WO2014182187A1

WO2014182187A1 - Production optimisation and control device and method for a thermoplastics injection-moulding process

Info

Publication number: WO2014182187A1
Application number: PCT/PT2014/000025
Authority: WO
Inventors: Bruno MARTINS; Pedro Jorge FERREIRA OLIVEIRA; Joaquim Henriques Martins; Joel OLIVEIRA CORREIA VASCO
Original assignee: Famolde - Fabricação E Comercialização De Moldes, Sa
Priority date: 2013-05-10
Filing date: 2014-05-08
Publication date: 2014-11-13
Also published as: PT106938A

Abstract

The present invention relates to a production optimisation and control method and device (1) for a thermoplastics injection-moulding process. The method applied by the device for optimising the thermoplastics injection-moulding process results from the incorporation of specific sensors in the tool, the mould (7) (8), the injection-moulding machine and any peripheral device where this might be required. The signals from these sensors as post-processed, making it possible to determine the actual processing conditions during injection-moulding, and to verify whether the actual processing conditions correspond to predetermined processing conditions. If that is not the case, data are supplied to the injection-moulding machine and/or peripheral devices in order to optimise processing conditions without any user intervention. The thermoplastics injection-moulding process is controlled during production on the basis of the results obtained, since these results also allow irregularities in the thermoplastics injection-moulding process to be detected. The method is similar, and the emphasis on data post-processing favours the production management side. The production control man-machine interface (10) is stratified, allowing local or remote operation, production monitoring or device management.

Description

DESCRIPTION

"DEVICE FOR OPTIMIZATION AND PRODUCTION CONTROL OF THE THERMOPLASTIC INJECTION PROCESS AND THEIR METHOD"

General Description of the Invention

The present invention (1) relates to a device for optimizing and controlling production of the thermoplastic injection process and method thereof. The methodology for optimizing the thermoplastic injection process provided by the device results from the incorporation of specific sensors into the tool, mold, injection machine and peripherals where required. The signals from these sensors are postprocessed, allowing the current injection processing conditions to be established, checking that the current processing conditions are as expected. If not, data is provided that is incorporated into the injection machine and / or peripherals to optimize processing conditions without any operator intervention. Control of the production of the process. Thermoplastic injection is performed based on the results obtained, as these also allow to detect nonconformities in the thermoplastic injection process. The methodology is similar, and the postprocessing approach focuses on production management. The human machine interface of production control is stratified, allowing operation, production supervision or device management (1). Control of the production of the process of Thermoplastic injection will be available in the form of a portal, which allows safe local and remote access.

Technical field of the invention

The scope of the present invention is focused on injection process optimization, namely, processing and production process optimization.

Processing optimization is performed based on the reading of pressure drops (ΔΡ) in the various segments defined over the injection time, cycle by cycle, in order to keep this variable constant throughout the injection cycle, allowing eliminate the compaction phase and thus reduce processing time. Maintaining constant pressure drop (ΔΡ) requires adjustments to the injection speed, so it is necessary to monitor the apparent shear stress (xapp), apparent shear rate (yapp) and apparent viscosity (napp) of the material. molten plastic to maintain the flow conditions of the material or to prevent its degradation.

Production control uses processing optimization data to identify possible non-compliance situations. Based on production orders, productivity indices and production cell efficiencies are calculated. This device component (1) allows local access for operation and supervision and remote access for supervision and management. Remote access can assume remote access settings within the industrial unit through a local area network (LAN) or remote access. anywhere in the world (WAN). In this situation and depending on the level of access granted, a remote user may change local settings such as production order elements or injection parameters.

The optimization of the thermoplastic injection process has been focused on the iterative adjustment of the injection machine parameters based on the quality control of the parts produced and using the user's technical knowledge and the history of the adjustment parameters.

