Advanced Materials Research Vols. 83-86

Abstract: This study was conducted to investigate the effect of preheating through inductive heating mechanism in end milling of AISI D2 hardened steel (60-62 HRC) by using coated carbide tool inserts. Apart from preheating, two other machining parameters such as cutting speed and feed were varied while the depth of cut constant was kept constant. Tool wear phenomenon and machined surface finish were found to be significantly affected by preheating temperature and other two variables. End milling operation was performed on a Vertical Machining Centre (VMC). Preheating of the work material to a higher temperature range resulted in a noticeable reduction in tool wear rate leading to a longer tool life. In addition, improved surface finish was obtained with surface roughness values lower than 0.4 μm, leaving a possibility of skipping the grinding and polishing operations for certain applications.

Abstract: This study investigated the mechanical properties and forming characteristics of flanged parts made of AZ61 magnesium alloys via hot working. The bearing cover of the gearbox in cars was selected as a carrier in hot forging to probe into the formability of magnesium alloys. A high-speed metal test machine was used for compression tests under different forming temperatures and strain rates to obtain stress-strain curves. The stress-strain data are applied to the Finite Element Method to analyze the formability of the bearing cover. Finally, based on the comparison of simulation and experimental results, we conclude that under the same billet heating temperature and low strain rate, the forming load was small and no cracks developed on the flanges of forged parts. However, under the same condition, the microstructure of the part was coarse. This study also attempted to identify a method for manufacturing a bearing cover with a low forging load, and determined how temperature influences hardness and microstructure of the bearing cover.

Abstract: The key of qualities of optical lens created by injection molding are geometric errors and distribution of residual stress. This study analyses a mobile phone camera lens with aspheric optical lens created by one mold and 16 cavities. Mold flow analysis was used to simulate geometric shapes of different gates and design cooling systems to control mold temperatures. Mold temperature was controlled during the actual injection process and simulation results were used as the basis for mold design. The effects of cold-wall-mold on lens residual stress are discussed. The experiment result showed that higher mold temperatures are helpful to reduce residual stress. An aspheric mould measurement system was used to measure both the mold and the product. The results showed that the replicating capacity is satisfactory with a molding error of 3.604μm.

Abstract: This paper aims at presenting an experimental investigation to obtain the optimum formability of light-weight alloys under the multi-stage forming process. Titanium alloy sheets (Ti-6Al-4V) and aluminium alloy sheets (AA5052) are selected as forming specimens. The special fixture with heating device is applied in order to carry out the prestraining process. The swift forming test at warm-forming condition is performed for measuring the limit dome heights after the multi-stage formign process. The outcomes of this investigation are valuable for engineers to design and fabricate high-quality light-weight components efficiently.

Abstract: In the last years, a number of studies on Incremental Sheet Forming have been focused on formability analysis and, in particular, on the development of models able to predict material response also in the design phase. Due to mechanics complexity, up to now process application is directly dependent on a preliminary experimental investigations based on the execution of trials and errors tests; a set of experiments, in fact, is necessary to determine the industrial feasibility. Of course this approach is very expensive and time consuming and, for this reason, new techniques to perform reliable guidelines for the designer are strongly requested. In the paper an effective statistical methodology has been applied with the aim to build a suitable base of knowledge minimising the number of experimental tests for identifying an optimal set of parameters which strongly impact on the process performance.

Abstract: Analytic calculation and Finite Element Method simulation are used to research the relationship between friction and bitten condition in cold ring rolling. It is found: if the ring can’t be bitten in groove, rolling process will be stopped. The rolling force will increase rapidly, which will cause the breakage of rolls and equipment. When the feed velocity and other technical parameters are kept unchanged, the bitten condition will be disappeared with the process of ring rolling even if the ring can be bitten at the beginning stage.

Abstract: The slab edge rolling has been widely used in the roughing stand of hot strip mill to control the width of the slab. However, the slab edge rolling and consequent horizontal rolling will cause a significant width change in the head part and tail part of the slab, which have to be trimmed before the finishing stands. The short stroke control (SSC) technology has been developed to overcome this problem. In this paper, the finite element method (FEM) has been used to simulate the unsteady edge rolling process. Three SSC control curves have been compared in order to obtain the best width control result. The optimized SSC control curve has been applied to the industrial rolling mill.

Abstract: The difficulty in forging of bevel gear with an outside diameter larger than 75mm is due to the high forming load requirement. In this paper, a new intuitive method for the punch and preform design of the bevel gear warm orbital forging is proposed to lower the forging load and improve the die filling. The geometry of the forged bevel gear are divided into characteristic features and mapped to the main dimensions of the preform design. The exact dimensions of the preform are determined utilizing constraints of the volume constancy and the section centroid balance. The surface of punch tip is designed using the section profile described by a Bezier curve with five control points which are related to the preform and the forged part geometry simultaneously. The forming process was analyzed via the FEM simulation. The die stress was also calculated to prevent die failure and improve tool life. A PXW-200 orbital forging press was adopted for the experimental tests of the proposed designs. The unfilled area at the teeth faces were examined via the laser scanner. The experimental results of the maximum unfilled distances were varied from 0.3 mm to 0.8mm depending on the different punch tip profile design. The predicted tooth profiles were in good agreement with the experimental measurements.

Abstract: The manufacturing of the ITER (International Thermonuclear Experimental Reactor) vacuum vessel involves the welding of thick deformed plates. The aim of this study is to investigate the influence of forming residual stresses on the welding distortions of two thick plates. The plates are deformed using a three point rolling process. A first numerical simulation is performed to investigate the residual stresses induced by this process. The forming residual stresses are taken into account as initial conditions to perform the electron beam welding simulation of a deformed plate. This simulation first requires calibrating the heat source. Two welding simulations are then performed: the first one with residual stresses and the second one without. The comparison of the simulation results points out a low effect of the residual stresses on the electron beam welding distortions. As a result, in the next electron beam welding simulations of the vacuum vessel, no forming residual stresses will be taken into account.

Abstract: Tube hydroforming technology is still considered a new technique growing fast in automotive and aircraft industries. Many researches on all aspects of this process are still required. Contact friction is one of the most effective parameters on tube wall thinning. To successfully fulfill the process without any common defects, it is very important to determine the proper internal pressure and axial feeding loading paths. In this paper, the effect of lubrication on tube wall thinning on ASTM C11000 copper alloy is discussed as well as the effect of internal pressure and axial feeding. An axisymmetric bulged tube is investigated using theoretical, numerical and experimental methods. Improved linear and non-linear pressure and feeding loading paths are applied and the predicted results are experimentally proved. It is observed that non-linear pressure application gives smoother results. Also proper lubrication plays an important role in success of the process.