Autodesk Whitepaper
Autodesk® Simulation Moldflow® Insight 2013
Cartridge Heater Implementation The release of Autodesk Simulation Moldflow Insight 2013 enhances the 3D transient cool solver by increasing its functionality and versatility. With this release the solver, known as Cool (FEM), will support various rapid mold heating and cooling processes whereby the heating is achieved through steam heating, pressurized water or electric cartridge heaters. The aim of a rapid mold heating and cooling process is to produce a glossy surface finish on the part which is free of weld lines without a drastic increase in cycle time. This is achieved by heating the mold up to a high temperature during the filling phase and then once injection has completed, the mold is cooled suddenly to the ejection temperature for part ejection. In this document, the use of cartridge heaters for heating the mold is discussed together with its implementation in Autodesk Simulation Moldflow Insight 2013.
CARTRIDGE HEATER IMPLEMENTATION
Contents Introduction ................................................................................................................. 3 Simulation ................................................................................................................... 4 Time option ............................................................................................................. 4 Thermocouple option ............................................................................................... 5 Cartridge heater with target temperature option ........................................................ 6 Extend mold-open time option. ............................................................................. 6 Extend mold close time before injection option...................................................... 6 Do not delay injection option ................................................................................ 6 Discussion................................................................................................................... 7 Conclusion .................................................................................................................. 9
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Introduction To manufacture high quality parts efficiently at a low cost, many injection mold designers are using heater cartridges to ensure a hot uniform cavity temperature during the filling phase. The hotter the cavity temperature, the lower the required injection pressure during filling and fewer gates are required. Fewer gates result in less weld lines which results in a part with a better surface finish that is also structurally stronger. Heater cartridges offer numerous benefits to the injection mold designer:
The hot surface temperature during filling results in a much glossier surface finish which may result in the part not requiring any post molding surface finish treatment. Hotter coolant temperatures could be used to achieve the same benefits from a hot mold. However, hotter mold temperatures also increase the cooling time required. The resulting increase in overall cycle time is not beneficial. Heater cartridges enable the heat control of specific areas of the mold during the injection molding cycle. Many high precision, high temperature or cutting edge technologies need to operate in a clean room environment. Cartridge heaters are a preferred means of maintaining a stable mold temperature in these situations. Traditional hot oil heating of the mold has the potential to contaminate the product. Cartridge heaters are readily available. They are very small components that can be inserted into the injection mold in strategic regions (Figure 1). Cartridge heaters come with a specific heater rating, can be switched on or off during the injection molding cycle, and controlled by either time or temperature. When controlled by time, the cartridge heater can turn on or off at specified times in the cycle. When operating on temperature control, the cartridge heater will turn on or off based on the temperature of a thermocouple in the mold. Both operations can be supported simultaneously. The ability to pin-point and control the heating of the mold means that cartridge heaters are a very useful tool for mold designers to supplement traditional rapid mold heating and cooling processes.
Figure 1: Diagram showing the placement of cartridge heaters in the mold
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Simulation Cartridge heaters with dynamic cycle control are now supported in Autodesk Simulation Moldflow Insight 2013. Both time control and temperature control are supported in various configurations. There are 5 options used in simulating the cartridge heaters in Moldflow Insight: 1. 2. 3. 4. 5.
Constant flux Temperature Time Thermocouple Time with target temperature
Constant flux and Temperature apply a constant value to the mold for the entire injection molding cycle. These are the only two options available for the boundary element cool solver. Time, Thermocouple and Time with target temperature use a constant heat flux while the heater is on. Cartridge heaters are rated in terms of the heat flux they deliver.
Time option When using Time, the cartridge heater will switch on or off at the designated time. Figure 2 shows the dialog used to set the off/on time, the value 0.0 corresponds to the start of injection. The example in Figure 2 will turn off the cartridge heater 1 second after the commencement of the filling phase. Commonly this is set to correspond to the end of filling or the commencement of packing to allow the mold to cool once the part is filled. The cartridge heater will turn on again after 15 seconds. Commonly this is set to correspond with the end of cooling at part ejection, hence the heater turns on to heat the mold in anticipation of the filling phase of the next cycle. During the period from 1 second to 15 seconds the cartridge heater is turned off, and for all other times during the cycle it is operating at a heat flux of 5000 W/m2.
