No abstract

Tube necking is a common process used for manufacturing pressure vessels, for example, compressed natural gas capsules, categorized under general spinning processes. An experimentally validated finite element model suited to the process is incorporated to study the deformation, and state of strain and stress in the contact zone. The in situ variation of stress and strain is illustrated via colored contour plots, and Cartesian and polar diagrams. It is shown that in some areas, there are similarities and differences between flow forming and tube necking; for example, like flow forming, the equivalent plastic strain decreases from the inner and outer layers toward the middle layer, and unlike flow forming, the axial strain at the outer layer is negative all around the tube while at the inner layer, axial strain possesses a maximum positive value at contact position. The state of stress and plastic strain in regions around the contact zone is shown at an instant of process duration, which is not quite similar to postprocess stress and strain distribution.

Tube spinning, without mandrel, is a common process used for manufacturing pressure vessels, e.g. CNG (Compressed Natural Gas) capsules for automotive industry and fire extinguishers. The process is carried out at an elevated temperature for forming a dome on thick wall steel tube ends. Two of the most important control parameters in the process are the “roller contact start point” (RCSP) and spinning feed (pitch), both of them highly affecting the process time and deformation behavior of the tubes and therefore success and quality of the product. In this article, using a three-dimensional dynamic explicit finite element model, the effects of these parameters are investigated on circumferential, axial and radial (thickness) strains of the formed tube in three thickness layers of the tube wall. The model is also verified by experiment. While circumferential strain is shown to be independent of the feed, axial and thickness strains are highly affected by both the feed and roller contact start point. It is shown that when the roller contact start point distance from the free end of the tube increases, there is a risk of indentation instead of normal bending behavior. It is also shown that axial strain has an inverse relation with feed, i.e. decreasing the feed results in further elongation of the tube. On the other hand, thickness strain increases by increasing the feed, so bigger thicknesses are expected in domes manufactured by higher feeds. In addition, it is shown that increasing the feed results in a decrease of the equivalent strain. The amount of residual stress (regardless of the temperature change) increases with increasing feed and its distribution is more uniform for higher distances of the contact start point from the free end.

A 3-D Dynamic explicit finite element model of metal shear spinning, is developed and solved for different nose radii and feed rates. Several amounts are applied to spinning roller nose radius and feed rate, then Axial, tangential and normal forces are calculated for each combination of parameters. The results are checked with a series of experimental tests in which the process parameters are varied according to the finite element model. The experimental values are shown to be in relatively good agreement with the outcomes of the finite element model.

Obtaining the resonance frequency of cutting tools is necessary for dynamic modelling and instability study in milling process. In this paper, two geometrically different endmills are modelled by analytical and Finite Element (FE) approaches and their natural frequencies are calculated. For evaluation of the results, modal testing is carried out. The discrepancies of the analytical results compared to the modal experiments are approximately 25% for both tools. FE results differ 18% and 22% from experimental values for respectively tool 1 and 2. FE values are closer to those of experiment in comparison with analytical results.