Thermoforming, part processing materials

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... 

The cost of manufacturing thermoformed, polystyrene foam sheet parts is less dependent on raw material cost than other extrusion processes. This is largely due to the combined effects of additional energy costs required to operate two extruders, heat removal requirements in the secondary extruder, cost of pelletizing (densifying) regrind and the relatively low output of the process for the equipment scale and cost. Typical cost factors for the manufacture of thermoformed polystyrene foam sheet products include raw materials 35%, labor 27%, sales and administration 16%, depreciation 8%, utilities 7% and other 7%. 

Thermoforming is a process where a sheet material is shaped into a three-dimensional part under the influence of heat and pressure. The process is a relatively old one that has been around for the past 40 years. The major improvements have occurred in throughput rates for lids and caps that are used in the packaging industry. For example, present machines can produce 113,000 coffee cup lids/h on a roll-fed machine in which 110 lids are formed at a time when a 3.5-s cycle is used (19). 

Thermoforming is a process for forming moderately complex shaped parts that cannot be injection molded because the part is either very large and too expensive or has very thin walls. It consists essentially of two stages elevation of the temperature of a thermoplastic sheet material until it is soft and pliable and forming the material into the desired shape using one of several techniques. 

First of all the process scheme with all thermoforming steps is shown in Fig. 1 in Chapter Secondary Forming of Plastics Structural Components Thermoforming. In most cases, the provision of the sheet material, and demolding and stacking in particular, constitute additional production steps that require an experienced hand. The forming step is only a small part of the whole production chain. 

Blow molded parts demonstrate that, from technical and cost standpoints, BM offers a promising alternative to other processes, particularly injection molding (IM) and thermoforming. The technical evolution of BM, plus accompanying improvements and new developments in plastics, has led to new BM parts. With the coextrusion technology now established and the hardware in place, the variety of achievable properties can readily be extended by the correct combination of different materials (see Chapter 3). The potential for BM products includes much more than the simple bottles that have been made for many decades. Now the expertise and economics of the method are such that many ideas once deemed futuristic are much closer to realization (2, 96, 186-212). 

This review on vacuum thermoforming can be related to most of the other forming processes. With a vacuum system a sheet is subjected to heat to meet its optional processing temperature, or technique that forces it against the shape of a mold. The hot, pliable material is moved rapidly to the mold (for example, by gear drives) and/or is moved by an air pressure differential, which holds it in place as it cools. When the proper set temperature is reached, the formed part can be removed and still retain its shape. 

---