DE102007061775A1 - Injection molding method, involves comparing mean value, maximum value, point of time, initial gradient and time constants with provided parameter set point, and determining dwell pressure value for subsequent injection molding operation - Google Patents

Abstract

The method involves measuring temporal characteristics of a tool internal pressure (Pw) during a dwell pressure phase (PN) of an injection molding operation. A mean value, a maximum value, a point of time, an initial gradient and time constants are determined from the measured characteristics of the internal pressure. The mean value, the maximum value, the point of time, the initial gradient and the time constants are compared with a provided parameter set point. A dwell pressure value is automatically determined for a subsequent injection molding operation based on the comparison result. An independent claim is also included for an injection molding system comprising an injection molding tool.

Description

The The invention relates to an injection molding method and to a Injection molding plant for implementation of the procedure.

A conventional Injection molding plant essentially comprises an injection molding tool, which is the actual "injection mold", as well as an injection molding machine, by means of the injection molding tool with a molten injection molding compound is charged. Internally of the injection molding tool, a cavity to be filled with the injection molding compound is formed. The injection molding tool further comprises a so-called sprue system of channels, over the the injection molding compound into the cavity is initiated. The injection molding machine usually includes one heated cylinder, with which the injection molding compound melted and is injected into the injection mold. Located in the cylinder a screw to propel the injection molding compound. A conventional one In addition, the injection molding machine usually includes a fully regulated one Drive for the snail, with the u. a. the pressure of the liquefied injection molding compound within the Cylinder (hereinafter referred to as in-cylinder pressure) set can be.

For monitoring the injection molding process are in conventional injection molding equipment partially also provided in the tool pressure sensors that a local Pressure of the liquid or solidifying injection molding compound within the cavity (hereinafter referred to as cavity pressure) measure.

One Duty cycle of an injection molding plant (hereinafter also referred to as injection molding essentially) is divided into two phases, namely one Injection phase (also as filling phase in which the injection molding compound is injected into the cavity will, as well as a subsequent Repressive phase (also referred to as compression phase), in which the cavity in the mold is already filled with injection molding material, but in the compaction of mass on the machine side a so-called Constant pressure is maintained constantly.

in the During the injection molding process results for the cavity pressure a characteristic curve. The cavity pressure increases in this case Area of transition From the injection phase in the emphasis phase first strong. After passing through a maximum, the cavity pressure then gradually decreases again to the value zero. This pressure drop - despite the machine side Constantly maintained reprint - is a consequence of increasing Cooling and the concomitant solidification of the injection molding compound in the tool.

For each Injection mold results in a detail individually different "ideal" shape of the cavity pressure curve. This ideal cavity pressure curve often becomes part of process optimization determined as a reference curve. The actual course of the cavity pressure in ongoing production depends with the same tool and the same setting of the cylinder internal pressure essentially from the flow behavior the injection molding compound. The flow behavior is again u. a. determined by the chemical composition of the injection molding compound. In current production, the in-cylinder pressure in the holding pressure phase usually becomes manually adjusted so that the cavity pressure about on the reference curve runs. Larger deviations lead from this to bad parts that have to be sorted out.

In industrial injection molding processes are subject to the flow behavior the injection molding variations, in particular by different Batches of injection molding compound with more or less different chemical composition and also caused by other influences become. If the set emphasis is not on the changing flow behavior adapted to the injection molding compound, this leads to the fact that the actual Mold internal pressure curve gradually out of a tolerance range around the optimized reference curve and thus bad parts are produced. In this case, the reprint readjusted to continue running the current internal pressure curve to approach the reference curve again. This manual adjustment requires a high level of Qualification and "instinct" with the operating personnel. The need to readjust the injection molding plant also results to comparatively high reject rates of an injection molding plant.

Of the The invention is based on the object, a Particularly effective injection molding process and a particularly for process implementation specify appropriate injection molding plant.

This object is achieved with respect to the method according to the invention by the features of claim 1. Thereafter, it is provided during the post-pressure phase of an injection molding the time Ver to measure the running of a cavity pressure. According to the method, at least one parameter is determined from the detected curve of the cavity pressure, which characterizes the course of the cavity pressure curve during the holding pressure phase, but which is not itself time-dependent on the time scale of an injection cycle. The or each parameter is compared with an associated, stored parameter setpoint. On the basis of the comparison result, an adjusted reprint value for a subsequent injection run is automatically determined.

