WO2013090993A1

WO2013090993A1 - A method for simulating bilaterally non-symmetrical injection moulding process

Info

Publication number: WO2013090993A1
Application number: PCT/AU2012/001553
Authority: WO
Inventors: Jayesh Modi; Pranoy MODI
Original assignee: MODI CONSULTING AND INVESTMENTS Pty Ltd
Current assignee: MODI CONSULTING AND INVESTMENTS Pty Ltd
Priority date: 2011-12-19
Filing date: 2012-12-19
Publication date: 2013-06-27
Anticipated expiration: 2014-06-19
Also published as: AU2012357709A1

Abstract

A method for simulating the injection moulding process consisting of but not limited to cycle time to ejection of the moulded article from tool and corresponding tool stabilisation temperature and the part thickness average temperature and the part midplane temperatures by application of published numeric formulas and methods that assume bilaterally symmetrical thermal balance between CORE and CAVITY of an injection moulding tool applied to numeric tasks in analysing injection moulding process in tools wherein the CORE and CAVITY may not be having bilaterally symmetrical thermal conditions.

Description

A METHOD FOR SIMULATING BILATERALLY NON-SYMMETRICAL INJECTION MOULDING PROCESS

Field of the Invention

This invention concerns the use of improved numeric techniques to enable computation of injection moulding cycle time and process parameters and predict process output by way of using published computation formulas as applicable to bi-laterally symmetrical heat transfer however enable its application to bi-laterally non symmetrical heat transfer condition.

Background to the Invention

Injection moulding tools are used in industry to form thermoplastic polymers into a variety of complex shapes. The process involves the injection of a pre-prepared pliable thermoplastic into a tool whereupon it acquires the shape of the mould CAVITY within the tool. The thermoplastic is then cooled so that it sets while retaining the shape of the CAVITY. Other common terms for the tool are mould or die.

In many industrial applications of injection moulding, profitability is dependent on having the shortest cycle time between each moulding process while ensuring the quality of the product produced by the tool remains within permissible limits. It is vital that the product produced by the tool reproduces the mould CAVITY accurately and that any residual stress in the product is minimised so that there is less potential for warpage of the product as it cools, and/or as it ages. Residual stress in the finished product can cause warpage over the life of the product due to differential shrinkage. A short cycle time means a more productive tool. However since the process involves thermodynamics, the cycle time is significantly influenced by the thermodynamic performance of the tool and quality is affected by uniformity of tool temperature all over the tool. Accurate estimate of part thickness average temperature is vital for prediction of mould shrinkage and thus size the mould.

Based on traditional formulas published in literature all cooling and temperature evolution happens in-between symmetrical walls having identical cooling on both faces and geometric mid plane is the plane having highest temperature.

However in practice this cooling is never identical due to:

Air gap developing on one side, by way of example CAVITY, as material shrinks away from CAVITY face and shrinks onto CORE. This causes additional impedance in cooling on the side with air gap.
Cooling layout on two sides of mould may be different, due to variety of reasons relating to tool manufacturing and restrictions imposed by presence of lifters, ejector pins, side COREs etc.
Various conductivity materials may have been used or combined with in different sides of tool.
Differing coolant temperatures and or flow rate may have beeen used on different sides to have preferential cooling.
In case of sequential two shot moulding the CORE from first shot will carry the first shot moulding and present it to second CAVITY (having additional gap). Second shot will then be moulded in this gap, and, cooling of this second shot will experience substantial difference in cooling rate on two sides as plastic from first shot generally will have lot less thermal conductivity than that of the tool face on the other side and hinder heat flow to CORE.

Many efforts have been made to date to address these thermodynamic properties related issues.

