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HENRI COANDA GENERAL M.R. STEFANIKAIR FORCE ACADEMY ARMED FORCES ACADEMY

ROMANIA SLOVAK REPUBLIC

INTERNATIONAL CONFERENCE of SCIENTIFIC PAPERAFASES 2012

Brasov, 24-26 May 2012

MODELING OF THE TEMPERATURE CONTROL SYSTEM OF THE

PLASTIFICATION CYLINDER OF INJECTION MOLDING MACHINE

Vadim CAZAC *, Ilie NUCA **

* TehElectro-SV Co, , ** Technical University of Moldova

Abstract:At present the development of industry of plastic products tends to grow up the quality ofproducts obtained by this method and increase productivity. The common denominator on quality,

productivity and cost efficiency in producing plastic objects, it is thermal process that must ensure the

material plastification in cylinder of plastification of machine for injection of the plastical materials.In this paper is elaborated a mathematical model describing the thermal process heating plasticizing

cylinder for injection molding machine with consideration of thermal influence between of heating zones

and cyclic variation of material speed in the cylinder. On the basis of elaborated mathematical model

were simulated transient processes at start and in working regime of the machine with different types of

regulators in the temperature control system in each thermal zone. Was made a comparison between the

quality of transient process with regulators P, PI, PID granted Ziegler-Nichols method and the results

obtained with the fuzzy controller.Profound study of transient processes in Simulink Matlab allowed

optimize the regulators for temperature control system for each heating zone. Implementation in practice

of a system of adjusting and control of plastic injection machine was in the company The electro-SVImplementing of this system is based on a universal controller of at the company .

Keywords:plastification, plastics, Injection Moulding Machine, plastification cylinder

1. INTRODUCTION

Processing by injection is thetechnological process by which plastics ,

brought in a state of flowing is introduced

under pressure into a mold for formation. Afterfilling the mold, the material is kept underpressure and hardened by cooling forthermoplastic and heating for thermosetting

polymers. The advantages of formation byinjection consist in possibility of obtainingobjects with complicated shapes different sizesand form a very wide range of polymers. Theoperations are automated and machines have ahigh performance.[3]

Processing conditions depend on

the properties of the material, technologicalparameters of processing and also of the

technical and technological parameters ofplastic injection machines.

At present the development of plasticsproducts tends to rise the quality of productsobtained by this method and and also to grow

the productivity proces. The commondenominator of the quality, productivity andcost in production proces is the heating

process. This is possible only by designing ofthe machines with parameters take intoaccount the specific properties of processedmaterials and ensure the specific of thetechnological process.

The study object is an injectionmolding machine type 3330 1 (Fig. 1)[7] with a control system based on

electromagnetic relays which ensures theworking cycle of the machine for the differentregimes and a temperature control system for


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injection unit which consists of four discretePID controllers with static power relays andresistive electrical heaters.

Figure 1. General view of the 3330 1type machine [7]

The main purpose of this paper is to designand simulate the optimal thermal control

system of the plastification cylinder ofinjection machine based on the analysis oftransient and stationary process with differenttypes of digital controllers: P, PI, PID andfuzzy.To come to ours main purpose we have tosolve some basically problems as:9 The analysis of the processes, and its

particularities of the operating regimes ofthe machine.

9Adapting of the mathematical model that

describes the physical nature of the processwithout losing the physical sense and thesimulation in Matlab.

9Determination of the criteria for grantingthe temperature control system, and thecalculation of the coefficients for selectedregulators.

2. THE MATHEMATICAL MODEL OF

THE INJECTION MOLDING

MACHINES

2.1 Calculation of the thermal regime of the

plastic injection machines

Calculation of the thermal regimeprocessing of plastics is very important todesigning and exploitation this type ofmachines, given the fact that thermoplasticmaterials processed are sensitive to changes intemperature.

In general in any screw casting

machine we have more temperature zones onthe length of plastification cylinder. Fromtechnological point of view for each type of

material it is recommended that each area tohave a certain temperature. For the calculationof thermal areas of plastification of castingsmachines is necessary to determine the amountof heat released during to the plasticdeformation of the polymer on each area of themachine, which is determined by: thegeometry of the screw, the number of rpm,

polymer viscosity, length of area. This energycan be determined by using the followingempirical relationship[5]:

(1)2 21110330.5 /plQ d m = l h

where: d1- effective diameter of the screw, m;m - number of revs, rpm;

- effective viscosity of the material (kg/h)/m2

;h - screw channel depth, m;l- the length of thermal area, m.

