Design and technological capabilities of a CNC skew rolling mill

Results of a study investigating a skew rolling process for elongated axisymmetric parts are presented. Despite the fact that the skew rolling technique for producing such parts was developed and implemented in the mid-twentieth century, there are no studies on this problem. The first part of this paper presents the results of FEM modelling of skew rolling stepped axles and shafts (solid and hollow). The FEM analysis was performed using the MSC Simufact Forming software. The numerical simulation involved the determination of metal flow patterns, the analysis of thermal parameters of the material during rolling, and the prediction of cracking by the Cockcroft-Latham ductile fracture criterion. Force parameters of rolling solid and hollow parts were also determined. The aim of the FEM analysis was to determine initial design assumptions and parameters for the development of the skew rolling mill. Later on in the paper, a design solution of a CNC skew rolling mill for rolling parts based on their envelope profile is proposed. FEM strength test results of a mill stand, obtained with MSC. NASTRAN, are presented. Finally, the performance test results of the constructed rolling mill are presented. The experiments involved rolling real stepped shafts that were modelled numerically. Obtained results show that the proposed skew rolling method has considerable potential. The designed and constructed rolling mill can be used to perform the rolling process according to the proposed method, with the tool and material kinematics being controlled based on the set parameters of a workpiece envelope.

Development of Digital Control Algorithms for the Mechatronics System Drives of Reversing Plate Mill Stands

Expanding the plate mill product range implies the improvement of control algorithms for the mechatronics control system drives of the reversing stands. The most important objectives include increasing the accuracy of geometric dimensioning and tolerancing, as well as improving the profile and surface flatness of rolled pro­ducts. The structure explaining the automatic ROLL-GAP CONTROL concept is provided, which allows controlling the thickness and gap between SMS-Demag AG rolls. This concept is implemented in the '5000' mill stand of Magnitogorsk Iron and Steel Works. The structural diagram of the automatic gauge control system (AGS) is presented. The functional diagram of the hydraulic gap control (HGC) system is presented, which includes a fast proportional control channel and a relatively slow integral position control channel. The principle of automatic thickness control is discussed, implemented in the automatic gauge control (AGC) system of the mill stand TCS controller. The diagram and dependences are prepared for the calculation of the nonlinear thickness controller parameters. The functions of the RAC regulator are described, intended for compensation of the tensile difference (gap spacing) at the mill stand sides. The dynamic impact compensation system functions are considered. The removal of the roll bending and deformation control signals is substantiated. The disadvantages of AGC are noted for sheets with a thickness below 10 mm. The most dangerous case is the tearing of metal fragments from the rear sheet side caused by the incorrect operation of the gauge control system. A method for hydraulic gap control is proposed based on the fast increase of the roll gap in the rear part of the rolled sheet during the last passage when rolling thin sheets. The results of experimental studies made on the '5000' mill are presented. The efficiency of the proposed control method has been confirmed. The oscillograms of signals are presented characterizing thickness variations. HGC and AGC systems with the proposed adjustments are proven to provide high-accuracy hydraulic position control and thickness control along the sheet length and width.

Estimation of reliability of the TPA 350 mill working stand housing after a long operation

Among the processes, taking place at the shells rolling at automatic mill, the least studied are a working stand housing behavior, which becomes apparent in the form of its dynamic shifting. It can be explained by the fact, that the shell interacting with the rollers and the mandrel is effected by rod mechanism of the mandrel holding at the rolling axis. The possibility of the non-controlled deformed state can be explained also by deviation from the regulation state of anchor bolts fastening system and various defects in the stand housing. It made a foundation to accomplish monitoring of the space state of the TPA 350 automatic mill stand, resulted in registration of the working stand housing stress-deformed state. Besides, it resulted in a task formulation for elaboration of the stand space model aimed at its application for the justification of the strategy of the TPA 350 mill further operation. Results of the study of stress-deformed state of the working stand housing of the TPA 350 automatic mill presented. The study was carried out by the method of finished elements at 3D models. Comprising of the obtained theoretical data with experiment studies of the housing tension confirmed the model adequateness. It was determined, that maximal stresses originate in the zones of the revealed cracks of the working stand housing. The locations of the maximal stresses concentration “migrate” at variation of fastening conditions and the stand housing loading. A function of risk obtained for the stage of a crack originating and for the stage of defect development in the housing. The automatic mill housing safety was exhausted after 50 years of operation. Currently the automatic mill housing operates in the zone of complete risk, accompanying by cracks formation. For the mixed mechanism of crushing, the periods of round defect development in the TPA 350 automatic mill housing determined.