In particular, according to the invention the provided by a cavity pressure sensor provided Mold cavity pressure used to set the machine side Automatically optimize reprinting. The idea, the time course the cavity pressure curve during reduce the emphasis phase to one or more non-time-dependent parameters, and only these parameters for the others Determining the adjusted reprint value allows one particularly simple and numerically modest implementation of the method, the with cheap Means is feasible. This favors a broad industrial Use of the method, and in particular a simple upgrade conventional Injection molding plants for implementation of the procedure.

By doing according to the procedure the reprint Automatically detects and adjusts, one reacts the procedure executive Injection molding system automatically and without delay to changing Working conditions, in particular a changing flow behavior the injection molding compound. This leaves the proportion of bad parts generated in current production to a considerable extent to reduce. Overall, when using the method of material use across from a conventional one Injection molding process can be reduced by up to 5%, in particular by that an unnecessary overcrowding of cavity can be avoided.

In preferred embodiment of the method are used as a non-time-dependent parameter for the temporal Course of the cavity pressure during the pressure phase individually or in any combination a maximum value, an associated time, an average or initial slope of the cavity pressure curve used. additionally or alternatively, a time constant is suitably used for the Increase and / or decrease of cavity pressure during the Repressing phase used as a parameter.

In a very precise one Variant of the method is the adjusted reprint value in the ongoing production during each injection run, or at regular intervals in the course of every nth injection run (n = 2, 3, 4, ...) determined. The emphasis is thus at least approximately continuously changing Working conditions adapted.

In an alternative embodiment of the method, which is numerically particularly undemanding and therefore technically particularly easy and inexpensive is to be realized, the reprint value is adjusted only if the determined parameter or at least one of the determined characteristics a predetermined threshold range leaves the assigned setpoint. The set reprint value is thus maintained unchanged in current production until the resulting curve of the cavity pressure curve is measured at the value of the ascertained parameter (s) - by more as a critical measure of deviates from the reference curve. Only in this case, the reprint customized. In this process variant, the emphasis is preferred adjusted in discrete steps of, for example, 1 bar.

In addition to the threshold range, exceeding it the adjustment of the reprint value triggers is in the above described variant of the method preferably a tolerance range the or each characteristic setpoint Are defined. A manufactured in the current injection molding molding is intended as then Bad part sorted out when raised in this injection molding process Characteristic or at least one of the measured parameters outside this tolerance range lies.

Of the Tolerance range is expediently chosen larger than the threshold range, such that the threshold range is in the tolerance range with safety distances to its limits. This excludes that at a drift of the characteristic or one of the parameters in the ongoing production bad parts are produced before the Adjustment of the emphasis is made.

With regard to the injection molding machine, the above object is achieved according to the invention by the features of claim 5. Thereafter, the injection molding machine comprises an injection molding tool which is provided with at least one internal pressure sensor for detecting a cavity pressure. The injection molding plant further comprises a pressure regulator for automatically adjusting the internal cylinder pressure during the reprinting phase of an injection molding process. The pressure regulator is designed here for carrying out the method described above in one of its variants.

Conveniently, The injection molding plant also includes an injection molding machine, the a cylinder for injecting a molten injection molding compound includes in the injection mold. In the cylinder is a propulsion device, z. Example in the form of a screw or a piston, for propelling the injection molding compound stored. On the propulsion device, more precisely on a drive same, acts a machine control, which is designed to set the cylinder's internal pressure to a preset setpoint. The reprint value determined by the post-pressure controller becomes hereby the machine control as setpoint for the adjustment of the in-cylinder pressure while the post-pressure phase of a subsequent to the determination of the Nachdruckwerts Injection molding available posed.

following Be exemplary embodiments of the invention explained in more detail with reference to a drawing. Show:

1 a schematic representation of an injection molding machine with an injection molding machine, an injection molding tool and a pressure regulator,

2 in a schematic diagram, the time course of the cavity pressure during a Spritzgußganges,

3 in schematic diagrams, the time change of an average value of the cavity pressure curve in the Nachdruckphase over several successive injection passes and on a corresponding time scale the course of an output from the pressure regulator Nachdruckwertes for a first variant of the executed by the pressure regulator method, and

4 in illustration according to 3 the course of the average cavity pressure and the Nachdrucksollwerts for a second variant of the method.

each other corresponding parts and sizes are always provided with the same reference numerals in all figures.

