At Peninsula Plastics, our vacuum forming process involves heating a plastic sheet until it is soft and then draping it over a mould. A vacuum is applied, sucking the sheet onto the mould. The sheet is then ejected from the mould in its final shape. The vacuum forming process utilizes sophisticated pneumatic, hydraulic, and heat controls, which enable higher production speeds and more detailed vacuum formed products.
Vacuum forming has several processing advantages over other forming processes. Low forming pressures are used, which enable comparatively low-cost tooling.
Since the process uses low pressures, molds can be made of inexpensive materials and mold fabrication time is reasonably short. Prototype and low quantity requirements of large parts, as well as medium and high volume size runs, become economical at Peninsula Plastics because of our proprietary forming and trimming processes.
Unlike other thermoplastic forming processes, which use powder or resin as the starting point, vacuum forming uses extruded plastic sheets. With vacuum forming, a secondary process may be required to trim the sheet after it has been formed. The trimmed waste can then be re-ground and recycled.
At Peninsula Plastics, the vacuum forming steps are: clamping, heating the sheet, pre-stretch, forming with plug assist, cooling with air and spray mist, release, and trimming They are explained in more detail under the following subheadings:
The special clamp frame at Peninsula Plastics is powerful enough to ensure that the plastic sheet is firmly held during the forming process. It is able to handle the thickest materials formed on the machine – up to 8mm with a single heater model and up to 20mm with the twin heater machines. If an automated process is used, the the moving parts are guarded and interlocked to avoid accidental damage.
Peninsula Plastics uses a variety of heating sources for making the plastic sheet pliable. Each type of thermoplastic sheet has different heating requirements and we match the material to the heating source for high-quality finished products.
Once the material is suitably stretched, a vacuum can be applied to assist in forming the sheet. At Peninsula Plastics, we use a vacuum reservoir in conjunction with a high volume capacity vacuum pump. Our two-stage vacuum application ensures rapid molding of the heated sheet.
Plug-assist forming is the term used to describe the use of a male plug tool to force the material into a female cavity within the molding area. It enables complicated and deep-draw moulds to be produced without webbing and with uniform thickness. The idea behind the plug-assist process is to feed as much material into the cavity prior to applying the vacuum in order to avoid thinning in certain areas.
Cooling and Release
Once formed, the plastic must be allowed to cool for a specified amount of time in order to control part shrinkage. If the plastic released too soon, it risks becoming deformed. Once cooled sufficiently, the sheet can be released using reverse pressure of the vacuum system. The part is then stripped from the mold and transferred to the trimming station.
Trimming and Finishing
Once the formed part has cooled and material shrinkage has been completed, excess material is removed. Holes, slots, and cutouts are then drilled into the part. Other post-forming processes include decoration, printing, strengthening, reinforcing, and assembly.
A variety of different trimming methods are used to trim the product from the sheet. We use different trimming processes based upon the type of cut necessary, the size of the part, the draw ratio, the thickness of the material, and the quantity of parts required. These criteria are also factors to consider when determining the investment cost of such equipment. Thin-gauge parts are normally trimmed on a mechanical trim press – otherwise known as a Roller press or die cutting press. Heavy-gauge parts can be removed, placed into trim “jigs” or fixtures and trimmed with any of the following tools: Horizontal / Vertical Band saw, Hand Held Air Powered Router, or CNC Routers (3, 4 and 5 axis).