State of the art of the invention

In the prior art search the following patent documents have been identified as the closest state of the invention:

US 5993704 A discloses a device for determining the optimum time for switching between injection rate process control to injection pressure process control and differs from the present invention in that it does not have effective control of the entire processing cycle. , the system is not prepared with a reference injection speed profile for comparison as well as the respective tolerances to allow the adjustment of the injection speed segment by segment, comparing the deviations obtained with the reference profile and interrupting the production process if the algorithm cannot converge to values within defined tolerances; EP 1717004 A1 discloses a device for selective temperature control in the mold and differs from the present invention in that it only optimizes processing in the cooling phase, not taking into account the previous history of cavity filling;

US 2004247724 A1 discloses a passive cycle and stop time monitoring device and differs from the present invention in that in addition to the cycle count, stop times and run times functions, it does not allow the integration of mold and mold data. injection machine related to operational events as well as not performing real time monitoring and / or local or remote actuation (physical or wireless connection) if necessary;

DE 202005013954 Ul - D4 discloses a real-time passive video surveillance monitoring device and differs from the present invention in that it only allows the viewing of operations and corresponding production parameters, having no ability to intervene in the injection machine processing parameters. The device shown in D4 refers to the existence of several fixed and mobile camcorders which can be selectively used by a local operator and does not use any type of sensor to assess the performance of the injection process as it proceeds.

In addition, the present invention:

• only requires connection to the injection machine control device to allow processing parameters and is therefore minimally intrusive as it does not imply any physical intervention on the injection machine wiring (9). This access to the injection machine parameters (9) allows instantaneous dosing volume values (dosing and pad) to be instantaneously controlled for injected melt volume. The pressure sensors (12 and 13) of the device (1) are placed in the molding zone (11) of the mold (7/8) for the purpose of calculating the pressure drop (ΔΡ). Device (1) incorporates an algorithm that uses the measured pressure drop values (ΔΡ) to compare with the optimized pressure drop curve for a particular mold. In addition, the device (1) includes temperature sensors in the mold cavity for process monitoring and control and joint plane load sensors to determine effective closing forces and imbalances in the closing operation. It also includes temperature and flow sensors to control the cooling system and its peripheral;

It incorporates all the sensors needed to optimize the processing in the mold itself, which simplifies the mold change process as the communication between the sensors and the processing module takes place wirelessly;

In addition to cycle counting, downtime and run time functions, it allows the integration of mold and injection machine data relating to operational events as well as real-time monitoring and / or local actuation or remote (physical or wireless connection) if necessary;

• provides for the use of constant pressure drop values (ΔΡ) in the mold cavity, with previously defined upper and lower limits. Maintaining the pressure drop (ΔΡ) in the molding zone (11) within the established limits allows it to be constant throughout the cycle, ensuring thermoplastic material compaction and reducing the total cycle time.

The differences between the present invention and the state of the art solve the above technical problems encountered in the state of the art of the present invention, as shown:

1. The placement of both sensors in the molding zone has the advantage of allowing the acquisition of pressure drop values (ΔΡ) resulting solely from the geometry of the plastic part, which will result in an effective calculation of the shear rate (yapp), stress. (rapp) and apparent viscosity (^ app) of the material being processed. The solution comprising a sensor in the mold and another sensor in the injection nozzle of the machine incurs the calculation that it has to account for the pressure losses resulting from the distance and filling obstacles that the plastic material has to overcome to fill the zone molding. The present device (1), by having both sensors in the mold, fulfills the effect recommended by reducing or eliminating errors in the instantaneous sensor readings taken at each injection cycle;

Another advantage of both sensors being located in the mold is their wireless connection to the controller where rheological calculations are performed. In this way, the signals of all sensors present in the mold are grouped in the acquisition module (2) coupled to the mold (7/8). This wireless connection allows the acquisition module (2) to transmit to the processing module (3) all the values required for calculation without any need for a physical connection. In the assembly operation of a mold equipped with the present device (1), regardless of the quantity and typology of the sensors present, the acquisition module (2) has an internal memory module where all its characteristics are identified. Thus, the operator simply assembles the mold (7/8) and recognizes the corresponding acquisition module (2), with no connection to sensors and amplifiers. These connections are all pre-made, thus eliminating the possibility of a connection error. When the mold finishes the operation, the acquisition module (2) automatically stores the last set of injection parameters used in memory. The operator will only have to physically disconnect the cooling, extraction or other connections. For this device (1) you only have to indicate the end of the operation for the wireless connection to be terminated. The above advantages result in the unexpected technical effect of the invention of eliminating the compaction phase, as the fact that optimizing the molding zone filling process depends on maintaining constant pressure drop (ΔΡ) read between the upstream sensor (12). ) and the downstream sensor (13), make it possible to inject the plastic material into the molding zone (11) with pressure values previously studied for each material and adapted to the geometry of the injected parts allowing the compaction phase to be eliminated, thus reducing the time of injection cycle.

