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This paper introduces a new formability test based on double-action radial extrusion to characterize material formability in the three-dimensional to plane-stress material flow transitions that are found in bulk metal-formed parts. The presentation draws from a multidirectional tool, which was designed to convert the vertical press stroke into horizontal movement of the compression punches towards each other, aspects of experimental strain determination, fractography, and finite element analysis. Results show that three-dimensional to plane-stress material flow transitions at the radially extruded flanges lead to different modes of fracture (by tension and by shear) that may or may not be preceded by necking, such as in sheet metal forming. The new formability test also reveals adequate characteristics to characterize the failure limits of very ductile wrought and additively manufactured metallic materials, which cannot be easily determined by conventional upset compression tests, and to facilitate the identification of the instant of cracking and of the corresponding fracture strains by combination of the force vs. time evolutions with the in-plane strains obtained from digital image correlation.

The material condition of a workpiece changes as it is formed. Typically, the workpiece hardens and undergoes geometrical and topographical changes. In progressive forming, where workpieces are formed in multiple steps, this means that the workpiece in subsequent steps is different from the as-received material. In this work, strip reduction of an as-received strip and of a pre-strained strip are compared. EN1.4404 stainless steel is pre-strained by bending-under-tension. This leads to changes in the material condition and the surface topography of the strip. Two different coatings are tested in a strip-reduction test to evaluate the effect of these changes to the workpiece state on the tribological performance of the tool coatings. A coating that performed poorly when used to reduce the as-received material exhibited an improved performance when used to reduce the pre-strained material.

Friction in sheet metal forming is largely governed by the flattening of surface asperities. Liquid lubricants can reduce flattening and friction by filling the surface valleys and carry a substantial amount of the pressure. Experimental and numerical work is presented for investigating the influence of the compressibility of the lubricant and the material strength on the deformation of a simple cylinder with an enlarged surface pocket filled with oil. Results show that deformation is not sensitive to differences in compressibility of typical lubrication oils under hydrostatic pressure conditions. This was observed independent of the material strength.

The changes in the automotive market and their effects on industry are nowadays hot topics in metal forming seminars and conferences around the world. The rise in the number of electric vehicles will inevitably lead to a decrease in the demand of components for combustion engines and power drive trains. Typical forming components such as pistons, connecting rods, valves, camshafts, crankshafts, multi-speed gear boxes and others that exist in diesel or petrol vehicles, will no longer be required. However, the lightweight construction requirements for the body-in-white of electric vehicles, the production of components for asynchronous motors and the fabrication of battery components, namely busbars, are bringing new challenges and opportunities for the metal forming industry. This chapter is focused on busbars, which are metallic strips or sheets that are utilized to distribute electric power to multiple equipment such as the electric motor, the electric power steering unit, and the AC/DC converters. In particular, the chapter addresses the challenge of replacing copper busbars by hybrid busbars made from copper and aluminium, due to the expected savings in weight and cost. For this purpose, the authors discuss the challenge of connecting copper to aluminium in hybrid busbars by means of existing joining technologies and introduce a new joining by forming process aimed at connecting hybrid busbars at room temperature without giving rise to material protrusions above and below the sheet surfaces. The effectiveness of the new process is compared against fastening by measuring the electric resistivities in both types of hybrid busbar joints. Finite element analysis gives support to the presentation and proves to be suitable for the electro-thermo-mechanical analysis of busbar connections.

This paper revisits double-sided self-pierce riveting to discuss the applicability limits related to the thickness of the sheets to be used in hidden lap joint connections. Special emphasis is given to thin sheets with thicknesses that are significantly smaller than those earlier reported in the literature. The overall methodology draws from experimental and numerical simulation to aspects related to the working principle of double-sided self-pierce riveting and geometric scalability of the chamfered tubular rivets. Results show that double-sided self-pierce riveting can be successfully applied in thin sheets and must be seen as an alternative to well-established joining processes such as conventional self-pierce riveting and resistance spot welding. In case of the latter, comparisons are made against double-sided self-pierce riveting regarding the force and energy requirements to assemble and destroy the resulting lap joints. Destruction of the joints is performed by means of shear tests and provides the maximum force and energy that both types of lap joints are capable to withstand without failure.

Characterisation of model asperity flattening under longitudinal subsurface elongation is presented with a variety of normal pressure, flank angle and strain hardening behaviour. A systematic investigation outlines an optimal specimen design to ensure a homogenous deformation field in the workpiece under stress-strain conditions, which are typical in sheet metal forming. Asperity flattening increases with normal pressure, and the longitudinal subsurface strain reduces the necessary yield pressure and promotes asperity flattening. When the flank angle is increased, the longitudinal stress component due to elongation gets smaller in the asperity, reducing the effect of longitudinal straining. Strain hardening decreases the asperity flattening rate as strain hardening extends the deformation field further into the underlying material, which results in less asperity flattening.

International audience; “Detachable iron particles” or iron fines due to abrasive interactions in the roll bite between the roll surface and the strip are one of the major cleanliness defects. They may induce surface defects in particular on galvanizing lines. Chrome plating of rolls is generally recognized to result in a better strip surface cleanliness. In the present paper, the reasons for the success of chrome plating in this respect are investigated. An end-of-life industrial roll has been ground by parts under several conditions (Ra = 0.4 μm, 1.0 μm, 1.6 μm ± 0.1 μm), then cut into pieces for observation as well as for manufacturing tribological test tools (Plane Strain Compression Test, PSCT). Some of these pieces have been chrome-plated, the others not for comparison. Careful examination of just ground and chrome-plated roll has revealed that ground surface bears a number of rather aggressive features. Chrome plating covers them with a gentler pattern, although preserving the roughness in terms of Ra to maintain sufficient friction for correct mill operation. PSCT confirms that there is less wear debris on the strip when using Cr-plated tools.