In the 1 illustrated injection molding plant 1 includes an injection molding machine 2 , an injection mold 3 and a pressure regulator 4 , The injection molding machine 2 includes a cylinder 5 in which a snail 6 rotatably mounted. The snail 6 is from a worm drive 7 rotationally driven in the form of an electric motor.

In operation of the injection molding machine 2 becomes the cylinder 5 at a rear end 8th a solid injection molding compound M, which is raw state usually in the form of granules, via a filler neck 9 fed. By rotation of the snail 6 the injection molding compound M is inside the cylinder 5 towards an exit end 10 propelled. When driving the injection molding compound M by means of a in or on the wall of the cylinder 5 provided heating 11 melted.

In a front area of the cylinder 5 , in the operation of the injection molding machine 2 the injection molding compound M is already completely melted, is a pressure sensor 12 provided, the hydrostatic pressure of the molten injection M in the interior of the cylinder 5 measures. This pressure is referred to below as the cylinder internal pressure p _Z. The pressure sensor 12 performs a corresponding measurement of the cylinder internal pressure p _{Z of} a machine control 13 as the actual value too. The machine control 13 compares the measured cylinder internal pressure p _Z continuously with a predetermined set value p _{Z, 0 of} the cylinder internal pressure p _Z and generates based on the comparison result a manipulated variable Y, with the worm drive 7 is controlled. The machine control 13 controls the worm drive 7 in such a way that the cylinder internal pressure p _{Z is} adjusted to the desired value p _{Z, 0} by varying the propulsion of the injection molding compound M.

In the injection mold 3 is a cavity 14 formed, which forms the negative mold of a molded part to be produced in the injection molding and which is filled in the course of the injection molding with the molten injection molding material M. The cavity 14 is with a sprue system 15 connected. The gate system 15 opens in an injection opening 16 on the surface of the injection molding tool 3 ,

In the course of a Spritzgußganges, ie a working cycle of the injection molding plant 1 , which leads to the production of a molded part, the cylinder 5 pressure-tight on the injection opening 16 put on and Spritzgussmas se M on the Angusssytem 15 into the cavity 14 injected. The injection process is divided into an injection phase P _I ( 2 ) and a subsequent post-pressure phase P _N ( 2 ). In the course of the injection phase P _I , the cavity 14 successively filled with injection molding compound M. The injection phase P _I is finished as soon as the cavity 14 completely filled with injection molding compound M. In the post-pressure phase P _N become the injection molding machine 2 and the injection mold 3 keep in contact, being in the cylinder 5 a constant in-cylinder pressure p _{Z is} maintained to that in the cavity 14 located injection molding compound M via the Angusssystem 15 to apply a hydrostatic pressure and that in the cavity 14 To compact injection molding compound M thereby.

During the holding pressure phase P _N cools down in the cavity 14 Injection molding M, wherein it gradually solidifies. At the end of the holding pressure phase P _N has become due to cooling and solidification of the injection molding compound M in the cavity 14 formed the finished molding, which is formed after completion of the holding pressure phase P _N and supplied for further processing.

The pressure in the cavity 14 located injection molding compound M is hereinafter referred to as cavity pressure p _W. In the course of the injection passage to a specific course against time t, the results in this cavity pressure p _W 2 is shown schematically. It can be seen from the illustration that the cavity pressure p _W has essentially the value zero over an initial region of the injection phase P _I (compared to room pressure). Only towards the end of the injection phase P _I does the mold cavity _pressure p _W rise to a comparatively low level. After the transition to the holding pressure phase P _N , the cavity pressure p _W then abruptly increases to a comparatively high value. After passing through a maximum, the cavity pressure p _W then gradually decreases again to the value zero. This drop in the mold pressure n _W is a consequence of the increasing cold and solidification in the cavity 14 located injection molding compound M.