Figure 2. Eliminated energy curve toplasticizing material (1) and temperature curve

in each zone of injection unit (2) [5]

2.2 The mathematical model of starting

regime of the injection unit

For the elaboration of the mathematicalmodel of the start thermal regime for machineand to modeling the process we use themethod of blocks. It is supposed that in thestarting regime all elementary blocks in eachzone are with concentrated parameters. In suchconditions the scheme will have the followingstructure shown in Figure 3where:Tnc.;Tcil.;Tmelc;Tiz.-average temperatureof the heater, cylinder, screw and insulation,Qel the power delivered for heaters, W;

According to the structural scheme are

elaborated equations of thermal balance indifferential form for eachblock:


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Figure 3 Block diagram of the mathematicalmodel of a region of injection unit [5]

z)(r,

Figure 4. Heat flow in the heating cylinder [2]

- for heater . .

. . . . . ..

( ) (2

inc incinc inc inc el inc cil

inc

Sdm c T Q T T

d h

= ) (2)

- for insulation

. .. . . . .

.

1 .

( ) ( )2

( )

inc inciz iz iz inc iz

inc

exter n iz mediu

Sdm c T T T

d h

S T T

=

(3)

- for zone cylinder

. .. . . . ..

. .

( ) (2

( )

inc inccil cil cil inc cil

inc

T cil cil melc

Sd m c T T T d h

k S T T

=

)

(4)

- for screw zone

. . . . .( ) (melc melc melc T cil cil melc

dm c T k S T T

d= )

(5)

In the relationships (2-5) we have: Minc.,Miz., Mcil., Mmelc,- the weight of heaters,insulation, cylinder, screw, kg;

cinc, ciz., ccil.,cmelc the specific heat ofmaterial, kcal/kgC;

nc., hnc., Snc.- thermal conductivity ofmaterial [W/m0C], the heater thickness, m;and total area of the heater m2;1 - heat transfer coefficient from the externalsurface of the insulation in the externalenvironment [W/(m20C)];kTheat transfer coefficient from the internal

surface of the cylinder through the airbetween cylinder and screw, [W/(m20C)];Tmed the ambient temperature,

0C

2.3 The mathematical model of the injection

unit in continuous working regime

The thermal calculation of injection unitin starting regime aims to determinenecessary power for heaters of the

plastification zones and which ensure thetemperature required for processing the

polymers in injection unit.To elaboration the mathematical model

of the injection unit in the normal work regimewe have take into consideration the movementof material through the cylinder.Was specifiedabove if the material is in the areas of

plastification and dosage, the structure of theflow of material is subject to a diffuse modelwith a single parameter, the load area (firsttechnology area) movement structure of

material in corresponding to the model of theideal moving .The mathematical model of the heating

model for a zone of plastification in normalexploitation, is developed with considerationto the fact that in this area begin removing heatfrom plastic deformation of the material andcylinder temperature to moving the material isa constant size determined by type of

processed material.Block diagram of mathematical model is

present in figure 5:


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Figure 5. Block diagram of the mathematical

model which describe the thermal workingregime for plastification area [5]

For each block are elaborated equationsheat balance in differential form:

1)for the cylinder:Tcil.i (l,) = const, i- thermal zone number(i= 1,2,3);

2) for material taking into account that theflow structure of the material is described

by a diffuse model with a parameter:

( )

1

1

. . . . .

. . . . .

( )

( )

( )

( )

i Mi Mi Mij

M i Mi Mi Mij Mij

M i Mi Mi Mij Mij

pl cil mat cil i j cil i Mij

mat melc melc med i melc i

dS l c T

d

u S c T T

u S c T T

Q k S T T

k S T T

+

=

= +

+ +

+ +

+

(6)

where: iS - the average of the surface of thecross section of thermal zone;

-l elementary length of the area;

plQ - heat from of plastic deformation on the

length ;l

.cil mat k . - heat transfer coefficient of the

cylinder to material;

. .cil i jS - heat transfer surface of the cylinder to

the material on the length ;l

.cil iT - cylinder temperature; MijT - temperature

of the material in zone j; j- index of thermalzone section [3]

3) for block which determining average

temperature [3]

.1

1 nmat i Mij

j

T Tn =

=

(7)

Based on equations (6-7) with prescribedinitial conditions is calculated heating of thematerial which moving through the cylinder inlength of the thermal zone. [3]

3. THE TEMPERATURE CONTROL

SYSTEM SIMULATION

The equations (2-7) describe only thermalprocesses in the system without automatictemperature control loops.

In this subparagraph is elaborated a modelwhich allows to simulate transient processes inthe system with the temperature controllers foreach zone separately and which allows todetermine the optimal parameters of regulatorsfor functioning the system as a whole and toconsider the influence of heat betweenneighboring zones.

The influence of the areas was modeled inthe basis of law to transfer the heat betweenobjects at different temperatures andtemperature gradients of zones the active partof the injection unit of machine, this allows usto determine the influence of each zones and toregulate the system temperature in zones whenthere is this influence.