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Figure 2: Cartridge heater time input specification
Thermocouple option The Thermocouple option simulates the maintenance of a mold region within a specified temperature range. Figure 3 shows the dialog used for the temperature control option. A thermocouple position is specified in the mold and the temperature of this thermocouple will dictate when the heater element turns itself on or off. The “Minimum off time” and “Minimum on time” allow the user to specify how long the heater will remain in the “on” condition or in the “off” condition after it has switched. In practice, these settings are used on thermocouple controllers to prevent the heater from constantly turning “on” and “off” when the temperature hovers around the switch on or switch off temperature. For simulation, there is also the option to specify where the thermocouple is placed. When “At heater” is selected, the average temperature of the nodes surrounding the heater are calculated and used to control the on/off condition of the heater. When “At node” is set the user must specify a node anywhere in the mold corresponding to the thermocouple location. If a part node is specified the solver will stop with an error message.
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Figure 3: Cartridge temperature control simulation option
Cartridge heater with target temperature option With this option the user specifies the time during which the heater is under temperature control. These times are fixed in the cycle relative to the start of injection. Outside these times the heater is off. The user must specify a thermocouple node and a target temperature on that node to define the temperature control. The cycle time may be controlled by this target temperature on the thermocouple node. With the “Cycle control” parameters the user has three options. Extend mold-open time option. The mold-open time is extended until the thermocouple node reaches its target temperature. While the mold is open, convective heat transfer to air occurs on the exposed mold parting plane. Extend mold close time before injection option The mold will open for ejection then close and wait in the mold closed position until the target temperature is reached on the thermocouple node. Do not delay injection option The thermocouple temperature does not delay the start of the next cycle, but may cause injection to occur while the mold is still colder than desired. Selecting any option other than Do not delay injection may alter the cycle time significantly.
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Figure 4: Catridge heater with target temperature specified
Discussion To demonstrate the influence of cartridge heaters, a simple model of a cover is initially simulated without any cartridge heaters (Figure 5). The mold for the part has a traditional circuit design.
Figure 5: Model of a cover with traditional circuit design An analysis is performed on this configuration and the temperature difference across the part is shown in figure 6. The transient temperatures on opposing nodes are shown for node 68382 located on the core and node 62518 located on the cavity. At the start of the cycle the temperature difference across the part is approximately 8 C with the core being
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hotter that the cavity. At the end of the cycle the core is approximately 4.5 C hotter than the cavity.
Figure 6: Temperature difference across the cover with traditional circuit design To demonstrate the effect the cartridge heaters will have on this design, two heater cartridges are inserted into the cavity side of the mold (figure 7). In this demonstration the cartridge heater is controlled by the time option with a constant flux of 50 kW/m 2 flux applied while the heater is on. The switch off time is at 2 seconds and the switch on time is at 15 seconds to ensure that the cartridge heater is heating the cavity before and during the filling phase. The cartridge heaters are off during the packing phase.
Figure 7: Model of a cover with cartridge heaters modeled in the cavity side of the mold After running the simulation with the cartridge heaters, the temperature difference across the part is examined again. Figure 8 shows the temperature evolution on the same two nodes shown previous in Figure 6. With cartridge heaters included in the mold, the temperatures of the two nodes are closer over the duration of the cycle.
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Figure 8: Temperature difference across the cover using cartridge heaters By increasing the time the cartridge heater is turned on by 3 seconds at the end of injection, the cavity side of the mold becomes hotter than the core side of the mold for the period between 1.6 and 8.5 seconds (figure 9). This result is as expected and shows how sensitive the temperature of the mold can be to the cartridge heater settings.
Figure 9: Temperature difference across the cover using an extended cartridge heating time
Conclusion Cartridge heaters are a very useful way of heating plastic injection molds during operation as they offer a localized method to influence the melt temperature. Their control via a timer or thermocouple node in the mold allows for application within processes such as
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CARTRIDGE HEATER IMPLEMENTATION
rapid mold heating and cooling to manipulate the melt temperatures particularly during the filling phase. As demonstrated here, the temperatures of the mold and hence the melt can be very sensitive to the settings of the cartridge heaters. Therefore the addition of this new functionality greatly increases the transient cool solver’s flexibility to simulate real world behavior.
Autodesk and Moldflow are registered trademarks or trademarks of Autodesk, Inc., and/or its subsidiaries and/or affiliates in the USA and/or other countries. All other brand names, product names, or trademarks belong to their respective holders. Autodesk reserves the right to alter product and services offerings, and specifications and pricing at any time without notice, and is not responsible for typographical or graphical errors that may appear in this document. © 2013 Autodesk, Inc. All rights reserved.