The maximum of in 2 illustrated cavity pressure curve is characterized by an associated time t _max and by an associated maximum value p _{max of} the cavity pressure p _W. The course of the cavity pressure curve in the post-pressure phase P _N can be further characterized by an average value p _{a of} the cavity pressure p _W. This (only schematically in 2 The mean value p _a can basically be defined in various ways. In a numerically particularly simple manner, the mean value p _{a is determined,} in particular, by the arithmetic mean of a specific number N of measured values of the cavity pressure p _W detected at specific times t _i (i = 1, 2,..., N) within the holding pressure phase P _N.

Furthermore, the cavity pressure curve in the post-pressure phase P _{N can} also be determined by determining an initial slope m, a time constant τ ₁ for the increase of the cavity pressure p _W in the post-pressure phase P _n and / or a time constant τ ₂ for the decrease of the cavity pressure p _W in the post-pressure phase P _{n be} characterized. For example, the initial slope m is defined by the slope of the tangent at the steepest point of the cavity internal pressure curve during the pressure increase in the hold pressure phase P _N - or equivalently by the maximum derivative of the cavity pressure curve. The time constant τ ₁ is defined, for example, by the time interval between the beginning of the hold-pressure phase P _N and the time at which the cavity pressure p _W within the hold-pressure phase P _{N is} a specific percentage of the maximum value p _max , in particular (1-1 / e) * p _max , reached. Similarly, the time constant τ _2, for example, defined by the time between the time t _max and the time at which the cavity pressure p _W within the Nachdruckphase P _N to a certain percentage of the maximum value p _max , in particular special to 1 / e · p _max dropped is. The constant e stands for the so-called Euler number (e = 2.718 ...).

All of the parameters p _max , t _max , p _a , m, τ ₁ and τ _{2 listed} above contain information about the shape of the cavity pressure curve, without being dependent on the time t on the time scale of a single injection run. The parameters p _max , t _max , p _a , m, τ ₁ and τ ₂ fall rather during each injection run in the form of a simple number value - for example in the form of a floating point number (float) - on. The cavity pressure curve can therefore be analyzed in numerically particularly undemanding manner by means of one or more of the aforementioned parameters p _max , t _max , p _a , m, τ ₁ and τ ₂ .

For measuring the cavity pressure p _W is the injection molding tool 3 with one in the wall of the cavity 14 used pressure sensor 17 Mistake. The pressure sensor 17 forwards a measured value of the tool gint pressure p _{W to} the pressure regulator 4 to. The pressure regulator 4 is preferably formed by a simple microcontroller with a control software implemented therein, but can also be realized purely software technology. The pressure regulator 4 can be present as a separate unit, or as a functional component in the machine control 13 be integrated.

Within the pressure regulator 4 is the time course of the cavity pressure through an analysis module 18 detected. The analysis module 18 detected in this case during the holding pressure phase P _N plurality of measured values of the cavity pressure p _W at different, predetermined times t _i during the holding pressure phase P _N and calculates one or more of the above parameters p _max described, t _max, p _a, m, τ ₁ or τ ₂ .

For simplicity, it is assumed below that the analysis module 18 as the sole parameter, the average value p _{a is} determined, for example, by recording N = 3 measured values of the cavity pressure p _W at fixed times t ₁ , t ₂ , t ₃ during the holding pressure phase P _N , and according to Eq. 1 summed up. The calculated mean value p _a is given by the analysis module 18 to a downstream control module 19 further. In the rule module 19 the mean value p _{a is} compared with a predetermined reference value p _{a, 0} , wherein the control module 19 determined on the basis of the comparison result in a manner described in more detail below an adapted reprint value p _N. The rule module 19 transmits this adapted reprint value p _N to the machine control 13 , In the machine control 13 this fitted emphasis value p _N is stored as a new desired value for the setting of the in-cylinder pressure p _Z during the holding pressure phase P _N of the subsequent injection molding passage.

In the rule module 19 is the mean value p _a further with a tolerance range T ( 3 and 4 ), which is spanned by boundary values T _min and T _max with T _min <p _{a, 0} <T _max . The tolerance range T is chosen such that a sufficient quality of the molded part produced in the current injection molding process can be ensured as long as the average value p _{a is} within the tolerance range T. Represents the rule module 19 determines that the mean value p _{a is} outside the tolerance range T, it generates an error signal F. This error signal F becomes one of the injection molding machine 1 fed downstream sorter (not shown) and causes the sorter to reject the molded part produced in the current injection molding passage as a bad part.

