IMPROVING GEOMETRICAL QUALITY BY INDIVIDUALIZING THE ASSEMBLY PROCESS

Licentiate thesis, 2019

Dimensional deviations are a consequence of the mass production of parts. These deviations can be controlled by tightening production tolerances. However, this solution is not always desired because it increases production costs. Availability of larger amounts of data and automatized production has opened new opportunities to improve the geometrical quality of products by individualization of the assembly process. This concept is proposed by Söderberg et al. as Smart Assembly 4.0 in which the individualized matching of parts, locator adjustments, weld sequence optimization, etc. are performed on an assembly line.
This study focuses on two techniques of individualizing the assembly process, individualized matching of parts and individualized locator adjustments in assembly fixtures. The existing studies and applications of these methods are reviewed and gaps defined. The previous applications of individual matching of parts, known as selective assembly, are limited to linear and rigid assemblies.
This study improves existing methods by presenting a multistage method of performing selective assembly technique without dimensional assumptions about the mating parts. This method results in improved geometrical quality compared to similar methods and no surplus parts. This study also develops the application of selective assembly for sheet metal assemblies. The assembly technique developed for sheet metals is applied to three industrial sample cases to evaluate its performance.
Another gap in the context of selective assembly covered by this study is a problem in the existing method of mapping in the utilized optimization algorithm. This research also studies individualized adjustments of locators in assembly fixtures. After evaluating the existing methods of locator adjustments, this study develops a new method that utilizes the scanned data of mating parts to predict the required adjustments. Afterward, a method for individualized adjustments is also developed. Considering applied and residual stresses during the assembly process as constraints is another contribution of this research to locator adjustments. Thereafter, both methods are applied to three industrial sample cases and the results evaluated. A modification is also proposed that reduces the required adjustments for the same amount of improvements in geometrical quality.
The results of this research evidence a promising improvement in the geometrical quality of assemblies by individual matching of parts and locator adjustments. The results illustrate that individualization in locator adjustments can increase geometrical quality improvements three to four times.