Influence of Plastic Machining on the Quality of a Clinching Joint in Aluminum

Permanent joints are commonly used in vehicle construction. The main methods used are gluing, welding and heat sealing. However, other joining methods that utilise plastic deformation of sheet metal are also becoming increasingly common. These methods include the sheet metal clinching joint. This is a joint that allows sheet metal to be joined, often in combination with bonding. Sheet metal of various thicknesses is used in vehicle construction and is subjected to plastic working. The main objective of the work was to assess the influence of plastic working of sheet metal on the strength of clinching joints. An additional objective was to determine the possibility of assessing the degree of aluminum sheet thickness reduction in a non-destructive manner using the ultrasonic (UT) method. The tests carried out showed that as the crumple increases, the strength of the clinched joint is reinforced. For sheet metal joints without crumpling, the strength was 608 N, and for 20% crumpling, the strength increased to 645 N, while for 47% crumpling, the strength increased to 671 N. For the largest crumpling of 60%, the strength was 712 N. In terms of non-destructive assessment of the degree of sheet thickness reduction, it was found that the best measure is the speed of the ultrasonic longitudinal wave. Other measures, such as decibel drops in pulse height for surface and longitudinal waves, show certain trends, but they are not conclusive.