Smart sensors used in plastic injection molding
- Posted On: February 6, 2025
- Posted By: admin
Smart sensors play an important role in plastic injection molding and enables real time monitoring of temperature, humidity, flow rates, errors and defects alongwith improving production efficiency and ensuring quality of molded parts
Pressure sensors
- Cavity Pressure Sensors – It measures the mold cavity’s internal pressure and help to optimise the material flow and preventing defects like improper shots or flash.
Start
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├──> Plastic Granules Heated & Injected into Mold
│
├──> Cavity Pressure Sensors Measure Pressure Inside Mold
│
├──> Sensor Sends Data to Machine Control System
│
├──> Control System Analyzes Pressure Readings
│
│ ├──> Normal Pressure? → Continue Process
│ │
│ ├──> Abnormal Pressure? → Adjust Parameters
│
├──> Cooling Phase (Monitored by Pressure Sensors)
│
├──> Part Ejection After Optimal Pressure Drop
│
└──> End
- Hydraulic Pressure Sensors – Regulates pressure inside the injection system. It helps balance the injection pressure and clamping pressure.
[Start]
↓
[Hydraulic Pump Activates]
↓
[Pressure Sensor Measures Hydraulic Pressure]
↓
[Sensor Sends Data to PLC]
↓
[PLC Analyzes and Adjusts Pressure]
↓
[Hydraulic System Controls Injection Force]
↓
[Plastic Injection into Mold]
↓
[Quality Monitoring & Adjustments]
↓
[End]
2. Temperature Sensors
- Thermocouples- They detect fluctuation of temperature inside the mold/melt flow to prevent overheating and ensure consistency in material properties.
- IR Sensors- They measure the surface temperature of the molds
- Melt temperature sensors- They monitor the plastic melt temperature for improved control of process
Start
│
├──> Plastic Granules Heated in Barrel
│
├──> Temperature Sensor Monitors Melt Temperature
│
│ ├──> Is Temperature Within Set Range?
│ │ ├──> Yes → Continue Injection
│ │ ├──> No → Adjust Heater Settings
│
├──> Molten Plastic Injected into Mold
│
├──> Mold Temperature Sensors Monitor Mold Surface & Cavity
│
│ ├──> Is Mold Temperature Optimal?
│ │ ├──> Yes → Maintain Cooling Rate
│ │ ├──> No → Adjust Cooling System
│
├──> Cooling & Solidification Process
│
├──> Temperature Sensors Ensure Proper Cooling Before Ejection
│
└──> Part Ejected & Process Repeats
3. Flow sensors
Cooling water flow sensors- These sensors monitor flow rate of the coolant alongwith temperature to ensure uniform cooling of mold.
Resin flow sensors– These sensors monitor the characteristics of plastic flow inside the mold for better filling and optimization of cycle time.
Start
│
├──> Cooling System Activated
│
├──> Flow Sensor Monitors Cooling Fluid Flow Rate
│
│ ├──> Is Flow Rate Within Set Range?
│ │ ├──> Yes → Maintain Cooling Process
│ │ ├──> No → Adjust Flow or Detect Blockage
│
├──> Proper Cooling Ensured
│
├──> Temperature Sensors Verify Cooling Effectiveness
│
├──> Part Solidifies & Prepares for Ejection
│
└──> End / Process Repeats
4. Humidity and Moisture sensors
Material moisture sensors- It measures moisture levels in raw plastic materials and prevents hydrolysis related defects.
Environmental humidity sensors- It detects humidity levels to maintain optimal drying and storage conditions.
Start
│
├──> Raw Plastic Material Fed into Hopper
│
├──> Moisture Sensor Checks Material Moisture Content
│
│ ├──> Is Moisture Within Acceptable Limit?
│ │ ├──> Yes → Continue Processing
│ │ ├──> No → Activate Material Dryer
│
├──> Dried Material Ready for Injection Molding
│
├──> Injection & Molding Process Continues
│
└──> End
Start
│
├──> Environmental Humidity Sensor Monitors Air Conditions
│
│ ├──> Is Humidity Within Safe Range?
│ │ ├──> Yes → Maintain Normal Operations
│ │ ├──> No → Adjust Dehumidifier / Air Conditioning
│
├──> Stable Humidity Ensured in Molding Area
│
├──> Prevents Material Moisture Absorption & Defects
│
└──> End
5. Vibration /Acoustic sensors
These sensors identify wear and tear, machine defects, temperature and pressure anamoly and defect in parts being produced by detecting injection molding machine vibrations
Start
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V
Is the injection molding machine powered on? ——————–> No —–> Power On the machine
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Yes
|
V
Is the sensor (vibration/acoustic) installed and calibrated? —> No —> Install & calibrate sensor
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Yes
|
V
Sensors detect vibration/acoustic signals during molding cycle
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V
Is the signal normal or within expected range? —————> No —> Identify the cause (e.g., mold misalignment, part defects)
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Yes
|
V
Signal conversion (physical signals to electrical signals)
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V
Signal filtering (noise reduction, frequency analysis)
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V
Signal amplification
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V
Signal processing (FFT, pattern recognition, anomaly detection)
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V
Is the signal indicative of an issue? (e.g., abnormal vibrations or acoustic patterns)
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Yes
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V
Trigger Alarm/Alert or Stop Process (automatic corrective action)
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V
Is further data analysis required for the issue? ———–> No —–> Resume molding process
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Yes
|
V
Send data to system/monitor for analysis (e.g., machine status, molding conditions)
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V
Adjust molding parameters (if necessary, based on analysis)
|
V
Monitor signals continuously for consistency and quality
|
V
End
1️⃣ Melt Preparation Stage
🔲 Process Box: Start monitoring barrel and mold temperatures using temperature sensors (thermocouples).
