Hengan Ou

Die Shape Compensation In Hot Forging of Titanium Aerofoil Sections

Abstract Dimensional accuracy is among the most important criteria in hot forging of titanium alloy into aerofoils for aeroengine applications. This paper presents a study of dimensional errors of hot forged aerofoil sections in an entire forging cycle using finite element (FE) simulation. It was found that the die-elasticity and thermal distortion had an important effect on thickness error and profile deviation of the aerofoil sections. By modifying die profiles using two weighting factors representing aerofoil errors due to the die elastic deflections in forging and aerofoil thermal distortion during cooling, a significant reduction of both the aerofoil thickness and profile errors was obtained.

Die Shape Optimisation in Forging of Aerofoil Sections

Abstract Dimensional tolerances are among the most important manufacturing criteria in the forging of aerofoil blades for aeroengine applications. A die shape optimisation system under development for the net-shape forging of aerofoil blades is outlined in this paper. In forging simulation using finite elements (FEs), a compensation approach was used in order to eliminate the aerofoil thickness errors due to die-elasticity. The optimised die shape is obtained by modifying the nominal die shape with a fraction of the die-elastic deflections through an introduced weighting factor. While forging simulation enables the evaluation of material flow, mechanical behaviour and die deflections, the compensation approach provides an effective means to minimise aerofoil thickness errors with only a small number of forging simulation iterations, suggesting substantial computing cost savings.

A virtual inspection framework for precision manufacturing of aerofoil components

The finite element method plays an extremely important role in forging process design as it provides a valid means to quantify forging errors and thereby govern die shape modification to improve the dimensional accuracy of the component. However, this dependency on process simulation could raise significant problems and present a major drawback if the finite element simulation results were inaccurate. This paper presents a novel approach to assess the dimensional accuracy and shape quality of aeroengine blades formed from finite element hot-forging simulation. The proposed virtual inspection system uses conventional algorithms adopted by modern coordinate measurement processes as well as the latest free-form surface evaluation techniques to provide a robust framework for virtual forging error assessment. Established techniques for the physical registration of real components have been adapted to localise virtual models in relation to a nominal design model. Blades are then automatically analysed using a series of intelligent routines to generate measurement data and compute dimensional errors. The results of a comparison study indicate that the virtual inspection results and actual coordinate measurement data are highly comparable and the procedures for registration and virtual inspection are computationally efficient, validating the approach as an effective and accurate means to quantify forging error in a virtual environment. Consequently, this provides adequate justification for the implementation of the virtual inspection system in the virtual process design, modelling and validation of forged aeroengine blades in industry. Highlights? The paper presents a virtual inspection framework to assess the accuracy of aero-engine. ? Both the 3-2-1 approach and the ICP method are developed for part registration. ? The ICP method achieves a better solution than the 3-2-1 approach in registration. ? A case study produces reveals a good correlation exists between the virtual inspection data and the actual measurement data.

Die-elasticity for precision forging of aerofoil sections using finite element simulation

Abstract Precision forging of material into turbine blades needs a clear understanding of the prevailing parameters in forging, appropriateness of preform design, process simulation and techniques for compensating component form errors due to die-elasticity. With this in mind, simulations are conducted to analyses the material flow during forging of aerofoil sections, forging force history, contact pressure distribution between die and component, and the elastic deflections of the forging dies are investigated using finite element simulation. Further, the compensation of die-elasticity is proposed by modifying die profiles in response to die deflections based on the nominal dimensions of forging dies. The minimisation of form errors of aerofoil sections due to die-elasticity is derived by iterations using FE. The results obtained enable the quantitative estimation of die-elasticity in precision forging of aerofoil sections, and the technique for compensating component-form errors to achieve net-shape forming production.

Preform design for forging of aerofoil sections using FE simulation

Abstract Finite element (FE) simulation for determining material flow, forging force history and die stress sustained during the forming of aerofoil sections is presented for different preform shapes, friction conditions and attitude of die parting-line. The results show that the above factors are essential considerations for the precision forging of aerofoil components; these factors particularly influence the material deformation in the forming process, the forging load, and the pressure contours at the contact interface. The optimal preform design for such forming processes would be with a view to minimising material removal processes, reducing the production cost and increasing the component accuracy.

A constitutive model of polyether-ether-ketone (PEEK)

A modified Johnson-Cook (JC) model was proposed to describe the flow behaviour of polyether-ether-ketone (PEEK) with the consideration of coupled effects of strain, strain rate and temperature. As compared to traditional JC model, the modified one has better ability to predict the flow behaviour at elevated temperature conditions. In particular, the yield stress was found to be inversely proportional to temperature from the predictions of the proposed model.

Cranial reconstruction using double side incremental forming

Incremental sheet forming (ISF) is a highly versatile and flexible process for rapid manufacturing of complex sheet metal parts. Comparing to conventional sheet forming processes, ISF is of a clear advantage in manufacturing small batch or customized products such as cranial implant. Although effort on cranial reconstruction by using incremental sheet forming approach has been made in recent years, research has been mostly based on the single point incremental forming (SPIF) strategy and there are still considerable technical challenges for achieving better geometric accuracy, thickness distribution and complex cranial shape. In addition, the use of a backing plate or supporting die reduces the process flexibility and increases the cost. To overcome these limitations, double side incremental sheet forming (DSIF) process is employed for forming Grade 1 pure titanium sheet by using different toolpath strategies. The geometric accuracy and thickness distribution of the final part are evaluated so the optimized tool path strategies are developed. This leads to an assessment of the DSIF based approach for the application in cranial reconstruction.

Stress analysis of functionally graded thick-walled cylindrical vessels

In this paper, a simple and accurate method is presented to determine deformations and stresses in thick-walled cylindrical vessels made of functionally graded materials under internal pressure and uniform temperature. The governing equation with the consideration of varying Young’s modulus and thermal expansion coefficient along the radial direction is derived from the basic equations of axisymmetric plane strain problems in elasticity. The comparison with the corresponding numerical solution indicates that the proposed solution has excellent convergence and accuracy. The effects of the coefficients, which affect Young’s modulus and the thermal expansion coefficient, on the deformation and stresses in thick-walled cylindrical vessels are investigated.

Reduction in post forging errors for aerofoil forging using finite element simulation and optimization

This paper reports on recent work in the development of a finite element (FE) based forging optimization methodology. It utilizes the commercial FE package ABAQUS and the optimization code VisualDOC. Taking into account the effect of die and press elastic deflections and thermal distortion in cooling, a direct compensation approach and optimized weighting factor method are used to achieve the optimized die shape for improved dimensional accuracy of forged aerofoil blades. The significant predicted reduction in aerofoil shape errors using a single 2D section from a forged nickel-based blade demonstrates the efficiency and potential for applying this approach to more complex, realistic and industrially relevant 3D forging problems.

Geometric processing for analysis

Processing geometric models for finite element analysis is a major factor in the time required to develop and optimise a design. Efficient analysis may require simplification of the geometric model by dimensional reduction (replacing thin sheets or slender bars of material with equivalent line or surface elements) or detail suppression (the removal of small features below the scale of interest in the analysis). There are many situations where detailed local models of full dimension could be combined with global models containing reduced dimensional elements, or in which the abstract models used in preliminary design could be used to generate an initial version of the 3D solid model. Furthermore, the most appropriate representation of an object is dependent on the analysis type. These requirements provide significant challenges for future generations of CAE software in feature recognition and the modelling and representation of geometric objects.