Shrink wrapping within an automatic assembly line

Shrink fitting within an automatic assembly line

2 steel bushings are to be joined with high precision in a cast aluminum motor housing. The joining process was integrated into a modular, fully automatic assembly and testing line. The workpieces to be processed are transported on workpiece carriers.

Customer benefit: flexible process solution

First, the aluminum housing is heated to 120 °C by a hot air blower. At the same time, the bushings are cooled to -150°C in liquid nitrogen. Sensors monitor the temperatures so that only parts with the ideal parameters are joined.

Producing the press-fit connection between a cast aluminum part and a steel part is problematic at room temperature and can lead to seizure of the parts without the aid of lubricants. An alternative to conventional press-fitting is cold expansion using liquid nitrogen. This process has the advantage that the joining process can be carried out with low joining force or without force.

Using a robot, 2 electric screw presses are each fitted with the corresponding bushing in succession. The presses insert the bushings into the housing at controlled speed and force. The temperature of the parts is monitored by sensors.

After joining, the parts are cooled to room temperature so that they can be safely fed into further processes. The nitrogen consumption of the system is monitored and the loss is automatically compensated.

The cycle time per part is 40 seconds.