Detailed Description of the Invention

For a better understanding of the detailed description of the invention, the definition of the following concepts is introduced in advance:

Equivalent section (If)

Considering that in general the plastic parts do not have a uniform and easily quantified cross section, for the present invention the concept of equivalent section was adopted that is determined based on the relation between the average thickness of the part to be injected and the width of the slot (w) to be considered for flow. Depending on the part geometry, this width may vary depending on the average part thickness in the area where the sensors are implanted. Taking into account the above variables, the equivalent section is calculated as the product between the average piece thickness and the defined width (w). Average speed of cast material

This velocity is defined by the ratio of the distance between the pressure sensors (12) (13) and the time interval (At) defined by the material touches on the respective pressure sensors (12) (13).

Flow Rate (Q)

Flow rate is defined by the product of the average speed previously defined and the equivalent section (Se).

The present invention relates to a device (1) for optimizing and controlling production of the thermoplastic injection process and method thereof. The methodology for optimizing the thermoplastic injection process provided by the device results from the incorporation of specific sensors in the mold (7/8), the injection machine (9) and peripherals where required, namely pressure sensors, temperature and load, deployed at strategic locations to assess processing conditions. This information is acquired by the acquisition module (2) and processed in the processing module (3). The module (3) communicates bidirectionally with the human machine interface (10), allowing the equipment operator or a remote user to access the information obtained.

Peripherals means equipment that is accessory to the injection process but is fundamental to its good performance. Among other peripheral equipment, the thermoregulator stands out, whose function is to supply the mold (7/8) with refrigerant so that the heat exchanges necessary to cool the parts are carried out. injected plastics. Temperature control of the mold may interact with the present invention (1) by allowing adjustment of the refrigeration conditions, namely, temperature and flow rate of the refrigerant. As peripherals we can also have manipulators, vacuum units, automatic assembly systems among others.

The signals of these sensors are postprocessed using mathematical models, allowing to establish the current conditions of injection processing. The same mathematical models verify that the current processing conditions are as expected. If not, the results of the mathematical models provide data that is incorporated into the injection machine (9) and / or peripherals to optimize processing conditions without any operator intervention.

The mathematical models used include the calculation of apparent shear stress (xapp), apparent shear rate (yapp) and apparent viscosity (app).

The apparent shear stress (xapp) is given by the expression

where ΔΡ is the pressure drop measured between the upstream (12) and downstream (13) sensors, L is the distance between the centers of the upstream (12) and downstream (13) sensors and h is the average wall thickness where the upstream (12) and downstream (13) sensors are located. The apparent cutoff rate (yapp) is given by the expression

where Q is the flow rate calculated from the material velocity given by the pressure peaks obtained from the upstream (12) and downstream (13) sensors, w is the slot width and h is the average wall thickness of the part where the sensors upstream (12) and downstream (13) are located.

The apparent viscosity (n, app) is given by the ratio of apparent shear stress (xapp) to apparent shear rate (yapp).

Mathematical models are incorporated in a control algorithm that aims to evaluate the evolution of pressure values within the mold and compare them with the reference values. For the sake of more rigorous control, the control algorithm uses the division of the dosing stroke into several segments, which allows the injection speed profile to be defined as a function of. current position of the spindle on the injection machine.

Segmentation of the dosing stroke allows speed variations to be imposed for each segment throughout the new processing cycle rather than using a constant injection speed, ie changes will only take effect on the next injection cycle. The objective of this algorithm is to maintain the pressure drop (ΔΡ) in the mold (7,8) within the previously defined reference values by adjusting the injection velocity curve.

The control of the production of the thermoplastic injection process is based on the results of the same mathematical models, since the results of these also allow to detect nonconformities in the thermoplastic injection process. The methodology is similar, and the data post-processing approach focuses on production management, because based on the processing data it is possible to obtain productivity indicators such as actual production times, reject rate, production rates. , among others .

The human machine interface of production control is stratified into user levels, allowing operation, production supervision or device management (1). Production control of the thermoplastic injection process will be available in the form of a gate, allowing secure local and remote access.

Process optimization is achieved using pressure sensors (12) (13) implanted in strategic locations to evaluate the processing conditions, namely located in the molding zone (11). The parameters that can be calculated cycle by cycle based on these sensors (12 and 13) are apparent shear stress (xapp), apparent shear rate (yapp) and apparent viscosity (app). Other sensors located in the mold may provide temperature or load data, the values of which may trigger alarms for the operator if they exceed the tolerances set.

