| Metal components tend to large scale and precision with the development of high-speed rail and engineering machinery, so it’s of great importance to improve the precision of the numerical metal bending parts and the precision of bending dies. The applied research focused on the precision bending was conduct related to a series of key technologies of large scale bending.The deflection and convex compensation for the slider and workbench of the large CNC bending machine under working load were studied. The bending process was modeled for analyzing the loading state using Timoshenko beam theory. After analyzing the correlations among shape, size and inertia, the deformation pattern was deduced:the deflection of the crown of the slider and workbench in length direction is proportional to load and the deformation curve of crowning is a quartic equation. The large bending parts cannot keep uniform along the lengthwise direction because of the deformation of bending machine. In order to bring auto compensation of crowning of bending into practice, a brand new crowning compensation machinery device was developed, which used the compensation data achieved from numeral simulation and experiment result, and the mechanism of simultaneous compensation on the corporation of multi-group wedge with different angle was proposed based on the compensation technology of geometric, hydraulic and machinery bending load, because the consistence of angle in length direction might not be guaranteed along with the deformation of bending machinery. The experiment results increased the bending angle of3meters bending part from the middle to both ends increased gradually, and the deviation reached to±1°, and straightness differentials between the endpoints and the midpoint of the bending part reached up to1.28mm, if compensation device was not adopted. With the compensation device, the part precision can be limited to GB standard of level1. Specifically, the straightness error was decreased to0.3mm, and the angle deviation was limited to the range of±25’.The influence of key process parameters to large bending angle was a new die cavity with adjustable opening structure, and a new die cavity with adjustable opening structure was invented, so the stepless adjustment is realizable. Taking the common8mm low carbon high strength plate as research object, the influence of the size of open structure, entrance radius, arc radius and punch distant on the stress, strain, and distribution of residual stress after spring back was conducted by numerical simulation method via analyzing deformation characteristics of bending process. The results showed the spring back angle reduced gradually and the reduced magnitude tends to mild. The influence order on bending angle is arc radius, press quantity, entrance radius and opening size achieved by adopting range analysis and variance analysis method, which was based on25group different tests using orthogonal experiment and numerical simulation technology. With the help of Delphi development platform, a rapid prediction software system of bending angle was developed, which is under the premise of the prediction model obtained by orthogonal test and RSM (response surface method). The immune algorithms and simulated annealing method were introduced into bending angle control. Using the above key process parameter as optical variables and the minimum deviations between bending angle and target angle as objective, forming process of bending employing adjustable die of block inserted type was optimized, and the simulation result coincided with experiment result. In order to adjust the size of open structure, a new adjustable die cavity was developed, and it made the opening size stepless adjustment possible by assembling transmission part, therefore processing magnitude is expanded naturally.In consideration of defect of the traditional treatment process, problem of hardening homogeneity for key part fit strip of bending mould and deformation of holes pitch after quenching were resolved, when equivalent heat capacity method was used to process latent heat of phase change and the FEM simulation and experiment research on cooling procedure of quenching were conduct. The research showed that temperature distribution of fit strip cross section appeared to gradient change from connection of two surfaces to central zone, specifically, it results in big temperature difference (maximum is256.29℃) in its surfaces and central region, because of the leading role in boundary condition of heat transfer to temperature distribution in the last0to15seconds before fit strip entering quenching liquid, however in15to60seconds, leading role of heat transfer in boundary condition was displaced by inner heat transfer, and surface cooling speed is lower than that of the inside, in addition, cooling speed reduce sharply due to the release of latent heat in marten site transformation at65seconds or so. The experiment results indicated that hardening in entire surface of fit strip was steady at57±2HRC, and hardening homogeneity improved compared with that of previous process which was steady at57±4HRC. Length of fit strip stretch to0.52mm, holes pitch in the ends increase by0.42mm after quenching, and it should take redundancy into consideration in holes pitch for long size fit strip. Linearity formula Axi=3.885×10-4x+0.1057(0<x≤4000) of fitting data was achieved for common precision redundancy, and quadratic polynomial formula△x2=-3.819×10-7x2+5.281×10-4x+0.0996(0<x≤4000) for higher precision redundancy.It provides technical assistance for production of high precision large scale bending part while using research findings of the paper, and new crowning compensation device of mechanical and the adjustable opening structure were successfully put to practice production. |
