Strain sensors improve the quality of injection molding process

Gefran Inc. 8 Low ell Ave Winchester, MA 1-888-888-4474 w w w .gefran.com North America 01890 [email protected]

STRAIN SENSORS IMPROVE THE QUALITY OF INJECTION MOLDING PROCESS

An Injection molding machine typically consists of two main parts, an injection unit and a clamping unit. It is quite common to see machines using load cells to monitor the force applied to the different parts, from the injection system to the platen. The tie-bars are parts of the injection machine where the application of load cells is harder: there is often no room for any kind of sensors, due to the mold movement, and it is not possible to mount any traditional load cell by drilling holes for the installation on their side. The main question is: is the tie-bar force measurement really important? Actually, yes. From the design to the normal operation, several are the ways a tie-bar force measurement can help improving the quality of the machine and the final product. R&D departments use tie-bar force measurement to improve the machine’s performance by detecting the best block locations and optimizing the strain links. During the commissioning, the machine’s reliability can be tested by measuring the tie-bar elongation that provides a direct information related to the clamping force. Maintenance can also benefit from the tie-bar force measurement because it allows to test the clamping process and check the machine’s stability.

So, how can you measure the force directly from the tie-bar without using a traditional load cell? The answer is in the technology. A PRESS-ON strain sensor can measure the surface-strain directly at the mounting location, in a similar way to what happens with bonded strain gauges. The strain gauges are protected, as they are positioned under a stainless protective foil, and they are strongly pressed onto the measuring surface. The friction obtained by pressing the strain gauge onto the surface replaces the bonding normally used to fix them. There are different ways to press the sensor against the tie-bar’s surface: the simplest one is by using a metal strap and tightening it around the tie-bar (see right picture). The most innovative system uses two strong magnets, integrated in the sensor, mounted on the two sides of the stain gauge, which allow to lock the sensor in its position and apply a force that is enough to create the needed friction.

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Using this magnetic installation system, the sensors can be installed very easily and just in few seconds. The sensor does not need to be recalibrated every time it’s installed.

Gefran Sensormate offers a wide selection of PRESS-ON strain gauge sensors for any kind of installations, on tie-bars as well as in other positions inside the injection molding machine. The solutions for tie-bar installation are again multiple but the magnetic system is without a doubt the most innovative and efficient. The QE1008(W) sensors offer this feature and are available in a standard, wired configuration or, as alternative, with an advanced wireless communication system that eliminates any kind of cable, making the installation easy and amazingly fast. Besides, each sensor has an integrated signal amplifier. Data are transmitted to the wireless receiver that is connected to the PC via USB. The supplied Inspectmate software shows the received measurement data in real-time.



The measurement data can be logged and saved in CSV format so that they can be easily processed by using Excel or any other spreadsheet software. Summarizing, Gefran Sensormate strain sensors for tie-bar force measurement provide several advantages:

the measurement is performed directly on the tie-bar

the accuracy is very high, like the strain gauge is bonded

using the sensors in couples for each tie-bar, the measurement is compensated from bending errors

the force can be displayed in different units: in kN, tons, US-tons or micro-epsilon

no cables for the wireless version


Engineering

Strain sensors improve the quality of injection molding process