Research and advances in fundamentals and industrial applications of hydroforming

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Abstract

The automotive industry, with an increasing demand for weight reduction in modern vehicle construction, is a driving factor in the research and development work carried out on the area of hydroforming technology by research facilities, supplier industry and users. Their research and investigations during the past few years have supported the increasing application of this technology, which offers decisive advantages regarding the manufacturing of complex shaped lightweight components. This article provides an overview of the state of the art and important advances of hydroforming regarding the design of process steps, semifinished products, presses and tools and briefly presents new hydroforming technologies like the use of heat energy to improve formability of lightweight materials.

Introduction

During the past few years, the demand for weight reduction in modern vehicle construction has led to an increase in the application of hydroforming processes for the manufacture of automotive lightweight components made from steel or aluminium. This trend results from the benefits offered by hydroforming compared to conventional techniques like the assembly of car body parts from several stampings, which consist in the possibility to form complex shaped components with integrated structures from single tubes, combined with improvements in stiffness and crash behaviour due to the reduction of welding seams, and with reduced assembly costs.

Numerous new developments resulting from the research work carried out by research facilities, suppliers for hydroforming technology and users have made a contribution to the status achieved today where hydroforming permits the economic mass production of high-quality lightweight components. Examples are measures to reduce cycle time, to increase tool life time and to improve formability by new semifinished products and new process variants. Also, advances in simulation techniques contributed to an improved understanding of hydroforming processes and enable today the rapid and reliable development of hydroformed components.

This article provides an overview of the state of the art and important advances of hydroforming regarding the design of process steps, semifinished products, presses and tools. Also, the use of heat energy to improve formability is briefly presented.

Section snippets

Process principle and semifinished products

Regarding existing variants of hydroform processes a general distinction is to be drawn between forming of tubular material and forming of sheet material. Today, predominantly tubular material is considered for the mass production of hydroformed parts. Hydroforming of sheet material is up to now mainly used for small batch production due to a comparatively high cycle time. Furthermore, sheet hydroforming requires higher clamping forces than tube hydroforming, causing more cost-intensive

Process chain

In the majority of cases the complexity of the components requires that additional preforming operations be considered together with the hydroforming process itself. These preforming operations can involve bending and mechanical forming of the initial component to ensure that it is capable of insertion into the hydroforming die or to obtain an optimised material distribution [19]. Fig. 4 shows the results of these preceding steps in the production of an engine cradle.

Typical bending processes

Applications

Hydroformed series parts are to be found predominantly in the construction of vehicles with a continuously increasing number of applications. Typical applications are chassis components like rear and front axles, engine cradles, exhaust system parts, structural body components and components of power transmission. Fig. 9, Fig. 10, Fig. 11, Fig. 12, Fig. 13, Fig. 14, Fig. 15 represent some examples of hydroformed parts for automotive application.

The light truck frame shown in Fig. 11 consists of

Press and tool

The economy of a hydroforming process is significantly influenced by the design of the hydroform press, which specifies investment costs and productivity. Regarding the productivity a reduction of cycle time of about 50% was achieved during the past few years by measures like decrease of fluid filling time of the workpiece using quick-filling-systems, fast transition from filling to forming, increase of forming speed and reduction of subsidiary operation times [19].

Several new press concepts

Warm forming with pressurizing media

Aluminium alloys and magnesium alloys offer a great potential for weight reduction in vehicle construction due to their high strength to weight ratio. However, the use of these alloys is in comparison with conventional steels restricted due to their low formability at room temperature. Therefore, to an increasing degree research facilities, hydroforming technology suppliers and users are carrying out investigations to increase the formability of sheet and tube hydroforming by the use of

Summary

Research and development work carried out intensively during the past few years by research facilities, suppliers for hydroforming technology and users have led to the status achieved today where hydroforming permits the economic mass production of high-quality lightweight components. Continuous improvements in hydroform press and tool technology, as well as in simulation methods, together with new developments regarding semifinished products, hydroforming of sheet materials and the use of heat

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