Pressure sensor in scientific injection molding is core component to achieve precise timing control (especially V/P switching point), its working principle and application directly affect quality of products. Following is an explanation from three aspects: working principle, quality impact, and supplier analysis:

 

In the field of injection molding, piezoresistive, piezoelectric and ceramic capacitive pressure sensors are mainly used:
1. Piezoresistive sensor
- Principle: Based on piezoresistive effect of semiconductor materials (stress causes resistance change), resistance change is converted into a voltage signal through a Wheatstone bridge. Silicon material is usually used, with high temperature stability, and a built-in temperature compensation circuit is required.
- Applicable scenarios: pressure monitoring in mold cavity, pressure holding control.
2. Piezoelectric sensor
- Principle: Using characteristics of piezoelectric materials (such as quartz and piezoelectric ceramics) to generate charge when subjected to force, output charge is proportional to pressure. However, charge is easy to leak, and it is only suitable for dynamic pressure measurement (such as high-speed pressure changes in filling stage).
- Applicable scenarios: Instantaneous pressure monitoring during high-speed injection.
3. Ceramic capacitive sensor
- Principle: Using ceramic diaphragm as electrode, pressure causes deformation and capacitance change. High temperature resistance and strong corrosion resistance, suitable for direct measurement of melt pressure.
- Applicable scenarios: Pressure monitoring of high-temperature melt (such as plastic melt).

Pressure sensor directly optimizes following quality indicators by accurately controlling V/P switching point (critical point from injection stage to pressure holding stage) and real-time pressure feedback:
1. Reduce internal stress and warpage
- Internal stress is mainly caused by uneven filling and cooling shrinkage differences. Pressure sensor monitors cavity pressure in real time to ensure that cavity filling rate is ≥95% when V/P is switched, avoiding premature switching (underfilling) or late switching (overpressure), thereby reducing orientation stress and temperature stress.
2. Control shrinkage and dimensional stability
- Insufficient pressure during holding stage will increase shrinkage of product (dents, undersized), and excessive pressure will increase internal stress. Sensor controls holding pressure through a closed loop to reduce shrinkage fluctuation range to ±0.3%.
3. Prevent defects
- Insufficient injection: Alarm is triggered when pressure at the end of cavity is zero.
- Weld marks/bubbles: Optimize flow front speed through multi-level pressure control.
4. Improve process reproducibility
- Pressure data, as a "process fingerprint", can reproduce same process on different injection molding machines, reducing number of mold trials by more than 30%.

Following are mainstream pressure sensor suppliers in injection molding field and their technical features:

- V/P switching optimization: Pressure sensor provides real-time pressure data of cavity, which is the only reliable basis for accurately switching V/P point, avoiding errors set by experience.
- Closed-loop quality control: Through pressure-time curve analysis, it can be directly linked to quality indicators such as internal stress and shrinkage, and realize adaptive adjustment of process parameters.
- Domestic substitution trend: Amperon and other companies have made breakthroughs in ceramic capacitor technology and gradually replaced imports (such as Sensata) in direction of high temperature resistance and integration.