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 in Profile Envelope Process of Form Cutter for Involute Gear and its Movement Control
In profile envelope process of form cutter for involute gear, the grinding depth is variable which causes grinding force to change on a large scale and the profile error of 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 is used to adjust parameters online. By measuring grinding force, characteristic information of grinding process is acquired. Regulation factor of feed rate is determined by grinding force ratio, force deviation and its change rate 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.
Neutron Residual Stress Measurements on Rail Sections for Different Production Conditions
Rail sectioning with subsequent neutron diffraction experiments has been used to assess residual stresses in the rails. In this study we present the results of neutron stress measurements performed at the NIST Center for Neutron Research (NCNR) on rail sections from rails that were produced under various conditions. Specifically, these are air-cooled, air-cooled and roller-straightened, head-hardened and head-hardened and roller-straightened. More significantly, a head-hardened and roller-straightened rail was also studied after service to elucidate evolution of the service-induced residual stresses. In the latter case both a transverse-cut slice and the central region of a 0.53 m long piece were studied. Measurements on this piece are the first in which triaxial stresses have been determined for an intact rail. Neutron strain measurements with 3×3×3 mm3 spatial resolution were successfully employed for transversally cut slices to verify the difference in the stress state depending on the production process. Although examination of slices allows determination of only two-dimensional stresses in the plane of the slice, additional measurements on obliquely-cut slices, which were also carried out, and utilization of FEM gives the possibility of reconstructing the full triaxial stress distribution. Together, these approaches provide a better understanding of rail fabrication and the possibility of improving the durability and safety of rails in the future.Copyright © 2004 by ASME