Patent number WO97/37823 in name of Kao Corporation (JP) discusses cycle time analysis when an In Mould Label is associated. When an In Mould Label is associated, it has impact on heat transfer as the heat has to traverse through the label on the side where label is and in turn impact cycle time and cooling characteristic. The Kao's approach is to use finite element method (FEM). This has a limitation in that you need to create accurate 3D model of tool, part and the label for such an analysis to take place. It requires expert operators to create such models and also to run such sophisticated FEM simulation tools. For each iteration of cooling variation, a new model has to be created and thus the whole analysis process takes substantial time and cost.

Patent number WO 2010/127772A2 in name of MAGMA GIESSERITECHNOLOGIE GMBH discusses cycle time analysis and arrives at time to eject the part after mould filling. This has approach to use finite element method (FEM). This has a very big limitation in that this too requires very detailed 3D model of tool with every detail you need to create accurate 3D model of tool and part for such an analysis to take place. It requires expert operators, very heavy duty computing power and it requires very long CPU time to run such sophisticated FEM simulation tools. For each iteration of cooling geometry, a new model has to be created and thus the whole analysis process takes substantial time and cost. Thus it cannot be employed for process development, simulation or scenario studies at early stage of process or even earlier at project bidding stage.

Research publication 'The Design of Conformal Cooling Channels in Injection Moulding Tooling, XiaorongXu, Emanual Sachs and Samuel Allen, of Massachusetts Insititute of Technology, Cambridge, MA 02139, published in Polymer Engineering and Science, July 2001, Vol41, No.7), has provided a very effective methodology to estimate tool stabilisation temperature and in turn cycle time and part average temperatures and midplane temperatures. However this method has biggest limitation in that it assumes bi-laterally symmetrical heat transfer and thus limits its use.

An aim of the present invention is to provide an injection moulding simulation tool with improved prediction of cooling or heating performance that is easy and cost effective to deploy that overcomes at least some of these aforementioned difficulties and particularly does not rely on complex Finite Element Method.

Summary of the Invention

A method for simulating the injection moulding process consisting of but not limited to cycle time to ejection of the moulded article from tool and corresponding tool stabilisation temperature and the part thickness average temperature and the part midplane temperatures by application of published numeric formulas and methods that assume bilaterally symmetrical thermal balance between CORE and CAVITY of an injection moulding tool applied to numeric tasks in analyzing injection moulding process in tools wherein the CORE and CAVITY may not be having bilaterally symmetrical thermal conditions, the said method comprising the following steps however not limited to:

Step1 dividing the part thickness in two fractions wherein by assuming a suitable starting figure of split proportion, arriving at the first thickness by multiplying component thickness with split proportion and doubling it and determining a complimentary thickness, the second thickness , by subtracting first thickness from doubled component thickness.

Step2 All properties related to CORE of tool under analysis is specified, for example cooling geometry consisting of cooling channel cross section height, width, fillet radius, distance to tool surface and distance between the two adjacent cooling channels, cooling channel friction factor. In addition the tool material properties consisting of density, thermal conductivity and specific heat of tool material are associated to the first thickness and the same related to CAVITY of tool under analysis are associated to the second thickness . From here on everything related to CORE side of tool under analysis will be linked and used in one side analysis, for example the first thickness and everything related to CAVITY side of tool under analysis will be linked and used in one side analysis, the second thickness

Step3 Now we specify coolant properties consisting of but not limited to Density, Specific heat, flow rate and temperature of coolant flowing through CORE is associated to the first thickness and coolant properties consisting of but not limited to Density, Specific heat, flow rate and temperature of coolant flowing through CAVITY is associated to the second thickness .

Step4 Cycletime components made up of Tool closing, Material injection, Machine Opening and Dwell are associated equally to the first thickness and the second thickness .

Step5 Polymer thermal and mechanical properties and melt temperature at time of injection are associated equally to both the first thickness and the second thickness.

Step6 Part ejection criterion is defined in the form of midplane temperature at ejection or part thickness average temperature at ejection.