The upstream pressure sensor (12) should be located near the inlet of molten plastic material in the cavity. The downstream pressure sensor (13) should be located in one of the last zones to be filled by the molten plastic material. In this way, the molten plastic material will initially touch the upstream sensor (12) and only then touch the downstream sensor (13).

Cavity pressure information obtained from these sensors (12 and 13) allows the calculation of the pressure drop (ΔΡ) as well as the calculation of the time interval (At) between the melt touches on the sensors (12 and 13). ). These calculations are achieved by the very definition of these variables presented at the beginning of the description of the invention.

The distance (L) between the upstream sensor (12) and the downstream sensor (13) is the distance between both sensors, considering the flow orientation of the molten plastic material when filling the molding zone (11). With the pressure drop (ΔΡ) and the distance (L) the shear stress (xapp) of the molten plastic material is calculated. With the equivalent section (Se) and time interval (At) the apparent shear rate (yapp) of the molten plastic material is calculated.

I

It is clarified that by the expression: v = -, the

At

average velocity (v) / by the expression: If = wxh, is calculated the equivalent section (If); finally, the flow rate (Q) is given by the expression: Q = vx Se.

These calculations can be performed cycle by cycle, further allowing the calculation of apparent viscosity (ap) by the ratio of shear stress (xapp) to apparent shear rate (yapp).

The pressure drop (ΔΡ), in addition to being the input variable in the shear stress calculation (xapp), is also used as a control variable for the internal pressure in the molding zone (11). This control depends on the injection speed profile imposed so that the injection phase may undergo some time increment. However, filling the molding zone (11) at constant pressure allows the subsequent compaction phase to be eliminated and thus to reduce the injection time and increase the productivity of the injection process itself.

Regarding set-up times, there are significant productivity increases resulting from the wireless connection between the mold-coupled acquisition module (2) (7/8) and the processing module (3). The present invention (1) will come pre-wired, eliminating connection errors and time spent assembling and disassembling.

In addition, the device control process (1) can be described according to the following steps:

1) Initial verification of the absence of alarm events by the injection machine in conjunction with the device start signal initially given by device operator or given automatically after each cycle when already in operation;

The first segment of the injection speed profile starts. The first segment varies between position 1 and position 2 of the spindle and only when position 2 is reached is the calculation made;

The deviation of the pressure drop value (ΔΡ) for the first segment from the reference curve is calculated (Figure 6);

It is determined:

The. the direction of deviation, ie whether it is negative or positive with respect to the reference curve, so that the direction of the increment to be made at the injection speed in the next cycle can be determined

B. If pressure drop is between lower and upper tolerance:

i. if outside the upper and lower tolerances, the increment to be made at the injection speed in this segment is calculated;

ii. if it is within the lower and upper tolerances there is no change of any kind;

then the apparent shear rate (yapp) of the material being injected is analyzed to prevent the user-defined maximum allowable cut-off value being exceeded for the shear rate of the material being injected;

Recalculated the new value for the injection speed, taking into account step 4. b) i., For the segment, this This value is saved and used for setting the injection speed curve to be used in the next cycle.

7) The set of steps 3) to 6) is repeated for all segments of the injection speed profile, after which it is possible to construct a table with the recalculated injection speeds for each segment for the following injection cycle;

8) At the end of the cycle the control variables for the next cycle are calculated, namely pressure drop (ΔΡ), time interval (At), flow rate (Q) and apparent cutoff rate (yapp).

In addition, the device (1) may preferably include a camcorder enabling the remote user to view the operation of the injection machine (9). This camera transmits its signal unidirectionally via two-way wireless communication (5), allowing the remote user to be in the industrial unit or anywhere in the world.

Description of the figures

Figure 1 - Schematic representation of the invention (1) coupled to an injection machine (9) comprising the acquisition module (2) coupled to the mold (7/8) establishing unidirectional wireless communication (4) to the processing module (3). The processing module (3) in turn establishes two-way wireless communication (5) with a local or remote terminal (6) via the Internet. Figure 2 - Schematic and simplified representation of Figure 1, where the invention (1) is represented, but where the injection machine (9) is omitted for a better interpretation of the operation of the device (1).

