Requirements and Constraints for a Robotized Roll Hemming Solution
The objective of this study is the design of a new roller hemming tool. For this purpose, main parameters affecting the final quality of the rolled hemmed part have been studied in order to identify and outline the key factors in roller design as well as in roller hemming process stages. A preliminary set of experiments has been carried out to study the pre-hemming force and springback relation in an aluminium sheet. Experiments showed the required forces in first pre-hemming stage and allowed to calculate a stiffness coefficient based on the springback deformation angle.
Influence of prestrain on the numerical simulation of the roller hemming process
Abstract This study focuses on the numerical simulation of roller hemming of an aluminium alloy sample with a curved geometry; this non-planar geometry is obtained by a prestrain procedure similar to deep drawing process. Material characterization was performed through tensile and simple shear tests at different orientations on the sheet plane. The influence of considering the Bauschinger effect, anisotropy, and the strain history on the final geometry was studied. A specific laboratory device for roller hemming was designed to forward an experimental database. The numerical simulation of the roller hemming of these samples is presented here, as well as the correlation between the calculations and the experimental tests, notably the roll-in value and the prediction of wrinkling.
Failure analysis for poor solderability of Au surface of PCB
Nonwetting is one of the common problems and is always rejected in electronic assemblies. ENIG pads of a PCBA exhibited nonwetting after lead-free reflow soldering. With the aid of stereomicroscope, SEM&EDS and XRF, a series of analysis was performed. And after visual inspection, surface and cross section analysis, thickness measurement and solderability test, it can be inferred that oxidation of plating surface was the main reason for nonwetting, and corrosion in Ni plating caused an adverse impact on solderalibity.