Thermoforming, part processing

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. 

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. 

For thermosets, the hollow part processes are filament winding and pultrusion. These processes are limited in shape and structure. There are three hollow part processes for thermoplastics (1) rotational molding, (2) twin sheet thermoforming, and (3) blow molding. 

There are also several principal limitations of thermoforming. The process is confined to the use of sheet material. Therefore, all parts must have fairly uniform wall thicknesses. Thick ribs or mounting bosses cannot be obtained. 

When thermoforming parts from textile composite materials, it is useful to understand the deformation mechanisms, which take place inside them, so that the forming process can be optimized to produce parts of the best quality. The experimental observations and measurements considered in Section 4 are helpful for a general understanding, but do not provide enough detail to reveal the actual mechanisms. The following sections attempt to investigate these mechanisms in more detail. 

The first part of our study analyzed the processability of thermoformed cups fabricated on a plug-assisted vacuum MTS thermoformer while the second part compared the sheet sag observed for parts processed on an AVT thermoformer The sagging of the sheet was measured as a function of the time spent by the extruded sheet in the oven. A comparison of this sag to the sag obtained through simulations conducted on FormSim a software program developed by the Industrial Materials... 

Figure 2, 3, and 4 show the different thermoformed parts obtained on the MTS thermoformer for the design of experiments represented in Figure 1. It should be noted that the cups are formed by pushing the mold cavity down onto the plug. It can be seen that the temperature window of processability was different for each of the three resins.

AH forms and compositions of reinforcements, ie, mats, woven roving, glass, carbon, and aramid, are commonly used with these processes. Special continuous glass strand mats with a thermoplastic binder aHow preforms to be made using thermoforming techniques. These processes are used for tmck and autobody components, medical equipment cabinets, transportation seating, and other parts needed in the intermediate volume range (1,000—10,000 parts/yr). 

Thermoforming is perhaps the process with the lowest unit cost. Examples of thermoformed articles are refrigerator-door and food-container liners, containers for dairy products, and luggage. Some of the largest formed parts are camper/trader covers and liners for refrigerated-radroad-car doors (236). 

Designers and processors to produce products at the lowest cost have unconsciously used the basic concept of the FALLO approach. This approach makes one aware that many steps are involved to be successful, all of which must be coordinated and interrelated. It starts with the design that involves specifying the plastic, and specifying the manufacturing process. The specific process (injection, extrusion, blow molding, thermoforming, and so forth) is an important part of the overall scheme and should not be problematic. 

An increasing variety of automotive parts is being made by thermoforming processes. Many of these products are made from rubber-toughened polypropylene, which are relatively stiff and can withstand a high level of physical abuse over a ivide range of temperatures. When such parts are used in high visibility areas, such as wheel arches, air dams, truck fenders, and... 

PBT-PC blends show increased melt strength allowing them to be easily processed by blow molding and profile extrusion. The PBT-PC blends have been extruded into sheet and thermoformed into parts. Enhanced melt strength allows PBT-PC blends to be foamed. Structural foam grades for injection molding (10-30% density reduction) are commercially available. 

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