13th International Conference on the Technology of Plasticity (ICTP 2021): Niels Bay Honorary Symposium
Program Organizers: Glenn Daehn, Ohio State University; Libby Culley, The Ohio State University; Anupam Vivek, Ohio State University; Jian Cao, Northwestern University; Brad Kinsey, University of New Hampshire; Erman Tekkaya, TU Dortmund; Yoshinori Yoshida, Gifu University
Wednesday 9:15 AM
July 28, 2021
Room: Virtual: Room A
Location: Virtual
Session Chair: Paulo Martins, IDMEC, Universidade de Lisboa
On the Characterization of Fracture Loci in Thin-walled Tube Forming: João Magrinho1; Maria Beatriz Silva1; Paulo Martins1; 1IDMEC, Universidade de Lisboa
This paper is focused on the formability limits by fracture of thin-walled tubes and provides for the first time ever the fracture forming limit lines associated to crack opening by tension (mode I), by in-plane shear (mode II) and by mixed-mode consisting of crack opening by modes I and II of fracture mechanics. This is accomplished by experimentation that combines digital image correlation and determination of gauge length strains in double notched tensile test (DNTT), staggered DNTT and shear test specimens. Results are plot in principal strain space and the crack opening modes are confirmed by fractography analysis performed with a scanning electron microscope. DNTT specimens are also used to determine fracture toughness in mode I. The utilization of DNTT, staggered DNTT and shear tests allow obtaining the strain loading paths and fracture loci across a wide range of forming conditions ranging from plane strain to pure shear.
50 Year’s Research and Development on Metal Forming and Joining: Niels Bay1; 1Technical University of Denmark
My first subject of research was cold pressure welding. Microscopic studies of the weld formation led to establishment of a theoretical model for bond formation based on continuum mechanics, and a new surface preparation method introducing brittle surface layers by chemical Ni-plating. In parallel to this work, I studied fundamentals of friction in metal forming. Together with Wanheim a theoretical model for friction was proposed based on slipline analysis of the flattening of surface asperities. The model was later improved including subsurface deformation using finite element analysis. The increasing focus on environmental aspects of lubrication in sheet metal forming tribologically difficult materials such as stainless steel motivated research on development and testing of environmental friendly lubricants and tribo-systems preventing galling. A universal sheet tribo-tester was developed, which can carry out consecutive tests at controlled sliding length, sliding speed and idle time between tests in order to emulate production conditions. The work resulted in the introduction of new, environmentally benign lubricants, new tool coatings diminishing the risk of galling and tailored tool surfaces facilitating micro-plasto-hydrodynamic lubrication, which prevents galling. The work on strategic surface coatings promoting bond formation in cold pressure welding was continued in work on resistance projection welding of dissimilar metals. Development of an FEM program for resistance welding was initiated in the 1990-ies resulting in the formation of a Danish spin-off company SWANTEC commercializing and further developing the program, which today is state-of-the art and applied by a large part of automotive industry and steel mills in the world.
Friction and Thermal Insulation: Influence of Oxide Scale on Hot Forging Sequences: Laurent Dubar1; 1LAMIH UMR CNRS 8201
In the field of hot forging processes, oxide scales are produced on steel billets by oxidation at high temperature. During forming, the oxide layer at the billet/tool interface affects not only friction but also the heat exchange. A global approach is first proposed with the determination of friction coefficients at high temperature with the presence of oxides. The tests are performed on the Warm and Hot Upsetting and Sliding Test. An investigation is conducted at microscale with pin on disk test at high temperature in a controlled atmosphere, in order to understand the phenomena involved during the substrate/oxide/soap/tool contact. The analysis of the results is conducted by integrating local material data. Finally, a thermomechanical finite element modeling of the forging process is developed considering the mechanical and thermal effects of the oxide layers. The impact on the forging sequence is investigated, by quantifying global and local improvements of the model.
