Flexible stretch-bending of multi-point roller dies technology is a new three-dimensional forming technology for profiles. Compared with the traditional stretch-bending process, the three-dimensional ...deformation of the profile can be formed at one time, and the cost of the die is greatly reduced and the production efficiency is improved. The die is an important component of flexible stretch-bending of multi-point roller dies equipment. Discrete die is the focus of this paper. The finite element model of flexible stretch-bending of multi-point roller dies is established. Taking T-profile and L-profile as research objects, the effect of die arrangement on strain, shape error, thickness distribution, and springback error is studied. The non-contact area between profile and die is one of the important factors that affect the 3D deformation of profile. By comparing the numerical simulation results with the experimental results, the effect of the non-contact area length on the three-dimensional deformation of profile is analyzed. The results show that with the increase of the non-contact area length, the shape error of profile increases, the thickness of profile web becomes thinner more seriously, and the springback error of profile increases after unloading.
It is necessary to fabricate individual dies in conventional hydroforming, to produce different tubular parts. This procedure is costly and time-consuming. Tube multi-point hydroforming is a new ...flexible forming technology which facilitates producing various tubular products by only one die. In this study, a new reconfigurable hydroforming die was designed and fabricated. The main difference of this die with conventional types is substitution of the rigid surface with a set of spaced pins. Different tubular sections could be produced by adjusting the pins position. Due to the low cost of changing the tool into a new die, this process is appropriate for producing small batch numbers of a tubular product. Numerical simulations were employed to determine the effects of pin diameter and polyurethane layer thickness on the characteristics of final products. Increasing the number of pins was found out to improve dimensional accuracy and surface quality. On the other hand, while using a thicker polyurethane layer reduced dimpling, it led to a poor dimensional accuracy. A bulged and a square brass 70/30 tube were produced with an initial thickness of 2 mm. Thereafter, experimental tests were performed to compare distribution of the thickness and variation of dimensions with the numerical results.
Multi-Point Sandwich Forming (MPSF) is a new flexible forming technology. In this process, one half of a conventional die set is substituted by a discrete die with wide spaced pins plus deformable ...die sheet and a polyurethane upper die is used as the other half. FE simulation using this tool design reveals the effect of the shape of the upper die on workpiece deformation and the role played by the deformable interpolator and die sheet. It is shown that the deformed shape is a result not only of the reconfigurable die shape, but of the elastic die shape and elastic interpolator stiffness also. Using an interpolator enables smooth workpiece surfaces to be obtained, even when the die sheet is dimpled by the pins of the reconfigurable die.
To significantly cut the time and cost of tooling development, a reconfigurable discrete die (that is, matrix of individually actuated pins) is being developed for aircraft fuselage parts made by ...forming sheet metal or molding of composite materials. Each pin in the die is a simple hydraulic actuator outfitted with an in-line NC solenoid valve to control its vertical position. Pin positions can either be set in a closed or open-loop fashion. Once the pins are “set,” then the entire matrix is clamped into a rigid tool. A single pin was constructed to resolve several design issues, including the removal of trapped air in the hydraulic circuit, prevention of hydraulic leakage, motion control, and quantifying the dynamic frictional forces. Because the performance of the single pin was deemed acceptable, a 4 × 4 test die of similar design has been constructed to establish the frictional interactions between adjacent pins, the workability of the pin matrix clamping scheme, and the feasibility of closed and open-loop control of pin positioning.
This book is a collection of more than 500 attractive open problems in the field. The largely self-contained chapters provide a broad overview of discrete geometry, along with historical details and ...the most important partial results related to these problems.
In recent years, several research works have been performed on the application of reconfigurable discrete dies (RDD) for forming sheet metals. Due to the rapid changing of these dies, they attracted ...the attention of flexible manufacturing systems. Meanwhile, only flat sheet metals were examined, and no research work has been reported on the application of the mentioned dies for tubular parts. In this paper, a new RDD for spinning tubular parts were designed and fabricated. The results obtained in this research illustrated that hollow axisymmetric parts could be produced using this type of die, and that this technique leads to the production of tubular parts with desired accuracy and quality. The strain distribution diagrams of formed samples showed that the length of samples decreases and the wall thickness of them increases after forming. Increase in wall thickness in the middle of the tube is more than the sides and decrease in length in the sides is more than the middle. The twisting deformation increases as the depth of forming area increases. The dimension accuracy of formed samples is acceptable by taking into consideration the likely errors.
Hypergraph Theory Bretto, Alain
2013, 20130418, 2013-04-18
eBook, Book
Recenzirano
This book presents hypergraph theory and covers traditional elements of the theory as well as original concepts such as entropy of hypergraph, similarities and kernels. It details applications in ...telecommunications and parallel data structure modeling.
This monograph leads the reader to the frontiers of the very latest research developments in what is regarded as the central zone of discrete geometry. It is constructed around four classic problems ...in the subject, including the Kneser-Poulsen Conjecture.
In the component order connectivity problem, we are given a finite undirected graph G = (V,E) and non-negative integers k, ℓ. The goal of this problem is to determine whether there exists a subset S ...⊆ V such that |S| ≤ k and the size of every connected component of the subgraph of G induced by V \ S is at most ℓ. In this paper, we consider the generalization of the component order connectivity problem where the condition on the sizes of connected components is generalized by non-decreasing subadditive functions defined on the subsets of V. We prove that the kernelization techniques for the component order connectivity problem proposed by Xiao can be generalized to our setting.