Figure 3 - Schematic and detailed representation of the mounting of upstream (12) and downstream (13) sensors in the molding zone (11) e _. physical connection to the acquisition module (2). The acquisition module (2) has a transmitting antenna for performing unidirectional wireless communication (4).

Figure 4 - Schematic representation of the open mold with the acquisition module (2) mounted on the injection side of the mold (7). This location is due to the fact that the injection side typically has fewer moving elements, therefore there is less risk of damage to the sensors. However, the location of the acquisition module (2) may be mounted on the extraction side of the mold (8) if the number of sensors warrants it.

Figure 5 - Schematic representation of the molding zone (11) visible with the mold closed. As shown, the acquisition module (2) should be located on the top face of the mold.

Figure 6 - Schematic representation of the desired profile for the pressure drop in the molding zone (11), illustrating the reference profile for the pressure drop, the upper and lower tolerances, and the actual pressure drop curve obtained by the acquisition of pressure values. pressure by the upstream (12) and downstream (13) sensors. The curve of The reference for the pressure drop (ΔΡ reference) is determined based on values derived from numerical simulations, according to the part geometry. The reference curve is based on information obtained by numerical simulation of the cavity filling process, where predicted upstream and downstream sensor cavity locations are predicted. By identifying these locations in the numerical simulation, it is possible to obtain realistic estimates of the pressure values at these locations and thus to evaluate in advance the behavior of the flow of plastic material within the cavity. The initial approximation by numerical simulation also allows to determine which segment from which the pressure drop (ΔΡ) stabilizes. Once the pressure drop trend (ΔΡ) is established, it will be possible to guarantee the flow of plastic material over the following segments at injection speeds calculated by the invention (1). Continued solidification of the part will make irrelevant the need to control the last segment. The cavity is completely filled with plastic material, the percentage of solidified volume of the part is quite high, so the pressure drop control (ΔΡ) in this segment is ineffective, making this segment an abrupt decrease in pressure drop (ΔΡ). ). To ensure that the process is not interrupted shortly after the reference curve is not met, a user tolerance is set in advance which results in the upper and lower tolerances. The process will proceed without any increase in injection speed where the points of the actual pressure drop curve (actual ΔΡ (acquired)) are both above the lower tolerance and below the upper tolerance (step 4.b) ii. in the description) . THE Maintaining the pressure drop between the lower tolerance and the upper tolerance in the last two to three segments of the actual pressure drop curve (actual Δ ((acquired)), as recommended in this figure, allows the part to be compacted shortly after the end. injection phase, thus eliminating the compaction phase. The compaction of the part is thus ensured even during filling of the cavity, ie during the injection phase. The use of the injection speed as a means of controlling the pressure within the cavity results in the cavity being rapidly filled, allowing the core to remain fluid though the workpiece already remains fluid, allowing for the continued flow of material will only be terminated as the core solidifies. Pressure drop stabilization (ΔΡ) gives the device (1) indication that there is still an established flow of material, allowing it to adjust the injection speed, segment by segment, to keep the pressure drop constant until that the part completely solidifies. The description of this figure is used to exemplify the unexpected technical effect that the invention has on the state of the art thereof. The graph can be divided into three areas, the growth of pressure values in upstream (12) and downstream (13) sensors, which is seen in segments 1 to 4; the stabilization of the pressure values in the sensors (12, 13) which translates into a stable pressure drop (ΔΡ) during segments 5, 6 and 7; the end of the injection represented in the eighth segment, where pressure values fall rapidly, resulting in an equally abrupt decrease in pressure drop (ΔΡ). In fact the presentation Preferably the invention can be advocated with this example.

Figure 7 - Schematic representation of the conventional injection process which may include the mold closure, injection, compaction, cooling and plasticization, mold opening, extraction and pause phases.

Figure 8 - Schematic representation of the injection process carried out with the invention, where the compaction phase can be removed from the process, decreasing the total injection cycle time and thus increasing the process productivity.

Figure 9 - Schematic representation of the arrangement of upstream (12) and downstream (13) sensors in the CD case. As illustrated, the sensors 12,13 are located on different faces, and there is a need to account for the pressure drop due to section change. Similarly, the distance (L) between the sensors (12, 13) must take into account the additional path that the plastic material will have to travel.

