Heißverstemmen

Heat caulking - process with DualStake

The process

The joining process of hot caulking is often used in the production of mechatronic parts. It enables a thermoplastic material to be joined to a material of the same type. For example, a circuit board can be fixed in a plastic housing.

The thermoplastic has domes, which are heated and formed into rivet heads using a punch under the influence of force. The result is an inseparable connection.

There are various versions of this process.

Heated stamp

Contact with a heated forming die heats and forms the plastic. There is a risk of burning on the surface of the plastic dome. In addition, the heat does not reach the inside of the material easily. After the rivet head has formed, the punch lifts off again. Only then does the plastic begin to cool down. As there is no longer any force applied and the plastic is still partially in a thermoplastic state, play can occur between the joining partners.

Cold stamp with preheating

Alternatively, hot air can be used to heat the plastic. A cold punch then reshapes the heated dome and allows the material to cool. This creates a backlash-free connection.

Both processes are susceptible to fluctuations in the volume of the plastic dome. If the dome contains too little material, the rivet head cannot be fully formed, resulting in reduced strength. If there is too much material available, expelled material can detach from the rivet head and lead to malfunctions in the component.

Another common problem is the so-called mushroom effect. In this case, the formed rivet head shows cracks that are not visible from the outside. This leads to reduced strength of the joint, especially under dynamic stress.

Our solution: DualStake - two-stage process

The plastic dome is heated homogeneously by a double-tube nozzle without thermally stressing the area around the caulking point. In the second step, a two-stage forming die is used, which achieves a complete force and form fit regardless of volume fluctuations in the dome. The resulting rivet head has a square cross-section instead of a mushroom shape.

The process significantly reduces the risk of cracking and has a higher strength. Even with larger tolerances in the volume of the dome, a reliable process is possible.

The two-stage process enables short cycle times in automated production and meets the highest quality requirements.