Dry Metal Shaping and Forming

In view of the 2 degree temperature target for climate change, sustainable manufacturing processes are playing an increasingly important role. There are different routes to achieve the goal. Besides the change to renewable energies, which are neutral in terms of CO2 emissions, energy saving is promising. Currently, in all areas of metal forming, lubricants are applied to reduce friction between work pieces and forming tools aiming at reducing tool load and tool wear and protecting goods against corrosion. These, mostly mineral oilbased, lubricants have to be produced, applied before, and in general removed after the forming process as well as be recycled at the end or in between the process chain. Doing without or reducing the quantity of the lubricants used has a big energy saving and environmental protecting effect. In 2014, a program named ‘‘Dry Metal Forming’’ was launched by the German Research Foundation aiming at new approaches in carrying out forming processes, in which the work piece leaves the forming tool with comparable forming results but without the necessity of cleaning or drying before the subsequent production steps. This special issue gives information about different research topics within this program. Approaches for dry sheet and bulk cold metal forming processes are:

In view of the 2 degree temperature target for climate change, sustainable manufacturing processes are playing an increasingly important role. There are different routes to achieve the goal. Besides the change to renewable energies, which are neutral in terms of CO 2 emissions, energy saving is promising. Currently, in all areas of metal forming, lubricants are applied to reduce friction between work pieces and forming tools aiming at reducing tool load and tool wear and protecting goods against corrosion. These, mostly mineral oilbased, lubricants have to be produced, applied before, and in general removed after the forming process as well as be recycled at the end or in between the process chain. Doing without or reducing the quantity of the lubricants used has a big energy saving and environmental protecting effect.
In 2014, a program named ''Dry Metal Forming'' was launched by the German Research Foundation aiming at new approaches in carrying out forming processes, in which the work piece leaves the forming tool with comparable forming results but without the necessity of cleaning or drying before the subsequent production steps. This special issue gives information about different research topics within this program.
Approaches for dry sheet and bulk cold metal forming processes are: Tool coatings with special microstructures or very low roughness Tool materials with advanced composition produced by additive processing Macroscopic tool structures changing the forming conditions and in turn reducing the forming forces Microstructuring the work piece Introduction of gaseous substances as the lubricant between the tool and the work piece Use of electrical currents to reduce adhesion.
They are introduced in the following seven papers.
The first paper, by Ditsche and Seefeld, deals with the fusion of tungsten carbide in a metal matrixcomposed tool surface using, in the first step, laser melt injection technology to place hard particles in the melt pool of a copper-based matrix before fusioning single spots by local laser particle fusion to produce local nuggets giving improved wear resistance.
Prieske introduces the meaningfulness of the peak material volume of polycrystalline CVD diamond coatings on dry friction by oscillating ball-on-plate tests under defined climate conditions, and their long-and short-term behavior. The wear rates were calculated and the detection of diamond and graphite was carried out using micro-Raman spectroscopy. As a result, the coefficient of friction as well as the wear rate of the aluminum counter-body can be estimated using the peak material volume. The lower the value, the lower the coefficient of friction.
The use of DLC coatings and their advantages for processing of aluminum sheets by deep drawing is presented in the following two papers, where Abraham et al. introduce the development of optimal coatings for use in dry metal forming by deep drawing, and Flegler et al. use them to produce real parts and to simulate the friction behavior using strip drawing tests. Polishing the sheets and using a-C:H-coated tools without further surface treatment, both dry friction and wear are reduced, but, compared to the experiments with smoothened a-C:H coatings, the necessary process forces are higher and might lead to an earlier rupture of the work piece.
The fifth paper, by Henn et al., focuses on the use of volatile lubricants (CO 2 and N 2 ) injected between the tool and the work piece by laser-drilled, flowoptimized microholes in the tool for deep drawing processes. The areas of microhole laser-drilling by ultrashort pulsed laser radiation, the characterization of the novel tribological system, and the realization of the system by means of a prototype tool are described. Friction conditions dependent on the number and arrangement, as well as on the pressure and flow-rate conditions, were analyzed Ó 2020 The Author(s), corrected publication 2021 using a newly developed testing rig. It could be identified that the best results (lowest friction) could be achieved using non-structured surfaces.
Welm et al. enter a completely different field, investigating the thermo-electrical effect (Seebeck effect) on adhesive wear reduction during blanking. The combination of the materials (tool and work piece) strongly influences the occurring thermoelectric current affecting the adhesive wear. Blanking experiments with aluminum EN AW 5083 were performed, measuring both the thermoelectric currents and the amount of adhesive wear. A variation of the tool material (high-speed steel 1.3343, stainless steel 1.4301, and cemented carbide CF-H40S) confirms the strong relationship between Seebeck coefficients, thermoelectric currents, and tool wear.
Finally, Schöler et al. use oxide layers on tool steel surfaces by selective oxidation under an inert gas atmosphere to improve the abrasive wear behavior. It turned out that tool surfaces containing larger near-surface chromium carbides are not suitable for dry sliding wear. Optimized heat treatment strategies resulted in smaller chromium carbides, which could be selectively oxidized. A FEM model was developed to calculate tool life and local layer removal as a function of the surface pressure.
To download any of these papers, follow the URL https://link.springer.com/journal/11837/72/7/page/1 to the table of contents page for the July 2020 issue (vol. 72, no. 7).

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