Key Engineering Materials Vol. 716

Abstract: This article shows the extension of an empirical model for the numeric calculation of the spread during rolling Freiberg in calibres developed at TU Bergakademie to Mg alloys AZ31, AZ81 und WE43.The material independent foundations were developed at the Institute of Metal Forming at TU Bergakademie Freiberg.The Freiberger spread model has, through numerous rolling trials and examinations of the material flow, been broadened. Furthermore, the results of the calculations were compared with these trials.The Freiberger model for spread takes the geometrical input and output parameters into consideration, as well as the material flow, the deformation rate v, the deformation temperature θ, the chemical composition of the material C_w, longitudinal tension CL, and friction C_μ between the rolling stock and rolls. And it further considers the diagonal ratio C_A∗a_KNⁿ of the box pass and the filling ratio of the box pass m.

Abstract: The application of finite element method (FEM) in the area of metal forming and material processing has significantly increased in the recent years. The presented study provides details of the development of a finite element modelling approach to form a part via sheet hydroforming (SHF) process. Both FEM analysis and experimental trials were introduced in this study to produce a complex shape component from Inconel 718 material. The FEM provides a robust feasibility study for forming this part in terms of blank design, load path and process design optimisation. The simulated hydroformed part was validated by performing experimental trials. The analysis demonstrated close correlation between the predicted FE model and the physical trial.

Abstract: Aluminum and its alloys are widely used as structural materials in aerospace, automotive and other industries due to low density and high specific strength. Efficient way to increase strength and other properties of aluminum alloys is to form an ultra fine grain structure using severe plastic deformation methods. Cryogenic asymmetric sheet rolling under liquid nitrogen temperature is a process of severe plastic deformation that can be used to improve the aluminum alloys structure and properties. Prediction of sheet temperature during plastic deformation is very important. The temperature of sheet is changed due to the conversion of mechanical work of deformation into heat through sliding on contact surfaces. This paper presents the results of the finite element simulation of heat transfer during cryogenic asymmetric sheet rolling of aluminum alloy 6061. The effect of thickness reduction, rolling velocity and friction coefficient on the deformation heating and temperature field of aluminum alloy 6061 was found. The results of investigation could be useful for the development of the optimal treatment process of aluminum alloys by cryogenic severe plastic deformation to obtain the ultra fine grain structure and high strength properties.

Abstract: High-ratio differential speed rolling (HRDSR) is a process of severe plastic deformation (SPD) that can be used to improve the structure and properties of aluminum alloys. The mechanism of SPD during HRDSR comes from its large equivalent strain, which is composed of compressive strain and additional shear strain. Plastic strain control of aluminum alloys are of importance for improvement of sheet microstructure and properties. This paper presents the results of the finite element simulation of shear strain during high-ratio differential speed rolling of aluminum alloy 5083. Four deformation routes UD, TD, RD and ND were simulated. By the route UD the sheet was not rotated between two deformation steps, while by the other three cases it was rotated with 180° degrees. By the route RD the rotation axis was the rolling direction, by the route TD the transverse direction and by the route ND the normal direction. The effect of rolls velocity ratio, friction coefficient and deformation route on the shear strain and the effective strain of Al 5083 was found. The results of investigation can be used to optimize the high-ratio differential speed rolling process to improve microstructure and mechanical properties of aluminum sheets.

Abstract: In Železiarne Podbrezová, cold drawing process is the final process in production of precision seamless steel tubes. This particular technology utilizes multiple drawing sequences and intermediate annealing. From the physical point of view, it is nothing just the optimal use of plastic deformation during cold forming that grants the final tube dimensions. The drawing process itself is significantly affected by physical and metallurgical properties of the tube, the tool geometry, the lubrication, and the sequence of operations. This paper deals with the relationship between the tool geometry and the drawing force. The FEM-based numerical model of the process was prepared in DEFORM 3D in order to optimize the geometry of the die; eight die geometries were investigated in total. The numerical simulation itself considered a hot rolled hollow at Ø32 mm × 4 mm, cold drawn into Ø25 mm × 4 mm using die drawing (sinking) sequences only. Calculated drawing force showed that the change of the run-in angle of the die led to a decrease of the drawing force.

