scholarly journals A Constitutive Friction Law for Sheet-Bulk Metal Forming

2016 ◽  
Vol 11 (5) ◽  
pp. 614-622 ◽  
Author(s):  
Florian Beyer ◽  
Kai Willner
Keyword(s):  
Metal Forming ◽  
Bulk Metal ◽  
Friction Law ◽  
Bulk Metal Forming

Development of a Friction Law Respecting Plastic Surface Smoothing

2013 ◽  
Vol 554-557 ◽  
pp. 1471-1477 ◽  
Author(s):  
Franz Hauer ◽  
Kai Willner
Keyword(s):  
Surface Pressure ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Surface Deformation ◽  
Surface Smoothing ◽  
Bulk Metal ◽  
Friction Law ◽  
Bulk Metal Forming ◽  
Plastic Surface ◽  
Contact Pressures

Friction has an essential influence on metal forming processes and affects the mould filling strongly. Numerical simulation is widely used because they allow for a efficient product design without the time and cost intensive production of prototype moulds. The quality of the simulation results and thus their reliability is determined by the accuracy of the modelling. For this purpose the applied friction law is of great importance. Characteristic of sheet-bulk metal forming is the coexistence of moderate contact pressures like in sheet metal forming and high contact pressures like in bulk metal forming. The Coulomb friction law is suitable for the sheet metal forming process but it predicts too high friction forces for high contact pressures. On the other hand the Tresca friction law is suitable for bulk metal forming but overestimates the friction for low contact pressures. A smooth transition between the Coulomb and Tresca friction law is described by the Shaw friction law and the Wanheim-Bay friction law. An unresolved problem remains the influence of plastic surface smoothing of structured workpiece surfaces. The tribological properties of the surface are altered by the plastic deformation of the surface roughness. As a consequence the real area of contact and thus the friction are larger in unloading and reloading than in the first loading at the same surface pressure. This plays a role in forming processes with multiple stages, where the surface is smoothed by prior forming operations like for example the forming of tailored blanks. Therefore efforts have been made in the numerical modelling of elasto-plastic surface deformation with a halfspace model. This model allows for the efficient modelling of large rough surfaces because it uses only a surface mesh and not an numerically expensive volume mesh like a Finite-Element model. This halfspace model is calibrated and verified with experimental investigations. A friction law taking into account the plastic surface deformation has been developed based on the halfspace simulations. It distinguishes between first loading, where the current surface pressure is higher than all surface pressures which occurred previously, and unloading or reloading, where the friction is higher because the surface is smoothed plastically in a previous load step, where the surface pressure was higher than currently.

Experimental and Simulative Investigations of Tribology in Sheet-Bulk Metal Forming

2015 ◽  
Vol 639 ◽  
pp. 283-290 ◽  
Author(s):  
Florian Beyer ◽  
Heribert Blum ◽  
Dustin Kumor ◽  
Andreas Rademacher ◽  
Kai Willner ◽  
...  
Keyword(s):  
Finite Element ◽  
Half Space ◽  
Metal Forming ◽  
Rough Surfaces ◽  
Bulk Metal ◽  
Friction Law ◽  
Space Model ◽  
Bulk Metal Forming ◽  
Discretisation Error ◽  
The Law

Friction has a considerable influence in metal forming both in economic and technical terms. This is especially true for sheet-bulk metal forming (SBMF). The contact pressure that occurs here can be low making Coulomb’s friction law advisable, but also very high so that Tresca’s friction law is preferable. By means of an elasto-plastic half-space model rough surfaces have been investigated, which are deformed in such contact states. The elasto-plastic half-space model has been verified and calibrated experimentally. The result is the development of a constitutive friction law, which can reproduce the frictional interactions for both low and high contact pressures. In addition, the law gives conclusion regarding plastic smoothening of rough surfaces. The law is implemented in the framework of the Finite-Element-Method. However, compared to usual friction relations the tribological interplay presented here comes with the disadvantage of rising numerical effort. In order to minimise this drawback, a model adaptive finite-element-simulation is performed additionally. In this approach, contact regions are identified, where a conventional friction law is applicable, where the newly developed constitutive friction law should be used, or where frictional effects are negligible. The corresponding goal-oriented indicators are derived based on the “dual-weighted-residual” (DWR) method taking into account both the model and the discretisation error. This leads to an efficient simulation that applies the necessary friction law in dependence of contact complexity.

scholarly journals Development of a numerical compensation framework for geometrical deviations in bulk metal forming exploiting a surrogate model and computed compatible stresses

2021 ◽  
Author(s):  
Lorenzo Scandola ◽  
Christoph Büdenbender ◽  
Michael Till ◽  
Daniel Maier ◽  
Michael Ott ◽  
...  
Keyword(s):  
Finite Element ◽  
Surrogate Model ◽  
Metal Forming ◽  
Computer Aided Design ◽  
Transition Process ◽  
Reference Points ◽  
Compensation Method ◽  
Tool Geometry ◽  
Bulk Metal ◽  
Bulk Metal Forming

