Papers by Keyword: Flow Forming

Abstract: Flow forming of metastable austenites is an innovative, incremental metal forming process with special capabilities due to the TRIP effect. However, the TRIP effect during flow forming is significantly affected by disturbances and especially batch fluctuations leading to process uncertainty. This aspect is further analyzed and quantified in this paper to give insights on how to minimize the impact of uncertainty. For this purpose, semifinished parts and resulting flow forming workpieces are systemically characterized concerning their properties and the property uncertainty supported by mathematical methods like correlation analysis and error propagation. A result is that the most influencing impact factor on the strain induced α’-martensite volume fraction as a material property are batch fluctuations, specifically the variations of the chemical composition. Those especially appear from batch to batch, but also within a batch accompanied by e.g. temperature effects. To counter this challenge, different methods from control theory like closed-loop property control and adaptive control can be applied to flow forming. Thus, uncertainty will be reduced to increase process robustness and to enable industrial exploitation of the TRIP effect in flow forming of metastable austenitic steels.

Abstract: This study introduces a novel flowformability test aimed at replicating the complex loading conditions of industrial flowforming processes—alternating stress triaxiality, large plastic strains, and high strain rates. A novel Conical Flowformability Test (CFT) configuration was selected for experimental validation due to its ability to achieve a high theoretical thickness reduction while respecting machine constraints. Experiments conducted on AA6061 in O-temper and W+3h states demonstrated substantial thickness reductions. Comparison between the numerical simulations using the software FORGE® and the experimental results is satisfactory despite certain unquantifiable experimental defects such as fish scales and material build-up. The current study paves way to establish a robust framework for assessing material flowformability and damage evolution under realistic process conditions.

Abstract: The production of complex multi-functional, high-strength parts is becoming increasingly important in the industry. Especially with small batch size, the incremental flow forming processes can be advantageous. The production of parts with complex geometry and locally graded material properties currently depicts a great challenge in the flow forming process. At this point, the usage of closed-loop control for the shape and properties could be a feasible new solution. The overall aim in this project is to establish an intelligent closed-loop control system for the wall thickness as well as the α’-martensite content of AISI 304L-workpieces in a flow forming process. To reach this goal, a novel sensor concept for online measurements of the wall thickness reduction and the martensite content during forming process is proposed. It includes the setup of a modified flow forming machine and the integration of the sensor system in the machine control. Additionally, a simulation model for the flow forming process is presented which describes the forming process with regard to the plastic workpiece deformation, the induced α’-martensite fraction, and the sensor behavior. This model was used for designing a closed-loop process control of the wall thickness reduction that was subsequently realized at the real plant including online measured feedback from the sensor system.

Abstract: A theoretical investigation of the influence of the profile radius of the deforming roller on the limiting degrees of deformation in the process of flow forming is performed. Analytical and graphical dependencies allowing to determine the limiting degrees of deformation are obtained depending on the ratio of the profile radius of the roller to the initial thickness of the workpiece wall. The main practical ways of using the obtained dependences are considered. The results of the theoretical study are in good agreement with the known experimental data. The developed engineering technique can be used in designing the process of flow forming of cylindrical blanks by a torus roller.

Abstract: Samples extracted from flow formed tubes made of 18% nickel maraging steel grade C18Ni1750 were subjected to tensile testing at room temperature in laboratory environment at two different strain rates. Testing was carried out in as flow formed as well as flow formed and aged conditions. Aging was carried out adopting four different cycles. Distinct loss of ductility was observed at the lower strain rate in all tested conditions. The embrittlement occurring during low strain rate testing is explained in terms of hydrogen induced damage, hydrogen coming from the moisture in the environment. It is also concluded that the heavy cold work imparted to the material during flow-forming is importantly responsible for the ductility loss observed at low strain rate.

Abstract: Modeling of the cold flow forming process for manufacturing of tube shaped solution annealed H30 Aluminum alloy has been considered in this present study. Three inputs (feed-speed ratio, roller in-feed and roller axial stagger) and three outputs viz. spring back, ovality and internal diameter have been considered for the present study.. Adaptive network-based fuzzy inference system (ANFIS) in Matlab platform has used for modeling purposes and its performance is compared with regression model. ANFIS has completely outperformed the regression models. Percentage accuracy in predicting all the three responses are found to be very high with ANFIS models. Prediction of ovality against the test data using regression analysis is found to be extremely erroneous. It indicates that additional process parameters are involved in predicting ovality which are not captured during the experimentation.

Abstract: Fatigue crack propagation has been measured in flow formed Inconel 718 (IN718). Test pieces were extracted from a flow formed tubular structure in the longitudinal direction, retaining the tube curvature across their width. Crack growth rates (da/dN) were measured at 20, 300, and 400oC. For comparison, tests were repeated on specimens with an identical geometry but machined from conventionally forged IN718. Detailed metallurgy of the flow formed material is presented.

Abstract: The feasibility of combining spinning, shear forming and flow forming processes has been demonstrated through manufacturing of a representative of a hub component using industrial scale hybrid-forming machine available at the Advanced Forming Research Centre (AFRC). The manufacturing cycle consisted of single to multiple passes of shear forming, spinning and flow forming. The research has proven that the spinning, shear forming and flow forming can be combined using a single machine with a single set of tooling and single process cycle. Circumferential and axial cracking was observed in initial set of trials which were eliminated using a series of experiments. The methodology that was used in these series of trials to remove the cracks/defects that may occur during forming of such component is presented here.

Abstract: In small batch manufacturing, flowforming may represent an optimal semi-finishing process for axisymmetric parts, due to its versatility, the reduced material waste, the good geometrical tolerances as well as the improvement of the mechanical characteristics it allows to attain. However, the main limiting factor often lies in the lack of knowledge for the process design, which implies expensive industrial trials often based on trial-and-error approaches. Due to these reasons Finite Element (FE) numerical simulation can provide a significant help in the design and management of the process, but its application is still facing relevant issues, mainly linked to: (i) the complex contact conditions between tooling and part, (ii) the high computation effort due to the 3D geometry rotating at high speed, and (iii) the complex strain paths that the material undergoes.The paper presents an optimized FE model of the flowforming process of AlSi7 alloy tubular components carried out at elevated temperature. An implicit solution scheme and an arbitrary Lagrangian-Eulerian meshing was adopted, while the constitutive parameters of the material model were calibrated on the basis of experimental compression tests carried out in the same thermo-mechanical conditions of the industrial reference process. The influence of the main process parameters, namely thickness reduction, feed rate and mandrel rotation speed were investigated and an algorithm for parametric process charts derivation was finally proposed.

Abstract: The present study reports the effect of the heat treatment on the tensile properties of the reverse flow-formed AA6082 Aluminum alloy tube. Tensile specimens obtained after each forming pass have been subjected to three different heat-treatment conditions viz., as-flow formed (AFF), as-flow formed followed by artificial aging (170°C/6h) and HT (solutionizing + 170°C/6h) treatments. Characterization of the tensile properties reveals that as-flow formed condition (followed by natural aging) gives the best combination of yield strength, UTS and percentage of elongation. The variations in tensile properties are correlated with microstructure of the materials.