Abstract: The finite element simulation has become an essential tool for the proper design of big size automotive components stamping tooling and their process optimization. Although big improvements have been made in the last years in terms of material and tribological modelling, the accuracy of the current models should be further improved to estimate the final post-forming springback of these components, in both AHSS and mild steels.In the present paper the forming of a B-Pillar reinforcement is numerically analyzed using a DX54D mild steel and a TRIP800 high strength steel. In the first part, the influence of the elastic behavior including variable young modulus, the yield criteria and the hardening law on the final springback is studied for both materials. Secondly, the friction coefficient is defined constant and pressure dependent and springback variation is analyzed in function of this variable.In order to stablish the material and friction variables and their typical deviation, results obtained from material characterization and strip drawing tests are used.

Abstract: With the steady increase in demand for roll formed products, due to their application in fields such as automotive, construction, architecture, etc., roll forming companies are challenged with rising customer demands. Companies are struggling to bring a product through from design to manufacture at improved rates, whilst achieving tighter tolerances. The roll forming process may also induce undesirable forming defects such as twist, distortion and straightness problems. Over the years, numerical simulations have been deployed to assist with the geometric validation of these effects. For the purpose of this paper, an investigation shall focus on an individual parameter within the finite element analysis of the cold roll forming process, i.e. the ’unknown’ spring effect acting of the top roll during the forming process due to the implementation of Belleville washers in the pillar set up. This parameter is assessed over a range of applied loads and compared with a standard friction model with fixed top and bottom rolls. The longitudinal strains on the final profile, the geometric accuracy and thickness variation are observed and presented in this paper. Reasoning is also provided to explain why the final profile bows in the vertical direction.

Abstract: Extending the range of finished product sizes from a given ingot or concast bloom or billet section is often limited by the minimum area reduction required to ensure effective central consolidation and final mechanical properties. Predicting effective consolidation or level of remnant porosity for a range of steel grade, billet size, pass schedule/roll design and thermo-mechanical conditions has always been an important issue on plant, much more lately in view of recent trends for larger ingots and development of combined forging/rolling strategies. This paper will focus primarily on a fast analytical technique based on roll gap shape and consolidation factors obtained from Finite Element (FEM) Models. New developments based on FEM submodelling are presented briefly. Healing capabilities based on diffusion bonding can be obtained from [1-3].

Abstract: In modern technological operation, the original sample could be provided by so-called pre-operation or pre-forming follows prior the main operation. In such case, the surface roughness of the tool set is directly owned by the surface of the pre-formed workpiece, as less rigid body compared with the tool set. In metal forming practice there are mainly several pre-forming processes, among them roll forging, cross-wedge rolling and electro-upsetting. In any non-convenient forging operation route, where pre-forming is done by casting, powder sintering or any additive technology (e.g. SLS, EBM), the surface roughness and wellness obtained pre-formed workpiece could influence stronger on the quality of the end part after main forging operation. In order to investigate the different materials’ behaviours depends on the surface artificial roughness the finite-element analysis (FEA) was carried out for the simple compression tests, thereby the cylindrical, made from aluminium and titanium alloys, and ring specimens, made from steel, were compressed between two flat dies with modelled zero and non-zero roughness at room and elevated temperatures. The behaviour of the lubricant (fluid phase) positioned between two neighboured peaks of the roughed surface was investigated in one direction material flow test as well. The results have shown the strong pressure increase in the bottom area of the peaks, which correspond the practice case, when the fluid phase is not completely evaporated after lubrication. Further, it can course the different microstructure evolution during hot forging operation and during cold bulk forming operation, additional surface pressure can result the material hardening near to the contact zone (not investigated here). In commonly, in observed results the peaks of the roughness can be easily broken due to enormous tangential stresses, as it is well known from the fundamental investigations. Moreover, the computation of geometry scaled tools and workpieces of the ring compression and one-direction material flow tests resulted the exponential dependency against the deformation forces.

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.