Flow Splitting Process Research Articles

Process Characteristics in Flexible Flow Splitting

Flexible flow splitting enables manufacturing a new kind of semi-finished goods: bifurcated sheet metal in integral style with non-linear progression of the bifurcation line. Beside special geometrical features, this forming process is associated with severe plastic deformation (spd) processes. Due to the strategy of process guidance, it is possible to process diverse parts with different geometry and mechanical behavior without changing of tools or programming. To predict complex flow splitting processes with the help of FEM simulation, methods like the cut and expand method (CEM) have been developed in the recent past, to decrease calculation time and increase efficiency of the simulation. As the flexible flow splitting process is a non-steady forming process, this method is no longer suitable and has to be adapted. A further development of the cut and flexible expand method (CfEM) will solve this problem. This paper will present the operation mode of the process and the simulation method. The characteristics of this forming process and a comparison of experimental and numerical results will be presented.

Simultaneous Forming and Joining by Linear Flow Splitting - From Basic Mechanisms to the Continuous Manufacturing Line

Abstract The public demand for an efficient and sustainable use of energy resources has led to a more consequent use of lightweight constructions. In the automotive sector for example, weight reduction is achieved by a structural construction with branched parts by reinforcing ribs or by a combination of materials with different strengths. To join these assemblies, different joining by forming processes are used. Mostly forming and joining takes place in separate processes. The innovative forming technology of linear flow splitting offers advantages with regard to the production of lightweight parts and the joining by plastic deformation at the same time. Residual stresses in the manufactured profiles are used in the linear flow splitting process for an additional mechanical joining of profiles and other parts. Here, the forming and mechanical joining zones do not coincide, which is different to conventional joining technologies. The study at hand presents the tensile joining mechanism in the forming process of linear flow splitting in detail and shows the implemented manufacturing line for simultaneous forming and joining in the process of linear flow splitting.

Benefits of stress superposition in combined bending-linear flow splitting process

Linear flow splitting is a multi-station sheet-bulk metal forming process which allows continuous production of bifurcated profiles without joining, lamination or external heating of sheet metal. This process induces high hydrostatic stresses in the forming zone which leads to an elevated formability of the workpiece material. The aim of this research is to bend linear flow split profiles in transverse direction in a continuous manner. This is achieved by combining the linear flow splitting process with a continuous bending process. An analytical and a numerical model are described in this paper which predict bending moments for different radii. Results from both models are validated with experimental results. It is found that combining the linear flow splitting with a bending process leads to a severe reduction in the bending moments due to superposition of stresses in the forming zone. The superposition maintains the cross sectional shape of the bent profiles.

A study on springback of bending linear flow split profiles

The bending of linear flow split profiles made up of high strength materials involves high bending loads leading to high springback and geometrical defects. In addition, the linear flow split profiles are made stronger due to the high plastic deformation applied by the process itself. The bending method proposed in this paper combines the linear flow splitting process with a movable bending tool. The aim of the research was to investigate the effect of superimposed stresses exerted by the linear flow splitting process on bending load and springback of the profile by using a finite element model. The latter was validated by means of experimental results. The results show that the bending loads and the springback were reduced by increasing the superposition of stress applied by the linear flow splitting process. The reduction in the bending loads leads to a reduction in the cross-sectional distortion. Furthermore, the springback was compensated by controlling the amount of superimposed stress.

Technology Pushed Process and Product Innovation – Joining by Linear Flow Splitting

In order to take full advantage of manufacturing technologies, designers have to use technology specific manufacturing-induced properties. An adequate selection and optimisation of the manufacturing technology and a consequent combination of product and process development can lead to product innovations. Linear flow splitting yields ultra fine grained (UFG) microstructures which are characterised by high hardness, ductility and fatigue strength. These manufacturing-induced properties are particularly suited for rolling contact areas of linear guiding systems. Multi-functional linear systems require an integration of additional functional elements. For the hereby necessary joining, using the mechanisms acting in the linear flow splitting process seems attractive. The paper introduces a mechanical joining process following this technology push approach. Thereby, manufacturing-induced properties and mechanisms induced during the linear flow splitting process are utilised to integrate additional functional elements. Necessary joining operations can be integrated into the continuous flow production, maintaining the technological potential to manufacture large quantities at low costs. Extensive experiments show the applicability of various joined elements and materials for process integrated mechanical joining. The potential for product innovations is illustrated by an innovative linear system. Its core component is an integrated rack as part of a rack and pinion drive of a facade cleaner.

