P.F. Bariani

Testing and Modelling of Material Response to Deformation in Bulk Metal Forming

Abstract As the virtual prototyping of forming operations and systems becomes a real prospect for industries, reliable and versatile simulation software must be created to efficiently and accurately predict the events products and processes are subjected to. Useful and efficient models and tests able to evaluate the different aspects of the material response to plastic deformation are among the most critical prerequisites. The knowledge of how the material performs during and after deformation has, in fact, a great impact on product design and manufacturing decisions. This paper attempts to critically assess the modelling and testing approaches and techniques for predicting material response that are available today and then to discuss the latest developments in research labs and industrial applications in the fields of modelling and testing. The emphasis is on what is changing and must still change in order to provide industrial process designers with more useful models and efficient tests that can meet the increasing demand for accurate processes and product simulation.

Computer-Aided Cold Forging Process Design: A Knowledge-Based System Approach to Forming Sequence Generation

Abstract This paper presents some developments on the design of a Knowledge-based system approach to generate technologically feasable preforming sequences for multi-stage cold forging of solid and hollow rotationally symmetric parts. The sequences are intended to be initial designs which need additional analyses and evaluations in order to identify the most appropriate forging sequence. The approach is based upon a backward direction of the generative process and takes advantage of the division of the design rules which govern, respectively, (i) the recognition of operations, (ii) determination of the relevant deformation, and (iii) sequencing and grouping of the different operations.

Physical simulation of longitudinal welding in porthole-die extrusion

Abstract In porthole-die extrusion, the metal flowing through the die has to split up around the webs and then rejoin creating longitudinal welds that extend along the whole profile. The formation and quality of these welds depend on the metal flow around the webs and a number of process parameters such as the thermal and mechanical history stored in the material in the welding area and the temperature and pressure in the welding chamber. The paper presents a new laboratory test principle based on physical-simulation experiments on real materials that proves to be particularly suitable for investigating and modelling longitudinal welds in hot extrusion. In the test, the conditions governing the formation of longitudinal welds in the real industrial process are accurately reproduced and the process parameters affecting the quality of the welds can be individually controlled as well. The results achieved in applications of the test to aluminum alloy AA 6060 are presented with a focus on the operating conditions in the welding chamber that determine the transition from partial to complete longitudinal welding.

Experimental evaluation and FE simulation of thermal conditions at tool surface during cooling and deformation phases in hot forging operations

Abstract In hot and warm forging operations, surface layers of tools at the tool-workpiece interface are not only exposed to high mechanical stresses but also to severe temperature cycles, which often lead to loss of strength and hardness and thermal fatigue failure as well. This paper offers an approach for determining heat transfer conditions at the surface of punches and dies during both the deformation and the cooling-lubrication phases of forging cycles. The approach is based on temperature readings inside the tool, FE simulation and inverse analysis. An application case is illustrated where operating conditions reproduce hot forging of turbine airfoil sections.

Computer Aided Design of Multi-Stage Cold Forging Process: Load Peaks and Strain Distribution Evaluation

Summary This paper describes some developments of an interactive program aimed at assisting the user in analysing for suitability the forming sequences for multi-stage cold forging of rotationally symmetric parts. The program capabilities include (i) the automatic analysis of sequences in forging solid as well as hollow parts and recognition of individual operations involved in each step, (ii) the evaluation of the load-peak distribution in the different forming stage-and (iii) the prediction of the strain distribution accumulated in the blanks and the finished part. The program is part of an integrated system consisting of a suite of interactive procedures whose purpose is facilitating all the engineering activities for the process planning functions involved in manufacturing components on automatic multi-station cold forging machines. The major implication of including the developed program in this CAD system is that of providing the user with the tools suitable to perform a complete producibility check and to identify the most appropriate forming sequence.

A New Approach to the Optimization of Blends Composition in Injection Moulding of Recycled Polymers

The use of recycled polymers is widespread for the injection moulding of many commodity plastic parts. Recycled polymers are usually blended with virgin polymers to obtain the best trade-off between cost and low melt viscosity. This last constraint is necessary to avoid short shots and to minimize the clamp force of the required injection moulding machine and, therefore, the process cost. The current industrial approach to this problem is to select the polymer blend by trial and error. In this paper a new approach to the minimisation of the overall manufacturing cost is proposed. It is based on a rheological model of the blend which has been developed from experimental tests according to the mixture design technique. The approach has been validated through an industrial case study.

Integrated Design Analysis for Product Simplification

A systematic methodology is presented for product structure simplification through an integration of Design for Manufacture and Assembly (DFMA) with the Theory of Invention Problem Solving (TRIZ). A new functional model is combined with a selection of TRIZ problem solving tools that are identified as effective in product structure simplification. DFMA analysis is used to evaluate alternative concepts. Application of the combined approach is illustrated through a case study of a heavy duty stapler.

Enhancing performances of SHPB for determination of flow curves

Abstract A compression test on a Split Hopkinson Pressure Bar (SHPB) is the most common testing method adopted to determine material flow curves in a quite wide range of high strain rates. However, in most ordinary SHPB applications material rheology can only be investigated up to a rather low strain. Furthermore, several phenomena, including friction at interfaces and radial and axial inertia, are potential sources of inaccuracy for flow stress data. The paper presents the main design-guidelines followed when developing a high-performance SHPB system for the determination of accurate flow curves. The results from hot compression tests carried out on Aluminium- and Nickel-alloys prove that with the developed system most of the limitations of ordinary-SHPBs are overcome and system performances significantly improve.

Effects of micro laser sintering process parameters on quality of nickel-titanium single tracks and thin walls

Micro laser sintering is a promising additive manufacturing process for production of parts with micro features and complicated geometries. Micro laser sintering of mechanically alloyed NiTi was performed in the present work. The effects of powder and laser defocusing distances and also process parameters on the surface quality of single tracks and thin walls were investigated by scanning electron microscopy and optical profilometry. A modified model was described in this research to calculate the height of thin walls produced by micro laser sintering. The experimental results showed that a high melting efficiency can be obtained when the focal point of the laser is situated 200 µm above the working plane of the specimen. Optical profilometry revealed a good agreement between the proposed model for thin wall’s height estimation and experimental results.

Real-time prediction of geometrical distortions of hot-rolled steel rings during cooling

The paper deals with the application of neural network modelling to the real-time prediction of the geometrical distortion of hot rolled steel rings during cooling from rolling to room temperature. The neural network model was designed and developed to be part of a new modular system for the in-line monitoring and real-time control of the geometrical quality of rings, even those with a complex profile, during hot and warm ring rolling operations. The data utilised to train the neural network were generated by numerical simulations of the cooling phase. In order to do these simulations, an FE model capable of coupling thermal, mechanical and metalllurgical events was accurately calibrated. The proposed model was then applied to an industrial case that is described in the paper.