Papers by Keyword: Shape Accuracy

Abstract: Multi-point stretch forming is a flexible manufacturing technique for three-dimensional shape forming of craft skin. Its die surface is constructed by many pairs of matrices of elements whose height is controlled by computer. It uses the curved surface of elements instead of the die surface. The element numberis an important parameter because it has great influence on the part quality. This paper simulates the forming process of paraboloid part and saddle-shaped part with different number of elements and studies the influence of element number on the shape accuracy of the part .That will provides guidance for the application of multi-point stretch forming.

Abstract: Drilling parameters have great influences on hole accuracy and defect production. In this study, single factor test is applied to obtain the relationship between the torque deviation and the spindle speed n at different feeds per revolution f_r. White Light Interferometer (WLI) is applied to measure the hole shape. Based on the frequency domain analysis of torque deviation, the cause of hole shape deviation is investigated. Relationship between the hole shape accuracy and drilling parameters is established, which can be used to predict the hole shape by analyzing the torque deviation. Moreover, the reasonable processing parameters can be selected to obtain drilling hole with ideal shape and satisfying production efficiency.

Abstract: Single Point Incremental Forming (SPIF) is a quite new sheet forming process which offers the possibility to deform complex parts without dedicated dies using only a single point tool and a standard 3-axis CNC machine. The process mechanics enables strains much higher than traditional sheet forming processes, but particular attention must be given to the final part geometrical accuracy. In this paper the capabilities of a dedicated explicit numerical model are quantitatively analyzed on pyramid-shaped parts. In particular a comparison between experimental and numerical results is reported. Three different shapes at the varying of the stamping angle were considered and the final shape was acquired, through a white light triangulation based optical scanner, after the removing of the punch and of the clamping fixture. LS-DYNA commercial code was used to simulate the three different case studies, and an explicit loading-implicit unloading approach was implemented in order to simulate also the shape distortions due to springback phenomenon. The effect of several numerical parameters on the final shape and the thickness distribution were investigated. In particular numerical results were analyzed at the varying of the material constituve law, of the shell element type and of the number of integration points along the thickness.

Abstract: In the recent years the rapid prototyping technology has become increasingly important as a manufacturing method for many medical devices. Although the advantage of such technology is evident, a precise presentation of the actual anatomical parts as well as shape accuracy and surface quality is a major indicator for choosing the best technique. In this paper, evaluation and validation of the shape accuracy of fabricated models using Fused Deposition Modelling technique is presented. The surface deviation between anatomical models (a mandible) derived from Computed Tomography and their virtual presentation was investigated. A high level of conformity with regard to the surface feature of the anatomical part was observed. Furthermore, surface deviations in the range of ±0.5 mm with an absolute mean deviation of 0.159 mm for the model were reported. The surface accuracies suggest that the reproduction of complex anatomical structures by FDM could potentially be used for surgical planning, custom-made implants and for surgical anatomy teaching.

Abstract: Oxidation in hot stamping of ultra high strength steel sheets was prevented by coating the sheets with an oxidation preventive oil. For four types of oxidation preventive oil, the degree of oxidation under natural cooling of the heated sheets without forming was first evaluated. The oil that forms a liquefied film at elevated temperatures exhibited high oxidation prevention, and this oil was chosen for a hot bending experiment. Hot hat-shaped bending of the coated sheets using resistance heating was carried out to examine the properties of the products. The bending load was markedly decreased, the shape accuracy of bent products was very high, the surface roughness was similar to that of the sheet, and the hardness was about 1.5 times larger than that of the sheet before the bending due the die quenching. In addition, the layer remaining on the surface of the formed product could be removed using phosphoric acid. It was found that the hot stamping operation using the oxidation preventive oil is effective in the precision forming of ultra high strength steel sheets.

Abstract: The effect of oscillation of internal pressure on the formability and shape accuracy of the products in a pulsating hydroforming process of T-shaped parts was examined by finite element simulation. The local thinning was prevented by oscillating the internal pressure. The filling ratio of the die cavity and the symmetrical degree of the filling was increased by the oscillation of pressure. The calculated deforming shape and the wall thickness are in good agreement with the experimental ones. It was found that pulsating hydroforming is useful in improving the formability and shape accuracy in the T-shape hydroforming operation.