Numerical simulation of edge effect in plasma arc forming of sheet metal
Edge effect was found in plasma arc forming process of sheet metal, which reduces the forming accuracy of sheet metal seriously. In order to reveal the forming mechanism and forming laws of the edge effect. A numerical model on forming of sheet metal using plasma arc with scanning along a straight line was established and the forming mechanism and forming laws of the edge effect were studied. The results showed that the upper material and the lower material of the edge were produced shrinkage along the scanning path and both shrinkage were different. The size relationship of the two shrinkage determines the direction of edge warp. The difference of the two shrinkage affects the warpage of the edge. In the comprehensive effect of shrinkage and warpage, the non scanning region in the both sides of the scanning path appears bulge or depression. The numerical analysis results were agree well with the experimental results. The conclusions provide a theoretical basis to reduce the effect of the edge effect on the accuracy of the sheet metal forming.
The Experimental Study on Flexible Forming of Sheet Metal Using Plasma Arc
In order to study the laws and mechanisms of plasma arc forming,an experimental investigation was performed with 1Cr18Ni9Ti and Q235 sheet metals scanned forward and backward by moving it with respect to the stationary plasma arc.The experimental results show that the bending angle caused by plasma arc scanning is approximately in proportion to the scanning times;with the heat input increasing and the thickness of sheet metal decreasing the bending angle is sharply increased under the same scanning times.While the heat input is low,the grain in heating area is refined,and its mechanical performance is improved;with the increasing of the heat input,the residual strain-hardening in the heating area becomes reinforced,which causes the micro hardness to be increased.The plasma arc forming can also decrease the residual stresses caused in the mechanical processes,which can be of great significance in preventing rebounding.
Traceability strategy for gear-pitch-measuring instruments: development and calibration of a multiball artifact
There is a strong demand to ensure the traceability of gear-measuring instruments (GMIs). We propose a multiball artifact (MBA) for the evaluation of pitch-measuring accuracy. The aim of the MBA is to transfer the minimum uncertainty from a calibrated value at the National Metrology Institute of Japan (NMIJ) to a measured value of GMIs at a shop floor. The MBA is composed of equally spaced high-accuracy balls around an axis. The pitch-measuring accuracy of GMIs is evaluated by measuring the angular pitch deviation of the balls instead of the angular pitch deviation of a gear. We calibrated the angular pitch deviation using a coordinate measuring instrument (CMM) at the NMIJ and adapting a multiple-orientation technique. We proposed a calibration strategy of the angular pitch deviation. The calibration value of the pitch deviation for the MBA at the NMIJ was obtained with a measurement uncertainty (U95) of 0.2 µm. We evaluated the pitch-measuring accuracy of a GMI using the calibrated MBA. Each value of U95 for the cumulative and single pitch deviations for the left and right flanks was less than or equal to 0.5 µm. The small uncertainty was transferred from the NMIJ to the GMI.