Christoph Schneeberger

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Schneeberger

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Christoph

ORCID

0000-0002-1496-4244

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Publications 1 - 6 of 6

A life cycle analysis of novel lightweight composite processes: Reducing the environmental footprint of automotive structures
Wegmann, Stephanie; Rytka, Christian; Diaz-Rodenas, Mariona; et al. (2022)
Journal of Cleaner Production
In this study, three novel thermoplastic impregnation processes were analyzed towards automotive applications. The first process is Thermoplastic Compression Resin Transfer Molding in which a glass fiber mat is impregnated in through thickness by a thermoplastic polymer. The second process is a melt-thermoplastic Resin Transfer Moulding (RTM) process in which the glass fibers are impregnated in plane with the help of a spacer. The third process, stamp forming of hybrid bicomponent fibers, coats the fibers individually during the glass fiber production. The coated fibers are used to produce a fabric, which is then further processed by stamp forming. These three processes were compared in a life cycle analysis (LCA) against conventional resin compression resin transfer moulding with either glass or carbon fibers and metal processes with either steel or aluminum that can be new, partly or fully recycled using the case study of the production, life and disposal of a car bonnet. The presented LCA includes the main phases of the process: extraction and preparation of the raw materials, production and preparation of the mold, process, and energy losses. To include the life of the analyzed bonnet, the amount of diesel that is used to drive the weight of the bonnet for 300′000 km is calculated. In this LCA, the disposal of the bonnet is integrated by analyzing the used energy for the recycling and the incineration. The results show the potential of the developed thermoplastic impregnation processes producing automobile parts, as the used energy producing a thermoplastic bonnet is in the same range as the steel production.
Pultrusion of hybrid bicomponent fibers for 3D printing of continuous fiber reinforced thermoplastics
Aegerter, Nicole; Volk, Maximilian; Maio, Chiara; et al. (2021)
Advanced Industrial and Engineering Polymer Research
Continuous lattice fabrication is a newly introduced method for additive manufacturing of fiber-reinforced thermoplastic composites that allows to deposit material where it is needed. The success of this technology lies in a printing head in which unconsolidated continuous fiber-reinforced composite is pulled through a pultrusion die before the material is extruded and deposited out of plane without the use of supporting structures. However, state-of-the-art composite feedstock like commingled yarns shows limits in achievable material quality and part dimensions due to the underlying fiber architecture where thermoplastic fibers are mingled with reinforcement filaments. Hybrid bicomponent fibers overcome these constraints because each individual reinforcement filament is clad in a thermoplastic sheath. This results in absence of time-consuming fiber impregnation steps that would negatively effect void content and material quality. This study compares the material quality of pultrudates made from hybrid bicomponent fibers to that of commercially available commingled yarns at various processing conditions. Experiments are reported in which polycarbonate composite profiles with a diameter of 5 mm containing 50 vol% to 60 vol% E-glass fibers are pultruded at different die filling degrees, mold temperatures and pultrusion speeds. The results show that the pultrudates obtained from hybrid bicomponent fibers have lower void content than those manufactured under the same conditions from commingled yarns. We assess this to be caused by the difference in consolidation mechanism which in the case of the hybrid bicomponent fibers is dominated by coalescing of the thermoplastic sheaths compared to the Darcian flow-dominated consolidation of commingled yarns.
Energy-efficient structural materials for mass-production of lightweight vehicles
Schneeberger, Christoph (2019)
Lightweight construction is an important topic in automotive design even as societies transition from combustion engines to electric drivetrains. Lighter cars emit less greenhouse gases during their lifetimes, but the automotive industry has been slow in adapting advanced lightweight materials due to their low production rates. This presentation introduces a novel preform concept which allows manufacturers of automotive body structures to employ lightweight fibre-reinforced plastics without having to compromise on output rate or production costs. These preforms are based on hybrid bicomponent fibres, which are reinforcement fibres individually clad in a thermoplastic polymer sheath. The talk outlines a proposed method for fabricating these fibres, presents experimental data on their performance in state of the art parts manufacturing, and concludes with an outlook on the ongoing research on this topic within SCCER Mobility.
Hybrid Bicomponent Fibres for Thermoplastic Composites
Schneeberger, Christoph (2020)
