An Explanation of Vacuum Forming Process
Injection Moulding | Stereolithography | Selective Laser Sintering | Ultrasonic Welding
As with injection moulding, once you have finalised the design and material type of your vacuum forming product, a vacuum forming tool has to be made which emulates the plastic part you require.
However, vacuum forming tools generally cost hundreds rather than thousands of pounds as they are made from wood, resins or low cost aluminium instead of hardened tool steels or alloys and do not require the same accuracy. The plastic formings cost significantly more than injection mouldings. This makes vacuum forming better suited for low-medium volume requirements where the need and thus cost of an operator or technician producing each forming does not counteract the initial low cost of the vacuum forming tool.
Once the vacuum forming tool has been manufactured, the vacuum forming process is undertaken as follows to produce the plastic formings you require.
1. The vacuum forming tool is loaded in to the vacuum forming machine and warmed.
2. The plastic material, in roll or sheet form, is loaded on to the vacuum forming machines material carrier.
3. Heaters, located above the sheet, then heat the sheet of vacuum forming material until it softens.
4. An automatic levelling device then supports the softened sheet of vacuum forming material with air.
5. The tool is then raised to meet the bottom surface of the sheet of material and a vacuum of air is applied in order to draw the sheet over the shape of the vacuum forming tool.
6. The plastic is then allowed to cool and set hard and the vacuum forming can be removed by hand or with the use of air to carry out any necessary secondary operations e.g. trimming or hole punching.
Vacuum Forming Process - Points to Note
When designing your product for the vacuum forming process please remember that all sections must have the same wall thickness and that holes and slots will have to produced as a secondary operation.
1. Injection moulding is much more suitable for tight tolerances than the vacuum forming process
2. If possible, make the gaps between pockets greater than 6 mm, otherwise webbing is likely to occur.
3. Ideally, allow 5° - 10° draft angle on side walls to enable the formings to be easily removed from the tool.
4. Don't make pockets deeper than their width and avoid very narrow slots - they're unlikely to form properly
5. To stop formings thinning excessively/cracking use large (3 mm+) curves/radii and avoid sharp corners
