Holzforschung 2018; aop Avishek Chanda* and Debes Bhattacharyya Formability of wood veneers: a parametric approach for understanding some manufacturing issues https://doi.org/10.1515/hf-2017-0186 Received November 16, 2017; accepted May 1, 2018; previously published online xx Abstract: The goal of the present work was to create a comprehensive guide to obtain 3-ply veneer laminates with a stable form. More precisely, a single curvature vee- bending test has been conducted on commercially avail- able radiata pine (Pinus radiata D. Don) veneer plywood, in which the veneer was pre-softened in water. Within the framework of a parametric study, the spring-back and spring-forward of the 3-ply laminates was quantitatively evaluated. The variability and final contributions of each parameter was observed by a statistical data evaluation. The forming temperature and pre-forming moisture con- tent were found to have the highest influences, while the experimental results could be satisfactorily simulated by calculations according to Taguchi. Keywords: 3-ply laminate, forming temperature, pre- forming moisture content, spring-back/-forward, Taguchi method, vee-bending Introduction Veneers of radiata pine are important raw materials for the production of plywood, with the advantage of having good laminating properties and turning and shaping characteristics (Srinivasan 2008). Commercially available veneers (usually less than 1 mm thick), may have even more value-added applications, if they can be formed into desired profiles, for example, to channel sections, hollow- sandwich structures, corrugated sheets, hollow pillars, auxetic structures, just to mention a few (Srinivasan et al. 2007). It is difficult to form veneers into stable structures due to their visco-elastic properties. This challenge can be tackled by applying heat, which modifies the cells at the forming point (Penneru et al. 2005) and thus facilitates the forming process (Galperin et al. 1995). However, the shape stability of complex plywood structures has received hith- erto little attention. Blomqvist (2016) studied the forming characteristic of veneers with various adhesives. The adhesives can act as lubricating agents (Grabner et al. 2016), as connectors (Navi and Sandberg 2012) and can influence the forming, which is dependent on the curing time, mechanical prop- erties (Sandberg and Ormarsson 2007) and the glue type (Srinivasan et al. 2007). Other parameters have also been investigated, such as the formability as a function of fiber orientation (Blomqvist et al. 2013), wood cutting orien- tation (Blomqvist et al. 2014; Blomqvist 2015), different forming techniques (Srinivasan et al. 2007; Srinivasan 2008) and various pre-forming techniques, for example, softening (Norimoto and Gril 1989) and pre-heating (Penneru et al. 2005). Whether the parameters influenced the formability characteristics of 3-ply radiata pine (Pinus radiata D. Don) veneers was the focus of this study. To this purpose, the standard process of soaking the veneers in hot water was followed (Srinivasan 2008; Rao 2009; Kavermann 2013) and the vee-bending process was applied, which is a single curvature bending. According to Norimoto and Gril (1989), veneer softening is a pre-requisite for pre- forming above the fiber saturation point (FSP), which is around 30% moisture content (MC) (Kininmonth and Whitehouse 1991). Temperatures above the glass transi- tion temperatures (Tg) of hemicelluloses and lignin are ideal for forming. Tg is dependent on the pre-forming MC of the veneers and decreases after the veneers have reached the FSP. The anisotropic nature of wood may result in unwanted and unaccounted distortions after forming (Norimoto and Gril 1989; Sandland 1998; Inoue et al. 2007; Wolcott and Shutler 2007). Thus, veneers show spring-back (SB) and spring-forward (SF) behav- ior after forming. In the present paper these behavior *Corresponding author: Avishek Chanda, Center for Advanced Composite Materials, Department of Mechanical Engineering, The University of Auckland, Building 903, 314-390 Khyber Pass Road, Auckland-1023, New Zealand, e-mail: acha553@aucklanduni.ac.nz, a.chanda91@gmail.com Debes Bhattacharyya: Center for Advanced Composite Materials, Department of Mechanical Engineering, The University of Auckland, Auckland, New Zealand Brought to you by | University of Sussex Library Authenticated Download Date | 6/24/18 7:56 AM