SPE Library

Thermoforming is an efficient, very cost-effective and widely used process for the production of large parts in transportation applications. The long-haul truck roof fairing demonstrates the feasibility of replacing traditional materials with thermoplastics in order to improve aerodynamics and, in turn, cut a truck’s fuel use. Simulation becomes a powerful means for a large part and complex process to arrive at, and optimize process conditions. This, in turn, helps to achieve the desired product quality for a given material. The present study describes the results from the use of thermoforming simulation as a tool for optimizing sheet thickness, sheet temperature, and processing conditions to achieve a desired thickness distribution and minimal weight of a truck fairing part without sacrificing its structural performance. The given design of truck roof fairing part is simulated using Accuform’s commercial thermoforming simulation software TSIM® for three different resin materials (acrylonitrile butadiene styrene (ABS), a blend of polycarbonate (PC) and ABS (PC/ABS); and thermoplastic olefin (TPO). These materials are modelled using nonlinear time-dependent viscoelastic K-BKZ model. The model parameters are estimated using stress-strain measurements. The average polymer sheet thickness and sheet temperature of each material varied to study thickness distribution and weight of the part. Finally, simulation results compare the thermoforming performance in terms of thickness distribution and part weight, and recommends optimal processing conditions for each material.

Thermoforming enables the cost-effective production of thin-walled packaging products. Pre-stretch plugs are used to adjust the resulting wall thickness distribution of the formed parts such as cups. Due to the friction and adhesion of the plastic material to the pre-stretch plug, the material is less stretched in areas having contact to the plug than in areas without contact and accordingly the wall thickness distribution is influenced. In addition to a wide range of process parameters, such as sheet temperature, stretching distance or the activation time of the forming air, the surface roughness of the pre-stretch plugs has an influence on the wall thickness distribution. In order to estimate the resulting wall thickness distribution of the formed parts, the influence of the surface roughness on the resulting wall thickness distribution was analyzed at the IKV. The use of pre-stretch plugs with different surface roughness showed, that the influence of the roughness on the wall thickness distribution depends especially on the plugs geometries and thus stretching conditions of the sheet.