In a first variant of the injection molding plant 1 is the rule module 19 essentially formed by a proportional controller. The properties variant are based on 3 clarified.

The rule module 19 determined in this case at each injection Z ⁽ⁱ⁾ (i = 1, 2, 3 ...), the deviation of the determined average p _a to the reference value p _{a, 0} and determined based on this deviation, the adjusted pressure value p _N according to the relation p (I + 1) N - p (I) N + K · (p a - p a, 0 ) Eq.2 where K is an empirically determined proportionality constant. In Glg. 2 are p _N ⁽ⁱ⁾ for the emphasis value p _N within the current injection passage Z ^(i), and p _N ^{(i + 1)} for reprinting value p _N in the respective next injection passage Z ^{(i + 1)} The reproduction value p _N - like out 3 recognizable - therefore in the sequence of successive injection passes Z ⁽ⁱ⁾ continuously or at least quasi-continuously varied in small steps. As a result of this continuous variation of the reprinting value p _N , the mean value p _{a is} always kept in the vicinity of the reference value p _{a, 0} .

In a by means of 4 clarified alternative version of the pressure regulator 4 compares the control module 19 the calculated average value p _a first with a threshold range W, which is spanned by boundary values W _min and W _max with T _min <T _min <p _{a, 0} <W _max <T _max . As long as the mean value p _{a is} within the threshold range W, the control module leaves 19 the reprint value p _N unchanged. Represents the rule module 19 On the other hand, it is clear that the mean value p _a exceeds or falls below the threshold value range W, it gradually reduces or increases the pressure value p _N by a predetermined difference of, for example, 1 bar. The difference is selected such that the mean value p _a calculated in the next injection run Z ^{(i + 1)} is again within the threshold range W in each case.

The threshold value range W is further selected such that sufficient safety margins are maintained between its limit values W _min and W _max and the corresponding marginal values T _min and T _{max of} the tolerance range T. In this way it is ensured that even if the mean value p _a in the current production leaves the threshold range W, no bad parts are produced before the pressure regulator 4 adjusts the emphasis value p _N.

The modules 18 and 19 are preferred software modules in the post-pressure regulator 4 implemented control software. Alternatively, however, they may also be wholly or partially realized in circuit technology.

1

injection molding machine

2

injection molding machine

3

injection mold

4

pressure regulator

5

cylinder

6

slug

7

screw drive

8th

The End

9

filler pipe

10

exit end

11

heater

12

pressure sensor

13

machine control

14

cavity

15

Angus system

16

Injection port

17

pressure sensor

18

analysis module

19

control module

τ ₁ , τ ₂

time constant

m

initial slope

p _a

Average (the cavity pressure)

p _{a, 0}

reference value (the mean)

p _max

maximum pressure

p _N

reprint value

p _W

Cavity Pressure

p _Z

Cylinder pressure

p _{Z, 0}

setpoint (of the in-cylinder pressure)

t

Time

t _i

time (i = 1, 2, ..., N)

t _max

time (the maximum pressure)

F

error signal

M

injection molding compound

P _I

Injection phase

P _N

pressure phase

T

tolerance

^T min

boundary value

T _max

boundary value

W

threshold range

W _min

boundary value

W _max

boundary value

Y

manipulated variable

Z ⁽ⁱ⁾

injection passage (i = 1, 2, 3, ...)

Claims (9)