Step7 There are many formulas available to simulate cycle time when tool stabilisation temperature is known. However the tool stabilisation is in turn dependent on cycle time. Hence MIT has published an algorithm (fig8, prior art) that enables computing tool stabilisation and cycle time reliably taking into computation their interdependence. Now suitable traditional numeric formulas to estimate cooling time and corresponding tool stabilization temperatures are applied to both the first thicknesses and the second thicknesses in bilaterally symmetrical analysis for a chosen split proportion of original thickness and defined ejection criterion. In case of error of tool stabilisation temperature the cycle time result is incremented in small increments till real solution is achieved.

Step8 Since we want to analyse both split proportions as pseudo analysis of main part under simulation, we must use same cycle time for the analysis to be meaningful. Higher of the cooling time for first thickness and the second thickness is associated to both the first thicknesses and the second thicknesses , and the revised tool stabilisation temperature and corresponding midplane temperature is determined.

Step9 Difference of midplane temperatures so determined from such analysis of two complimentary thicknesses is determined.

Step10 The split proportion is incrementally changed, accordingly revised figures of the first thickness and the second thickness are obtained and above process is repeated till such time that the midplane temperature difference is a very small number.

Step11 Tool stabilisation temperature, the part average temperature is computed for the first thickness and the second thickness and a symmetrical graph is generated for part temperature profile for the first thickness and the second thickness having axis of symmetry being line showing midplane temperature and end of temperature profile showing temperature on part surface.

Step12 Now we synthesize graph of temperature profile of part under simulation. To this end we generate simulated part temperature profile by combining one half the graph between midplane temperature and part surface temperature from the first thickness part temperature profile on one side and one half the graph between midplane temperature and part surface temperature from the second thickness part temperature profile from other side and connecting them such that the midplane temperatures, here we ignore small difference between the midplane temperature and replace them for example with average values of the two, and are superimposed and part surface temperature from the first thickness graph and that from the second thickness graph make two opposite ends of combined graph, this graph represents base solution.

In an alternative embodiment of the invention the moulding tool consists of more than one material, for example may contain H13 and high conductivity BeCu layers. Here we can use any applicable formulas to compute equivalent thermal conductivity, equivalent density and equivalent specific heat. Now this allows us to use any standard formulas in analysis as if it were a single homogenous material and used as input to material property in CORE or the CAVITY as the case may be.

The second layer in tool as discussed above may be Air and thickness of the air layer is equivalent to or proportionate to that of thickness shrinkage in polymer at end of cooling cycle and is computed based on melt temperature and thickness averaged eject temperature.

The second layer referred above may be moulding from first shot as is the case with sequential two shot moulding process or overmoulding process. That is also analyzed same way as an insulation layer on tool face, typically on core side of tool. In this case also we compute equivalent or effective tool properties combining with thermal properties of plastic layer and that of the tool steel.

The part average temperature for the first thickness and that for the second thickness according to previous discussion are used to predict bending of the moulding by applying suitable structural formulas. Typically the bimetal strip relies on differential shrinkage due to coefficient of thermal expansion between two strips which are bonded together. The same technique can be deployed here, slightly differently, to apply differential shrinkage caused by the two sides having different thickness averaged temperature.

Coolant temperature differential according to previous evaluation between the CORE side and the CAVITY side coolant is varied such that the part thickness averaged temperature differential between the CORE side and the CAVITY side of geometric midplane through part thickness is reduced representing optimized solution. It should be understood that a small differential in two sides having similar values of part thickness average temperature will shrink uniformly when part returns to room temperature and thus will exhibit less warpage and part will hold shape more accurate to designed geometry.

Once the temperature differential reaches within specified permissible toleranceas above, it may happen that the part average temperature is found to be below tolerance for specified ejection criterion, in other words has cooled more than our desired target value. This can lead to less shrinkage when part cools to room temperature after ejection from the tool. Hence we have to raise part eject average temperature maintaining the differential in limit already achieved above and hence both sides namely the CORE and the CAVITY, coolant temperatures are raised equally to such level that the part average temperature reaches within tolerance of the eject average temperature specification (not shown).

