Thermoforming Research Papers - Academia.edu (original) (raw)

This work reports the effects of thermoform molding process conditions on polyvinylchloride (PVC) and polyethylene (PE) double layer package materials. Mechanical and microstructural properties of the package material were examined by... more

This work reports the effects of thermoform molding process conditions on polyvinylchloride (PVC) and polyethylene (PE) double layer package materials. Mechanical and microstructural properties of the package material were examined by different test methods which are tensile properties, tear resistances and scanning electron microscopy (SEM). Furthermore, package materials, which are produced in different conditions by thermoform molding. Effect of different mold depths and process temperatures on the samples are determined by thermal aging process at 60°C in first, third, and seventh days. With increase in mold depth from 25 mm to 75 mm, there is a significant increase in tensile strength from ∼45 MPa to ∼55 MPa, thermoform temperature at 150°C. The highest elongation of the material was obtained thermoform temperature at 165°C as 80%, mold depth at 35 mm. Tensile strength and elongation (%) of the material generally decrease by aging time with changing of mold depth (25, 35, and 75 mm) of the double layer package material. In addition, tear resistances of the material decrease via aging time in various thermoform temperatures (150°C, 165°C, and 175°C) due to the orientation of the segments. Scanning electron microscopic (SEM) images of the materials were taken for aging process in first, third, and seventh days. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Plastics have been highly successful in replacing such conventional materials as metals, glass, and wood in a wide variety of applications due to their special property advantages such as high strength-to-weight ratio, corrosion... more

Plastics have been highly successful in replacing such conventional materials as metals, glass, and wood in a wide variety of applications due to their special property advantages such as high strength-to-weight ratio, corrosion resistance, versatility of part design, and ease of fabrication. The various plastic products are formed by processing polymers by one of the number of available techniques such as injection molding, compression molding, blow molding, profile extrusion, and sheet extrusion followed by stamping or thermoforming. In all these processes, the molten polymer is subjected to a wide range of shear rates and temperatures. During deformation, viscous heat is dissipated due to the friction between the highly viscous polymer melt and the various parts of the processing equipment that it comes in contact with. The viscous heat dissipated leads to a temperature rise, resulting in an offset of the setting of the extruder temperature profile with respect to throughput rate or screw speed. For all high output rate operations, it is essential to know the viscous heat generated in order to appropriately design the conventional extruder screw so as to minimize the temperature increase in the process of plastication and to optimize the extruder temperature profile with respect to the throughput rate or screw speed. Viscous heat estimation is also critical when processing heat- sensitive polymers so as to maintain the melt temperature well below the degradation point.

A temperature and strain rate dependent model for the thermoforming process of amorphous polymer materials is proposed. The polymeric sheet is heated at a temperature above the glass transition temperature then deformed to take the mold... more

A temperature and strain rate dependent model for the thermoforming process of amorphous polymer materials is proposed. The polymeric sheet is heated at a temperature above the glass transition temperature then deformed to take the mold shape by the means of an applied pressure. The applied process temperature is taken uniform throughout the sheet and its variation is due only to the adiabatic heating. The behavior of the polymeric material is described by a micromechanically-based elastic-viscoplastic model. The simulations are conducted for the poly(methyl methacrylate) using the finite element method. The polymer sheet thickness and the orientation of the polymer molecular chains show an important dependence on the process temperature, the applied pressure profile, and the contact forces with the mold surface. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Thermo-mechanical behaviors of thin thermoplastic sheets under thermoforming conditions are generally studied in the frameworks of hyperelasticity and large deformations. The boundary conditions of the mechanical problem which represents... more

