What you need to know about Force Displacement Monitoring?

In modern manufacturing, checking only the final dimensions of an assembled component may not be enough to confirm that the process was completed correctly. A part can meet a final dimensional requirement while still having an underlying assembly problem.

Force Displacement Monitoring provides a way to monitor what happens during the pressing or assembly process itself. Manufacturers can evaluate the complete relationship between force and displacement throughout a machine cycle by measuring pressing force and tool or ram movement at the same time.

This makes Force Displacement Monitoring particularly useful for press-fit, insertion, forming, staking and other controlled assembly operations where changes in force and movement can reveal process abnormalities.

Force Displacement Monitoring is an in-process quality monitoring method that measures force and displacement simultaneously during a pressing cycle.
A force sensor measures how much force is being applied, while a displacement or position measuring system records how far the press ram or tool has moved. The controller synchronizes these signals and creates a force displacement curve.

The curve can then be compared with predefined acceptance criteria or tolerance windows to determine whether the process is within the required conditions.

Instead of asking only, “Did the component reach the final position?”, manufacturers can examine how the component reached that position.

This distinction is important because abnormal resistance, unexpected movement or changes in the force pattern can indicate an assembly problem before the finished product leaves the production process.

1. A typical monitoring cycle involves several key steps:
2. The press begins its machine cycle.
3. The force sensor measures pressing force continuously.
4. The displacement or position sensor tracks ram/tool movement.
5. The controller synchronizes both signals using a common time base.
6. The system generates a force displacement curve.
7. The measured curve is evaluated against programmed criteria.
8. The controller provides an OK/NOK process result.
9. Depending on the system configuration, the curve and process result can be stored for traceability.

Because each force measurement is associated with a corresponding tool position, manufacturers can see how force changes as the component moves through the assembly operation.

This provides considerably more process information than monitoring peak force alone.

A force-displacement curve represents the relationship between the force applied to a component and the displacement of the pressing tool.

For a typical press-fit or insertion operation, the curve may begin with relatively low force while the tool approaches the component. Once contact occurs, force begins to increase. As insertion continues, interference and friction can cause further increases before the component reaches its intended final position.

The exact curve depends on the part, material, tooling and assembly process. Therefore, there is no single curve shape that can be considered “normal” for every application.

Manufacturers may look for changes such as:

• Unexpectedly high or low force
• Changes in curve slope
• Force increases occurring earlier than expected
• Sudden force drops
• Incorrect final position
• Unusual friction behaviour
• The curve failing to pass through a defined tolerance window

This allows the monitoring system to evaluate important stages of the assembly rather than relying on one measurement.

The exact monitoring capabilities depend on the press and controller, but typical variables include:

Depending on the controller, time, cycle duration or speed-related values may also be available. Using several criteria together can provide a more reliable assessment of the assembly process than using a single peak-force value.

The controller compares the measured cycle with programmed acceptance criteria.

For example, an application may require the force to remain within an upper and lower limit while the component moves through a particular displacement range. The system can also check whether the curve enters, passes through or exits a predefined tolerance window correctly.

Depending on the controller, other evaluation methods can include:

• Upper and lower force limits
• Displacement limits
• Tolerance windows
• Peak-force monitoring
• Position at a specific force
• Reference-curve or curve-envelope comparison

The appropriate evaluation method depends on the application and the controller’s capabilities.

Force Displacement Monitoring is not limited to one type of press. It can be applied to pressing or assembly equipment capable of providing reliable force and position signals.

Examples include:

• Industrial Electric Press
• Servo presses
• Hydro-pneumatic presses
• Pneumatic presses
• Manual presses equipped with suitable sensors
• Customized assembly stations

The monitoring system typically works alongside the press, sensors, controller, machine control or PLC interface, HMI/software and, where required, data-storage or MES connectivity.

The technology can be applied across different industries. In practice, the type of assembly process is often more important than the industry itself.

It can be useful for applications in:

• Automotive manufacturing
• Electronics
• Semiconductor and electromechanical assembly
• Medical device manufacturing
• Appliances
• General manufacturing

The system is particularly useful when changes in force and displacement can indicate whether an assembly or production step has been completed correctly.

Common applications include:

• Bearing, bush, pin and shaft insertion
• Connector and housing assembly
• Press-fit electrical/electronic components
• Spring compression or seating verification
• Riveting, staking and forming operations
• Processes where a missing, wrong or misaligned part changes the force/stroke signature

Therefore, when evaluating whether Force Displacement Monitoring is suitable, manufacturers should focus on the characteristics of the process, such as whether force and position change predictably during the operation and whether process variations can be identified through the force displacement curve.

Electric press systems are particularly suitable for applications requiring controlled force and stroke measurement.

For SCHMIDT® ElectricPress systems, such as the EP343, as an example where force and stroke are measured directly within the press system. With PRC control and the appropriate software options, production criteria can be evaluated and process data or curves can be stored or transferred.

This type of integrated approach can help manufacturers combine controlled pressing with in-process quality monitoring within the same production station.