Effects of ultrasonic surface rolling process on tribological behavior of 4Cr13 stainless steel

Ultrasonic surface rolling (USR) process is a novel surface strengthening technique based on the tool head's high-frequency impact on the workpiece. USR can cause severe plastic deformation on the superficial surface of metal material, and greatly improving the mechanical properties of the material. This paper elucidates the effects of USR passes on the surface roughness, sample height, microstructure, microhardness, residual stress, and tribological properties of 4Cr13 stainless steel. The results revealed that multiple USR treatments refined the near-surface layer grain of the sample. Compared with untreated sample, USR treatments significantly improved the surface roughness and microhardness of the samples. Obvious compressive residual stress and plastic deformed with a maximum value of about -723 MPa and a depth of about 229 μm were also introduced into the sample surface. Under a dry friction environment, the samples that underwent the USR treatments exhibited significantly enhanced wear resistance, and six rolling passes were found to be the most suitable treatment.

Analysis of 3D Plastic Deformation in Vertical Rolling Based on Global Weighted Velocity Field

Energy method is an essential theoretical approach to analyze plastic forming, which is widely used in rolling. An analysis model for vertical rolling process is established according to energy theory. By using global weighted method firstly, the 3D continuous velocity field, strain rate field and the corresponding power functional are proposed. The unknown variables are solved numerically based on the principle of minimum energy. Then, deformation parameters and rolling force are determined. The analysis on specific examples with the width reduction rate of 0.03~0.05 shows that the theoretical prediction value of weighted model is in good agreement with experimental results. Moreover, the effects of several shape and rolling parameters on rolling force, rolling power and edge deformation are studied. Both the width reduction rate and initial slab thickness have significant influences on dog-bone size and rolling force. A wider slab slightly increases the nonuniformity of dog-bone deformation. An increase of vertical roller radius can weaken the edge deformation.

Overlapping optimization of hybrid deposited and micro-rolling additive manufacturing

Purpose This paper aims to summarize the influence law of hybrid deposited and micro-rolling (HDMR) technology on the bead morphology and overlapping coefficient. A better bead topology positively supports the overlapping deposited in multi-beads between layers while actively assisting the subsequent layer's deposition in the wire and arc additive manufacturing (WAAM). Hybrid-deposited and micro-rolling (HDMR) additive manufacturing (AM) technology can smooth the weld bead for improved surface quality. However, the micro-rolling process will change the weld bead profile fitting curve to affect the overlapping coefficient. Design/methodology/approach Weld bead contours for WAAM and HDMR were extracted using line lasers. A comparison of bead profile curves was conducted to determine the influence law of micro-zone rolling on the welding bead contour and fitting curve. Aiming at the optimized overlapping coefficient of weld bead in HDMR AM, the optimal HDMR overlapping coefficient curve was proposed which varies with the reduction based on the best surface flatness. The mathematical model for overlapping in HDMR was checked by comparing the HDMR weld bead contours under different rolling reductions. Findings A fitting function of the bead forming by HDMR AM was proposed based on the law of conservation of mass. The change rule of the HDMR weld bead overlapping spacing with the degree of weld bead rolling reduction was generated using the flat-top transition calculation for this model. Considering the damming-up impact of the first bead, the overlapping coefficient was examined for its effect on layer surface flatness. Originality/value Using the predicted overlapping model, the optimal overlapping coefficients for different rolling reductions can be achieved without experiments. These conclusions can encourage the development of HDMR technology.

Improvement of the coiling stress calculation model for a mandrel-sleeve-coil

The steel rolling process employs a coiling-uncoiling process in which a steel sheet is wound and unwound in a coil shape using a coiler to efficiently produce a long steel sheet with a constant thickness. As front and rear tension is required when the steel sheet enters and exits the rolling mill, the coiler introduces tension in the steel sheet through the control of the rotational speed. As the coil is produced, coiling tension accumulates, and pressure is applied to the inside of the coil. Finite element analysis and stress calculation analysis were derived from previous studies to prevent such pressure increases in the sleeves and coils. However, the radial and circumferential stresses at arbitrary positions inside the coil cannot be accurately determined by considering without the stresses’ difference in the thickness direction based on the assumption that the coil’s thickness is thin. In this study, an analytical model that can accurately calculate the sleeve and coil stress during elastic deformation was established by improving the internal circumferential stress generated when the steel sheet is bent into a coil and the radial stress equation associated with the beam bending theory. In addition, by comparing the finite element analysis model results reflecting the same coiling condition, this model’s validity was verified by confirming the consistency of the results.

NUMERICAL SIMULATION OF ECCENTRICITY CREATION IN THE PRODUCTION OF HOT ROLLED TUBES

The paper deals with the issue of eccentricity in the technological node of the piercing press, under selected conditions, which result from the possibilities of production in the conditions of ŽP a.s. These conditions were verified and adapted to the rolling process. This process consisting of individual technological nodes on the rolling mill, in which eccentricity is created on the piercing press and the following steps eliminate it in other technological nodes. For quality analysis of manufacturing tubes using numerical simulation, it is necessary to know the actual state of eccentricity creation on the rolling mill. A numerical simulation of piercing under different input conditions was used (software DEFORM-3D) and was performed for several different charge states before entering onto the piercing press. The eccentricity itself has a significant effect on the resulting geometric quality of the tubes.