Fügen durch Umformen

Beim Fügen durch Umformen wird die zu fügende Struktur oder das Hilfsfügeteil wesentlich plastisch verformt (DIN 8593). Dagegen beschränkt sich beim Schrauben diese Verformung auf den Mikrobereich (z.B. Einebnung von Rauigkeiten). Die Kräfte beim Umformfügen werden üblicherweise hydraulisch oder in modernerer Ausführung mechanisch durch Spindeltriebe aufgebracht. Die mechanische Fügetechnik bietet innovative, kostengünstige und energieeffiziente Verfahren für das Verbinden gleicher und verschiedenartiger Werkstoffe. Das vorliegende Kapitel befasst sich mit dem Clinchen (Durchsetzfügen) und den Stanznietverfahren mit Halbhohl- oder Vollniet, da diese vorlochfreien und deshalb sehr effektiven Verfahren seit Mitte der 1990er Jahre an Bedeutung gewinnen. Im Hinblick auf aktuelle Leichtbaukonzepte und der damit verbundenen Mischbauweise stoßen thermische Fügeverfahren zunehmend an ihre Grenzen

Deep drawing with local hardening on digital multi-axis servo press

The paper discusses a new drawing technology, based on a synchronized Movement of ram and cushion with multiple bending operations in alternating directions called "bi-directional deep drawing (BDD)." The goal is to avoid local thinning by strengthening the weak point using local hardening. BDD operations are realized before the conventional deep drawing process. This results in a local strain hardening at the weak point of the workpiece, which is usually located at the bottom punch radius. Two major aspects have to be given attention due to the high number of process parameters. On the one hand, for process design, it is helpful to have a tool by means of which it is possible to simultaneously create both the machine program for the servo press and the initial configuration for the process simulation. From the authors' point of view, this complexity can only be represented by a numerical analysis method, on the other hand. Consequently, both aspects are given attention in this paper

Optimierte Vorform- und Prozessführung für das IHU-Presshärten komplexer Geometrien

The process combination of Hot Metal Gas Forming and Press Hardening (HMGF-PF) with various materials was carried out as part of the predecessor projects (AiF 161182BR and 16961BR). HMGF-PH was successfully realised in this projects. Depending on the material and temperature regime, complex component geometries could be completely formed in experimental investigations. However, the thinning was at a maximum of 60 percent, depending on radius, initial wall thickness and material. The data on HMGF-PH determined in these studies show that this process has a high potential to produce components in one forming stage with an almost completely hardened microstructure. However, the project results also shows deficits in the state of the art in the field of process control with regard to the homogeneity of the wall thickness in critical radius areas and the flow behaviour of the material under changing temperature regimes in combination with complex component geometries to be formed. The influence of different preform geometries and a favourable material pre-distribution was investigated within the scope of this project. The two working hypotheses form the basis for this are:1. A favourable material pre-distribution (surface expansion) should have a constant distance to the engraving for further forming in order to achieve a homogeneous temperature distribution during the forming.2. High strain rates, which are caused by short pressure build-up times, work against a high thinning during the forming and support the process-safe forming of the component geometry. The aim of the research project is to investigate the two hypotheses with the aim of combining both phenomena. The aim is to develop a process model for the design of optimized preform geometries and suitable process control strategies for HMGF-PH. In the state of the art the current possibilities for HMGF-PH and in particular for preforming are shown. The two underlying working hypotheses mentioned above and a goal-oriented solution has been developed. In work package (WP) one, a classification of possible HMGF-PH parts with regard to potential preforming strategies is carried out. Based on this, extensive simulations were carried out regarding different circumferential preforms for the realization of a rectangular component cross-section as well as regarding different process strategies regarding the influence of component circumference and preform geometry on the production of components with a trapezoidal cross-section. The simulations served as a basis for the selection of the most promising process strategies. On the one hand, these were subjected to an economic feasibility study on the trapezoidal components in WP two, and on the other hand, they were experimentally implemented in the work packages WP three (definition of the real tests and test planning using DoE for the test geometry), WP four (design and manufacture of the test tool and manufacture of the preform geometries) and WP five (experimental investigations of various preforms and variation of the process parameters for the test geometry). The economic feasibility study showed that a separate embossing step as a preform at room temperature is cheaper than realizing a forming step when closing the HMGF-PH tool. The reason for this is the expected high tool wear when pre-forming the hot parts in the HMGF-PH tool. The moulds were equipped with sensors to detect component temperature and internal pressure curves over the entire process. This information was later used in WP seven to compare the realized components with the simulation results. The manufactured components were analysed in WP six with regard to the target parameters of shaping and wall thickness reduction in the corner radii. In WP eight, functional correlations were derived and an empirical process model was created. It was found that the choice of the process strategy (diameter of the starting semi-finished product, preform concept) has a large influence on the geometric cross-sectional pre-distribution before the HMGF-PH step and thus also on the wall thickness reduction of the components in the radii. The process parameters of the HMGF-PH, such as calibration pressure and pressure build-up time, however, mainly have an influence on the component forming. Based on the results, a demonstrator geometry for further experimental tests was defined in WP nine together with the project-accompanying committee (PbA). In addition to the trapezoidal cross-section of the geometry investigated to date, this has a deflection along the longitudinal axis of the component as well as optional dome geometries in the concave and convex component area. The investigation of the preforming for the realization of the deflection of the component was carried out when the tool was closed, both with and without internal pressure. The components realized according to a test plan previously developed on the basis of Desgin of Exerimentes (DoE) were measured and evaluated in WP ten with regard to the influence of the process parameters on the shaping and wall thickness reduction of the components. In addition to the results from WP 8, it was shown that the pressure build-up time in particular has a significant influence on the wall thickness reduction of the components and should, if possible, not exceed 1.5 s for the selected component geometry and process control. Furthermore, the influence of the geometric cross-sectional pre-distribution through the preforming process on the wall thickness reduction could be demonstrated. The project results were summarized in WP eleven. In particular, statements on the design of suitable preform geometries and process control strategies were derived. The working hypothesis one "A favorable material pre-distribution should have a constant distance to the engraving for further shaping" could be refuted in WP one based on simulations. Hypothesis two "Short pressure build-up times counteract strong thinning during forming", however, was confirmed. The necessary knowledge and experience for the design of HMGF-PH processes for components with complex geometries could be intensively expanded in the project

