Sag in thermoforming

Giacomin, A. Jeffrey; Mix, A. W.; Mahmood, Omar Talal

doi:10.1002/pen.21734

Cited by 16 publications

(29 citation statements)

References 10 publications

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“…Initially, both radius of curvature and tensile stress are infi nite. There will always be some sag in the sheet before forming, making the radius of curvature fi nite [2] . There is a peak when ρ = 1 corresponding to a α Σ θ θ = 0.333.…”

Section: Free Forming Resultsmentioning

confidence: 99%

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Viscoelasticity in thermoforming

Johnson¹,

Giacomin²,

Mix³

2012

Journal of Polymer Engineering

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This analysis for thermoforming cones from a viscoelastic melt gives the speed of the stresses in the deforming melt. We follow the mechanics of Kershner and Giacomin developed for thermoforming cones from a Newtonian melt, deriving an analytical solution for the corotational Maxwell (CM) model.We have distinguished what happens before and after the melt touches the conical mold (free vs. constrained forming). The CM reduces to the Newtonian solution of Kershner and Giacomin. The upper convected Maxwell (UCM) model is also investigated, but does not yield an analytical solution for conical thermoforming. Our results are confi ned to forming with a conical mold, the simplest relevant problem in thermoforming, using the simplest relevant constitutive equation, the CM model.

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Section: Free Forming Resultsmentioning

confidence: 99%

“…Giacomin et al [2] analyzed a heated sheet as it sags under its own weight, and this occurs after heating but before shaping. In practice, thermoforming engineers often neglect sag and use a fl at uniform sheet as the initial condition for design.…”

Section: Introductionmentioning

confidence: 99%

Viscoelasticity in thermoforming

Johnson¹,

Giacomin²,

Mix³

2012

Journal of Polymer Engineering

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“…17, and Ω S is given by Eq. 33 in [1]. Here $\varepsilon_\infty$ is the equilibrium recoil, that is, the maximum amount of recoil exhibited by the softened sheet.…”

Section: Discussionmentioning

confidence: 99%

“…Our sheet bowing analysis also serves as an accurate initial condition for a proper sag analysis because the bowing extends the width of the softened sheet [1]. The lay‐flat of the bowed sheet, once softened, thus immediately becomes the initial width of the sagging sheet.…”

Section: Introductionmentioning

confidence: 99%

Sheet bowing in thermoforming

Vodak

Mix

Giacomin

2011

Polymer Engineering & Sci

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Sheets to be thermoformed are often heated unevenly, with a higher temperature above the sheet. This results in upward bowing of the sheet, and this is caused by thermal expansion. We combine the analytical solution for the temperature gradient in a slab heated by radiation with a relationship developed from the cylindrical geometry of the sheet as it bows. We thus derive a dimensionless equation for sheet bowing as an implicit function of time for both top and dual heating. We thus uncover a new dimensionless group which we call sheet bowability. We find good agreement between our theory and our new top‐heated sheet bowing measurements. We provide a worked example so that the engineer can see how to apply our results. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

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“…This model is developed from the previous studies on hanging materials [32][33][34][35][36][37] and axially moving materials [19,27]. We introduce a numerical method to calculate the shape of moving thin-sheet materials between rolls, taking into account the position and size of rolls.…”

Section: Introductionmentioning

confidence: 99%

Research on the Transportation of Low-Strength Composites Sheets

Chang

Wang

et al. 2017

Applied Sciences

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Abstract:The novel non-combustible sandwich panel is extremely fragile in manufacturing and cannot be tensioned between rolls. Previous studies on the roll-to-roll system, which mainly focused on the high-tension situations and little described the low-strength materials, are insufficient. To explore the transportation of low-strength materials, we study the tension distribution of continuous moving flexible one-dimensional materials on a steady-state track. First, we propose a numerical method to calculate the steady-state track of low-strength sheet between rolls considering the gravity, as well as size and position of rolls. Then we obtain the optimum sag at different size and position of rolls. We find out that there is a lower limit of the sheet's strength-density ratio (the Minimum Specific Strength) for a specific set of size and position of rolls. Finally, we establish a method to calculate the lower limit approximately for engineering use. Our method can be generalized in manufacturing other low-strength flexible thin-sheet materials as well.

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Sag in thermoforming

Cited by 16 publications

References 10 publications

Viscoelasticity in thermoforming

Viscoelasticity in thermoforming

Sheet bowing in thermoforming

Research on the Transportation of Low-Strength Composites Sheets

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