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.