Geometric Accuracy of a Design Based Process Chain Simulation in Comparison to the Results of Real Car Body Manufacturing: Presentation held at Automotive Engineering Expo, Prozesskette Karosserie - Vom Konzept zur Endmontage, 30.-31.05.2017, Nürnberg

With increasing complexity of vehicle design, the numerical car body process chain analysis during the planning phase gets a noticeable dominant role. This lecture will focus on springback and accuracy analysis along the complete process chain. In cooperation between Audi AG and Fraunhofer IWU numerical methods will be introduced and each single step from deep drawing till complete assembly evaluated with regard to its influence on the dimensional accuracy and applicability in practice. For this the entire process chain for the production of an assembly was experimentally metrological accompanied and compared with the numerical generated results. The center of attention lies on the question, which quality level can be achieved on design data based simulation in comparison with the real process, with modified tool surfaces, stiffness influences and tolerances in the construction of the tools. Based on the results, the causes of differences between simulation and reality and approaches for better representation are discussed

Deep drawing with local hardening on digital multiaxis servo press

The paper discusses a new drawing technology, based on a synchronized movement of ram and cushion with multiple bending operations in alternating directions called “Bi-Directional-Deep Drawing“ (BDD). The goal is to avoid local thinning by strengthening the weak point using local hardening. BDD operations are realized before the conventional deep drawing process. This results in a local strain hardening at the weak point of the workpiece, which is usually located at the bottom punch radius. Two major aspects have to be given attention due to the high number of process parameters. On the one hand, for process design, it is helpful to have a tool by means of which it is possible to simultaneously create both the machine program for the servo press and the initial configuration for the process simulation. From the authors’ point of view, this complexity can only be represented by a numerical analysis method, on the other hand. Consequently, both aspects are given attention in this paper

Clinching - an innovative joining technology for trucks

In commercial vehicle construction the focus is still on the reduction of kerb weight and production costs. An efficient joining technology – such as the clinching of thick sheet metal – can help saving costs and production time. Clinching of thick sheet metal has been investigated in various research projects. However, there are currently no systematic investigations on: clinching hot-dip galvanized sheet metal, keeping protection from corrosion at the clinched joint and design concept for static calculation. These issues are under investigation in the current FOSTA research project P1172 “mechanical joining of steel structures”. First selected results of the project are presented in this paper