Thickness Distribution Of Products Research Articles

Contact Analysis for Contact Thermoforming of PMMA Sheet

Abstract The ability to produce products with more uniformity in the wall thickness distribution makes contact thermoforming the most suitable optical product processing method. Among all the process parameters, the contact condition significantly affects the structural strength and the optical properties of the product. Thus, it is imperative to investigate the effect of change in the contact conditions on product thickness. Hence, in this study, experimental investigations on contact conditions were performed considering poly(methyl methacrylate) as the sheet material and stainless steel 304 as the punch material. Experiments were conducted to examine the effect of temperature on the coefficient of friction (mechanical contact condition) and the effect of pressure on the thermal contact conductance (thermal contact condition). It was found that the contact conditions change significantly with changes in the operating conditions. Furthermore, numerical simulations were performed, considering isothermal processing and nonisothermal processing with constant and variable contact conditions to identify the effect of the change in contact condition on the product thickness. It was found that the change in contact condition has a considerable effect on the product thickness distribution. This study shows the importance of incorporation of the change in the contact condition for realistic simulations.

Analyses of Plastic Flow and Die Design during Hot Extrusion of Magnesium Alloy Strips

This study involves analyses and experiments of hot extrusion of magnesium alloy strips. Hot compression tests were firstly conducted to obtain the magnesium alloy’s plastic flow stresses at high temperatures. These data are used in the finite element simulations of the thin strip extrusion process. Using the FE simulations, the flow pattern of the magnesium alloy billet within the die, the temperature variation and the thickness distribution at the die exit were analyzed. The effects of different die bearing height design, initial billet temperatures and ram speed on the extrusion load, the temperature at the die exit and the product thickness distribution were also discussed. Finally, hot extrusion experiments were conducted and the experimental values of the extrusion load and dimensions of the products were compared with the analytical values to validate the analytical model. Sound products were obtained using the best designed bearing heights and other appropriate extrusion conditions.

Optimization of a sheet metal forming process using successive multipoint approximations

An automated optimization method based on multipoint approximations and applied to the design of a sheet metal forming process is presented. Due to the highly complex nature of the design functions, it was decided to focus on the characterization of the final product thickness distribution as a function of the preforming die shape variables. This was achieved by constructing linear approximations to the noisy responses usingresponse surface methodology (RSM). These approximations are used to obtain an approximate solution to an optimization problem. Successive approximations are constructed, which improve the solution. An automated panning-zooming scheme is used to resize and position the successive regions of approximation. The methodology is applied to optimally design the preforming die shape used in the manufacture of an automotive wheel centre pressing from a sheet metal blank. The die shape is based on a cubic spline interpolation and the objective is to minimize the blank weight, subject to minimum thickness constraints. A weight saving of up to 9.4% could be realized for four shape variables. Restart is introduced to escape local minima due to the presence of noise and to accelerate the progress of the optimization process.

Analysis of superplastic blow-forming in a conical closed die

A mathematical model using the finite-difference method has been proposed in this work to examine the plastic deformation behavior of the sheet during blow-forming in a conical closed die. In the formulation of this mathematical model, nonuniform thinning in the free bulged region and the contact condition including the sticking and sliding friction modes between the sheet and die are considered. Effects of various forming parameters such as the die entry radius, friction coefficient, inclined angle of the die, etc., upon the optimized pressurization profile, forming time and the thickness distribution of products were discussed systematically. Furthermore, experiments on superplastic blow-forming in a conical closed die were carried out using 8090 Al-Li sheets. It is found that the theoretical predictions agree with experimental results. The thickness distributions of the SPF-ed product obtained with different friction coefficients along the die entry, sidewall and bottom are closer to the experimental data than those obtained with a constant friction coefficient.

Computer Simulation of Superplastic Blow-Forming in a Conical Closed-Die Considering Uniform Thinning.

A mathematical model for analyzing the plastic deformation behavior of a sheet during a conical closed-die blow-forming is proposed. In the formulation of this mathematical model, uniform thinning in the free bulged region is considered. Using this model, the effects of various forming parameters, such as the die entry radius, friction coefficient, and inclined angle of the die, on the optimized pressurization profile, forming time and the thickness distribution of products can be discussed systematically. Furthermore, experiments using 8090 Al-Li sheets are carried out in conical closed-die superplastic blow-forming. The predicted thickness distributions of the SPFed product obtained with different friction coefficients along the die enty, sidewall and bottom are found to be closer to the experimental data than those obtained with a constant friction coefficient.