Welding of Aluminum in Chip Extrusion: André Schulze1; Oliver Hering1; A. Erman Tekkaya1; 1Institute of Forming Technology and Lightweight Components (IUL), TU Dortmund University
The reduction of energy consumption and CO2 emissions in the aluminum profile production can be achieved by solid state recycling. By direct hot extrusion, aluminum chips can be directly processed into semi-finished or near-netshape products requiring relatively low energy and having a high material yield. Since the mechanical properties of the extruded profiles highly depend on the welding of the individual chips, the main focus is to achieve a sufficient bonding between the chips. For this, the oxide layer covering the aluminum surface has to be broken. In order to predict the welding of the individual chips and estimate the process success a weld prediction model is developed. The influence of process parameters such as extrusion ratio, temperature and speed is analysed. The weld model is applied to further profiles and validated by experimental tryouts.
Testing Method of Anti-galling Ability of Lubrication Coatings in Multi-stage Cold Forging: Zhigang Wang1; Shinobu Komiyama2; 1Gifu University; 2Nihon Parkerizing Co. Ltd.
An upsetting-ball ironing test has been developed to investigate the lubricating performance of coatings in multi-stage cold forging. By using this test, the lubricating performance of a zinc phosphate free coating called “dry in-place coating” has been evaluated and improved, and now the dry in-place coating is used worldwide due to its high anti-galling ability and low environmental impact. In the present paper, the feature of the testing method, galling process and the performance of lubricaiton coatings are discussed.
In Search of the Perfect Sheet Metal Forming Tribometer: Lukas Schell1; Peter Groche1; 1Institute for Production Engineering and Forming Machines
Due to increasing variant diversity and mass customization, time and cost-efficient process design has gained importance for several years. Tribological investigations are playing a key role as part of the process design. In particular, the desires for extended process limits, reduction of lubricant amount and reliable determination of friction coefficients for FE simulations place high requirements on tribometers in sheet metal forming.For quite some time, the strip drawing test with several variations has been considered as an efficient and meaningful method for tribological investigations. This paper summarizes the development of the strip drawing test to date. In particular, design principles for experimental modelling of tribological conditions of deep drawing processes and approaches for friction measurement are described. Moreover, the current state and future requirements for the development of the “perfect” tribometer are discussed in this paper.
Deformation Mechanisms in Tool-workpiece Asperity Contact in Metal Forming: Chris Nielsen1; Xiaodan Zhang1; Marcel Moghadam1; Niels Hansen1; Niels Bay1; 1Technical University of Denmark
The contribution to friction stemming from dissipation of plastic energy is studied by numerical simulations and experiments. The geometrical setup consists of a single model asperity, which is first flattened against a tool with grooves on a smaller length scale. Relative, tangential sliding between the model asperity and the tool is induced subsequently until a steady state is reached. The flank angle of the grooves on the tool is varied. Comparison between the simulations and the experiments leads to validation of the simulations at low tool flank angles, while the current numerical implementation cannot handle the complicated flow around the tool grooves with a large flank angle. At low flank angles, the simulated tangential tool force is in agreement with experiments when keeping one determined friction factor. This proves that the change in tangential force, corresponding to a change in apparent friction factor, is only due to the dissipated energy from the plastic waves. The validated numerical model can be used to determine a wider range of apparent friction factors for strain hardening materials.
Tribological Conditions in Hot Bending of 22MnB5 Tubes: Enrico Simonetto1; Andrea Ghiotti1; Stefania Bruschi1; 1University of Padua
Thanks to the high stiffness-to-weight ratio given by the closed-section geometry, tubular components are particularly suitable for automotive applications that require extreme lightness to reduce the energy consumption and increase the crashworthiness. Tube bending processes are traditionally performed in cold conditions, but to overcome the dramatic problems of accuracy and formability that the new high strength steels present, a novel draw bending set at high temperature has been proposed. The paper presents the results of the investigations carried out on the tribological conditions of the hot draw bending of 22MnB5 tubes to obtain tubular parts with tailored mechanical properties. Investigations about the process thermal cycle has been performed with focus on the influence of the contact pressure on the heat transfer. The results show the practicability of the new process chain to obtain hot stamped tubular parts.
Effect of Production Rate on Lubrication Performance in Combined Forward-Can and Backward-Can Cold Extrusion Test: Kunio Hayakawa1; Ippei Takahashi1; Yoshihiro Kubota1; Itaru Ishibashi2; Tamotsu Nakamura1; 1Shizuoka University; 2ILUB Co., Ltd.