Method for simulating the injection moulding processaccording to invention described above is a computer program and preferably runs in automatic mode for most part of computation including but not limited to application of do loops and or goal seek methodology.

Furthermoremethod for simulating the injection moulding processis a computer program and provides for graphic user interface (GUI) enabling user interaction for defining input parameters as well as executing preset commands.

Furthermore methodfor simulating the injection moulding processis a computer program and provides output including but not limited to temperature profile through part thickness graph, tool temperature information, part temperature information and cycle time,includes information of skin thickness having temperature below specified temperature that is computed automatically by computing intersection between the part temperature profile and that of the specified skin temperature.

Output as referred to above is produced in the form of PDF document made up of preselected cell range of the program, for example only but not limited to select range/ ranges of an Microsoft excel or like file.

Furthermore the output includesthermal response to heating of tool for a specified time with specific fluid having specific temperature and pressure.

Brief Description of the Drawings

In order that the invention may be more fully understood there will now be described, by way of example only, preferred embodiments and other elements of the invention with reference to the accompanying drawings where:

Figure 1 Temperature profile of a part from a tool having bilaterally symmetrical thermal design.

Figure 2 Temperature profile of a part from a tool having bilaterally NON-symmetrical thermal design.

Figure 3 Temperature profile of a part having a second shot moulded on top of first shot in sequential two shot moulding.

Figure 4 Temperature profile of a part from a tool having bilaterally symmetrical thermal design having thermal design on both sides same as that of a CAVITY of a tool having bilaterally NON-symmetrical thermal design.

Figure 5 Temperature profile of a part from a tool having bilaterally symmetrical thermal design having thermal design on both sides same as that of a CORE of a tool having bilaterally NON-symmetrical thermal design.

Figure 6 Temperature profile of a part from a tool having bilaterally NON-symmetrical thermal design made up by combining parts of graph from figure 4 and figure 5.

Figure 8 Prior Art-Schematic of numeric calculation of cycle time, part average temperature and part midplane temperature.

Figure 9 Schematic of numeric calculation of cycle time, part average temperature and part midplane temperature of a component moulded out of a tool having bilaterally NON-symmetrical thermal design.

Figure 10 An output graph showing heating response in one side of tol, by way of example CAVITY.

Figure 11 We are shown temperature profile through part same as in figure 2 after optimization for reduced warpage.

Description of the Preferred Embodiment and Other Examples of the Invention

Referring to Figure 1, we are shown temperature profile through a part bounded between tool face at CORE (1) and tool face at CAVITY (2). As can be seen the temperature profile is symmetrical about plane having highest temperature (3) also coincides with geometric midplane and average temperatures bounded by plane having highest temperature and CORE tool face (4) and that between plane having highest temperature and CAVITY face(5) are same. This is expected temperature profile of a tool having bilaterally symmetrical thermal heat transfer, typical when it is assumed that there is no thermal resistance on interface of polymer and tool face and cooling geometry made up of cooling channel size, distance to tool face and placement is identical on both sides of tool - CAVITY and the CORE and temperature and flow arte of coolant is assumed identical.

Turning to Figure 2, we are shown temperature profile through a part bounded between tool face at CORE (1) and tool face at CAVITY (2). As can be seen the temperature profile is NON-symmetrical about plane having highest temperature (3) also the plane does not coincides with geometric midplane (6) and average temperatures bounded by plane having highest temperature and CORE tool face (4) and that between plane having highest temperature and CAVITY face(5) are not the same. This is expected temperature profile of a tool having bilaterally NON-symmetrical thermal heat transfer, typical when it is assumed that there is thermal resistance on interface of polymer and tool face, typical when air gap develops on shrinking of polymer and or cooling geometry made up of cooling channel size, distance to tool face and placement is not identical on both sides of tool - CAVITY and the CORE having different cooling line geometry and or temperature and flow rate of coolant may be assumed non-identical.

