Thermoforming Essay, Research Paper

Thermoforming is one of many manufacturing processes that converts plastic resin

into usable everyday products. Thermoforming is greatly relied on in today’s

society because of the tremendous need for high volume plastic products.

Thermoforming is considered to be one of the most cost-effective processes in

plastics manufacturing. Thermoforming is considerably economical because of the

low molding costs and fast molding cycles. Speed and cost efficiency are the

highlighted qualities that thermoforming offers which lead the way for the

process becoming so important in industry today. The basic concept of

thermoforming is quite simple. A premanufactored thermoplastic sheet is heated

until it becomes soft and pliable. It is then forced against the contours of a

mold until it cools to its original state. Once it has cooled it is removed from

the mold while still obtaining the shape of the mold. Usually the product is

then trimmed to produce the finished product. The operation seems simple and

straight foreword but there are many different applications associated with the

process. Thermoforming is a broad term; there are many different types of

thermoforming processes. These processes all have similar traits but they do

differ in certain aspects of the overall process. Trapped Sheet Forming is a

specialized type of thermoforming. In trapped sheet forming a hot blow plate is

used in both the heating and forming process. A plastic sheet is positioned

between the hot blow plate and the female mold cavity. Air forced through the

plate and pressure from the female mold combine to thrust the sheet onto the hot

plate. The sheet is then heated and forced into the female mold by the use of

air pressure. One advantage to trapped sheet forming that is such a simplified

process that many products can be produced from this method. Also the process

uses contact heating, which is easily used and is not subject to temperature

fluctuation. The contact heating is a definite advantage but is also a slight

disadvantage. The problem with contact heating is that heat can only be applied

to the underside of the sheet. This slows down the process and restricts the use

of the more durable heavier -gauge sheets. Plug-assist forming is one of the

most widely used thermoforming processes today. In plug-assist forming a heated

sheet is sealed over a female cavity. Once the plastic is sufficiently heated

the plug-assist, which is shaped like the female cavity but slightly smaller in

size, pushes the plastic sheet and forces it in the cavity. Vacuum force pulls

the sheet onto the mold surface. The main advantage associated with plug-assist

forming is that the walls of the container can be measured precisely with the

assist. Wall thickness is uniformly the same throughout the container.

Plug-assist forming works well with both heavy and light gauge materials and is

commonly used to form deep-drawn containers. Pressure bubble plug-assist vacuum

forming is similar to plug-assist forming. In this forming process a portion of

the sheet is stretched to guarantee an even thickness of walls. The heated sheet

is positioned over the female cavity. Air is then blown up through the base

plate channel. This air causes the sheet to billow upward. The sheet is then

pushed into the cavity by the plug-assist. Vacuum is then applied to transport

the sheet to the mold. The advantage to this forming technique is that the wall

thickness can be measured with great accuracy. This process, as with plug-assist

forming, is used to create deep-drawn containers. Pressure bubble snapback

forming is similar to bubble plug-assist forming except for one aspect. The

plastic sheet is not formed by the female mold but rather the male mold. The

sheet is snapped back to form against the male mold. This forming process

improves material distribution because of its prestrecthing procedures. The

snapback vacuum forming method is popular because of its simplified process. A

sheet is clamped over a female cavity, air pressure through the base plate then

stretches the plastic. The pressure is then turned off while the vacuum is

turned on to pull the plastic into the mold. This process is widely used to

produce auto parts and luggage due to its ability to create external deep draws.

It works well with all medium to heavy -gauge sheets. The processes mentioned

are just a handful of the many thermoforming processes out in the industry

today. Everyday better more reliable products are being manufactured by

thermoforming methods. Improvements are consistently being applied to the

different processes to ultimately create better products. Thermoformings place

in the plastics industry will continue to remain strong because of the dynamics

of its manufacturing process.