Antonio Del Prete

Computer Aided Modelling of Rubber Pad Forming Process

Rubber pad forming (RPF) is a novel method for sheet metal forming that has been increasingly used for: automotive, energy, electronic and aeronautic applications [1]. Compared with the conventional forming processes, this method only requires one rigid die, according to the shape of the part, and the other tool is replaced by a rubber pad [1]. This method can greatly improve the formability of the blank because the contact surface between the rigid die and the rubber pad is flexible. By this way the rubber pad forming enables the production of sheet metal parts with complex contours and bends. Furthermore, the rubber pad forming process is characterized by a low cost of the die because only one rigid die is required [2]. The conventional way to develop rubber pad forming processes of metallic components requires a burdensome trial-and-error process for setting-up the technology, whose success chiefly depends on operator’s skill and experience [4][5]. In the aeronautical field, where the parts are produced in small series, a too lengthy and costly development phase cannot be accepted. Moreover, the small number of components does not justify large investments in tooling. For these reasons, it is necessary that, during the conceptual design, possible technological troubles are preliminarily faced by means of numerical simulation [4],[6]. In this study, the rubber forming process of an aluminum alloy aeronautic component has been explored with numerical simulations and the significant parameters associated with this process have been investigated. Several effects, depending on: stamping strategy, component geometry and rubber pad characterization have been taken into account. The process analysis has been carried out thanks to an extensive use of a commercially finite element (FE) package useful for an appropriate set-up of the process model [7],[8]. These investigations have shown the effectiveness of simulations in process design and highlighted the critical parameters which require necessary adjustments before physical tests.

Tool Engage Investigation in Nickel Superalloy Turning Operations

This paper reports the results of an experimental study of the tool wear and cutting forces in turning of Inconel 718 with coated carbide inserts. Inconel 718 is a difficult-to-cut nickel-based super-alloy commonly used in aerospace industry. The effects of cutting speed, feed rate and cutting tool geometry on tool wear have been widely analyzed in literature. Turning operations on complex components such as aircraft engines casings require the insert replacement at the end of each geometric feature manufacturing, independently from the actual tool wear level. For this reason, it is important to preserve tool integrity mainly in the most critical phase of operation (i.e., when the tool engages the workpiece). In fact, if the tool is damaged in this stage the quality of the whole operation is compromised. The attention has been focused on engage cutting conditions because the phenomenon that appears in this critical step plays a wide influence on tool integrity and, consequently, on the quality of the operation. For this purpose a nickel-based super alloy ring-workpiece, (Inconel 718), has been machined in lubricated cutting conditions by using a CNC lathe with carbide coated tools. Two variables have been investigated in this study: the Depth Of Cut (DOC) and the approaching Engage angle (En). In the studied working conditions Speed (S), Feed-rate (F) and removed volume (Vrim) were kept constant. Both tool wear and cutting forces evolution during cutting have been analyzed.

Inverse Analysis Procedure to Determine Flow Stress and Friction Data for Metal Cutting Finite Element Modeling

This paper describes an automated procedure developed for the identification of Johnson-Cook (JC) law material parameters and Coulomb friction coefficient at the tool-chip interface, in the specific case of metal cutting FE analysis. The procedure has been developed in iSight environment, through the integration between AdvantEdge metal cutting FE code and an appropriately selected optimization algorithm. The identification of JC and friction parameters, in fact, has been performed considering it as an optimization problem, in which the objective function is the numerical/experimental error function minimization (in the specific case, it is related to the forces and temperatures responses). The calibration and validation phases have been performed using forces and temperatures experimental data, collected in orthogonal cutting test on SAF2507 superduplex steel.

Feasibility Evaluation of Sheet Metal Hydroformed Components through Shape Factors Application

Sheet hydroforming has gained increasing interest in the automotive and aerospace industries because of its many advantages such as higher forming potentiality, good quality of the formed parts which may have complex geometry. The main advantage is that the uniform pressure can be transferred to any part of the formed blank at the same time [1]. In this paper, a “shape factors” set has been defined with the proper goal to understand if it can be used to help engineers to define “process rules” for the studied non conventional technology [2]. A specific prediction model, obtained thanks to a numerical factorial fractional plane, has been used in order to preview the process responses vs each defined shape factor. These shape factors have been used to track the process performances through their variation thanks to the usage of the numerical simulation that has been validated with an appropriate experimental campaign executed thanks to the usage of a specific equipment properly designed.

Multi Shape Sheet Hydroforming Tooling Design

In order to value the process of variables influence in sheet metal hydroforming, a special hydroforming cell has been developed. Generally, sheet hydroforming is obtained using appropriate press tooling. This option requires large investments completely dedicated to this technology of production. As an alternative, conventional hydraulic presses can be used for sheet hydroforming in combination with special hydraulic tooling named “hydroforming cells”. A special “hydroforming cell” concept has been developed to perform experimental analysis for different shapes using the same tooling set up. CAE tools had a strategic role just to develop the best layout and to find the optimum solutions for the process variables. FEA has been used to define the distribution of the blank holder variable forces: a solution which implies the use of twelve independent actuators have been implemented. The position and the load path of each one of them has been chosen for each formed shape, in accordance with the FEA results. Customized actuators have been used to solve interferences between mechanical parts of the hydroforming cell. For this specific aspects the virtual 3D design was necessary for the appropriate decisions. The developed process system is very effective so that is possible to set up experimental campaigns for sheet hydroformed components.

