Process Design for Hybrid Sheet Metal Components

doi:10.1007/s40195-015-0352-3

Abstract

Abstract:

The global trends towards improving fuel efficiency and reducing CO₂ emissions are the key drivers for lightweight solutions. In sheet metal processing, this can be achieved by the use of materials with a supreme strength-to-weight and .jpgfness-to-weight ratio. Besides monolithic materials such as high-strength or light metals, in particular metal-plastic composite sheets are able to provide outstanding mechanical properties. Thus, the adaption of conventional, well-established forming methods for the processing of hybrid sheet metals is a current challenge for the sheet metal working industry. In this work, the planning phase for a conventional sheet metal forming process is studied aiming at the forming of metal-plastic composite sheets. The single process steps like material characterization, FE analysis, tool design and development of robust process parameters are studied in detail and adapted to the specific properties of metal-plastic composites. In material characterization, the model of the hybrid laminate needs to represent not only the mechanical properties of the individual combined materials, but also needs to reflect the behaviour of the interface zone between them. Based on experience, there is a strong dependency on temperature as well as strain rate. While monolithic materials show a moderate anisotropic behaviour, loads on laminates in different directions generate different strain states and completely different failure modes. During the FE analysis, thermo-mechanic and thermo-dynamic effects influence the temperature distribution within tool and work pieces and subsequently the forming behaviour. During try out and production phase, those additional influencing factors are limiting the process window even more and therefore need to be considered for the design of a robust forming process. A roadmap for sheet metal forming adjusted to metal-plastic composites is presented in this paper.

Key words: Characterization, Hybrids, Interface, Layered structures, Processing, Sheet forming

Rico Haase, Roland Müller, Dirk Landgrebe, Peter Scholz, Matthias Riemer. Process Design for Hybrid Sheet Metal Components[J]. Acta Metallurgica Sinica (English Letters), 2015, 28(12): 1518-1524.

Figures/Tables 13

Fig. 1 Layered material Glare with fibre reinforcement in multiple directions [8]

Fig. 2 Experimental data from tensile test of a 0.58-mm DX54 and fitted analytical descriptions

Fig. 3 Forming limit curve (FLC) of a 0.58-mm DX54 steel sheet, geometries of specimens are sketched into the diagram

Fig. 4 Absolute stress value depending on tensile and compression strain for PA6 material under room temperature and 45% moisture

Fig. 5 Shear strength dependent on different types of surface treatment [15]

Fig. 6 Sketch of mechanical interlocks by out-of-plane deformation of metal core layer with designed trim line shape

Fig. 7 a Delamination of a metal-polymer-metal laminate at the layer interface after bending; b wrinkling of cover sheets into the core material in the flange area of a deep drawn square cup

Fig. 8 Schematic representation of manufacturing strategies, the bonding process can be operated before, after or during forming process

Table 1 Comparison of possible process routes and key advantages and disadvantages

Manufacturing strategy	Process route	Advantages	Disadvantages
Laminate bond established before forming operation	Hybrid sheets used as pre-material	Process quite similar to conventional (monolithic) sheet metal forming; no bonding process of single components needs to be considered	Lowest formability limit
Laminate bond established after forming operation	Metallic and organic sheets are formed in the same or separate mould	High formability limit, as sliding of loose layers is possible	Bonding needs to be performed in a separate process step
Laminate bond established during forming operation	Metallic and organic sheets are assembled in mould	High formability limit; forming tool can be used for shaping and clamping during bonding	Highest cycle time due to heating and cooling of die and component

Fig. 9 Schematic diagram of tempered forming tool

Fig. 10 Temperature field on actively liquid-tempered die after 300-s cooling time (half model) [18]

Fig. 11 Temperature behaviour of closed tool and clamped part during heating

Fig. 12 Position of temperature sensors on part surface

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