Edge grinding process and edge checking control for screw cutter
In envelope process of cutter, profile and tool-path of cutter are complicated, and the grinding depth is variable which causes grinding force to change on a large scale and the error of edge envelope to increase. To improve cutter accuracy, the theoretical model of cutter edge and theoretical tool-path of CNC tool grinder were calculated. Closed-loop control system was designed to accomplish control of envelope process. By adjusting feed-rate, constant force grinding process is accomplished to improve the precision of edge. The methods of edge design, tool-path calculation and manufacture processing of cutter on CNC tool grinder were discussed. Machining test indicates that cutter error is 8~11μm, and coherence error of sample thickness is reduced to only 3μm, by constant force grinding.
Fuzzy Control of Edge Envelope Process For Screw Milling Cutter
In edge envelope process of milling cutter CAD/CAM, the grinding depth is variable which causes grinding force to change on a large scale and the error of edge envelope to increase. To improve form cutter accuracy, a closed-loop control system was designed to accomplish control of envelope process. For complicated dynamic process, fuzzy controller was used to adjust parameters online. By measuring grinding force, characteristic information of grinding process was acquired. Regulation factor of feed rate is determined by grinding force ratio, and force deviation and its change rate which are used as evaluation indexes. Thus, fuzzy control of constant force grinding process is accomplished. Simulation and cutter grinding test indicates that the system has high precision and stability, and reduces cutter error effectively.
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.