Fixture (cavity, holder) for parts
On the one hand, the part fixture ensures that the component is always in the same position. On the other hand, it supports the lower part below the weld seam, so that the pressure force of the upper part primarily acts in the weld seam and is not lost in other areas.
The cavity is usually made of aluminium. For prototypes, 3D plastic printing is also used.
The fixture can also have additional inserts or sliders to provide better local support for the weld seam. For example, in the case of a hole in the side wall, the pressure can be lost without an additional support. Such a insert or slider can be operated manually, with springs, or pneumatically.
Sensors can be placed in the fixture to detect that a part to be welded has been inserted and whether the position is correct.