On the Origin of Specimen: Load-adapted Integral Sheet Metal Products

Flexible flow splitting is a novel forming process allowing the production of a new class of semi-finished goods: nonlinear branched sheet metal parts. This advancement of the linear flow splitting process combines both, the benefits of flexibility in cross-section shape and the flexibility of the part's curvature progression in feed direction and discloses new potentials in lightweight designed sheet metal formed parts. The paper presents the implementation of this new manufacturing process, the challenges of processing bifurcated and curved band edge sheet metal parts and a strategy to enhance the part accuracy by a closed loop controlled tooling system.

Application of the local strain approach on a rolling point contact model

A newly developed cold forming process, the linear flow splitting process, allows the bifurcation of thin metal sheets by severe plastic deformation (SPD). This process produces flanges with an ultra-fine grained (UFG) microstructure, which is characterized by an increased hardness and lower surface roughness in comparison to the material in as-received state. The technology is researched within the Collaborative Research Centre 666 (CRC 666) “Integral Sheet Metal Design with Higher Order Bifurcations”. The increased hardness and reduced surface roughness of the flanges make this technology suitable for manufacturing linear guide rails. In order to achieve the required reliability and fatigue strength, the assessment of the performance of the linear flow-split profiles with gradient microstructure is of great importance. When considering rolling contact fatigue, the examination of the mechanical behavior of the side of the flange with higher hardness due to the UFG microstructure is required. In order to reduce time and costs, a numerical method to determine the rolling contact fatigue behavior would be useful minimizing the normally applied experimental effort. The present work aims to check the applicability of the local strain approach for the evaluation of the rolling contact fatigue behavior of linear flow split components by a Finite Element (FE) analysis. The Hertzian theory is only valid for homogeneous materials and cannot be directly applied to the flanges with gradient microstructure. Therefore an accurate modeling of the material in order to take into account the gradient in the mechanical properties is required. In this paper the characterization of the material behavior under axial cyclic loading will be presented. These results will be used for the Bergmann damage parameter to analyze the rolling contact fatigue behavior. Some parameters required for the application of the Bergmann approach are determined by a numerical simulation of the rolling contact. Results are compared to rolling contact fatigue tests performed on a recently developed test rig under the assumption of rolling without sliding and neglecting the effect of surface roughness and residual stresses.

Quantification of local and global elastic anisotropy in ultrafine grained gradient microstructures, produced by linear flow splitting

Severely deformed materials often show strong plastic strain gradients, which can lead to a variety of gradients in microstructure and texture. Since the elastic behavior of a material is in most cases linked to its crystallographic texture, gradients in the elastic properties are also possible. Consequently, the macroscopic elastic behavior results from the local elastic properties within the gradient. In the present investigation profiles produced by the linear flow splitting process were examined with respect to local and global elastic anisotropy, which develops during the complex forming process. The local grain orientations determined by EBSD measurements were used to calculate the elastic tensors at several positions along the strain gradient. Based on the geometric mean, the calculated local elastic constants were transferred into global ones by appropriate weighting. Ultrasonic measurements were carried out to determine the macroscopic stiffness tensor of the severely deformed parts, showing a good agreement with the global stiffness tensor calculated from orientation data.

Roll forming of branched profiles

Due to the new mass forming process “linear flow splitting” forming of branched profiles in integral style out of sheet metal without joining, lamination of material or heating of the semi-finished part becomes feasible. Since the resulting flanges provide extra stiffness without increasing the weight of the semi-finished product, split profiles are suitable especially for lightweight applications. The combination of the linear flow splitting process with a following roll-forming process enables the continuous production of one- or multi-chambered profiles with free flanges. In this paper phenomena occurring during roll forming of branched profiles are described and discussed.