Thermo-mechanical behaviors of thin thermoplastic sheets under thermoforming conditions are generally studied in the frameworks of hyperelasticity and large deformations. The boundary conditions of the mechanical problem which represents the shaping operation are defined by the clamping configuration of the free edges of the sheet. By heating a flat thermoplastic sheet of totally or partially constrained edges during a thermoforming process, incontrollable changes of the initial boundary conditions manifest by buckling and warpage. Without consideration of the real process conditions, the mechanical problem risks to be ill posed. The current study focuses on representative unidirectional stretching tests under isothermal conditions conducted on high impact polystyrene (HIPS) specimens with free lateral edges. The aim is to identify the parameters of the Mooney-Rivlin hyperelastic model which is generally admitted in the case of the HIPS for temperatures above the glass transition. To measure the non-negligible out-of-plane deformations which manifest during the stretching operation, a hybrid numerical-experimental approach is introduced. This approach combines kinematic fields measured by the stereo digital image correlation (stereo-DIC) technique and a finite element model updating (FEMU) procedure. First, a dataset of displacement fields measured during stretching tests at controlled temperatures and strain rates is constructed. Second, sequential quadratic programming (SQP) based inverse identification procedure is implemented to minimize an objective function which combines the experimental and numerical displacement fields. A case of study is presented to test the limits of the hybrid numerical-experimental approach under incremental stretching levels. The optimization results indicate that the extent of the kinematic fields compared to the effective size of the tested specimen and the excessive stretching of the stereo-DIC speckle are the major limits to the applicability of the approach. The conducted study constitutes a preliminary step towards more accurate consideration of real boundary conditions to simulate thermoforming of thin thermoplastic sheets.

This paper mainly treats the thermal effects during the thermoforming process while most of the previous analyses consider an isothermal deformation. A non isothermal three dimensional finite element model of the thermoforming process is... more

This paper mainly treats the thermal effects during the thermoforming process while most of the previous analyses consider an isothermal deformation. A non isothermal three dimensional finite element model of the thermoforming process is proposed. It couples the thermal equations in the thickness and mechanical equations on the mean surface of the sheet. The mechanical resolution is done by a finite element method using a membrane approximation. The deformation is driven by a pressure difference through the sheet. The thermal resolution uses a one dimension finite element method in the thickness with convection or conduction at the surface and dissipation of mechanical energy. The polymer cooling is very efficient during the contact with tools. The coupling is done by the thermal dependent rheology. The respective contribution of friction and thermal effects in the thickness of the part during the process are discussed. The model also considers a possible multilayered material, with specific rheological parameters inside each layer. The rheology of a polystyrene was measured under elongation as a function of temperature, strain and strain-rate and described by a visco-plastic law. The predictions of the model were compared with measurements on an instrumented thermoforming machine and with the local thickness of axisymmetrical parts and with 3-D parts thermoformed with the same polystyrene.

In this study, 5% and 15% in weight carbon fiber reinforced polypropylene (PP) sheets were formed under appropriate vacuum and temperature conditions by using truncated cone-shaped thermoforming mold. In addition to this, 5% in weight... more

In this study, 5% and 15% in weight carbon fiber reinforced polypropylene (PP) sheets were formed under appropriate vacuum and temperature conditions by using truncated cone-shaped thermoforming mold. In addition to this, 5% in weight glass fiber reinforced High Density Polyethylene (HDPE) sheets were formed using truncated cone-shaped, cylindrical, and cubic shaped thermoforming molds by thermoforming. Composite sheets used in this work were produced with a laboratory-type plastic extruder which has a screw diameter of 50 mm. In production of HDPE composite sheets, as a reinforcing material, chopped glass fibers (E-glass) which were provided from glass fiber manufacturer SISECAM A.S. Company were used. Using the same procedure PP (Borealis BE50-7032) thermoplastic granules were used as a matrix material in production of carbon fiber composite sheets. In carbon fiber reinforced sheets, chopped fibers were added during manufacturing. After thermoforming, composite semi-products were ...

Remarkable characteristics of high temperature thermoplastic (HTP) matrix used in composite materials reinforced with continuous fibres causes growing application in composite industry. Because of high processing temperature of some semi,... more

Remarkable characteristics of high temperature thermoplastic (HTP) matrix used in composite materials reinforced with continuous fibres causes growing application in composite industry. Because of high processing temperature of some semi, crystalline matrix there is limited number of technologies that can be used for part manufacturing. Press forming is an example of technology that allows manufacturing high quality complex parts made of HTP reinforced fibres composite. In order to manufacture part with acceptable quality and mechanical properties, uniform pressure distribution during the process is required. In this article, tooling design process focused on uniform pressure distribution for manufacturing of supporting rib was presented. In order to satisfy this requirement, the rubber stamp was proposed as a tool for manufacturing. Typical press forming process defects were identified and the requirements for rubber stamp were described. It was assumed that the forming process has...