Loucas Papadakis

Considering manufacturing effects in automotive structural crashworthiness: A simulation chaining approach

The simulation of the structural crashworthiness of automotive shells is a key function during the product design and development phase. Modern road vehicles require high-complexity product design in order to satisfy the demanding market and the increasing requirements of crash test safety regulations. Product safety issues are highly related to the development of manufacturing processes and material treatment, which will allow for the necessary product structural properties and crash safety. The consideration of the structural properties after the forming process of sheet metal parts and their welding into body assemblies emerge to be essential for a more accurate modelling of the crash behaviour. In this paper, a practical approach for realising the simulation chaining of forming, welding and crash for structural shell assemblies is proposed. The attained structural results of single-sheet metal components are transferred into an integrated model, which enables the side impact simulation of a B-pillar assembly considering the preliminary manufacturing effects.

Interaction between laser beam, process effects, and structural properties during welding using models based on the finite element analysis

The aim of this contribution is to study the influence of the laser beam on the structural properties of sheet metals during welding by considering particular process effects. The interaction between process parameters, such as the exact positioning of the laser focus and the weld gap between sheets, affects the stability of the laser beam welding process and thus the quality of weld seams. Furthermore, additional interaction of the welding process with manufacturing tolerances and structural properties, i.e., material thinning and residual stresses after forming, influence the behavior of structures. Heat effects during and after the laser beam welding process produce residual stresses as well as phase transformation, in the case of steel alloys, in the weld seam and the heat affected zone. For this reason distortion of the whole welded structure is caused. Depending, next to the laser beam parameters, on the type of welded joint, on the structure geometry and on the clamping conditions, the residual str...

Experimental and computational appraisal of the shape accuracy of a thin-walled virole aero-engine casing manufactured by means of laser metal deposition

Laser metal deposition (LMD) of metallic powders, especially of high-strength nickel based alloys, allows for the manufacturing of components of high shape complexity and load capacity. However, high temperature gradients, induced during laser processing may have an impact on the product quality, especially when it comes to the geometrical accuracy of thin-walled components. This paper aims to provide a modelling approach of the heat effects during LMD manufacturing of a thin-walled virole aero-engine structure, in order to calculate possible shape deviations compared to the target CAD geometry. Hereby, a model reduction method is facilitated which allows the finite element analysis of such larger components in reasonable time. Major process characteristics as heat input, molten region geometry, material deposition (i.e. layer thickness), temperature dependent material and powder properties, phase transformation, process sequence and convection effects are taken into account. The proposed model aims to decrease time consuming trial-and-error testing effort during process design and development by providing reliable results on the shape accuracy of components. The computed final shape of the final product was compared to 3D measurements on a real demonstrator virole component.

A Simulation Approach for Chaining the Forming-Welding-Crash Behaviour of Sheet Metal Structures

In recent years the simulation of manufacturing chains and of the crash behaviour of automotive sheet metal structures has gained more ground on its way to be established in accompanying the overall product cycle. In the automotive press and welding plants high accuracy and quality of sheet metal structures is essential in order to achieve the intended passive crashworthiness of the overall vehicle body. So as to describe the manufacturing process chain more precisely and to predict the structural behaviour at early stages of product and production planning, an interlinking of forming, welding and crash models within a structural computation chain is necessary. Considering the structural properties of sheet metal parts after the forming process for simulating welding tasks and finally the crash behaviour requires a multifaceted modelling method. In this paper a practicable strategy of realising the simulation chain forming-welding-crash of sheet metal structures is introduced by means of shell element models. The complete computed results of a forming process simulation, such as residual stresses, plastic strains and material thinning are transferred onto a prepared shell mesh based on the CAD geometry of the component, which satisfies the requirements of a welding computation. Further on, the structural properties after forming, the thermal distribution due to the welding process and the mechanical clamping conditions are combined in a thermo-mechanical computation of the welding effects to calculate the final shape, residual stresses and material thinning of the manufactured sheet metal structure. Finally, the attained structural results are converted into the required data-format by means of a developed conversion routine, which enables the setup of a crash model considering the entire preliminary manufacturing chain. In this contribution the structural behaviour along the introduced simulation chain is analysed step by step and the rendered results are discussed and compared with performed measurements.