UFG-Microstructures by Linear Flow Splitting

Linear flow splitting is a new continuous cold forming process where the edge of a sheet metal is formed into two flanges by splitting and supporting rolls. Thus the production of bifurcated profiles from sheet metal without lamination of material becomes feasible. The production of such structures takes place incrementally in a modified roll forming machine. Experimental investigateons on a HSLA steel show, that even at a surface increase of the sheet edge of about 1800% no cracks were nucleated in the profiles. EBSD measurements in the splitting centre reveal that similar to other SPD processes UFG microstructures develop in the processing zone. Thus a steady state is reached in the processing zone where increasing strain has no more (or little) influence on the materials properties i.e. its deformability, as it is typical for SPD-processes. The formation of UFG microstructures is considered to be a mandatory condition for the linear flow splitting process, as it improves the formability of the material to the extremely high level required for this process. The mechanical properties of profiles produced by linear flow splitting are characterised by large gradients, depending on the local deformation and the resulting microstructure. Very high hardness is measured at the former processing zone, i.e. the splitting centre and the flange surface, where severe plastic deformation takes place and UFG microstructures are present. In direction to lower deformation i.e. with increasing distance to the splitting ground or flange surface the hardness decreases close to the level of the undeformed material. In the present paper the linear flow splitting process is introduced and the microstructural development in the process zone is discussed on the base of EBSD measurements on profiles of the steel ZStE 500. The repartition of mechanical properties in a bifurcated profile is demonstrated by detailed hardness measurements.

Severe plastic deformation by linear flow splitting

AbstractDue to the new linear flow splitting forming process the production of bifurcated profiles from sheet metal without lamination of material becomes feasible. The continuous production of such structures takes place incrementally in a modified roll forming machine. By producing those complex parts process‐related changes in the material properties occur as a result of the cold forming. Thus, the assumption of homogeneous properties in the processed part is not valid and a reliable analysis of structural durability is only possible by considering changes in material properties. Investigations on linear flow split profiles show large gradients in the microstructure and properties over the profile cross section. In the areas of low plastification the degree of deformation and the flow stress can be determined by microstructure and hardness measurements. In the severely deformed areas, like the upper flange surface, this determination becomes doubtable. Therefore the electron backscattered diffraction method was used to investigate, if an ultrafine‐grained structure is occurring as it evolves in the processes of severe plastic deformation. Thus, the aim of this paper is the numerical analysis of the linear flow splitting process, the metallographic characterisation of bifurcated profiles and the numerical evaluation of the structural durability with consideration of the gained insights.

New Forming Processes for Sheet Metal with Large Plastic Deformation

Due to the high effort involved, bifurcated constructions in mass market products made from sheet metal remained largely unused. Extruded profiles with cross-sections containing bifurcations show the possibility to increase the stiffness and allow modern lightweight design using load optimized structures as well as in box strap, sandwich and stringer constructions or different profiles. The two new forming processes linear flow splitting and linear bend splitting developed at the PtU enable the production of bifurcated profiles in integral style made of sheet metal without joining, lamination of material or heating of the semi-finished product. These forming processes use obtuse angled splitting rolls and supporting rolls to transform the sheet metal at ambient temperature. Whereas the linear flow splitting process increase the surface of the band edge and forms the band into two flanges. At linear bend splitting a bended sheet metal as semi finished product is used. Thereby bifurcations at nearly any place of a sheet metal can be produced. Both processes induce high hydrostatic compressive stresses in the local forming zone during the process which leads to an increased formability of the material and thereby to the realization of large strains. Parts produced are characterized by increased stiffness, high surface hardness and low surface roughness. Experimental investigations have shown an increasing of the band edge surface at maximum splitting depth up to 1800%. By a following forming process new multi-chambered structures and integral stringer construction can be realized with thin walled cross-sections from steel of higher strength.

Tooling and process control for splitting of disk blanks

Conventional splitting processes are today applied to manufacturing pulleys and flywheels from disk blanks. Usually, the splitting process is performed on a modified spinning lathe. However, the attainable radial splitting depths are limited and, to increase the formability of the machined part, new process concepts have to be developed. An innovative approach is the so-called flow-splitting process. In this case the tool configuration consists of three rolls, one splitting roll and two supporting rolls. While the splitting roll causes the workpiece material to flow into the two flange areas, the supporting rolls interact with the workpiece underneath the deformation zone. The distance between the splitting roll and each supporting roll can be adjusted to a specified value. Thus, the generated flange areas are given a predefined thickness. During the beginning of the forming process, the supporting rolls keep the workpiece from buckling. Once the edge of the blank has some deformation, the supporting rolls induce compressive stresses and thus increase the formability of the blank. In realizing the process concept, the described properties have to be transferred to a tooling system. Simultaneously, process control and measuring methods have to be developed.