Meaning
Mechanical deformation measurements track the physical stretching of the horizontal steel supports on an injection moulding machine during the application of high clamping forces to a tool. Monitoring tie-bar strain is necessary to ensure that the clamping force is evenly distributed across the four bars and that the mould is being held closed with the correct pressure. If one bar is stretched more than the others, the mould will tilt slightly, leading to flash and uneven part thickness.
Sensors are used to measure this tiny elongation, which is then converted into a force reading. This information allows the operator to adjust the machine settings to balance the load. The measurement is a key part of the setup and validation of a moulding process.
Clamping Balance
Achievement of a perfectly uniform force across the mould face is difficult but necessary for high-quality production. When the tie-bar strain is unbalanced, it indicates that the tool is not sitting flat or that the machine is out of alignment. This imbalance causes the mould to open slightly on one side during the injection phase.
The result is a part that has flash on one edge and a short shot on the other. It also puts excessive stress on the machine components, leading to premature wear of the bushings and the bars themselves. By measuring the strain on each bar, the technician can identify the problem and make the necessary adjustments to the clamping system.
This ensures that the tool is protected and the parts are consistent.
Machine Accuracy
Calibration of the clamping force is a standard part of the maintenance routine for any injection moulding press. The machine’s internal sensors provide a reading of the total force, but the tie-bar strain measurements provide a more detailed look at how that force is being applied. Over time, the bars can stretch permanently or the platen can warp, which changes the relationship between the machine settings and the actual force.
Regular checks with external strain gauges help to verify that the machine is performing as intended. This is particularly important for large machines where the forces are massive and the risk of damage is higher. A well-calibrated machine is more repeatable and produces fewer defects over the long run.
Tooling Alignment
Protection of the mould is another important reason for monitoring the forces during the clamping cycle. If the tie-bar strain is too high, it can crush the tool or damage the delicate shut-off surfaces. If it is too low, the tool will open under the pressure of the injected plastic.
The ideal clamping force is just enough to keep the tool closed without causing excessive deformation. By using the strain data, the engineer can find this balance and optimize the process. This also helps to identify when the tool needs to be repaired, as an uneven load can be a sign of a warped mould base.
Correct alignment between the machine and the tool is the foundation of a stable moulding operation.