Adhesive Bonding of Attachments in Automotive Final Assembly

In modern societies there is an increasing concern regarding the environmental impact of automotives is driving automotive manufacturers to develop lighter and, thus, less fuel consuming vehicles. Customers’ protection during crash is a major demand which motivates automotive manufacturers to improve production processes which can satisfy the highly demanding market. Simultaneously, the introduction of new manufacturing techniques is strongly correlated with additional costs, which should be analyzed and quantified, in order to prove the sustainability of such processes for automotive production. This chapter considers adhesive bonding for joining attachments (i.e. roof components) on painted automotive shell surfaces as a potential technique in volume production. In order to introduce such type of adhesive joining process in current production lines, different process chain scenarios are proposed depending on the paint type in order to achieve the required strength of connection, especially during crash loads. Production costs are gathered and a proposed cost analysis is presented for evaluating the suggested scenarios aiming to identify cost intensive procedures.

A computer aided chaining approach for predicting the shape accuracy in manufacture of automotive structures

The increasing competition and the urge to reduce costs and shorten product-life-cycles in the automotive industries imply the application of virtual manufacturing mock-ups. Computer aided engineering methods including simulations of the structural behavior during manufacturing and assembly contribute to eliminate trial-and-error along the production chains of vehicle structures. Such digital mock-ups also provide an input for additional tolerance analyses and allow the identification of the pending quality of structure components in advance. In this way large numbers of experiments and adjustments on the existent production lines can be avoided. In this paper an approach is introduced, which allows the replication of the physical effects along manufacturing chains based on thermo-mechanical models. The rendered results after considering successive operational steps provide the basis for initial estimations regarding the shape accuracy of structure assemblies. For a specific example of the automotive body-in-white a first run of a manufacturing process chain is investigated in order to predict the shape quality of a probable production cycle by applying a tolerance chain analysis. The results enable the scrap identification due to non-satisfied quality of assemblies. Finally, based on the achieved results a re-engineering of the manufacturing chain is suggested in order to fulfill quality requirements.

Interaction between laser beam, process effects and structural properties during welding using models based on the FEA

Aim of this contribution is to study the influence of laser beam on structural properties of sheet metals during welding by considering particular process effects. The interaction between process parameters, such as the exact positioning of the laser focus and the weld gap between sheets, affect the stability of the laser beam welding process and thus the quality of weld seams. Furthermore additional interaction of the welding process with manufacturing tolerances and structural properties, i.e. material thinning and residual stresses after forming, influence the behaviour of structures. Heat effects during and after the laser beam welding process produce residual stresses as well as phase transformation, in case of steel alloys, in the weld seam and the heat affected zone. For this reason distortion of the whole welded structure is caused. Depending, next to the laser beam parameters, on the type of welded joint, on the structure geometry and on the clamping conditions, the residual stresses and the distortion of structures may vary. In order to examine the process design variation, three different types of welded joints were considered. A lap and a fillet seam as well as a heat conduction seam on a formed sheet of steel were produced and the distortion was measured. Finally the results are compared with the finite element analysis.Aim of this contribution is to study the influence of laser beam on structural properties of sheet metals during welding by considering particular process effects. The interaction between process parameters, such as the exact positioning of the laser focus and the weld gap between sheets, affect the stability of the laser beam welding process and thus the quality of weld seams. Furthermore additional interaction of the welding process with manufacturing tolerances and structural properties, i.e. material thinning and residual stresses after forming, influence the behaviour of structures. Heat effects during and after the laser beam welding process produce residual stresses as well as phase transformation, in case of steel alloys, in the weld seam and the heat affected zone. For this reason distortion of the whole welded structure is caused. Depending, next to the laser beam parameters, on the type of welded joint, on the structure geometry and on the clamping conditions, the residual stresses and the dist...