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Cartridge Heater Implementation The release of Autodesk Simulation Moldflow Insight 2013 enhances the 3D transient cool solver by increasing its functionality and versatility. With this release the solver, known as Cool (FEM), will support various rapid mold heating and cooling processes whereby the heating is achieved through steam heating, pressurized water or electric cartridge heaters. The aim of a rapid mold heating and cooling process is to produce a glossy surface finish on the part which is free of weld lines without a drastic increase in cycle time. This is achieved by heating the mold up to a high temperature during the filling phase and then once injection has completed, the mold is cooled suddenly to the ejection temperature for part ejection. In this document, the use of cartridge heaters for heating the mold is discussed together with its implementation in Autodesk Simulation Moldflow Insight 2013.
CARTRIDGE HEATER IMPLEMENTATION
Contents Introduction ................................................................................................................. 3 Simulation ................................................................................................................... 4 Time option ............................................................................................................. 4 Thermocouple option ............................................................................................... 5 Cartridge heater with target temperature option ........................................................ 6 Extend mold-open time option. ............................................................................. 6 Extend mold close time before injection option...................................................... 6 Do not delay injection option ................................................................................ 6 Discussion................................................................................................................... 7 Conclusion .................................................................................................................. 9
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CARTRIDGE HEATER IMPLEMENTATION
Introduction To manufacture high quality parts efficiently at a low cost, many injection mold designers are using heater cartridges to ensure a hot uniform cavity temperature during the filling phase. The hotter the cavity temperature, the lower the required injection pressure during filling and fewer gates are required. Fewer gates result in less weld lines which results in a part with a better surface finish that is also structurally stronger. Heater cartridges offer numerous benefits to the injection mold designer:
The hot surface temperature during filling results in a much glossier surface finish which may result in the part not requiring any post molding surface finish treatment. Hotter coolant temperatures could be used to achieve the same benefits from a hot mold. However, hotter mold temperatures also increase the cooling time required. The resulting increase in overall cycle time is not beneficial. Heater cartridges enable the heat control of specific areas of the mold during the injection molding cycle. Many high precision, high temperature or cutting edge technologies need to operate in a clean room environment. Cartridge heaters are a preferred means of maintaining a stable mold temperature in these situations. Traditional hot oil heating of the mold has the potential to contaminate the product. Cartridge heaters are readily available. They are very small components that can be inserted into the injection mold in strategic regions (Figure 1). Cartridge heaters come with a specific heater rating, can be switched on or off during the injection molding cycle, and controlled by either time or temperature. When controlled by time, the cartridge heater can turn on or off at specified times in the cycle. When operating on temperature control, the cartridge heater will turn on or off based on the temperature of a thermocouple in the mold. Both operations can be supported simultaneously. The ability to pin-point and control the heating of the mold means that cartridge heaters are a very useful tool for mold designers to supplement traditional rapid mold heating and cooling processes.
Figure 1: Diagram showing the placement of cartridge heaters in the mold
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CARTRIDGE HEATER IMPLEMENTATION
Simulation Cartridge heaters with dynamic cycle control are now supported in Autodesk Simulation Moldflow Insight 2013. Both time control and temperature control are supported in various configurations. There are 5 options used in simulating the cartridge heaters in Moldflow Insight: 1. 2. 3. 4. 5.
Constant flux Temperature Time Thermocouple Time with target temperature
Constant flux and Temperature apply a constant value to the mold for the entire injection molding cycle. These are the only two options available for the boundary element cool solver. Time, Thermocouple and Time with target temperature use a constant heat flux while the heater is on. Cartridge heaters are rated in terms of the heat flux they deliver.
Time option When using Time, the cartridge heater will switch on or off at the designated time. Figure 2 shows the dialog used to set the off/on time, the value 0.0 corresponds to the start of injection. The example in Figure 2 will turn off the cartridge heater 1 second after the commencement of the filling phase. Commonly this is set to correspond to the end of filling or the commencement of packing to allow the mold to cool once the part is filled. The cartridge heater will turn on again after 15 seconds. Commonly this is set to correspond with the end of cooling at part ejection, hence the heater turns on to heat the mold in anticipation of the filling phase of the next cycle. During the period from 1 second to 15 seconds the cartridge heater is turned off, and for all other times during the cycle it is operating at a heat flux of 5000 W/m2.