Ring rolling process simulation for geometry optimization

Ring Rolling is a complex hot forming process where different rolls are involved in the production of seamless rings. Since each roll must be independently controlled, different speed laws must be set; usually, in the industrial environment, a milling curve is introduced to monitor the shape of the workpiece during the deformation in order to ensure the correct ring production. In the present paper a ring rolling process has been studied and optimized in order to obtain anular components to be used in aerospace applications. In particular, the influence of process input parameters (feed rate of the mandrel and angular speed of main roll) on geometrical features of the final ring has been evaluated. For this purpose, a three-dimensional finite element model for HRR (Hot Ring Rolling) has been implemented in SFTC DEFORM V11. The FEM model has been used to formulate a proper optimization problem. The optimization procedure has been implemented in the commercial software DS ISight in order to find the combina...

Experimental springback evaluation in hydromechanical deep drawing (HDD) of large products

Springback is a really troublesome effect in sheet metal forming processes. In fact changes in geometry after springback are a big and costly problem in the automotive industry. In this paper the authors want to analyse the springback phenomenon experimentally in sheet metal hydroforming. Compared with conventional deep drawing, sheet hydroforming technology has many remarkable advantages, such as a higher drawing ratio, better surface quality, less springback, better dimensional freezing and capability to manufacture complicated shapes. The springback phenomenon has been extensively analysed in deep drawing processes but there are not many works in the literature about springback in sheet metal hydroforming. In order to study it, the authors have performed an accurate measuring phase on the chosen test cases through a coordinate measuring machine and the obtained measurements have been utilised for the determination of springback parameters, taking into account the method proposed by Makinouchi et al. The authors have focused their attention on the possibility of adopting a modified Makinouchi et al. approach in order to measure the springback of the large size considered test cases. Through the implemented methodology it has been possible to calculate the values of the springback parameters. The obtained results correspond to the observed experimental deformations. Analysing the springback parameter values of the different combinations investigated experimentally, the authors have also studied the pre-bulging influence on the springback amount.

Numerical-Experimental Correlation of Distortions Induced by Machining Process on Thin-Walled Nickel Super Alloy Forged Components

AeroEngines main components made by nickel super alloys are mainly obtained by machining of large forged components. The work piece machining process generates some distortions that may also be relevant. In this contest, in many cases the removed volume in the machining operations represents a large percentage of the forged component in order to obtain the thin-walled wanted geometry. Due to this reason, the residual bulk stresses induced by the process history can lead to significant 3D geometric distortions in the machined component with unacceptable dimensions and shapes of the obtained product for comparison with the wanted geometry. Moreover, it is a matter of fact how, the final component distortions depend by the cutting strategy adopted in the machining process. The experimental study of such cutting strategies on real components are particularly time consuming and costly and for this reason the chance to study the problem using reliable numerical models it is particularly welcome. In the present work authors reports the numerical model development of the forging and machining processes needed for the production of a aircraft engine component and the comparison of the obtained results with the ones physically measured. The objective is to develop and validate a modeling method able to predicts the shape and the magnitude of the distortion induced by the machining operation on the considered component and to establish a possible strategy to suggest machining working steps able to improve the quality of the manufactured component reducing the needed production time.

Experimental analysis of influence of cutting conditions on machinability of waspaloy

Taking into account the main importance of nickel-based superalloy in aerospace, marine and chemical industries concerning the production of high performance artifacts, in this paper experimental results of cutting forces, chip morphology, tool wear and temperatures were investigated during orthogonal machining of Waspaloy (45 HRC). All the experiments were performed in dry and lubricated cutting conditions, analyzing and comparing the collected results for a range of different cutting parameters: cutting speed and feed rate. The results show a good trends coherence, highlighting the influence of lubrication during machining.

Numerical simulation of machining distortions on a forged component obtained by ring rolling process

Residual stresses induced in the component by previous thermal/mechanical processes are compressive or tensile stresses having a zero resultant. In particular, they arise as consequence of thermo-mechanical processes (e.g. ring-rolling process), casting and heat treatments. When machining stressed components, volume removal leads to a re-arrangement of residual stresses, which inevitably causes distortions in the workpiece. If distortions are excessive, they can lead to a large number of scrap parts. This paper describes the development of a numerical procedure for the analysis of the distortions on a waspaloy turbine case, obtained by ring rolling process. A 3D model of ring rolling process has been set in the commercial software DEFORM 3D. Three different ring rolling strategies have been analyzed, in order to find the combination of process parameters which allows to obtain the best component in terms of geometrical precision. Then, the heat treatments (air cooling, solubilization, stabilization and ag...