claims 1 to 13, characterized in that the determined values for the compressibility (κ) and / or the flowability (η) of the injection-moldable material from the machine control ( 4 ) are used to determine the amount of admixture of the second component ( 9 ), in particular the binder component, and / or on the intensity of the mixing of the first component ( 8th ), in particular the powder component ( 8th ), and second component ( 9 ), in particular the binder component, in such a way that the values for the compressibility (κ) and / or the flowability (η) of the injection-molding compound are within a predetermined value range. Injection molding machine ( 1 ) comprising a plasticizing unit ( 2 ), an injection unit ( 3 ), a machine control ( 4 ) and an injection molding tool ( 5 ) with a cavity ( 6 ), wherein injection-moldable mass via a from the injection unit ( 3 ) into the cavity ( 6 ) of the injection molding tool ( 5 ) extending melt flow path ( 7 ) in the injection mold ( 5 ) and wherein the injection-moldable mass of at least one first component ( 8th ), in particular a powder component ( 8th ), and at least one second component ( 9 ), in particular a binder component, in particular for carrying out the method according to one of claims 1 to 14, characterized in that in the melt flow path ( 7 ) in the area between the injection unit ( 3 ) and the cavity ( 6 ) a valve element ( 12 ), which is optionally in a first position ( I ) the melt flow path ( 7 ) and in a second position ( II ) the melt flow path ( 7 ) blocked. Injection molding machine according to claim 15, characterized in that the valve element ( 12 ) continue a measuring flow path ( 11 ), which is in a third position ( III ) fluidly to the from the injection unit ( 3 ) upcoming melt flow path ( 7 ) is coupled. Injection molding machine according to claim 15 or 16, characterized in that the plasticizing unit ( 2 ) and the injection unit ( 3 ) are designed as a combined shear screw plasticizing and injection unit.