Three‐dimensional forming of plastic‐coated fibre‐based materials using a thermoforming process

Abstract

Three-dimensional (3D) forming of fibre-based materials has been a topic of growing interest over recent years and 3D forming processes using hydroforming, press forming and deep drawing processes have been widely explored. Thermoforming as a potential alternative method for forming these materials remains, however, relatively understudied. This research attempts to provide a fundamental understanding of the thermoforming limitations of plastic-coated paperboards. In the work, a variety of commercial paperboards are subjected to experimental tests with different forming parameters and moulding depths. Shape accuracy, maximum acquired depth, thickness distribution behaviour and damage mechanisms are used to evaluate thermoformability, and the results linked to the material properties and forming conditions. The research findings indicate that the plastic-coated paperboards studied are thermoformable but only in simple geometric shapes and with low mould depths.Unlike plastic, thermoforming can result in thickness increase in plastic-coated paperboards, which is thought to be a result of out-of-plane auxetic behaviour of paperboards. Paperboard thermoforming was also found to be hindered by rupture, blistering and curling defects. Tensile strain at break is the key factor determining thermoformability. Additionally, the density of the paperboard can impact the heating step and the rate at which the moisture content of the material changes during the forming process. Furthermore, it was observed that changes in process parameters affected materials differently, with the direction and rate of change differing based on the material being used.

Effects of thermoforming operation and tooling on the thermoformability of plastic‐coated fibre‐based materials

“…Material properties, mould variables, and forming operations may all influence the inability of material to reach the mould; thus, evaluation of their influence is of paramount importance for this quality factor. Earlier research focused on the effect of material properties such as strain‐at‐break on thermoformed products and the extent to which optimisation of forming parameters may affect the depth achieved 19 . However, the results of this study shed light on the influence of mould design variables and the forming operation on the depth of thermoformed paperboard products.…”

“…With the existing materials and thermoforming processes, neither can the coated paperboards be shaped into the desired shapes (including radii and curvatures) nor can the thickness of the materials vary greatly compared with the raw state. The rate of change has already been identified in a previous study 19 . Generally, this thickness change falls within the range of thickness variations that are inherent in inhomogeneous structures, such as paperboards; it is therefore difficult to relate those thickness changes to other factors such as forming operations or mould variables.…”

“…An industrial thermoforming–filling–sealing machine, Variovac Primus thermoforming line (Zarrentin, Germany), was used for the thermoforming experiments. A detailed description of the machine can be found in Afshariantorghabeh et al 19 The machine operates by feeding materials, clamping, heating, and forming them. Different methods of thermoforming can be employed to carry out the process, including vacuum forming, air pressure forming, or a combination thereof as well as plug‐assisted forming.…”

“…To this end, a numerical study examined the effects of microwave heating over infrared heating during the heating stage of the process, aiming to improve the distribution of temperatures and enhance the thermoforming efficiency 18 . For uncoated and plastic‐coated paperboards, thermoformability analyses have previously been conducted to examine the material properties and structure 3,19 . Their findings have shed light on the impact of material properties and structure on the limitations encountered in thermoforming performance, encompassing challenges related to achieving desired depth and shape as well as the damage mechanisms.…”

IR-Thermoforming Window Design via a Thermal Approach: for CFRTP and Hybrid Thermoplastic Composites

“…In thermoforming, the material is heated to its softening point, after which it is shaped to conform the forming profile by employing pressure or mechanical forces [7]. The glass transition (Tg) and/or melting (Tm) temperature are determined using the modulated mode of Differential Scanning Calorimetry (DSC).…”