Custom Plastic Vacuumforming Processes

Vacuum forming is a type of plastic thermo forming that involves placing a sheet of plastic into a frame and applying heat. When the plastic is malleable and the proper temperature has been reached the plastic sheet begins to sag. The frame lowers and the plastic starts to cover the mold. A seal is created around the outside edges of the mold and a vacuum removes any air inside the cavity. The vacuum action causes the plastic to be pulled down around the mold. Once the plastic has hardened, the vacuum is shut off and the frame lifts up along with the newly formed plastic part. The part is then removed from the frame and all excess plastic is trimmed off around the edges of the part. Some products that are usually made by the vacuum forming process include: dashboards, display racks and beverage holders.

Plug assisted vacuum forming (molding) is used when straight vacuum forming is unable to distribute the thermoplastic sheet evenly to all areas of the mold. To help spread the sheet out more evenly, a device known as a plug is utilized to push the sheet into the mold before the vacuum is applied. This process enables more of the thermoplastic material to reach the bottom of the mold and thus more material is available to fill the corners of the mold and limit the plastic from thinning out.

Often times a customer will want their part to have a fairly even wall thickness. Sometimes this can't be achieved through conventional vacuum forming alone. A vacuum forming company may need to rely on the utilization of a pre-draw box. The pre-draw box is used to pre-stretch the hot plastic sheet prior to forming. A pre-stretched sheet will often times result in a part with a more even wall thickness than what would have been obtained otherwise. The pre-draw box can also be utilized to help the overall appearance of the part when the mold geometry causes cosmetic imperfections on the surface of the plastic.

Drape forming is a process similar to vacuum forming. In fact, drape forming can be described as vacuum forming without the vacuum. Instead of relying on vacuum to shape the heated plastic sheet, gravity performs this function. Drape forming is often used to minimize thinning, make a part with a very even wall thickness or produce a part with good clarity. Drape forming is very limited in the types of parts it can be used to produce and can only be used when compound curves or complex geometry is not present on the desired part.

Strip heating and bending is a process of forming plastic sheet using only a single heater (usually calrod) and a forming fixture. The straight calrod is used to heat the sheet along a specific area. The heated sheet is then placed onto a forming fixture. The forming fixture is made to a certain angle and the heated sheet is bent around this angle. Just like with drape forming, strip heating and bending is very limited in its application. However, when strip heating and bending can be used, the customer will end up with a part with a uniform wall thickness, minimal waste and which required a minimal investment in tooling.

Vinyl wrapping is a process that involves wrapping a preformed part with a piece of vinyl sheet. The vinyl wrapping process involves a few different steps. First, a part is formed from some type of rigid plastic or fiberglass. Then, this part is trimmed and sprayed with adhesive. After the adhesive has been applied, the part is put back on the vacuum forming machine. A piece of vinyl is then heated in the machine and brought out when hot. The previously formed plastic part acts as a type of mold and is pushed into the hot vinyl. Vacuum is applied and the vinyl is pulled against the surface of the plastic part. The excess vinyl is then trimmed off and wrapped around the edges of the part.

Many times this process is used to produce parts such as instrument clusters and dashboards where the customer wants the final part to have the rigidity of plastic or fiberglass but with a softer feeling surface. Advances in thermoplastics have been made that have enabled sheet suppliers to cap their plastic sheet with a soft touch material (typically a TPE) that can be formed in conjunction with the rigid substrate. The types of vinyl wrapped parts that these multi-layer sheets can be used to make is limited. However, when they can be used, they help to bring the entire vinyl wrapping process together into a single process involving only one machine cycle. The technology for this type of multilayered sheet is still somewhat in its infancy. Thus, material color, type and grain are limited.