Preform Tool Research Articles

Experimental and simulation studies on hybrid incremental sheet forming

In the present research work, parts are formed using two-step hybrid incremental sheet forming (HISF) process. The effect of process parameters such as preform tool size, tool diameter, and preforming depth on thinning in the formed part is studied. A simulation model is developed and simulation results are compared with the experimental results. Also, results of HISF process are compared with the results of single point incremental sheet forming. The simulation results are in good agreement with the experimental results. It is observed that HISF process results in lower thinning as compared to SPIF process. Further, it is found that preform tool size has considerable influence on the minimum thickness of formed part. Large preform tools result in relatively lower thinning.

A Comprehensive Study on Fitness Approximation Techniques in Shape Optimization of Aerofoil Forging Preform Tools

In the process of complex engineering designs or optimizations, a large number of physical experiments or numerical simulations are required to evaluate certain performance qualities before a satisfactory result can be obtained. In both cases, constructing an approximate model is often necessary to provide a reliable response as an alternative to experiments or simulations. In this paper, three types of approximation models were developed and applied in a shape design of an aerofoil forging preform tool. Their modeling techniques are presented in detail. An optimal Latin hypercube technique was employed for the design of the experiment and sampling with the expected coverage of parameter space. Finite element (FE) simulations of multistep forging processes were implemented to acquire the objective function values for evaluating the forging performance. By a parametric study, the effects of design variables on objective responses and correlations were investigated for a clear insight into their functional nature. Comprehensive analyses and comparisons between different approximate models have been carried out. Finally, an optimization design of a preform tool was successfully achieved based on a particle swarm (PSO) algorithm combined with the proposed approximate model.

Shape optimization of preform tools in forging of aerofoil using a metamodel-assisted multi-island genetic algorithm

ABSTRACTPreform design plays an important role in improving the material flow, mechanical properties and reducing defects for forgings with complex shapes. In this paper, a study on shape optimization of preform tools in forging of an airfoil is carried out based on a multi-island genetic algorithm combined with a metamodel technique. An optimal Latin hypercube sampling technique is employed for sampling with the expected coverage of parameter space. Finite element (FE) simulations of multistep forging processes are implemented to obtain the objective function values for evaluating the forging qualities. For facilitating the optimization process, a radial basis function surrogate model is established to predict the responses of the hot forging process to the variation of the preform tool shape. In consideration of the compromise between different optimal objectives, a set of Pareto-optimal solutions are identified by the suggested genetic algorithm to provide more selections. Finally, according to the proposed fitness function, the best solution of multi-objective optimization on the Pareto front is confirmed and the corresponding preform tool shape proves optimal performances with substantially improved forging qualities via FE validation.

An Experimental Investigation on Thinning and Formability in Hybrid Incremental Sheet Forming Process

Single point incremental forming (SPIF) has several advantages over conventional sheet forming process, but due to its inherent drawbacks such as localized thinning, poor formability of parts having steep walls and long processing time make it unsuitable in many industrial applications. In present experimental investigation, two-step hybrid incremental sheet forming (HISF) process is proposed which combines stretch forming (SF) and SPIF process. Stretch forming or preforming is done in order to get intermediate shape and desired thickness distribution. On the same setup final part shape is obtained using SPIF process. From the literature review it is found that sophisticated tooling is used for stretching process. In present experimental investigation simple tooling comprising wooden preforming tool is used for stretching followed by SPIF process to form final part shape. Full factorial design of experiments is used to quantify influence of wall angle, preforming and preform tool radius on minimum thickness. From the experimental results it is observed that wall angle has significant influence on thinning which is in good agreement with the previous literature. Further, from the same set of experiments, the influence of preforming depth and preform tool radius on minimum thickness is studied keeping wall angle as constant. It is found that preforming has significant influence on minimum thickness and formability. For conical frustum of 30o and 50o wall angle, 70 mm preform tool radius and 10 mm preforming results in minimum thinning. Also, improvement of 18% in minimum thickness is observed while forming parts with 50o wall angle. Using preform tool radius 70 mm and preforming depth 18 mm, an improvement of around 40 % in forming depth of part having 70o wall angle is achieved in HISF process as compared to SPIF process.

Optimisation and modelling of thinning and geometric accuracy in incremental sheet forming combined with stretch forming

In the present experimental study incremental sheet forming is combined with stretch forming in order to obtain uniform thickness distribution, minimise thinning and to improve geometric accuracy of formed part. Preforming or stretch forming is initially done in order to obtain initial thickness distribution. Incremental sheet forming is then employed to obtain final part shape and thickness distribution. Forming time is also minimised considerably because of initial stretch forming process. The experiments are designed using central composite design (CCD) of response surface methodology. From the results, it is observed that preforming and preform tool shape have significant influence on sheet thinning. Also the combination of ISF and stretch forming processes yields in reduced thinning and uniform thickness distribution. Multi-performance optimisation using desirability function is also performed to improve thinning and geometric accuracy. Further mathematical models are developed which are in good agreement with the experimental results.

