Application of laser shock in micro-shear riveting of metal foil

Update:16-08-2019
Summary:

Clinching or press-joining is a bulk-sheet metal-formin […]

Clinching or press-joining is a bulk-sheet metal-forming process that joins thin metal sheet without additional component. The process is used primarily in the automotive, appliance and electronics industries as an alternative to spot welding. Moreover, increasing development of small devices has led to high demand for joining processes for various lightweight metal foils in the micro dimension. However, the use of conventional mechanical clinching process is not feasible for foils in micro dimension.

The laser shock forming process is a non-contact loading technology and a potential option for plastic deformation in the micro field. However, a material removal process is required in micro mechanical joining by laser shock forming.Now, a team of researchers from Jiangsu University assessed joint deformation process to enhance fundamentals of micro-shear clinching. Micro-shear clinching by laser shock consists of a focused laser, blank holder, confinement layer, ablative layer, soft punch, upper foil, lower foil, shearing mold, spacer, and mold substrate. The process can be divided into three stages drawing and shearing; flattening; and  re-striking and fitting.

The team used two types of metal foils pure aluminum foil and pure T2 copper foil . The team found that laser pulse in Stage 1 offers major contribution of the two foils.The formation area of preliminary joint narrows and the three dimensions gradually decrease when soft punch thickness is increased from 100 to 300 μm. The soft punch thickness of 100 μm can enhance the use of each laser pulse to maximize deformation. All four kinds of soft punches can cause sheared parts to separate from raw foils.

Two laser pulses on the upper foil side can induce the sufficient joint formation and ensure process efficiency. The team found that perpendicular shear strength was higher than parallel shear strength of different combinations. Moreover, a larger loading stiffness was also observed. The team observed one failure mode in the parallel shear test and four failure modes in the perpendicular shear test of the micro-shear clinching of  combinations. 

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