Basic technological investigation of a new high-performance process for the production of internal threads and microstructure-based characterization of their performance

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Conventional threading processes, such as tapping or forming, take up a large proportion of machining time of a component. Due to the defined thread pitch, the spindle rotation must be synchronized with the feed axis. In addition, the retraction movement takes place at the same feed rate in the reverse direction of rotation. The resulting loss of time due to the necessary acceleration and deceleration processes results in high main times.Within the scope of this research project, a process-safe concept for the innovative thread forming process "axial thread forming" for the aluminum cast alloy AlSi10Mg is to be developed in order to generate highly productive detachable joints. The innovative high-performance process offers enormous time saving potentials in contrast to conventional thread forming methods, since the thread is not formed continuously, but is completely produced by half a revolution of the tool.The basic aim of this research project is to acquire a basic knowledge of axial thread forming. The novel kinematics as well as the tool design, however, require the investigation of correlations between the machining itself and the result. The analysis of the mechanical tool loads as well as the forming processes during axial thread forming are just as important as the investigation of the thread quality. The transferability of the results to other material systems will be demonstrated using the brass alloy CuZn40.In order to characterize the internal threads, efficient test sequences for the investigation of the mechanical properties are to be further developed, which guarantee detailed knowledge of the quasi-static and cyclic material behavior based on application-optimized physical sensor technology with an appropriate number of specimens. The aim of the investigations is to obtain the highest possible information about the thread quality and the failure mechanisms with a relatively small number of specimens. In particular, the influence of the broaching channels generated during axial thread forming and the associated stress increase under load as well as the reduced overlap on the mechanical strength and fatigue life are investigated. Selected process-relevant parameters are varied during machining and evaluated using mechanical characterization methods. The feedback of the results into the manufacturing process enables resource-saving and efficient machining. In addition, the results are compared with threads produced conventionally by thread forming in order to classify the test results.The process-related geometric and microstructural properties of the internal threads are correlated with the mechanical properties, which results in a structure-based analysis of the damage mechanisms to generate a knowledgebase for the design of optimum process conditions based on a basic process-structure-property-understanding.