Infeed Rotary Swaging Research Articles

Mechanical properties of rotary swaged steel components

The radial infeed rotary swaging is widely used as a diameter reduction forming process of axisymmetric workpieces, improving the mechanical properties with excellent near net shape forming. In the present study, rotary swaging experiments with different parameter setups were performed on steel tubes and bars under different material states and several resulting property modifications were investigated such as stress-strain curve, hardness, fatigue strength and surface residual stresses. The results show a significant work hardening induced by the rotary swaging process and an improvement in the static and dynamic mechanical properties was observed. Furthermore, the hardness distribution was homogenous in the cross section of the rotary swaged workpieces. Moreover, depending on the process conditions, different residual stresses distribution were generated along the surface.

Development of residual stresses by infeed rotary swaging of steel tubes

Additionally to the achievable tight geometrical tolerances, rotary swaging can influence intrinsic material properties by work hardening and residual stresses generation. Although residual stresses should be usually avoided, they can be used on purpose to improve the performance properties of a produced part. To find prospective process settings, 2D FEM simulation of the rotary swaging process was developed and revealed the development of residual stresses distributions in E355 steel tubes in the whole longitudinal section. Besides the closing time, also geometric features of the dies were varied. It was found that the closing time affects the residual stresses significantly at the surface, but not in the depth of the part. By shortening the calibration zone, the axial tensile residual stresses near the outer surface could be lowered, while compressive residual stresses near the inner surface remained almost unaffected. By applying a higher die angle, the tensile axial residual stresses were increased while reducing the compressive axial residual stresses. Experimental investigations of residual stresses were performed by X-ray diffraction which revealed a good agreement between simulation results and physical measurements. With these findings, the rotary swaging process can be optimized for shaping residual stresses profiles to improve the performance properties of the produced parts.

Material Flow in Infeed Rotary Swaging of Tubes.

Rotary swaging is an incremental metal forming process widely used to reduce the cross–section of parts. For tubular parts, the final wall thickness also changes during the process. The lubricant condition is a factor, which affects these geometry changes. Beneath the change of the geometry, the complex material flow during the process determines the final geometry and the mechanical properties. Therefore, with a thorough insight into the material flow, it could be understood how to control it in order to achieve desired properties. Producing tubes with uniform outer diameter and changing inner profiles is an application of this method. Furthermore, applying this method, different local cold hardening could be achieved by different total strain. In this study, the dependency of the material flow on the lubrication conditions was investigated. Simulations with combined hardening material models were verified by the change of the wall thickness of tubes. It was found that friction condition significantly influences the back shifting of the workpiece and the elongation caused by each stroke. Results from simulations and experiments showed that a certain lubricant condition leads to the highest axial elongation of the workpiece.

Plastic Deformation Components in Mandrel Free Infeed Rotary Swaging of Tubes

Abstract In metal forming processes, the forging load as well as the mechanical and geometrical properties of the final product are affected by the actual material flow. Especially for incremental open die forming processes like rotary swaging, the material flow is very complex. By a profound knowledge about how to control this material flow during the process, the final product properties can be controlled. By using FEM, the material flow during infeed rotary swaging of tubes without mandrel was investigated by the history of the plastic strain components (PEi) in different directions. The influence of the friction coefficient value on the material flow for steel tubes was studied. By the history of plastic strain components tracked during the process, the material flow was analyzed in different radial positions. Based on that, the influence of friction conditions on PEi was discussed during one single stroke. It was found that with an increasing friction coefficient value, the radial plastic strain firstly increased and then decreased, while the axial plastic strain behaved just the other way round. Thus, the material flow is significantly affected by friction conditions. The simulation results were validated by measurements of wall thickness values of physically formed tubes.

High productivity micro rotary swaging

Rotary swaging is an incremental forming process with two main process variations plunge and infeed rotary swaging. With plunge rotary swaging, the diameter is reduced within a limited section whereas the infeed rotary swaging enables a diameter reduction over the entire workpiece length. The process is now subject to intensive investigation for manufacturing of micro parts. By increasing the process speed, failures occur particularly due to inappropriate material flow. In plunge rotary swaging, the workpiece material can flow radially into the gap between the dies and thus the workpiece quality suffers. In infeed rotary swaging the workpiece material flows against the feeding direction and can provoke bending or braking of the workpiece. Therefore, additional measures to control both the radial and the axial material flow to enable high productivity micro rotary swaging are investigated. The radial material flow during plunge rotary swaging can be controlled by elastic intermediate elements that enable an increase of productivity by factor three. A spring-loaded clamping device that enables an increase of the productivity by factor four can temporarily buffer the axial material flow in infeed rotary swaging against the feeding direction.