Figure 10 - Graphical representation of pressure values obtained from CD case injection for a 10-segment configuration lasting 1 second for each segment. The graph in the figure represents the values measured by the upstream sensor (12) and the downstream sensor (13) with an acquisition frequency ranging from 50 to 200Hz and processed in real time by the invention (1). As recommended above, the pressure drop (ΔΡ) increases tendentially during segments 1 to 4, stabilizing during segments 5 to 9 and tending to zero in segment 10, where the cavity is already and the part compacted.

Preferred embodiment of the invention

The present invention has been applied in the case of a CD case, where the upstream (12) and downstream (13) sensors were both located in the cavity but in geometrically different areas of the part. In this case, the distance between the sensors (12,13) does not correspond to the distance between the axes of the sensors (L), and the effective distance (L ') to be calculated by the material travel over the average plane of the workpiece wall. where the sensors are located. The location of the sensors (12,13) should be selected so that they are oriented according to the flow of plastic material. In this case, the upstream sensor (12) is located near the material inlet in the part and the downstream sensor (13) is located in alignment between the injection point and the upstream sensor (12). The fact that the sensors (12,13) are not located on the same face introduces an additional pressure drop that should be accounted for but does not affect the performance of the invention (1). The distance between the sensors (12, 13) was in this case 42.78mm, considering the transition from the face where the upstream sensor (12) is to the other face where the downstream sensor (13) is located.

A numerical simulation was performed for the filling for this part where nodes were created in the simulation mesh of where pressure and temperature values could be taken. Based on this information, a 10-segment injection speed profile was obtained, which numerically resulted in a pressure drop that was found to be approximately constant from the fifth segment. This approach allows the sixth, seventh, eighth and ninth segments to be used to control pressure drop (ΔΡ), assuming that in the tenth segment the plastic material will already have more than 50% of its sodified volume, it is not intended to control the pressure drop (ΔΡ) in this segment. The injection machine has been configured for 10 segments to allow the introduction of the obtained injection speed profile.

The process begins with the injection of the part. The sensors (12,13) transmit the pressure values read to the acquisition module (2), which in turn transmits them to the processing module (3). It is in this module (3) that the pressure drop (ΔΡ) is monitored, segment by segment, and whenever deviations occur, this information is stored and entered in the human machine interface of the injection machine (10) in the form of increments or decreases in injection rate in segments where the detected deviations occurred for the next injection cycle. This injection speed correction process will be repeated whenever pressure drops occur outside the imposed tolerances.

Claims

Device (1) for the optimization and production control of the thermoplastic injection process characterized by its constitution:

The. sensors in the mold itself (7) (8), the injection machine (9) and peripherals, including: i. pressure sensors (12) (13) located in the molding zone (11) of the mold (7) (8), wherein the upstream pressure sensor (12) should be located near the inlet of molten plastic material in the cavity and the downstream pressure sensor (13) shall be located in one of the last zones to be filled by the molten plastic material; ii. temperature sensors in the mold cavity;

iii. temperature and flow sensors;

B. data acquisition module (2) having an internal memory module;

ç . wireless connection between the acquisition module (2) coupled to the mold (7/8) and the processing module (3).

2. Device according to a. claim 1, characterized in that it includes a camcorder which transmits its signal unidirectionally by bidirectional wireless communication (5).

Device control method (1) according to claim 1, characterized by the following steps: a) initial verification of the absence of alarm events by the conjugate injection machine with the device start signal initially given by the device operator or automatically given after each cycle when already in operation;

b) initiation of the first segment of the injection speed profile;

c) calculation of the deviation of the pressure drop value (ΔΡ) by the acquisition of pressure values by the upstream (12) and downstream (13) sensors for the first segment from the reference curve based on values derived from of numerical simulations;

d) determination:

i. the direction of deviation and the direction of increment to be made at the injection speed in the next cycle;

ii. If pressure drop is between lower and upper tolerance:

The. if outside the upper and lower tolerances, the increment to be made at the injection speed in this segment is calculated;

B. if it is within the lower and upper tolerances there is no change of any kind;

e) analysis of the apparent shear rate (yapp) of the material being injected so that it is less than the maximum allowable value previously defined by the user;

f) calculating the new value for the injection speed, taking into account step e) i., for the segment; This value is saved for setting the injection speed curve to be used for the next cycle. g) repeating steps c) to g) for all segments of the injection speed profile;

h) calculation of pressure drop (ΔΡ), time interval (At), flow rate (Q) and apparent cut-off rate (yapp) for the next cycle.