Figure3 We are shown temperature profile through a part made up of two materials sequencially moulded,

Figure 4 We are shown temperature profile of a part by way of example having thickness of 1.65 mm. and having symmetrical cooling geometry on both sides having 15 mm. distance between top of cooling channel and tool surface and 35 mm. centre distance between cooling channels having 7 mm. cooling channel width.

Figure 5 We are shown temperature profile of a part by way of example having thickness of 2.35 mm. and having symmetrical cooling geometry on both sides having 6 mm. distance between top of cooling channel and tool surface and 10 mm. centre distance between cooling channels having 7 mm. cooling channel width. It is important to note here that the graph represented here is that of a moulding process having same cooling time and all machine parameters and the polymer parameters identical to that used for the part described by way of figure 4 and also has same midplane temperature as for the part described by way of figure 4.

In Figure 6 , We are shown temperature profile of a part by way of example having thickness of 2.00 mm. and having NON-symmetrical cooling geometry on CAVITY sides having 6 mm. distance between top of cooling channel and tool surface and 10 mm. centre distance between cooling channels having 7 mm. cooling channel width and on CORE side having 15 mm. distance between top of cooling channel and tool surface and 35 mm. centre distance between cooling channels having 7 mm. cooling channel width. This part thickness is essentially half of combined thickness of part described with help of figure 4 and 5 and tool geometries described by way of example are essentially that from figure 4 and fig 5 applied to CAVITY and CORE respectively. It should be noted that the temperature profile is essentially made up of two parts, one on left of plane having highest temperature is made up of left side half of that described in Figure 4 and one on right of plane having highest temperature is made up of right side half of that described in Figure 4. It is important to note here that this synthesizing of graph is possible because the two mouldings as described by way of

graph

4 and 5 have identical polymer input, have identical cycle time breakdown and have identical midplane temperature. It should be noted that there will exist only one unique thickness of the part in figure 4 and that of figure 5 such that meets above described condition namely for identical cycle time breakdown and have identical midplane temperature such that when the two thicknesses are combined are double of that used in figure 6.

Figure 7 We are shown graphical representation of scheme of synthesizing the part temperature profile described in the figure 6.

Turning to Figure 8 We are shown an example of prior art published by the MIT(XiaorongXu, Emanual Sachs and Samuel Allen), showing a process flow to compute tool stabilisation temperature and corresponding cycle time and part average temperature and midplane temperatures, applicable to bilaterally symmetrical thermal design of tool.

In Figure 9 , process flow to compute tool stabilisation temperature and corresponding cycle time and part average temperature and midplane temperatures, applicable to bilaterally NON-symmetrical thermal design of tool. As will be clear following the flow diagram we start by inputting all material, tool and coolant data. We assume a split proportion to divide the actual part thickness under analysis in two parts such that the sum of two parts is same as that actual part thickness they were separated from. Now one part is used after doubling it with bilaterally symmetrical thermal design same as that of CORE and another part is used after doubling it with bilaterally symmetrical thermal design same as that of CAVITY. For example if air gap is to develop on CAVITY face in final design, it is used in bilaterally symmetrical mode in the design with CAVITY as if air gap exists on both faces of tool. The purpose of doubling it is such that when integrating graph of temperature profile from figure 4 and figure 5, two halves will be used and since two together were already doubled, we arrive at final thickness as required for final design in graph in figure 6. Now we solve these two systems of CORE and CAVITY for cooling time to reach required ejection temperature as specified by user. In case of error a small time increment is added to achieve a real value of cooling time that will produce eject temperature that is no more than specified by user. Now the midplane temperatures are calculated and difference computed. If the difference is more than specified maximum value which is typically a small number, the split values is changed and whole process repeated till the two midplane temperatures are same within small permissible tolerance as mentioned above. Now the final product moulding temperature profile can be predicted in a non-thermally symmetrical tool by combining above two graphs in half, one from left side and one from right side and will form respective side of final analysis as they were arrived at from CAVITY or CORE as shown in

graph

4,5,6 and 7.

