Economics of clinched joint compared to riveted joint and example of applying calculations to a volume product

Clinching is a mechanical joining method especially for sheet metal parts based on forming of joined materials, and no additional joining elements are needed. Remarkable benefits in the process can be shown particularly when joining pre-coated materials. The process was implemented for a mass production in a car manufacturing industry in 1980. Nowadays, a wide range of applications covers all sheet metal production industries. Another interesting mechanical joining method developed in 1990s is self-piercing riveting. This method is nowadays widely used for sheet metal joining, especially in car manufacturing industry where aluminium as a material for chassis is used. The process does not need any pre-working such as drilling or hole punching, joining takes less than a second of time, and no post-work is needed, either. Joining with and without additional elements differ significantly from each other on the basis of cost formation principles. In a technique without any additional element the unit and total costs decrease as the tool life increases. On the case of joining sheets with an additional element (e.g. self-piercing rivets), tooling costs can even be ignored, due to their minor significance. The total costs increase directly in proportion to the amount of joints. An economic comparison of the above-described mechanical joining methods is presented in this paper. Several points of view are discussed and mathematical calculations for, e.g. marginal costs are presented. The aim of the study is to present a general procedure for comparing joining costs of each method.