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Figure 2: Cartridge heater time input specification
Thermocouple option The Thermocouple option simulates the maintenance of a mold region within a specified temperature range. Figure 3 shows the dialog used for the temperature control option. A thermocouple position is specified in the mold and the temperature of this thermocouple will dictate when the heater element turns itself on or off. The “Minimum off time” and “Minimum on time” allow the user to specify how long the heater will remain in the “on” condition or in the “off” condition after it has switched. In practice, these settings are used on thermocouple controllers to prevent the heater from constantly turning “on” and “off” when the temperature hovers around the switch on or switch off temperature. For simulation, there is also the option to specify where the thermocouple is placed. When “At heater” is selected, the average temperature of the nodes surrounding the heater are calculated and used to control the on/off condition of the heater. When “At node” is set the user must specify a node anywhere in the mold corresponding to the thermocouple location. If a part node is specified the solver will stop with an error message.
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Figure 3: Cartridge temperature control simulation option
Cartridge heater with target temperature option With this option the user specifies the time during which the heater is under temperature control. These times are fixed in the cycle relative to the start of injection. Outside these times the heater is off. The user must specify a thermocouple node and a target temperature on that node to define the temperature control. The cycle time may be controlled by this target temperature on the thermocouple node. With the “Cycle control” parameters the user has three options. Extend mold-open time option. The mold-open time is extended until the thermocouple node reaches its target temperature. While the mold is open, convective heat transfer to air occurs on the exposed mold parting plane. Extend mold close time before injection option The mold will open for ejection then close and wait in the mold closed position until the target temperature is reached on the thermocouple node. Do not delay injection option The thermocouple temperature does not delay the start of the next cycle, but may cause injection to occur while the mold is still colder than desired. Selecting any option other than Do not delay injection may alter the cycle time significantly.
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Figure 4: Catridge heater with target temperature specified
Discussion To demonstrate the influence of cartridge heaters, a simple model of a cover is initially simulated without any cartridge heaters (Figure 5). The mold for the part has a traditional circuit design.
Figure 5: Model of a cover with traditional circuit design An analysis is performed on this configuration and the temperature difference across the part is shown in figure 6. The transient temperatures on opposing nodes are shown for node 68382 located on the core and node 62518 located on the cavity. At the start of the cycle the temperature difference across the part is approximately 8 C with the core being
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hotter that the cavity. At the end of the cycle the core is approximately 4.5 C hotter than the cavity.
Figure 6: Temperature difference across the cover with traditional circuit design To demonstrate the effect the cartridge heaters will have on this design, two heater cartridges are inserted into the cavity side of the mold (figure 7). In this demonstration the cartridge heater is controlled by the time option with a constant flux of 50 kW/m 2 flux applied while the heater is on. The switch off time is at 2 seconds and the switch on time is at 15 seconds to ensure that the cartridge heater is heating the cavity before and during the filling phase. The cartridge heaters are off during the packing phase.
Figure 7: Model of a cover with cartridge heaters modeled in the cavity side of the mold After running the simulation with the cartridge heaters, the temperature difference across the part is examined again. Figure 8 shows the temperature evolution on the same two nodes shown previous in Figure 6. With cartridge heaters included in the mold, the temperatures of the two nodes are closer over the duration of the cycle.
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Figure 8: Temperature difference across the cover using cartridge heaters By increasing the time the cartridge heater is turned on by 3 seconds at the end of injection, the cavity side of the mold becomes hotter than the core side of the mold for the period between 1.6 and 8.5 seconds (figure 9). This result is as expected and shows how sensitive the temperature of the mold can be to the cartridge heater settings.
Figure 9: Temperature difference across the cover using an extended cartridge heating time
Conclusion Cartridge heaters are a very useful way of heating plastic injection molds during operation as they offer a localized method to influence the melt temperature. Their control via a timer or thermocouple node in the mold allows for application within processes such as
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CARTRIDGE HEATER IMPLEMENTATION
rapid mold heating and cooling to manipulate the melt temperatures particularly during the filling phase. As demonstrated here, the temperatures of the mold and hence the melt can be very sensitive to the settings of the cartridge heaters. Therefore the addition of this new functionality greatly increases the transient cool solver’s flexibility to simulate real world behavior.
Autodesk and Moldflow are registered trademarks or trademarks of Autodesk, Inc., and/or its subsidiaries and/or affiliates in the USA and/or other countries. All other brand names, product names, or trademarks belong to their respective holders. Autodesk reserves the right to alter product and services offerings, and specifications and pricing at any time without notice, and is not responsible for typographical or graphical errors that may appear in this document. © 2013 Autodesk, Inc. All rights reserved.
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