It is understood the whole process described above will be programmed into a software algorithm such that it operates automatically and finds ideal value of split and generates final tool analysis without any more manual operation by the user and the code for such an implementation is not the purpose of this invention and as such not disclosed. It will be obvious that such an implementation or variation in algorithm by any code will be obvious to anyone competent in art of writing software code and as such that will be covered by essence of the invention.

Now turning to Figure 10 This invention also is applicable for predicting thermal response for a tool having bilaterally non symmetrical thermal design of RHCM (Rapid Heat Cycle Moulding) providing the benefits of a high quality surface and quick cycle times. Heating response of tool on each side of tool is computed (Figure 10) by using published formulas available in literature however this algorithm enables doing so when the tool has non-symmetrical thermal design, as is the case in just about every tool.

Finally in figure 11 It should be noted that any temperature differential between two halves of plane will lead to higher shrinkage in one plane relative to another and that will lead to bending of the whole part known as warpage-more specifically out of plane warpage and it will be beneficial to have this difference as small as practically and commercially feasible. As shown in figure 9, flow chart, last operation step is that of minimizing warpage. In figure 11 we are shown temperature profile of the same part as in figure 2 where it can be noted that the differential between the temperatures shown at

point

4 and 5 has been reduced substantially, by way of example only from 11 degrees C to 3 degrees C, through the process of optimization described above, by changing coolant temperature by way of example only from 30 degC, , on both sides of tool to 53 and 33 deg. C respectively for CAVITY and CORE. It may be noted that once the temperature differential reaches within specified permissible tolerance, the part average temperature if found to be below tolerance for specified ejection criterion, both side coolant temperatures are raised equally to such level that the part average temperature reaches within tolerance of the eject average temperature specification (not shown).

Whilst the above description includes the preferred embodiments of the invention, it is to be understood that many variations, alterations, modifications, combinations and/or additions may be introduced into the computational process flow previously described without departing from the essential features or the spirit or ambit of the invention.

It will be also understood that where we refer to injection moulding are used in this specification variations such as die casting, glass moulding, rubber curing are included and form part of the invention.

It will be also understood that where the word 'comprise', and variations such as 'comprises' and 'comprising', are used in this specification, unless the context requires otherwise such use is intended to imply the inclusion of a stated feature or features but is not to be taken as excluding the presence of other feature or features.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that such prior art forms part of the common general knowledge.

Claims

CLAIM1 A method for simulating the injection moulding process consisting of but not limited to cycle time to ejection of the moulded article from tool and corresponding tool stabilisation temperature and the part thickness average temperature and the part midplane temperatures by application of published numeric formulas and methods that assume bilaterally symmetrical thermal balance between CORE and CAVITY of an injection moulding tool applied to numeric tasks in analyzing injection moulding process in tools wherein the CORE and CAVITY may not be having bilaterally symmetrical thermal conditions, the said method comprising the following steps however not limited to:

Step1 dividing the part thickness in two fractions wherein by assuming a suitable starting figure of split proportion, arriving at the first thickness by multiplying component thickness with split proportion and doubling it and determining a complimentary thickness, the second thickness , by subtracting first thickness from doubled component thickness.

Step2 All properties related to CORE of tool under analysis is specified, by way of example only, cooling geometry consisting of, but not limited to, cooling channel cross section height, width, fillet radius, distance to tool surface and distance between the two adjacent cooling channels, cooling channel friction factor and the tool material properties consisting of but not limited to density, thermal conductivity and specific heat of tool material are associated to the first thickness and the same related to CAVITY of tool under analysis are associated to the second thickness .

Step3 specifying coolant properties consisting of but not limited to Density, Specific heat, flow rate and temperature of coolant flowing through CORE is associated to the first thickness and coolant properties consisting of but not limited to Density, Specific heat, flow rate and temperature of coolant flowing through CAVITY is associated to the second thickness .