⬇️
📥 Input Box: Collect data on ambient humidity using humidity sensors (to prevent moisture-related defects).
⬇️
🔲 Process Box: Adjust drying time and temperature based on humidity readings to ensure optimal melt quality.
⬇️
🔺 Decision Box: Has the target barrel temperature been reached?
- Yes → Proceed to Injection Phase
- No → Continue heating and moisture monitoring
2️⃣ Injection Phase
🔲 Process Box: Monitor the injection screw’s position using linear position sensors and injection pressure with pressure sensors.
⬇️
📥 Input Box: Analyze screw speed and injection pressure data.
⬇️
🔲 Process Box: Regulate injection speed and volume to maintain melt flow consistency.
⬇️
🔺 Decision Box: Is the pressure within acceptable range?
- Yes → Proceed to Packing Phase
- No → Adjust pressure settings
3️⃣ Packing Phase
🔲 Process Box: Maintain consistent cavity pressure using pressure sensors to ensure proper packing of the part.
⬇️
🔺 Decision Box: Has the packing pressure stabilized?
- Yes → Proceed to Cooling Phase
- No → Increase packing pressure and rechecking
4️⃣ Cooling Phase
🔲 Process Box: Monitor cooling water flow using flow sensors and mold temperature using thermocouples.
⬇️
📥 Input Box: Verify cooling time and flow rate.
⬇️
🔲 Process Box: Analyze mold vibrations using vibration sensors to detect early signs of mechanical issues (e.g., misalignment or wear).
⬇️
🔺 Decision Box: Is mold temperature stable and vibration within limits?
- Yes → Proceed to Mold Opening & Part Ejection
- No → Adjust cooling and inspect mold alignment
5️⃣ Mold Opening & Part Ejection
🔲 Process Box: Detect mold opening and part ejection position using proximity sensors.
⬇️
📥 Input Box: Use ultrasonic sensors to confirm the presence of parts in the mold cavity before closing.
⬇️
🔺 Decision Box: Is the part successfully ejected?
- Yes → Proceed to Quality Inspection
- No → Recheck ejector pins and retry
6️⃣ Quality Inspection & Defect Detection
🔲 Process Box: Inspect the part for defects using optical sensors for visual quality control and gas sensors to detect trapped gases or volatiles in the part.
⬇️
🔺 Decision Box: Is the part defect-free?
- Yes → End process and prepare for the next cycle
- No → Flag the part for manual inspection and corrective action
Additional Sensors and Their Roles:
- Humidity Sensors: Monitors moisture content to avoid defects of splay and voids.
- Vibration Sensors: Monitors vibrations in the machine to prevent damage/misalignment.
- Ultrasonic Sensors: Ensure proper ejection of parts and confirms removal of remnants in the mold cavity so that the mold doesnt get destroyed or non-functional for use the next time
- Gas Sensors: Removes surface blemishes and other internal defects caused by bubbling by identifying volatiles which are trapped.
Compelling Statistics
- Prevalence of Injection Molding: Approximately one-third of global plastic production is processed through injection molding, underscoring the importance of efficient process monitoring.
- Pressure Monitoring Precision: Modern pressure sensors in injection molding can measure ranges up to 2,500 bar, enabling precise control during high-pressure processes.
- Fault Detection Efficiency: Advanced statistical quality monitoring methods utilizing machine-integrated sensors have achieved a fault detection success rate of 91.48% at a 99% confidence level.
- Industry Adoption: The integration of in-mold sensors is a critical component of Industry 4.0, facilitating enhanced process transparency and control in injection molding.
- Multi-Cavity Mold Optimization: Research indicates that in-mold pressure sensors are effective for optimizing clamping force, switchover points, and holding times in multi-cavity molds, leading to improved process efficiency.
- Real-Time Data Acquisition: Connected sensors in injection molding provide continuous real-time data on key parameters such as temperature, pressure, and flow rates, enhancing process monitoring and control.
- Process Parameter Measurement: In-mold sensors are capable of measuring critical process parameters, including direct temperature and pressure, as well as indirect parameters like viscosity, warpage, and shrinkage.
- High-Temperature Processing: Sensors like the 4004A melt pressure sensor operate effectively at temperatures up to 350°C, supporting quality control during high-temperature processing.
- Correlation with Product Quality: Studies have shown that variations in cavity pressure curves during injection and packing stages are directly related to the final deformation and quality of molded parts.
- Emerging Sensing Technologies: Beyond traditional temperature and pressure monitoring, new sensing methods are being developed to characterize additional variables such as material viscosity and flow characteristics, further enhancing process understanding.