Optimization and Modelling of Thinning and Geometric Accuracy in Incremental Sheet Forming Combined with Stretch Forming

In the present experimental study incremental sheet forming is combined with stretch forming in order to obtain uniform thickness distribution, minimise thinning and to improve geometric accuracy of formed part. Preforming or stretch forming is initially done in order to obtain initial thickness distribution. Incremental sheet forming is then employed to obtain final part shape and thickness distribution. Forming time is also minimised considerably because of initial stretch forming process. The experiments are designed using central composite design (CCD) of response surface methodology. From the results, it is observed that preforming and preform tool shape have significant influence on sheet thinning. Also the combination of ISF and stretch forming processes yields in reduced thinning and uniform thickness distribution. Multi-performance optimisation using desirability function is also performed to improve thinning and geometric accuracy. Further mathematical models are developed which are in good agreement with the experimental results.

Optimization of cold forging perform tools using Pseudo Inverse Approach

A new fast method called “Pseudo Inverse Approach” (PIA) for the multi-stage axi-symmetrical cold forging modelling is presented. The approach is based on the knowledge of the final part shape. Some intermediate configurations are introduced and corrected by using a free surface method to consider the deformation paths without contact treatment. A new direct algorithm of plasticity is developed using the notion of equivalent stress and the tensile curve, leading to a very efficient and robust plastic integration procedure. Numerical tests show that the Pseudo Inverse Approach is very fast compared with the incremental approach. The PIA is used in an optimization procedure for the preliminary preform tool design in multi-stage cold forging processes. This optimization problem aims to minimize the equivalent plastic strain and the punch force during the forging process. The preform tool shapes are represented by B-Spline curves. The vertical positions of the control points of B-Spline are taken as design variables. The evolution of the objective functions shows the importance of the tool preform shape optimization for the forging quality and energy saving. The forging results obtained by using the PIA are compared with those obtained by the classical incremental approaches to show the efficiency and accuracy of the PIA.

Preform tool shape optimization and redesign based on neural network response surface methodology

Preform tool shape optimization using response surface method (RSM) was developed in this work. Neural network approximation model was employed for response surface construction in order to overcome the limitation of quadratic polynomial model in solving non-linear problems. A two-step axisymmetric forging problem was studied as an example using proposed method. Optimum was achieved by using pattern search optimization method to search response surface describing relationship between preform shape and die cavity fill ratio. In addition to that, with respect to the complexity of the optimum solution, the knowledge-based redesign concept was proposed. Simplified preform shape description model was built based on the knowledge extracted from previous optimization and additional shape optimization in terms of a new optimization objective was conducted to obtain a better redesign preform shape. Finally, comparison was made between the original optimal shape and redesigned one; better result was achieved by using the concept proposed.

OPTIMAL DESIGN FOR NON-STEADY-STATE METAL FORMING PROCESSES—I. SHAPE OPTIMIZATION METHOD

We suggest a shape optimization method for a non-linear and non-steady-state metal forming problem. It consists in optimizing the initial shape of the part as well as the shape of the preform tool during a two-step forging operation, for which the shape of the second operation is known. Shapes are described using spline functions and optimal parameter values of the splines are searched in order to produce, at the end of the forging sequence, a part with a prescribed geometric accuracy, optimal metallurgical properties and for a minimal production cost. The finite element method, including numerous remeshing operations, is used for the simulation of the process. We suggest using a least-squares-type algorithm for the unconstrained optimization method (based on external penalty) for which we describe the calculation of the derivatives of the objective function. We show that it can reduce to calculations which are equivalent to the derivative calculations of steady-state processes and to evolution equations. Therefore, the computational cost of such an optimization is quite reasonable, even for complex forging processes. Lastly, in order to reduce the errors due to the numerous remeshings during the simulation, we introduce error estimation and adaptive remeshing methods with respect to the calculation of derivatives.

Effect of Resin System Parameters on Resin Transfer Molding of Vinyl Ester Based Composites—A Statistically Designed Study

Abstract Although the area of composites has advanced significantly over the past three decades, there is still a lack of understanding as to the coupling between materials and processing variables, especially as related to the use of resin systems in emerging processes such as resin transfer molding (RTM). As materials are tailored through the use of additives to resin systems, intricate fiber architectures, and the use of specific processing parameters, the need for a thorough understanding of the effect of minor variations in the materials system and the ultimate need for process control techniques increases. The current investigation is aimed at developing an understanding of variation in performance in three similar vinyl ester resin based composite systems as a function of mold release agent concentration, presence of a wetting/dispersion agent, and preform tool temperature. It is seen that the concentration of mold release agent has a significant influence on performance, which can be correlated wi...