Injection molding process in which during the post-pressing phase (P _N ) of an injection molding operation (Z ⁽ⁱ⁾ ) the time profile of an internal cavity pressure (p _W ) is measured, in which at least one non-time-dependent parameter (P _W ) is determined from the recorded profile of the cavity pressure (P _W ). p _a , p _max , t _max , m, τ ₁ , τ ₂ ) is determined, in which the or each parameter (p _a , p _max , t _max , m, τ ₁ , τ ₂ ) with a stored characteristic setpoint (p _{a, 0} ) is compared, and in which on the basis of the comparison result automatically an adjusted pressure value (p _N ) for a subsequent injection cycle (Z ^{(i + 1)} ) is determined. Injection molding method according to claim 1, wherein a maximum value (p _max ), an assigned time (t _max ), an average value (p _a ) and / or an initial gradient (m) of the detected profile of the cavity pressure (p _W ) and / or or a time constant (τ ₁ , τ ₂ ) for the increase or decrease of the detected cavity pressure (p _W ) are used. Injection molding method according to claim 1 or 2, wherein the adapted reprinting value (p _N ) is determined only if the parameter (p _a ) or at least one of the parameters (p _a , p _max , t _max , m, τ ₁ , τ ₂ ) is outside a predetermined threshold range (W) to the respectively associated characteristic setpoint (p _{a, 0} ). Injection molding method according to claim 3, wherein a molded part produced in the injection molding passage (Z ⁽ⁱ⁾ ) is sorted out as a bad part if the parameter (p _a ) or at least one of the parameters (p _a , p _max , t _max , m, τ ₁ , τ ₂ ) lies outside a predetermined tolerance range (T) around the respectively associated parameter setpoint value (p _{a, 0} ), wherein the threshold value range (W) is selected such that it lies within the tolerance range (T) by far. Injection molding plant ( 1 ) - with an injection molding tool ( 3 ), which with at least one internal pressure sensor ( 17 ) is provided for detecting a cavity pressure (p _W ), and - with a pressure regulator ( 4 ), which is adapted to the from the internal pressure sensor ( 17 ) During the holding pressure phase (P _N) of an injection passageway (Z ⁽ⁱ⁾⁾ detected time curve of the cavity pressure (p _Z) at least one non-time-dependent characteristic variable (p _a; p _max, t _max, m, τ _1, τ ₂₎ to determine the or each parameter (p _a , p _max , t _max , m, τ ₁ , τ ₂ ) to compare with a stored parameter setpoint (p _{a, 0} ), and based on the comparison result, an adapted reprint value (p _N ) for determining the in-cylinder pressure (p _Z ) to be set in the post-pressure phase (P _N ) of a subsequent injection pass (Z ^{(i + 1)} ). Injection molding plant ( 1 ) according to claim 5, wherein the post-pressure regulator ( 4 ) is designed as a characteristic value a maximum value (p _max ), an associated time (t _max ), an average value (p _a ) and / or an initial slope (m) of the detected curve of the cavity pressure (p _w ) and / or a Time constant (τ ₁ , τ ₂ ) for the increase or decrease of the cavity pressure (p _w ) to determine. Injection molding plant ( 1 ) according to claim 5 or 6, wherein the post-pressure regulator ( 4 ) is adapted to determine the adjusted pressure value (p _N ) only if the characteristic (p _a ) or at least one of the parameters (p _a , p _max , t _max , m, τ ₁ , τ ₂ ) outside one predetermined threshold value range (W) to the respectively associated parameters setpoint (p _{a, 0)} is located. Injection molding plant ( 1 ) according to claim 7, wherein the post-pressure regulator ( 4 ) is designed to mark a molded part produced in the injection molding passage (Z ⁽ⁱ⁾ ) as a bad part to be sorted out if the parameter (p _a ) or at least one of the parameters (p _a , p _max , t _max , m, τ ₁ , τ ₂ ) is outside a predetermined tolerance range (T) around the respectively associated characteristic setpoint value (p _{a, 0} ), wherein the threshold value range (W) is predetermined such that it lies within the tolerance range (T) by far. Injection molding plant ( 1 ) according to one of claims 5 to 8, with an injection molding machine ( 2 ), which is a cylinder ( 5 ) for injecting a liquefied injection molding compound (M) into the injection molding tool ( 3 ), one in the cylinder ( 5 ) mounted propulsion device ( 6 ) for propelling the injection molding compound (M) and one on the propulsion device ( 6 ) acting machine control ( 13 ) for adjusting the in-cylinder pressure (p _Z ), wherein the engine control ( 13 ) of the pressure regulator ( 4 ) is supplied with certain pressure value (p _N ) as the set value for the adjustment of the internal cylinder pressure (p _Z ) during the pressure phase (P _N ) of the subsequent injection process (Z ^{(i + 1)} ).