Hybrid preforms are used in thermoplastic composite manufacturing processes to reduce the potentially long consolidation times caused by the high viscosities of thermoplastic melts. Darcy's law for fluid flow through a porous medium indicates that the negative effects of high viscosities on impregnation time can be offset by reducing the maximum distances the thermoplastic melts must flow for complete consolidation. In thermoplastic composite preforms, the total impregnation length is reduced by increasing the degree of mingling between reinforcement and matrix. Currently, mingling in such preforms is found on the level of the laminate down to the level of the yarn, but may occur on any of the hierarchical tiers found in fibre-reinforced composite materials. The level and quality of mingling in existing arrangements - such as organosheets, commingled yarns, powder-impregnated yarns and fibre impregnated thermoplastics (FITs), co-woven yarns or stacked laminates - greatly influence the flow lengths, cycle times, achievable part complexity, raw material costs, and suitable manufacturing routes. Given the limited selection of commercially available preform architectures, manufacturers must choose between the low cycle times of organosheets and the better drapeability of unconsolidated hybrids, e.g. commingled yarns, in thermoforming. The development of a material architecture which combines the fast processing of fully impregnated products with the flexibility of unconsolidated preforms would render thermoplastic composites significantly more attractive to high volume production markets, e.g. automotive parts. This thesis proposes hybrid bicomponent fibres - which consist of continuous reinforcement fibres individually sheathed in a thermoplastic polymer - as a new class of preform materials for thermoplastic composites. By reducing the scale of mingling between the reinforcement and matrix materials to the level of the fibre, a full wet-out of the fibres is ensured while the unconsolidated nature of the material allows the fibres to shift and deform with respect to each other to ensure drapeability even at room temperature. It is hypothesized that preforms made from hybrid bicomponent fibres can be stamp formed with cycle times similar to those of pre-consolidated blanks. Furthermore, it is expected that the void content of laminates stamp formed from hybrid bicomponent fibre preforms is greatly influenced by sintering mechanisms and the removal and/or collapse of air pockets. The presented research aims to answer these hypotheses by developing suitable methods to manufacture such hybrid bicomponent fibres and by processing them into consolidated laminates. The basic idea of hybrid bicomponent fibres is motivated and introduced in further detail in part I. Part II moves on to discuss materials and their corresponding processing methods for their suitability in realizing bicomponent fibres. A fibre forming approach based on glass-melt spinning combined with an in-line coating process is chosen. Multiple versions of the latter are investigated empirically, namely dip-coating of newly spun glass fibres in either a polymer solution or a sparsely nanofilled polymer melt, as well as the so-called kiss-roll coating method. It is found that drawing glass monofilaments of finite length over a rotating roll which is partially immersed in a dilute polymer solution yields a coating method which can endure high fibre velocities while ensuring the deposition of a sufficiently thick thermoplastic sheath for down-stream conversion into a structural grade composite laminate. The validity of this strategy is proven in the realization of a pilot plant which employs solution kiss-roll coating in-line with melt-spinning of a glass monofilament for the continuous fabrication of bicomponent fibres. Unidirectional layups of specimens of aluminium borosilicate glass fibres clad in polycarbonate produced with the pilot plant were characterized for their consolidation behaviour, the results of which are reported in part III. Supported by theoretical treatments on issues related to void collapse and autohesion, a parameter study on rapid stamp forming of these preforms was performed and complemented with stamp forming trials processing cross-ply layups of different thicknesses. All experiments yielded excellent laminate qualities with void contents <0.7%, supporting the conclusion that issues related to air removal and void collapse are insignificant. Laminates with a consolidated thickness of 1 mm and a fibre volume content of 0.69 were consolidated with holding times inside the press as low as 5 s, illustrating that virgin hybrid bicomponent fibre preforms can be stamp formed with similar process parameters as pre-consolidated blanks. Overall, it is concluded that the concept of hybrid bicomponent fibres as a novel type of preform provides enormous advantages for manufacturing continuous fibre-reinforced thermoplastic polymer composites. The combined value chain of stamp forming solution kiss-roll coated glass fibres offers a first opportunity for the production of continuous fibre-reinforced polymer composites without relying on Darcian impregnation flows anywhere between fibre formation and part production. The research presented in this thesis provides experimental proof for these claims and has established pilot equipment for the continuous spinning of glass/thermoplastic polymer bicomponent fibres, bringing this potentially disruptive technology closer to reality and expediting the adaptation of thermoplastic composites for high volume manufacturing.
Direct stamp forming of flexible hybrid fibre preforms for thermoplastic composites
Schneeberger, Christoph; Aegerter, Nicole; Birk, Sara; et al. (2021)
SAMPE Europe Conference 2020 Amsterdam: The Future Composite Footprints
Hybrid fibres combine individual reinforcing filaments with a precise amount of thermoplastic polymer matrix, providing an alternative solution to pre-consolidated blanks in stamp forming of thermoplastic composites. Preforms made from such fibres remain flexible at ambient conditions. This study investigates the consolidation behaviour of unidirectional arrangements made from E-glass monofilaments clad in polycarbonate sheaths (69 vol% glass). It assesses the influence of pre-heating temperature, press temperature, and holding time inside the press on the resulting laminates’ void content. The results prove that preforms made from hybrid fibres can be directly stamp formed while achieving void contents below 0.35 vol% with dwell times inside the press as low as 5 s for 1 mm thick laminates.
Hybrid Prepreg/Liquid Composite Molding Processes: Potential of Numerical Tools for Process Parameter Definition
Schneeberger, Christoph; Danzi, Mario; Ermanni, Paolo (2018)
SAMPE Europe Conference 15 Amiens

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