Extrusion Machining Research Articles

Production analysis of new machining-based deformation processes for nanostructured materials.

Nanostructured materials, composed of sub-micron sized grains (crystals), show novel attributes not commonly found in their microcrystalline counterparts. Furthermore, these attributes can be varied by changing the grain size. Nanostructured solids have high hardness, strength and ductility; and interesting electrical and magnetic properties. Superplasticity has been observed at relatively low temperatures in some of these materials [1]. Many new and exciting applications of these materials have been sought; however, the cost of creating these materials, frequently quoted in excess of three hundred euros per kilogram [2], and an inability to make these on a large-scale with reproducible properties have restricted their broad application. We describe new machining-based manufacturing processes for making nanostructured alloys that are likely to be much less expensive. These processes are structured around chip formation by large-strain machining. It has been found that chips of a variety of metals and alloys produced during normal machining operations are composed entirely of nanocrystalline and/or ultrafine grained (UFG) structures of high hardness and strength [3-5]. Furthermore, by imposing a constraint to the chip at the point of its formation, it is feasible to produce nanostructured metals and alloys directly in bulk forms (e.g., sheet, bar, foil); the constrained chip formation process is called large-strain extrusion machining [6].

Mechanical properties of an extruded pyramidal lattice truss sandwich structure

Metallic sandwich structures with lattice topology cellular cores are being developed for weight-sensitive applications. A combination of extrusion and electrodischarge machining has been used to fabricate pyramidal lattice sandwich structures from 6061 aluminum, where the nodes have identical properties to those of the trusses/facesheets. Inelastic buckling dictated the compressive behavior, whereas tensile fracture of the extensionally strained trusses governed the shear response. No nodal failure modes were observed and the compression and shear properties agree well with predictions of micromechanical models.

Friction and wear of nanostructured metals created by large strain extrusion machining

Tribological behavior of nanocrystalline oxygen-free high conductivity (OFHC) copper and commercially pure titanium produced by large strain extrusion machining (LSEM) is compared with the coarse grained counterparts. Friction and wear of these materials have been determined using a pin-on-disk tribometer, sliding against AISI 52100 steel pins. Although friction coefficients are very similar, microstructure refinement reduces wear factors for these conditions. Wear mechanisms are discussed from optical microscopy and SEM observation of wear tracks, wear debris morphology and transfer tribolayers.

Bulk nanostructured materials by large strain extrusion machining

Large strain extrusion machining (LSEM) is presented as a method of severe plastic deformation for the creation of bulk nanostructured materials. This method combines inherent advantages afforded by large strain deformation in chip formation by machining, with simultaneous dimensional control of extrusion in a single step of deformation. Bulk nanostructured materials in the form of foils, plates, and bars of controlled dimensions are shown to result by appropriately controlling the geometric parameters of the deformation in large strain extrusion machining.

Some slip-line fields for swaging or expanding, indenting, extruding and machining for tools with curved dies

Using a known solution for the expanding or swaging of a semi-circular-section hole in a semi-infinite body, attention is drawn to many related problems including that of the squashing of a pointed wedge. These plane strain solutions are then adapted for investigating indentation duo to 2- and 3-plane dies and particular solutions for indenting with curved dies are arrived at. In turn, solutions to indentation are adjusted to accommodate the cases of extrusion and simple machining with a restricted length of cutting edge. Many inverse solutions are presented—a hodograph being assumed and the physical problem it solves, then deduced.