Effect of production rate on the lubrication performance of environmentally friendly lubricant was investigated using the tribological test of Forward Can – Backward Can Extrusion. In this test, the lubrication performance is examined from both finite element analysis and experiment. For the lubricant, double-layer-type lubricant was used. The calibration diagram on the relationship between the extruded geometry and the punch stroke was prepared at the forming rate of 20 spm (strokes per minute) and 1 spm using FE analysis. As workpiece materials, annealed steel SCM420 and aluminum alloy A4032 with three different surface treatment conditions was used. As a result, the friction coefficient value estimated was higher when the production rate was smaller. The dependency of the friction coefficient on the production rate was able to be reasonably evaluated by the present method.
Exploring the Fragmentation of Surface Films during Solid State Welding: Daniel Cooper1; Gregory Oberhausen1; 1University of Michigan
Aluminum solid state welding occurs when intimate contact is achieved between substrates on the two sides of the interface. This contact requires the fragmentation of any intervening surface films. The fragmentation determines the threshold deformation needed to initiate welding and the final exposed area of the substrate, which determines the strength of the weld. Previous work has tended to focus on plane strain conditions but solid state welds may form under more complex stress conditions as found between billets in extrusion. In this talk, we explore the fragmentation and subsequent weld strength of aluminum bonded samples under varying surface conditions (e.g., roughness and lubricity) and deformation conditions. Experiments are conducted using accumulative asymmetric rolling of novel plate geometries to induce combinations of shear and in-plane compressive stress at the interface. Shear tests then determine the weld strengths and identical experiments on anodized samples are used to explore the oxide fragmentation.
Oscillation-free Determination of Material Properties at High Strain Rate: Xiangfan Fang1; 1Inistitute of Automotive Light Weight Design
The determination of plastic deformation properties of materials under high speed loading is a challenge. The system ringing in a conventional servo-hydraulic tensile machine deteriorates the quality of force measurement. A precise determination of the plasticity and damage is thus difficult. In this work, the system ringing effect of the entire test system incl. machine, sample etc. were analyzed. We found out that the system ringing is location and geometry dependent. Inspired by the principle of the SHPB a new type of tensile sample has been developed. In a certain restricted area of this new sample, the tensile forces can be measured without any ringing effect. The plastic deformation and damage behavior can be determined using this type of specimen for a wide range of strain rate of 0.0001 - 1000 /s. To explain the functionality of the sample and the sample design, a physical model has been developed.
Influence of Forming Conditions on Metal Flow and Lubrication in Cold Backward-cup Extrusion: Kazuhiko Kitamura1; Kazuhito Asai2; Takaji Mizuno1; 1Nagoya Institute of Technology; 2National Institute of Technology, Toyota College
Backward-cup extrusion has hard lubrication conditions such as high pressure, elevating temperature, and large surface expansion. This study focuses on the relationship between the surface expansions and forming conditions is experimentally measured. According to the main results, the minimum surface expansion ratio appears at the extrusion ratio of 3 to 4, and the punch nose without sharpness and roundness helps to inhibit the increase in the surface expansion. These evidences will be valuable to design the process conditions and the punch shape.
A Contact and Friction Model for Forming of Galvanized Steel Sheet Based on Fractal Theory: Yao Huang1; Leigang Wang1; Mingxiao Shi2; Xiang Ma3; 1Jiangsu University; 2Jiangsu University of Science and Technology; 3SINTEF Industry
Galvanized steel sheets are increasingly used in automotive industry due to excellent corrosion resistance, sufficient weldability and formability. During sheet forming of galvanized metals, material failures such as exfoliation and cracking can be found in the zinc coated layers of the sheet under severe friction. Thus, the evaluation of the influences of surface topography, pressure and lubrication on friction could provide valuable guidance in forming of galvanized metals. A hot-dip galvannealed sheet and a hot-dip galvanized sheet are chosen in this tribology study. The surface topographies of the materials are measured using profile meter and the fractal parameters are calculated using the fractal theory. The contact model between the sheet and the die is established using the real contact area. The friction model concerning the surface topography of galvanized sheet and the pressure is thus formulated. The friction coefficients of the theoretical values are in reasonable agreement with the experimental.