Numerical and Experimental Study on Constrained Groove Pressing

Constrained groove pressing (CGP) is a new severe plastic deformation method suitable for producing ultra-fine grained sheet metals. Based on Taguchi optimization method, the influence of processing parameters such as groove width, groove angle, friction coefficient and deformation rate on deformation homogeneity of constrained groove pressing (CGP) was studied numerically utilizing DEFORM-3D. A multi-pass CGP was carried out on 1060 commercially pure aluminium, copper and Ni sheets. Through a series of experimental research, the evolution of microstructure, tensile properties, forming load, and die parameters during the process was investigated

A Mandrel Feeding Strategy in Conical Ring Rolling Process

A mathematical model for radial conical ring rolling with a closed die structure on the top and bottom of driven roll, simplified as RCRRCDS, was established. The plastic penetration and biting-in conditions in RCRRCDS process were determined. A mandrel feeding strategy for RCRRCDS process was proposed. The mandrel feed rate and its reasonable value range were deduced. The coupled thermal-mechanical FE model of RCRRCDS process was established. The reasonable value range of the mandrel feed rate was verified by using numerical simulation method. The results indicate that the reasonable value range of the mandrel feed rate is feasible, the proposed mandrel feeding strategy can realize a steady RCRRCDS process, and the forming quality of conical ring rolled by using the proposed feeding strategy is better than that of conical ring rolled by using a constant mandrel feed rate

The Effects of Forming Parameters on Conical Ring Rolling Process

The plastic penetration condition and biting-in condition of a radial conical ring rolling process with a closed die structure on the top and bottom of driven roll, simplified as RCRRCDS, were established. The reasonable value range of mandrel feed rate in rolling process was deduced. A coupled thermomechanical 3D FE model of RCRRCDS process was established. The changing laws of equivalent plastic strain (PEEQ) and temperature distributions with rolling time were investigated. The effects of ring’s outer radius growth rate and rolls sizes on the uniformities of PEEQ and temperature distributions, average rolling force, and average rolling moment were studied. The results indicate that the PEEQ at the inner layer and outer layer of rolled ring are larger than that at the middle layer of ring; the temperatures at the “obtuse angle zone” of ring’s cross-section are higher than those at “acute angle zone”; the temperature at the central part of ring is higher than that at the middle part of ring’s outer surfaces. As the ring’s outer radius growth rate increases at its reasonable value ranges, the uniformities of PEEQ and temperature distributions increase. Finally, the optimal values of the ring’s outer radius growth rate and rolls sizes were obtained

A Feeding Strategy in Inner L-Shape Ring Hot Rolling Process

In order to make the inner L-shape ring polling process with a closed die structure (ILRRCDS) on the top and bottom of the driven roll stable, at first, this paper established the mathematical model for ILRRCDS. Then, the plastic penetration and biting-in conditions for ILRRCDS were deduced based on plain ring rolling theory. Moreover, a feeding strategy that can realize a constant growth of the ring’s outer radius was proposed and the reasonable value ranges of the feed rate of the mandrel were determined. The numerical simulation model for ILRRCDS is established based on ABAQUS software. Finally, the equivalent plastic strain (PEEQ) and temperature distributions of rolled ring were obtained. The results indicated that the proposed feeding strategy can realize a stable ILRRCDS. At the end of ILRRCDS, the PEEQ at the inner radius surface of the ring is maximum, the PEEQ at the outer radius surface of the ring takes the second place, and the PEEQ at the middle part of ring is minimum. With the increase of rolling time, the higher temperature zone of the rolled ring gradually moves from the center part of the ring to the “inner corner zone” of the ring

The Fracture Behavior and Thermal Stability of Commercially Pure Nickel Sheets Processed by Constrained Groove Pressing

Constrained groove pressing (CGP) is one of the most promising severe plastic deformation (SPD) techniques suitable for producing ultra-fine grained (UFG) sheet or plane metallic materials with unique physical, chemical, and mechanical properties. However, the heavily deformed sheets are usually with high strength but low ductility due to work hardening and micro-cracking, and the UFG microstructure and high strength are unstable especially when exposed to high temperatures. Thus, in this work, CGP was conducted on commercially pure nickel sheets and, firstly, the fracture mechanism of the processed sheets was examined. Then, the annealing behavior of CGP nickel sheets was investigated in detail to explore their thermal stability and improve their ductility. The results showed that significant grain refinement and strength improvement of the nickel sheets were achieved with great loss of ductility. The fracture surface morphology of the sheet sample exhibited typical characteristics of fatigue fracture, and inhomogeneous strain distribution and work hardening determined the micro-crack initiation position and propagation direction. The CGP sheets by one and two passes showed high thermal stability up to 650 and 600 °C, respectively, owing to different stored internal stresses and accumulated energy. In both cases, obvious recovery of elongation to failure from 12.7% and 10.6% to 29.3% and 27.3% were achieved by CGP with post-deformation annealing treatment, respectively, with acceptable drop of strength

Groove pressing and its research progress

In order to systematically study the application of groove pressing in preparing bulk mass ultra-fine grain sheet metal, the fundamental principles, plastic mechanics analysis and classification of groove pressing are introduced, and on the basis of which, the influence rules and mechanism of processing factors such as pass number, deformation temperature and die structure on groove pressing are reviewed, and some key problems such as thermal stability of processed materials, process improvements and deformation path, deformation homogeneity analysis and process optimization are summarized. The research trends of groove pressing in the fields of application to sheet metals difficult to deform at room temperature, improvement of ductility, toughness and formability of processed sheets as well as its plastic deformation mechanism are prospected: in the future, groove pressing will be used for sheet metals which have limited formability but wide industrial applications such as magnesium alloys and titanium alloys, and much attention should be paid to investigation on performance adjustment mechanism and methods for processed sheets and exploration of effective technological measures for preventing cracks; meanwhile, the evolution mechanism of microstructure and properties of groove pressed materials must be systematically and thoroughly revealed

Experimental investigation of pure aluminum sheets processed by constrained groove pressing

121-127Recently, a new severe plastic deformation method named constrained groove pressing (CGP) has been invented for producing ultra-fine grained sheet metals. Here, a multi-pass CGP is carried out on 1060 commercially pure aluminum sheets. Through a series of experimental research, the evolutions of microstructure, tensile properties, forming load and surface residual stress during the process are investigated. The grain size is greatly refined from 29 μm of annealed samples to about 18 μm after pass four. Polygonized and dislocation-free substructures of submicron level with well-defined boundaries is obtained. The ultimate tensile strength and yield strength increase continuously until pass three and then decrease by further deformation. Residual tensile stress is observed on the surface of all pressed samples due to the unique stress-strain state, and it increases dramatically during the first pass. The results show that lubrication reduces the average residual tensile stress and its distribution homogeneity along the longitudinal direction