Axial and Radial Material Flow Analysis in Infeed Rotary Swaging of Tubes

In rotary swaging – an incremental cold forming production technique to reduce the diameter of axisymmetric parts – the material flow can be assumed to be predominantly axial and radial. The actual ratio of this axial and radial flow influences the mechanical properties and especially in tube forming the final geometry. It is known that during mandrel free infeed rotary swaging of tubes the wall thickness changes. The change is depending on the process parameters like incremental and cumulated strain. Hence, the ratio of axial and radial material flow changes. Consequently, the analysis of the wall thickness of rotary swaged tubes enables fundamental insight how to control the material flow direction. In this study, the infeed rotary swaging process of steel tubes with different wall thicknesses from 3 mm to 7 mm and rods were investigated with FEM under two feeding velocities. The axial and radial material flow and the resulting geometry were studied by the relative wall thickness. It could be seen that the relative wall thickness was affected by the feeding velocity as well as the initial wall thickness. The findings of the simulation were validated by rotary swaging experiments.

Dry Rotary Swaging with Structured Tools

Rotary swaging is a cold bulk forming process. The diameter of the workpiece is reduced incrementally by oscillating movement of the tools. The established processes use lubricants which fulfill necessary functions such as lubricating, cooling and cleaning of the tools. Disadvantages caused by the use of lubricant are costs of recycling, replacement of lost coolant and for the cleaning of the workpiece. To eliminate the lubricant it is necessary to substitute the functions of the lubricant in other ways. For example by means of coating and structuring of the tools.In this study infeed rotary swaging with structured tools is investigated using finite element simulations. Different structures are implemented in the reduction zone of the tools. The influence is investigated by the radial and axial process forces. Additionally first structured tools are manufactured and experimentally tested. The results of modeling and testing are discussed.

Investigation of Deformation Induced Martensitic Transformation during Incremental Forming of 304 Stainless Steel Wires

Wires with 1 mm initial diameter have been reduced between 10 and 64 percent at different temperatures and strain rates by infeed rotary swaging, which is an incremental cold forming process mainly used for rods and pipes. The volume fraction of martensite in the deformed wires has been determined by X-Ray diffraction and by magnetic induction for different processing parameters. Measurements show that for already small percentage of reduction, martensite is present in the wires and its amount changes with the strain rate and temperature. While for smaller strain rates at room temperature the formation of martensite is promoted, it is restrained for higher strain rates and higher temperatures. Results also reveal that the martensite distribution in the sample is inhomogeneous. Further investigations have been made to analyze the microstructure by optical microscopy and to determine mechanical properties by tensile testing.

Influence of the relative rotational speed on component features in micro rotary swaging

Micro rotary swaging is a cold forming process for production of micro components with determined geometry and surface. It is also possible to change the microstructure of wires and hence the material properties. Swaging dies revolve around the work piece with an overlaid radial oscillation. Newly developed tools (Flat Surface Dies, FSD) feature plain surfaces and do not represent the geometry of the formed part as in conventional swaging. Using these tools allows for producing wires with triangle geometry (cross section) as well as a circular shape. To test the influence of FSD on material properties by micro swaging a new method is investigated: the variation of the relative speed between the specimen and dies in infeed rotary swaging. During this specific process copper (C11000) and steel (304 Alloy) wires with diameter d 0 = 1 mm are formed. It is noticed that the mechanical characteristics such as ductility and strength differ from the characteristics after conventional swaging. Moreover this approach enables new possibilities to influence the geometry and the surface quality of wires. The impact of the relative speed on the processed wire features is described in this paper.

FEM simulation of infeed rotary swaging with structured tools

Rotary swaging is an incremental cold forming process for rods and tubes. Infeed rotary swaging with structure in the reduction zone of the tools is investigated using a two dimensional finite element simulation. A few geometrical parameters are varied, for cosine and skew stairway shapes. The effective tool angle is kept constant. The influence is evaluated by the radial and axial process forces. Furthermore, the material flow is visualized by the neutral plane. The simulation results are quantitatively compared to each other to analyse the reaction force F A , which acts against the feeding force. Also, the results serve to find suitable geometries to be transferred to rotary swaging tools for practical application. It is shown that the shapes have a significant effect on the forces and the location of the neutral plane. Finally a first swaging tool is modified with an exemplary geometry for experimental investigations.

2D-simulation of Material Flow During Infeed Rotary Swaging Using Finite Element Method

FE simulation was applied to study the material flow during infeed rotary swaging. The neutral plane according to the process parameters was investigated and compared with experimental results. A single forming stroke was analyzed precisely by using small time points of 10-4s. For analysis the essential steps between the first contact of wire and forging die and the last contact before the die opens again are represented. In that range the feed velocity is eliminated and the neutral plane can be observed as spatial velocity at nodes in the axial direction equal 0mm/s. During a single stroke the location, the geometry and the orientation of the neutral plane is changing.

Application of Stochastic Regression for the Configuration of Microrotary Swaging Processes

In micromanufacturing, a precise adjustment of manufacturing, handling, and quality control processes constitutes an essential factor for success. The continuing miniaturization of workpieces and production devices results in ever decreasing tolerances, whereas machines and processes become increasingly more specialized. Thereby, the so-called size effects render the direct application of knowledge from the area of macromanufacturing impossible. In this context, this paper describes the application of theμ-ProPlAn method for the configuration of an infeed rotary swaging process for microcomponents. At this, the cause-effect relationships between relevant process parameters are analyzed using stochastic regression models, in order to determine cost-efficient process configurations for the manufacturing of bulk and tubular microcomponents.