Thermoformed Parts

These calculations can give a useful first approximation of the dimensions of a thermoformed part. However, they will not be strictly accurate because in a real situation, when the plastic sheet is being stretched down into the cold mould it will freeze off at whatever thickness it has reached when it touches the mould. 

This work was motivated by cracking of a thermoformed part while cooling on the mold, the complexity of the problem could be immediately appreciated since the effect was sensitive to very delicate changes in material composition. Due to coupling between the heat transfer and stress evolution, both problems were solved simultaneously ... 

SB copolymers are produced via anionic polymerization by sequential addition of styrene and 1,3-butadiene monomers. These clear, tough plastics are easily processed with conditions and equipment similar to those used for HIPS. Various amounts of GPPS are usually mixed with the SB copolymers during sheet extrusion to maximize rigidity and economics in the thermoformed parts. Typical applications include drinkware, medical packaging, lids, containers, and blister packages. 

Fabricators will use t]Q as a metric of melt strength for creeping flows. For example, selection of resins with higher values of tj0 should minimize sag in thermoformed parts, and allow a more uniform part wall thickness. Similarly, t and n are metrics of the onset and rate of shear thinning. They are used to identify low-f/(y) conditions (easy flow) in an extruder, which are often critical to fast part fabrication rates. 

Fibers and other non-spherical fillers change their orientation during thermoforming. Small strains are sufficient to orient fibers. Experiments have demonstrated that particles of talc orient themselves parallel to the surface of thermoformed parts.The crystallites are oriented in a direction perpendicular to the either the talc or the mold surface. This is because the mechanism of crystallite growth begins on the surface of talc and grows outwards. 

HiD. [Chevron] HDPE resin resin for pressure pipe, sheets used for toys, housewares, thermoformed parts, films fcHT shipping bags, muldwall liners. 

In designing a new thermoformed part, it is necessary to consider the application, the function of the part, and its lifetime. Each of these areas has many subparts that must be considered also, in order to select the material and refine the design... 

From the three basic categories of polypropylene, namely, homopolymers, heterophasic copolymers, and random copolymers (with ethylene), there are specialty resins with enhanced capabilities for specific applications. Producers of large blow-molded or thermoformed parts can thus utilize grades with high melt strength to fabricate heat-resistant under-the-hood automotive parts. 

As reviewed, molds used with vacuum or pressure techniques require holes, channels, slits, ducts, and so on, for the evacuation of air or the buildup of pressure. To avoid visible marks on the surface of thermoformed parts, holes should be kept as small as possible, such as 0.010 to 0.025 in. Careful placement of the holes will be helpful in providing fast, efficient air flow during forming. Logic and experience provide guidelines for the placement of openings. 

As a rigid thermoplastic, PLA has basic properties comparable with those of PET and PS (Table 3), but rather different from those of polyethylene (PE) and polypropylene (PP). PLA has many unique beneficial characteristics (Table 4), such as superb transparency, glossy appearance, high rigidity (which allows downgauging of thermoforming parts), printing effects, and twist retention. These special characteristics make PLA a perfect fit for some market sectors, such as fibers, disposable... 

The types of thermoforming processes are vacuum forming, pressure forming, melt phase thermoforming, and matched mold forming. Examples of applications of thermoformed parts are ... 

Machining is also used in combination with other processes. Some processes require that gates be removed or parts trimmed by mechanical means before they are ready to be used. Machining may be used to create details the process cannot create. An example of this type of application would be holes in thermoformed parts. Finally, machining may be used because the product s production volume is too low to warrant the additional tooling cost necessary to mold the detail into the part. An example of this type of application would be a hole in an injection-molded part parallel to the parting line that would require an expensive side action. The additional amortization cost could exceed the cost of drilling the hole for low volumes. 

Force fits and snap fits have been used for thermoformed parts, however the difficulty of holding tight tolerances limits their utility for these applications. Outside walls can be held to 0.015 in for the first 1 in plus 0.002 in/in thereafter. Tolerances of 0.010 in plus 0.001 in can be held for projections such as the rib in Fig. 8.39. 

Typical applications automotive/transportation, apphance, films, closures, tapes/stripes, opaque and matte finish oriented film, breafhable, microporous film, opaque thermoformed parts, and opaque or translucent injection molded parts, foam, food packaging film, overwrap film, bottles and rigid articles, food trays, tubing... 

Polypropylene (PP) is semi-crystalline polymer used in many industrial applications, including extruded pipes, films and fibres, and injection-moulded and thermoformed parts, as a result of its physical, thermal and chemical properties (low density, high melting... 

If the sheet is formed over the male or positive mold and the inner surface of the thermoformed part touches and replicates, the mold is called positive forming (Figure 10.2a). In other way, if the thermoformed part is in the cavities of a female or negative mold and the outer surface of the part replicates, the mold is called negative forming (Figure 10.2b)... 

Most amorphous polymers linearly shrink about 0.4-0.6%. Crystalline polymers such as high density polyethylene and polypropylene linearly shrink about 2.0% (42). Thermoformed parts shrink away from female molds and onto male molds. Male molds must have typical draft angles of 2-5°, but sufficiently great enough to allow release of the formed parts. Female molds need minimal, if any, draft angles. 

Many thermoformed parts contain undercuts. Detents and interlocking lugs are frequently used in thin-gauge packages with integral lids. Undercuts in... 

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