Step4 Cycle time components made up of Tool closing, Material injection, Machine Opening and Dwell are associated equally to the first thickness and the second thickness .

Step5 Polymer thermal and mechanical properties and melt temperature at time of injection are associated equally to both the first thickness and the second thickness.

Step6 Part eject criterion is defined in the form of midplane temperature at ejection or part thickness average temperature at ejection.

Step7 Now suitable traditional numeric formulas to estimate cooling time and corresponding tool stabilization temperatures are applied to both the first thicknesses and the second thicknesses in bilaterally symmetrical analysis so computed for a chosen split proportion and defined ejection criterion. In case of error of tool stabilisation temperature the cycle time result is incremented in small increments till real solution is achieved.

Step8 Higher of the cooling time for first thickness and the second thickness is associated to both the first thicknesses and the second thicknesses , and the revised tool stabilisation temperature and corresponding midplane temperature is determined.

Step9 Difference of midplane temperatures so determined from such analysis of two complimentary thicknesses is determined.

Step10 The split % is incrementally changed, accordingly revised figures of the first thickness and the second thickness are obtained and above process is repeated till such time that the midplane temperature difference is a very small number.

Step11 Tool stabilisation temperature, the part average temperature is computed for the first thickness and the second thickness and a symmetrical graph is generated for part temperature profile for the first thickness and the second thickness having axis of symmetry being line showing midplane temperature and end of temperature profile showing temperature on part surface.

Step12 Simulated part temperature profile is generated by combining one half the graph between midplane temperature and part surface temperature from the first thickness part temperature profile on one side and one half the graph between midplane temperature and part surface temperature from the second thickness part temperature profile from other side and connecting them such that the midplane temperatures, ignoring small difference, are superimposed and part surface temperature from the first thickness graph and that from the second thickness graph make two opposite ends of combined graph, this graph represents base solution.
In an alternative embodiment of the invention claimed at 1 the moulding tool consists of more than one material layers and equivalent thermal conductivity, equivalent density and equivalent specific heat are computed as if it were a single homogenous material and used as input to material property in CORE or the CAVITY as the case may be.
The second layer in tool according to claim2 is Air and thickness of the air layer is equivalent to or proportionate to that of thickness shrinkage in polymer at end of cooling cycle and is computed based on melt temperature and thickness averaged eject temperature.
The second layer in tool according to claim2 is moulding from first shot as is the case with sequential two shot moulding process or overmoulding process.
The part average temperature for the first thickness and that for the second thickness according to claim1 are used to predict bending of the moulding by applying suitable structural formulas.
Coolant temperature differential according to claim5 between the CORE side and the CAVITY side coolant is varied such that the part thickness averaged temperature differential between the CORE side and the CAVITY side of geometric midplane through part thickness is reduced representing optimized solution.
Once the temperature differential reaches within specified permissible toleranceaccording to claim 6,if the part average temperature if found to be below tolerance for specified ejection criterion, both sides namely the CORE and the CAVITY, coolant temperatures are raised equally to such level that the part average temperature reaches within tolerance of the eject average temperature specification (not shown).
Method for simulating the injection moulding processaccording to claim1 is a computer program and preferably runs in automatic mode for most part of computation including but not limited to application of do loops and or goal seek methodology.
Method for simulating the injection moulding processaccording to claim1 is a computer program and provides for graphic user interface enabling user interaction for defining input parameters as well as executing preset commands.
Method for simulating the injection moulding processaccording to claim1 is a computer program and provides output including but not limited to temperature profile through part thickness graph, tool temperature information, part temperature information and cycle time,includes information of skin thickness having temperature below specified temperature that is computed automatically by computing intersection between the part temperature profile and that of the specified skin temperature.
Output according to claim10 wherein the output is produced in the form of PDF document made up of preselected cell range of the program, for example only but not limited to atleast one select range of an Microsoft excel or like file.
Output according to claim11 wherein the output includes thermal response to heating of tool for a specified time with specific fluid having specific temperature and pressure.