Manufacture of Defined Residual Stress Distributions in the Friction-Spinning Process: Investigations and Run-to-Run Predictive Control

Friction-spinning as an innovative incremental forming process enables high degrees of deformation in the field of tube and sheet metal forming due to self-induced heat generation in the forming area. The complex thermomechanical conditions generate non-uniform residual stress distributions. In order to specifically adjust these residual stress distributions, the influence of different process parameters on residual stress distributions in flanges formed by the friction-spinning of tubes is investigated using the design of experiments (DoE) method. The feed rate with an effect of −156 MPa/mm is the dominating control parameter for residual stress depth distribution in steel flange forming, whereas the rotation speed of the workpiece with an effect of 18 MPa/mm dominates the gradient of residual stress generation in the aluminium flange-forming process. A run-to-run predictive control system for the specific adjustment of residual stress distributions is proposed and validated. The predictive model provides an initial solution in the form of a parameter set, and the controlled feedback iteratively approaches the target value with new parameter sets recalculated on the basis of the deviation of the previous run. Residual stress measurements are carried out using the hole-drilling method and X-ray diffraction by the cosα-method.

Analysis of Flangeability by Single-Stage SPIF and Press-Working in AA7075-O Sheet

Recently, the research interest of hole-flanging has turned from conventional press-working to SPIF as a viable process for small- and medium-sized batches. Both technologies have been studied separately using different approaches and, therefore, most studies cannot be easily compared. Besides, some studies that measured the formability in SPIF using the classical Limiting Forming Ratio (LFR) showed conflicting results that still need to be clarified. Under these circumstances, the aim of this work is to provide a better understanding of the deformation process and the material formability in hole-flanging by critically comparing both forming processes. To this end, a series of experimental tests on AA7075-O sheet of 1.6-mm thickness by press-working and single-stage SPIF, using forming tools with different profile radii, are analysed. The material formability and flange geometry are compared and discussed in detail. The process limits are analysed by using both the Forming Limit Diagram (FLD) and the LFR. The failure modes by necking and fracture are clearly identified and assessed on both processes along with the influence of the bending induced by the tools during the flange forming. Results conclude that the LFR is not an adequate parameter to compare formability between processes other than press-working and, accordingly, two additional variables based on either the flange height or the average thickness reduction are proposed to successfully analyse flangeability.

Numerical simulation study on multi-pass non-axisymmetric spinning of cylindrical parts with oblique flange

A non-axisymmetric cylinder with an oblique flange has broad application prospects. Spinning is the main production process for this kind of workpiece. Finite element modeling is a necessary method to study some key problems that are difficult to be solved merely through experiments, such as the strain and stress fields in the development of this spinning technology. In this study, the spinning process of a non-axisymmetric oblique flange cylindrical part was established and simulated using ABAQUS/explicit software. The credibility of the simulation result was validated through an experiment. The influence of the axial roller feed along the cylinder wall on the distribution of wall thickness and stress and strain during the forming process was analyzed. The change in stress field and strain field with time was analyzed, and the quantitative relationship between forming conditions and forming results was described. Furthermore, the forming principle of the flange was analyzed. It would be beneficial for flange forming to reduce the increasing distance of the cylinder wall in the 180° direction (parameter c) and the vertical distance from the closest point to the spindle as the roller returns back in the 180° direction (parameter d), to a certain extent. Hence, a workpiece with an ideal appearance was obtained. By comparing the wall thickness distribution, the design and optimization of the roller path were once again verified to be reasonable.

Numerical and Experimental Investigation on the Effect of Billet Preforming in the Flange Forming

Finite element method and experiments have been used to study a cold forming method for fabrication of a flange using the effect of billet preforming. Three dimensional finite element methods carried out to obtain the forming load, die filling, material flow, effective stress, effective strain with DEFORM-3D software, and a series of experimental works has been performed using lead metal with four types of billet preforming in the first stage. Pressing process has been done using computerized hydraulic press machine with 100 tons. The forming sequence is carried out in two stages. In the first stage, the cylindrical billet is preformed by upsetting and in the second stage forming it in a die. Results indicate that the process of formation is influenced by preforming of billet with fixed volume in the final stage of pressing, improve the mechanical properties of the metal and thus facilitates the final deformation process with less stress and better flow of the metal inside the die. Simulation results show that the effective stress, maximum principal stress, effective strain, velocity and damage are maximum at locations where flange open out and rib growth begins across the geometrical interlocking between the two halves of die-set and the component surface.

FEM Analysis of Cold Flaring Process of SUS304 Pipe

This paper describes a production process for experiment and finite element method (FEM) analysis of cold forming of SUS304 pipe. These large diameter pipes such as φ114.3 mm are used for a plant as a flow channel of gas and liquid. The connection of pipes are generally welded at the plant. However, the other connecting method are required from a viewpoint of making the plant environment worse by welding. Therefore, flaring process of large diameter pipes were proposed. This flaring process is one of a method of pipe flange forming. The formed pipes were connected used with loose flange. Flaring process was generally hot process, thus it has some problem such as becoming complex of forming machine and accuracy of dimension. In this study, cold flaring process of SUS304 pipe was proposed to satisfy these requisitions. Experiment and FEM analysis of cold flaring process were performed to clarify the optimum forming conditions for the flat length of connecting surface such as a diameter of punch, punch stroke and taper angle of dies. As a result, a gap between punch and die was needed to match the pipe wall thickness.

Interfacial damage identification of steel and concrete composite beams based on piezoceramic wave method

Introduction: Steel-concrete composite structures are playing an increasingly important role in economic construction because of a series of advantages of great stiffness, good seismic performance, steel material saving, cost efficiency, convenient construction, etc. However, in service process, due to the long-term effects of environmental impacts and dynamic loading, interfaces of a composite structure might generate debonding cracks, relative slips or separations, and so on, lowering the composite effect of the composite structure. Methods: In this paper, the piezoceramics (PZT) are used as transducers to perform experiments on interface debonding slips and separations of composite beams, respectively, aimed at proposing an interface damage identification model and a relevant damage detection innovation method based on PZT wave technology. Results: One part of various PZT patches was embedded in concrete as “smart aggregates,” and another part of the PZT patches was pasted on the surface of the steel beam flange, forming a sensor array. Conclusions: A push-out test for four specimens was carried out and experimental results showed that, under the action of the external loading, the received signal amplitudes will increasingly decrease with increase of debonding slips along the interface. The proposed signal energy-based interface damage detection algorithm is highly efficient in surface state evaluations of composite beams.

Hole-flange forming of high-strength steel sheet using one-step hot stamping-forging method

A process of one-step hot stamping-forging for increasing the tensile strength of the hole-flanging of the high-strength steel sheets with flange thickening was developed. In this proposed method, the high-strength steel sheet is directly formed within the designed die, which is simultaneously accompanied with a resistance heating, a hole punching, and the flanging and forging processes. The electrode material is SKD61. This material is not only used as the forming of the high-strength steel sheet but also directly served as the heating of the high-strength steel sheet within the die. The experimental results indicated that the high-strength steel sheet could be heated to 850 °C in 30 s by the SKD61 die. It demonstrates the successful completion of heating, hole punching, flanging and forging in a one-step process. Furthermore, it is found that the tensile strength of M18 tapped hole with forged part is increased by about 7.4% than that without forged part, and the breaking toughness is increased by about 33%.