Force Measurement in all its variety
Force measurement in welding processes
- to improve welded joints
Welding is one of the most important joining processes in industry for permanently joining workpieces – for both metals and thermoplastics (plastics).
In pressure welding processes, the force applied during the joining process (pressing together) plays a decisive role in the quality and reliability of the weld seam. In contrast to the so-called fusion welding processes, it is not only the temperature that is an important parameter here, but above all the precise dosing of the force. Continuous force measurement makes a significant contribution to increasing the safety of the process and ensuring the quality of the welded joint.
Welding is used, for example::
- Body and vehicle parts
- Packaging
- Tubes
- Textiles
- Office supplies
- Sporting goods
Welding process
In pressure welding processes, a distinction is made between the following process variants in which the joining forces are monitored and controlled with the aid of force transducers:
Resistance spot welding
Typical application in the automotive industry with C or X tongs for body parts, for example. Sheets are welded at the points of contact by electric current and simultaneously applied pressure. The current flow generates heat at the contact point and the pressure ensures the connection.
Butt welding
Workpieces are pressed flat against each other, brought to welding temperature by electrical heating and then joined under pressure. This creates an even, full-surface connection.
Heating element butt welding
The ends of plastic pipes, for example, are pressed against a heated element, melted, the heating element removed and the ends joined together under pressure.
Ultrasonic welding
Used e.g. in electronics or medical technology for fine and sensitive components. In ultrasonic welding, high-frequency mechanical vibrations (ultrasound) generate friction at the joint. Simultaneous pressure creates a firm connection.
Friction welding
The parts to be joined rotate or oscillate against each other, generating heat through friction. Once the welding temperature has been reached, the joint is created using high pressure.
Projection welding
Here, protrusions or elevations are embossed on the components, which serve as welding points. These melt under the influence of current and pressure, which firmly joins the components together.
Laser welding
During laser welding, a highly focused laser beam melts the material at the joint.
Force measurement in the welding process
- Precise and reliable with strain gauge-based force sensors
The quality of a welded joint essentially depends on three parameters:
- the force with which the components are pressed together
- the strength of the welding current
- the period of time during which welding current is applied
With the increasing use of servo drives instead of pneumatic or hydraulic systems in modern welding systems, the pressure measurement previously used to record the force is no longer necessary. Servo drives offer numerous advantages: they require significantly less maintenance and service, work more precisely and consume less energy.
By integrating force sensors directly on the servo drive, the contact force can be precisely recorded when joining the workpieces and the welding process can be actively controlled. This enables a consistently high joint quality.
Strain gauge-based force sensors from Primosensor are perfectly suited for this purpose. They are specially designed for use in welding machines and welding systems in conjunction with servo drives.
Standard output signals of our sensors are:
- 4...20 mA (2- and 3-wire)
- Redundant with 2 x 4...20 mA
- 0...10 V
- +/-10 V
- mV/V
- CANopen
Advantages over piezoelectric sensors
Compared to the piezoelectric sensors also used in welding processes, strain gauge-based systems offer the following advantages, among others:
- Significantly cheaper to purchase and operate
- Technically more advantageous for static and quasi-static processes, due to negligible zero-point drift
- No manual “zeroing” required before each measurement
Typical force sensor geometries in welding systems and machines
Different types of force sensors are used in welding systems, welding machines and welding robots, depending on the application. The most common designs include
- Compression force transducers (load cells)
- Tension- and Compression Force Transducers
- Ring Force Transducers
- Double shear bars
- Measuring axes (load measuring pins)
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