AbstractThe optimal design of the tools in bulk metal forming is a crucial task in the early design phase and greatly affects the final accuracy of the parts. The process of tool geometry assessment is resource- and time-consuming, as it consists of experience-based procedures. In this paper, a compensation method is developed with the aim to reduce geometrical deviations in hot forged parts. In order to simplify the transition process between the discrete finite-element (FE) mesh and the computer-aided-design (CAD) geometry, a strategy featuring an equivalent surrogate model is proposed. The deviations are evaluated on a reduced set of reference points on the nominal geometry and transferred to the FE nodes. The compensation approach represents a modification of the displacement-compatible spring-forward method (DC-SF), which consists of two elastic FE analyses. The compatible stress originating the deviations is estimated and subsequently applied to the original nominal geometry. After stress relaxation, an updated nominal geometry of the part is obtained, whose surfaces represent the compensated tools. The compensation method is verified by means of finite element simulations and the robustness of the algorithm is demonstrated with an additional test geometry. Finally, the compensation strategy is validated experimentally.

Fundamental investigations on the material flow at combined sheet and bulk metal forming processes

CIRP Annals ◽  
2011 ◽  
Vol 60 (1) ◽  
pp. 283-286 ◽  
Author(s):  
M. Merklein ◽  
J. Koch ◽  
S. Opel ◽  
T. Schneider
Keyword(s):  
Metal Forming ◽  
Material Flow ◽  
Bulk Metal ◽  
Bulk Metal Forming

Amorphous Carbon Coatings for Locally Adjusted Tribological Properties in Sheet Bulk Metal Forming

2012 ◽  
Vol 504-506 ◽  
pp. 969-974 ◽  
Author(s):  
Harald Hetzner ◽  
Stephan Tremmel ◽  
Sandro Wartzack
Keyword(s):  
Amorphous Carbon ◽  
Tribological Properties ◽  
Metal Forming ◽  
Friction And Wear ◽  
Wear Properties ◽  
Carbon Coatings ◽  
Bulk Metal ◽  
Bulk Metal Forming ◽  
Friction And Wear Properties ◽  
Amorphous Carbon Coatings

In sheet bulk metal forming, locally adapted friction properties of the contact tool/workpiece are an appropriate means for the targeted enhancement of the material flow, enabling an improved form filling and lowered forming forces. However, the implementation of desirable friction conditions is not trivial. And further, friction is inseparably linked to wear and damage of the contacting surfaces. This calls for a methodological approach in order to consider tribology as a whole already in the early phases of process layout, so that tribological measures which allow fulfilling the requirements concerning local friction and wear properties of the tool surfaces, can already be selected during the conceptual design of the forming tools. Thin tribological coatings are an effective way of improving the friction and wear properties of functional surfaces. Metal-modified amorphous carbon coatings, which are still rather new to the field of metal forming, allow tackling friction and wear simultaneously. Unlike many other types of amorphous carbon, they have the mechanical toughness to be used in sheet bulk metal forming, and at the same time their friction properties can be varied over wide ranges by proper choice of the deposition parameters. Based on concrete research results, the mechanical, structural and special tribological properties of tungsten-modified hydrogenated amorphous carbon coatings (a-C:H:W) are presented and discussed against the background of the tribological requirements of a typical sheet bulk metal forming process.

scholarly journals Development of a Constitutive Model for Friction in Bulk Metal Forming

Lubricants ◽  
2018 ◽  
Vol 6 (2) ◽  
pp. 42 ◽  
Author(s):  
Marco Lüchinger ◽  
Igor Velkavrh ◽  
Kerstin Kern ◽  
Michael Baumgartner ◽  
Stefan Klien ◽  
...  
Keyword(s):  
Constitutive Model ◽  
Metal Forming ◽  
Bulk Metal ◽  
Bulk Metal Forming

Numerical and Experimental Investigations of Multistage Sheet-Bulk Metal Forming Process with Compound Press Tools

2015 ◽  
Vol 651-653 ◽  
pp. 1153-1158 ◽  
Author(s):  
Bernd Arno Behrens ◽  
Anas Bouguecha ◽  
Milan Vucetic ◽  
Sven Hübner ◽  
Daniel Rosenbusch ◽  
...  
Keyword(s):  
Metal Forming ◽  
Solid Metal ◽  
Experimental Investigations ◽  
Metal Component ◽  
Forming Process ◽  
Bulk Metal ◽  
Bulk Metal Forming ◽  
Process Sequence ◽  
Metal Forming Process ◽  
Flange Forming

Sheet-bulk metal forming is a manufacturing technology, which allows to produce a solid metal component out of a flat sheet. This paper focuses on numerical and experimental investigations of a new multistage forming process with compound press tools. The complete process sequence for the production of this solid metal component consists of three forming stages, which include a total of six production techniques. The first forming stage includes deep drawing, simultaneous cutting and following wall upsetting. In the second forming stage, flange forming combined with cup bottom ironing takes place. In the last stage of the process sequence, the component is sized. To investigate and to improve process parameters such as plastic strain distribution, resulting dimensions and process forces, FEA is performed. Based on these results the developed process is designed.

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