Also in this model is simulated theelimination of heat by the material processed

in depending on the coefficient of viscosityand pressure exerted on it during the injection.As an example in Figure 6 is shown the

scheme of the model with fuzzy regulator.The simulation of model with regulators

P, PI, PID was performed also with thisscheme then where they were replaced withthe fuzzy controllers so that we simulated themodel with different regulators and performeda qualitative analysis of transient processeswith different types of regulators.


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T mj-1

from controller

T pvc

T cylinder

the zone 3

T mj-1

from controller

T pvc

T cylinder

the zone 2

from controller

Tpvc

T cylinder

the zone 1

T mj-1

from controller

T pvc

the nozzle

T cycle

the model of cycle

-K-

scale

coefficient

T pvc

white

black

5

-5

150

T 4

130

T 3

100

T 2

80

T 1

A

Goto

Fuzzy Logic

Controller4

Fuzzy Logic

Controller3

Fuzzy Logic

Controller1

Fuzzy Logic

Controller

0 500 1000 1500 2000 2500 3000 3500 4000-20

0

20

40

60

80

100

120

140

160

180

200

Time

The zone 1

The zone 2The zone 3

The nozzle

pvc speed

Figure 6 Simulink model of the temperaturecontrol system

The results obtained in simulation the model

without temperaturecontrol system:

Figure 7 The temperature variation in eachzone of the cylinder in starting regime without

a regulating system

Figure 8 The temperature variation of materialwith PID regulator

0 1000 2000 3000 4000 5000 6000 70000

50

100

150

200

Time (Seconds)

Simularea_Incalzire_termo

T, C

The nozzle

The zone 3The zone 2

The zone 1PVC speed

Figure 9 The temperature variation of materialwith PI regulator

0 1000 2000 3000 4000 5000 6000 7000-200

20

40

60

Figure 10 The temperature variation of

material with Fussy regulator

80

100

120

140

160

180The nozzle

The zone 3

Time

The zone 2The zone 1T, oC

PVC speed

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2x 10

4

0100200300400500600700

Time (Seconds)

The zone 1 The zone 2

The zone 3The nozzle


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Figure 11 The temperature variation of

material with P regulator

Simulation of the heating system ofinjection unit allows us to observe the

temperature changes in every heating zone ofcylinder in starting regime of the machine andworking regime under a cyclic speed variationof material processed through the plastificationcylinder.

The comparative analysis of the results offigure 7-10 are resulting that the best

performance for this system is ensures with aPID controller, with a minimum override oftemperature in the nozzle of only 7%,stationary error of 1.4 %, the transitory time is1000 s.

The influence of the zones is morepronounced when the temperature differencebetween zones is higher which causing anerror occurs the temperature control to thezone to which is prescribed lower temperature.

CONCLUSIONS

The resultants of this work are:

1. Was elaborated a mathematical modelof the plastification cylinder of injectionmolding machine by analyzing the physical

process of plastification with elimination anamount of heat of processed material underthe influence of pressure exerted by the screw.The model is liable to be user for the differenttypes of machines with different constructive

parameters of the injection unit.2. Computer simulation permitted to

optimization of static and dynamic process of

the automatic control system of temperature ofthe real machine in report to rapidity andexclusion of oscillations and override oftemperature to the thermal areas of the

plastification cylinder and nozzle.3. The results of this study was used to

modernization the control system with PLC ofplastic injection machine type 3330 1[7]. To practical tests of the upgradedmachine, has been demonstrated that digitaltemperature control for each thermal areaensure to the slow output to stationary regime,avoiding thermal shocks that lead to increaseof the reboot, maintaining constant parametersand compensating disturbing factors .

REFERENCES

1. Tomoyuki AKASHI: Temperature Controlof Heating Cylinder of Injection MouldingMachine by Decoupling Method, Trans. ofthe Society of Instrument and ControlEngineers Vol.E-1, No.1, 51/59 (2001)

3. Dominick V. Rosato, Donald VRosato,Marlene G. Rosato: Injectionmolding handbook, ed. 3 ISBN 0-7923-

8619-1, 19974. Tehnologii de injecie n matri:ndrumar de proiectare, UniversitateaPolitehnica Bucureti, Facultatea Ingineriai Managementul Sistemelor Tehnologice,CatedraTehnologia Construcilor de Maini,2009

5. Douglas M. Bryce:Plastic Injectionmolding; Manufacturing ProcessFundamentals . SME, 1996. ISBN 0-87263-472-8

6. Cazac Vadim: Automatizarea mainii deinjecie a materialelor plastice; Tez demaster, Chisinau, 2012.

7.http://www.impuls95.ru/catalog/item/thermoplastic_3330_f1.html

0 500 1000 1500 2000 2500 3000 3500 4000 4500 50000

20

40

60

80

100120140160180200

Time

The nozzleT, oC

The zone 3

The zone 2

The zone 1PVC speed

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