Sensor Position
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Three typical positioning methods are used when measuring mold cavity pressure. The method chosen depends on the geometry and application of the part.
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Sensor in first third of flow path
For parts with non-critical flow lengths and wall thicknesses a sensor is positioned in the first third of the flow path. This location allows good process evaluation, because a useful pressure signal is available throughout the entire injection, compression and holding pressure phase. This provides comprehensive information about the variation in mold cavity pressure.
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Sensor at end of flow path
This method is recommended for thin-walled parts such as connectors and parts with critical long flow paths. These parts are usually injected at high speed with a short holding pressure phase. Slightly changed injection conditions lead to underfilling or dimensional errors at the end of the flow path. The sensor is therefore positioned towards the end of flow. This allows the mold cavity pressure to be used to monitor for short shots or part dimensions. It can also be used to check the quality of a weldline near the end of flow.
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One sensor near gate and one near end of flow
Parts with a large flow path to wall thickness ratio, such as car bumpers, distort as a result of internal stress. The pressure drop in the cavity is therefore measured with two sensors. The first is positioned in the near the gate and the second towards the end of flow. These pressure measurement can also be used to monitor overpacking in the gate area.
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Fill simulation
A simulation can be used to determine a suitable position for the sensor. It shows the progression of the melt front and indicates fill problems, such as short shot.
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