Ultrasound-based detection of flow fronts in injection molds
The quality of the injection molding process depends largely on the filling process and on the ability to achieve uniform flow front of the plastic within the mold .
Uneven flow front s can lead to weaknesses in the material, unwanted weld lines, and defective components, which in turn reduce profits from the sale of the final product.
Challenges in flow front detection:
Detecting flow fronts in injection molds is a complex task.
Uneven flow front s can be caused by these various factors:
- Changes in material properties
- Tool design
- Changes in the injection molding process
To date, there have been a wide variety of approaches to flow front detection, such as optical sensors, pressure sensors, and temperature sensors. However, these methods have certain drawbacks, such as sensitivity to abrasive materials or limited dynamic range.
A promising alternative to this isnon-contact measurement using ultrasonic sensors.
How ultrasonic flow front detection works:
Ultrasonic flow front detection relies on the continuous transmission of ultrasonic pulses toward the cavity during the injection molding process.
With an empty cavity, 100 % of the ultrasonic energy is reflected at the steel/air interface. If the plastic now hits the measuring point, part of the ultrasonic energy is coupled into the plastic and precisely this difference is subsequently detected by the MoldFront sensor system.
MoldFront electronic unit mounted on an injection molding machine
Click here to view the sensor product mentioned:
Advantages of ultrasonic flow front detection
Ultrasonic flow front detection offers several advantages over other methods:
- Die Methode erfasst dynamisch und in Echtzeit Veränderungen der Fließfront, was eine schnelle Reaktionszeit im Bereich von < 5 Millisekunden ermöglicht.
- The method is resistant to external factors such as abrasive media, high spray pressures, or humidity.
- The method is independent of the material and tool design and can therefore be applied to a wide range of applications.
- This method allows for noncontact measurement at many different points within the mold, resulting in a high degree of design freedom.
Comparison of MoldFront flow front detection and pressure sensors
The use of pressure sensors is a common method for measuring pressure and detecting flow fronts in industry.
Similarly, the MoldFront ultrasonic sensor system can be used. While the pressure sensor system measures the increase in pressure within the cavity to detect the “ flow front ,” the MoldFront ultrasonic sensor system utilizes changes in density within the cavity. It precisely detects whether the steel/air or steel/plastic interface is present at the measurement point. This also works for other metals, such as aluminum or copper.
The major advantage of ultrasonic flow-front detection thus lies in the ability to measure the flow front independently of the pressure conditions in the cavity. In other words, no response pressure is required, and there is no longer a limitation to a predetermined maximum pressure.
In addition, due to the non-invasive or non-contact measurement, ultrasonic flow front detection can also be used with abrasive media or vacuum applications without any problems.










